Does CRASH/EDCRASH include restitution?

General Questions related to the CRASH Program and clones
Damage Analysis & Momentum Based Analysis programs
Post Reply
MSI
Site Admin
Posts: 1410
Joined: Thu Jun 18, 2009 12:37 pm

Does CRASH/EDCRASH include restitution?

Post by MSI »

Q: Does CRASH/EDCRASH include restitution?
A: No!
  • Restitution is not included in the fundamental equations of CRASH.
  • Restitution is NOT included in any commercial version of CRASH.
Restitution consists of two separate aspects:
  • (1) A partial dimensional recovery and
    (2) A partial restoration of kinetic energy.
During a motor vehicle collision, the maximum dynamic deformation generally exceeds the residual deformation.
Subsequent to the peak dynamic deformation, the collision partners begin a restitution phase as the deformed structures restore kinetic energy, or "spring" back.
The restitution force level and duration determine the impulse that acts on the collision partners during the restitution phase.
At the present time, crush coefficients for vehicle collision analysis are predominantly based on impact speeds and damage measurements from rigid, fixed barrier crash tests.
The residual damage is correlated with the impact speed by means of fitted linear relationships.
In general, there is no consideration given to the effects of restitution in applications of the fitted crush coefficients.
However, the ignored effects of restitution on the total impact speed change, corresponding to a given amount of residual crush, are compounded by the fact that restitution acts to reduce the amount of residual deformation, for a given maximum dynamic crush, while also acting to increase the total impact speed change.
Thus, substantially different vehicles can share nearly equal slopes and intercepts in CRASH-type plots of the approach period speed-change as a function of residual crush. This can occur even though the actual exposure severity for a given residual crush may be significantly different.

Our 1997 paper, 97-0960, Effects of Restitution in the Application of Crush Coefficients", which initially encountered misguided erroneous criticism, has now taken its rightful place as one of the "significant steps forward within the field of crash reconstruction" in a recent SAE book Crash Reconstruction Research: 20 Years of Progress (1988-2007).

We have not created a commercial version of CRASH with our restitution enhancements partially because of the joyous reception the paper received these past 10 years. ;-), and secondly because we have numerous other research projects that are keeping us busy.

One last note, don't think that the lack of consideration of restitution in CRASH will stop some folks (`experts') from saying that it DOES consider restitution.
Yep. Seen it in testimony wherein they relayed
  • "that since the measurements to determine the crush stiffness values are the restituted crush measurements then obviously CRASH includes restitution!"
That is misleading and incorrect!

Restitution is NOT included in any commercial version of CRASH.
Question? Comment? Please email forum@mchenrysoftware.com. Also see the McHenry Forum Index
Visit McHenrySoftware.com for technical information & software.
(c) McHenry Software, Inc ALL Rights Reserved.

Post Reply