Design Analysis and Optimization of Front Underrun Protection Device

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Master's Degree Thesis ISRN: BTH-AMT-EX--2018/D03--SE

Supervisors: J. Karthik and P. Praneeth, AK Hypercad Solutions, Hyderabad, India Ansel Berghuvud, BTH

Department of Mechanical Engineering Blekinge Institute of Technology

Karlskrona, Sweden 2018

Anil Sharma

Design Analysis and Optimization of Front Underrun Protection

Device

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Design Analysis and Optimization of Front Underrun

Protection Device

Anil Sharma

Department of Mechanical Engineering Blekinge Institute of Technology

Karlskrona, Sweden 2018

Thesis submitted for completion of Master of Science in Mechanical Engineering with emphasis on Structural Mechanics at the department of Mechanical Engineering. Blekinge Institute of Technology, Karlskrona, Sweden.

Abstract

Under-running of passenger vehicle is one of the major parameters to be considered during the design and development of truck chassis. Front Under-run Protection Device (FUPD) plays an important role in avoiding under-running of vehicles from front side of a truck. This thesis is used to develop additional device which stops the impact from frontal area, which will not allow the passenger car inside the truck. The complete thesis was started from an idea of adding FUPD to truck chassis. Design of FUPD is done using 3D CAD software CATIA V5R20, then complete FUPD assembly is imported and done pre-processing using Altair Hyper Mesh, for visualizing the results. Crash analysis is done using Altair Radioss & results interpretation is done using HyperView and Hypergraph.

FUPD is designed based on ECE R93 which satisfies the failure criteria (Standard) of displacement less than 400 mm. An Initial Design is generated along with Holding Brackets as an assembly using CATIA V5 as a tool. Base design is further optimized for getting light weight structure that meets structural performance criteria. By assuming all the loading conditions as per the standards, an amount of 27% mass reduction is obtained in FUPD Assembly along with holding bracket.

Keywords:

Finite Element Method, Topology Optimization, Crash Analysis.

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ACKNOWLEDGEMENTS

This work was carried out at AK Hypercad Solutions, Hyderabad, India in collaboration with Department of Mechanical Engineering, Blekinge Institute of Technology (BTH), Sweden from January 2018 to June 2018 under the supervision of Dr. Ansel Berghuvud (BTH), Karthik (AKHS) and Praneeth.P (AKHS). Working with the bumper and chassis team at AKHS with learning experiences that helped me to grow both personally and professionally.

I had taken many efforts in this project but it would not have been possible without the constant guidance and supervision of AKHS officials. I would like to extend sincere thanks to Karthik, Jhansi

I would like to extend our boundless appreciation to B.Apoorva (HR-AKHS) for giving us an opportunity to intern with an esteemed organization like AK Hypercad Solutions.

I would award credit to BTH and our course director/thesis supervisor Dr. Ansel Berghuvud for his academic teachings and the support provided while pursuing this thesis work.

I would like to express our special thanks to our parents and friends for their kind co-operation and encouragement in completion of this project

Hyderabad, India, June 2018.

Anil Sharma.

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List of Figures

Figure 1.1. Example of car-to-truck accident. ... 10

Figure 1.2. Example of car-to-truck accident. ... 11

Figure 1.3. Relative height of front strength parts. ... 11

Figure 1.4. Truck without proper front under run protection device. ... 12

Figure 1.5. Accident in the absence of Front under run protection device.13 Figure 1.6.FUPD European Standard Dimension [1]. ... 13

Figure 1.7. FUPD European Vehicle. ... 14

Figure 1.8. Regulations [2]. ... 15

Figure 1.9. Outline of ECE-R93 Standard... 15

Figure 2.1. Approximate Dimensions from European standard [3]. ... 18

Figure 2.2. Approximate Dimensions from European standard [3]. ... 19

Figure 2.3. Example of a crash test [4]. ... 20

Figure 2.4. Deformation of the small sedan in 100% Collision with the heavy truck [5]. ... 21

Figure 3.1. Bumper. ... 25

Figure 3.2. C-Beam... 26

Figure 3.3. C-Section. ... 27

Figure 3.4. Complete Drawing. ... 28

Figure 3.5. FUPD Drawing. ... 29

Figure 3.6. Positioning of FUPD. ... 29

Figure 3.7. 3D CAD Assembly Model without Front Under-run Protection Device. ... 30

Figure 3.8. 3D CAD Assembly Model with Design 1Front Under-run Protection Device... 30

Figure 4.1. Midsurface Extract option in pre-processor interface. ... 34

Figure 4.2. Midsurface Extract option. ... 34

Figure 4.3. Basic Design 2D Shell Mesh and hex mesh using Auto mesh panel. ... 35

Figure 4.4. Number of Nodes 175456 and Number of Elements 161895. .. 35

Figure 4.5. Complete overview of FUPD Meshed model. ... 37

Figure 4.6. Self-contact type-7... 37

Figure 4.7. Fixed Boundary condition for chassis base (pink region). ... 38

Figure 4.8. FUPD Loading Diagram. ... 39

Figure 5.1. Work flow of Topology optimization ... 41

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Figure 5.2. Optimization Objective Function. ... 42

