Motor Vehicle Structure

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Chapter 1

INTRODUCTION

TO MOTOR VEHICLE STRUCTURE

By

Kumbhar AppasoME 103506



Contents

Objective

Preface

SSS Method Conceptual Design Stages

Design Concept to FEA model

Vehicle Loading Condition



Glossary of body-in-white components



Glossary of underfloor structure components



To describe the purpose of a simplified

approach to conceptual design.

Can benefit the development of modernpassenger car structure design, especially

during the conceptual stage.

Overall structural design starting at the initial

concept of the vehicle.



SSS originated from the work of Dr Janusz

Pawlowski

It is organizing the process for rationalizing thebasic vehicle body structure load paths.



Initial design of a modern passenger car

Sketches

Full-size tape drawings

Three-dimensional clay models. Detailed design-Outside shape are finalized

Packaging



The basic analysis used is limited to the

equations of statics and strength of materials.

Specialists in advanced structural analysistechniques like finite element analysis will also

find this relevant



Simple Structural Surfaces (SSS) method is

used for studying the load paths in a vehicle

structure

Compared to modern finite element methods

it is a relatively easy method to understand

and apply.



It model or represent the structure of thevehicle as a number of plane surfaces.

Used at the concept stage of the designprocess or when there are fundamentalchanges to the structure.

Surfaces with high curvature, the structure

behind the surfaces can be approximated tocomponents or subassemblies that can berepresented as plane surfaces.



Each plane surface must be held inequilibrium by a series of forces.

These forces will be created by the weight of components attached to them.

The adjacent members have equal andopposite forces acting on them.

This procedure of determining the loads oneach SSS is continued through the structurefrom one axle to the other.



If an SSS has insufficient supports or reactions

and hence that the structure has a deficiency

The SSS method is useful for determiningcontinuity for load paths and integrity of the

structure.



The SSS method enables the engineer to know

the type of loading condition that is applied

It ensure continuity for the load path through

the structure.

surfaces with high curvature can be

approximated to components or

subassemblies that can be represented asplane surfaces.





The role of the SSS method for

± Qualitative conceptual design of joints and

attachment point modifications

± Assisting interpretation of the computer aided

results and rationalizing load paths

± Selecting subsequent iterations to be performed

on the FEA models for further development



Limitations of SSS method

It will not give a complete understanding of

how a structure behaves.

It cannot be used to solve for loads onredundant structures i.e.more than one load

path

It does not enable stiffness values to bedetermined.



The SSS method can provide a tool for

rationalizing structural concepts prior to and

during the application of CAE tools for certain

load conditions.

Alternative concepts need to be studied

within the vehicles dimensional, packaging,

cost and manufacturing constraints before the

commencement of detail design



Another approach is to develop concepts

starting with knowledge of basic engineering

principles (which comprise the SSS method)

Then progress to more tangible

representations of the vehicle structure using

FEA.



Begin with a qualitative free body diagram

(FBD) of the fundamental loads acting on the

structure

Followed by shear and bending moment

diagrams for beam members and shear flow

for panels



It might be identified early that

(1) The structure will need to carry more

bending moment in a particular area, or(2) That a particular suspension attachment

point will see higher vertical loads because of

the movement of a spring or damper, or

(3) The elimination of a structural member will

now require an alternative load path.







Conceptual design is defined as the activity

that precedes the start of detailed design.

The conceptual stage may be performed inconjunction with the preliminary study of

alternative platforms

One of the objectives of conceptual design is

to establish the boundaries or limits from

which the detailed design can start



Alternative load paths will be considered, as

well as overall sizing envelopes for the major

structural members

There are a few governing load cases-

crashworthiness,

overall stiffness (i.e. bending and torsion),extreme road loading conditions.



Q uestions about the major structural

members will be asked such as:

What are the particular governing load cases?,

How big should the members be sized overalland what are the packaging constraints?,

Where should load paths be placed?,

What are the range of materials and thickness toconsider?,

What are the capabilities of alternative platform

structures to sustain the loads?, What manufacturing processes will be required?

What is the structure likely to weigh?



Alternative load paths and structural member

optimization may be studied using relatively

coarse finite element models



The SSS method may be regarded as a tool tohelp qualitatively filter design alternatives duringthe conceptual stage for certain fundamental

load cases. Coarse finite element models act to help filter out

and select the concept to be used at the start of detailed design.

Larger (more degrees of freedom) finite elementmodels are generally applied in the detaileddesign phase.



These are the loads that occur in normal

service, including extreme conditions of road

irregularities and vehicle manoeuvres.

The main running load cases are the bending

of the vehicle due to the weight of the

components and/or those due to the

symmetrical bump load and the torsion loadcase.



The lateral load case due to the vehicle

turning a corner and

The longitudinal load due to braking. Crash loads or crashworthiness



Global load cases

1. V ertical symmetrical ( bending case) causes

bending about the YY axis

2. V ertical asymmetric (torsion case) causes

torsion about the XX axis and bending about

the YY axis.

3. F ore and aft loads ( braking, acceleration, obstacles,

towing)

4. Lateral (cornering, nudging ker b , etc. )5. Local load cases, e.g. door slam, etc.

6. Crash cases









Thank you

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Motor Vehicle Structure