Deformation effects in shocked metals and alloys

Abstract

Plane wave shock loading produces twins or twin faults in many metals and alloys, and, especially for fcc materials with decreasing stacking fault energy (SFE), a critical twinning pressure (CTP), and crystallographic orientations which control the onset and extent of twinning. The CTP increases with increasing SFE, and is lowest in [001] orientations for fcc. The deformation associated with plane shock is generally within the realm of the plastic regime of the stress–strain diagram. Correspondingly, spherical shock, characteristic of impact cratering, produces large strains through solid state flow and sliding of overlapping shear bands composed of dynamically recrystallised grains, and is therefore only partly encompassed in the realm of the stress–strain diagram. Below this zone for impact craters, and similar to plane shock loading, there is a slip–twinning or slip–microbanding transition in fcc materials, which depends on the SFE; twinning persists for low SFE while microbands dominate in high SFE fcc materials such as nickel or copper. A simple model is used to explain differences in residual microstructures in plane shock loading and spherical shock or impact cratering as they relate to SFE and shock wave geometry. Simple schematics are used to explain the connection between plane shock and spherical shock loading in relation to the stress–strain diagram as a paradigm.