Figure 5.3. Optimization analysis setup. ... 42

Figure 5.4. FUPD Loading in Opti struct-FEA. ... 43

Figure 6.1. Displacement 1.804mm. ... 45

Figure 6.2. Stress 295MPa. ... 46

Figure 6.3. Topology Optimization Result for FUPD. ... 46

Figure 6.4. Topology Optimization Result for FUPD Holding Bracket. .... 47

Figure 7.1. Design 2 FUPD CAD Design. ... 48

Figure 7.2. Meshed model of Optimized Design FUPD. ... 49

Figure 7.3. Design 2 FUPD Holding Bracket. ... 49

Figure 7.4. Displacement 2.92mm. ... 50

Figure 7.5. Stress 429MPa. ... 51

Figure 8.1. Internal Energy and Kinetic Energy Graph. ... 52

Figure 8.2. Displacement 105.403mm at 0.006sec. ... 53

Figure 8.4.Displacement 509.7mm at 0.016sec. ... 54

Figure 8.6. Displacement 781.0mm at 0.013sec. ... 56

Figure 8.8. Displacement is zero at time zero. ... 57

Figure 8.9. Displacement is 88.129mm at time 0.004sec. ... 57

Figure 8.15. Displacement 58.524mm at 0.0037seconds. ... 63

Figure 8.17. Displacement is 68.123 at time 0.0036sec. ... 64

Figure 8.19. Displacement is 104.955 at time 0.0037sec. ... 66

Figure 9.1. Speed Vs Displacement. ... 67

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List of Tables

Table 4.1. Material properties……….36

Table 4.2. Hot rolled steel material properties………36

Table 4.3. Mild steel material properties………36

Table 4.4. ECER93 Safety Regulation………38

Table 9.1. Shows the displacement (U) of FUPD at respective speeds………67

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Abbreviations:

ARAI Automotive Research Association of India CAD Computer Aided Design

CAE Computer Aided Engineering ECE Economic Commission for Europe

EEVC European Experimental Vehicle Committee FEA Finite Element Analysis

FEM Finite Element Method

FMVSS Federal Motor Vehicle Safety Standards FUPD Front Under run Protection Device RUPD Rear under run Protection Device

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1 INTRODUCTION

1.1 Overview

In automobile collisions, cars often move on trucks that cause serious damage Figure 1.1. The safety of car accidents depends on how the components are connected to the vehicle's structural part. Figure 1.2. shows the accident due to lack of Front under run protection device. Vehicle and truck accident incidents are among the top on road accidents. This phenomenon causes serious and dangerous damage to car drivers due to the intrusion of the vehicle structure into the passenger compartment.

Figure 1.1. Example of car-to-truck accident.

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Figure 1.2. Example of car-to-truck accident.

Figure 1.3. Relative height of front strength parts.

Need for FUPD:

This led to the development of pilot procedures for the front under run protection systems for energy-absorbing in vehicles. Figure 1.3 represents the design of FUPD. Where we can read about 48,000 people who died in a

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car accident in 1992, 13,000 were killed in a crash, with a car with about 7,000 passengers 4200 in the car were killed in clashes from car to car[8].

It's very common that during accident, you accidentally get struck into a truck in the back or front. In the case of a passenger car, there is a danger of impact in the rear or from the front of the car, there is a possibility of serious injury to passenger. Design and strength of FUPD is made keeping in mind that it should absorb the impact energy and avoid the under run. The IS 14812-2005 standard specifies the safety requirements of the FUPD. Exercise is performed by 5 impactors (Point Loads) with specific load and sequence.

This virtual validation is important for saving costs, costing equipment, vehicle testing and related costs.

Government of India felt the need for a permanent agency to speed up the publication of standards and the development of tests in place, while work on the preparation of standards continues to the development of an improved parts that are important for safety, For this purpose, Department of Transport created a standing committee of the Committee for Standardization in Automotive Industry Standardization (AISC), No. 15/1997 / MVL September 15, standardized by AISC 1997 and approved by the CMVR Standing Technical Committee (CTSC). After obtaining approval from the Indian Automotive Research Association (ARAI), Pune, the secretariat of the AIS Committee, published the standard.

Figure 1.4. Truck without proper front under run protection device.

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Figure 1.5. Accident in the absence of Front under run protection device In India, FUPD is not used commonly. Figure 1.4 shows truck without FUPD.

Figure 1.5 depicts accidents in the absence of FUPD & an FUPD is designed with European standard ECE R93 and then crash test is done at different speeds and the forces on FUPD are evaluated. It is an iterative process with base as European standards. The design proceeds according to the approximate dimensions provided in the Figure 1.6

Figure 1.6. FUPD European Standard Dimension [1].

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Figure 1.7. FUPD European Vehicle.

Figure 1.7 shows the front protection equipment and how the FUPD is connected to chassis of the truck.

1.2 Aim and Objective

The Aim of thesis is to design a structurally efficient FUPD and integrate it with the vehicle chassis which reduces impact on the vehicle.

The Design objective is to develop an FUPD in accordance with European Standard Regulations (ECE R93). The crash test is done virtually using CAE and the loads and failures are calculated using Finite Element Analysis using Hyper works tool. The crash test is done at different speeds and the impacts on FUPD are analysed. The study helps in improvising the design for better performance. Topology optimization helps in achieving mass reduction of the Basic Design of FUPD and the mounting bracket for FUPD. A CAD Design is developed based on global automotive references. An Optimization study to be carried out on the base design.

