Comparison of tungsten carbide penetrator impact behavior in soft and hard copper targets

摘要

The cratering effects of dense tungsten carbide spheres (3.175 mm diameter and a density of 15 g/cm~3) impacting hard (0.89 GPa) and soft (0.7 GPa) copper targets (density of 8.9 g/cm~3) at velocities from 0.55 km/s to 2 km/s have been examined in comparison to similar impact conditions for soda-lime glass (2.2 g/cm~3) and ferritic stainless steel (7.8 g/cm~3) projectiles in previous studies. This range of impact velocities (0.55 to 2 km/s) illustrates a penetration anomaly where maximum values of crater depth (p) to crater diameter (D_c) ratio (or p/D_c) near 1 km/s are roughly 1.4 and 1.7 for hard and soft copper respectively. This is in contrast to an expected threshold or steady-state value of < 1 at hypervelocities ( > 5 km/s). These values also differ greatly from p/D_c values of ～0.9 at 1 km/s impact velocity for the stainless steel/copper system, where the hypervelocity threshold was observed to be p/D_c = 0.6. The hard copper targets were characterized by an equiaxed grain size of 85 μm and a dislocation density of ～10~(10) cm~(-2) while the soft plates were cast copper plates with a large, columnar grain structure (grain size 3.2 mm) and a dislocation density roughly two orders of magnitude less than the hard copper target The microstructures (observed by light metallography and transmission electron microscopy) surrounding the crater walls are characterized by dynamic recrystallization zones and microbands extending away from this narrow flow zone, and these zone widths increased with impact velocity and corresponding shock pressures. Residual hardness mapping was also performed on selected samples. These maps reveal a difference in affected zone size between hard and soft copper, as does the microstructure.