Plate impact investigation of the dynamic response of commercial tungsten carbide under shock-induced compression and combined compression-and-shear loading

Abstract

This article presents results from a series of plate-impact experiments designed to study dynamic response of commercial purity (99.6%) tungsten carbide (WC) under shock-induced normal compression and simultaneous compression-and-shear stress wave loading. The normal shock compression experiments utilize a heated WC flyer plate which impacts a WC target at room temperature, enabling inelastic response of the WC target plate as well as the elevated temperature shock-impedance of the heated WC flyer plate to be probed simultaneously. The measured normal particle velocity profiles at the free surface of the WC target plate exhibit an elastic precursor, which corresponds to a longitudinal stress of ∼5.9–6.2 GPa, and decreasing particle velocity levels in the shocked state with increasing temperature of the WC flyer. The shock impedance of the heated WC flyer is estimated to decrease from 1.05 × 108 to 8.23 × 107 kg/m2s over the temperature range 23–600°C. The simultaneous compression-and-shear loading experiments are conducted using a symmetric oblique plate-impact experimental configuration with progressively increasing angles of inclination (5°, 10°, and 22°), resulting in increasing shear to longitudinal stress ratios upon impact in the WC flyer and target plates. The measured longitudinal and transverse components of the free surface particle velocity in experiments with inclination angles of up to 10° and impact velocities ∼100 m/s (corresponding to shear and longitudinal stress levels of 0.5 GPa and 4.5 GPa, respectively), coincide well with their corresponding elastic particle-velocity predictions. However, the free-surface normal particle velocity profiles for experiments conducted at an oblique impact angle of 22° (corresponding to shear stresses ∼1.3 GPa and longitudinal stress of ∼4.9 GPa) are remarkably different and exhibit a sudden increase in particle velocity from their plateau levels reminiscent of failure waves observed by other investigators in soda lime glass and silicon carbide (SIC-B). The new normal particle velocity level, after the arrival of the recompression/re-acceleration signal, exceeds the magnitude of the impact velocity, suggesting failure of the WC target plate during the stress wave loading process. The relatively large undulations present in the measured free-surface transverse particle velocity profiles provide further evidence for the heterogeneous brittle failure processes in WC under the resulting simple-shear state of stress, and is used to provide estimates for the critical range of simple-shear loading that can initiate catastrophic failure (fracture) in pure WC.