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1.2.1 Regulations and Standards

According to global automotive regulations, the FMVSS 223/224 Rear and ECE R93 FUPD test forces have been changed for the following two regulations.

Figure 1.8. Regulations [2].

The FUPD is designed based on ECE R93 Figure1.8 (Regulation), According to ECE R93, impacts will be tested at a speed of 55 km / h and at 70 km / h and at 100 km / h.

Figure 1.9. Outline of ECE-R93 Standard.

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1.3 Research Questions

The aim of the research is addressed through the following research questions:

1. Role of FUPD during an accident and its Significance

2. Base Design Vs Optimized Design and Evaluation of key parameters.

3. Importance of Topology Optimization and savings achieved?.

1.4 Purpose and Motivation

A demand for a Robust FUPD design in India arises due to severe fatalities encountered during accidents between heavy vehicles and passenger cars.

There is lot of scope for Design Improvements and cost reduction studies associated in this area of under run protection devices. There are few challenges as mentioned below to overcome.

• Lack of universal design.

• Reparability.

• Reusability.

• Retrofitting not possible.

• No energy absorption.

• Cost-effectiveness.

An FUPD is designed to lower the impact on passengers during an accident.

The purpose is to develop the design of the FUPD for trucks so that it can be applied to all vehicles.

The prime purpose of FUPD has been discussed in above chapters and the scope of Engineering in the above area gives immense motivation to perform the study on under run protection devices.

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2 LITERATURE REVIEW

Traffic accident is a major factor. In an overview of traffic accidents, The European problem (1997), about 20% of fatal accidents was with trucks and about 60% of them are car accidents. The risk of serious injury accidents seems to be higher for light motor vehicles, especially for cars and the risk increases in the case of car to truck collisions.

EEVC WG14 started the research program in 1994 to identify the requirements for the FUPD for trucks and to establish test procedures for these devices.

In March 1995, the Working Group 14 concluded a statistical analysis of accident data, including car and truck collision violations in most European countries. A possible test configuration is displayed and Analysis is done.

The analysis is led with the usual acceleration parameters for front and rear collisions, and the type of accidents represented. The usual parameters of the hazard were chosen:

• Speed of impact: 75 km / h.

• Overlap: 75%.

• Collision angle 0 °.

• Two passengers in the front seat.

During the EEVC WG14 program (started in September 1995) to create the effects of FUPD on injuries, many vehicle crash tests were carried out:

• The first car crash matrix was carried out. The truck was equipped with Rigid FUPD and the speed was about 55 km/h.

• On the second car crash test, the car was equipped with an energy absorbing FUPD and at a speed of about 75 km/h.

These tests provide protection information for energy-absorbing FUPDs installed in the truck. At the same time, they provide information on the correct definition of the proposed evaluation.

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Figure 2.1. Approximate Dimensions from European standard [3].

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Figure 2.2. Approximate Dimensions from European standard [3].

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2.1 Test Conditions

To test the effectiveness of FUPD vehicle, the car head impact test was conducted. In these truck with and without FUPD are used. For each test, the same type of vehicle and crash speed is used in each test.

The test conditions are as follows.

• Hybrid-II dummy with seat belt installed in driver's seat. The hazard criteria for is measured for reference. Only small cars are fitted with the driver's airbag.

• Trucks used are heavy trucks.

• The truck is equipped with FUPDs which is in accordance with the regulations of ECE-R93 for a height of 400 mm. In these cases, the existing resin bumpers is separated. Many examples of these crashes are shown below, by keeping the robots in the car and then they will crash and check whether the safety gains with the FUPD.

Figure 2.3. Example of a crash test [4].

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2.2 Test Results

The deformation of a car at 100% overlaps crash with a heavy truck. In the collision without a FUPD car crashes hit the wheel. In contrast, the car collapsed on the front tires only in collision with FUPD. Figure 2.3 shows the abnormality of small cars in 50% danger with heavy vehicles. The upper part is crushed to the A-pillar in the collision without FUPD even though the LM did not collapse. The collapse did not reach the A pillar in colliding with the FUPD.

Figure 2.4. Deformation of the small sedan in 100% Collision with the heavy truck [5].

2.3 Forecast of Front Under run Protection Device Effect

Based on FUPD installed at the current truck, reducing motor vehicle mortality is predicted for the following conditions.

• Traffic accidents caused by cars and heavy vehicles.

• Mortality depends on a fall of over 100%.

• It is assumed that all trucks are equipped with FUPD according to ECE-R93.

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FUPD efficiency is calculated as follows.

The number of declining victims per year multiplies the "FUPD Impact" and period average of the car driver fatality.

2.4 Methodology

• To design the under-run devices with the use of different energy absorbing materials.

• To design and allot materials by computer aided engineering.

• To make prototype of the under-run devices.

• To test the devices for its performance, energy absorbing capacity, and ease of reparability.

Method Overview:

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3 MODELLING OF FRONT UNDER RUN PROTECTION DEVICE

3.1 Technical Requirements of FUPDs

FUPD in the front must be sufficiently strong enough. The forces applied parallel to the vehicle's longitudinal axis and to meet specific dimensions requirements. These are monitored in accordance with the test procedures and conditions set out in this regulation.

