Micromechanical strength effects in shock compression of solids

Time‐resolved shock‐wave measurements and post‐shock recovery techniques have long been used as means of inferring the underlying micromechanics controlling high‐rate deformation of solids. This approach requires a considerable amount of subjective interpretation. In spite of this feature, progress has been made in experimentation and theoretical interpretation of the shock‐compression/release cycle and some of the results are reviewed here for weak shocks. Weak shocks are defined to be those with peak amplitudes (typically 10–20 GPa for most solids) that do not overdrive the elastic precursor. The essential elements of a typical shock‐compression/release cycle involve, in order, (a) the elastic precursor, (b) plastic loading wave, (c) pulse duration, (d) release wave, and (e) post‐mortem examination. These topics are examined in turn, with some emphasis given to elements (b) and (d). If the plastic loading wave is traveling without change of shape, it is possible to convert the particle‐velocity/time records to a shear‐stress/plastic‐strain‐rate path. Shock data in this form can be compared directly with low‐to‐intermediate strain‐rate tests. Results for copper and tantalum show how shock data can be used to determine the transition from the deformation mechanism of thermal activation to that of dislocation drag. An important result of release‐wave studies is that the leading observable release disturbance in FCC metals may not be propagating with the ideal, longitudinal elastic‐wave speed, but at a lower velocity dependent on the elastic bulk and shear moduli and the product of the dislocation density times the pinning separation squared for dislocation segments in the region behind the shock and ahead of the release wave.