COMPRESSION-INDUCED HIGH-STRAIN RATE VOID COLLAPSE, TENSILE CRACKING, AND RECRYSTALLIZATION IN DUCTILE SINGLE AND POLYCRYSTALS

A series of dynamic compression experiments were performed on single-crystal and polycrystal copper specimens, as well as on mild steel (AISI 1018 steel) and pure iron, containing pre-existing cavities, using the split Hopkinson compression bar. It is found that void collapse occurring under purely compressive axial loading leads to tensile cracking (presumably upon unloading). Microcracks are nucleated at intersections of slip planes, growing along slip lines as well as in the general direction normal to the applied compression. The resistance to void collapse in loading and the extent of fracturing in unloading increase with increasing overall nominal rate of compressive loading. For pure copper single crystals, recrystallization occurs when the strains and strain rates are sufficiently high. Tensile cracks are then observed to grow into the newly formed crystal grains.