A meso-model of spalling with thermal coupling for hard metallic materials

Study and modeling of physical mechanisms of spalling observed via plate impact experiments for two industrial alloys are the subject of this paper. Because spalling is a specific kind of fracture, which is loading history dependent, the aspects of the initial microstructure and its evolution during plastic deformation are very important. In order to understand better the physical mechanisms of spall, numerous scanning electron microscopy pictures of the free surface created by spalling have been taken for two materials, a hard aluminum alloy and an armor steel. It has been confirmed that the microstructure has a direct influence on the mechanism of nucleation, growth and coalescence of micro-cavities or micro-cracks by means of distribution of nucleation sites and decohesion between the harder particles and the softer lattice. The results of measurements in the form of statistical distribution of horizontal micro-segments of fractured surfaces of targets, corresponding to quasi-brittle fracture, and vertical micro-segments, corresponding to ductile or adiabatic shear banding, all along the entire cross-section of a target, are reported for armor steel. As a result a new model has been proposed, based on the meso-scale approach. The model is in agreement with physical mechanisms which are present during spall fracture.