Page 1
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i
Design of a Tomahawk Cruise Missile Booster Rocket Motor
by
Devon K Cowles
An Engineering Project Submitted to the Graduate
Faculty of Rensselaer Polytechnic Institute
in Partial Fulfillment of the
Requirements for the degree of
MASTER OF MECHANICAL ENGINEERING
Approved
_________________________________________Ernesto Gutierrez-Miravete Project Adviser
Rensselaer Polytechnic InstituteHartford Connecticut
May 2012
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ii
copy Copyright 2012
by
Devon K Cowles
All Rights Reserved
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iii
CONTENTS
LIST OF TABLES v
LIST OF FIGURES vi
LIST OF EQUATIONS vii
LIST OF SYMBOLS ix
Glossary xii
ABSTRACT xiii
1 IntroductionBackground 1
11 Rockets 1
12 Mission Requirements 2
13 Structural Requirements 3
2 Methodology 4
21 Assumptions 4
22 Flight Performance 5
23 Motor thrust requirements 6
24 Motor Casing Sizing 9
25
Material 11
251
Aluminum Alloy 11
252
Composite Material 11
3
Results 16
31
Engine Parameters 16
32
Aluminum Alloy Casing Design 16
321
Aluminum Casing Geometry 16
322
Finite Element Analysis 17
33 Composite Casing Design 21
331 Layup 21
332 Composite Casing Geometry 22
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iv
333 Finite Element Analysis 24
334 Aluminum to Composite Comparison 27
4 Conclusion 29
References 30
Appendix A ndash Classical Lamination Matlab Code 31
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v
LIST OF TABLES
Table 11 Mission Requirements 2
Table 12 Tomahawk Cruise Missile Specifications 2
Table 13 Available Composite Propellant 3
Table 21 E357 T-6 Casted Aluminum 11
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties 12
Table 31 Engine Parameters 16
Table 32 Aluminum Engine Weight 17
Table 33 Laminate Properties Calculated by CLT 22
Table 34 Composite Engine Weight 23
Table 35 Laminate Properties in ANSYS 24
Table 36 Composite Casing Stress and Margins 27
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vi
LIST OF FIGURES
Figure 11 Typical Rocket Components [2] 1
Figure 21 Rocket Free Body Diagram [3] 5
Figure 22 Aluminum Engine Casing Concept 10
Figure 23 Composite Engine Casing Concept 10
Figure 24 Finite Element Load and Boundary Conditions 11
Figure 31 Aluminum Alloy Casing Detail 17
Figure 32 Maximum Stress Aluminum Engine Casing Upper 18
Figure 33 Maximum Stress Aluminum Engine Casing Lower 19
Figure 34 Assembly Flight Path 19
Figure 35 Flight Performance 20
Figure 36 Rocket Angle Altitude and Velocities 21
Figure 37 Composite Casing Detail 23
Figure 38 FEA Geometry for Composite Casing 24
Figure 39 Load and Boundary Conditions Composite Casing 25
Figure 310 Maximum Total Deformation Composite Casing 26
Figure 311 Top Radius Stress Composite Casing 26
Figure 312 Flight Performance Comparison 28
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vii
LIST OF EQUATIONS
Equation 21 ndash Flight path angle to ground 5
Equation 22 ndash Axial acceleration at 1000 feet 6
Equation 23 ndash Axial acceleration below1000 feet 5
Equation 24 ndash Radial acceleration above 1000 feet 6
Equation 25 ndash Radial acceleration below 1000 feet 6
Equation 26 ndash Axial velocity 6
Equation 27 ndash Radial velocity 6
Equation 28 ndash Axial dispacement 6
Equation 29 ndash Radial dispacement 6
Equation 210 ndash Horizontal distance and altitude matrix 6
Equation 211 ndash Propellant burn Area 6
Equation 212 ndash X Function 7
Equation 213 ndash Nozzle exit area 7
Equation 214 ndash Nozzle throat area 7
Equation 215 ndash Combustion chamber pressure 7
Equation 216 ndash Propellant burn rate 7
Equation 217 ndash Expansion ratio 7
Equation 218 ndash Exit pressure 8
Equation 219 ndash Ideal thrust coefficient 8
Equation 220 ndash Actual thrust coefficient 8
Equation 221 ndash Specific impulse 8
Equation 222 ndash Propellant core area 8
Equation 223 ndash Propellant core volume 8
Equation 224 ndash Combustion chamber volume 8
Equation 225 ndash Propellant volume 8
Equation 226 ndash Propellant mass 8
Equation 227 ndash Mass flow 8
Equation 228 ndash Burn time 8
Equation 229 ndash Total impulse 9
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viii
Equation 230 ndash Laminae StressStrain relationship 13
Equation 231 ndash Laminae Reduced Compliance StressStrain relationship 13
Equation 232 ndash Laminae Global Reduced Compliance StressStrain relationship 13
Equation 233 ndash Transformation matrix 13
Equation 234 ndash Laminae Transformed StressStrain relationship 13
Equation 235 ndash Laminae global x stiffness 13
Equation 236 ndash Laminae global y stiffness 13
Equation 237 ndash Laminae global shear modulus 13
Equation 238 ndash Laminae Poissonrsquos ratio xy 13
Equation 239 ndash Laminae Poissonrsquos ratio yx 14
Equation 240 ndash Laminae Global Reduced Stiffness StressStrain relationship 14
Equation 241 ndash Reduced Stiffness Matrix definition 14
Equation 242 ndash Extensional stiffness matrix 14
Equation 243 ndash Couplingstiffness matrix 14
Equation 244 ndash Bending stiffness matrix 14
Equation 245 ndash Laminate LoadStrain relationship 14
Equation 246 ndash Tsai-Hill failure criteria 15
Equation 31 ndash Yield stress margin of safety 18
Equation 32 ndash Ultimate stress margin of safety 18
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ix
LIST OF SYMBOLS
Motion
a ndash Acceleration (fts2)
awing ndash LiftMass of Missile Wing (32174 fts
2
)Cd ndash Coefficient of Drag
Cl ndash Coefficient of Lift
F ndash Engine Thrust (lbf )
g ndash Acceleration of Gravity on Earth (32174 fts2)
ld ratio ndash Ratio of Cl to Cd
tn ndash Time at Increment n (s)
Ψ ndash Engine Thrust Relative to Horizontal (degrees)
ρair ndash Density of Air (lbft3)
θ ndash Direction of Flight Relative to Horizontal (degrees)
v ndash Velocity in Rocket Coordinates (fts)
x ndash Axial Displacement in Rocket Coordinates (ft)
y ndash Radial Displacement in Rocket Coordinates (ft)
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x
Engine
A ndash Nozzle Throat Cross-Sectional Area (in2)
A b ndash Propellant Burning Area (in2)
Aconduit ndash Area of Core in Propellant Charge (in2)
Ae ndash Cross Sectional Area of Exhaust Cone (in2)
Cf ndash Thrust Coefficient
dc ndash Propellant Outer Diameter (in)
de ndash Diameter of Exhaust Cone (in)
ε ndash Expansion Ratio
Fn ndash Engine Thrust (lbf )
γ ndash Specific Heat Ratio
Isp ndash Specific Impulse (s)
It ndash Total Impulse (lbf -s)
k ndash Propellant Burn Rate Factor
Lc ndash Length of Propellant (in)
ṁ ndash Mass Flow Rate (lbms)
mc ndash Mass of Propellant (lbm)
n ndash Propellant Burn Rate Factor
Pc ndash Chamber Pressure (psi)
Po ndash Atmospheric Pressure (psi)
R ndash Gas Constant (lbf -inlbm-R)
r b ndash Propellant Burn Rate (ins)
t b ndash Propellant Burn Time (s)
ρ p ndash Density of Propellant (lbmin3)
Tc ndash Propellant Burn Temperature (degR)
V0 ndash Volume of No Core Propellant (in3)
Vc ndash Propellant Volume (in3)
Vconduit ndash Conduit Volume (in3)
X ndash Non-Dimensional Mass Flow Rate in Nozzle Throat
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Material
E ndash Youngrsquos Modulus (psi)
ε ndash Normal Strain (inin)
γ ndash Shear Strain (inin)
Fcy ndash Yield Compressive Strength (psi)
Fcu ndash Ultimate Compressive Strength (psi)
Fty ndash Yield Tensile Strength (psi)
Ftu ndash Ultimate Tensile Strength (psi)
Fsu ndash Ultimate Shear Strength (psi)
G ndash Shear Modulus (psi)
MSyld-comp ndash Yield Strength Margin of Safety ndash Compressive
MSult-comp ndash Ultimate Strength Margin of Safety ndash Compressive
MSyld-tensile ndash Yield Strength Margin of Safety ndash Tensile
MSult-tensile ndash Ultimate Strength Margin of Safety ndash Tensile
ν ndash Poissonrsquos Ratio
σ ndash Normal Stress (psi)
[Q] ndash Laminae Reduced Stiffness Matrix (psi)
[Q ] ndash Laminae Transposed Reduced Stiffness Matrix (psi)
[S] ndash Laminae Reduced Compliance Matrix (in2lb)
[S ] ndash Laminae Transposed Reduced Compliance Matrix (in2lb)
τ ndashShear Stress (psi)
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
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983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 2
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ii
copy Copyright 2012
by
Devon K Cowles
All Rights Reserved
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iii
CONTENTS
LIST OF TABLES v
LIST OF FIGURES vi
LIST OF EQUATIONS vii
LIST OF SYMBOLS ix
Glossary xii
ABSTRACT xiii
1 IntroductionBackground 1
11 Rockets 1
12 Mission Requirements 2
13 Structural Requirements 3
2 Methodology 4
21 Assumptions 4
22 Flight Performance 5
23 Motor thrust requirements 6
24 Motor Casing Sizing 9
25
Material 11
251
Aluminum Alloy 11
252
Composite Material 11
3
Results 16
31
Engine Parameters 16
32
Aluminum Alloy Casing Design 16
321
Aluminum Casing Geometry 16
322
Finite Element Analysis 17
33 Composite Casing Design 21
331 Layup 21
332 Composite Casing Geometry 22
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iv
333 Finite Element Analysis 24
334 Aluminum to Composite Comparison 27
4 Conclusion 29
References 30
Appendix A ndash Classical Lamination Matlab Code 31
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v
LIST OF TABLES
Table 11 Mission Requirements 2
Table 12 Tomahawk Cruise Missile Specifications 2
Table 13 Available Composite Propellant 3
Table 21 E357 T-6 Casted Aluminum 11
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties 12
Table 31 Engine Parameters 16
Table 32 Aluminum Engine Weight 17
Table 33 Laminate Properties Calculated by CLT 22
Table 34 Composite Engine Weight 23
Table 35 Laminate Properties in ANSYS 24
Table 36 Composite Casing Stress and Margins 27
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vi
LIST OF FIGURES
Figure 11 Typical Rocket Components [2] 1
Figure 21 Rocket Free Body Diagram [3] 5
Figure 22 Aluminum Engine Casing Concept 10
Figure 23 Composite Engine Casing Concept 10
Figure 24 Finite Element Load and Boundary Conditions 11
Figure 31 Aluminum Alloy Casing Detail 17
Figure 32 Maximum Stress Aluminum Engine Casing Upper 18
Figure 33 Maximum Stress Aluminum Engine Casing Lower 19
Figure 34 Assembly Flight Path 19
Figure 35 Flight Performance 20
Figure 36 Rocket Angle Altitude and Velocities 21
Figure 37 Composite Casing Detail 23
Figure 38 FEA Geometry for Composite Casing 24
Figure 39 Load and Boundary Conditions Composite Casing 25
Figure 310 Maximum Total Deformation Composite Casing 26
Figure 311 Top Radius Stress Composite Casing 26
Figure 312 Flight Performance Comparison 28
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vii
LIST OF EQUATIONS
Equation 21 ndash Flight path angle to ground 5
Equation 22 ndash Axial acceleration at 1000 feet 6
Equation 23 ndash Axial acceleration below1000 feet 5
Equation 24 ndash Radial acceleration above 1000 feet 6
Equation 25 ndash Radial acceleration below 1000 feet 6
Equation 26 ndash Axial velocity 6
Equation 27 ndash Radial velocity 6
Equation 28 ndash Axial dispacement 6
Equation 29 ndash Radial dispacement 6
Equation 210 ndash Horizontal distance and altitude matrix 6
Equation 211 ndash Propellant burn Area 6
Equation 212 ndash X Function 7
Equation 213 ndash Nozzle exit area 7
Equation 214 ndash Nozzle throat area 7
Equation 215 ndash Combustion chamber pressure 7
Equation 216 ndash Propellant burn rate 7
Equation 217 ndash Expansion ratio 7
Equation 218 ndash Exit pressure 8
Equation 219 ndash Ideal thrust coefficient 8
Equation 220 ndash Actual thrust coefficient 8
Equation 221 ndash Specific impulse 8
Equation 222 ndash Propellant core area 8
Equation 223 ndash Propellant core volume 8
Equation 224 ndash Combustion chamber volume 8
Equation 225 ndash Propellant volume 8
Equation 226 ndash Propellant mass 8
Equation 227 ndash Mass flow 8
Equation 228 ndash Burn time 8
Equation 229 ndash Total impulse 9
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viii
Equation 230 ndash Laminae StressStrain relationship 13
Equation 231 ndash Laminae Reduced Compliance StressStrain relationship 13
Equation 232 ndash Laminae Global Reduced Compliance StressStrain relationship 13
Equation 233 ndash Transformation matrix 13
Equation 234 ndash Laminae Transformed StressStrain relationship 13
Equation 235 ndash Laminae global x stiffness 13
Equation 236 ndash Laminae global y stiffness 13
Equation 237 ndash Laminae global shear modulus 13
Equation 238 ndash Laminae Poissonrsquos ratio xy 13
Equation 239 ndash Laminae Poissonrsquos ratio yx 14
Equation 240 ndash Laminae Global Reduced Stiffness StressStrain relationship 14
Equation 241 ndash Reduced Stiffness Matrix definition 14
Equation 242 ndash Extensional stiffness matrix 14
Equation 243 ndash Couplingstiffness matrix 14
Equation 244 ndash Bending stiffness matrix 14
Equation 245 ndash Laminate LoadStrain relationship 14
Equation 246 ndash Tsai-Hill failure criteria 15
Equation 31 ndash Yield stress margin of safety 18
Equation 32 ndash Ultimate stress margin of safety 18
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ix
LIST OF SYMBOLS
Motion
a ndash Acceleration (fts2)
awing ndash LiftMass of Missile Wing (32174 fts
2
)Cd ndash Coefficient of Drag
Cl ndash Coefficient of Lift
F ndash Engine Thrust (lbf )
g ndash Acceleration of Gravity on Earth (32174 fts2)
ld ratio ndash Ratio of Cl to Cd
tn ndash Time at Increment n (s)
Ψ ndash Engine Thrust Relative to Horizontal (degrees)
ρair ndash Density of Air (lbft3)
θ ndash Direction of Flight Relative to Horizontal (degrees)
v ndash Velocity in Rocket Coordinates (fts)
x ndash Axial Displacement in Rocket Coordinates (ft)
y ndash Radial Displacement in Rocket Coordinates (ft)
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x
Engine
A ndash Nozzle Throat Cross-Sectional Area (in2)
A b ndash Propellant Burning Area (in2)
Aconduit ndash Area of Core in Propellant Charge (in2)
Ae ndash Cross Sectional Area of Exhaust Cone (in2)
Cf ndash Thrust Coefficient
dc ndash Propellant Outer Diameter (in)
de ndash Diameter of Exhaust Cone (in)
ε ndash Expansion Ratio
Fn ndash Engine Thrust (lbf )
γ ndash Specific Heat Ratio
Isp ndash Specific Impulse (s)
It ndash Total Impulse (lbf -s)
k ndash Propellant Burn Rate Factor
Lc ndash Length of Propellant (in)
ṁ ndash Mass Flow Rate (lbms)
mc ndash Mass of Propellant (lbm)
n ndash Propellant Burn Rate Factor
Pc ndash Chamber Pressure (psi)
Po ndash Atmospheric Pressure (psi)
R ndash Gas Constant (lbf -inlbm-R)
r b ndash Propellant Burn Rate (ins)
t b ndash Propellant Burn Time (s)
