A Study on Optimal Design of Vehicle Structure for Small Overlap Frontal Impact

다국어 초록 (Multilingual Abstract)

Road traffic continues to cause more than a million fatalities worldwide every year. Although many steps have been taken to improve occupant protection in car crashes, challenges still remain for car designers. In the present study, real-world data derived from frontal crashes have been used as a base for identifying crash situations where occupants are severely or fatally injured in cars, despite having been awarded top-ratings in crashworthiness evaluation tests. One situation identified is small overlap crashes, where injuries are commonly related to intrusion. Another is large overlap situations, where injuries are not directly linked to intrusion but rather to vehicle deceleration and interaction with restraint systems.
The aim of the studies constituting this thesis was to develop design methods for robust crashworthiness of future vehicles and to propose solutions to mitigate injuries in small overlap crash situations. This thesis presents a study on the optimal design of vehicle structure for improving the small-overlap rating, based on a computer-based crash simulation model. An analysis of vehicle structural performance during small overlap frontal impact was proposed. Based on the results of the analysis, two methods were conducted to improve the vehicle structural performance in the event of a SOFI. The first method is thickness optimization. And the second method is two reinforced component models such as longitudinal reinforcement and rocker panel reinforcement which were developed for the small-overlap frontal impact (SOFI) simulation following the real test conditions. The crash simulation results were used to evaluate the overall vehicle structure through a comparison of intrusion measurements with the rating guidelines of the Insurance Institute for Highway Safety (IIHS). The response surface method (RSM) was applied to optimal vehicle structures in order to improve the small-overlap rating. The RSM function proposed the optimal values of the variables as the new design. The crash analysis results showed that the serious damage to the vehicle structure occurred when the minivan model collided with barrier model at 25% overlap. In this study, the grade of the overall structure was upgraded from “poor” to “acceptable” in the case of Flat 150 (the Flat barrier with a 150 mm radius and 25% overlap).

목차 (Table of Contents)

• Table of contents i
• Definitions and abbreviations iii
• List of figures iv
• List of tables vii
• Declaration ix
• Acknowledgements x
• Abstract xi
• 1. Introduction 1
• 1.1 Problem statement and motivation 1
• 1.2 Review of relevant literatures 3
• 1.2.1 Occupant protection in vehicle crashworthiness 3
• 1.2.2 Vehicle structure design for different impact modes 4
• 1.2.3 Current crash test standards 5
• 1.3 The objective of the present study 7
• 1.4 Thesis organization 9
• 2. Crashworthiness tests 10
• 2.1 Vehicle in full-width frontal impact crash test 10
• 2.2 Vehicle in moderate overlap crash test 11
• 2.3 Vehicle in small overlap crash test 12
• 3. Finite element model for small overlap frontal impact 17
• 3.1 Description of vehicle finite element model 17
• 3.2 Validation of vehicle finite element model 19
• 3.2.1 Comparison of simulation results and NCAP test results 19
• 3.2.2 Comparison of simulation results and IIHS test results 23
• 4. Small overlap frontal impact simulation 26
• 4.1 Barrier finite element model 26
• 4.2 Small overlap crash test model 26
• 4.3 Small overlap frontal impact simulation rating 28
• 4.4 Analysis of vehicle structural performance during SOFI 29
• 5. Optimal design of frontal structures 32
• 5.1 Optimal design techniques for vehicle structures 32
• 5.1.1 Taguchi algorithm 32
• 5.1.2 Box-Behnken design and Response Surface Method (RSM) 33
• 5.2 Optimal design of A-pillar and rocker panel 34
• 5.2.1 RSM-based optimization procedure 34
• 5.2.2 The results of optimal design 41
• 5.3 Optimal design of reinforcements 44
• 5.3.1 Evaluation of SOFI performance of reinforcements 44
• 5.3.2 Sensitivity analysis of design and material of reinforcements 46
• 5.3.2.1 Design of longitudinal reinforcement 46
• 5.3.2.2 Design of rocker panel reinforcement 51
• 5.3.2.3 Material of reinforcements 56
• 5.3.3 RSM-based optimization procedure 61
• 5.3.4 The results of optimal design 68
• 5.3.4.1 Optimal design of longitudinal reinforcement 68
• 5.3.4.2 Optimal design of rocker panel reinforcement 69
• 5.4 The comparison between optimal design and original model 72
• 5.4.1 The overall structural rating 72
• 5.4.2 Energy absorption and deformation 76
• 5.4.3 Full frontal crash performance 79
• 6. Conclusions 81
• References 83
• Appendices 93