Oct 18, 2015
Page | 1
1. INTRODUCTION
1.1 Introduction
A suspension system or shock absorber is a mechanical device designed
to smooth out and dissipate kinetic energy. The shock absorbers function is to absorb
or dissipate energy. In a vehicle, it reduces the effect of traveling over rough ground,
leading to improve ride quality, and increase in comfort due to substantially reduced
amplitude of disturbances.
Basic safety and also traveling ease and comfort to get a cars motorist are usually equally influenced by the particular vehicles suspension method. Safety refers to the vehicles handling and braking capabilities. Shock absorbers are a critical part of a suspension system, connecting the vehicle to its wheels. Basically
shock absorbers tend to be products which lessen a good behavioral instinct skilled
with an automobile, as well as properly absorb the actual kinetic power. Almost all
suspension systems consist of springs and dampers, which tend to limit the
performance of a system due to their physical constraints. Suspension systems,
comprising of springs and dampers are usually designed for passengers safety and do little to improve passenger comfort.
One particular strategy to this can be the application of productive
suspension devices, wherever highway circumstances are generally found
employing detectors, plus the technique in a flash adapts on the placing. A shock
absorber is a device which is designed to smooth out sudden impulse responses, and
dissipate kinetic energy. Any moving object possesses kinetic energy, and if the
object changes direction or is brought to rest, it may dissipate kinetic energy in the
form of destructive forces within the object. The purpose of a shock absorber, within
any moving object, is to dissolve the kinetic energy evenly while eliminating any
decelerating force that may be destructive to the object.
Shock absorbers are an important part of automobile and motorcycle
suspensions, aircraft landing gear, and the supports for many industrial machines.
Large shock absorbers have also been used in structural engineering to reduce the
susceptibility of structures to earthquake damage. A transverse mounted shock
absorber, helps keep railcars from swaying excessively from side to side and are
important in passenger railroads systems because they prevent railcars from
damaging station platforms. In a vehicle, it reduces the effect of traveling over rough
ground, and leading to improved ride quality. Without shock absorbers, the vehicle
Page | 2
would have a bouncing ride, as energy is stored in the spring and then released to
the vehicle, possibly exceeding the allowed range of suspension movement.
A typical shock absorber may simply comprise of a compression spring
that is capable of absorbing energy. Commonly shock absorbers are known as
dashpots, which is simply a fluid filled cylinder with an aperture through which fluid
could escape under controlled conditions. The dashpot is the building block for
pneumatic and hydraulic shock absorbers. These shock absorbers essentially consist
of a cylinder, filled with air or fluid, with a sliding piston that moves to dissipate or
absorb energy, and in these cases the energy is usually dissipated as heat.
Page | 3
1.2 Objectives of the Project
Study the causes of bouncing problems of the vehicle. Compare the failure parts performance in terms of its yield strength between
beryllium copper and spring steel.
Springs in parallel combination is used further for a comfortable ride.
1.3 Scope of Study
The scope of study for this project includes:-
Applying structural and modal analysis on the shock absorber.
Applying dynamic analysis on the shock absorber.
Page | 4
2. LITERATURE SURVEY
2.1 Shock Absorber
The shock absorber is really a mechanized gadget made to lessen
or even moist surprise behavioral instinct, as well as dissolve kinetic power. It's a
kind of dashpot. The shock absorber function is to absorb or dissipate energy. One
design consideration, when designing or choosing a shock absorber, is where that
energy will go. In many dashpots, power is actually transformed into warmth within
the viscous liquid. Within hydraulic cylinders, the actual hydraulic liquid gets hotter,
during atmosphere cylinders, the actual heat is generally worn out towards the
environment. In other types of dashpots, such as electromagnetic types, the
dissipated energy can be stored and used later. In general terms, shock absorbers
help cushion vehicles on uneven roads.
Shock absorbers tend to be an essential a part of car as well as
motorbike suspensions, plane getting equipment, and also the facilities for a lot of
commercial devices. Big shock absorbers are also utilized in structural architectural
to lessen the actual susceptibility associated with buildings in order to earthquake
harm as well as resonance. The transverse installed shock absorber, known as the
yaw damper, helps maintain railcars through swaying too much laterally and
therefore are essential within traveler railroads, commuter train as well as quick
transit techniques simply because they avoid railcars through harmful train station
systems.
Inside a vehicle, shock absorbers slow up the effect associated
with travelling more than rough floor, leading in order to improve trip quality as well
as increase within comfort. While surprise absorbers serve the objective of limiting
extreme suspension motion, their meant sole purpose would be to dampen
springtime oscillations. Shock absorbers make use of valve associated with oil as
well as gasses to soak up excess energy in the springs. Spring prices are chosen
through the manufacturer in line with the weight from the vehicle, packed and
unloaded. Some individuals use shocks to change spring prices but this isn't the
proper use. Together with hysteresis within the tire by itself, they dampen the power
stored within the motion from the unsparing weight down and up. Effective steering
wheel bounce damping may need tuning shocks for an optimal opposition.
Spring-based surprise absorbers generally use coils springs or
even leaf comes, though torsion bars are utilized in torsion shocks too. Ideal comes
Page | 5
alone, nevertheless, are not really shock absorbers, as come only store and don't
dissipate or even absorb power. Vehicles usually employ each hydraulic surprise
absorbers as well as springs or even torsion pubs. In this particular combination,
"shock absorber" pertains specifically towards the hydraulic piston which absorbs as
well as dissipates vibration.
