## Follow Up Questions on CRASH

General Questions related to the CRASH Program and clones
Damage Analysis & Momentum Based Analysis programs
MSI
Posts: 1386
Joined: Thu Jun 18, 2009 12:37 pm

### Follow Up Questions on CRASH

More via email.I had responded that they should simply review these responses to questions on CRASH they responded:
Q: These questions are a little bit different, than the ones you answered earlier (April, June 2018).

Q1: When "Crash3 Technical Manual” was written, they stated that collisions with moving trains/ large trucks are one of nonapplicable accident types. When can we say, that the vehicle is a large truck? How big (dimensions), and how heavy (mass) does a vehicle have to be, to name it a large truck?
• A1: There are very limited crash tests for heavy large trucks. If there are no crash tests then there is no way to create the CRASH damage analysis crush coefficients.
If you are doing a momentum only analysis, the larger the difference between the weights of the vehicles the higher the probability that there will be sensitivities to the large vehicle
• From How is Monte-Carlo method used in Accident reconstruction?:
• A classic example of problems with the sensitivity of a linear momentum solution is when it is applied to a t-bone type collision.
• When a lighter car crosses the path of a heavier car/truck and the lighter vehicle is struck in the side by the heavier vehicle. If the heavier striking car/truck happens to swerve before the impact, either to the left or the right, the degree or two of change of impact angle can result in dramatic changes in the results of a linear momentum solution.
Why?
The swerve by the heavier vehicle will produce a change in the separation angles.
The change in separation angles, if all attributed to the smaller vehicle speed (which it will be if the impact angle of the striking heavier vehicle is assumed to be 0 (zero) degrees) will dramatically change the linear momentum solution approximated speed of the smaller lighter vehicle.
The result is that depending on the direction of the swerve, the small vehicle will be 'reconstructed' as either going very fast in the forward or reverse direction. Depending on the difference in the weights of the vehicles the assumption for impact angle of the heavier vehicle can result in very large errors in the analysis.
What that ‘classic’ example is meant to illustrate is that when applying a Linear Momentum solution procedure to ANY accident you need to test sensitivities of inputs (angles at impact and angles at separation). If a small change in an angle makes a dramatic change in the results then obviously you need to focus on defining and refining the inputs as well as consider using a more sophisticated solution procedure (like a SMAC simulation).
Q2. In the publication "The algorithms of Crash" it was written that:
"The crush stiffnesses (coefficients A and B) have been empirically derived from data generated in crash tests. Obviously the uniformity notion does not account for the fact that a vehicle side is fairly stiff near the axles but less so near the doors".
Therefore, I have a question: are the values of stiffness coefficients averaged (variable stiffness along the side of the body is taken into account)?
• A2: NO. that is why CRASH damage analysis is a first approximation technique since side impacts are based on moving barrier crashes or vehicle to vehicle crash tests which may or may not engage the sill (bumper height and pre-impact braking may engage the sill) and/or tires (where on the side was the impact? did it include the tires/rims?) and so can show a wide variation in the approximate 'residual' Crush stiffness of the side of a vehicle can occur.
Q3. You mentioned the publication of Tumbas and Smith: "Measuring Protocol for Quantifying Vehicle Damage from an Energy Basis Point of View" 880072. I was searching the Internet, but I can't find these papers. How can I get (where can I find) these papers?
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