When and why were CRASH A & B coefficients created?

Questions/Topics Related to the CRASH computer program
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MSI
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When and why were CRASH A & B coefficients created?

Post by MSI »

Q: Looking at Campbell's SAE paper 740565 "Energy Basis for Collision Severity" I see b0 and b1 defined in equation (2) :
Campbell Eq 2.jpg
Campbell Eq 2.jpg (5.77 KiB) Viewed 9115 times
And then as a0 & a1 in the APPENDIX
Campbell Appendix Ao A1.jpg
Campbell Appendix Ao A1.jpg (6.66 KiB) Viewed 9115 times
When and why were these changed to the CRASH A&B coefficients?

A: For an introduction please see What is CRASH for background on the CRASH program.
  • A quick overview:
    • The damage analysis procedure of CRASH was developed as an auxiliary program to help with the NHTSA crash investigations come up with initial speeds to run the much more sophisticated SMAC Program. So much of the early development of CRASH was done as appendix material while refining and developing SMAC. Ultimately NHTSA adopted mainly the CRASH damage analysis procedure for their NASS crash investigations due to simplicity and inexpensive cost to run the program
      • The 1970s were the days of mainframe timeshare computers like MCAUTO where you paid for computer the memory space & CPU time for each computer program run. For a peek at the mainframe to mini to PC computer transitions see our 1996 discussion Why develop for the PC?.
And in answer to your question, the following provides some background on when and why the CRASH A&B coefficients came into existence:
  • From the McHenry SAE Paper 750893 "Comparison of Results Obtained with Different Analytical Techniques for Reconstruction of Highway Accidents":
    • From bottom of page 6
      • DAMAGE ANALYSIS
        • "Hand calculation techniques for damage analysis that yield reasonable estimates of the impact velocity in frontal collisions (i.e., the relative velocity of approach) have been developed initially by Emori SAE 68-0016 , and Emori SAE 70-0017 (full width contact only) and then further refined by Campbell SAE 74-0565(partial width contact) , using linear approximations of the relationship between residual crush and impact velocity. The SMAC program applies a similar analytical approach to the entire peripheral structure, and it has been demonstrated to yield good approximations of both impact velocity and speed change, DeltaV, in general collision configurations including oblique, non-central impacts. The objective of the present research has been to develop a simple, closed-from damage analysis technique that is applicable to general collision configurations."
      and further on page 11:
      • Absorbed Energy -
        "The calculation of absorbed energy is based on residual crush and is patterned after that developed by Campbell. The only significant differ­ence is in the treatment herein of the energy absorbed without residual crush as being proportional to the contact width rather than a constant".
        The following relationship is applied:
        McHenry Energy Absorbed.jpg
        McHenry Energy Absorbed.jpg (14.76 KiB) Viewed 9115 times
    Additional discussion/presentation of the why is contained in McHenry The Algorithms of CRASH, 2001 page 20:
    The Force per unit width (F) as a function of A, B & C:
    CRASH Force equation.jpg
    CRASH Force equation.jpg (47.42 KiB) Viewed 9102 times
Please refer to the cited references for additional information and clarification: ___________________________________________________
For additional information on damage analysis & CRASH, please see: