Surface preparation methods to enhance dynamic surface property measurements of shocked metal surfaces

Abstract

This effort investigates surface-preparation methods to enhance dynamic surface-property measurements of shocked metal surfaces. To assess the ability of making reliable and consistent dynamic surface-property measurements, the amount of material ejected from the free surface upon shock release to vacuum (ejecta) was monitored for shocked Al-1100 and Sn targets. Four surface-preparation methods were considered: Fly-cut machine finish, diamond-turned machine finish, polished finish, and ball rolled. The samples were shock loaded by in-contact detonation of HE PBX-9501 on the front side of the metal coupons. Ejecta production at the back side or free side of the metal coupons was monitored using piezoelectric pins, optical shadowgraphy, and x-ray attenuation radiography.

Mass-velocity and size-velocity distributions of ejecta cloud from shock-loaded tin surface using atomistic simulations

“…Typically, pressures of ~ 27 GPa were obtained with explosively driven experiments in references [7][8][9][10][11][12][13][14]. Therefore, what seems the most informative for us is to compare our results with some recently developed ejecta models [1,19], based on the nonlinear evolution of RMI [1,19].…”

“…Indeed, when the release waves issued from the reflection of the shockwave onto the free surface reach the backside of our crystal, the system comes off the piston that was applied to support the shock. Then the crystal becomes isolated, and when the sheets are ejected, it loses a very small part of its velocity (momentum conservation) that can no more be compensated by the piston, unlike what occurs in hydro computations [1,[17][18] and experiments [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] where the samples have "infinite" (very large) dimensions. Other sources may also explain this difference; in particular the conditions of simulation (supported shockwave at extreme pressure).…”

“…Experimentally and numerically, the ejecta cloud has been and continues to be characterized mainly globally, at the continuum level, through the measure of the total amount of ejected mass as a function of the velocity [7][8][9][10][11][12][13][14][15][16] and by using the conservation laws of hydrodynamics in computations [1,[17][18]. From these studies, is now well admitted that the phenomenon is a limiting case of Richtmyer-Meshkov instabilities (RMIs) [1,[19][20].…”

Experimental study of ejecta on lead surface at different loading rates and amplitudes

“…Therefore, a high density layer of material will appear between the high velocity ejection and the free surface. The phenomenon is sometimes described as micro-spall, an effect that enhances ejecta production [1][2][3][4][5]. Currently, the characteristics of micro-jetting parcels, such as the distribution mass density and the velocity and size of particles, are clear when the target remains in solid state under shock compression.…”

“…When the target remains in solid state, rapid ejection of fine fragments usually happens, with the mass ejection linked to surface defects and inhomogeneities, such as surface roughness, inclusions and voids. In such cases, micro-jetting is the main, or the only, ejection source [1]. When melting is initiated on shock compression or on release, the tensile stresses are generated in a liquid state, and a cloud of liquid debris expands from the surface.…”