Ejecta velocities from twice-shocked metals

We extend a recently proposed velocity model for spikes¹ to the situation in which the metal is shocked successively by two shocks originating in the dense material. The velocity model is
empirical, and accounts for the modification of the ejecta velocity due to initial amplitudes,
curvature and Mach number effects. The model has been validated extensively by comparison
with numerical simulations and published experimental data. In this work, we present an extension to ejecta from twice-shocked metals, where we find that taking the effective wavelength of the bubble in the model produces the most favorable comparison with data. Specifically, we compare with detailed continuum hydrodynamics and molecular dynamics simulations using the FLASH² and SPASM³ numerical codes. Experimental data is obtained from target experiments in which two successive shocks were generated using a specially designed physics package⁴, while the ejecta velocities were measured using LDV techniques.
¹V. Karkhanis et al., J. Appl. Phys., 123, 025902 (2018).
²B.Fryxell et al., Astrophys. J. Suppl. Ser., 131, 273 (2000).
³K. Kadau, T.C. Germann, and P.S. Lomdahl, Int. J. Mod. Phys. C 17, 1755 (2006).
⁴W.T. Buttler et al., J. Appl. Phys., 116, 103519 (2014).