Q: In calculating A & B Coefficients from crash tests which speed is correct to use, the test impact speed or the delta-v speed? Were the A & B formulas developed from using test impact speeds or delta-v speeds? This forum post indicates “The Impact Speed”. Some other references mention test impact speed and some instructors teach that the proper method is to use the actual delta-v from the crash test.
Which is correct?
A: The confusion may comes from a couple factors:
- 1) CRASH damage analysis is based on simple linear relationships which equate the Impact speed to the extent of residual crush.
2) Some refer to it as the Impact Speed Change, but the Impact Speed change must be ONLY to the point of common velocity.
2) There is no provision in CRASH for inclusion of restitution.
- See forum topic CRASH does not include restitution
4) For other collision types, because the A&B coefficient fitting procedure requires the impact speed, some have misinterpreted that to mean 'Total impact speed 'change' which included restitution.
- That is incorrect!
- Again, that is another fundamental error!
- IMPACT SPEED
IMPACT SPEED CHANGE TO THE POINT OF COMMON VELOCITY
*except in the case of a "perfectly-plastic" collision!