Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session E6: Inelastic Deformations, Fracture and Spall II: Ejecta |
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Chair: Nicola Bonora, University of Cassino, Danny Sorenson, Los Alamos National Laboratory Room: 8/9/10 |
Monday, June 15, 2015 3:30PM - 3:45PM |
E6.00001: Mass-velocity and size-velocity distributions of ejecta cloud from shock-loaded tin surface using large scale molecular dynamics simulations Olivier Durand, Laurent Soulard The mass (volume and areal densities) versus velocity as well as the size versus velocity distributions of a shock-induced cloud of particles are investigated using large scale molecular dynamics (MD) simulations. A generic 3D tin crystal with a sinusoidal free surface roughness is set in contact with vacuum and shock-loaded so that it melts directly on shock. At the reflection of the shock wave onto the perturbations of the free surface, 2D sheets/jets of liquid metal are ejected. The simulations show that the distributions may be described by an analytical model based on the propagation of a fragmentation zone, from the tip of the sheets to the free surface, within which the kinetic energy of the atoms decreases as this zone comes closer to the free surface on late times. As this kinetic energy drives (i) the (self-similar) expansion of the zone once it has broken away from the sheet and (ii) the average size of the particles which result from fragmentation in the zone, the ejected mass and the average size of the particles progressively increase in the cloud as fragmentation occurs closer to the free surface. Though relative to nanometric scales, our model reproduces quantitatively experimental profiles and may help in their analysis. [Preview Abstract] |
Monday, June 15, 2015 3:45PM - 4:00PM |
E6.00002: Ejecta Particle-Size Measurements from the Break-Up of Micro-Jets in Vacuum and Helium Gas Using Ultraviolet In-Line Fraunhofer Holography. Danny Sorenson, Peter Pazuchanics, Randall Johnson, Robert Malone, Morris Kaufman, Thomas Tunnell, Duane Smalley, Daniel Marks, Gene Cappelle, Mike Grover, Bruce Marshall, Gerald Stevens, Dale Turley, Brandon LaLone An ultraviolet (UV) in-line Fraunhofer holography diagnostic has been developed for making high-resolution spatial measurements of ejecta particles traveling at many mm/$\mu $sec. Recent results will be presented for high-explosive shock-driven tin ejecta experiments. Particle-size distributions will be shown that cover most of the ejecta velocities for experiments conducted in both a vacuum, and helium gas environments. In addition, a modification has been made to the laser system that produces two laser pulses separated by 6.8 ns. This double-pulsed capability allows a superposition of two holograms to be acquired at two different times, thus allowing ejecta velocities to be measured directly. Results from this double-pulsed experiment will be described. [Preview Abstract] |
Monday, June 15, 2015 4:00PM - 4:15PM |
E6.00003: Experimental study of microjetting from triangular grooves in laser shock-loaded samples Caroline Roland, Thibaut de Resseguier, Emilien Lescoute, Arnaud Sollier, Didier Loison, Laurent Berthe, Gabriel Prudhomme, Patrick Mercier When a shock wave interacts with a free surface, geometrical defects such as scratches, pits or grooves can lead to the production of high velocity, micrometer-size debris. Because their ballistic properties are a key safety issue for a variety of applications involving high pressure dynamic loading such as pyrotechnics, and because these debris may inhibit surface measurements commonly used in shock physics, this process sometimes referred to as ``material ejection'' or ``microjetting'' has motivated extensive research work for many years. Recently, we have started a systematic investigation of microjetting under laser driven shock loading of thin metallic samples with calibrated grooves in their free surface. Transverse shadowgraphy and PDV measurements provide jet velocities for different metals, various groove angles, over a range of shock pressure, both below and above shock-induced melting. Besides, the short duration of pressure application allows partial recovery of both samples and ejecta, which provides original insight into the early stage of jet formation as well as spall fracture in such non-planar geometries. [Preview Abstract] |
Monday, June 15, 2015 4:15PM - 4:30PM |
E6.00004: Ejecta from shocked metals: comparative simulations using molecular dynamics and smoothed-particle hydrodynamics Sergey Dyachkov, Anatoly Parshikov, Vasily Zhakhovsky The machining of materials produces regular micrometer-sized surface perturbations. The microscopic cumulative jets can be generated from such surface under shock loading. It is a problem to trace space-time evolution of such jets with good enough resolution in experimental conditions. Comparative simulations by molecular dynamics (MD) and smoothed-particle hydrodynamics (SPH) methods, using an equation of state consistent with the employed interatomic potential, can shed of light on details of jet formation. The realistic experimental samples can be directly simulated by SPH method, while the linear size of a MD sample is restricted by the order of 100 nm. To compare the SPH and MD simulations the MD results must to be scaled to micrometer-sized samples. We demonstrate that the scaling provides the similar jet velocity profiles and mass distributions obtained by both methods. Furthermore, the simulated results agree well with the experimental observations with Copper and Tin. The effect of surface tension, which guides evolution of nanoscale-sized jet shape, may lead to discrepancies between MD and SPH simulations, especially for weak shocks and small surface perturbations. [Preview Abstract] |
Monday, June 15, 2015 4:30PM - 4:45PM |
E6.00005: Power and Energy of Exploding Wires Cole Valancius Exploding wires are used in many high-energy applications, such as initiating explosives. Analysis of gold wire burst in detonator applications has shown Burst Current and Action metrics to be incapable of explaining burst phenomenon as the inductance of a firing circuit is changed. Energy Density better captures the correlation between different wire geometries, different electrical inputs, and explosive initiation. This idea has been expanded upon, to analyze the burst properties in Power-Energy space. Further inconsistencies in the understanding of wire burst and its relation to peak voltage have been found. An argument will be made for redefining the definition of burst. The result is a more broad understanding of rapid metal phase transition and the physical applications of the released shock wave. [Preview Abstract] |
Monday, June 15, 2015 4:45PM - 5:00PM |
E6.00006: Microstructure effects on shock-induced surface jetting Bo Li, Sheng-Nian Luo We investigate shock-induced surface jetting from grooved Cu as regards microstructure effects, including jetting mass/velocity ratios, directionality, jetting phase diagram, secondary jetting, and underlying mechanisms. The grooves are of wedged, cylindrical, and rectangular shapes. Other microstructure features explored are half angles, crystal structure asymmetry as represented by grain boundaries, geometrical asymmetry, and deformation heterogeneity. The common fundamental mechanism is that jetting is driven by stress gradients due to transverse mass collision. For symmetrical wedged grooves, the velocity ratio increases linearly with decreasing half angle. However, the jetting factor or mass ratio reaches the maximum at certain intermediate half angle. An impact strength vs. half angle phase diagram is established for a typical case of wedged grooves, useful for predicting the critical parameters for jetting. Small asymmetries may induce considerable deviation of the jetting direction. Wedged, cylindrical, and rectangular grooves form a geometrical hierarchy. Primary jetting can be well described with wedged grooves, and secondary jetting is a result of collision of primary jets. Rectangular grooves may yield pronounced, velocity-enhanced, secondary jetting. [Preview Abstract] |
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