Analysis and Structural Optimization Of Chassis
Mini-Project work report submitted in partial fulfillment of the
requirements for the award of
BACHELOR OF TECHNOLOGYINMECHANICAL ENGINEERING
Work done by - N.Kaushik kumar
Reddy,M.S.Navyadeep,G.Rajesh,K.Ravichandra Reddy,Y.Sri Sai Phani
Harsha,C.Nihanth
Under the guidance ofG.DURGA PRASAD
DEPARTMENT OF MECHANICAL ENGINEERINGKONERU LAKSHMAIAH
UNIVERISTYGREEN FIELDS, VADDESWARAM
2011-2012
CERTIFICATE
This is to certify that the
students________________________________________ Studying _3/4
BTECH FIRST Semester branch MECHANICAL has done a project work on
Design Analysis and Manufacturing of Cylinder Liners during the
academic year 2009-2010.
HEAD OF THE DEPARTMENT PROJECT GUIDE(DR Y.V.HANUMANTHA RAO)
(G.DURGA PRASAD)
ACKNOWLEDGEMENT
We are extremely thankful to Dr. Y.V.HANUMANTHA RAO, Professor
& Head of the Department for the help and support he has
provided in completing this work.
We express our sincere gratitude to G.DURGA PRASAD, Professor,
Department of MECHANICAL ENGINEERING for guidance and assistance he
has provided in completing this work. We take immense pleasure in
thanking him for the freedom of thought and action. We have enjoyed
during the entire course of paper work. We shall always cherish our
association with him.
We are thankful to the staff of our department for their
continuous encouragement in completing our work successfully. We
also thank the authorities of our college for providing us
necessary facilities.
N.Kaushik kumar ReddyM.S.Navya DeepG.RajeshK. Ravi Chandra
ReddyY.Sri Sai Phani HarshaC.Nihanth
DECLARATION
The project report entitled ANALYSIS AND STRUCTURAL OPTIMIZATION
OF CHASSIS are original and are carried out by us under the
supervision of G.DURGA PRASAD, Asst-Professor, Department of
Mechanical, Koneru Lakshmaiah University, Vaddeswaram. This work
has not been submitted for the award of any degree or diploma in
part or full time prior to this date.
N.Kaushik kumar ReddyM.S.Navya DeepG.RajeshK. Ravi Chandra
ReddyY.Sri Sai Phani HarshaC.Nihanth
OBJECTIVE
To study about the chassis and model it in a CAD package .The
CAD model is analyzed for various loading conditions in an analysis
package .The chassis is re-modeled as a combination of solid blocks
and optimization is carried out using an Optimizer.
ABSTRACT
The project was aimed to model the frame & chassis of the
Society of Automotive Engineers (SAE) Baja car which is a
single-seated all-terrain vehicle and is used for off road usage
and endurance on a rough terrain. In many aspects it is similar to
an All-Terrain Vehicle (ATV) except that it is much smaller in size
and has safer rollover capabilities. The modeling of the frame and
chassis is done by using CATIA V5R20 software. This design is
checked by Finite Element Analysis after estimating the load and
the weight of the frame optimized.
CONTENTS:
1) INTRODUCTION2) DEFINATION OF CHASSIS3) TYPES OF CHASSIS4)
LOADS ACTING ON THE CHASSIS5) CHASSIS USED IN OUR MINI
PROJECT&ITS DESCRIPTION6) MATERIALS USED IN MANUFACTURING OF
CHASSIS7) ANALSYS &DESCRIPTION8) OPTIMIZATION9) TYPES OF
OPTIMIZATION10) RESULTS AND DISCUSSION11) CONCLUSION12)
REFERENCES
INTRODUCTION TO BAJA VEHICLEAn international Mini Baja design
competition is organized by the Society of Automotive Engineers
(SAE) Mini Baja is an intercollegiate engineering design
competition for undergraduate and graduate engineering students.
The objective is for a team of students to design fabricate, and
race an off-road vehicle powered by a ten horsepower Briggs and
Stratton gasoline engine. The vehicle is required to have a
combination frame and roll cage consisting of steel members. As
weight is critical in a vehicle powered by a small engine, a
balance must be found between the strength and weight of the
design. This project aims to design the chassis for a mini Baja
according to the SAE guidelines. Typical capabilities on basis of
which these vehicles are judged are hill climbing, pulling,
acceleration & manoeuvrability on land as well as water. This
project is an attempt to design the chassis of a Mini Baja from a
scratch and based on the guidelines given by SAE, certain practices
by the Off-road vehicles industry and the concepts of mechanical
engineering.
