VEHICLE CRASHWORTHINESS AND OCCUPANT PROTECTION Paul Du Bois Clifford C. Chou Bahig B. Fileta Tawfik B. Khalil Albert I. King Hikmat F. Mahmood Harold J. Mertz Jac Wismans Editors: Priya Prasad Jamel E. Belwafa Sponsored by: Automotive Applications Committee American Iron and Steel Institute Southfield, Michigan Disclaimer The opinions included in this publication are those of the indi- vidual authors and in no way represent endorsement of the Edi- tors or American Iron and Steel Institute (AISI) Safety Panel members. copyright c 2004 American Iron and Steel Institute 2000 Town Center Southfield, Michigan 48075 Contents Introduction........................................................ 1 1.1 Motor Vehicle Safety..................................................................... 1 1.2 The Automobile Structure .............................................................. 3 1.3 Materials ...................................................................................... 4 1.4 Crashworthiness ........................................................................... 4 1.5 Crashworthiness Goals ................................................................. 5 1.6 Crashworthiness Requirements .................................................... 6 1.7 Achieving Crashworthiness ........................................................... 7 1.8 CrashworthinessTests ................................................................... 8 1.9 Crashworthiness Models Requirements ...................................... 10 2.1 Introduction ................................................................................. 11 2.2 Current Design Practice .............................................................. 12 2.2.1 Comparison Between LMS and FE-Based Crashworthiness Processes ....................................................................... 13 2.2.2 Lumped Mass-Spring Models ............................................... 16 2.2.3 Limitations of LMS Models ................................................... 20 2.3 Crash/Crush Design Techniques for Front Structures .................. 26 2.3.1 Some Basic Principles of Designing for Crash Energy Manage- ment ................................................................................ 28 2.3.1.1 Desired Dummy Performance........................................ 29 2.3.1.2 Stiff cage Structural Concept ......................................... 29 2.3.1.3 Controlled Progressive Crush or Deformation With Limited Intrusion ......................................................................... 30 2.3.1.4 Weight Efficient Energy Absorbing Structures and Support- ing Frame ....................................................................... 31 2.3.2 Review of Analytical Design Tools for Crash Energy Manage- ment ................................................................................ 32 2.3.2.1 Hybrid Models ............................................................... 32 2.3.2.2 Collapsible Beam Finite Element .................................. 35 2.3.2.3 Dynamic Effects ............................................................ 36 2.3.3 New Design Methodology .................................................... 38 2.4 Analytical Design Tools ............................................................... 40 2.4.1 Component Design .............................................................. 40 2.4.1.1 Collapse Modes ............................................................ 41 2.4.1.2 Axial Collapse ............................................................... 42 2.4.1.3 Bending Collapse Mathematical Models ........................ 61 2.4.1.4 Combined Loading ........................................................ 70 Page iii 2.4.1.5 Structural Joints ............................................................ 74 2.4.2 Design of Substructures ....................................................... 75 2.4.2.1 General Analysis Methods ............................................ 76 2.4.2.2 Super-Collapsible Beam ................................................ 78 2.4.2.3 Thin-Walled Finite Beam Element ................................. 80 2.4.2.4 Structural Programming ................................................. 81 2.5 Vehicle Front Structure Design for Different Impact Modes .......... 84 2.5.1 Vehicle Front Structure Design for Current Standards ........... 85 2.5.1.1 FMVSS 208 .................................................................. 85 2.5.1.2 NCAP Test .................................................................... 85 2.5.1.3 IIHS Test ....................................................................... 87 2.5.2 Vehicle-to-Vehicle Frontal Collisions .................................... 88 2.5.2.1 Preliminary Relationships in Head-on Frontal Collision .. 89 2.5.2.2 Strategies for Designing Front Structures for Head-on Impact ............................................................................ 93 2.5.3 Assessment of Analytical Tools ............................................ 98 2.5.4 Conclusion ......................................................................... 100 2.6 References ............................................................................... 102 3.1 Historical Background ................................................................111 3.2 Overview of Explicit FE Technology ........................................... 117 3.2.1 Formulation ........................................................................ 118 3.2.2 Explicit Integration ............................................................ 120 3.2.3 Shell Element .................................................................... 121 3.2.4 Plasticity ........................................................................... 123 3.2.5 Contact Treatment ............................................................. 124 3.3 Models Development Between 1987 and 1997 ...................... 125 3.4 Software Development Between 1987 and 1997 ........................ 130 3.5 Limitations of Current Technology ............................................. 132 3.6 Applications .............................................................................. 136 3.6.1 Component Models ............................................................ 137 3.6.2 Substructure Models .......................................................... 139 ................................................................................................... 139 3.6.3 Full-scale vehicle structure models .................................... 139 3.6.3.1 Model Statistics: ......................................................... 142 3.6.3.2 Contact Definitions ...................................................... 143 ............................................................................................... 143 3.6.3.3 Initial Condition ........................................................... 143 3.6.3.4 Results ........................................................................ 143 3.6.4 Integrated Vehicle-Occupant-Restraints Model ................... 143 ................................................................................................... 143 Fig. 3.6.4.1 Integrated model ................................................... 146 ............................................................................................... 146 Page iv Fig. 3.6.4.2 Integrated model deformations .............................. 146 ............................................................................................... 147 Fig. 3.6.4.3 Energy balance of integrated model simulation ..... 147 ............................................................................................... 147 Fig. 3.6.4.4 Rear rocker velocity .............................................. 147 3.7 Summary .................................................................................. 148 3.8 References ............................................................................... 151 4.1 Introduction ............................................................................... 159 4.2 Barrier Collision ........................................................................ 162 4.3 Basic Laws and Concepts of Motion ......................................... 164 4.3.1 Basic Principles of Postulates ........................................... 167 4.3.2 Particle Under Given Forces .............................................. 167 4.3.3 Interactions ........................................................................ 168 4.3.4 Two Additional Postulates .................................................. 169 4.3.5 Idealizations ....................................................................... 169 4.3.6 Energy and Work ............................................................... 169 4.3.7 Conservation of Energy ...................................................... 170 4.4 Application of Concepts to Vehicle/Occupant Analysis .............. 170 4.4.1 Background ....................................................................... 170 4.4.2 Vehicle Response .............................................................. 172 4.4.3 Pulse Waveform Efficiency (h)............................................ 174 4.4.4 Equivalent Square Wave (ESW): ........................................ 177 4.4.5 Effect of Pulse Shape ........................................................ 177 4.4.6 Occupant Response .......................................................... 178 4.5 Axioms