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CRASH3 based computer programs model a vehicle structure as a homogeneous body. Crush stiffness coefficients determined from full-overlap crash tests, when used in these computer programs allow for an accurate reconstruction of collisions where the accident damage profiles are full-overlap. The structures of vehicles, however, might not be purely homogeneous in their crush response. How accurately do crush stiffness coefficients that were determined from full-overlap crash tests represent the crush response of that same vehicle in a partial-overlap/offset frontal collision? Before this question can be answered a method needs to be developed for determining crush stiffness coefficients from partial-overlap/offset frontal test collisions. These crush stiffness coefficients then could be used in a comparative analysis of the crush response of vehicles tested in both full-overlap and partial-overlap/offset frontal collisions.

A revision of the modeling of restitution properties in the SMAC computer program and the introduction of restitution properties in the CRASH3 program have been proposed by McHenry [1], the author of M-CRASH and M-SMAC [2]. The accuracy of an accident reconstruction, which uses the proposed restitution model, is directly related to the accuracy of the crush stiffness coefficients employed. The ideal condition for determining crush stiffness coefficients for these programs requires crash tests of a vehicle structure through a wide range of impact speeds with a rigid barrier. Reports from these crash tests should contain the usual data found in NHTSA crash test reports plus rebound velocity and maximum dynamic crush. Unfortunately, such comprehensive tests are very rare. As a result, certain vehicle properties need to be generalized from the existing available crash tests. These generalized properties can then be used to calculate crush stiffness coefficients for these programs.

The CRASH3 computer program increasingly is being used by engineers as a tool to reconstruct automobile accidents. The damage analysis portion of CRASH3 provides a useful means for quantifying the change of velocity, ΔV, that was experienced by a vehicle during the collision phase of a traffic accident. The degree of usefulness of the damage analysis portion of the program, however, is dependent upon the availability of valid crush stiffness coefficients. Published crush stiffness coefficients are available for a large number of vehicles *[1] & [2]. These publications, however, contain only a limited number of coefficients that describe the stiffness characteristics of the side structure of vehicles. Engineers are often asked to perform an accident reconstruction when there are neither published stiffness coefficients for the side structure of an involved vehicle nor crash test data from which to determine the stiffness.

The CRASH3 computer program models a vehicle structure as a homogeneous body with linear force-deflection characteristics. Crush stiffness coefficients determined from full-overlap crash tests, when used in this computer program, allow for an accurate reconstruction of collisions where the accident damage profiles are full-overlap. In the past, partial-overlap frontal crash tests were not performed. The lack of partial-overlap frontal crash tests meant that a reconstructionist only had crush stiffness coefficients available that were determined from full-overlap frontal crash tests. In a reconstruction, the assignment of stiffness coefficients to a partial-overlap damage profile required engineering judgement. Often the basis of such judgement was questioned because of the lack of supporting partial-overlap test data. Recently partial-overlap crash tests have been performed and the test data has been made available to the public.

The accuracy of an accident reconstruction, which employs the damage analysis feature of the CRASH3 computer program, is directly related to the accuracy of the crush stiffness coefficients employed. Crush stiffness coefficients, however, are available only through a limited number of publications and for a limited number of vehicles. In addition, assumptions made in the determination of these published stiffness coefficients bring their accuracy into question and, as a result, limit their value to a reconstructing engineer. It is concluded, therefore, that an engineer must use a critical eye when viewing the results of a CRASH3 reconstruction in which these stiffness coefficients were employed. A method is set forth for quantifying stiffness coefficients from crash test data available in a database which can be obtained from the National Highway Traffic Safety Administration (NHTSA).