2.2 Main components of Shock Absorber
Shock absorber has three main components to make it function well.
They are damper, spring and bushing. These all three part are playing an important
role to work together and absorb the impact or bouncing.
2.2.1 Damper
Damper shock absorber or simply damper is device that is designed
for providing absorption of shock and smooth deceleration in linear motion
applications. The dampers can be either mechanical or rely on a fluid. Dampers like
other shock absorber absorb shock by controlling the flow of the fluid from outer to
inner chamber of a cylinder during piston actuation. The damper shock absorbers
Page | 6
can be adjusted to different road conditions and provides good balance to the
vehicles.
2.2.2 Spring
Spring shock absorber as the name suggests is used to absorb the
jerks or bumps by using coil spring. The spring shock absorber is given stiffer
character by tightening the spring. The center of the spring shock absorber usually
contains rebound dampening unit. As the shock absorber changes the length the flow
fluid inside the shock absorber starts.
Springs length is usually controlled by turning the disc at the
bottom of the spring on the threads. The shorter spring length increases the preload,
making the rear wheel more resistant to upward motion. The dampening is both
controlled and adjusted in the spring shock absorber by controlling the fluid
reservoir. If the dampening is increased the motion of the shock is slowed down.
The spring type of shock absorbers are usually utilized for
protecting the delicate mechanisms, like instruments, from direct impact or loads
that are applied instantaneously. These types of springs are often made of rubber or
similar elastic material.
The springs that are used in different spring based shock absorbers
are coil springs or leaf springs. In tensional shocks, torsion bars can be used. In most
of the vehicles, springs or torsion bars as well as hydraulic shock absorbers are used.
2.2.3 Bushing
A bushing or rubber bushing is a type of vibration isolator. It
provides an interface between two parts, damping the energy transmitted through the
bushing. A common application is in vehicle suspension systems, where a bushing
made of rubber (or, more often, synthetic rubber or polyurethane) separates the faces
of two metal objects while allowing a certain amount of movement. This movement
allows the suspension parts to move freely, for example, when traveling over a large
bump, while minimizing transmission of noise and small vibrations through to the
chassis of the vehicle. A rubber bushing may also be described as a flexible mounting
or anti vibration mounting.
Page | 7
2.3 Dynamics of shock absorber
2.3.1 Response due to harmonic excitation of support
Consider the mass-spring-dashpot system of Figure 2.3.1. The
spring and dashpot are in parallel with one end of each connected to the mass and
the other end of each connected to a moveable support. Let y (t) denote the known
displacement of the support and let x (t) denote the absolute displacement of the
mass.
FIGURE 2.3.1 (a) FIGURE 2.3.1 (b)
(a) Block is connected through parallel combination of spring and viscous damper to a moveable support.
(b) FBDs at an arbitrary instant. Spring and viscous damper forces include effects of base motion.
Application of Newtons law to the free-body diagrams of Figure yields
.. (1)
.(2)
(3)
As the displacement of the mass relative to the displacement of its support. Above
equation (2) is rewritten using z as the dependent variable
.(4 )
Dividing Equations (2) by (4) by m yields
Page | 8
.. (5)
.... (6)
If the base displacement is given by a single-frequency harmonic of the form
y (t) =Y sin t
Then Equations (5) and (6) become
..(7)
..(8)
Equation (8) shows that a mass-spring-dashpot system subject to harmonic base
motion is yet another example in which the magnitude of a harmonic excitation is
proportional to the square of its frequency.
(9)
(10)
When Equations (9) and (10) are substituted into Equation (3) the absolute
displacement becomes
. (11)
Using the trigonometric relationship for the sine of the difference of two angles, it
is possible to express Equation (11) in the form
. (12)
. (13)
(14)
. (15)
Page | 9
X/Y is the amplitude of the absolute displacement of the mass to the amplitude of
displacement of the base.
Multiplying the numerator and denominator by 2 leads to
..(16)
Equation (15) is plotted in Figure The following are noted about
..(17)
GRAPH - 1
Page | 10
(18)
4. The maximum T(r, ) corresponding to the frequency ratio of Equation (18)
(19)
Page | 11
3. METHODOLOGY
3.1 Springs in parallel
FIGURE 3.1
When two springs are connected in parallel, both springs will deflect by
same amount and the load is shared between two springs.
It is observed from the figure, when force F1 is acting on spring of stiffness s1, spring
deflects by an amount . When force F2 (greater than F1) is acting on spring on
stiffness s2, spring deflects by same amount . When force F1+F2 is acting on both
springs, equivalent spring deflects by same amount .
So spring in spring or concentric springs has the following advantages:
Since there are two springs, the load carrying capacity is increased and heavy load can be transmitted in a restricted space.
In concentric spring, the operation of the mechanism continues even if one of the springs breaks.
