Y. Girard

Shock Enhancement due to Shock Front Propagation in Cellular Materials

In this study, crushing experiments are performed on four kinds of cellular materials using a large diameter (60 mm) nylon Hopkinson bar. The impact velocities are chosen around the critical velocity corresponding to the occurrence of a shock front predicted by the classical RPPL model (Reid and Peng, 1997). The experimental setup allows to measure the stress enhancement due to the shock front propagation. In particular, for one type of material, a high speed camera is used to capture about ten images at 20,000 fps and then the strain field during testing is obtained by a special image correlation program (CorreliLMT). This strain field allows to measure directly the shock front velocity. Moreover, an improved model, including the hardening curve, is proposed to predict this shock enhancement. Finally, numerical analyses using Ls-Dyna explicit code show that for all experiments a macroscopic homogeneous phenomenological material law can reproduce essential features of stress enhancement due to shock front propagation.