Expanded Characterization of Force-Deflection Properties of Vehicle-to-Vehicle Systems

This paper reports on seventy additional tests conducted using a mechanical device described by Bonugli et al. [4]. The method utilized quasi-static loading of bumper systems and other vehicle components to measure their force-deflection properties. Corridors on the force-deflection plots, for various vehicle combinations, were determined in order to define the system stiffness of the combined vehicle components. Loading path and peak force measurements can then be used to evaluate the impact severity for low speed collisions in terms of delta-v and acceleration. The additional tests refine the stiffness corridors, previously published, which cover a wide range of vehicle types and impact configurations. The compression phase of a low speed collision can be modeled as a spring that is defined by the force-deflection corridors. This is followed by a linear rebound phase based on published restitution values [1,5]. Load cell barrier data obtained through NHTSA’s Load Cell Analysis toolbox was compared with the stiffness corridors from the quasi-static loading and incorporated into a novel method for assessing low speed collisions. This method allows the reconstructionist to use vehicle specific stiffness properties from barrier testing in order to further refine the analysis. The NHTSA based stiffness values are derived from the initial or “toe” region of the vehicle’s force-deflection plot. When used in series with the stiffness corridors they can be used to approximate the spring constant of the system.