Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session Y3: Particulate/Porous Materials III: Theoretical and Computational |
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Chair: Ilya Lomov, Lawrence Livermore National Laboratory Room: Renaissance Ballroom AB |
Friday, July 1, 2011 9:15AM - 9:30AM |
Y3.00001: Scaling of Waves in Heterogeneous Materials Tracy Vogler The fourth power scaling of strain rate with stress described by Swegle and Grady describes steady waves in many homogeneous materials, but heterogeneous materials can display different scaling relationships. In particular, layered materials exhibit a second power scaling of strain rate with stress, while first power scaling has been observed in granular materials. To better understand these scaling behaviors, numerical simulations of wave propagation in layered and granular materials are performed. The simulations demonstrate that the heterogeneous nature of these materials can cause behavior similar to what has historically been termed viscosity when observed in homogeneous materials. From these simulations, non-dimensional groups that control the scaling of the waves are identified. These groups collapse the available experimental data reasonably well onto a single curve. Finally, a simple model for the first power scaling in granular materials is proposed that illustrates the importance of void space between particles to the wave structure. [Preview Abstract] |
Friday, July 1, 2011 9:30AM - 9:45AM |
Y3.00002: Shock-induced formation of a disordered solid from a dense particle suspension Andrew Higgins, Oren Petel, David Frost, Simon Ouellet Shock wave propagation in multiphase media is dominated by the relative compressibility of the mixture components. If these components are chosen such that the suspended solid is incompressible in the loading range of interest, then the wave dynamics are dominated by the compressibility of the liquid. Furthermore, the relative compressibility of the components can result in shock-induced variations in the volume fraction of the suspension. As the shock wave strength is increased, the post-shock volume fraction of a dense suspension can tend towards the random close packing limit for the system and a disordered solid can take form. The present study investigates the formation of disordered structures within dense suspensions as well as the effect that such structures have on wave propagation. Shock Hugoniot data will be presented for dense suspensions of silicon carbide in ethylene glycol. Analytical models will be used to illustrate the shock-induced variations of the mesostructure within the suspensions. [Preview Abstract] |
Friday, July 1, 2011 9:45AM - 10:00AM |
Y3.00003: Intense Shock Compression of Porous Mixtures: Application to Tungsten Carbide Powders Gregg Fenton, Dennis Grady, Tracy Vogler The intense shock states achievable within granular or porous mixtures can be quantified through the application of continuum thermodynamic models. Here emphasis is on distended granular solids for the purpose of calculating compression paths and shock temperatures. In the present paper thermo-physical relations are developed and applied to the shock compression of tungsten carbide powders. This material has been selected because of previous studies available in literature and recent high-pressure test results obtained at the Sandia National Laboratories Z-Facility. The relations developed herein have been implemented in the Sandia Laboratories CTH code, specifically within a newly modified version of the $P-\lambda $ equation of state. Analytic equations of state similar to $P-\lambda $ are usually considered highly inefficient for hydrocode computation because of the many sub-cycle calculations needed to determine the pressure. However, the main advantage of this newly modified EOS is it allows for the easy creation of novel heterogeneous mixture models, which are usable from the low-pressure crush-up response to the extreme pressure and temperature states of the mixture. Comparison between numerical simulation using the new model and experimental data show good agreement. [Preview Abstract] |
Friday, July 1, 2011 10:00AM - 10:15AM |
Y3.00004: Mesoscale Simulations of Granular Materials with Peridynamics Christopher Lammi, David Littlewood, Tracy Vogler The dynamic behavior of granular materials can be quite complex due to phenomena that occur at the scale of individual grains. For this reason, mesoscale simulations explicitly resolving individual grains with varying degrees of fidelity have been used to gain insight into the physics of granular materials. The vast majority of these simulations have, to date, been performed with Eulerian codes, which do a poor job of resolving fracture and grain-to-grain interactions. To address these shortcomings, we utilize a peridynamic modeling framework to examine the roles of fracture and contact under planar shock and other loading conditions. Peridynamics is a mesh-free Lagrangian technique that uses an integral formulation to better enable simulations involving fracture. Although some aspects of the peridynamic codes currently available are not well suited to the shock regime, the simulations provide results that are more physically realistic than the Eulerian simulations for some non-planar loading conditions. [Preview Abstract] |
Friday, July 1, 2011 10:15AM - 10:30AM |
Y3.00005: Application of a Generalized Multiphase Riemann Solver to a Finite-Volume Method with Nozzling Sources Michael Crochet, Keith Gonthier Hyperbolic model equations governing the flow of solid particles in a gas contain nonconservative nozzling sources that can introduce numerical instability in commonly used finite-volume methods. Modifications to these methods have been recently proposed involving both exact and approximate solutions to the two-phase Riemann problem with gamma-law equations of state. The present work extends this approach to multiphase systems including an arbitrary number of solid phases described by general equations of state. The exact Riemann solver is implemented within the second-order, semidiscrete, cell-centered Kurganov-Tadmor (KT) technique. The resulting method is used to predict wave structures and energetics for 1D piston-impact of mixtures having initial spatial variations in solid volume fraction (0.2-0.6). An alternative formulation of the KT technique is also proposed to reduce the additional computational expense of the exact solver while preserving numerical stability. [Preview Abstract] |
Friday, July 1, 2011 10:30AM - 10:45AM |
Y3.00006: Heating in Microstructures of HMX/Estane PBX during Dynamic Deformation Ananda Barua, Min Zhou The thermomechanical response of HMX/Estane over a range of initial temperatures (210 - 300 K) and strain rates (10$^{4}$ - 10$^{5}$ s$^{-1})$ is analyzed using a Lagrangian cohesive finite element method (CFEM) framework. The analysis focuses on the correlation between grain-level failure mechanisms and the overall response. Digitized micrographs of actual PBX materials are used. Calculated results show a transition in failure mode from brittle fracture at temperatures below the glass transition temperature (T$_{g})$ of the binder to shear band formation at temperatures above T$_{g}$. At the same level of overall deformation, earlier fracture and more severe temperature rises are observed in the grains for lower initial temperatures due to more brittle responses of the binder. Enhanced frictional heating along crack surfaces resulting from the failure contributes to the more severe heating. On the other hand, transgranular fracture is pronounced at higher strain rates, owing to the viscoelastic nature of the binder. The size and distribution of hot spots are quantified over the ranges of initial temperature and strain rate considered. The results are useful in establishing microstructure-performance relations of advanced energetic materials. [Preview Abstract] |
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