• This device can be designed so that it can change its position in front of the vehicle. In this case, there is a guaranteed methodology to ensure service status to eliminate any unintentional changes.

• The operator must be able to change the position of the device by applying force not more than 400 Nm.

• Maximum Mass of vehicle must not exceed the value specified on the FUPD designed for the vehicle.

• The FUPD height must not be less than 100 mm for vehicles with a maximum weight of 3.5 to 12 tons and not less than 120 mm for vehicles with a maximum mass exceeding 12 tons.

• Maximum ground clearance with respect to the bottom of FUPD must not exceed 400 mm between two points (P1) in the installed state.

• Outside any point (P1), the height may be above 400 millimetres allowing the underside surface not above the plane passing through the underside of FUPD directly below point(P1) and creating a 15 ° slope above the horizontal.

• The FUPD must sufficient strength that the horizontal distance measured in the rear direction between the foremost part of the vehicle after the application of test forces and the test ram contact surface does not exceed 400 mm.

• The edges on the side of the passenger should not bend to front or have sharp edges outside. This condition is fulfilled when the edge at the side of the transverse plate is rounded off and has a curved edge of not less than 2.5 mm.

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• The outer surface of each frontal protective installation is shaped smooth. If the head of the bolts or rivets can’t exceed the surface more than 10 millimetres.

• FUPD width does not exceed the width of the mud guard nor shall it be more than 100 mm.

• P1 point located up to 200 mm from longitudinal plane and tangential to the outer tire surface on the front axle (not including near-ground inflation).

• The symmetrical P2 point is relative to the vehicle along the median longitudinal plane of car at a distance from each other of 700 to 1200 mm. The exact position is determined by the manufacturer (the location of the vehicle).

• The height of the points of the points P1 and P2 is determined by the manufacturer of vehicles in the line connecting the front of the device.

However, the height should not exceed 445 mm.

• P3 is in a vertical longitudinal median plane of the vehicle.

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3.2 CAD Model With all the Dimensions of Front Under run Protection Device

Figure 3.1. Bumper.

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Figure 3.2. C-Beam.

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Figure 3.3. C-Section.

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Figure 3.4. Complete Drawing.

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Figure 3.5. FUPD Drawing.

Figure 3.6. Positioning of FUPD.

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Figure 3.7. 3D CAD Assembly Model without Front Under-run Protection

Device.

Figure 3.8. 3D CAD Assembly Model with Design 1Front Under-run

Protection Device.

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A Chassis frame model is developed based on some standard requirements.

The Model shown in Figure 3.7 is without an FUPD Model.

The Initial Base Design of an FUPD is derived from general literature study and a crude solid design is generated as shown in Figure 3.8. The frontal protective model is made based on the standard specifications and Positioning requirements as shown in Figure 3.6. The design is developed using CatiaV5R20. All dimensions are taken out of the European standard.

According to Indian law and regulations, these measures have been slightly changed, the approximate dimensions taken from Figure 3.6.

Now the FUPD is assembled to the chassis and is tested with an encounter of underrun protection equipment. The full mount model is shown in the Figure 3.8 for reference.

An Initial Study is carried out for the base design to check for Strength and Stiffness. The base design is imported as 3D CAD model into hyper mesh pre-processing for meshing and Altair Radioss is the Solver to perform crash tests.

The results of Initial study are presented in Page 54 to 57 and they clearly indicate that there is a scope for topology optimization as the design is satisfying all the requirements and one of the key parameters such as displacement is well within the limits. The design is assumed to be robust and it can undergo a mass reduction study. Topology optimization can help us yield better results in terms of reducing mass of the FUPD. The optimized design is also studied for given set of loads and conditions and evaluated.

The results are discussed in the upcoming chapters regarding the behaviour of the base design and the Optimized Design. A detailed study has been conducted and comparison study will be discussed in the upcoming chapters.

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4 FINITE ELEMENT MODELLING OF FRONT UNDER RUN PROTECTION DEVICE

4.1 Finite Element Method

FEM is a prominent Numerical method for solving problems of engineering and mathematical physics. Typical problem areas of interest include structural analysis, heat transfer, fluid flow, mass transport, and electromagnetic potential.

The analytical solution of these problems generally require the solution to boundary value problems for partial differential equations. The finite element method formulation of the problem results in a system of algebraic equations.

The method yields approximate values of the unknowns at discrete number of points over the domain. The huge model is divided into multiple parts called finite elements.

It uses simple equations to solve the model, these finite elements are then assembled into a larger system of equations that models the entire problem.

FEM then uses several methods from the calculus of variations to approximate a solution by minimizing an associated error function.

In order to divide the model, we use Hypermesh as a tool which does the discretization of the model. More insight on the FE Modelling and Hyperworks usage is provided in the next sub sections. To provide an overview of pre- processing of the model, different kinds of meshing types and techniques are discussed in the upcoming sub chapters.

4.2 Best in Class Meshing

Hyper Mesh presents users with an advanced suit of easy-to-use tools build and edit CAE models. For 2D and 3D model generation, user has accessibility to a variety of mesh generation techniques, as well as Hyper mesh’s powerful auto meshing module

.