ρ p ndash Density of Propellant (lbmin3)
Tc ndash Propellant Burn Temperature (degR)
V0 ndash Volume of No Core Propellant (in3)
Vc ndash Propellant Volume (in3)
Vconduit ndash Conduit Volume (in3)
X ndash Non-Dimensional Mass Flow Rate in Nozzle Throat
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xi
Material
E ndash Youngrsquos Modulus (psi)
ε ndash Normal Strain (inin)
γ ndash Shear Strain (inin)
Fcy ndash Yield Compressive Strength (psi)
Fcu ndash Ultimate Compressive Strength (psi)
Fty ndash Yield Tensile Strength (psi)
Ftu ndash Ultimate Tensile Strength (psi)
Fsu ndash Ultimate Shear Strength (psi)
G ndash Shear Modulus (psi)
MSyld-comp ndash Yield Strength Margin of Safety ndash Compressive
MSult-comp ndash Ultimate Strength Margin of Safety ndash Compressive
MSyld-tensile ndash Yield Strength Margin of Safety ndash Tensile
MSult-tensile ndash Ultimate Strength Margin of Safety ndash Tensile
ν ndash Poissonrsquos Ratio
σ ndash Normal Stress (psi)
[Q] ndash Laminae Reduced Stiffness Matrix (psi)
[Q ] ndash Laminae Transposed Reduced Stiffness Matrix (psi)
[S] ndash Laminae Reduced Compliance Matrix (in2lb)
[S ] ndash Laminae Transposed Reduced Compliance Matrix (in2lb)
τ ndashShear Stress (psi)
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
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983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 3
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iii
CONTENTS
LIST OF TABLES v
LIST OF FIGURES vi
LIST OF EQUATIONS vii
LIST OF SYMBOLS ix
Glossary xii
ABSTRACT xiii
1 IntroductionBackground 1
11 Rockets 1
12 Mission Requirements 2
13 Structural Requirements 3
2 Methodology 4
21 Assumptions 4
22 Flight Performance 5
23 Motor thrust requirements 6
24 Motor Casing Sizing 9
25
Material 11
251
Aluminum Alloy 11
252
Composite Material 11
3
Results 16
31
Engine Parameters 16
32
Aluminum Alloy Casing Design 16
321
Aluminum Casing Geometry 16
322
Finite Element Analysis 17
33 Composite Casing Design 21
331 Layup 21
332 Composite Casing Geometry 22
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iv
333 Finite Element Analysis 24
334 Aluminum to Composite Comparison 27
4 Conclusion 29
References 30
Appendix A ndash Classical Lamination Matlab Code 31
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v
LIST OF TABLES
Table 11 Mission Requirements 2
Table 12 Tomahawk Cruise Missile Specifications 2
Table 13 Available Composite Propellant 3
Table 21 E357 T-6 Casted Aluminum 11
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties 12
Table 31 Engine Parameters 16
Table 32 Aluminum Engine Weight 17
Table 33 Laminate Properties Calculated by CLT 22
Table 34 Composite Engine Weight 23
Table 35 Laminate Properties in ANSYS 24
Table 36 Composite Casing Stress and Margins 27
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vi
LIST OF FIGURES
Figure 11 Typical Rocket Components [2] 1
Figure 21 Rocket Free Body Diagram [3] 5
Figure 22 Aluminum Engine Casing Concept 10
Figure 23 Composite Engine Casing Concept 10
Figure 24 Finite Element Load and Boundary Conditions 11
Figure 31 Aluminum Alloy Casing Detail 17
Figure 32 Maximum Stress Aluminum Engine Casing Upper 18
Figure 33 Maximum Stress Aluminum Engine Casing Lower 19
Figure 34 Assembly Flight Path 19
Figure 35 Flight Performance 20
Figure 36 Rocket Angle Altitude and Velocities 21
Figure 37 Composite Casing Detail 23
Figure 38 FEA Geometry for Composite Casing 24
Figure 39 Load and Boundary Conditions Composite Casing 25
Figure 310 Maximum Total Deformation Composite Casing 26
Figure 311 Top Radius Stress Composite Casing 26
Figure 312 Flight Performance Comparison 28
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vii
LIST OF EQUATIONS
Equation 21 ndash Flight path angle to ground 5
Equation 22 ndash Axial acceleration at 1000 feet 6
Equation 23 ndash Axial acceleration below1000 feet 5
Equation 24 ndash Radial acceleration above 1000 feet 6
Equation 25 ndash Radial acceleration below 1000 feet 6
Equation 26 ndash Axial velocity 6
Equation 27 ndash Radial velocity 6
Equation 28 ndash Axial dispacement 6
Equation 29 ndash Radial dispacement 6
Equation 210 ndash Horizontal distance and altitude matrix 6
Equation 211 ndash Propellant burn Area 6
Equation 212 ndash X Function 7
Equation 213 ndash Nozzle exit area 7
Equation 214 ndash Nozzle throat area 7
Equation 215 ndash Combustion chamber pressure 7
Equation 216 ndash Propellant burn rate 7
Equation 217 ndash Expansion ratio 7
Equation 218 ndash Exit pressure 8
Equation 219 ndash Ideal thrust coefficient 8
Equation 220 ndash Actual thrust coefficient 8
Equation 221 ndash Specific impulse 8
Equation 222 ndash Propellant core area 8
Equation 223 ndash Propellant core volume 8
Equation 224 ndash Combustion chamber volume 8
Equation 225 ndash Propellant volume 8
Equation 226 ndash Propellant mass 8
Equation 227 ndash Mass flow 8
Equation 228 ndash Burn time 8
Equation 229 ndash Total impulse 9
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viii
Equation 230 ndash Laminae StressStrain relationship 13
Equation 231 ndash Laminae Reduced Compliance StressStrain relationship 13
Equation 232 ndash Laminae Global Reduced Compliance StressStrain relationship 13
Equation 233 ndash Transformation matrix 13
Equation 234 ndash Laminae Transformed StressStrain relationship 13
Equation 235 ndash Laminae global x stiffness 13
Equation 236 ndash Laminae global y stiffness 13
Equation 237 ndash Laminae global shear modulus 13
Equation 238 ndash Laminae Poissonrsquos ratio xy 13
Equation 239 ndash Laminae Poissonrsquos ratio yx 14
Equation 240 ndash Laminae Global Reduced Stiffness StressStrain relationship 14
Equation 241 ndash Reduced Stiffness Matrix definition 14
Equation 242 ndash Extensional stiffness matrix 14
Equation 243 ndash Couplingstiffness matrix 14
Equation 244 ndash Bending stiffness matrix 14
Equation 245 ndash Laminate LoadStrain relationship 14
Equation 246 ndash Tsai-Hill failure criteria 15
Equation 31 ndash Yield stress margin of safety 18
Equation 32 ndash Ultimate stress margin of safety 18
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ix
LIST OF SYMBOLS
Motion
a ndash Acceleration (fts2)
awing ndash LiftMass of Missile Wing (32174 fts
2
)Cd ndash Coefficient of Drag
Cl ndash Coefficient of Lift
F ndash Engine Thrust (lbf )
g ndash Acceleration of Gravity on Earth (32174 fts2)
ld ratio ndash Ratio of Cl to Cd
tn ndash Time at Increment n (s)
Ψ ndash Engine Thrust Relative to Horizontal (degrees)
ρair ndash Density of Air (lbft3)
θ ndash Direction of Flight Relative to Horizontal (degrees)
v ndash Velocity in Rocket Coordinates (fts)
x ndash Axial Displacement in Rocket Coordinates (ft)
y ndash Radial Displacement in Rocket Coordinates (ft)
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x
Engine
A ndash Nozzle Throat Cross-Sectional Area (in2)
A b ndash Propellant Burning Area (in2)
Aconduit ndash Area of Core in Propellant Charge (in2)
Ae ndash Cross Sectional Area of Exhaust Cone (in2)
Cf ndash Thrust Coefficient
dc ndash Propellant Outer Diameter (in)
de ndash Diameter of Exhaust Cone (in)
ε ndash Expansion Ratio
Fn ndash Engine Thrust (lbf )
γ ndash Specific Heat Ratio
Isp ndash Specific Impulse (s)
It ndash Total Impulse (lbf -s)
k ndash Propellant Burn Rate Factor
Lc ndash Length of Propellant (in)
ṁ ndash Mass Flow Rate (lbms)
mc ndash Mass of Propellant (lbm)
n ndash Propellant Burn Rate Factor
Pc ndash Chamber Pressure (psi)
Po ndash Atmospheric Pressure (psi)
R ndash Gas Constant (lbf -inlbm-R)
r b ndash Propellant Burn Rate (ins)
t b ndash Propellant Burn Time (s)
ρ p ndash Density of Propellant (lbmin3)
Tc ndash Propellant Burn Temperature (degR)
V0 ndash Volume of No Core Propellant (in3)
Vc ndash Propellant Volume (in3)
Vconduit ndash Conduit Volume (in3)
X ndash Non-Dimensional Mass Flow Rate in Nozzle Throat
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xi
Material
E ndash Youngrsquos Modulus (psi)
ε ndash Normal Strain (inin)
γ ndash Shear Strain (inin)
Fcy ndash Yield Compressive Strength (psi)
Fcu ndash Ultimate Compressive Strength (psi)
Fty ndash Yield Tensile Strength (psi)
Ftu ndash Ultimate Tensile Strength (psi)
Fsu ndash Ultimate Shear Strength (psi)
G ndash Shear Modulus (psi)
MSyld-comp ndash Yield Strength Margin of Safety ndash Compressive
MSult-comp ndash Ultimate Strength Margin of Safety ndash Compressive
MSyld-tensile ndash Yield Strength Margin of Safety ndash Tensile
MSult-tensile ndash Ultimate Strength Margin of Safety ndash Tensile
ν ndash Poissonrsquos Ratio
σ ndash Normal Stress (psi)
[Q] ndash Laminae Reduced Stiffness Matrix (psi)
[Q ] ndash Laminae Transposed Reduced Stiffness Matrix (psi)
[S] ndash Laminae Reduced Compliance Matrix (in2lb)
[S ] ndash Laminae Transposed Reduced Compliance Matrix (in2lb)
τ ndashShear Stress (psi)
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
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983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 4
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iv
333 Finite Element Analysis 24
334 Aluminum to Composite Comparison 27
4 Conclusion 29
References 30
Appendix A ndash Classical Lamination Matlab Code 31
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v
LIST OF TABLES
Table 11 Mission Requirements 2
Table 12 Tomahawk Cruise Missile Specifications 2
Table 13 Available Composite Propellant 3
Table 21 E357 T-6 Casted Aluminum 11
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties 12
Table 31 Engine Parameters 16
Table 32 Aluminum Engine Weight 17
Table 33 Laminate Properties Calculated by CLT 22
Table 34 Composite Engine Weight 23
Table 35 Laminate Properties in ANSYS 24
Table 36 Composite Casing Stress and Margins 27
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vi
LIST OF FIGURES
Figure 11 Typical Rocket Components [2] 1
Figure 21 Rocket Free Body Diagram [3] 5
Figure 22 Aluminum Engine Casing Concept 10
Figure 23 Composite Engine Casing Concept 10
Figure 24 Finite Element Load and Boundary Conditions 11
Figure 31 Aluminum Alloy Casing Detail 17
Figure 32 Maximum Stress Aluminum Engine Casing Upper 18
Figure 33 Maximum Stress Aluminum Engine Casing Lower 19
Figure 34 Assembly Flight Path 19
Figure 35 Flight Performance 20
Figure 36 Rocket Angle Altitude and Velocities 21
Figure 37 Composite Casing Detail 23
Figure 38 FEA Geometry for Composite Casing 24
Figure 39 Load and Boundary Conditions Composite Casing 25
Figure 310 Maximum Total Deformation Composite Casing 26
Figure 311 Top Radius Stress Composite Casing 26
Figure 312 Flight Performance Comparison 28
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vii
LIST OF EQUATIONS
Equation 21 ndash Flight path angle to ground 5
Equation 22 ndash Axial acceleration at 1000 feet 6
Equation 23 ndash Axial acceleration below1000 feet 5
Equation 24 ndash Radial acceleration above 1000 feet 6
Equation 25 ndash Radial acceleration below 1000 feet 6
Equation 26 ndash Axial velocity 6
Equation 27 ndash Radial velocity 6
Equation 28 ndash Axial dispacement 6
Equation 29 ndash Radial dispacement 6
Equation 210 ndash Horizontal distance and altitude matrix 6
Equation 211 ndash Propellant burn Area 6
Equation 212 ndash X Function 7
Equation 213 ndash Nozzle exit area 7
Equation 214 ndash Nozzle throat area 7
Equation 215 ndash Combustion chamber pressure 7
Equation 216 ndash Propellant burn rate 7
Equation 217 ndash Expansion ratio 7
Equation 218 ndash Exit pressure 8
Equation 219 ndash Ideal thrust coefficient 8
Equation 220 ndash Actual thrust coefficient 8
Equation 221 ndash Specific impulse 8
Equation 222 ndash Propellant core area 8
Equation 223 ndash Propellant core volume 8
Equation 224 ndash Combustion chamber volume 8
Equation 225 ndash Propellant volume 8
Equation 226 ndash Propellant mass 8
Equation 227 ndash Mass flow 8
Equation 228 ndash Burn time 8
Equation 229 ndash Total impulse 9
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viii
Equation 230 ndash Laminae StressStrain relationship 13
Equation 231 ndash Laminae Reduced Compliance StressStrain relationship 13
Equation 232 ndash Laminae Global Reduced Compliance StressStrain relationship 13
Equation 233 ndash Transformation matrix 13
Equation 234 ndash Laminae Transformed StressStrain relationship 13
Equation 235 ndash Laminae global x stiffness 13
Equation 236 ndash Laminae global y stiffness 13
Equation 237 ndash Laminae global shear modulus 13
Equation 238 ndash Laminae Poissonrsquos ratio xy 13
Equation 239 ndash Laminae Poissonrsquos ratio yx 14
Equation 240 ndash Laminae Global Reduced Stiffness StressStrain relationship 14
Equation 241 ndash Reduced Stiffness Matrix definition 14
Equation 242 ndash Extensional stiffness matrix 14
Equation 243 ndash Couplingstiffness matrix 14
Equation 244 ndash Bending stiffness matrix 14
Equation 245 ndash Laminate LoadStrain relationship 14
Equation 246 ndash Tsai-Hill failure criteria 15
Equation 31 ndash Yield stress margin of safety 18
Equation 32 ndash Ultimate stress margin of safety 18
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ix
LIST OF SYMBOLS
Motion
a ndash Acceleration (fts2)
awing ndash LiftMass of Missile Wing (32174 fts
2
)Cd ndash Coefficient of Drag
Cl ndash Coefficient of Lift
F ndash Engine Thrust (lbf )
g ndash Acceleration of Gravity on Earth (32174 fts2)
ld ratio ndash Ratio of Cl to Cd
tn ndash Time at Increment n (s)
Ψ ndash Engine Thrust Relative to Horizontal (degrees)
ρair ndash Density of Air (lbft3)
θ ndash Direction of Flight Relative to Horizontal (degrees)
v ndash Velocity in Rocket Coordinates (fts)
x ndash Axial Displacement in Rocket Coordinates (ft)
y ndash Radial Displacement in Rocket Coordinates (ft)
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x
Engine
A ndash Nozzle Throat Cross-Sectional Area (in2)
A b ndash Propellant Burning Area (in2)
Aconduit ndash Area of Core in Propellant Charge (in2)
Ae ndash Cross Sectional Area of Exhaust Cone (in2)
Cf ndash Thrust Coefficient
dc ndash Propellant Outer Diameter (in)
de ndash Diameter of Exhaust Cone (in)
ε ndash Expansion Ratio
Fn ndash Engine Thrust (lbf )
γ ndash Specific Heat Ratio
Isp ndash Specific Impulse (s)
It ndash Total Impulse (lbf -s)
k ndash Propellant Burn Rate Factor
Lc ndash Length of Propellant (in)
ṁ ndash Mass Flow Rate (lbms)
mc ndash Mass of Propellant (lbm)
n ndash Propellant Burn Rate Factor
Pc ndash Chamber Pressure (psi)
Po ndash Atmospheric Pressure (psi)
R ndash Gas Constant (lbf -inlbm-R)
r b ndash Propellant Burn Rate (ins)