Page | 12
3.2 Design Calculations of Helical springs for Shock absorbers
Mean diameter of a coil = D=60mm
Diameter of wire d = 8mm
Total no of coils n= 10
Height h = 185mm
Outer diameter of spring coil Do= D +d =68mm
No of active turns n = 8
Weight of bike = 125 Kgs
Let weight of 1 person = 75 Kgs
Weight of 2 persons = 150 Kgs
Weight of bike + persons = 275 Kgs
Rear suspension = 65% of W
65% of 275 = 165 Kgs
Considering dynamic loads it will be double
W = 330 Kgs = 3234 N
For single shock absorber weight = w/2= 1617 N = W
We Know that, compression of spring () = 8Wxc3xn
Gxd
= 8x1617x83x10 = 201.92 mm
41000x8
10 x 8 =80 mm
10x8+201.92+0.15x201.92=312.2 mm
1617/201.92=8
(312.2+80)/10=39.22 mm
Page | 13
(0.97x8x1617x8)/ (3.14x82) =499.26 Mpa
312.2/60=5.2
Wcr = 8x 0.05 x 312.2 = 124.88 N
Page | 14
4. INTRODUCTION TO CAD & NX 7.5
4.1. INTRODUCTION TO CAD
4.2. TECHNOLOGY OF CAD
4.3. PRODUCT DEVELOPMENT THROUGH CAD PROCESS
4.4. INTRODUCTION TO NX 7.5
4.5. SOLID GEOMETRIC MODELING
4.1 INTRODUCTION TO CAD
Computer Aided Design (CAD) is a technique in which man and
machine are blended into problem solving team, intimately coupling the best
characteristics of each. The result of this combination works better than either man
or machine would work alone, and by using a multi discipline approach, it offers the
advantages of integrated team work. The advances in Computer Science and
Technology resulted in the emergence of very powerful hardware and software
tool. It offers scope for use in the entire design process resulting in improvement in
the quality of design. The advent of CAD as a field of specialization will help the
engineer to acquire the knowledge and skills needed in the use of these tools in an
efficient and effective way on the design process. Computer Aided Design is an
interactive process, where the exchange of information between the designer and
the computer is made as simple and effective as possible. Computer aided design
encompasses a wide variety of computer based methodologies and tools for a
spectrum of engineering activities planning, analysis, detailing, drafting,
construction, manufacturing, monitoring, management, process control and
maintenance. CAD is more concerned with the use of computer-based tools to
support the entire life cycle of engineering system of design.
The modern manufacturing environment can be characterized by
the paradigm of delivering products of increasing variety, smaller batches and
higher quality in the context of increasing global competition. Industries cannot
survive worldwide competition unless they introduce new products with better
quality, at lower costs and with shorter lead-time. There is intense international
competition and decreased availability of skilled labor. With dramatic changes in
computing power and wider availability of software tools for design and production,
engineers
Page | 15
are now using Computer Aided Design (CAD), Computer Aided Manufacturing
(CAM) and Computer Aided Engineering (CAE) systems to automate their design
and production processes. These technologies are now used every day for sorts of
different engineering tasks. Below is a brief description of how CAD technology is
being used during the product realization process.
4.1.1 PRODUCT REALIZATION PROCESS:
The product realization process can be roughly divided into two
phases; design and manufacturing. The design process starts with identification of
new customer needs and design variables to be improved, which are identified by
the marketing personnel after getting feedback from the customers. Once the
relevant design information is gathered, design specifications are formulated. A
feasibility study is conducted with relevant design information and detailed design
and analyses are performed. The detailed design includes design conceptualization,
prospective product drawings, sketches and geometric modeling. Analysis includes
stress analysis, interference checking, kinematics analysis, mass property
calculations and tolerance analysis, and design optimization. The quality of the
results obtained from these activities is directly related to the quality of the analysis
and the tools used for conducting the analysis. This project is mainly concentrated
on product design and its analysis only.
4.1.2 BRIEF HISTORY OF CAD
The roots of current CAD/CAM technologies go back to the
beginning of civilization when engineers in ancient Egypt recognized graphics
communication. Orthographic projection practiced today was invented around the
1800s. Therell development of CAD/CAM started in the 1950s. CAD/CAM went through four major phases of development in the last century. The 1950s was known as the era of interactive computer graphics. MITs Servo Mechanisms Laboratory demonstrated the concept of numerical control (NC) on milling
machine. Development in this era was slowed down by the shortcomings of
computers at the time. During the late 1950s the development of Automatically Programmed Tools (APT) began and General Motors explored the potential of
interactive graphics.
The 1960s was the most critical research period for interactive
computer graphics. Ivan Sutherland developed a sketchpad system, which
demonstrated the possibility of creating drawings and altercations of objects
interactively on a cathode ray tube (CRT). The term CAD started to appear with
the word design extending beyond basic drafting concepts. General Motors
Page | 16
announced their DAC-1 system and Bell Technologies introduced the
GRAPHIC 1 remote display system. During the 1970s, the research efforts of the previous decade in computer graphics had begun to be fruitful, and potential of
interactive computer graphics in improving productivity was realized by industry,
government and academia. The 1970s is characterized as the golden era for computer drafting and the beginning of ad hoc instrumental design applications.
National Computer Graphics Association (NCGA) was formed and Initial Graphics
Exchange Specification (IGES) was initiated. In the 1980s, new theories and algorithms evolved and integration of various elements of design and manufacturing
was developed. The major research and development focus was to expand
CAD/CAM systems beyond three-dimensional geometric designs and provide more
engineering applications. The present day CAD/CAM development focuses on
efficient and fast integration and automation of various elements of design and
manufacturing along with the development of new algorithms. There are many
commercial CAD/CAM packages available for direct usages that are user-friendly
and very proficient.
Below are some of the commercial packages in the present market.
AutoCAD and Mechanical Desktop are some low-end CAD software systems, which are mainly used for 2D modeling and drawing.
NX, Pro-E, CATIA and I-DEAS, DSS SOLID WORKS are high-end modeling and designing software systems that are costlier but more powerful. These software
systems also have computer aided manufacturing and engineering analysis
capabilities.