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4.2.1 High Fidelity Meshing [6]

• Surface meshing

• Solid map hex mesh

• Tetra meshing

• CFD meshing

• SPH meshing

4.3 Surface meshing

The Surface meshing in HyperMesh is a robust method for mesh generation that provides user a high amount of flexibility and functionality. This includes the ability to adjust various parameters to optimize based on a set of user-defined quality parameters and create mesh using a wide array of complex methods.

4.4 Solid map hex mesh

Using solid geometry, Hypermesh can use both standard and advanced procedures for binding, isolating, or separating solid geometry for hex or tetra meshing.

Separating these models is quick and easy when combined with powerful hypermesh visibility features for solid. This allows users to spend less time preparing geometry. This module allows users to create fast, high-quality meshes for multiple volumes.

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4.5 Midsurface Extract

Front under run protection device is a solid part and remaining all are sheet metal component which will have thickness to each part. For sheet metal parts finite element method introduced a midsurface extraction to apply thickness. So midsurfaces have been extracted for FUPD assembly component. Solid hex/tetra mesh is assigned to FUPD.

Using HyperMesh interface Midsurface is generated, HyperMesh is powerful to generate midsurface.

Figure 4.1. Midsurface Extract option in pre-processor interface.

Figure 4.2. Midsurface Extract option.

4.6 FE Model Generation of FUPD

The figures below show a CAD model transformed as a completed FE Model ready for Analysis. The meshing parameters are used as per the standards and guidelines needed for FUPD Structures.

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Figure 4.3. Basic Design 2D Shell Mesh and hex mesh using Auto mesh panel.

Figure 4.4. Number of Nodes 175456 and Number of Elements 161895.

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4.7 Material and Properties

Component Material

Bumper Mild Steel

Chassis Mild Steel

FUPD Hot Rolled

Steel FUPD Holding

Brackets Mild Steel Cross Members Mild Steel Table 4.1. Material properties.

Material used for FUPD and holding bracket is hot rolled steel for remaining parts the material is assumed as mild steel.

Hot rolled Steel

Properties Metric

Tensile strength, yield 440 MPa Modulus of elasticity 210 GPa

Bulk Modulus 140 GPa

Poisson ratio 0.3

Table 4.2. Hot rolled steel material properties.

Mild Steel

Properties Metric

Tensile strength, yield 215 MPa Modulus of elasticity 200 GPa

Poisson ratio 0.3

Bulk Modulus 140 GPa

Table 4.3.Mild steel material properties

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4.8 Loads and Boundary Conditions

Figure 4.5. Complete overview of FUPD Meshed model.

In Figure 4.5 the truck weight of 2500kgs is added at CG location. The top chassis frame nodes and cross members are connected to CG location.

From the front side rigid wall will be impacted to FUPD with different speeds to check the strength of the Basic Design and Optimized Design.

Figure 4.6. Self-contact type-7.

For the above meshed model having a weight of truck at assumed centre of gravity location. Weight is about 2500Kgs is added and for frontal crash the weight of car is added. Car weight is about 1050Kgs.

MASS 2500KG

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Figure 4.7. Fixed Boundary condition for chassis base (pink region).

Complete chassis frame is fixed in all degrees of freedom as shown in above Fig 4.7.

Rigid Wall is created and given initial velocity as an input for doing crash simulation to FUPD and Without FUPD simulations.

First analysis is carried out for Base Design FUPD which was designed using ECE R93 regulation. Loading and Boundary conditions are considered from global automotive safety regulations, as per ECE R93 regulation the loads are mentioned as below.

Table 4.4. ECER93 Safety Regulation.

Test Load (KN) ECE R93 (FUPD)

Loads Applied in CAE and Design Maintained

Outer edge P1 80 KN Load is applied

Centre P3 80 KN Load is applied

Off Centre P2 160 KN Load is applied

Allowed

Deflection 400 mm

Deflection need to check in crash results

Height 400 mm

Maintained 450mm height from Ground

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Figure 4.8. FUPD Loading Diagram.

4.9 Load Cases

• To get light weighted FUPD and holding bracket model topology optimization is carried out. Once that simulation is done, new shape of FUPD is obtained and as well as new holding bracket shape. That optimized results will be designed using CATIA V5R20 software.

• The new optimized model is also solved for static loading conditions as for the Base Design model.

• Crash analysis is carried out for three different speeds like 55kmph, 70kmph and 100kmph. The crash analysis will be carried out for basic model of Ashok Leyland truck chassis without adding FUPD.

• Crash analysis will be carried out for Base Design and Optimized Design of FUPD.

The tools used are HyperMesh, Opti Struct, Radios, HyperView and Hypergraph

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5 TOPOLOGY OPTIMIZATION OF FRONT UNDER RUN PROTECTION DEVICE

5.1 Overview

Altair Opti Struct is one of the best CAE technologies for conceptual design developing and structural optimization. When Topology optimization is done the excess amount of material is removed so that its properties are not changed for its workability.

5.2 Structural Design and Optimization

Structural design tools provide topology optimization.