1. INTRODUCTIONIt is the under part of a vehicle, consisting of
the frame (on which the body is mounted) with the wheels and
machinery..As it bears all the loads of the vehicle parts ,it
should be sufficiently strong and light in weight .so optimization
of chassis is necessary.The automotive chassis is tasked with
holding all the components together while driving ,and transfering
vertical and lateral loads, caused by accelerations, on the chassis
through the suspension and two the wheels. Most engineering
students will have an understanding of forces and torques long
before they read this. It is suggested that the reader has a good
understanding of the concepts of axial forces, shear forces,
bending, torsion, angular and normal deflections, and finally mass
moment of inertia. The key to good chassis design is that the
further mass is away from the neutral axis the more rigid it will
be. This one sentence is the basis of automotive chassis design.
Some people stress full triangulation and material choice but once
you are into these specifics some critical understanding is missed.
People familiar with space frames maybe thinking that full
triangulation is the key to a good space frame. While this will
make the design better it can still benefit from this more general
designprinciples. The design section of the book will talk more
about these items in relation to the types of chassis but the first
part is the theory.
FUNCTIONS OF A CHASSIS:1.To carry load of the passengers or
goods carried in the body. 2. To support the load of the body,
engine, gear box etc., 3. To withstand the forces caused due to the
sudden braking or acceleration 4. To withstand the stresses caused
due to the bad road condition. 5. To withstand centrifugal force
while cornering.TYPES OF CHASSIS: There are five types of chassis
frames1. Ladder frame2. Tubular Space Frame3. Monocoque4. Back bone
space frame5. Space frame
Ladder frame: This is the earliest kind of chassis. From the
earliest cars until the early 60s, nearly all cars in the world
used it as standard. Even in today, most SUVs still employ it. Its
construction, indicated by its name, looks like a ladder - two
longitudinal rails interconnected by several lateral and cross
braces. The longitude members are the main stress member. They deal
with the load and also the longitudinal forces caused by
acceleration and braking. The lateral and cross members provide
resistance to lateral forces and further increase torsional
rigidity.
ADVANTAGES:1. Easy to manufacture2. It is cheap and can be built
with hand
DISADVANTAGES:Since it is a 2 dimensional structure, torsion
rigidity is very much lower than other chassis, especially when
dealing with vertical load or bumps
APPLICATIONS: Most SUVs, classic cars, Lincoln Town Car, Ford
Crown Victoria etc.
TUBULAR SPACE FRAME: As ladder chassis is not strong enough,
motor racing engineers developed a 3 dimensional design - Tubular
space frame. Tubular space frame chassis employs dozens of
circular-section tubes (some may use square-section tubes for
easier connection to the body panels, though circular section
provides the maximum strength), position in different directions to
provide mechanical strength against forces from anywhere. These
tubes are welded together and forms a very complex structure.For
higher strength required by high performance sports cars, tubular
space frame chassis usually incorporate a strong structure under
both doors ,hence result in unusually high door sill and difficult
access to the cabin.Many high-end sports cars also adopted tubular
space frame to enhance the rigidity / weight ratio. However, many
of them actually used space frames for the front and rear structure
and made the cabin out of monocoque to cut cost.
ADVANTAGES: Very strong in any direction.(compare with ladder
chassis and monocoque chassis of the same weight)
DISADVANTAGES:Very complex, costly and time consuming to be
built. Impossible for robotised production. Besides, it engages a
lot of space, raise the door sill and result in difficult access to
the cabin.
APPLICATIONS:Lamborghini Diablo, Jaguar XJ220, Caterham,
TVRMonocoque: Today, 99% cars produced in this planet are made of
steel monocoque chassis, thanks to its low production cost and
suitability to robotised production.Monocoque is a one-piece
structure which defines the overall shape of the car. While ladder,
tubular space frame and backbone chassis provides only the stress
members and need to build the body around them, monoque chassis is
already incoporated with the body in a single piece. In fact, the
one-piece chassis is actually made by welding several pieces
together. The floorpan, which is the largest piece, and other
pieces are press-made by big stamping machines. They are spot
welded together by robot arms (some even use laser welding) in a
stream production line. The whole process just takes minutes. After
that, some accessories like doors, bonnet, boot lid, side panels
and roof are added. Monocoque chassis also benefit crash
protection. Because it uses a lot of metal, crumple zone can be
built into the structure.Another advantage is space efficiency. The
whole structure is actually an outer shell, unlike other kinds of
chassis, therefore there is no large transmission tunnel, high door
sills, large roll over bar etc. Obviously, this is very attractive
to mass production cars.Although monocoque is suitable for mass
production by robots, it is nearly impossible for small-scale
production. The setup cost for the tooling is too expensive - big
stamping machines an expensive mouldings.
