Evaluation of the Performance and Testing Techniques of Vehicle Frontal Protection Systems By Paul Bignell BE (Mech) A THESIS SUBMITTED TO THE SCHOOL OF CIVIL ENGINEERING QUEENSLAND UNIVERSITY OF TECHNOLOGY IN PARTIAL FULFILMENT OF REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY JUNE 2004 KEYWORDS Frontal Protection Systems, Bull bars, Impacts, Energy absorbed, Air bags, Quasi- static testing, Dynamic testing, Finite Element Analysis i ABSTRACT Frontal Protection Systems (FPS) have become a popular accessory for passenger vehicles. They are used to protect the front of a vehicle during minor impacts, and to attenuate the impact energy during major impacts. With the increased safety of modern passenger vehicles, the fitment of a FPS to a vehicle requires careful consideration to the design and installation of the FPS as they may modify vehicle crush characteristics. This is particularly important in vehicles fitted with air bags. These community and industry concerns triggered the research discussed in this thesis, which is the first comprehensive project undertaken in this particular area. This project generated comprehensive research knowledge on the impact response and energy absorption of FPS in order to evaluate performance. This involved a range of experimental testing supplemented by finite element analysis. Experimental testing was conducted using quasi-static and dynamic techniques to assess the overall performance of current FPS available. Finite element models were then generated and analysed using both implicit and explicit techniques, and calibrated against the experimental testing results. These models were used throughout the project to assess the FPS response, in particular the energy absorbed, to changes in impact characteristics. FPS assessment guidelines were developed from the knowledge generated from the numerous FPS tests and analyses carried out in this research project. These guidelines have been used in the design and evaluation of a number of FPS for air bag compatibility. The real life performance of vehicles fitted with these FPS, have given confidence to the assessment criteria developed in this research project. This project has demonstrated that FPS can be designed to complement the safety systems of modern passenger vehicles, and thus passenger safety. This would not have been possible without the comprehensive research carried out in this project. ii TABLE OF CONTENTS Chapter 1 Introduction ................................................................................................. 1 1.1 Aims and Objectives .......................................................................................... 1 1.2 Research and Methodology................................................................................ 1 1.2.1 Experimental Testing .................................................................................. 2 1.2.1.1 Quasi-Static Evaluation of FPS............................................................ 2 1.2.1.2 Dynamic Evaluation of FPS................................................................. 2 1.2.2 Finite Element Analysis.............................................................................. 3 1.2.3 FPS Evaluation............................................................................................ 3 1.3 Thesis Layout..................................................................................................... 3 Chapter 2 Literature Review ........................................................................................ 5 2.1 Frontal Protection Systems ................................................................................ 5 2.1.1 FPS Types ................................................................................................... 6 2.1.2 FPS Components......................................................................................... 7 2.1.3 FPS Material ............................................................................................... 9 2.1.4 Fitment Numbers....................................................................................... 10 2.1.5 FPS Accessories........................................................................................ 10 2.1.6 FPS standards............................................................................................ 11 2.1.7 Pedestrian Safety....................................................................................... 12 2.2 Mechanics of Impacts ...................................................................................... 14 2.3 Air Bags ........................................................................................................... 22 2.3.1 The Air Bag System.................................................................................. 23 2.3.2 Air Bags .................................................................................................... 24 2.3.3 Air Bag Sensors ........................................................................................ 24 2.3.3.1 Mechanical Sensors............................................................................ 25 2.3.3.2 Electronic Sensors.............................................................................. 25 2.3.4 Air Bag Triggering Characteristics ........................................................... 28 2.4 Testing.............................................................................................................. 29 2.4.1 Quasi-Static Testing.................................................................................. 29 2.4.2 Dynamic Testing ....................................................................................... 30 2.4.2.1 Barrier Testing ................................................................................... 30 2.4.2.2 Pendulum Testing .............................................................................. 30 2.4.3 Comparison of Testing Techniques .......................................................... 32 iii 2.4.4 Finite Element Analysis ............................................................................34 2.5 Summary ..........................................................................................................35 Chapter 3 Experimental Testing.................................................................................37 3.1 FPS Behaviour during an Impact .....................................................................37 3.2 Test Setup.........................................................................................................40 3.2.1 Data Analysis ............................................................................................42 3.2.2 Failure Modes............................................................................................43 3.2.3 Summary of FPS Tested............................................................................46 3.3 Dynamic Testing ..............................................................................................53 3.3.1 Pendulum Test Rig....................................................................................54 3.3.2 Data Acquisition........................................................................................54 3.3.3 FPS Mounting ...........................................................................................55 3.3.4 Pendulum Velocity....................................................................................55 3.3.5 Testing Results ..........................................................................................56 3.3.5.1 Data Analysis .....................................................................................56 3.3.5.2 Results Summary................................................................................58 3.4 Summary ..........................................................................................................63 Chapter 4 Additional Experimental Testing...............................................................65 4.1 Further Testing with Strain Gauges .................................................................65 4.1.1 Additional FPS ..........................................................................................65 4.1.1.1 Assembly............................................................................................66 4.1.1.2 Strain Gauges and LVDTs .................................................................67 4.1.1.3 Results ................................................................................................68 4.1.2 Replacement Bar .......................................................................................72 4.1.2.1 Assembly............................................................................................72 4.1.2.2 Strain Gauges and LVDTs .................................................................75 4.1.2.3 Results ................................................................................................78 4.2 Vehicle Frontal Structures................................................................................83 4.2.1 Monocoque Structure ................................................................................84 4.2.2 Chassis Structure.......................................................................................85 4.2.3 Summary ...................................................................................................86 Chapter 5 Finite Element Analysis.............................................................................89