Simulation Driven Innovation 1

Design and Analysis of Mahindra FAV Using MBD and FEA for Weight Optimisation

R. Srinivasan

Director Hinode Technologies (P) Ltd. 1st Floor, No.1, Pulla Avenue

Road, Shenoy Nagar Chennai -600 030, India

Pushkar Sheth Sr. CAE Engineer

Hinode Technologies (P) Ltd. 1st Floor, No.1, Pulla Avenue

Road, Shenoy Nagar Chennai - 600 030, India

T. Rahul Sr. CAE Engineer

Hinode Technologies (P) Ltd. 1st Floor, No.1, Pulla Avenue

Road, Shenoy Nagar Chennai - 600 030, India

Raj Pandey Head – R & D

DLSI (Mahindra Defence) 49th MileStone, Delhi – Mathura Road, Village Prithla, Dist and

Tehsil Palwal (Haryana) - 121 102

Sanjit Mahajan Sr. Engineer – R & D

DLSI (Mahindra Defence) 49th MileStone, Delhi – Mathura Road, Village Prithla, Dist and

Tehsil Palwal (Haryana) – 121 102

Abbreviations: ROPS = Rollover Protective Structure Keywords: Mahindra, Radioss, Rollover, ROPS, durability.

Abstract

The objective was to reduce the weight of the chassis of the new FAV vehicle developed at DLSI. CAD geometry of new FAV model was used

for preparing FE Model using Altair’s HyperMesh. Detailed Multi Body model of complete vehicle was built in MBD software. The durability load

cases were applied in MBD model and forces at the suspension mount points were obtained. These loadings were further used in the Finite element

model of the chassis and stress values obtained. Design iterations on the CAD geometry and FE analyses were made to get the stress values within

the allowable levels.

Other analysis includes testing of the roof structure or Rollover Protective Structure (ROPS) to meet ISO 8082 standard which is for quasi-

static loading on the structure. Also NHTSA 208 for simulation of rollover of the vehicle was done using Radioss, and the ROPS was modified so

that occupants are safe incase of a rollover.

Following simulations have been carried out on the Mahindra FAV using Altair’s Radioss

1. Finite element Mesh preparation of chassis in HyperMesh

2. Durability Analysis of chassis in Radioss Linear.

3. ROPS analysis (ISO 8082) using Radioss Non-Linear solver

4. ROPS analysis (NHTSA 208) of vehicle roll over using Radioss Non-Linear solver.

Introduction

Simulation Driven Innovation 2

Manufacturing of a vehicle is a long process and in the past few decades, engineers have strived to reduce the time in which the vehicle is released for use. Standards need to be followed for each type of analysis respectively. The FAV is an off-road vehicle and is expected to undergo high stresses because of the conditions.

For the static durability analysis various load cases were calculated according to road abuse loads on the vehicle. Some of them namely 3g Bump, Pothole Braking, cornering etc. These loadcases were calculated from the available vehicle data and then applied on an MBD Model from which reaction forces were obtained on suspension brackets and applied on an FE Model. The ISO 8082 test for ROPS integrity was done as per test specifications mentioned in the standard and will be discussed in this paper. NHTSA 208 test setup was also replicated from prescribed standard and vehicle rollover simulation was performed using Radioss.

Methodology for Static Durability Analysis:

FE Mesh preparation of chassis in HyperMesh:

Majority of the parts of the Chassis are made out of sheet metal. The CAD model received from DLSI was checked thoroughly and meshing was done on the midsurface of all components. Weld connections were replicated by connecting components with rigid elements on weld lines.

Figure 1: Geometry and FE Mesh.

Figure 2: Meshed Model.

Additional Masses:

Additional masses are added as point mass elements. These represent structures that need to be considered but are geometrically not required. Following are considered in the form of point masses:

1. Engine

2. Front and rear differentials

3. Passengers (6 Nos.)

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4. Fuel Tank

5. Spare Tyre

Additional masses are connected using RBE2 or RBE3 elements according to the component being considered as a mass element.

Pressure Loads:

Pressure loads are also applied to represent some of the loading on the vehicle:

1. Seat loads are represented as 150 kg and the pressure is distributed on the sill assembly. 2. Luggage load as 500 kg distributed on the rear cage area.

FE Methodology – Inertia Relief Method:

Inertia relief method is used for linear static simulation of road loads on the chassis. The loading on the vehicle is that which it will undergo in real situations or on a test track.