ADVANTAGES:Cheap for mass production. Inherently good crash
protection. Space efficient. Backbone Chassis:Backbone chassis is
very simple: a strong tubular backbone (usually in rectangular
section) connects the front and rear axle and provides nearly all
the mechnical strength. Inside which there is space for the drive
shaft in case of front-engine, rear-wheel drive layout like the
Elan. The whole drivetrain, engine and suspensions are connected to
both ends of the backbone. The body is built on the backbone,
usually made of glass-fibre. It's strong enough for smaller sports
cars but not up to the job for high-end ones. In fact, the original
De Tomaso Mangusta employed chassis supplied by Lotus and
experienced chassis flex. TVR's chassis is adapted from this design
- instead of a rigid backbone, it uses a lattice backbone made of
tubular space frames. That's lighter and stronger.
ADVANTAGES:
Strong enough for smaller sports cars. Easy to be made by hand
thus cheap for low-volume production. Simple structure benefit
cost. The most space-saving other than monocoque chassis.
DISADVANTAGES:
Not strong enough for high-end sports cars. The backbone does
not provide protection against side impact or off-set crash.
Therefore it need other compensation means in the body. Cost
ineffective for mass production.
Applications:Lotus Esprit, Elan Mk II, TVR, Marcos.
VARIOUS LOADS ACTING ON THE CHASSIS:1. Static loads- loads due
to chassis parts2. Impact loads-due to the collision of the
vehicle3. Momentary duration loads-while taking curve.
ANALYSIS:Detailed examination of the elements or structure of
something, typically as a basis for discussion or
interpretation.NEED FOR ANALYSIS:
In olden days manufacturers used to produce prototype of the
model and did the analysis manually so because of that there used
to be a waste of material and time. Even though if the mode is
manufactured there were sudden failures during the real time usage
to overcome the wastage of materials and time now a days the
prototypes is designed in any available designing software the cad
model is imported into analysis software and the necessary load
conditions are simulated using the software and experimental
results are found out.If the desired results are obtained then the
prototype is further processed for manufacturing .If the desired
results are not obtained, then the prototype is re modeled and
again analysis is carried out until the desired results are
obtained .SOFTEWARES USED FOR ANALYSIS: HyperMeshAltair HyperMesh
is a high-performance finite element pre-processor that provides a
highly interactive and visual environment to analyze product design
performance.
With the broadest set of direct interfaces to commercial CAD and
CAE systems, HyperMesh provides a proven, consistent analysis
platform for the entire enterprise.
With a focus on engineering productivity, HyperMesh is the
user-preferred environment for: Solid and surface geometry modeling
Shell meshing Model morphing Detailed model setup Solid mesh
generation Automatic mid-surface generation Batch meshing
RADIOSS:RADIOSS is a finite element solver for linear and
non-linear simulations. It can be used to simulate structures,
fluid, fluid-structure interaction, sheet metal stamping, and
mechanical systems. Multi-body dynamics simulation is made possible
through the integration with MotionSolve. The CAD model is
pre-processed(i.e. importing CAD model ,meshing ,loading conditions
are setup) in hypermesh .Then the finite element model is submitted
to the RADIOSS ,which carries out the analysis.HyperView:HyperView
is a complete post-processing and visualization environment for
finite element analysis (FEA), CFD, multi-body system simulation,
digital video, and engineering data. Amazingly fast 3-D graphics
and unparalleled functionality set a new standard for the speed and
integration of CAE results post-processing. HyperView enables you
to visualize data interactively as well as capture and standardize
your post-processing activities using process automation features.
HyperView combines advanced animation and XY plotting features with
window synching to enhance reults visualization. HyperView also
saves 3-D animation results in Altair's compact H3D format so you
can visualize and share CAE results within a 3-D web environment
using HyperView Player. After the analysis is carried out in
RADIOSS ,the results(displacements and Von-mises stresses) are
viewed in HyperView.
DIFFERENT TYPES OF ANALYSIS:1. STATIC2. MODAL3. TRANSIENT1.
STATIC ANALYSIS: Static analysis is used to determine the stress,
strain, reactions and displacements of the element In this type of
analysis linear data is given as input linear data means the data
which does not change with respect to time or any other factor 2.
