Experimental and numerical investigation of shock-induced full vaporization of zinc

A systematic computational and experimental study is presented on shock-induced full vaporization of zinc resulting from record-high impact speeds recently achieved on the Sandia Hyper-Velocity Launcher. In these experiments, a thin target plate of zinc is impacted by a tantalum flier plate at speeds ranging from 8 to 10.1 km/s, producing pressures from 3 Mbar to over 5.5 Mbar and temperatures as high as 39000 K (similar to 3.4 eV). Such high pressures produce essentially full vaporization of the zinc because the thermodynamic release isentropes pass into the vapor dome near the critical point. To characterize vapor flow, the velocity history produced by stagnation of the zinc expansion products against a witness plate is measured with velocity interferometry. For each experiment, the time-resolved experimental interferometer record is compared with wavecode calculations using an analytical equation of state, called ANEOS, that is known to have performed well at lower impact speeds (less than similar to 7 km/s) where vaporization is negligible. Significant discrepancies between experiment and calculation are shown to exist under conditions of the more recent higher impact speeds in excess of 7 km/s. Numerical predictions underestimate witness-plate velocity for impact speeds up to about 9 km/s but overestimate witness-plate velocity for impact speeds exceeding 9 km/s. This qualitative change in the character of the discrepancy is conjectured to occur when the temperature on the release isentrope at the critical density lies above the critical temperature. These experiments can be used to develop and refine models representing the dynamics of the shock-induced vaporization process.