Influence of Defects on the Shock Hugoniot of Tantalum*

Using molecular dynamics simulations, we investigate the effect of vacancies and dislocations on the dynamic response of single crystal tantalum to shock loading. A Hugoniostat technique is employed, for which a series of states along the Hugoniot are sampled by many individual simulations. We show that defects have a limited effect on the shock/particle velocity relationship and that the shock pressure/volume relationship can be well predicted by taking into account the changes in the initial density and sound speeds of the samples. The principal effect of initial defects is the activation of heterogeneous dislocation nucleation and expedited dislocation multiplication during shock. The heat generated by plastic work, caused by defects moving through the lattice, is substantial. The result is significantly divergent final shock temperatures for different initial defect concentrations and pronounced changes in the resultant shock melting temperatures. The motion of dislocations also leaves behind a inconsequential concentration of vacancies that is quantified.