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It is well known that occupant protection in side impacts involves technical complexities, and the development of effective countermeasures has become more urgent due to recent US Government rulemaking. The additional difficulties of experimental measurement and observation have caused an increased emphasis to be placed on simulation models for side impacts. There are several complex three-dimensional occupant models which provide representations of occupant kinetics, but simulations of the occupant's interaction with the vehicle are not well developed. In contrast, the simpler lumped-mass models are good at simulating vehicle structural dynamics, including door intrusion, but may not model the occupant well (head movements, for example). The present simulation is a lumped-mass model that seeks a middle ground.

In frontal crashes, lateral deformations can occur as a result of various mechanisms. Unfortunately, the crush energy associated with such deformations cannot be assessed as long as the structural properties are unknown. That has been the situation to date, due to the lack of appropriate crash test data. The present research attempts to address this deficit. A passenger car was crash-tested in a mode designed to induce lateral deformations that are significant compared to longitudinal crush. This was done via a series of three repeated impacts on the same vehicle so as to obtain, in a cost-effective manner, structural characterization data at increasing crash severities. Various cause-and-effect relationships (structural characterization models) were considered with an eye to selecting the one that best predicts the crush energy. Insights obtained from analyzing the behavior of the front structure are presented.

Crush energy assessment methods rely on the characterization of a vehicle’s structure, through a comparison with crash tests of a similar vehicle. For frontal impacts, the vast majority of these tests involve a flat rigid barrier. When the reconstructionist is presented with a frontal underride/override crash, however, the structural load pattern and the deformation mode suggest that the comparison with flat barrier tests may not be valid. This has been confirmed by prior studies. With few exceptions, for any given vehicle, there are no crash data in an underride/override mode that are useful for analysis purposes. The purpose of this research was to bridge the gap so that flat barrier data, specific to the vehicle in question, could be applied to underride/override cases. This entailed the development of a measurement protocol, a structural model for such crashes, and a procedure for analyzing the load cell data that exist for many barrier crash tests.

A key aspect of accident reconstruction is the calculation of how much kinetic energy is dissipated as crush. By far the most widely used methods are derivatives of Campbell’s work, in which a linear relationship between residual crush and closing speed is shown to imply an underlying linearity between force and crush. “Consant-stiffness model” is the term used for such a representation of structural behavior. Difficulties arise, however, when significant non-uniformities are present in the crush pattern (as in narrow-object and/or side impacts, for example). The term “residual crush” becomes more ambiguous. Do we mean maximum crush, area-weighted average crush, or some other measure of residual deformation? And is it sufficient to represent the non-uniform crush pattern by a single parameter? Such considerations led to a re-development of the fundamental structural models, with an eye to determining whether the classical constant-stiffness model is the most appropriate.