In the formulation of design and optimization problems, the following responses can be applied as the objective or as constraints: compliance, frequency, volume, mass, moment of inertia, center of gravity, displacement, velocity, acceleration, buckling factor, stress, strain, composite failure, force, synthetic response, and external (user defined) functions. Static, inertia relief, nonlinear quasi-static (contact), normal modes, buckling, and frequency response solutions can be included in a multi-disciplinary optimization setup.

5.3 Topology Optimization

Topology optimization generates the right amount of material distribution for a given set of loads and constraints on it. The design space is recognized by the software using shell or solid elements, or both. Manufacturing constraints can be imposed using a minimum size constraint, draw direction constraints, extrusion constraints, symmetry planes, pattern grouping, and pattern repetition. Free-size optimization is available for shell design spaces. The shell thickness or composite ply-thickness of each element will be the design variable.

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5.4 Optimization Process

Optimization is done on the Front underrun protection device. The work flow for the optimization technique are shown in the below.

An FE Model is generated out of a CAD design and with defined constraints and volume fractions along with manufacturing constraints an Optimized Design is achieved. The feasibility of the design is also checked and provided as an output after completion of the optimization process.

Optistruct is used as an Optimization tool for achieving a feasible design of FUPD and the optimized design is also analysed further to check the evaluation criteria.

Figure 5.1. Work Flow of Topology optimization

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5.4.1 Objective Function

The Objective function is a model response to be maximized or minimized.

There are two ways to specify an objective in Opti Struct. Either a single response can be minimized or maximized or you can choose to minimize the maximum value, or maximize the minimum value, of a number of normalized responses.

The Design space is the complete model excluding all the 12 clamping holes.

The constraints of this Design are, the base of the chassis is fixed as in Figure 4.8 and all the 12 holes (non-design space) in Figure 5.4 are fixed. Here the Weight is optimized based on the given set of loads and conditions.

Figure 5.2. Optimization Objective Function.

Objective function of FUPD is to optimize the weight of base design. By using above Topology setup is prepared and solved using Opti Struct and results are evaluated.

Figure 5.3. Optimization analysis setup.

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While running the Opti Struct the material will be distributed appropriately in an iterative manner. The optimization results are discussed in the forth coming sections.

5.5 Topology Optimization using Altair Opti Struct

As per above loading diagram of FUPD the loads are applied on the 3D CAD model. Using finite element modelling the FUPD is meshed and used hot rolled steel material and solved for structural loading case.

Figure 5.4. FUPD Loading in Opti struct-FEA.

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The above image is shown for reference, the loads have been considered using ECE R93 regulation. The point P1, P2 and P3 loads are assigned to the above FUPD model. 12 holes are fixed in all degrees of freedom as shown in the Figure 5.4

The above simulation is to check the strength of the Base Design of FUPD.

FUPD holding bracket design is also very crucial in this crash test. Due to that the FUPD is designed and attached to the assumed design. Using Topology optimization technique, we would get biologically evolved shape for FUPD and holding bracket.

According to the ECE R93 Regulations, the FUPD design is a complete solid part which is very heavy in weight.so in order to reduce weight by removing the unwanted material topology optimization is carried out. Hence a light weight structure is formed.

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6 OPTIMIZATION RESULTS

6.1 Topology Optimization Results for FUPD and Holding Bracket

6.1.1 Displacement Plot

Displacement plots are shown for base design and maximum displacement is around 1.8mm for set of loading conditions discussed earlier.(4.9)

Figure 6.1. Displacement 1.804mm.

.

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6.1.2 Stress Plot

Stress for base design of FUPD is found to be around 295 MPa and is found to be well within the yield limits (440MPa).

Figure 6.2. Stress 295MPa.

Figure 6.3. Topology Optimization Result for FUPD.

Optimized Design Proposal is provided with the given set of loads. The above Figure 6.3 shows proposed optimized pattern for given loading conditions.

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Figure 6.4. Topology Optimization design proposal for FUPD Holding Bracket.

The above results re-interpreted from applied loading conditions, as mentioned loads are considered from safety regulation standard.

The design proposal provided is to be evaluated based on the required loading conditions. The proposed design is 27% lighter in weight and it needs to be evaluated against the base design.

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7 ANALYSIS RESULTS OF OPTIMIZED DESIGN

The output from topology optimization result is smoothened and the redesigned as a CAD Model using CatiaV5R20.

Below is the Optimized model of FUPD and FUPD holding Bracket optimized model.

Figure 7.1. Design 2 FUPD CAD Design.

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Figure 7.2. Meshed model of Optimized Design FUPD.

Figure 7.3. Design 2 FUPD Holding Bracket.

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Fixed holes are considered as fixations similar to base design and load application points also remain the same as they were all part of non-design areas.

The next level of analysis is crash for base design and optimized design to compare which is best light weight and strength efficient structure.

7.1 Displacement Plot

Figure 7.4. Displacement 2.92mm.

Displacement for the Optimized design is around 2.92mm and is slightly higher than the base design but seems to be well within the limits. Crash analysis to be conducted results and evaluated against base design. Crash study may help in better comparison of results which is discussed in the upcoming chapter.

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Figure 7.5. Stress 429MPa.

Maximum Stress for Optimized design is found to be around 429 MPa at constraint location.

The stress observed is very local at constraint location. Stresses at sharp edges and support location are ignored and considerable stress for optimized stress observed is around 308MP and is comparatively higher compared to base design and its well within the allowable stress limits(yield) which is 440MPa.