t b ndash Propellant Burn Time (s)
ρ p ndash Density of Propellant (lbmin3)
Tc ndash Propellant Burn Temperature (degR)
V0 ndash Volume of No Core Propellant (in3)
Vc ndash Propellant Volume (in3)
Vconduit ndash Conduit Volume (in3)
X ndash Non-Dimensional Mass Flow Rate in Nozzle Throat
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xi
Material
E ndash Youngrsquos Modulus (psi)
ε ndash Normal Strain (inin)
γ ndash Shear Strain (inin)
Fcy ndash Yield Compressive Strength (psi)
Fcu ndash Ultimate Compressive Strength (psi)
Fty ndash Yield Tensile Strength (psi)
Ftu ndash Ultimate Tensile Strength (psi)
Fsu ndash Ultimate Shear Strength (psi)
G ndash Shear Modulus (psi)
MSyld-comp ndash Yield Strength Margin of Safety ndash Compressive
MSult-comp ndash Ultimate Strength Margin of Safety ndash Compressive
MSyld-tensile ndash Yield Strength Margin of Safety ndash Tensile
MSult-tensile ndash Ultimate Strength Margin of Safety ndash Tensile
ν ndash Poissonrsquos Ratio
σ ndash Normal Stress (psi)
[Q] ndash Laminae Reduced Stiffness Matrix (psi)
[Q ] ndash Laminae Transposed Reduced Stiffness Matrix (psi)
[S] ndash Laminae Reduced Compliance Matrix (in2lb)
[S ] ndash Laminae Transposed Reduced Compliance Matrix (in2lb)
τ ndashShear Stress (psi)
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
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983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
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983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 5
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v
LIST OF TABLES
Table 11 Mission Requirements 2
Table 12 Tomahawk Cruise Missile Specifications 2
Table 13 Available Composite Propellant 3
Table 21 E357 T-6 Casted Aluminum 11
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties 12
Table 31 Engine Parameters 16
Table 32 Aluminum Engine Weight 17
Table 33 Laminate Properties Calculated by CLT 22
Table 34 Composite Engine Weight 23
Table 35 Laminate Properties in ANSYS 24
Table 36 Composite Casing Stress and Margins 27
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vi
LIST OF FIGURES
Figure 11 Typical Rocket Components [2] 1
Figure 21 Rocket Free Body Diagram [3] 5
Figure 22 Aluminum Engine Casing Concept 10
Figure 23 Composite Engine Casing Concept 10
Figure 24 Finite Element Load and Boundary Conditions 11
Figure 31 Aluminum Alloy Casing Detail 17
Figure 32 Maximum Stress Aluminum Engine Casing Upper 18
Figure 33 Maximum Stress Aluminum Engine Casing Lower 19
Figure 34 Assembly Flight Path 19
Figure 35 Flight Performance 20
Figure 36 Rocket Angle Altitude and Velocities 21
Figure 37 Composite Casing Detail 23
Figure 38 FEA Geometry for Composite Casing 24
Figure 39 Load and Boundary Conditions Composite Casing 25
Figure 310 Maximum Total Deformation Composite Casing 26
Figure 311 Top Radius Stress Composite Casing 26
Figure 312 Flight Performance Comparison 28
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vii
LIST OF EQUATIONS
Equation 21 ndash Flight path angle to ground 5
Equation 22 ndash Axial acceleration at 1000 feet 6
Equation 23 ndash Axial acceleration below1000 feet 5
Equation 24 ndash Radial acceleration above 1000 feet 6
Equation 25 ndash Radial acceleration below 1000 feet 6
Equation 26 ndash Axial velocity 6
Equation 27 ndash Radial velocity 6
Equation 28 ndash Axial dispacement 6
Equation 29 ndash Radial dispacement 6
Equation 210 ndash Horizontal distance and altitude matrix 6
Equation 211 ndash Propellant burn Area 6
Equation 212 ndash X Function 7
Equation 213 ndash Nozzle exit area 7
Equation 214 ndash Nozzle throat area 7
Equation 215 ndash Combustion chamber pressure 7
Equation 216 ndash Propellant burn rate 7
Equation 217 ndash Expansion ratio 7
Equation 218 ndash Exit pressure 8
Equation 219 ndash Ideal thrust coefficient 8
Equation 220 ndash Actual thrust coefficient 8
Equation 221 ndash Specific impulse 8
Equation 222 ndash Propellant core area 8
Equation 223 ndash Propellant core volume 8
Equation 224 ndash Combustion chamber volume 8
Equation 225 ndash Propellant volume 8
Equation 226 ndash Propellant mass 8
Equation 227 ndash Mass flow 8
Equation 228 ndash Burn time 8
Equation 229 ndash Total impulse 9
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Equation 230 ndash Laminae StressStrain relationship 13
Equation 231 ndash Laminae Reduced Compliance StressStrain relationship 13
Equation 232 ndash Laminae Global Reduced Compliance StressStrain relationship 13
Equation 233 ndash Transformation matrix 13
Equation 234 ndash Laminae Transformed StressStrain relationship 13
Equation 235 ndash Laminae global x stiffness 13
Equation 236 ndash Laminae global y stiffness 13
Equation 237 ndash Laminae global shear modulus 13
Equation 238 ndash Laminae Poissonrsquos ratio xy 13
Equation 239 ndash Laminae Poissonrsquos ratio yx 14
Equation 240 ndash Laminae Global Reduced Stiffness StressStrain relationship 14
Equation 241 ndash Reduced Stiffness Matrix definition 14
Equation 242 ndash Extensional stiffness matrix 14
Equation 243 ndash Couplingstiffness matrix 14
Equation 244 ndash Bending stiffness matrix 14
Equation 245 ndash Laminate LoadStrain relationship 14
Equation 246 ndash Tsai-Hill failure criteria 15
Equation 31 ndash Yield stress margin of safety 18
Equation 32 ndash Ultimate stress margin of safety 18
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ix
LIST OF SYMBOLS
Motion
a ndash Acceleration (fts2)
awing ndash LiftMass of Missile Wing (32174 fts
2
)Cd ndash Coefficient of Drag
Cl ndash Coefficient of Lift
F ndash Engine Thrust (lbf )
g ndash Acceleration of Gravity on Earth (32174 fts2)
ld ratio ndash Ratio of Cl to Cd
tn ndash Time at Increment n (s)
Ψ ndash Engine Thrust Relative to Horizontal (degrees)
ρair ndash Density of Air (lbft3)
θ ndash Direction of Flight Relative to Horizontal (degrees)
v ndash Velocity in Rocket Coordinates (fts)
x ndash Axial Displacement in Rocket Coordinates (ft)
y ndash Radial Displacement in Rocket Coordinates (ft)
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x
Engine
A ndash Nozzle Throat Cross-Sectional Area (in2)
A b ndash Propellant Burning Area (in2)
Aconduit ndash Area of Core in Propellant Charge (in2)
Ae ndash Cross Sectional Area of Exhaust Cone (in2)
Cf ndash Thrust Coefficient
dc ndash Propellant Outer Diameter (in)
de ndash Diameter of Exhaust Cone (in)
ε ndash Expansion Ratio
Fn ndash Engine Thrust (lbf )
γ ndash Specific Heat Ratio
Isp ndash Specific Impulse (s)
It ndash Total Impulse (lbf -s)
k ndash Propellant Burn Rate Factor
Lc ndash Length of Propellant (in)
ṁ ndash Mass Flow Rate (lbms)
mc ndash Mass of Propellant (lbm)
n ndash Propellant Burn Rate Factor
Pc ndash Chamber Pressure (psi)
Po ndash Atmospheric Pressure (psi)
R ndash Gas Constant (lbf -inlbm-R)
r b ndash Propellant Burn Rate (ins)
t b ndash Propellant Burn Time (s)
ρ p ndash Density of Propellant (lbmin3)
Tc ndash Propellant Burn Temperature (degR)
V0 ndash Volume of No Core Propellant (in3)
Vc ndash Propellant Volume (in3)
Vconduit ndash Conduit Volume (in3)
X ndash Non-Dimensional Mass Flow Rate in Nozzle Throat
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Material
E ndash Youngrsquos Modulus (psi)
ε ndash Normal Strain (inin)
γ ndash Shear Strain (inin)
Fcy ndash Yield Compressive Strength (psi)
Fcu ndash Ultimate Compressive Strength (psi)
Fty ndash Yield Tensile Strength (psi)
Ftu ndash Ultimate Tensile Strength (psi)
Fsu ndash Ultimate Shear Strength (psi)
G ndash Shear Modulus (psi)
MSyld-comp ndash Yield Strength Margin of Safety ndash Compressive
MSult-comp ndash Ultimate Strength Margin of Safety ndash Compressive
MSyld-tensile ndash Yield Strength Margin of Safety ndash Tensile
MSult-tensile ndash Ultimate Strength Margin of Safety ndash Tensile
ν ndash Poissonrsquos Ratio
σ ndash Normal Stress (psi)
[Q] ndash Laminae Reduced Stiffness Matrix (psi)
[Q ] ndash Laminae Transposed Reduced Stiffness Matrix (psi)
[S] ndash Laminae Reduced Compliance Matrix (in2lb)
[S ] ndash Laminae Transposed Reduced Compliance Matrix (in2lb)
τ ndashShear Stress (psi)
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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7
The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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8
+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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26
Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 6
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vi
LIST OF FIGURES
Figure 11 Typical Rocket Components [2] 1
Figure 21 Rocket Free Body Diagram [3] 5
Figure 22 Aluminum Engine Casing Concept 10
Figure 23 Composite Engine Casing Concept 10
Figure 24 Finite Element Load and Boundary Conditions 11
Figure 31 Aluminum Alloy Casing Detail 17
Figure 32 Maximum Stress Aluminum Engine Casing Upper 18
Figure 33 Maximum Stress Aluminum Engine Casing Lower 19
Figure 34 Assembly Flight Path 19
Figure 35 Flight Performance 20
Figure 36 Rocket Angle Altitude and Velocities 21
Figure 37 Composite Casing Detail 23
Figure 38 FEA Geometry for Composite Casing 24
Figure 39 Load and Boundary Conditions Composite Casing 25
Figure 310 Maximum Total Deformation Composite Casing 26
Figure 311 Top Radius Stress Composite Casing 26
Figure 312 Flight Performance Comparison 28
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vii
LIST OF EQUATIONS
Equation 21 ndash Flight path angle to ground 5
Equation 22 ndash Axial acceleration at 1000 feet 6
Equation 23 ndash Axial acceleration below1000 feet 5
Equation 24 ndash Radial acceleration above 1000 feet 6
Equation 25 ndash Radial acceleration below 1000 feet 6
Equation 26 ndash Axial velocity 6
Equation 27 ndash Radial velocity 6
Equation 28 ndash Axial dispacement 6
Equation 29 ndash Radial dispacement 6
Equation 210 ndash Horizontal distance and altitude matrix 6
Equation 211 ndash Propellant burn Area 6
Equation 212 ndash X Function 7
Equation 213 ndash Nozzle exit area 7
Equation 214 ndash Nozzle throat area 7
Equation 215 ndash Combustion chamber pressure 7
Equation 216 ndash Propellant burn rate 7
Equation 217 ndash Expansion ratio 7
Equation 218 ndash Exit pressure 8
Equation 219 ndash Ideal thrust coefficient 8
Equation 220 ndash Actual thrust coefficient 8
Equation 221 ndash Specific impulse 8
Equation 222 ndash Propellant core area 8
Equation 223 ndash Propellant core volume 8
Equation 224 ndash Combustion chamber volume 8
Equation 225 ndash Propellant volume 8
Equation 226 ndash Propellant mass 8
Equation 227 ndash Mass flow 8
Equation 228 ndash Burn time 8
Equation 229 ndash Total impulse 9
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viii
Equation 230 ndash Laminae StressStrain relationship 13
Equation 231 ndash Laminae Reduced Compliance StressStrain relationship 13
Equation 232 ndash Laminae Global Reduced Compliance StressStrain relationship 13
Equation 233 ndash Transformation matrix 13
Equation 234 ndash Laminae Transformed StressStrain relationship 13
Equation 235 ndash Laminae global x stiffness 13
Equation 236 ndash Laminae global y stiffness 13
Equation 237 ndash Laminae global shear modulus 13
Equation 238 ndash Laminae Poissonrsquos ratio xy 13
Equation 239 ndash Laminae Poissonrsquos ratio yx 14
Equation 240 ndash Laminae Global Reduced Stiffness StressStrain relationship 14
Equation 241 ndash Reduced Stiffness Matrix definition 14
Equation 242 ndash Extensional stiffness matrix 14
Equation 243 ndash Couplingstiffness matrix 14
Equation 244 ndash Bending stiffness matrix 14
Equation 245 ndash Laminate LoadStrain relationship 14
Equation 246 ndash Tsai-Hill failure criteria 15
Equation 31 ndash Yield stress margin of safety 18
Equation 32 ndash Ultimate stress margin of safety 18
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ix
LIST OF SYMBOLS
Motion
a ndash Acceleration (fts2)
awing ndash LiftMass of Missile Wing (32174 fts
2
)Cd ndash Coefficient of Drag
Cl ndash Coefficient of Lift
F ndash Engine Thrust (lbf )
g ndash Acceleration of Gravity on Earth (32174 fts2)
ld ratio ndash Ratio of Cl to Cd
tn ndash Time at Increment n (s)
Ψ ndash Engine Thrust Relative to Horizontal (degrees)
ρair ndash Density of Air (lbft3)
θ ndash Direction of Flight Relative to Horizontal (degrees)
v ndash Velocity in Rocket Coordinates (fts)
x ndash Axial Displacement in Rocket Coordinates (ft)
y ndash Radial Displacement in Rocket Coordinates (ft)
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x
Engine
A ndash Nozzle Throat Cross-Sectional Area (in2)
A b ndash Propellant Burning Area (in2)
Aconduit ndash Area of Core in Propellant Charge (in2)
Ae ndash Cross Sectional Area of Exhaust Cone (in2)
Cf ndash Thrust Coefficient
dc ndash Propellant Outer Diameter (in)
de ndash Diameter of Exhaust Cone (in)
ε ndash Expansion Ratio
Fn ndash Engine Thrust (lbf )
γ ndash Specific Heat Ratio
Isp ndash Specific Impulse (s)
It ndash Total Impulse (lbf -s)
k ndash Propellant Burn Rate Factor
Lc ndash Length of Propellant (in)
ṁ ndash Mass Flow Rate (lbms)
mc ndash Mass of Propellant (lbm)
n ndash Propellant Burn Rate Factor
Pc ndash Chamber Pressure (psi)
Po ndash Atmospheric Pressure (psi)
R ndash Gas Constant (lbf -inlbm-R)
r b ndash Propellant Burn Rate (ins)
t b ndash Propellant Burn Time (s)
ρ p ndash Density of Propellant (lbmin3)
Tc ndash Propellant Burn Temperature (degR)
V0 ndash Volume of No Core Propellant (in3)
Vc ndash Propellant Volume (in3)
Vconduit ndash Conduit Volume (in3)
X ndash Non-Dimensional Mass Flow Rate in Nozzle Throat
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Material
E ndash Youngrsquos Modulus (psi)
ε ndash Normal Strain (inin)
γ ndash Shear Strain (inin)
Fcy ndash Yield Compressive Strength (psi)
Fcu ndash Ultimate Compressive Strength (psi)
Fty ndash Yield Tensile Strength (psi)
Ftu ndash Ultimate Tensile Strength (psi)
Fsu ndash Ultimate Shear Strength (psi)
G ndash Shear Modulus (psi)
MSyld-comp ndash Yield Strength Margin of Safety ndash Compressive
MSult-comp ndash Ultimate Strength Margin of Safety ndash Compressive
MSyld-tensile ndash Yield Strength Margin of Safety ndash Tensile
MSult-tensile ndash Ultimate Strength Margin of Safety ndash Tensile
ν ndash Poissonrsquos Ratio
σ ndash Normal Stress (psi)
[Q] ndash Laminae Reduced Stiffness Matrix (psi)
[Q ] ndash Laminae Transposed Reduced Stiffness Matrix (psi)
[S] ndash Laminae Reduced Compliance Matrix (in2lb)
[S ] ndash Laminae Transposed Reduced Compliance Matrix (in2lb)
