Validation of Damage Analysis in Low Speed Impacts

Questions/Topics Related to the CRASH computer program
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MSI
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Validation of Damage Analysis in Low Speed Impacts

Post by MSI »

Q: I’m involved in a low speed case and the opposing expert has said in so many words that using crush (based on NHTSA test data) isn’t real reliable and shouldn’t be used. I’m looking for papers that validate crush (i.e.-looked at crash tests with known speeds, did crush analysis, then compared them to each other and have listed the percentages of accuracy). Are you aware of any studies like that?

A: Probably a good place to start since it is a low speed impact is our restitution paper:
  • Abstract:Effects of restitution on damage interpretations are compounded by the fact that restitution reduces the residual deformation while increasing the total impact speed change. This paper presents a revised analytical procedure to include restitution effects for the CRASH program and refinements to the restitution modeling within the SMAC program. The conversion of vehicle impact test results into inputs for the two revised programs is also included. The effects of the refinements to the damage analysis procedures on reconstruction results are illustrated by direct comparisons with corresponding results produced by the original SMAC and CRASH programs and with measured data from full scale vehicle impact tests.
In the paper we demonstrate that due to lack of consideration of restitution in damage analysis, you will tend to underestimate the speed change in a damage analysis particularly in low speed collisions due to restitution. The reason I point that out is that it may be the ‘worst case’ scenario for damage analysis.
Since you have a low speed impact you are in the restitution phase for damage analysis and so need to consider it.
Therefore be sure to consider a “range of speeds” in lower speed impacts due to restitution.

In addition, there have been a lot of papers on low speed impacts, restitution, damage analysis, for example: Getting back to basic damage analysis, some validation papers on damage analysis:
  • Further Validation of EDCRASH Using the RICSAC Staged Collisions, SAE paper 89-0740
    • I caution you that the creative 'comparison' techniques for the EDCRASH trajectory analysis validation by EDC is somewhat sketchy, see Validation for vehicle to vehicle collision models? for a discussion of problems with their use of ‘combined impact speeds’ and ‘95% confidence’ to perhaps hide 40% error problems with the trajectory solution of EDCRASH. However i think the damage analysis validation in the paper isn't subjected to that same treatment.
    Neptune has made a cottage industry out of crush coefficients, vehicle specs and damage analysis techniques, some of which may be useful and/or what you are looking for in your situation.
It's been a several years since we've done research in the specific area of damage analysis (we are working on some other things) so i haven't recently reviewed all these references so be sure to read each to form your own opinion as to the veracity and usefulness of the information contained in the papers.

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