Numerical and experimental evaluation of the coefficient of restitution for repeated impacts

In this paper, a method to evaluate the coefficient of restitution for multiple impacts between material bodies is presented. The loss of kinetic energy which is described by the coefficient of restitution is due to the initiation of waves and plastic deformation of the colliding bodies. Especially in the case of slender bodies a large amount of energy is transformed into waves. For the numerical investigation a combination of a modal approach describing the global elastodynamic behavior of the bodies and a finite element model for the contact region, including the effects of plasticity, is used. The investigation includes repeated impacts with identical initial conditions with the exception of the deformation history of the contact region due to previous impacts. The simulations of repeated impacts on different aluminum rods show, due to plastic deformation of the contact area and the resulting residual stresses, an increase of the coefficient of restitution with the number of impacts until a stationary value is reached. Finally, plastic deformation does not spread out and all energy loss is due to wave propagation. The numerical investigations are verified by experiments.