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Rollover of Bus

Manjinder Singh SidhuEngineer-R&D

SML ISUZU Ltd.Village Asron, Ropar,

Distt Nawanshahar-144 533, Punjab (India)

Abstract

Passenger and Driver Safety is the primary concern of all Automotive OEMs. Stringent ARAI (Automotive Research

Association of India) norms has further strengthened this field. Bus manufacturers should ensure that their design

confirm to these norms using virtual.

Rollover of the Bus structure as per AIS-031 is one of the safety standard that a bus body design should meet. Nearly

60% of the Collision Configuration in the Bus Accidents is Rollover and 55% Injuries are due to this.

During Rollover, about 50% of the Head and 30% of the Neck is exposed to Accident and this being critical parts of

human body, design should ensure that it provides maximum safety to these parts during roll over. This led to the

change in the Design, material usage and manufacturing Processes in the Bus Industry.

The norm identifies the Passenger Survival Zone inside the Bus and this must not interfere with the Superstructure of

the Bus in the event of roll over. Efforts are being made to perform the test virtually in the initial stages of Design to

reduce Cost, Time and Efforts.

In this paper, the Rollover Crash Simulation of the Complete Bus Structure is performed as per AIS-031 regulation and

the structure is verified for the Clear Survival Space. HyperMesh V11.0 and HyperCrash are used for Pre Processing;

Explicit Solver Radioss Block V11.0 is used solving and HyperView, HyperGraph are used for, Post-processing the

results

Introduction

The Bus Rollover is considered as most stringent test for the Bus that shows the load bearingcapacity of the superstructure and the strength of the Bus in terms of Passenger Safety. In

this, the bus is rolled over from a platform as per AIS-031 standard (issued by Automotive

Research Association of India) and is allowed to fall freely about the stopper as pivot. The

governing parameters are the CG of the Bus, the wheel track, the overall height of the bus

and the radius of gyration.

During Rollover, the Potential Energy is converted to the Rotational Kinetic Energy and is

further converted to the Impact Energy on touching the ground. The energy on crashing is

absorbed by the members attached to form the structural cage of the Bus in the form of

deformations and stresses produced.

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THE BUS CONSTRUCTION

The bus body can be divided into three parts; the chassis and engine, structural body, interior

and exterior parts. The chassis and engine are quite important. They must pass the standard

test by domestic and international organization. The chassis consists of frame, which is a box

type section and varies longitudinally as per the load and strength required for Body. Some

Stiffeners are also added at the locations where the effect of Bending and Torsion is

maximum.

The second part is the bus body structure. The body comprises of six main components; the

left frame side, the right frame side, the front frame side, the back frame side, the top frame

side and the bottom frame side. The top frame side is sometime called the roof frame side.

The bottom frame side is also called the floor frame side. The left and the right side aresimilar but the left side is normally composed of passenger door(s). On the other hand, the

right side has two doors; the driver door and the emergency door. The sides are concerned to

be critical parts and they must be strong.

The parts need to be analyticaly tested either by simulation or through physical test. Torsion

and bending tests are widely simulated by FE analysis. However, the strength is affected by

the manufacturing processes. For example, the special type of welding such as MIG, TIG and

spot welding arc much better than the normal arc welding process. However, such

manufacturing process is not concerned in this study.

The third part, top frame or roof frame is considered as the critical part. It should be strong

part in order to ensure safety of passengers. This part must support different loads such asinterior components, air conditioners; luggage loads and aerodynamic load. The back frame

and front frame are mostly supported and joined with the left and right sides as well as the

roof frame and the floor (bottom side) frame. These two parts need to be both Aesthetically

good and strong. Therefore the shape is quite become curvature, slop and good

aerodynamic. The last part is bottom frame side, also called the floor, which is welded or

joined with the chassis and the other five parts. Each part is further combined by a lot of

pieces which is here called gussets. After this, the outer body paneling is done that gives the

aesthetics and also absorbs energy in case of Rollover.

This assembly further goes through Primer Coating and Painting Process; the assembly at

this stage is known as the Body Shell. This shell is docked over chassis through U-Bolts or is

welded to integrate the Bus. The interior and exterior is finished and other accessories are

installed to complete the Bus. Bus undergoes thorough inspection before delivering to the

customer. In The existing bus body structure safety is achieved by the strong structural

members. Important frames are roof frame, left frame right frame, and floor frame. In this

study, we aim to carry out the Rollover Analysis of the Bus as per AIS-031 and find the

strength requirements of each member attached to the superstructure. The FE analysis

method is used to validate the Bus as per the AIS Standard.

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Standard

The Automotive Research Association of India (ARAI) has framed the standard to evaluate

the strength of superstructure of Large Passenger Vehicles or AIS-031 that specifies the

method to test the structure for Passenger Safety

The standard defines safe survival zone. In the event of rollover structure should not enter

into this zone. The space extends from 150mm from the wall at the position of R-Point and to

250mm at the height of 750mm from R-Point as shown.

