On the presence of the elastic precursor in re-shock experiment: an unorthodox explanation

According to the stress wave theory, for an elastic-plastic material reloading from the shocked state, the expected response should be entirely plastic because the initial compression beyond the HEL should produce a material state on the yield surface. Experiments show the presence of a step anticipating the arrival of the plastic reloading wave, which is commonly recognized as an unexpected ``elastic precursor.'' Several explanations have been proposed assuming that the shocked material is not on the current yield surface. Lipkin and Asay (1977) justify this assumption with the fact that neighboring grains have different slip system orientations and they proposed a model to duplicate the key features of the shock-re-shock experiment; Swegle and Grady (1986) believed that the phenomenon is due to a thermal trapping localized shear deformation regions. Here, a continuum mechanics approach is used to justify the presence of the step and to demonstrate that it is not an elastic precursor. According to the authors interpretation, a justification of this should be found in the non uniform residual plastic deformation distribution along the target thickness caused by dissipative processes during the first compressive stress wave travel. The proposed interpretation of the phenomenon can explain the reason why the initial part of the release and recompression velocity profiles should not be completely centered as confirmed by experimental observations.