ANSYS, ABAQUS, NASTRAN, Fluent and CFX are packages mainly used for analysis of structures and fluids. Different software are used for different proposes.
For example, Fluent is used for fluids and ANSYS is used for structures.
Alibre and Collab CAD are some of the latest CAD systems that focus on collaborative design, enabling multiple users of the software to collaborate on
computer-aided design over the Internet.
Page | 17
4.1.3. DEFINITION OF CAD/CAM/CAE
Following are the definitions of some of the terms used in this tutorial.
4.1.3a.Computer Aided Design CAD
CAD is technology concerned with using computer systems to assist
in the creation, modification, analysis, and optimization of a design. Any
computer program that embodies computer graphics and an application program
facilitating engineering functions in design process can be classified as CAD
software. The most basic role of CAD is to define the geometry of design a mechanical part, a product assembly, an architectural structure, an electronic circuit,
a building layout, etc. The greatest benefits of CAD systems are that they can save
considerable time and reduce errors caused by otherwise having to redefine the
geometry of the design from scratch every time it is needed.
4.1.3b.Computer Aided Manufacturing CAM
CAM technology involves computer systems that plan, manage, and control
the manufacturing operations through computer interface with the plants production resources. One of the most important areas of CAM is numerical control (NC).
This is the technique of using programmed instructions to control a machine tool,
which cuts, mills, grinds, punches or turns raw stock into a finished part. Another
significant CAM function is in the programming of robots. Process planning is also
a target of computer automation.
4.1.3c.Computer Aided Engineering CAE
CAE technology uses a computer system to analyze the functions of a
CAD-created product, allowing designers to simulate and study how the product
will behave so that the design can be refined and optimized. CAE tools are available
for a number of different types of analyses. For example, kinematic analysis
programs can be used to determine motion paths and linkage velocities in
mechanisms. Dynamic analysis programs can be used to determine loads and
displacements in complex assemblies such as automobiles. One of the most popular
methods of analyses is using a Finite Element Method (FEM). This approach can
be used to determine stress, deformation, heat transfer, magnetic field
distribution, fluid flow, and other continuous field problems that are often too
tough to solve with any other approach.
Page | 18
4.2. Technology of CAD
CAD technology makes use of drawings of parts and assemblies on
computer files which can be further analyzed and optimized. The
functional, ergonomic and aesthetic features of the product can be
evaluated on the computers. This has been made possible through the use
of the design workstations or CAD terminals and graphics and analytic
software, which help the designer to interactively model and analyze
object or component.
CAD can be put to a variety of uses, some of which are listed below.
1. Create conceptual product model/models.
2. Editing or refining the model to improve aesthetic, ergonomics and
performance,
3. Display the product in several colors to select color combination
most appealing to customers,
4. Rotate and views the object from various sided and direction.
5. Create and display all inner details of the assembly.
6. Check for interference or clearance between mating parts in static
and /or dynamic situations.
7. Analyze stress, static deflection and dynamic behavior for different
mechanical and thermal loading configurations and carry out quickly any
necessary design modifications to rectify deficiencies in design.
8. Study the product from various aspects such as material
requirements, costs, value engineering manufacturing processes,
Page | 19
standardization, simplification, weight reduction, service life, lubricants,
servicing and maintenance aspects etc.
9. Prepare detailed component drawings giving full details of
dimensions, tolerances, surface finish requirements, functional
specification etc.
10. Prepare assembly drawing depicting the orientation of components,
11. Assembly procedures and requirements and incorporation, as
required, such
12. Prepare exploded view of the assemblies. These views could be so
oriented as to provide better visibility and improved comprehension of the
design. Plot to print the picture/drawing stored in a computer file or the
computer screen on different media.
13. Store the database of the object. Part of the drawing in a magnetic
disc or tape for the retrieval at the later date for the use in some other
design.
4.2.1. Modification of existing design
The above description reveals that CAD technologies give the
design engineer a powerful tool for graphical tasks .Modern CAD
systems are based on interactive computer graphics communicates data
and commands to the computer through the several input devices, to create
an image or model on the computer screen by entering command to call
and active the required software subroutines stored in the computer.
In a 2-dimensional drafting system the images are constructed out of basic
geometric elements or entities like points, lines, arcs, circles etc. These
images can then be modified. Rotated, scaled or transformed in several
ways depending upon the designers requirement.
Page | 20
4.3. PRODUCT DEVELOPMENT THROUGH CAD PROCESS:
The product begins with a need that is identified based on
costumer and markets demands. The product goes through two main processes from the idea conceptualization to the finished product the
design process and the manufacturing process. Product development
through CAD product. Synthesis and analysis are the main sub processes
that constitute the deign process. Synthesis is crucial to design an analysis.
The philosophy, functionality and uniqueness of the product are all
determined during the synthesis. The major financial commitment to turn
the conceived product idea into reality is also made. Most of the
information generated during the synthesis sod process is qualitative
and consequently is hard to captured in a computer system expert and
knowledge based systems have made a great deal of progress in this regard and the interested conceptual design of the prospective product.
Typically, this design takes the form of a sketch or surrounding constrains.
It is also employed during brainstorming discussions among various
design terms and the presentation purpose.
4.4. Introduction to NX 7.5
NX is one of the worlds most advanced and tightly integrated CAD/CAM/CAE product development solutions. Spanning
the entire range of product development, NX delivers immense value to
enterprises of all sizes. It simplifies complex product designs, thus
speeding up the process of introducing products to the market.
