This effort investigates the relation between ejecta production and shock-breakout pressure (PSB) for Sn shocked with a Taylor shockwave (unsupported) to pressures near the solid-on-release/partial melt-on-release phase transition region. The shockwaves were created by detonation of high explosive (HE) PBX-9501 on the front side of Sn coupons. Ejecta production at the backside or free side of the Sn coupons was characterized through use of piezoelectric pins, optical shadowgraphy, x-ray attenuation radiography, and optical-heterodyne velocimetry. Ejecta velocities, dynamic volume densities, and areal densities were then correlated with the shock-breakout pressure of Sn surfaces characterized by roughness average of Ra=16 μin or Ra=32 μin.

Effects of shock-breakout pressure on ejection of micron-scale material from shocked tin surfaces

http://absimage.aps.org/image/SHOCK07/MWS_SHOCK07-2007-000101.pdf

Effects of Shock-Breakout Pressure on Ejection of Micron-Scale Material from Shocked Tin Surfaces

Ejecta production from the free surface of metals under shock loading is investigated using large-scale molecular dynamics (MD) simulations performed with a new (hybrid) method. A copper crystal, in contact with vacuum and with a sinusoidal surface finish representative of the roughness produced by a machine polishing, is divided in two zones, bulk and surface, calculated with, respectively, Hugoniostat and NVE ensembles. The bulk part is simulated using the Hugoniostat technique, which allows a very large number of particles to reach a Hugoniot equilibrium state in a short physical time by the mean of a quasi-equilibrium MD simulation. The surface part is simulated with the NVE ensemble (microcanonical ensemble in which the total number N of particles, the total volume V, and the total energy E of the system are constant) in order to account for the non-equilibrium character of the ejection process. With this method, the morphology and the size distribution of the ejecta cloud generated by a system with 125 × 106 atoms are studied over 1 ns. The simulations show that the ejection phenomenon tends toward a steady state on long times (typically above 200 ps). The ejected particles remain spherical with time and their size distribution exhibits a power law scaling followed by a large-size residual in the large size limit. This behavior is in good agreement with most of distributions measured in fragmentation processes. In particular, the power law scaling reflects a self-similar behavior which seems to be successfully reproduced within the framework of a 2D percolation model although a direct analogy is still difficult to establish.

Large-scale molecular dynamics study of jet breakup and ejecta production from shock-loaded copper with a hybrid method

This effort investigates the dynamic properties of ejecta from explosively shocked, melted Pb targets. The study shows that the ejecta cloud that expands beyond the shocked surface is characterized by a high density and low velocity fragment layer between the free-surface and the high velocity micro-jetting particle cloud. This slow, dense ejecta layer is liquid micro-spall. The properties of micro-spall layer, such as the mass, density and velocity, were diagnosed in a novel application of an Asay window, while micro-jetting particles by lithium niobate piezoelectric pins and high speed photography. The total mass-velocity distribution of ejecta, including micro-spall fragments and micro-jetting particles, is presented. Furthermore, the sensitivity of ejecta production to slight variations in the shockwave drive using the Asay foil is studied.

Experimental study of ejecta from shock melted lead

We have assembled together our ejecta measurements from explosively shocked tin acquired over a period of about ten years. The tin was cast at 0.99995 purity, and all of the tin targets or samples were shocked to loading pressures of about 27 GPa, allowing meaningful comparisons. The collected data are markedly consistent, and because the total ejected mass scales linearly with the perturbations amplitudes they can be used to estimate how much total Sn mass will be ejected from explosively shocked Sn, at similar loading pressures, based on the surface perturbation parameters of wavelength and amplitude. Most of the data were collected from periodic isosceles shapes that approximate sinusoidal perturbations. Importantly, however, we find that not all periodic perturbations behave similarly. For example, we observed that sawtooth (right triangular) perturbations eject more mass than an isosceles perturbation of similar depth and wavelength, demonstrating that masses ejected from irregular shaped perturbations cannot be normalized to the cross-sectional areas of the perturbations.

Experimental observations on the links between surface perturbation parameters and shock-induced mass ejection

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/μs. 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...

/pdf/ejecta-particle-size-distributions-for-shock-loaded-sn-and-5ap5hmkxq6.pdf

Ejecta particle size distributions for shock loaded Sn and Al metals

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/{micro}sec. 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.

/pdf/ejecta-particle-size-distributions-for-shock-loaded-sn-and-2lq9wqqqqc.pdf

Ejecta particle size distributions for shock loaded Sn and Al metals.

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/μsec. 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.

/pdf/ejecta-particle-size-distributions-for-shock-loaded-sn-and-2g15fpig9j.pdf

Ejecta Particle Size Distributions for Shock‐Loaded Sn and Al Targets

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//spl mu/sec. The driving cylinder impacts a smaller target cylinder where shock waves of many hundreds of kilobars can be reached and ejecta formation proceeds. The ejecta particle sizes are measured using an in-line Fraunhofer holography technique. Over the years much work has gone into characterizing ejecta mass, but very little has been done to understand the particle size distributions. In this report, ejecta particle size distributions are presented for shocked Al and Sn targets at pressures of 300 kb and 400 kb respectively. For the first time, particle distributions that results from microjet production are presented. Results from these experiments are presented along with predictions from percolation theory.

/pdf/ejecta-particle-size-distributions-for-shock-loaded-sn-and-1uao76gdmw.pdf

J. L. Romero

Papers

Ejecta particle size distributions for shock loaded Sn and Al metals

Ejecta particle size distributions for shock loaded Sn and Al metals.

Ejecta Particle Size Distributions for Shock‐Loaded Sn and Al Targets

Ejecta particle size distributions for shock loaded Sn and Al targets