Experimental investigation of liquid spall in laser shock-loaded tin

Abstract

When a metal is shocked above its melting pressure or melted on release, the tensile stresses generated upon reflection of the compressive pulse from a free surface are induced into a liquid state. Instead of the well-known spallation process observed in solid targets, cavitation is expected in the melted material, and liquid fragments are ejected from the free surface. Their size, velocity, and temperature distributions are issues of increasing interest, as well as their impact on other nearby materials, but data are limited on the subject. Here, we present an experimental study performed on tin samples subjected to high pressure laser shocks (ranging from about 50to200GPa) of short duration (∼5ns). The results include post-test observations of the ejecta recovered after impact on a polycarbonate shield and time-resolved measurements of the free surface velocity through the shield. For shock pressures below some 80GPa, the velocity profiles are compared to the predictions of one-dimensional simulations involving a multiphase equation of state. For higher loading pressures, the emergence of the shock at the free surface produces a rapid loss of reflectivity so the particle velocity cannot be determined. In all cases, solidified fragments of tin are recovered on the shield. Their sizes, their shapes, and the induced damage depend significantly on shock pressure, and are indicative of a very wide range of ejection velocities. The data provide a basis for a phenomenological description of the process.

Foreword to the Special Issue on Ejecta

“…For example, ejecta from materials shock loaded with a laser drive were reported [32], where the researchers studied fragmentation of Sn, even capturing the fragments for post experimental reconstruction of the size and fragmentation patterns. Another sizing diagnostic, an optical microscope, was reported in [33].…”

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

“…For example, velocity interferometer system for any reflector (VISAR) measurements fail [2,3], and the reflectivity of the shocked sample changes greatly [4]. In this paper, we report on experiments to understand these changes.…”

Exploration of the fragmentation of laser shock-melted aluminum using x-ray backlighting

“…If the incident shock wave-pulse has a triangular-or Taylor-shaped profile, tensile stress will be generated immediately when the shock wave reflects from the sample's free surface, leading to successive fragmentation of the sample and the formation of a cloud of solid debris and/or fine droplets that are ejected from the sample with high velocity. This process, referred to as microspalling by some authors, 1,2 has been of increasing interest because of its scientific and engineering significance. [3][4][5][6][7][8][9] However, high-quality experimental work on the subject remains limited and experimental data, such as the mass distribution of the fragmentation products in space, particle size distribution, successive evolution of the fragmentation product topology and the thermodynamic states, are quite sparse.…”