τ ndashShear Stress (psi)
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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7
The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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8
+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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10
motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 7
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vii
LIST OF EQUATIONS
Equation 21 ndash Flight path angle to ground 5
Equation 22 ndash Axial acceleration at 1000 feet 6
Equation 23 ndash Axial acceleration below1000 feet 5
Equation 24 ndash Radial acceleration above 1000 feet 6
Equation 25 ndash Radial acceleration below 1000 feet 6
Equation 26 ndash Axial velocity 6
Equation 27 ndash Radial velocity 6
Equation 28 ndash Axial dispacement 6
Equation 29 ndash Radial dispacement 6
Equation 210 ndash Horizontal distance and altitude matrix 6
Equation 211 ndash Propellant burn Area 6
Equation 212 ndash X Function 7
Equation 213 ndash Nozzle exit area 7
Equation 214 ndash Nozzle throat area 7
Equation 215 ndash Combustion chamber pressure 7
Equation 216 ndash Propellant burn rate 7
Equation 217 ndash Expansion ratio 7
Equation 218 ndash Exit pressure 8
Equation 219 ndash Ideal thrust coefficient 8
Equation 220 ndash Actual thrust coefficient 8
Equation 221 ndash Specific impulse 8
Equation 222 ndash Propellant core area 8
Equation 223 ndash Propellant core volume 8
Equation 224 ndash Combustion chamber volume 8
Equation 225 ndash Propellant volume 8
Equation 226 ndash Propellant mass 8
Equation 227 ndash Mass flow 8
Equation 228 ndash Burn time 8
Equation 229 ndash Total impulse 9
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viii
Equation 230 ndash Laminae StressStrain relationship 13
Equation 231 ndash Laminae Reduced Compliance StressStrain relationship 13
Equation 232 ndash Laminae Global Reduced Compliance StressStrain relationship 13
Equation 233 ndash Transformation matrix 13
Equation 234 ndash Laminae Transformed StressStrain relationship 13
Equation 235 ndash Laminae global x stiffness 13
Equation 236 ndash Laminae global y stiffness 13
Equation 237 ndash Laminae global shear modulus 13
Equation 238 ndash Laminae Poissonrsquos ratio xy 13
Equation 239 ndash Laminae Poissonrsquos ratio yx 14
Equation 240 ndash Laminae Global Reduced Stiffness StressStrain relationship 14
Equation 241 ndash Reduced Stiffness Matrix definition 14
Equation 242 ndash Extensional stiffness matrix 14
Equation 243 ndash Couplingstiffness matrix 14
Equation 244 ndash Bending stiffness matrix 14
Equation 245 ndash Laminate LoadStrain relationship 14
Equation 246 ndash Tsai-Hill failure criteria 15
Equation 31 ndash Yield stress margin of safety 18
Equation 32 ndash Ultimate stress margin of safety 18
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ix
LIST OF SYMBOLS
Motion
a ndash Acceleration (fts2)
awing ndash LiftMass of Missile Wing (32174 fts
2
)Cd ndash Coefficient of Drag
Cl ndash Coefficient of Lift
F ndash Engine Thrust (lbf )
g ndash Acceleration of Gravity on Earth (32174 fts2)
ld ratio ndash Ratio of Cl to Cd
tn ndash Time at Increment n (s)
Ψ ndash Engine Thrust Relative to Horizontal (degrees)
ρair ndash Density of Air (lbft3)
θ ndash Direction of Flight Relative to Horizontal (degrees)
v ndash Velocity in Rocket Coordinates (fts)
x ndash Axial Displacement in Rocket Coordinates (ft)
y ndash Radial Displacement in Rocket Coordinates (ft)
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Engine
A ndash Nozzle Throat Cross-Sectional Area (in2)
A b ndash Propellant Burning Area (in2)
Aconduit ndash Area of Core in Propellant Charge (in2)
Ae ndash Cross Sectional Area of Exhaust Cone (in2)
Cf ndash Thrust Coefficient
dc ndash Propellant Outer Diameter (in)
de ndash Diameter of Exhaust Cone (in)
ε ndash Expansion Ratio
Fn ndash Engine Thrust (lbf )
γ ndash Specific Heat Ratio
Isp ndash Specific Impulse (s)
It ndash Total Impulse (lbf -s)
k ndash Propellant Burn Rate Factor
Lc ndash Length of Propellant (in)
ṁ ndash Mass Flow Rate (lbms)
mc ndash Mass of Propellant (lbm)
n ndash Propellant Burn Rate Factor
Pc ndash Chamber Pressure (psi)
Po ndash Atmospheric Pressure (psi)
R ndash Gas Constant (lbf -inlbm-R)
r b ndash Propellant Burn Rate (ins)
t b ndash Propellant Burn Time (s)
ρ p ndash Density of Propellant (lbmin3)
Tc ndash Propellant Burn Temperature (degR)
V0 ndash Volume of No Core Propellant (in3)
Vc ndash Propellant Volume (in3)
Vconduit ndash Conduit Volume (in3)
X ndash Non-Dimensional Mass Flow Rate in Nozzle Throat
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Material
E ndash Youngrsquos Modulus (psi)
ε ndash Normal Strain (inin)
γ ndash Shear Strain (inin)
Fcy ndash Yield Compressive Strength (psi)
Fcu ndash Ultimate Compressive Strength (psi)
Fty ndash Yield Tensile Strength (psi)
Ftu ndash Ultimate Tensile Strength (psi)
Fsu ndash Ultimate Shear Strength (psi)
G ndash Shear Modulus (psi)
MSyld-comp ndash Yield Strength Margin of Safety ndash Compressive
MSult-comp ndash Ultimate Strength Margin of Safety ndash Compressive
MSyld-tensile ndash Yield Strength Margin of Safety ndash Tensile
MSult-tensile ndash Ultimate Strength Margin of Safety ndash Tensile
ν ndash Poissonrsquos Ratio
σ ndash Normal Stress (psi)
[Q] ndash Laminae Reduced Stiffness Matrix (psi)
[Q ] ndash Laminae Transposed Reduced Stiffness Matrix (psi)
[S] ndash Laminae Reduced Compliance Matrix (in2lb)
[S ] ndash Laminae Transposed Reduced Compliance Matrix (in2lb)
τ ndashShear Stress (psi)
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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7
The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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8
+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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10
motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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11
Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 8
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viii
Equation 230 ndash Laminae StressStrain relationship 13
Equation 231 ndash Laminae Reduced Compliance StressStrain relationship 13
Equation 232 ndash Laminae Global Reduced Compliance StressStrain relationship 13
Equation 233 ndash Transformation matrix 13
Equation 234 ndash Laminae Transformed StressStrain relationship 13
Equation 235 ndash Laminae global x stiffness 13
Equation 236 ndash Laminae global y stiffness 13
Equation 237 ndash Laminae global shear modulus 13
Equation 238 ndash Laminae Poissonrsquos ratio xy 13
Equation 239 ndash Laminae Poissonrsquos ratio yx 14
Equation 240 ndash Laminae Global Reduced Stiffness StressStrain relationship 14
Equation 241 ndash Reduced Stiffness Matrix definition 14
Equation 242 ndash Extensional stiffness matrix 14
Equation 243 ndash Couplingstiffness matrix 14
Equation 244 ndash Bending stiffness matrix 14
Equation 245 ndash Laminate LoadStrain relationship 14
Equation 246 ndash Tsai-Hill failure criteria 15
Equation 31 ndash Yield stress margin of safety 18
Equation 32 ndash Ultimate stress margin of safety 18
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ix
LIST OF SYMBOLS
Motion
a ndash Acceleration (fts2)
awing ndash LiftMass of Missile Wing (32174 fts
2
)Cd ndash Coefficient of Drag
Cl ndash Coefficient of Lift
F ndash Engine Thrust (lbf )
g ndash Acceleration of Gravity on Earth (32174 fts2)
ld ratio ndash Ratio of Cl to Cd
tn ndash Time at Increment n (s)
Ψ ndash Engine Thrust Relative to Horizontal (degrees)
ρair ndash Density of Air (lbft3)
θ ndash Direction of Flight Relative to Horizontal (degrees)
v ndash Velocity in Rocket Coordinates (fts)
x ndash Axial Displacement in Rocket Coordinates (ft)
y ndash Radial Displacement in Rocket Coordinates (ft)
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x
Engine
A ndash Nozzle Throat Cross-Sectional Area (in2)
A b ndash Propellant Burning Area (in2)
Aconduit ndash Area of Core in Propellant Charge (in2)
Ae ndash Cross Sectional Area of Exhaust Cone (in2)
Cf ndash Thrust Coefficient
dc ndash Propellant Outer Diameter (in)
de ndash Diameter of Exhaust Cone (in)
ε ndash Expansion Ratio
Fn ndash Engine Thrust (lbf )
γ ndash Specific Heat Ratio
Isp ndash Specific Impulse (s)
It ndash Total Impulse (lbf -s)
k ndash Propellant Burn Rate Factor
Lc ndash Length of Propellant (in)
ṁ ndash Mass Flow Rate (lbms)
mc ndash Mass of Propellant (lbm)
n ndash Propellant Burn Rate Factor
Pc ndash Chamber Pressure (psi)
Po ndash Atmospheric Pressure (psi)
R ndash Gas Constant (lbf -inlbm-R)
r b ndash Propellant Burn Rate (ins)
t b ndash Propellant Burn Time (s)
ρ p ndash Density of Propellant (lbmin3)
Tc ndash Propellant Burn Temperature (degR)
V0 ndash Volume of No Core Propellant (in3)
Vc ndash Propellant Volume (in3)
Vconduit ndash Conduit Volume (in3)
X ndash Non-Dimensional Mass Flow Rate in Nozzle Throat
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Material
E ndash Youngrsquos Modulus (psi)
ε ndash Normal Strain (inin)
γ ndash Shear Strain (inin)
Fcy ndash Yield Compressive Strength (psi)
Fcu ndash Ultimate Compressive Strength (psi)
Fty ndash Yield Tensile Strength (psi)
Ftu ndash Ultimate Tensile Strength (psi)
Fsu ndash Ultimate Shear Strength (psi)
G ndash Shear Modulus (psi)
MSyld-comp ndash Yield Strength Margin of Safety ndash Compressive
MSult-comp ndash Ultimate Strength Margin of Safety ndash Compressive
MSyld-tensile ndash Yield Strength Margin of Safety ndash Tensile
MSult-tensile ndash Ultimate Strength Margin of Safety ndash Tensile
ν ndash Poissonrsquos Ratio
σ ndash Normal Stress (psi)
[Q] ndash Laminae Reduced Stiffness Matrix (psi)
[Q ] ndash Laminae Transposed Reduced Stiffness Matrix (psi)
[S] ndash Laminae Reduced Compliance Matrix (in2lb)
[S ] ndash Laminae Transposed Reduced Compliance Matrix (in2lb)
τ ndashShear Stress (psi)
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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7
The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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8
+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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10
motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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11
Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 9
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ix
LIST OF SYMBOLS
Motion
a ndash Acceleration (fts2)
awing ndash LiftMass of Missile Wing (32174 fts
2
)Cd ndash Coefficient of Drag
Cl ndash Coefficient of Lift
F ndash Engine Thrust (lbf )
g ndash Acceleration of Gravity on Earth (32174 fts2)
ld ratio ndash Ratio of Cl to Cd
tn ndash Time at Increment n (s)
Ψ ndash Engine Thrust Relative to Horizontal (degrees)
ρair ndash Density of Air (lbft3)
θ ndash Direction of Flight Relative to Horizontal (degrees)
v ndash Velocity in Rocket Coordinates (fts)
x ndash Axial Displacement in Rocket Coordinates (ft)
y ndash Radial Displacement in Rocket Coordinates (ft)
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x
Engine
A ndash Nozzle Throat Cross-Sectional Area (in2)
A b ndash Propellant Burning Area (in2)
Aconduit ndash Area of Core in Propellant Charge (in2)
Ae ndash Cross Sectional Area of Exhaust Cone (in2)
Cf ndash Thrust Coefficient
dc ndash Propellant Outer Diameter (in)
de ndash Diameter of Exhaust Cone (in)
ε ndash Expansion Ratio
Fn ndash Engine Thrust (lbf )
γ ndash Specific Heat Ratio
Isp ndash Specific Impulse (s)
It ndash Total Impulse (lbf -s)
k ndash Propellant Burn Rate Factor
Lc ndash Length of Propellant (in)
ṁ ndash Mass Flow Rate (lbms)
mc ndash Mass of Propellant (lbm)
n ndash Propellant Burn Rate Factor
Pc ndash Chamber Pressure (psi)
Po ndash Atmospheric Pressure (psi)
R ndash Gas Constant (lbf -inlbm-R)
r b ndash Propellant Burn Rate (ins)
t b ndash Propellant Burn Time (s)
ρ p ndash Density of Propellant (lbmin3)
Tc ndash Propellant Burn Temperature (degR)
V0 ndash Volume of No Core Propellant (in3)
Vc ndash Propellant Volume (in3)
Vconduit ndash Conduit Volume (in3)
X ndash Non-Dimensional Mass Flow Rate in Nozzle Throat
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Material
E ndash Youngrsquos Modulus (psi)
ε ndash Normal Strain (inin)
γ ndash Shear Strain (inin)
Fcy ndash Yield Compressive Strength (psi)
Fcu ndash Ultimate Compressive Strength (psi)
Fty ndash Yield Tensile Strength (psi)
Ftu ndash Ultimate Tensile Strength (psi)
Fsu ndash Ultimate Shear Strength (psi)
G ndash Shear Modulus (psi)
MSyld-comp ndash Yield Strength Margin of Safety ndash Compressive
MSult-comp ndash Ultimate Strength Margin of Safety ndash Compressive
MSyld-tensile ndash Yield Strength Margin of Safety ndash Tensile
MSult-tensile ndash Ultimate Strength Margin of Safety ndash Tensile
ν ndash Poissonrsquos Ratio
σ ndash Normal Stress (psi)
[Q] ndash Laminae Reduced Stiffness Matrix (psi)
[Q ] ndash Laminae Transposed Reduced Stiffness Matrix (psi)
[S] ndash Laminae Reduced Compliance Matrix (in2lb)
[S ] ndash Laminae Transposed Reduced Compliance Matrix (in2lb)
τ ndashShear Stress (psi)
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 10
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x
Engine
A ndash Nozzle Throat Cross-Sectional Area (in2)
A b ndash Propellant Burning Area (in2)
Aconduit ndash Area of Core in Propellant Charge (in2)
Ae ndash Cross Sectional Area of Exhaust Cone (in2)
Cf ndash Thrust Coefficient
dc ndash Propellant Outer Diameter (in)
de ndash Diameter of Exhaust Cone (in)
ε ndash Expansion Ratio
Fn ndash Engine Thrust (lbf )
γ ndash Specific Heat Ratio
Isp ndash Specific Impulse (s)
It ndash Total Impulse (lbf -s)
k ndash Propellant Burn Rate Factor
Lc ndash Length of Propellant (in)
ṁ ndash Mass Flow Rate (lbms)
mc ndash Mass of Propellant (lbm)
n ndash Propellant Burn Rate Factor
Pc ndash Chamber Pressure (psi)
Po ndash Atmospheric Pressure (psi)
R ndash Gas Constant (lbf -inlbm-R)
r b ndash Propellant Burn Rate (ins)
t b ndash Propellant Burn Time (s)
ρ p ndash Density of Propellant (lbmin3)
Tc ndash Propellant Burn Temperature (degR)
V0 ndash Volume of No Core Propellant (in3)
Vc ndash Propellant Volume (in3)
Vconduit ndash Conduit Volume (in3)
X ndash Non-Dimensional Mass Flow Rate in Nozzle Throat
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xi
Material
E ndash Youngrsquos Modulus (psi)
ε ndash Normal Strain (inin)
