The Interplay between Dislocation Nucleation and Glide in the origin of the Hugoniot Elastic Limit Spike and Precursor Decay

A common feature in plate impact experiments in annealed body-centered cubic (BCC) metals at room temperature are the “spike and valley” shape of the elastic precursor wave, as well as the decay of the precursor wave called “elastic precursor decay”. In this work, we propose a dislocation-based multiscale continuum strength model that can capture these distinct features. We propose that the origin of these features is in the interplay between dislocation nucleation and dislocation glide. We employ the overstress framework with dislocation glide rules, extracted from atomistic simulations, and we incorporated an Arrhenius-type, stress-dependent, homogenous dislocation nucleation term. Our simulations shed light on the origin of the elastic precursor decay and its fine details. We show that in the early stages of plastic deformation the spike and valley are controlled by dislocation nucleation rather than dislocation glide. As the shock propagates into the specimen, the strain rate decreases, and the relative contribution of dislocation glide to the stress relaxation increases, diminishing the contribution of dislocation nucleation. As a result, the spike and valley vanish and the amplitude of the elastic precursor decays until reaching a steady-state value above a certain propagation distance. The nucleation parameters are calibrated using a metamodel optimization technique using two plate impact experimental results of annealed Ta and V. Using the fitted model we show how the initial microstructure density and temperature affect the elastic precursor evolution, in accordance with experimental results.