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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