Contact/Impact Dynamics Applied to Crash Analysis

Abstract

The methods for predicting the impact responses of mechanical systems, such as a vehicle’s response in a crash, can primarily be classified into two groups. In one, the impact is treated as a discontinuous event. A simple form of this type of analysis is usually conducted for accident reconstruction purposes for which each vehicle is modeled as a single body or object. For impact analysis of constrained or jointed systems such as a truck-and-trailer, and also for determination of the structural crash responses of the individual components of a mechanical system, such as the impact responses of the vehicle chassis, suspension systems, steering mechanism, etc., the extension of these traditional procedures are presented here, which involve both normal and frictional impulses, for impact analysis of any general multibody mechanical system. This method might sometimes be of limited use, since no significant change must occur in the system’s configuration before and after impact. In the second group of methods used for impact analysis of mechanical systems, the local deformations and the contact forces are treated as continuous. The application of these methods requires the knowledge of the variations of the contact forces. Several models, including nonlinear visco-elastic, Hertzian-based, and visco-plastic models are presented. The suitability of each model depends on the material properties of the surfaces in contact and also the range of impact velocities. The unknown parameters are determined utilizing the energy and momentum considerations. These models are then generalized to the impact between two bodies of a multibody mechanical system. Experimental testing procedures, utilizing a quasi-static approach to measure impact responses of fixed plates and simply supported beams, are conducted for verification of the developed contact force models. Examples, including a two-car side-swipe collision and a complex vehicle rollover are presented as applications of the presented methodologies.