More Questions on CRASH: Accuracy, DeltaV

Topics related to collision & Trajectory analysis formerly on our 'Registrants only' area however which we get asked about frequently so believe shoud be in the open forum too
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MSI
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More Questions on CRASH: Accuracy, DeltaV

Post by MSI » Wed Oct 03, 2018 5:55 pm

Oct 2018: email: Q: Could you please answer the following questions?
  • 1. What is the accuracy of calculating the DeltaV using the Crash3 model?
    2. Have tests been performed in which the measured (real) DeltaV was compared with the DeltaV calculated from car body deformation? Are there publications/ papers, that contain the results of such tests?

Q1: What is the accuracy of calculating the DeltaV using the Crash3 model?
  • A1: That depends...if you use the original NHTSA CRASH3 technical manual using the CRASH3 tables the following is the accuracy from Figure 1.1 "Comparison of True Vs CRASH3 Damage estimates for DELTAV for 53 staged collisions" (page 1.4): (and this is the3 same for EDCRASH and other CRASH clones)
    CRASH3 accuracy fig.jpg
    CRASH3 accuracy fig.jpg (35.77 KiB) Viewed 130 times
    This is from the Introduction of CRASH3:
    CRASH3 caution.jpg
    CRASH3 caution.jpg (49.5 KiB) Viewed 130 times
    Now since then NHTSA and other crash tests have been used to create custom fitted coefficients for vehicles and/or clones of vehicles. However, from our 1997 paper we note:
    • "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 [and we add normally from a single test and an assumption of approx 4 mph for a 0" damage intercept]. 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"
Q2: Have tests been performed in which the measured (real) DeltaV was compared with the DeltaV calculated from car body deformation? Are there publications/ papers, that contain the results of such tests?

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