The NX software integrates knowledge-based principles,
industrial design, geometric modeling, advanced analysis, graphic
simulation, and concurrent engineering. The software has powerful
hybrid modeling capabilities by integrating constraint-based feature
modeling and explicit geometric modeling. In addition to modeling
standard geometry parts, it allows the user to design complex free-form
shapes such as airfoils and manifolds. It also merges solid and surface
modeling techniques into one powerful tool set.
Page | 21
4.5. SOLID GEOMETRIC MODELING:
A solid model of an object is a completed representation of the
object. This model is capable of complex geometry data representation
that is the art completely defined ,solid modeling techniques based on
information ally complete, valid and unambiguous of object solid
modelers store more information (geometry and topology) than wire
frame modelers of surface (geometry only). Both wire frame and surface
modelers are incapable of handling special address ability as well as
verifying that the model is well framed or not. Solid models can be quickly
created without having to define individual locations as with wire
frames. Solid modeling produces accurate designs, provides complete
three-dimensional improves the quality of the design, improves and
has potential for functional automation and integration.
The first step in working in NX is to log on to a workstation and
start an NX session. After you start NX, you see the No Part interface.
You can change defaults and preferences, open an existing part file, or
create a new part file.
FIG4.5
Page | 22
4.5.1. MODELLING OF SHOCK ABSORBER
1. Outer spring
FIGURE 4.5.1a
Page | 23
2. Inner spring
FIGURE 4.5.1b
Page | 24
3. Solid model of outer spring
FIGURE 4.5.1.c
4. Solid model of Inner spring
FIGURE 4.5.1d
Page | 25
5. Cylinder
FIGURE 4.5.1e
Page | 26
6. Solid model of cylinder
FIGURE 4.5.1f
7. Hat
FIGURE 4.5.1 g
Page | 27
8. Rings and Rod
FIGURE 4.5.1 h
FIGURE 4.5.1 i
Page | 28
FIGURE 4.5.1 J
9. Sequence of assembly
FIGURE 4.5.1K
Page | 29
FIGURE 4.5.1 L
FIGURE 4.5.1 m
Page | 30
10. Final model of shock absorber
FIGURE 4.5.1 n
Page | 31
5. INTRODUCTION TO FEA
Finite Element Analysis (FEA) was first developed in 1943 by R. Courant,
who utilized the Ritz method of numerical analysis and minimization of variational
calculus to obtain approximate solutions to vibration systems. Shortly thereafter, a
paper published in 1956 by M. J. Turner, R. W. Clough, H. C. Martin, and L. J. Topp
established a broader definition of numerical analysis. The paper centered on the
"stiffness and deflection of complex structures".
By the early 70's, FEA was limited to expensive mainframe computers
generally owned by the aeronautics, automotive, defense, and nuclear industries.
Since the rapid decline in the cost of computers and the phenomenal increase in
computing power, FEA has been developed to an incredible precision. Present day
supercomputers are now able to produce accurate results for all kinds of parameters.
FEA consists of a computer model of a material or design that is stressed
and analyzed for specific results. It is used in new product design, and existing
product refinement. A company is able to verify a proposed design will be able to
perform to the client's specifications prior to manufacturing or construction.
Modifying an existing product or structure is utilized to qualify the product or
structure for a new service condition. In case of structural failure, FEA may be used
to help determine the design modifications to meet the new condition.
There are generally two types of analysis that are used in industry: 2-D
modeling, and 3-D modeling. While 2-D modeling conserves simplicity and allows
the analysis to be run on a relatively normal computer, it tends to yield less accurate
results. 3-D modeling, however, produces more accurate results while sacrificing the
ability to run on all but the fastest computers effectively. Within each of these
modeling schemes, the programmer can insert numerous algorithms (functions)
which may make the system behave linearly or non-linearly. Linear systems are far
less complex and generally do not take into account plastic deformation. Nonlinear
systems do account for plastic deformation, and many also are capable of testing a
material all the way to fracture.
FEA uses a complex system of points called nodes which make a grid called
a mesh. This mesh is programmed to contain the material and structural properties
which define how the structure will react to certain loading conditions. Nodes are
assigned at a certain density throughout the material depending on the anticipated
stress levels of a particular area. Regions which will receive large amounts of stress
usually have a higher node density than those which experience little or no stress.
Points of interest may consist of: fracture point of previously tested material, fillets,
corners, complex detail, and high stress areas. The mesh acts like a spider web in
that from each node, there extends a mesh element to each of the adjacent nodes.
Page | 32
This web of vectors is what carries the material properties to the object, creating
many elements. A wide range of objective functions (variables within the system)
are available for minimization or maximization:
Mass, volume, temperature
Strain energy, stress strain
Force, displacement, velocity, acceleration
Synthetic (User defined)
There are multiple loading conditions which may be applied to a system. Some
examples are shown:
Point, pressure, thermal, gravity, and centrifugal static loads Thermal loads from solution of heat transfer analysis Enforced displacements Heat flux and convection Point, pressure and gravity dynamic loads
Each FEA program may come with an element library, or one is constructed over
time. Some sample elements are:
Rod elements Beam elements Plate/Shell/Composite elements Shear panel Solid elements Spring elements Mass elements Rigid elements Viscous damping elements
Many FEA programs also are equipped with the capability to use multiple materials
within the structure such as:
Isotropic, identical throughout Orthotropic, identical at 90 degrees General anisotropic, different throughout
Page | 33
5.1. Types of Engineering Analysis:
Structural analysis consists of linear and non-linear models. Linear
models use simple parameters and assume that the material is not plastically
deformed. Non-linear models consist of stressing the material past its elastic
capabilities. The stresses in the material then vary with the amount of deformation
as in.