MODAL ANALYSIS: Modal analysis is used to determine the natural
frequency and the mode shape(vibration characteristics) By finding
the natural frequency of the element we ca predict the failure of
the element due to resonance 3. TRANSIENT ANALYSIS Transient
analysis is used to determine the stress, strain and displacement
similar to that of the static analysis In this non linear data is
given as the input non linear data means the data which changes
with respect to time It used when the loading condition on a
element is continuous over a period of time It is used when
analysis is carried out on materials like composites
Force caluclations :mass of the vehicle = 450kgspeed of the
vehicle = 50kmph =13.89 mpstime for stopping = .5secTotal force =
(m*v)/t = 12500Considering the worst case(i.e. the buggy has been
hit by another buggy),the total force during impact would be around
20000N.Let us assume force acting for both impact and rollover be
20000N.
Fig: CAD model of SAE BAJA
The chassis is imported into the hypermesh. First it is auto
meshed by using an element size of 2.Then the mesh is extended to
the whole component using the 3-D tetramesh.
Rigids: These are the 1-D elements available in hypermesh. These
can be used for transmitting loads equally among different nodes of
the FE model. These are created by first selecting the master node
and then the slave nodes, for whom the force have to be
transmitted. 1.rigids at front 2.rigids at top 3.rigids at rearThe
loads are applied on the rigid elements The areas where the axle of
the wheels are connected to the chassis are constrained in 3
directions(i.e. translations along x, y and z axis. 1.constraints
at front axle 2.constraints at rear axle
Analysis results:
OptimizationDefinition:Optimization can be defined as the
automatic process to make a system or component as good as possible
based on an objective function and subject to certain design
constraints. Simply, optimization is the act of improving
something. Structural optimization methods are rather peculiar ways
of applying more traditional optimization algorithms to structural
problems solved by means of finite elements analysis. These
techniques are an effective approach through which large structural
optimization problems can be solved rather easily.What is the need
of optimization?Optimization practices allow you to produce a
better product. The goal of this optimization was to minimize
chassis weight by iterating tubing size (increasing vehicle
performance and efficiency).Optimization is key in all industries,
but especially in the automotive industry where every single
component in a vehicle to come to the lightest and best possible
result. Finally, Optimization is not a need, it is a
wish.Structural optimization:Structural optimization of mechanical
components leads to considerable energy saving and to other
efficiency gains. Preventing the occurrence of high stress areas in
an individual component increases average component lifetime and
can also have important safety benefits. The aim of this project
was to efficiently find the optimum design of a mechanical
component subject to given operating and/or manufacturing
restrictions
Types:There are many different methods or algorithms that can be
used to optimize a structure. In particular, with the term
structural optimization methods we refer to:
1. Topology optimization2. Topography optimization3. Size
optimization4. Shape optimization.
1. Topology optimization:Topology optimization was firstly
introduced by Bedsore and Sigmund. Topology optimizationis a
mathematical approach that optimizes material layout within a given
design space, for a given set of loads andboundary conditionssuch
that the resulting layout meets a prescribed set of performance
targets. Topology optimization is used at the concept level of the
design process to arrive at a conceptual design proposal that is
then fine tuned for performance and manufacturability. This
replaces time consuming and costly design iterations and hence
reduces design development time and overall cost while improving
design performance.It has developed in several directions giving
birth to rather different approaches, the most simple and known of
which is the SIMP (Single Isotropic Material with Penalization). In
topology optimization it is supposed that the elements density can
vary between 0 (void) and 1 (presence of the material).
2. Topography optimization:Topography optimization is an
advanced form of shape optimization in which a design region for a
given part is defined and a pattern of shape variable-based
reinforcements. Topography optimization can be applied only to 2D
or shell elements and aims at finding the optimum beads pattern in
a component. The concept is yet similar to the previous cases and,
simply speaking, the variables are given by the set of the elements
offsets from the component mid-plane. Topography Optimization is an
optimization capability which allows the user to find the location
and shape of bead patterns to stiffen panel structures.
Free Size: It is a mathematical technique that produces an
optimized thickness distribution per element for a 2D structure. It
can be broadly classified in to size and shape optimization.
3. Size optimization:Sizing Optimization is an optimization
capability which allows the user to find the best dimensions of any
designable elements like bars, shells and composites. Size
optimization is the same as topometry optimization, but in this
case the number of variables is greatly reduced in that the shell
thicknesses of components are considered in place of the single
elements of the domain It is an automated way to modify the
structure parameters (Thickness, 1D properties ,material
properties, etc) to find the optimized size.
4. Shape optimization:It is an automated way to modify the
structure shape based on set of nodes that can move totally free on
the boundary to find the optimal shape.Shape Optimization- is an
optimization capability which allows the user to find the best
shape possible. The typical problem is to find theshapewhich is
optimal in that it minimizes a certain costfunctionalwhile
satisfying givenconstraints.In many cases, the functional being
solved depends on the solution of a given partial differential
equation defined on the variable domain.
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