γ ndash Shear Strain (inin)
Fcy ndash Yield Compressive Strength (psi)
Fcu ndash Ultimate Compressive Strength (psi)
Fty ndash Yield Tensile Strength (psi)
Ftu ndash Ultimate Tensile Strength (psi)
Fsu ndash Ultimate Shear Strength (psi)
G ndash Shear Modulus (psi)
MSyld-comp ndash Yield Strength Margin of Safety ndash Compressive
MSult-comp ndash Ultimate Strength Margin of Safety ndash Compressive
MSyld-tensile ndash Yield Strength Margin of Safety ndash Tensile
MSult-tensile ndash Ultimate Strength Margin of Safety ndash Tensile
ν ndash Poissonrsquos Ratio
σ ndash Normal Stress (psi)
[Q] ndash Laminae Reduced Stiffness Matrix (psi)
[Q ] ndash Laminae Transposed Reduced Stiffness Matrix (psi)
[S] ndash Laminae Reduced Compliance Matrix (in2lb)
[S ] ndash Laminae Transposed Reduced Compliance Matrix (in2lb)
τ ndashShear Stress (psi)
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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7
The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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8
+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
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983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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26
Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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28
Figure 312 Flight Performance Comparison
983088
983089983088983088
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983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 11
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xi
Material
E ndash Youngrsquos Modulus (psi)
ε ndash Normal Strain (inin)
γ ndash Shear Strain (inin)
Fcy ndash Yield Compressive Strength (psi)
Fcu ndash Ultimate Compressive Strength (psi)
Fty ndash Yield Tensile Strength (psi)
Ftu ndash Ultimate Tensile Strength (psi)
Fsu ndash Ultimate Shear Strength (psi)
G ndash Shear Modulus (psi)
MSyld-comp ndash Yield Strength Margin of Safety ndash Compressive
MSult-comp ndash Ultimate Strength Margin of Safety ndash Compressive
MSyld-tensile ndash Yield Strength Margin of Safety ndash Tensile
MSult-tensile ndash Ultimate Strength Margin of Safety ndash Tensile
ν ndash Poissonrsquos Ratio
σ ndash Normal Stress (psi)
[Q] ndash Laminae Reduced Stiffness Matrix (psi)
[Q ] ndash Laminae Transposed Reduced Stiffness Matrix (psi)
[S] ndash Laminae Reduced Compliance Matrix (in2lb)
[S ] ndash Laminae Transposed Reduced Compliance Matrix (in2lb)
τ ndashShear Stress (psi)
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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7
The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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8
+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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10
motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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11
Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 12
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xii
Glossary
Adiabatic ndash A thermodynamic process in which heat is neither added nor removed from
the system
AL ndash Aluminum powder used as a solid fuel in a solid rocket motorANSYS ndash Software created by ANSYS Inc used for finite element analysis
AP ndash A solid oxidizer made of Ammonium Perchlorate
BurnSim ndash Software created by Gregory Deputy to simulate the performance of a solid
propellant rocket motor
BATES ndash A cylindrical solid propellant configuration with a cylindrical core
CATIA ndash Software created by Dassault Systeacutemes to perform 3 dimensional computer
aided design
CLT ndash Classical Laminate Theory used to calculate laminate properties from the
properties of the individual layers
Condi Nozzle ndash A convergentdivergent nozzle
CTPB ndash A polymer binder material made of Carboxyl Terminated Polybutadiene
Isentropic ndash A thermodynamic process in which there is no change in entropy of the
system
Laminae ndash A single layer of a composite matrix
Laminate ndash A stack of laminae
Slinch ndash Unit of mass in the United States customary units 12 Slugs = 1 Slinch
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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8
+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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11
Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 13
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xiii
ABSTRACT
The purpose of this project is to design a ground launched rocket booster to meet
specific mission requirements The mission constraints include minimum speed
maximum flight altitude as well as length and weight limits The mission is to launch a3000 lb payload such as a Tomahawk cruise missile to an altitude of 1000 feet and
accelerate the missile to 550 MPH (807 fps) To meet these mission requirements the
weight of the rocket body should be as light as possible while maintaining the required
structural integrity and reliability The motor parameters such as the nozzle size
expansion ratio propellant size and shape are determined through an iterative process
The thrust performance from a preliminary motor design is used to calculate the
resulting flight performance based on the calculated thrust overcoming gravity inertia
and aerodynamic drag of the booster rocket and cruise missile assembly The engine
nozzle parameters are then varied to meet the mission requirements and to minimize
excess capability to ensure a weight efficient motor The initial motor casing design
will be made of light weight cast aluminum The aluminum motor design will be
compared to a design made of a fiber and resin composite material The composition and
layup of the composite material and the thickness of the aluminum material will be
designed to meet industry standard safety margins based on the materialrsquos strength
properties This paper will present the calculated engine parameters as well as the
engine weight and engine size for both the aluminum casing and the composite casing
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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7
The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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8
+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
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983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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26
Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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28
Figure 312 Flight Performance Comparison
983088
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983094983088983088
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983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 14
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1
1 IntroductionBackground
11 Rockets
Rockets are a type of aircraft used to carry a payload at high speeds over a wide range of
distances depending on the design Rockets are powered by a reaction type engine
which uses chemical energy to accelerate and expel mass through a nozzle and relies on
the principles of Sir Isaac Newtonrsquos third law of motion [1] to propel the rocket forward
Rocket engines use either solid or liquid fuel They carry both the fuel and the oxidizer
required to convert the fuel into thermal energy and gas byproducts The gas byproducts
under pressure are then passed through a nozzle which converts the high pressure low
velocity gas into a low pressure high velocity gas
The following figure shows the different components of a typical rocket
Figure 11 Typical Rocket Components [2]
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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7
The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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8
+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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10
motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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11
Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 15
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2
12 Mission Requirements
The rocket considered in this study is a ground launched booster that is used to launch a
payload such as a Tomahawk cruise missile to a prescribed altitude and to a required
velocity The mission can be viewed in three phases In the first phase the booster is onthe ground at rest and launches vertically In the second phase the assembly transitions
from a vertical orientation to a horizontal orientation while climbing to 1000 feet In the
third phase the booster accelerates the payload horizontally to 550 MPH (807 fps) The
rocket engine must be sized appropriately to meet the mission requirements as
summarized in Table 11 The Tomahawk cruise missile specifications are listed in
Table 12 The cruise missile in this mission will use an onboard gas turbine engine to
continue flight once the missile has reached 1000 ft altitude and 550 MPH (807 fps) In
the horizontal portion of the flight the cruise missile will deploy the stowed wings to
provide lift which will allow the thrust of the booster to be used solely to accelerate the
missile to the appropriate speed Once the missile has reached the target altitude and
speed and the solid propellant has been consumed the booster will be jettisoned from the
cruise missile assembly to fall back to earth The total assembly is limited to 3500 lbm
and the payload is 2700 lbm The properties of the fuel to be used in this mission are
shown in Table 13
Table 11 Mission Requirements
Value Units
Altitude range 0 - 1000 ft
Minimum Velocity 550 MPH
Maximum Mass 3500 lbm
Payload Mass 2700 lbm
Table 12 Tomahawk Cruise Missile Specifications
RGM 109DLength (in) Diameter (in) Weight (lb)
219 209 2700
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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10
motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
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983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
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983090983088983088
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983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 16
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3
Table 13 Available Composite Propellant
Oxidizer AP (70)
Fuel Binder CTPB (12)
Metallic Fuel AL (16)
Curative Epoxy (2)Flame Temperature (R) 6840
Burning Rate Constants
k 0341
n 04
Density (slinchin ) 164E-4
Molecular Weight (kgkmole) 293
Gas Constant (lb-inslinch-R) 2386627
Ratio of Specific Heats 117
Characteristic Velocity (ins) 62008
13 Structural Requirements
The rocket engine casing must be able to withstand the internal engine pressure loads
and the force applied to the payload through the attachment point In some locations the
casing materials must be able to withstand high pressures and elevated temperatures dueto the combustion of the fuel
In this project the casing design will be determined based on the stress analysis using
closed form equations and the finite element method The nozzle and casing will be
sized using E357-T6 aluminum alloy and then resized using carbon fiberresin composite
materials The components will be sized based on the maximum load and pressure the
casing will be subjected to during the mission This maximum load will be referred to as
the limit load
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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7
The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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8
+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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10
motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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11
Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 17
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4
2 Methodology
21 Assumptions
The following assumptions are made for the motor design to simplify the analysis
1)
The booster is an ideal rocket This is to assume the following six assumptions
are true or they are corrected for with an efficiency factor See Equation 220
2) The specific heat ratio (γ) of the exhaust gases is constant throughout the booster
The specific heat ratio is a function of temperature and temperature is assumed to
be constant due to thermal insulation and low dwell time
3) Flow through the nozzle is adiabatic isentropic and one dimensional This
assumption claims the process is reversible no heat is lost and pressure and
temperature changes only occur in the axial direction The true losses in thesystem are accounted for in the efficiency factor
4)
There is no loss of total pressure during combustion True pressure losses are
accounted for with the efficiency factor
5)
The flow area in the combustion chamber is large compared to the nozzle area so
the velocity at the nozzle entrance is negligible
6)
All of the exhaust gasses exit the nozzle in the axial direction Due to the low
altitude range of this mission the nozzle can be design such that the exhaust flow
is axial
7)
The nozzle is a fully expanding Condi nozzle Due to the narrow altitude range
of this mission the nozzle can be designed such that the exhaust is fully
expanding and not over or under expanded
8) The coefficient of drag for the payload and booster assembly is 075 The actual
drag coefficient will be based on tests
9) In the rocket combustion chamber there is a 2mm (0079 inch) liner is made of a
material of sufficient properties to keep the casing temperatures below 300
degrees Fahrenheit This assumption is reasonable based on similar designs and
preliminary thermal analysis not presented here
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5
22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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7
The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
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983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
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983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
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983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
