Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session B6: Focus Session: Ejecta Physics I |
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Chair: Olivier Durand, CEA Room: Regency Ballroom E |
Monday, July 10, 2017 9:15AM - 9:30AM |
B6.00001: The development of a smaller Asay foil diagnostic David Bell, Nathan Routley, Glenn Whiteman, Peter Keightley The Asay foil has been a ubiquitous diagnostic in ejecta research since its design was first reported. An Asay foil is a foil of a known mass, whose change in velocity, as it is impacted by ejecta, is measured using velocimetry. The mass of the impacting ejecta can then be inferred from the change in momentum of the foil. To field an Asay foil requires the foil to be held in position; this is normally achieved by holding the foil at its edge. However, holding a foil at its edge perturbs the movement of the foil and undermines the assumptions used to calculate the mass of ejecta. One approach, to limit the perturbation, is to make the foil sufficiently large so that the centre of the foil is not influenced by its edge for the duration of an experiment. Research has been conducted to minimise the perturbation caused by holding the foil and therefore develop a smaller diameter Asay foil. A number of Asay foil designs were investigated and then fielded on gas gun driven ejecta experiments. The results from the Asay foils are reported and compared for consistency and also compared with results from piezoelectric probes. The research has resulted in a smaller diameter Asay foil being developed which has allowed smaller areas of ejecta sprays to be measured. [Preview Abstract] |
Monday, July 10, 2017 9:30AM - 9:45AM |
B6.00002: Miniaturized Asay foil assemblies for measurement of ejecta mass. Paul Steele, Steve Compton, Barry Jacoby, Louis Ferranti, John Densmore, Danial Phillips, Jose O. Sinibaldi An Asay foil diagnostic consists primarily of a metal foil suspended over an ejecta source. As ejecta strike the foil, they transfer momentum to it. The velocity of the foil is measured using Photonic Doppler Velocimetry (PDV). In subsequent data analysis, the foil velocity reveals the foil momentum, which is related to ejecta momentum. If ejecta velocity is known, ejecta momentum is easily converted to ejecta mass. In historical experiments at Lawrence Livermore National Laboratory, a 6mm diameter, 100um thick, titanium-alloy foil was simply placed over a 5mm hole in a mask. This basic design has been shown to produce results consistent with radiography. Recent work has succeeded in producing a miniature assembly matching the diameter of common piezoelectric pins (2.4mm) that can be used in any orientation with respect to gravity. Testing has already shown performance matching that of the larger historical design. Experiments are planned to compare directly with radiography. LLNL-ABS-723838 [Preview Abstract] |
Monday, July 10, 2017 9:45AM - 10:00AM |
B6.00003: Constraining ejecta particle size distributions with light scattering Martin Schauer, William Buttler, Daniel Frayer, Michael Grover, Brandon Lalone, Shabnam Monfared, Daniel Sorenson, Gerald Stevens, William Turley The angular distribution of the intensity of light scattered from a particle is strongly dependent on the particle size and can be calculated using the Mie solution to Maxwell's equations. For a collection of particles with a range of sizes, the angular intensity distribution will be the sum of the contributions from each particle size weighted by the number of particles in that size bin. The set of equations describing this pattern is not uniquely invertible, i.e. a number of different distributions can lead to the same scattering pattern, but with reasonable assumptions about the distribution it is possible to constrain the problem and extract estimates of the particle sizes from a measured scattering pattern. We report here on experiments using particles ejected by shockwaves incident on strips of triangular perturbations machined into the surface of tin targets. These measurements indicate a bimodal distribution of ejected particle sizes with relatively large particles (median radius 2-4 $\mu $m) evolved from the edges of the perturbation strip and smaller particles (median radius 200-600 nm) from the perturbations. We will briefly discuss the implications of these results and outline future plans. [Preview Abstract] |
Monday, July 10, 2017 10:00AM - 10:15AM |
B6.00004: Multiphase Modeling of Secondary Atomization in a Shock Environment Jeffrey St. Clair, Thomas McGrath, Sivaramakrishnan Balachandar Understanding and developing accurate modeling strategies for shock-particulate interaction remains a challenging and important topic, with application to energetic materials development, volcanic eruptions, and safety/risk assessment. This work presents computational modeling of compressible multiphase flows with shock-induced droplet atomization. Droplet size has a strong influence on the interphase momentum and heat transfer. A test case is presented that is sensitive to this, requiring the dynamic modeling of the secondary atomization process occurring when the shock impacts the droplets. An Eulerian-Eulerian computational model that treats all phases as compressible, is hyperbolic and satisfies the 2nd Law of Thermodynamics is applied. Four different breakup models are applied to the test case in which a planar shock wave encounters a cloud of water droplets. The numerical results are compared with both experimental and previously-generated modeling results. The effect of the drag relation used is also investigated. The computed results indicate the necessity of using a droplet breakup model for this application, and the relative accuracy of results obtained with the different droplet breakup and drag models is discussed. [Preview Abstract] |
Monday, July 10, 2017 10:15AM - 10:30AM |
B6.00005: Using the Richtmyer-Meshkov flow to infer the strength of LY-12 aluminum at extreme conditions Jianwei Yin, Hao Pan, Jiangxiang Peng, Zihui Wu, Yuying Yu, Xiaomian Hu An improved analytical model of the Richtmyer-Meshkov (RM) flow in the elastoplastic materials is presented in this paper. This model describes the stabilization by yield strength (Y) effect on the RM flow in solids and linear relationships between initial configurations of perturbation and the growth. Then we make use of the model to analysis the explosion driven RM flow experiments with solid LY12 and test our model by comparing the predicted Y of existing strength models. Finally, we perform a plate impact experiment with solid LY12 aluminium alloy to validate our model and infer Y is about 1.23 GPa for a 28 GPa shock and a strain rate of 7.5\times 10^{6} [Preview Abstract] |
Monday, July 10, 2017 10:30AM - 10:45AM |
B6.00006: Momentum Enhancement due to Crater Ejecta during Hypervelocity Impact of Highly Porous and Consolidated Rock James Walker, Sidney Chocron, Donald Grosch, Daniel Durda, Kevin Housen Experiments were performed with impacts of 2.54- to 4.45-cm-diameter aluminum spheres at 2.1 km/s into both consolidated rock (granite) and highly porous rock (pumice). Measured in these experiments was the momentum enhancement – that is, how much momentum is transferred to the rock by the impactor. The transferred momentum is greater than the impactor due to the crater ejecta. The momentum enhancement is characterized by $\beta,$ which is the ratio of the momentum transferred to the target and the momentum of the impactor. High speed video recorded the impact event, the ejecta from the target, and the motion of the target (hung in a ballistic pendulum arrangement). Constitutive models of rock that include porosity and crush-up behavior when incorporated into impact physics codes (specifically CTH and EPIC) show good agreement with crater depth, but they do not show good agreement with momentum enhancement. This paper will review the data and place it in the context of other momentum enhancement data, including the nonlinear effect of scale size. It will also explore the difficulties in large-scale numerical modeling of the momentum enhancement. An application of this data is determining the effectiveness of deflecting asteroids and comet nuclei by hypervelocity impacts. [Preview Abstract] |
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