Vibrational analysis is used to test a material against random vibrations,
shock, and impact. Each of these incidences may act on the natural vibrational
frequency of the material which, in turn, may cause resonance and subsequent
failure.
Fatigue analysis helps designers to predict the life of a material or
structure by showing the effects of cyclic loading on the specimen. Such analysis
can show the areas where crack propagation is most likely to occur. Failure due to
fatigue may also show the damage tolerance of the material.
Heat Transfer analysis models the conductivity or thermal fluid
dynamics of the material or structure. This may consist of a steady-state or transient
transfer. Steady-state transfer refers to constant thermo properties in the material that
yield linear heat diffusion.
5.2. Results of Finite Element Analysis
FEA has become a solution to the task of predicting failure due to unknown
stresses by showing problem areas in a material and allowing designers to see all of
the theoretical stresses within. This method of product design and testing is far
superior to the manufacturing costs which would accrue if each sample was actually
built and tested. In practice, a finite element analysis usually consists of three
principal steps:
1. Preprocessing: The user constructs a model of the part to be analyzed in which
the geometry is divided into a number of discrete sub regions, or elements,"
connected at discrete points called nodes." Certain of these nodes will have fixed
displacements, and others will have prescribed loads. These models can be
extremely time consuming to prepare, and commercial codes vie with one another
to have the most user-friendly graphical preprocessor" to assist in this rather tedious chore. Some of these preprocessors can overlay a mesh on a preexisting CAD file,
so that finite element analysis can be done conveniently as part of the computerized
drafting-and-design process.
Page | 34
2. Analysis: The dataset prepared by the preprocessor is used as input to the finite
element code itself, which constructs and solves a system of linear or nonlinear
algebraic equations
Kijuj = fi
Where u and f are the displacements and externally applied forces at the nodal points.
The formation of the K matrix is dependent on the type of problem being attacked,
and this module will outline the approach for truss and linear elastic stress analyses.
Commercial codes may have very large element libraries, with elements appropriate
to a wide range of problem types. One of FEA's principal advantages is that many
problem types can be addressed with the same code, merely by specifying the
appropriate element types from the library.
3. Post processing: In the earlier days of finite element analysis, the user would
pore through reams of numbers generated by the code, listing displacements and
stresses at discrete positions within the model. It is easy to miss important trends and
hot spots this way, and modern codes use graphical displays to assist in visualizing
the results. A typical postprocessor display overlays colored contours representing
stress levels on the model, showing a full field picture similar to that of photo elastic
or moir experimental results.
5.3. INTRODUCTION TO ANSYS WORKBENCH
ANSYS is general-purpose finite element analysis (FEA) software
package. Finite Element Analysis is a numerical method of deconstructing a
complex system into very small pieces (of user-designated size) called elements. The
software implements equations that govern the behavior of these elements and solves
them all; creating a comprehensive explanation of how the system acts as a whole.
These results then can be presented in tabulated, or graphical forms. This type of
analysis is typically used for the design and optimization of a system far too complex
to analyze by hand. Systems that may fit into this category are too complex due to
their geometry, scale, or governing equations.
ANSYS is the standard FEA teaching tool within the Mechanical
Engineering Department at many colleges. ANSYS is also used in Civil and
Electrical Engineering, as well as the Physics and Chemistry departments.
ANSYS provides a cost-effective way to explore the performance of
products or processes in a virtual environment. This type of product development is
Page | 35
termed virtual prototyping. With virtual prototyping techniques, users can iterate
various scenarios to optimize the product long before the manufacturing is started.
This enables a reduction in the level of risk, and in the cost of ineffective designs.
The multifaceted nature of ANSYS also provides a means to ensure that users are
able to see the effect of a design on the whole behavior of the product, be it
electromagnetic, thermal, mechanical etc.
An overview of ANSYS WORK BENCH
FIGURE 5.3
5.4. Generic Steps to Solving any Problem in ANSYS:
Like solving any problem analytically, you need to define (1) your solution
domain, (2) the physical model, (3) boundary conditions and (4) the physical
properties. You then solve the problem and present the results. In numerical
methods, the main difference is an extra step called mesh generation. This is the step
that divides the complex model into small elements that become solvable in an
otherwise too complex situation. Below describes the processes in terminology
slightly more attune to the software.
Page | 36
Build Geometry
Construct a two or three dimensional representation of the object to be
modeled and tested using the work plane coordinate system within ANSYS.
Define Material Properties
Now that the part exists, define a library of the necessary materials that
compose the object (or project) being modeled. This includes thermal and
mechanical properties.
Generate Mesh
At this point ANSYS understands the makeup of the part. Now define
how the modeled system should be broken down into finite pieces.
Apply Loads
Once the system is fully designed, the last task is to burden the system
with constraints, such as physical loadings or boundary conditions.
Obtain Solution
This is actually a step, because ANSYS needs to understand within what
state (steady state, transient etc.) the problem must be solved.
Present the Results
After the solution has been obtained, there are many ways to present
ANSYS results, choose from many options such as tables, graphs, and contour plots.
5.5. Specific Capabilities of ANSYS:
5.5.1. Structural
Structural analysis is probably the most common application of the finite
element method as it implies bridges and buildings, naval, aeronautical, and
mechanical structures such as ship hulls, aircraft bodies, and machine housings, as
well as mechanical components such as pistons, machine parts, and tools.