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983094983088983088
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983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 18
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22 Flight Performance
Thrust is required to accelerate the payload fuel and motor casing mass to 1000 feet and
550 MPH (807 fps) overcoming the forces of gravity mass inertia and aerodynamic
body drag As the propellant is consumed the thrust increases and the mass of the booster assembly decreases As a result the axial and the radial acceleration velocity
and displacement are calculated in a discretized fashion for time steps of 001 seconds
The displacements are then transformed from the rocket reference frame to the ground
reference frame to determine altitude and horizontal velocity
The flight path is predetermined to transitions from a vertical flight to a horizontal path
based on the function [3]
[21]
θ is the angle of the rocket axis to the ground as shown in Figure 21 The rocket at the
beginning of the launch is vertical (θ=90deg)
Figure 21 Rocket Free Body Diagram [3]
The axial acceleration of the body is calculated by the following equation below 1000feet
[22]
The axial acceleration is calculated by the following equation when the cruise missile
wings are deployed at 1000 feet
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[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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10
motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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11
Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 19
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6
[23]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when below 1000 ft is
[24]
The acceleration in the direction perpendicular to the cruise missile wingspan plane is
calculated as follows when the cruise missile wings are deployed at 1000 ft
+ [25]
The axial (x) and radial (y) velocity is calculated using
+ lowast [26] + lowast [27]
And the displacement is similarly calculated
+ lowast [28] + lowast [29]
The displacement values are then transformed into the ground reference frame to
determine the horizontal distance and the altitude
+ [210]
Where m=cos(θ) and n=sin(θ)
23 Motor thrust requirements
The equations above are dependent on the thrust (F) of the booster engine The thrust is
calculated using equations found in [4] For the preliminary sizing of the rocket motor
these closed form equations are used to calculate the engine performance The
maximum diameter of the engine is sized to be similar to that of the cruise missile The
length of the propellant is limited to 26 inches to minimize the length of the booster
motor Knowing the diameter and the length of the charge the burn diameter can be
calculated
∙ ∙ [211]
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7
The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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8
+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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10
motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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26
Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 20
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The X-function is the non-dimensional mass flow of the motor and is calculated by
lowast radic [212]
The exhaust cone diameter is a variable that can influence thrust and is adjusted as
needed in the design to get the appropriate thrust based on a given expansion ratio The
chosen diameter for this rocket motor is 13 inches The exit area is calculated from the
cone diameter
[213]
The nozzle area is calculated from the exit area and the prescribed expansion ration
epsilon The expansion ratio can be adjusted in the design phase in an iterative nature to
achieve the required thrust
lowast [214]
The chamber pressure can now be calculated based on the propellant properties and the
nozzle area
∙ ∙ lowast∙lowast [215]
The burn rate of the propellant is sensitive to the chamber pressure The burn rate is
calculated as ∙ [216]
As can be seen in the previous two equations the chamber pressure is dependent on
the burn rate and the burn area Both the burn rate and the burn area are increasing as
the propellant is consumed which provides a progressive burn rate To minimize this
effect creative cross sectional areas can be made so that the total area does not increase
with propellant consumption
In order to calculate the thrust coefficient the exit velocity or exit Mach number need to be calculated Due to the nature of the following equations an iterative process is used
to solve for Me
+ ∙ [217]
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+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
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983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 21
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+ ∙ [218]
Knowing the exit velocity and the chamber pressure the thrust coefficient is calculated
as shown
+ lowast [219]
These calculations are based on an ideal nozzle with full expansion Due to thermal and
other losses the actual thrust coefficient will be about 90 of the ideal thrust
coefficient
∙ [220]
A measure of the efficiency of the rocket design is the specific impulse The specific
impulse can provide an idea of the propellant flow rate required for the given thrust The
theoretical specific impulse is calculated by
lowast∙ [221]
The area of the core in the BATES type fuel configuration or a cylindrical configuration
should be four times the area of the nozzle to prevent erosive burning From this area
the volume of the core can be calculated using the propellant length The propellant
volume is calculated by subtracting this core volume from the combustion chambervolume From this volume the mass of the propellant can be determined
∙ lowast [222] lowast [223] [224] [225] ∙ [226]
To calculate the burn time the mass flow rate is determined and then the burn time iscalculated based on the propellant mass
∙ [227]
[228]
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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10
motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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11
Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 22
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9
An important characteristic of the motor performance is the total impulse This is the
average thrust times the burn time
∙ [229]
All of the above calculations are performed in Microsoft Excel The internal iterative
solver in Excel is used to determine the appropriate nozzle diameter and exhaust cone
diameter to meet the mission requirements The Excel spreadsheet also calculates
additional engine parameters including chamber pressure which is required to properly
size the structural components of the engine casing
The BurnSim software is then used to more accurately calculate the engine thrust
chamber pressure and the mass flow These parameters are then imported into Excel to
calculate the flight performance based on the BurnSim results
24 Motor Casing Sizing
Based on the thrust load and the chamber pressure the stresses in the initial casing
design is analyzed using closed form equations provided in Roarkrsquos Handbook [5]
ANSYS finite element software is then used to determine the stresses in the final casing
design The stresses are compared to the yield and ultimate strength of the material Anaerospace standard factors of safety of 15 for ultimate strength and 115 for yield
strength The metal alloy version of the rocket casing is to be made of a cast E357-T6
aluminum Casting the casing will minimize the number of bolted joints and maximize
the strength of the structure which will minimize the weight The aluminum casing
concept is shown in Figure 22 The filler is a light weight polymer designed to prevent
end burning of the propellant opposite the nozzle The liner is a thin coating on the
casing made of a material designed to keep the casing temperature below 300degF The
filler liner and propellant can be poured into the casing with a core plug and then cured
The plug is then removed The nozzle can be made of high temperature material
designed for the direct impingement of hot gases There are many such materials listed
in [3] The nozzle could be segmented into axially symmetric pieces to facilitate
assembly and then bonded into place The composite material version of the rocket
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10
motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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11
Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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13
[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
8102019 02935booster_missilepdf
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 23
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motor casing will be designed of a similar shape as shown in Figure 23 The composite
assembly will be assembled similar to the aluminum version except the Thrust Plate is
bonded to the top of the casing
Figure 22 Aluminum Engine Casing Concept
Figure 23 Composite Engine Casing Concept
Figure 24 shows a typical 2 dimensional axisymmetric finite element model used to
analyze the motor casing Pressure is applied to the internal surfaces up to the nozzle
where the pressure drops to near ambient values A thrust load is applied to the top
surface in the axial direction (depicted as ldquoCrdquo) This load application represents wherethe thrust is transferred to the payload The casing is grounded at the end of the nozzle
The load is typically distributed throughout the nozzle and not concentrated on the end
but the nozzle is structurally sturdy and not an area of concern for this project
Propellant
Casing
Nozzle
Liner
Filler
Propellant
Filler
Liner Nozzle
Casing
Thrust Plate
Igniter Housing
Integral igniter
housing
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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12
maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 24
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Figure 24 Finite Element Load and Boundary Conditions
25 Material
251
Aluminum Alloy
The Table 21 shows the material properties for E357T-6 cast aluminum prepared per
AMS 4288 [6] This alloy is used since it has a relatively high strength to weight ratio
for a cast alloy
Table 21 E357 T-6 Casted Aluminum
AMS 4288 Ftu (ksi) Fty (ksi) Fcy (ksi) Fsu (ksi) E (ksi) ν ρ (lbin )
T=72degF 45 36 36 28 104E3 033 0097
T=300degF 39 37 - - 106E3 - -
252 Composite Material
A carbon epoxy composite material from Hexcel [8] is chosen for the composite version
of the casing The properties for unidirectional fibers are shown in Table 22 The
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maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 25
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maximum casing temperature is 300degF and so the strength is reduced by 10 based on
similar material trends The strength is further reduced by 50 as an industry standard
ultimate strength safety factor
Table 22 Hexcel Intermediate Modulus Carbon FiberResin Properties Ftu 1
(psi)
Fcu 1
(psi)
Ftu 2
(psi)
Fcu 2
(psi)
F12
(psi)
E1
(psi)
E2
(psi)
G12
(psi) ν12
room
temperature348000 232000 11000 36200 13800
2466000 1305000 638000 027300degF 313200 208800 9900 32580 12420
15 Safety
Factor208800 139200 6600 21720 8280
This unidirectional material is layered several plies thick into a laminate In this project
the laminate is made of 84 layers with each layer being 0006 in thick for a total of 0504
thick Some of the layers will be at different angles from the others to tailor the material
for the mission loads This allows the composite material to be optimized to minimize
weight without sacrificing strength The overall laminate properties will be calculated
based on the material properties in Table 22 utilizing Classical Laminate Theory and
Kirchoffrsquos Hypothesis [7] The following assumptions are made
1) Lines normal to the midplane of a layer remain normal and straight and normal
during bending of the layer
2) All laminates are perfectly bonded together so that there is no dislocation
between layers
3) Properties for a layer are uniform throughout the layer
4) Each ply can be modeled using plane stress per Kirchoffrsquos Hypothesis
The following are the equations used to model the composite For details see [7]
The stress strain relationship of the laminate is defined by
This equation is expanded to
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[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 26
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[230]
Using plane stress assumptions the equation can be reduced to the following
[231]
Where [S] in Equation 212 is the reduced compliance matrix This matrix istransformed for each layer to equate the properties into the laminate coordinate system
as follows
[232]
Where
[233]
This can be represented by
[234]
The global properties for the laminate can be calculated as follows
[235] [236]
[237]
[238]
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[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 27
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14
[239]
In the laminate coordinate system the stress to strain relationship for a single layer can
be written as
[240]
where
[Q ] = [S ]-1 [241]
To create the overall laminate load to strain relationship the ABD matrix is created as
follows
( )sum=
minusminus= N
1k 1k k ij
_
ij zzQAk
[242]
( )sum=
minusminus= N
1k
21k
2k ij
_
ij zzQBk
[243]
( )sum=
minusminus= N
1k
31k
3k ij
_
ij zzQDk
[244]
Where zk is the z-directional position of the ply number k In a symmetric layup z=0 at
the midplane and is positive in the lower layers and negative in the upper layers
The complete load to strain relationship matrix is
[245]
The maximum stress for the laminate is based on Tsai-Hill failure criteria for each
layer The laminate will be considered to have failed when any layer exceeds the
maximum allowed stress An Excel spreadsheet is used to calculate the stress in the
layers based on the laminate stress from the finite element model The layer stresses are
=
0XY
0Y
0X
0XY
0Y
0X
66
26
26
22
16
12
161211
66
26
16
26
22
12
16
12