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8 CRASH ANALYSIS RESULTS

Crash analysis is carried out for three different designs one is without FUPD actual position of crash is simulated and then base design of FUPD and optimized FUPD crash analysis is carried out. The results are shown below for reference.

8.1 Crash Analysis of Regular Chassis frame without FUPD

The Displacements results are viewed at the converged time for Internal and kinetic Energy. The converged plots are shown for all the cases in crash analysis.

8.1.1 Crash results for 55kmph

Figure 8.1. Internal Energy and Kinetic Energy Graph.

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Figure 8.1 The time converged plots graph shows that the results are considered at 0.006 seconds.

Figure 8.2. Displacement 105.403mm at 0.006sec.

Due to high impact of car from frontal side the bumper has failed. Car weight is assumed 1050 kgs.

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By observing the Figure 8.3 graph the results for 0.016 seconds is shown below

Figure 8.4.Displacement 509.7mm at 0.016sec.

Displacement observed at bumper is about 509mm which is more than the allowable limit as per safety regulation.

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The energy balance of a system in an impact is governed by the law of conservation of energy. In case of an impact the kinetic energy possessed by the system in motion is converted into potential energy, sound energy and heat energy. The majority of the converted energy is the potential energy. In other words, the total kinetic energy is absorbed by the structure of the vehicle, since the energy must be conserved.

Kinetic energy is the work input and internal energy is the work output.

Internal energy is the energy absorbed by the system and is directly proportional to the product of force and deformation. The energy balance of the entire system for the target point simulation is shown in the above Figure 8.5.

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Figure 8.6. Displacement 781.0mm at 0.013sec.

8.2 Crash Analysis of Base Design FUPD

By observing the Figure 8.7 graph the results for 0 and 0.004 seconds is shown below

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Figure 8.8. Displacement is zero at time zero.

Figure 8.9. Displacement is 88.129mm at time 0.004sec.

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8.3 Crash Analysis of Optimized Design FUPD

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Figure 8.15. Displacement 58.524mm at 0.0037seconds.

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Figure 8.17. Displacement is 68.123 at time 0.0036sec.

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Figure 8.19. Displacement is 104.955 at time 0.0037sec.

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9 SUMMARY AND CONCLUSION

9.1 Observations

• Base design was around 400Kgs & the displacement observed after Loading was far ahead from the criteria and there was a scope for optimization.

• Topology Optimization was carried out on the base design. The New recommended optimized design was around 293 Kgs.

• The new optimized design has been validated with similar loading conditions of the base design and compared against same criteria.

• The displacements along with comparison against both designs in the Table 9.1 and are also graphically represented.

Table 9.1.Shows the displacement (U) of FUPD at respective speeds Displacements Vs Speeds

FUPD

U in mm at 55 KMPH

U in mm at 70 KMPH

U in mm at 100 KMPH

Criteria Verification

55 70 100

Within Limits Base

Design (400 Kgs)

88.129 115.202 164.195

< 400 mm

Within Limits Optimized

Design (293 Kgs)

58.524 68.123 104.955 < 400 mm

Within Limits

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For 55kmpH

Type of Design Displacement

Regular Chassis Frame 105.403

Base Design 88.129

Optimized Design 58.524

For 70kmpH

Regular Chassis Frame 509.7

For 100kmpH

Regular Chassis Frame 781

Note: Stress is not considered for crash Analysis

Figure 9.1. Speed Vs Displacement.

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Hypothesis of research questions:

During an accident between a truck and a car, because of its high ground clearance for a truck the car may underrun into the truck. It means the car goes below the truck which causes fatal injuries or death inside the car. In order to avoid underrun FUPD is used. The FUPD acts as a shield and doesn’t allow the underrun of the car. During an accident the FUPD deforms by absorbing. So that the damage caused to car stops somewhere near front wheels to front bonnet region. Hence the impact to the passengers will be reduced.

From research studies as per global safety regulation ECE93 has been used for so many vehicles in the market. As per the same regulation the base design has been developed using CAD software and applied static loads for checking strength of the FUPD. The base design is over designed by considering the dimensions from safety standard. To reduce the weight of base design topology optimization has been carried out to achieve light weight design of FUPD. The key parameters are displacement which should not cross 400mm when we carried out crash analysis. The results are discussed in results chapter.

Topology Optimization on FUPD makes the FUPD lightweight by removing the excess amount of material that is already in the design. By material reduction the FUPD becomes light in weight which means less material cost and also less weight of the structure is an added advantage to the vehicle as the weight of the vehicle is inversely proportional to the mileage of the vehicle.

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9.2 Validation

During a crash the stresses on the structures are varied very highly and are not of our concern because it is basically the displacement (deflection) of the structures on both the vehicles matters. The displacement of each structure upon the impact describes the failure of the structure, so in this thesis the displacements on FUPD upon crash test at different speeds prescribed by ECE R93 regulations are calculated. According to the safety standards provided by ECE R93 the displacement on FUPD must be less than 400 mm.

From the crash test analysis the displacements obtained for speeds 50 Km/h, 70Km/h, 100Km/h are 88.29mm, 115.202mm, 164.95mm respectively, which are well under the limit of 400 mm.