The Kerb Weight and Center of Gravity of the vehicle is calculated as per IS: 9211-1979 and

IS: 11849-1986 respectively. These are the most important parameters that govern theamount of Energy that will be absorbed by the structure as can be inferred from below.

The vehicle is allowed to fall freely under the action of gravity from the platform (as shown

above) onto a rigid floor. Due to the Impact, the bus gets deformed. As per the standard, this

deformed structure must not intrude in the Survival Zone of Passengers for their safety. If the

Bus Superstructure enters this zone, then the Bus fails as per the standard and if not, the test

is said to be cleared and the Bus is safe proving its strength.

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Preprocessing (Using Hyper

The CAD model of Superst

form of six sub-assemblies

similar members in a single

mid-surfaces keeping the

assigned to each collector t

The shape of the original m

are checked and corrected t

of the structure, the assem

structure, handholds and all

their respective positions.

Superstruct

Chassis is meshed in the

Steering Assembly, Axles a

and Exhaust Pipe. After d

components are attached.

of the Bus, the physical ma

and center of gravity of the

the Rollover Energy wil l be s

Mesh & HyperCrash)

ructure is imported to the HyperMesh for Pre-

as explained. After reorganizing the model a

ollector, the model is shell meshed using the 2D

lement quality in check. Then the material an

make the FE model

odel is shown in figure. Normals, Penetrations

o avoid any kind of deviations. After combining

bly components, exterior and interior paneling,

kind of structural members are attached to the

ure Chassis

similar process including the Engine Assembl

nd Differential Casing, Fuel Tank, Propeller sh

cking the Bus Structure onto the chassis, the

e must ensure that after connecting all the part

ss and center of gravity of the Bus must coinci

AD model or the proto model (if available). Thi

ame as that of the Impact Energy when done ph

Wheel and Driveline

rocessing in the

nd grouping the

elements on the

d properties are

nd Interferences

ll the six frames

passenger seat

ain assembly in

Frame

y, Transmission,

aft, Suspensions

other assembly

and assemblies

e with the mass

will ensure that

sically.

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BUS ASSEMBLY

a) Quality Checks: T

members and coars

components under t

The following quality

e average element size is kept as 10 units (m

e mesh was used for depicting the Inner and O

e chassis frame were made rigid to save the co

checks were maintained while creating the FE

m) in the critical

uter panels. The

putational time.

odel.

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b) Joints: The Weld C

between the springthe spring elements.

c) Rollover Setup: The setu

1. Creating a Passenger Sur

2. Creating the Stopper for ti

3. Creating the Rigid Floor o

4. Rotating the Bus at the an

5. Applying the Gravity at th

6. Setting up the output requ

7. Assigning the solver input

onnections are modeled as the spring elements

nd the Structure Member. The high stiffness cur

p is done in the following stages following the AI

vival Zone in the structure.

re about which the Bus will topple.

n which the structure will collide.

gle of instability (stable angle+1).

CG point of the Bus.

ests.

s such as solving time etc.

ith Tied Contact

ve is assigned to

S-031 standard.

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Analysis Is Done Using Radioss

Post Processing (Using HyperView & HyperGraph)The output of the above deck shows us the rupture in the superstructure in the form of

deformations as shown below.

Position Just Before Impact Position after Stabilization @ 2.15 Sec

The energy plot that is obtained during the analysis shows that; as the body becomes

deformable (@ 1.85 Sec), the Rotational Kinetic Energy, due to impact transfers the forces to

the Superstructure in the form of Axial and Bending Load. And due to this combined effect,

the beams get deflected giving deformations to the structure as:

, / &

. .

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ENERGY PLOT BELOW-INDIVIDUAL PART WISE

Results And Discussions

The Results shows that the effect of Impact in terms of Energy on different members

MAJOR LOAD CARRYING MEMBERS ARE AS UNDER:

1.

.

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10

.

.

.

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11

.

.

. &

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The effect of Axial and Bending Loads on the Vertical Pillars, Truss, Roof Stick, Front and

Rear members in the form of Normal and Tangential Forces are.

1. ( )

.

.

.

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.

Benefits Summary

After studying the results and the stress pattern on the bus, benefits of virtual rollover using

HyperWorks are as under:-1. Maximum load carrying/critical members are strengthened to provide strength and

support.

2. Safety of the Passengers/Driver/Co-Driver.

3. Time saving.

4. Cost saving.

5. Reduction in number testing vehicle.

6. To understanding the nature and pattern of forces acting on the BUS (structure) in

normal and tangential directions, which helped the designer to use the correct cross-

section of tubes at right location saving the overdesign of the Bus.

Future PlansThe study proved to be effective in terms of Cycle Time, Cost and Crashworthiness of the

Structure. We can further extend this study for Vehicle Weight Reduction to improve the

overall performance of the Bus & Frontal Crash of Bus for Driver / Co-Driver /Passenger

Safety.

Conclusions

The Rollover Simulation proved to be an effective method to validate the Structural

Crashworthiness as per AIS-031 standard. The software gave the freedom to study and

analyze the output in different forms and sections which is difficult to workout practically.