Crush Energy Assessment in Frontal Underride/Override Crashes 2009-01-0105
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.
The measurement protocol was derived from a series of ten crash tests (the Volpe tests) conducted by the National Highway Traffic Safety Administration, in conjunction with the Volpe Transportation Research Center. It was found crush energy could be apportioned to various parts of the structure, and that the total crush energy was well predicted from the load cell barrier (LCB) data.
The structural model was based on observations of vehicles actually involved in underride/override crashes, in addition to results that have been reported in the literature. Such crashes indicated the existence of shear deformations and the corresponding shear deformation energy. A model was postulated so as to account for shear energy. The model was applied to all the underride/overrride fixed-object crashes that are reported in the literature and known to the authors. Comparison of the Energy Equivalent Speeds showed agreement as good as in full-width barrier impacts, subject to certain limitations of crash severity range.