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Impact Analysis Based Upon the CRASH3 Damage Algorithm

950358

James A. Neptune, James E. Flynn, Howard W. Underwood, and Philip A. Chavez

J2 Engineering, Inc.

ABSTRACT

The accuracy of an accident reconstruction is dependent upon the availability and quality of relevant data. Often by the time an engineer is asked to reconstruct a traffic accident the only source of scene data is a police report. Important scene data, such as the point of impact and the points of rest of the vehicles, usually are set forth in the police report. Occasionally, however, the points of rest are not indicated in the police report and they can not be determined by other means.

in a typical scenario a left turning "target" vehicle is struck an its right side by the front end of a "bullet" vehicle. The vehicles are available for inspection and the configuration of the roadway at the scene has not been altered since the time of the accident. The point of impact is set forth in the police report, however, the points of rest of the vehicles are not specified. No other sources of information regarding the points of rest of the vehicles are available.

This lack of data limits the engineering models that can be used to analyze the accident and quantify the impact velocities of the vehicles. The absence of information regarding the post impact trajectories of the vehicles prevents the modeling of the vehicles as particles and the use of conservation of linear momentum. The CRASH3 linear momentum analysis, which models the vehicles as rigid bodies, is not useable since it also requires the post impact trajectories of the vehicle to be known. The application of conservation of energy also can not be used as a means to quantify the speeds at impact due to the post impact kinetic energies of the vehicles being unknown.

A method is set forth in this paper that will allow a quantification of the impact velocity of the bullet vehicle. The method is based on the rigid body dynamics of the CRASH3 damage algorithm and analyzes the momentum exchange at impact. The condition of a common velocity occurring at the impulse center of the damage is an essential component of the method. The method requires an estimation of the impact velocity of the target vehicle.

The estimated impact velocity, in conjunction with the calculated change of velocity, DV, of the target vehicle, are used to solve the velocity polygon located at the impulse center of the target vehicle. This provides a quantification of the common velocity vector, V_common. The common velocity vector is then used, in conjunction with the calculated DV of the bullet vehicle, to solve the velocity polygon located at the impulse center of the bullet vehicle. This results in a quantification of the impact velocity vector of the bullet vehicle.