Spall fracture and twinning in laser shock-loaded single-crystal magnesium

As a major failure process in materials subjected to dynamic loading, spall fracture is one of the most widely studied issues in shock physics. To investigate its dependence on the microstructure, including both initial and shock-induced features, laser shock experiments were performed on single crystal magnesium. Shock loading was applied in directions parallel and perpendicular to the c-axis of the crystals. Both the spall strength and the fracture surface morphology are found to depend on the direction of the shock application with respect to crystal orientations. The results complement data obtained previously over ranges of lower strain rates. A detailed analysis of the residual microstructure and crack patterns in the recovered samples shows strong correlations between damage localization and twins, both pre-existing and shock-induced. Thus, cracks match specific twinning directions, which is discussed on the basis of deformation mechanisms reported under quasi-static loading conditions, either prismatic slip or twinning depending on local orientations. Published by AIP Publishing.