Ejecta particle size distributions for shock loaded Sn and Al metals

Abstract

Abstract. When a shock wave interacts at the surface of a metal sample "ejected matter" (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 target. To understand this phenomena, experiments have been conducted at the Pegasus Pulsed Power Facility (PPPF) located at Los Alamos National Laboratory (LANL). The facility is used to implode cylinders to velocities of many mm/msec. The driving cylinder impacts a smaller target cylinder where shock waves of a few hundreds of kilobars can be reached and ejecta formation proceeds. The ejecta particle sizes are measured for shock loaded Sn and Al metal samples using an in-line Fraunhofer holography technique. The distributions will be compared to calculations from 3 and 2 dimensional percolation theory.

A new method for large scale molecular dynamics simulations of shock-induced ejecta production

“…excluding the largest aggregates), the number N of aggregates as a function of radius R follows the scaling law: This scaling law is consistent with 2D percolation theory. Indeed, many experimental and theoretical studies show that clusters production seems to be a universal mechanism that is remarkably well reproduced with the framework of percolation theory [10]. This theory suggests that the production of ejecta clusters is due to large scale fluctuations present near a critical point, with no dominant characteristic scale.…”

High-resolution UV relay lens for particle size distribution measurements using holography

“…2,3 Holography offers the unique capability to record distributions of particles over a 3-D volume. We applied a holographic technique to measure ejecta particle size distributions for shock-loaded Sn over phase space that covers well below melt, near melt, and well above melt conditions.…”

“…Earlier attempts at collecting particle size distributions onto holograms used a high-resolution lens with 1000 lp/mm resolution. 3 A 532-nm pulsed laser exposed the hologram with 50 mJ of energy in 80 ps. This high-resolution lens consisted of two lens groups, each with five elements that required precision alignment.…”

A three-dimensional numerical simulation of particle-gas mixing in an ejection with a spherical sample surface

“…And the correctness factor of compressibility is introduced to original drag coefficient to reflect high Mach number characteristics. The initial location, velocity and size of each ejecta particle are modeled and simplified according to references data [2,5]. As gas computation is concerned, third order piecewise parabolic method [11] is adopted.…”

“…Ejection is an important issue in shock dynamics [1][2][3][4], which happens as strong shock reflects at free surface of metal material sample. Interaction between shock and the inhomogeneous or disfiguration around the free surface will cause the material to form microjets, fragmentations, micro-spallation, shock-melting, unload-melting and other processes, and furtherly form ejection [5].…”