The Base Design is further optimised for weight reduction and it is observed that weight has been reduced from 400 Kgs to 293 Kgs. From the crash test analysis the displacements obtained for speeds 50 Km/h, 70Km/h, 100Km/h are 58.524, 68.123, 104.955 respectively. The displacements on the optimized Design got further reduced compared to Base Design proving that the optimized Design is more efficient.

9.3 Conclusions

• Displacements shown in the Table 9.1 are comparative and found to be lower for Optimized Design than base design.

• The graph for displacements also shows similar trend for optimized design with base design and also falls within the requirements.

• As the Optimized design meets the requirements, it is recommended to go with the optimized design over base design with appropriate field tests.

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9.4 Future Scope

• The process followed can be extended to range of speeds.

• This process can be done using elastic material so that it reduces the impact energy.

• The process followed can be extended to range of materials such as composite and carbon elements.

• The methodology followed can be extended to different load cases and multiple designs.

• This methodology can be studied for Rear Underrun Protection Devices.

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References

[1] Professor Mechanical Department, Vasavi College of Engineering/

Osmania University, India and T. R. Rao, “Design and Optimization of Front Underrun Protection Device,” IOSR J. Mech. Civ. Eng., vol. 8, no.

2, pp. 19–25, 2013.

[2] G. BAL, “AUTOMOTIVE SAFETY REGULATIONS,” p. 66, 2015.

[3] S. Corr-, “Status chart of the Standard to be used by the purchaser for updating the record,” Automot. Res. Assoc. India Pune, p. 19, Sep. 2006.

[4] (Mechanical Departmen,Sreenidhi Institute of Science and

Technology/JNTUH, INDIA) and S. Pandimukkula, “Crash Analysis of Front under Run Protection Device using Finite Element Analysis,” IOSR J. Mech. Civ. Eng., vol. 9, no. 1, pp. 49–56, 2013.

[5] A. Krusper, Structural interaction between vehicles: an investigation of crash compatibility between cars and heavy goods vehicles. Göteborg:

Chalmers Univ. of Technology, 2014.

[6] “Large Model Finite Element Preprocessing | Altair HyperMesh.”

[Online]. Available: https://altairhyperworks.com/product/hypermesh.

[Accessed: 27-May-2018].

[7] “ Chayan Basak, Altair Engineering, (2009), Concept Level Design Optimization,Altair Engineering,Sweden.”

[8] http://internationaljournalofresearch.org/

[9] Hirak Patel, Khushbu C. Panchal, Chetan S. Jadav.” Design Optimization for Weight Reduction. International Journal of Engineering and Advanced Technology (IJEAT) ISSN: 2249 – 8958, Volume-2, Issue-4, April 2013 [10] “Dr.Johan Wall, (2015) Design optimisation, Department of Mechanical Engineering, Blekinge Institute of Technology, Sweden.”

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Department of Mechanical Engineering Blekinge Institute of Technology SE-371 79 Karlskrona, SWEDEN

Telephone:

E-mail:

+46 455-38 50 00 info@bth.se

Design Analysis and Optimization of Front Underrun Protection Device

Anil Sharma

Design Analysis and Optimization of Front Underrun Protection

Device

Design Analysis and Optimization of Front Underrun

Protection Device

Anil Sharma

ACKNOWLEDGEMENTS

Table of Contents

List of Figures

List of Tables

Abbreviations:

1 INTRODUCTION

1.1 Overview

1.2 Aim and Objective

1.3 Research Questions

1.4 Purpose and Motivation

2 LITERATURE REVIEW

2.1 Test Conditions

2.2 Test Results

2.3 Forecast of Front Under run Protection Device Effect

2.4 Methodology

3 MODELLING OF FRONT UNDER RUN PROTECTION DEVICE

3.1 Technical Requirements of FUPDs

3.2 CAD Model With all the Dimensions of Front Under run Protection Device

4 FINITE ELEMENT MODELLING OF FRONT UNDER RUN PROTECTION DEVICE

4.1 Finite Element Method

4.2 Best in Class Meshing

.

4.3 Surface meshing

4.4 Solid map hex mesh

4.5 Midsurface Extract

4.6 FE Model Generation of FUPD

4.7 Material and Properties

Component Material

4.8 Loads and Boundary Conditions

4.9 Load Cases

5 TOPOLOGY OPTIMIZATION OF FRONT UNDER RUN PROTECTION DEVICE

5.1 Overview

5.2 Structural Design and Optimization

5.3 Topology Optimization

5.4 Optimization Process

5.4.1 Objective Function

5.5 Topology Optimization using Altair Opti Struct

6 OPTIMIZATION RESULTS

6.1 Topology Optimization Results for FUPD and Holding Bracket

7 ANALYSIS RESULTS OF OPTIMIZED DESIGN

8 CRASH ANALYSIS RESULTS

8.1 Crash Analysis of Regular Chassis frame without FUPD

8.2 Crash Analysis of Base Design FUPD

8.3 Crash Analysis of Optimized Design FUPD

9 SUMMARY AND CONCLUSION

9.1 Observations

For 55kmpH

For 70kmpH

For 100kmpH

9.2 Validation

9.3 Conclusions

9.4 Future Scope

References