Methodology for ROPS Tests Simulation:

Beam Model Preparation on HyperMesh:

Using HyperMesh and HyperBeam, making a mathematically equivalent beam model of the Chassis was considered time saving and hence was used for analysing the ROPS. This is elaborated more in further parts of this paper.

Figure 3: Line Diagram of FAV.

a. ISO 8082 for ROPS Integrity:

The objective of the ISO 8082:1994 is to study deflection performance of the ROPS under prescribed static loading.

ISO 8082 – An overview:

For understanding this test procedure to let this paper remain in context, a few excerpts have been briefed:

• The full vehicle or a part to be tested is fixed at the bottom. • A lateral load is applied using a load distribution plate for a sufficient time until deflection has ceased. • After that, the lateral load is removed and the structure is subjected to vertical load. Here too, load is

applied till deflection ceases. • No changes/repairs in the structure is allowed between the two tests.

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Figure 4: Test Schematic from ISO 8082 Standard Document.

FE Model Setup:

Figure 5: ISO 8082 FE Model Setup.

The ROPS frame is fixed at the bottom. As mentioned in the methodology, the lateral load is applied first and then the vertical load is applied. These forces have been calculated from empirical formulae given in the standard.

b. NHTSA 208 – Vehicle Roll Over simulation for ROPS integrity:

The objective of the NHTSA 208 is to replicate roll over accident of vehicle and thus study the effect of it on vehicle structure especially on the ROPS. Major structural members are represented using beam elements. Relevant geometric cross sectional properties are defined for all members. The engine and differentials have been considered as rigid and mass elements have been added.

NHTSA 208 Standard – An Overview:

• The vehicle is mounted on a dolly without any restraints or belts holding the vehicle • The dolly is accelerated to a velocity of 30 mph. • Once the said velocity is reached, the dolly is decelerated to 0 mph within a distance of 3 feet. • The vehicle thus flips over the dolly and the effects of the roof structure can be observed.

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Figure 6: Typical device for rollover test.

Figure 7: NHTSA 208 FE Model Setup.

Results & Discussions

1. Static Durability: The road abuse loads caused stresses higher than yield limit of material at certain locations. This was amended by adding reinforcements at vulnerable areas. Hence, the FAV was analysed for various iterations until stress was reduced at all areas and the vehicle was considered safe for road abuse loads.

Figure 8: Full FAV Static Durability Stress Results.

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2. ISO 8082 Test: Here too, a number of iterations were done until a safe design for the ROPS was obtained.

Figure 9: Lateral Loading Displacement on ROPS Structure

Figure 10: Vertical Loading Displacement on ROPS Structure

For the final design, the maximum deflection was 4.9 mm and 6.2 mm for lateral and vertical loading respectively

3. NHTSA 208: Design changes were made to a large extent to make the structure safe for the passengers.

Figure 11: Roll Over Simulation of FAV

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Benefits Summary

HyperMesh data structure made the implementation of design changes (iterations) on the base model easier and thus saving time in pre-processing of such a huge model. The Radioss solver has proven very robust in solving the model in both Linear and Non-Linear solver. The static durability model was 1.2 million element model.

Future Plans

Future plans include implementation of advanced welding options available in the HyperWorks Suite and compare them with the testing data.

Conclusions

The majority of the tests conducted on the FAV were simulated on Radioss hence saving costs in the number of prototypes built and using them for durability and rollover testing. Especially for the ISO 8082, number of iterations can be tested and only after having a safe design from FEA an actual prototype can be built and test it in laboratory. Also, for NHTSA 208, where actual vehicle need not be assembled and put to test unless a safe FEA result is achieved.

REFERENCES 1. Gillespie, T., (1992), Fundamentals of Vehicle Dynamics, Warrendale, PA : Society of Automotive Engineers. 2. Altair HyperWorks User Manual

Mahindra Defence Systems is provider of world class armouring solutions for Light Combat Vehicles, Multi-Utility Vehicles and Sports Utility Vehicles for the Indian Army, Indian Air Force, Paramilitary and State Police forces in India. Hinode Technologies (P) Ltd. is an engineering consultancy service provider of concept design, engineering design, analysis/simulation using CAE validation and prototyping services, for the automotive, aerospace, defence and general mechanical engineering applications.