Static Analysis - Used to determine displacements, stresses, etc. under static
loading conditions. ANSYS can compute both linear and nonlinear static analyses.
Page | 37
Nonlinearities can include plasticity, stress stiffening, large deflection, large strain,
hyper elasticity, contact surfaces, and creep.
Transient Dynamic Analysis - Used to determine the response of a structure
to arbitrarily time-varying loads. All nonlinearities mentioned under Static Analysis
above are allowed.
Buckling Analysis - Used to calculate the buckling loads and determine the
buckling mode shape. Both linear (eigenvalue) buckling and nonlinear buckling
analyses are possible.
In addition to the above analysis types, several special-purpose features are
available such as
Fracture mechanics, Composite material analysis Fatigue, and Both p-Method and Beam analyses.
5.5.2. Thermal
ANSYS is capable of both steady state and transient analysis of any solid
with thermal boundary conditions.
Steady-state thermal analyses calculate the effects of steady thermal loads
on a system or component. Users often perform a steady-state analysis before doing
a transient thermal analysis, to help establish initial conditions. A steady-state
analysis also can be the last step of a transient thermal analysis; performed after all
transient effects have diminished. ANSYS can be used to determine temperatures,
thermal gradients, heat flow rates, and heat fluxes in an object that are caused by
thermal loads that do not vary over time. Such loads include the following:
Convection Radiation Heat flow rates Heat fluxes (heat flow per unit area) Heat generation rates (heat flow per unit volume) Constant temperature boundaries
A steady-state thermal analysis may be either linear, with constant material
properties; or nonlinear, with material properties that depend on temperature. The
thermal properties of most material vary with temperature. This temperature
dependency being appreciable, the analysis becomes nonlinear. Radiation boundary
Page | 38
conditions also make the analysis nonlinear. Transient calculations are time
dependent and ANSYS can both solve distributions as well as create video for time
incremental displays of models.
5.5.3. Acoustics / Vibration
ANSYS is capable of modeling and analyzing vibrating systems in order to
that vibrate in order to analyze Acoustics is the study of the generation, propagation,
absorption, and reflection of pressure waves in a fluid medium. Applications for
acoustics include the following:
Sonar - the acoustic counterpart of radar
Design of concert halls, where an even distribution of sound pressure is desired
Noise minimization in machine shops
Noise cancellation in automobiles
Underwater acoustics
Design of speakers, speaker housings, acoustic filters, mufflers, and many other similar devices.
Geophysical exploration
Within ANSYS, an acoustic analysis usually involves modeling a fluid
medium and the surrounding structure. Characteristics in question include pressure
distribution in the fluid at different frequencies, pressure gradient, and particle
velocity, the sound pressure level, as well as, scattering, diffraction, transmission,
radiation, attenuation, and dispersion of acoustic waves. A coupled acoustic analysis
takes the fluid-structure interaction into account. An uncoupled acoustic analysis
models only the fluid and ignores any fluid-structure interaction.
The ANSYS program assumes that the fluid is compressible, but allows only
relatively small pressure changes with respect to the mean pressure. Also, the fluid
is assumed to be non-flowing and in viscid (that is, viscosity causes no dissipative
effects). Uniform mean density and mean pressure are assumed, with the pressure
solution being the deviation from the mean pressure, not the absolute pressure.
5.5.4. Coupled Fields
A coupled-field analysis is an analysis that takes into account the interaction
(coupling) between two or more disciplines (fields) of engineering. A piezoelectric
analysis, for example, handles the interaction between the structural and electric
fields: it solves for the voltage distribution due to applied displacements, or vice
versa. Other examples of coupled-field analysis are thermal-stress analysis, thermal-
electric analysis, and fluid-structure analysis.
Page | 39
Some of the applications in which coupled-field analysis may be required are
pressure vessels (thermal-stress analysis), fluid flow constrictions (fluid-structure
analysis), induction heating (magnetic-thermal analysis), ultrasonic transducers
(piezoelectric analysis), magnetic forming (magneto-structural analysis), and micro-
electro mechanical systems (MEMS).
5.5.5. Modal Analysis
A modal analysis is typically used to determine the vibration characteristics
(natural frequencies and mode shapes) of a structure or a machine component while
it is being designed. It can also serve as a starting point for another, more detailed,
dynamic analysis, such as a harmonic response or full transient dynamic analysis.
Modal analyses, while being one of the most basic dynamic analysis types available
in ANSYS, can also be more computationally time consuming than a typical static
analysis. A reduced solver, utilizing automatically or manually selected master
degrees of freedom is used to drastically reduce the problem size and solution time.
5.5.6 Harmonic Analysis
Used extensively by companies who produce rotating machinery, ANSYS
Harmonic analysis is used to predict the sustained dynamic behavior of structures to
consistent cyclic loading. Examples of rotating machines which produced or are
subjected to harmonic loading are:
Turbines o Gas Turbines for Aircraft and Power Generation o Steam Turbines o Wind Turbine o Water Turbines o Turbo pumps
Internal Combustion engines
Electric motors and generators
Gas and fluid pumps
Disc drives
A harmonic analysis can be used to verify whether or not a machine
design will successfully overcome resonance, fatigue, and other harmful effects of
forced vibrations.
