Surface Specularity as an Indicator of Shock-Induced Solid-Liquid Phase Transitions in Tin

Abstract

Abstract. When highly polished metal surfaces melt upon release after shock loading, they exhibit features that suggest significant surface changes accompany the phase transition. The reflection of light from such surfaces changes from specular (pre-shock) to diffuse upon melting. Typical of this phenonmenon is the loss of signal light in velocity interferometer system for any reflector (VISAR) measurements, which usually occurs at pressures high enough to melt the free surface. Unlike many other potential material phase-sensitive diagnostics (e.g., reflectometery, conductivity), that show relatively small (1%-10%) changes, the specularity of reflection provides a more sensitive and definitive (>10x) indication of the solid-liquid phase transition. Data will be presented that support the hypothesis that specularity changes indicate melt in a way that can be measured easily and unambiguously.

A molecular dynamics study of the role of grain size and orientation on compression of nanocrystalline Cu during shock

“…The Hugoniot state (the equilibrium state behind the shockwave front) and solid-liquid phase transformations have been extensively studied over the last several decades using molecular dynamics (MD) simulations and experimental methods [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. For example, Bringa et al [3] investigated the Hugoniot state during shock of single crystal copper along several different crystallographic directions for Hugoniot pressures between 2 and 800 GPa and reported that the shock velocity magnitude as a function of particle velocity was anisotropic.…”