Vehicle stiffness assessment for energy loss evaluation in vehicle impacts

The energy loss in a vehicle-to-vehicle impact is an important compatibility indicator between the real event and the reconstruction made by the expert. For its estimate, stiffness characteristics for the vehicle are typically referred to, evaluated by the residual deformation obtained in a crash test. In frontal vehicle into rigid barrier crash tests, residual deformation on the vehicle front is generally measured as the bumper displacement in respect to its undeformed shape; nevertheless, in real crashes, the bumper is subject to restitution which differs from the rest of the vehicle structure, or is often detached. For these reasons, the present work proposes a methodology for vehicle stiffness calculation based on the dynamic crush experienced by the vehicle in a crash test; this datum is independent from bumper restitution. To apply the methodology, a video analysis approach is proposed for the derivation of dynamic crush: dynamic crush can be obtained without the processing of accelerometer signals, which are not always publicly available from consumer programs. The proposed video analysis approach represents a valid alternative to already existing procedures, because of its superior accuracy. By application of this approach to dynamic crush calculation in some crash tests, the drawbacks deriving from the possible use of residual deformation of the bumper are shown; consequently, it is highlighted how residual deformation measures should be cautiously employed in the accident reconstruction process.