Comparison of tungsten heavy-alloy rod penetration into ductile and hard metal targets: microstructural analysis and computer simulations

Complete penetration of thick OFHC copper and 7039 aluminum alloy targets by tungsten heavy-alloy rod penetrators at 1.5 km/s impact velocity has been examined by light and electron microscopy. The penetration channel-related microstructures were distinctly different except for a narrow zone of dynamically recrystallized grains at the channel walls. The half-hard OFHC Cu exhibited a hardening beyond the recrystallized zone which was associated with severe grain distortion and evolved into a zone of mixtures of microbands, microtwins and dislocation cells which increased in size as the hardness decreased. The full hard 7039 Al target exhibited a continuous hardness beyond the soft recrystallized zone. A profusion of cracks and adiabatic shear bands composed of dynamically recrystallized grains were distributed along the penetration channel walls. Experimentally measured microhardness maps were compared with computer simulated residual yield stress maps after geometrically valid penetration simulations. These validations were rather poor for the 7039 Al, but qualitative penetration geometries were reasonably well simulated. The occurrence of shear bands appears to be a feature of fully work-hardened targets where dislocation slip is limited.