Different dislocation processes are shown to be operative under high rate loading by impact-induced shock tests as compared with shockless isentropic compression experiments ͑ICEs͒. Under shock loading, the plastic deformation rate dependence of the flow stress of copper is attributed to dislocation generation at the propagating shock front, while in shockless ICEs, the rate dependence is attributed to drag-controlled mobile dislocation movement from within the originally resident dislocation density. In contrast with shock loading, shockless isentropic compression can 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 are explained in terms of plasticity-control via the nucleation of deformation twins at the propagating shock front.

The constitutive deformation behavior of copper, Armco iron, and tantalum materials is described over a range of strain rates from conventional compressive/tensile testing, through split Hopkinson pressure bar (SHPB) test results, to shock-determined Hugoniot elastic limit (HEL) stresses and the follow-on shock-induced plasticity. A mismatch between the so-called ZerilliArmstrong (Z-A) constitutive equation description of pioneering SHPB measurements for copper provided initial evidence of a transition from the plastic strain rate being controlled by movement of the resident dislocation population to the strain rate being controlled by dislocation generation at the shock front, not by a retarding effect of dislocation drag. The transition is experimentally confirmed by connection with Swegle-Grady-type shock vs plastic strain rate measurements reported for all three materials but with an important role for twinning in the case of Armco iron and tantalum. A model description of the shock-induced plasticity results leads to a pronounced linear dependence of effective stress on the logarithm of the plastic strain rate. Taking into account the Hall-Petch grain size dependence is important in specifying the slip vs twinning transition for Armco iron at increasing strain rates.

Fragmentation of metal casings is an important issue in a variety of problems like weapon effectiveness, safety distances or collateral damage. To be able to describe the intended or unintended effects of naturally fragmenting shells, one needs to know the mass distribution of the fragments produced after detonation of the explosive charge. In the present study the fragmentation behavior of very light and heavier casings has been investigated. The data collection method is outlined and applied to the fragment mass distribution of four different shells. The results are given in diagrams. It was found that an existing fragmentation model adequately predicts the dependence of circumferential fragment size on material strength. Fracture in axial direction should also be considered to predict correct fragment masses, but currently a suitable model for this purpose is not available.

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