Shock and High-Strain Effects and other Shocking Effects in Materials

In the early 1960s, a novel fixture designed by Penn State colleagues Fred Grace and Frank Rose allowed thin plates of metals and alloys to be exposed to a range of plane-wave shock pressures and then recovered for observations in the transmission electron microscope(TEM). These observations clearly demonstrated that stacking-fault free energy plays a role in the evolution of dislocation, stacking fault, and twin microstructures in fcc metals and alloys. Correspondingly, and for extreme strain and strain-rate deformation in explosive welding, forming, impact cratering, and rod penetration in metals and alloys, as well as processes like friction-stir welding, all exhibit dynamic recrystallization, which accommodates solid-state shear flow. This occurs by vortex and microband/shearband development, independent of stacking-fault free energy or related fundamentals; observed by optical and electron metallography.

Even more fundamental deformation studies in metals and alloys reveal that there are no UFOs (Unidentified Fundamental Observations) in materials sciences. TEM studies in particular show clearly that Frank-Read sources producing dislocations in grain centers are a perpetual myth. Grain boundary and other interfacial (including surfaces) ledges provide strain-activated dislocation sources, and dislocation propagation is controlled by stacking -fault free energy in fcc metals and alloys as observed by systematic TEM studies.