Laser Shock Compression of Copper Monocrystals: Mechanisms for Dislocation and Void Generation

Copper with two orientations ([001] and [134]) was subjected to high intensity laser (energy levels of 40-300 J; energy densities of 15-70 MJ/m and durations below 10 ns). The defects created are characterized by transmission electron microscopy. An orientation-dependent threshold stress for twinning is observed. The results are rationalized in terms of a criterion in which slip and twinning are considered as competing mechanisms. A constitutive description is applied to the two orientations, incorporating both slip and twinning. The predictions are in agreement with experiments. The threshold stress for twinning in the [001] orientation is 20-40 GPa, whereas the one for the [134] orientation is 40-60 GPa. The threshold stress is calculated, considering the effect of shock heating. The constitutive description provides a rationale for the experimental results; the calculated thresholds are 18 GPa for [001] and 25 GPa for [134]. A mechanism for void generation and growth based on the emission of geometrically necessary dislocations is proposed and analytically formulated.