Estimating Crush Stiffness when Reconstructing Vehicle Accidents 930898
Energy equivalence calculations from damage deformation have evolved through the years as a principal analysis technique for the accident reconstructionist. The foundation for this analytical technique is the crash test data that has accumulated over the last few decades for specific vehicles crashed into or by barriers. During a reconstruction, the problem that often arises is that crash test data is not available for one of the vehicles involved in the collision. In such a situation, it is customary to use crush stiffness values from vehicles of similar wheel base and weight or abandon the crush energy approach altogether. Alternate approaches to calculating vehicle speeds prior to impact, however, often require the use of other undesirable uncertainties. The ideal situation would be for the reconstructionist to have the facility in each case of utilizing crush energy techniques either as a direct method of analysis or as a check on other methods of choice, such as momentum analysis and estimates based on experience. In the method discussed in this paper, the stiffness coefficients for a vehicle that does not have crash test data available are obtained from the equivalence of the principal force between impacting vehicles. In conjunction with a historical review of the damage deformation analysis, appropriate analytical expressions for the principal force are derived based on the stiffnesses of the opposing vehicle for which crash test data does exist. In this way, crush stiffnesses can be obtained for vehicles that have not been tested, and those stiffnesses used in the reconstruction. Furthermore, with this approach, the degree of involvement of hard points such as wheels and suspension members for side impacts, becomes apparent. The analysis some times dictates the use of stiffness coefficients that are higher than those found in the tabular data. This paper presents the analytical basis of the underlying principal force equivalence, the equations utilized, and examples of the approach in reconstructing vehicle accidents.