A: I am also not sure on what values for ECF were used by BRACH (It's the weekend and the book is at the office. The ECF is built into the actual program so if he simply ran CRASH3 then the program would use the correct ECF. However since he ran CRASH3 he used the questionable update of the crush coefficients performed by Monk & Gunther.
CRASH3 can provide a basis for good approximations of impact speeds and impact speed changes in many applications.
As we published in our SAE paper CRASH97:
- "The original form of the CRASH computer program, which culminated in the CRASH3 version, was not intended to be a detailed, highly accurate reconstruction program. Rather, it was developed to serve as a simple preprocessor for the SMAC program. While the results of CRASH3 applications can be useful in providing approximate measures of accident severity for use in statistical studies, where the average error is most important, it has been demonstrated in validation tests to produce results which when compared to those of full-scale crash tests can include individual errors as great as 45%. The possible error levels of the CRASH3 computer program are also applicable to all other versions of CRASH (EDCRASH, WinCRASH, etc.) and linear momentum solutions procedures in general” .
And from our 1981 paper "National Crash Severity Study--Quality Control, Task 5. Analysis to Refine Spinout Aspects of CRASH"
A realistic appraisal of residual scatter in the empirical fits led to the conclusion:
- "To achieve a general improvement in the reliability and accuracy of approximations of the angular and linear velocities at separation, a step-by-step time history form of trajectory solution should be implemented."
In summary, the results from any and all simplified solution procedures (damage, momentum, planar impact mechanics, etc) for the reconstruction of automobile collisions should also be tested and refined with more sophisticated reconstruction procedures such as SMAC.