Page | 40
5.6. Results:
5.6.1. Structural Analysis for bike weight (165 kgs) using Spring Steel as
Spring material
FOR 165 kg load
Material used: structural steel
E: 210000N/mm^2
Poissons Ratio (PRXY): 0.29
Density: 0.000007850kg/mm3
imported model from NX 7.5
Figure 5.6.1
Page | 41
5.6.2. Meshed Model
FIGURE 5.6.2
5.6.3. Solution step
FIGURE 5.6.3
Page | 42
5.6.4. Modal analysis
FIGURE 5.6.4 a
FIGURE 5.6.4 b
Page | 43
FIGURE 5.6.4.c
FIGURE 5.6.4 d
Page | 44
5.7. Structural Analysis for bike weight (165kgs) using Beryllium
Copper as spring material
Load=165 kg
Material used: beryllium copper
E : 280000N/mm2
Poissons Ratio (PRXY) : 0.285
Density :0.000001850kg/mm3
FIGURE 5.7
Page | 45
5.7.1. Modal Analysis for beryllium copper spring
FIGURE 5.7.1 a
FIGURE 5.7.1 b
Page | 46
FIGURE 5.7.1 c
FIGURE 5.7.1 d
Page | 47
5.8. Static structural Analysis of concentric springs
Load=165 kg
Material used: beryllium copper and spring steel
Inner spring: beryllium copper
Outer spring: spring steel
FIGURE 5.8
Page | 48
5.8.1. Modal analysis of concentric springs
FIGURE 5.8.1 a
FIGURE 5.8.1 b
Page | 49
FIGURE 5.8.1 c
FIGURE 5.8.1 d
Page | 50
5.9. Graphical Results
Steel vs Beryllium copper
GRAPH 2
Single Spring vs Concentric Springs
Graph 3
-5
0
5
10
15
20
25
30
35
40
45
0 10000 20000 30000 40000 50000 60000
Stress
Nodes
x(steel) y(Berilium copper)
-5
0
5
10
15
20
25
30
35
40
45
0 10000 20000 30000 40000 50000 60000
Stress
Nodes
x(one spring) y(concentric springs)
Page | 51
6. DYNAMIC ANLAYSIS USING SOLID WORKS
COSMOS Motion is a simulation software package for motion study
of any mechanism. Motion study is a term for simulating and analyzing the
movement of mechanical assemblies and mechanisms. Motion studies are two types;
one is kinematics and the other dynamics. Kinematics is the study of motion without
regard to forces that cause it, and dynamics is the study of motions that result from
forces. Kinematic simulations show the physical positions of all the parts in an
assembly with respect to the time as it goes through a cycle. Dynamic simulation
shows joint reactions, inertial forces.
The traditional method of performing dynamic and kinematic analysis
of any mechanism is preparing the data, solving the algorithms, which involves the
solution of simultaneous equations, and analyzing the results. For a complex
mechanism like vehicle suspension shown in the following Fig 6. Solving the
dynamic equations for motion "by hand" requires intensive calculations, and even
with the help of computerized spreadsheet it may take a few hours to get the results
and plot the graphs. One can develop a program using software to solve the dynamic
equations of motion, but if the geometry of any component changes then the whole
program has to be changed again. A design engineer can successfully overcome
these problems in motion analysis by using COSMOS Motion simulation software.
To analyze the shock absorber using COSMOS Motion, one needs to
know:
1. Each joint in the mechanism will have how many degrees of freedom
2. Spring stiffness and damping force in the shock absorber
3. Which parts are moving and which parts are fixed.
4. Input loads such as normal force, lateral force and longitudinal force.
Page | 52
6.1. Motion Analysis in Solidworks
The road profile is approximated by a sine wave represented by
q= Y sint Where,
q = Road surface excitation at time t in m.
Y= Amplitude of sine wave = 0.02 m. and
l = Wavelength of road surface = 6 m.
INPUT VARIABLES:
Time=3sec
Page | 53
Figure 6.1 (a) single degree of damping system
FIGURE 6.1 b
Page | 54
Analysis of Spring characteristics on an uneven road
Figure 6.1 c
Page | 55
Responses of model:
GRAPH 4
Page | 56
GRAPH 5
Page | 57
7. CONCLUSION
In this project we have modelled shock absorber by using nx7.5.
To validate the strength of the design we have done the structural analysis on shock absorber. We have done analysis by varying
pitch and spring materials i.e., spring steel and beryllium copper.
Also the shock absorber design is modified by adding spring in parallel to the existing spring and structural analysis is done on
shock absorber.
In this paper half bike model is developed for analysis of vibrational effect when it is subjected to harmonic excitation by
road profile.
Page | 58
8. FUTURE SCOPE
A numerical model using ADAMS has to be developed in order to simulate the dynamic behavior of the shock absorber and to
describe and evaluate its damping coefficient in compression and
rebound cycles.
The design of interchangeable shock absorber test rig has to be developed and fabricated for the dynamics measurement system.
A full vehicle simulation model has to be developed to get better results.
Page | 59
9. BIBILOGRAPHY
Design of machine elements v.b.bhandari
Patel Quarter Model Analysis of Wagan-R cars Rear Suspension using ADAMS
Mechanical vibrations theory and applications graham Kelly
Comparative Analysis Of Vehicle Suspension
System in Matlab-SIMULINK and MSc-ADAMS with the help of Quarter Car Model
PSG, 2008.DESIGN DATA, kalaikathir achachgam publishers, COIMBATORE, INDIA
Gilles, T. (2005). Automotive Chassis: Brake, Steering & Suspension.: Cencage Learning