When a shock wave interacts at a metal vacuum interface "ejected particulates" (ejecta) can be emitted from the surface. The mass, size, shape, and velocity of the ejecta varies depending on the initial shock conditions and the material properties of the metal sample. To understand this phenomena, experiments have been conducted at the Pegasus Pulsed Power Facility located at Los Alamos National Laboratory. For the experiments reported in this article, the facility is used to implode a cylinder to a velocity of 3.4 mm/mus. When this cylinder impacts a smaller diameter target cylinder, shock pressures of 30 and 40 GPa can be obtained in Al and Sn metals, respectively. Ejecta formation proceeds as the shock wave in the metal sample interacts at the metal vacuum interface. The size of the ejected particles is then measured using an in-line Fraunhofer holography technique. In this report, ejecta particle size distributions will be presented for shocked Al and Sn metals. The measured particle size distributions exhibit a power law scaling with critical exponents in the same universality class as for two- or three-dimensional percolation theory. The similarity suggests that fragmentation has its origin in an instability that manifests large-scale fluctuations at breakup. (C) 2002 American Institute of Physics. References: 30
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