Werner Arnold

Dislocation mechanics of copper and iron in high rate deformation tests

Different dislocation processes are shown to be operative under high rate loading by impact-induced shock tests as compared with shockless isentropic compression experiments (ICEs). 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.

DISLOCATION MECHANICS OF IRON AND COPPER IN HIGH RATE DEFORMATION TESTS

For shocked iron, there is competition between grain size dependent slip or deformation twinning responses at the Hugoniot elastic limit (HEL) while, at higher stress, there is predicted control of the shock‐induced plastic strain rate by the grain size independent generation at the propagating shock front of relatively high density deformation twinning structures. The obtainment of isentropic compression experiment (ICE) results on copper differ from the shock case on a physical mechanism basis in that the initially resident, much lower, dislocation density is required to “carry the load” by moving at very high drag‐resisted velocities.

DISLOCATION MECHANICS UNDER EXTREME PRESSURES

Dislocation effected plastic flow stress levels in shock experiments are accounted for in terms of control by defect creation at the shock front: in the fcc case, of a high dislocation density; and, in the bcc case, of deformation twins. Isentropic compression experiment (ICE) results differ in that the initially resident, much lower, dislocation density is required to “carry the load” by moving at very high drag‐resisted velocities.

An Analytic Model of Close‐Range Blast Fragment Loading

The effects of blast‐fragmentation warheads need to be carefully characterized in a variety of applications like passive and active vehicle protection or hard target defeat and TBM defense. With these applications in mind, we have developed a collection of tools called FI‐BLAST (Fast Interface for Blast‐Fragment Load Analysis of Structures). In the present paper we describe the essential part of these tools, namely the close range blast‐fragment model. The meaning of “close range” is here defined as the standoff to a charge at which blast effects can inflict serious damage on massive structures. In order to quantify our model’s range of validity, examples of measured and calculated momentum of bare and confined charges are given in the present paper. Short (L/D = 0.5) and long (L/D = 5) cylindrical charges are included as well as spherical charges. The presented examples demonstrate that the model gives reasonable results in the intended domains of application.