11
662616662616
262212262212
161211161211
XY
Y
X
XY
Y
X
κ
κ
κ
γ
ε
ε
D
D
D
D
D
D
DDD
B
B
B
B
B
B
B
B
BBBBAAA
BBBAAA
BBBAAA
M
M
M N
N
N
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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17
engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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18
as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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19
Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 28
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15
used with the Tsai-Hill equation to determine a static margin The Tsai-Hill failure
criteria equation is as follows
+
+
lt [246]
Where
X1=F1t if σ1gt0 and F1c if σ1lt0
X2=F1t if σ2gt0 and F1c if σ2lt0
Y=F2t if σ2gt0 and F2c if σ2lt0
S=F12
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16
3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 29
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3 Results
31 Engine Parameters
The predicted engine parameters based on the chosen nozzle diameter expansion ratio
and fuel size are shown in Table 31
Table 31 Engine Parameters
Parameter Value Units
Maximum Thrust 13481 lb
Max Chamber Pressure 1104 psi
Total Impulse 120150 lbf-s
Specific Impulse 237 s
Burn Diameter 2087 in
Conduit Diameter 655 in
Propellant Length 26 in
Burn Time 1288 s
Nozzle Diameter 328 in
Nozzle Exit Diameter 802 in
Expansion Ratio 60 -
Exit Mach Number 286 -
Optimal Thrust
Coefficient161 -
Thrust Coefficient Actual 145 -
32 Aluminum Alloy Casing Design
321
Aluminum Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 21 The
maximum casing temperature is 300degF and so the material properties are reduced from
the room temperature properties as shown in the table Figure 31 shows the final
dimensions of the engine casing Table 32 shows the final weight of the aluminum
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engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 30
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engine casing assembly The engine casing is frac12 inch thick throughout most of the
design Some areas of the casing are thicker to accommodate the stresses due to the
thrust load transmitted to the payload through the top of the casing in addition to the
internal pressure load
Figure 31 Aluminum Alloy Casing Detail
Table 32 Aluminum Engine Weight
Component Weight (lb)
Engine Casing 172
Fuel 507
LinerFiller 50
Nozzle 7
Total 736
322 Finite Element Analysis
Linear elastic finite element analysis is performed using ANSYS Workbench V13 The
loads and boundary conditions are applied as shown in Figure 24 in section 2 The
results are shown in Figure 32 and Figure 33 The peak stress occurs in the top of the
casing in Figure 32 where the structure is supporting the internal pressure load as well
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
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983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 31
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as a bending load due to the thrust load The thickness of the casing in this area is
increased to 120 inches as shown in Figure 31 Figure 33 shows the stresses for the
lower section which are not as high as in the upper section This peak stress in this
figure occurs where the structure is supporting a bending load in addition to the internal
pressure load The thickness in this area is increased to 07 inches as shown in Figure
31 to accommodate the higher stresses The margins of safety are calculated using the
maximum casing stress with a 15 safety factor on the ultimate strength and a 115 safety
factor on the yield strength
[31]
[32]
With a maximum stress of 25817 psi the margin of safety for the aluminum casing is
024 for yield strength and 001 for ultimate strength
Figure 32 Maximum Stress Aluminum Engine Casing Upper
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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20
Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
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983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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Figure 312 Flight Performance Comparison
983088
983089983088983088
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983093983088983088
983094983088983088
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983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 32
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Figure 33 Maximum Stress Aluminum Engine Casing Lower
The predicted flight performances based on the total assembly weight and predicted
engine thrust is shown in Figure 34Figure 35 and Figure 36 Figure 34 shows
ground distance covered by the cruise missile as it reaches the 1000 foot target altitude
This figure shows the transition from vertical to horizontal flight This transition was
chosen to provide a smooth transition
Figure 34 Assembly Flight Path
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983089983090983088983088
983089983092983088983088
983088 983090983088983088 983092983088983088 983094983088983088 983096983088983088 983089983088983088983088 983089983090983088983088 983089983092983088983088 983089983094983088983088 983089983096983088983088 983090983088983088983088
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983111983154983151983157983150983140 983108983145983155983156983137983150983139983141 983080983142983156983081
983110983148983145983143983144983156 983120983137983156983144
983137983148983156983145983156983157983140983141 (983142983156983081
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
8102019 02935booster_missilepdf
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
8102019 02935booster_missilepdf
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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26
Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 33
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Figure 35 shows the thrust altitude and the horizontal velocity over time As shown
the assembly reaches the target altitude of 1000 feet at about 10 seconds and then
continues to accelerate until it reaches the target velocity of 807 ftsec at 126 seconds
The thrust shown in Figure 35 is predicted by BurnSim The thrust profile is
progressive since the burn rate accelerates with increased burn area and increased
chamber pressure The thrust has a drop at approximately 96 seconds The hypothesis
as to why this occurs is the propellant is divided into 3 stages in BurnSim The bottom
stage is allowed to burn on the nozzle end which is open as shown in Figure 22 The
other two segments are prevented from burning on the ends As the propellant is
consumed the bottom charge is burning both axially and radially and eventually there
will no longer be an end face At this point the total burn area will drop resulting in a
pressure drop which will result in a thrust decrease This phenomenon can be further
explored with the aid of the software designer to verify accuracy
Figure 35 Flight Performance
Figure 36 shows vertical and horizontal acceleration and altitude of the assembly in
shiprsquos coordinates with respect to time These are contrasted with θ which is the angle
of the flight path with respect to the ground horizontal
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983090983088983088983088
983092983088983088983088
983094983088983088983088
983096983088983088983088
983089983088983088983088983088
983089983090983088983088983088
983089983092983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087
983155 983141 983139 983081
983124 983144 983154 983157 983155 983156 983080 983148 983138 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983124983144983154983157983155983156 (983148983138983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
8102019 02935booster_missilepdf
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
8102019 02935booster_missilepdf
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26
Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
8102019 02935booster_missilepdf
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28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
8102019 02935booster_missilepdf
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4447
31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 34
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21
Figure 36 Rocket Angle Altitude and Velocities
33 Composite Casing Design
The composite version of the engine casing has the same general shape as the aluminum
version but is made of wound fibers over a sand mold The fibers are coated in an epoxy
resin The thickness of the material is tailored to optimize the weight and strength of the
structure For ease manufacturing and analysis the casing is of uniform thickness
331
Layup
The composite layup is [9020245-45]s Each layer is 0006 inches thick The sub-
laminate has 12 layers and the sub-laminate is layered 7 times The engine casing is 05
inches thick made up of a total of 84 layers The 0 degree orientation is in-line with the
casing axis but following the contour of the shell from top to bottom and the 90 degree
orientation is in the hoop direction This layup will give strength in the hoop direction
for the pressure loading with the 90 degree fibers The 0 and 45 degree fibers give the
laminate strength for bending in the curved geometry at the top and bottom of the casing
to react thrust load
The overall properties of this layup are calculated using classical laminate plate theory
The resulting three dimensional stiffness properties of the laminate as well as the
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088
983089983088
983090983088
983091983088
983092983088
983093983088
983094983088
983095983088
983096983088
983097983088
983088 983090 983092 983094 983096 983089983088 983089983090
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081 983137 983150 983140
983126 983141 983148 983151 983139 983145 983156 983161
983080 983142 983156 983087 983155 983141 983139 983081
θ 983080 983140 983141 983143 983154 983141 983141 983155 983081
983124983113983149983141
983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
θ (983140983141983143983154983141983141983155983081
983137983148983156983145983156983157983140983141 (983142983156983081
983144983151983154983145983162983151983150983156983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081983158983141983154983156983145983139983137983148 983158983141983148983151983139983145983156983161
(983142983156983087983155983141983139983081
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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23
Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4347
30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4447
31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 35
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22
Poissonrsquos ratios are shown in Table 33 The stress allowable for this laminate would
ultimately be determined through physical testing of the laminate The safety factors are
calculated based on the unidirectional material properties and CLT with Tsai-Hill failure
criteria
Table 33 Laminate Properties Calculated by CLT
Ex
10^6 psi
Ey
10^6 psi
Ez
10^6 psi
Gxy
10^6 psi
Gxz
10^6 psi
Gyz
10^6 psi νxy νzx νzy
1068 1068 173 254 053 053 020 038 038
332 Composite Casing Geometry
Based on the engine parameters shown in Table 31 an engine casing is designed and
optimized for weight based on the material strength as shown in Table 22 Figure 37
shows the final dimensions of the engine casing Table 34 shows the final weight of the
composite engine casing assembly Figure 37 shows the dimensions of the composite
casing Due to the superior strength of the composite material over the aluminum the
thickness of the structure is 05 inches throughout Since the composites are lower in
density than the aluminum and the structure is thinner the composite casing is lighter
even with the additional thrust plate hardware
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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26
Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
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28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
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29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
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30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
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31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
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for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
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33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
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GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 36
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Figure 37 Composite Casing Detail
Table 34 Composite Engine WeightComponent Weight (lb)
Engine Casing 97
Fuel 507
LinerFiller 50
Nozzle 7
Thrust Plate 1
Total 662
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24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
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25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
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26
Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4147
28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4247
29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4347
30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4447
31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4547
32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4647
33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 37
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 3747
24
333 Finite Element Analysis
A two dimensional axi-symmetric analysis is performed similar to the aluminum casing
The two dimensional geometry is split into segments as shown in Figure 38 so that the
coordinates of the finite elements in the curved sections can be aligned with the
curvature of the geometry This allows the material properties to be as will the fibers
aligned with the geometric curvature The material stiffness properties as applied in
ANSYS are shown in Table 35 These values are the same as in Table 33 but
