The Linear Elastic-Plastic Vehicle Collision 921073
The well known vehicle planar collision model having constant stiffness is reexamined with the inclusion of elastic rebound after reaching common contact velocity. Quantitative analysis of ground friction and windage shows that they can generally be disregarded for collision impulses involving significant barrier equivalent velocity. On the other hand, elastic rebound is significant at a 30 mph barrier equivalent velocity.
Comparisons of the inputs to analyses which include crush energy and the inputs to analyses which consider only impulse-momentum show that the principal direction of force and the intervehicle coefficient of friction are equivalent estimates. Further, the energy correction for a non-normal impulse in CRASH3 is seen to be an assumption of isotropic stiffness, while the stiffness coefficient commonly described as preload describes the elastic deformation.
While crush energy analyses commonly assume a zero coefficient of restitution, impulse-momentum analyses use an estimate of the coefficient of restitution as an input. The linear elastic-plastic model establishes the coefficient of restitution and the related dynamic (elastic) amplification in a collision as properties of the involved vehicle structures and the collision conditions. The subject vehicle structural properties are determinable from barrier impact tests. These relationships are developed for central normal fixed barrier collisions; and the coefficient of restitution is determined for general vehicle collisions.
Finally, analysis of the crush energy in a two vehicle collision enables the determination of barrier equivalent velocity. This equivalence is developed for fixed and moving rigid barrier collisions.