Different dislocation processes were shown to be operative under high rate loading by impact-induced shock tests as compared with shockless isentropic compression experiments. Under shock loading, the plastic deformation rate dependence of the flow stress of copper was attributed to dislocation generation at the propagating shock front, while in shockless isentropic compression experiments, the rate dependence was attributed to drag-controlled mobile dislocation movement from within the originally resident dislocation density. In contrast with shock loading, shockless isentropic compression could lead to flow stress levels approaching the theoretical yield stress and dislocation velocities approaching the speed of sound. In iron, extensive shock measurements reported for plate impact tests were explained in terms of plasticity-control via the nucleation of deformation twins at the propagating shock front.

Dislocation Mechanics of Copper and Iron in High Rate Deformation Tests. R.W.Armstrong, W.Arnold, F.J.Zerilli: Journal of Applied Physics, 2009, 105[2], 023511