transposed to align with the coordinate system used in ANSYS In the ANSYS model
the hoop direction is the z-coordinate the axial direction is the y-coordinate and the
radial direction or through thickness is the x-coordinate
Figure 38 FEA Geometry for Composite Casing
Table 35 Laminate Properties in ANSYS
Ex
106
psi
Ey
106
psi
Ez
106
psi
Gxy
106
psi
Gxz
106
psi
Gyz
106
psi νxy νzx νzy
173 1068 1068 053 053 254 006 006 020
Figure 39 shows the load and boundary conditions similar to that of the aluminum
casing shown in Figure 24 The additional remote displacement is used on the top
section of the casing to represent the bonded thrust ring shown in Figure 23 This
Top
Top Radius
Barrel
Bottom Radius
Bottom
Throat
Cone Radius
Cone
Throat Top
Radius
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 3847
25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 3947
26
Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4047
27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4147
28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4247
29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4347
30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4447
31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4547
32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4647
33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 38
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 3847
25
constraint prevents the edges of the top hole from expanding or contracting radially but
allows all rotations and axial displacement Figure 310 shows the deformation of the
casing and Figure 311 shows the peak stresses in the top curved section The peak
stresses occur in areas similar to the aluminum casing as expected The margins are
calculated using Tsai-Hill failure criteria A summary of the margin of safety is listed in
Table 36
Figure 39 Load and Boundary Conditions Composite Casing
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 3947
26
Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
8102019 02935booster_missilepdf
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27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4147
28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4247
29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4347
30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4447
31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4547
32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4647
33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 39
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 3947
26
Figure 310 Maximum Total Deformation Composite Casing
Figure 311 Top Radius Stress Composite Casing
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4047
27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4147
28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4247
29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4347
30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4447
31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4547
32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4647
33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 40
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4047
27
Table 36 Composite Casing Stress and Margins
Stress (psi)
LocationAxial
min
Axial
max
Hoop
min
Hoop
max
Shear
min
Shear
maxMargin
Cone -20144 -47292 -48973 -56672 -31246 7948 2081Cone radius -13465 -6717 -60744 -18762 -72242 67468 3716
Nozzle -97186 -80954 -27453 29522 -42646 18322 5415
Throat Top
Radius-14915 24486 -413 28774 -20148 50471 0696
Bottom -13401 24279 15498 28629 -12322 18099 0718
Bottom
Radius-54632 17727 30158 23340 -11887 18518 1163
Barrel 37015 13574 13057 24296 -11448 11166 1198
Top Radius -14147 29048 29513 19953 -14829 11581 0793
Top -21888 34018 82417 40858 12488 54751 0129
The lowest margin in the composites is similar to that of the aluminum casing in the top
section which is reacting the thrust forces as well as internal pressures These margins
include the temperature knock downs as well as the 15 safety factor Since composites
behave as a brittle material in that they do not significantly plastically deform prior to
failure only ultimate margins are calculated
334 Aluminum to Composite Comparison
Comparing the total weight of the aluminum engine as shown in Table 32 to that of the
composite engine as shown in Table 34 the total weight savings is only 74 lb in an
assembly that weighs over 3000 lb As show in Figure 312 this weight savings has a
minor effect on the flight performance of the assembly
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4147
28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4247
29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4347
30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4447
31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4547
32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4647
33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 41
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4147
28
Figure 312 Flight Performance Comparison
983088
983089983088983088
983090983088983088
983091983088983088
983092983088983088
983093983088983088
983094983088983088
983095983088983088
983096983088983088
983097983088983088
983088
983090983088983088
983092983088983088
983094983088983088
983096983088983088
983089983088983088983088
983088 983090 983092 983094 983096 983089983088 983089983090
983112 983151 983154 983145 983162 983151 983150 983156 983137 983148 983126 983141 983148 983151 983139 983145 983156 983161 983080 983142 983156 983087 983155 983141 983139 983081
983105 983148 983156 983145 983156 983157 983140 983141 983080 983142 983156 983081
983124983113983149983141
983105983148983157983149983145983150983157983149 983158983155 983107983151983149983152983151983155983145983156983141 983110983148983145983143983144983156 983120983141983154983142983151983154983149983137983150983139983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983107983151983149983152983151983155983145983156983141 983107983137983155983145983150983143
983105983148983156983145983156983157983140983141
983105983148983157983149983145983150983157983149 983107983137983155983145983150983143
983126983141983148983151983139983145983156983161
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4247
29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4347
30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4447
31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4547
32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4647
33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 42
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4247
29
4 Conclusion
A rocket motor provides a great deal of power for a short duration of time In this
project a solid fuel rocket motor is designed to produce over 13000 lb of thrust for
almost 13 seconds which is capable of lifting over 3000 lb of mass to a height of 1000feet and accelerate it to over 550 mph There are many options for size and shape of the
propellant which can have a great influence on the thrust profile A simple cylindrical
propellant shape was utilized in this project for simplicity but other options can be
explored The thrust profile is progressive in that the thrust increases with time The
chamber pressure is a moderate pressure of about 1000 psi The pressure makes it
feasible to use metal alloy and composite casings The advantage of the composite is the
high strength to weight which allows for weight savings For this design the weight
savings is only 74 lb in an assembly that weighs more than 3000 lbs This weight
savings provides marginal flight performance increase as shown in Figure 312 Further
refinements can be done for the composite casing design to decrease the thickness in
high margin locations Varying the thickness will require ply drop offs or fiver
terminations which requires special stress analysis Overall composites can be more
expensive and more technically challenging to manufacture than metal alloys A further
cost and manufacturing analysis would need to be performed to determine if the use of
composites is justified
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4347
30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4447
31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4547
32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4647
33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 43
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4347
30
References
[1] Newton Isaac The Mathematical Principles of Natural Philosophy pg 19 1729
[2]
Solid Rocket Motor Wikipedia The Free Encyclopedia WikimediaFoundation Inc 2 February 2012 Web 19 May 2008
[3] Sutton George Paul Rocket Propulsion Elements New York John Wiley ampSons 1992
[4] Ward Thomas A Aerospace Propulsion Systems Singapore John Wiley ampSons 2010
[5] Young Budynas and Sadegh Roarkrsquos Formulas for Stress and Strain NewYork McGraw-Hill 2011
[6] Metallic Materials Properties Development and Standardization (MMPDS-05)US Federal Aviation Administration
[7]
Hyer M W and S R White Stress Analysis of Fiber-reinforced CompositeMaterials Pennsylvania DEStech Publications 2009
[8]
Hexcel (2005 March) Prepreg Technology Pg 26 Retrieved February 022012 from httpwwwhexcelcomResourcesDataSheetsBrochure-Data-SheetsHexForce_Technical_Fabrics_Handbook
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4447
31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4547
32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4647
33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 44
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4447
31
Appendix A ndash Classical Lamination Matlab Code
Tsai_hill_marginmThis program is to calculate the Tsai-Hill margin of a laminate fromFEA stress Assumption- all layers are at the same stress state in global
coordinates (not ply coordinates) Enter the sxsysxy stresses from FEA for the LAMINATE and thelaminate thickness Program will calculate the layer stresses and perform Tsai-Hillcalculation
clear allclc Normalstressx=40858 user input laminate stress Normalstressy=34018 user input laminate stress Normalstressxy=54751 user input laminate stress plystacktheta=[90045-45-4545090] user input ply orientation plystackz=[084084042042042042084084] user input of plythickness
graphitepolymer user input of ply material
h=size(plystacktheta2) determines how many layers t=0 for n=1h t=t+plystackz(1n)end calculates ply thickness
Nx=Normalstressxt Ny=Normalstressyt Nxy=Normalstressxyt Mx=0My=0 Mxy=0
z(1)=-t2 sets z0 dimension (shifted +1 for matlab purposes)
for N=2h+1 z(N)=z(N-1)+ plystackz(1N-1) end for k=1h
theta=plystacktheta(1k)pi180 Qbar=qbar(thetaE1E2poisson12shear12) for i=13
for j=13 Qbar3d(ijk)=Qbar(ij)
end end
end
A=[000000000]B=[000000000]D=[000000000] for i=13
for j=13 for k=1h A(ij)=A(ij)+Qbar3d(ijk)(z(k+1)-z(k)) B(ij)=B(ij)+Qbar3d(ijk)2((z(k+1))^2-(z(k))^2) D(ij)=D(ij)+Qbar3d(ijk)3((z(k+1))^3-(z(k))^3) end
end end
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4547
32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4647
33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 45
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4547
32
for i=13 for j=13
ABD(ij)=A(ij) end
end for i=46
for j=13 ABD(ij)=B(i-3j)
end end for i=13
for j=46 ABD(ij)=B(ij-3)
end end for i=46
for j=46 ABD(ij)=D(i-3j-3)
end end
ABD abd=ABD^-1 e0k=abd[NxNyNxyMxMyMxy] e0=[e0k(1)e0k(2)e0k(3)] k=[e0k(4)e0k(5)e0k(6)] for j=122h creates matrix with 2h columns so to have top andbottom values for each layer
jmod=5j+5 converts j back to j=1h for layer properties theta=plystacktheta(jmod)pi180 epsilonxytop=e0+z(jmod)k epsilonxybottom=e0+z(jmod+1)k stiffness=qbar(thetaE1E2poisson12shear12) sigxytop=stiffness epsilonxytop sigxybottom=stiffness epsilonxybottom sig12top=tmatrix(theta)sigxytop sig12bottom=tmatrix(theta)sigxybottom epsilon12top=tmatrix(theta)epsilonxytop epsilon12bottom=tmatrix(theta)epsilonxybottom for i=13
stressxy(ij)=sigxytop(i1) stress12(ij)=sig12top(i1) strainxy(ij)=epsilonxytop(i1) strain12(ij)=epsilon12top(i1)
end for i=13
stressxy(ij+1)=sigxybottom(i1) stress12(ij+1)=sig12bottom(i1)
strainxy(ij+1)=epsilonxybottom(i1) strain12(ij+1)=epsilon12bottom(i1)
end end S =compliancematrix(E1E2E3poisson12poisson13poisson23shear12shear13shear23) deltaH=0 for i=122h
imod=5i+5
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4647
33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 46
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4647
33
epsilon3(imod1)=S(13)stress12(1i)+S(23)stress12(2i) deltah(imod1)=epsilon3(imod1)plystackz(imod) deltaH=deltaH+deltah(imod1)
end for i=12h
if (stress12(1i)lt0) X1=Fcu1
else X1=Ftu1
end if (stress12(2i)lt0)
X2=Fcu1 Y1=Fcu2else
X2=Ftu1 Y1=Ftu2 end S1=F12 tsaihill(1i)=(stress12(1i)X1)^2-
stress12(1i)stress12(2i)(X2^2)+(stress12(2i)Y1)^2+(stress12(3i)S1)^2
ms(1i)=1tsaihill(1i)-1
end
Ex=1(abd(11)t) Ey=1(abd(22)t) Gxy=1(abd(33)t) poissonxy=-abd(12)abd(11) stress12 ms
epsilon3 deltah deltaH
epsilonz=deltaHt poissonxz=-epsilonze0(1) poissonyz=-epsilonze0(2)
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)
Page 47
8102019 02935booster_missilepdf
httpslidepdfcomreaderfull02935boostermissilepdf 4747
GraphitepolymerE1=2465610^7 E2=130510^6 E3=E2 shear12=638000 shear13=shear12 poisson12=027 poisson13=poisson12 poisson23=1-(E2E1)(1+(E1(34shear12)-1)2sqrt(2)poisson12) shear23=E2(2(1+poisson23)) Ftu1=208800 Fcu1=139200 Ftu2=6600 Fcu2=21720 F12=8280
compliancematrixm function [S] =
compliancematrix(E1E2E3poison12poison13poison23shear12shear13shear23) S=[1E1-poison12E1-poison13E1000-poison12E11E2-poison23E2000-poison13E1-poison23E21E30000001shear230000001shear130000001shear12] end
qbarm function [qbar] = qbar(thetaE1E2poisson12shear12) S=[1E1-poisson12E10-poisson12E11E20001shear12] Sbar(11)=S(11)cos(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)sin(theta)^4
Sbar(12)=(S(11)+S(22)-S(33))sin(theta)^2cos(theta)^2+S(12)(sin(theta)^4+cos(theta)^4) Sbar(13)=(2S(11)-2S(12)-S(33))sin(theta)cos(theta)^3-(2S(22)-2S(12)-S(33))sin(theta)^3cos(theta) Sbar(21)=Sbar(12) Sbar(22)=S(11)sin(theta)^4+(2S(12)+S(33))sin(theta)^2cos(theta)^2+S(22)cos(theta)^4 Sbar(23)=(2S(11)-2S(12)-S(33))sin(theta)^3cos(theta)-(2S(22)-2S(12)-S(33))sin(theta)cos(theta)^3 Sbar(31)=Sbar(13) Sbar(32)=Sbar(23) Sbar(33)=2(2S(11)+2S(22)-4S(12)-S(33))sin(theta)^2cos(theta)^2+S(33)(sin(theta)^4+cos(theta)^4)
qbar=inv(Sbar) end
tmatrixm function [T] = tmatrix(theta) n=sin(theta)