Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session U5: PPCM: Validating Porous Models |
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Chair: Christopher Neel, AFRL Room: Broadway I/II |
Thursday, June 20, 2019 3:15PM - 3:30PM |
U5.00001: (U) The Effect of Initial Pressed Density on the Dynamic Densification Behavior of Brittle Granular Materials Travis Voorhees, Justin Steiner, D. Anthony Fredenburg, Gregory Kennedy, Naresh Thadhani In this study, the effect of initial density ($\rho_{\mathrm{00}})$ on the dynamic densification behavior of a brittle granular system, cerium dioxide (CeO$_{\mathrm{2}})$, is investigated. Specifically, the consolidation behavior of pressed powder compacts at four initial pressed densities (33, 44, 55, {\&} 62.5{\%} TMD) is examined at densities within the compaction range via gas gun driven plate-on-plate impact. The shock Hugoniot data collected from these experiments are presented and used to calibrate P-$\alpha $ model parameters. The dependency of these P-$\alpha $ model parameters on initial density are presented and discussed. [Preview Abstract] |
Thursday, June 20, 2019 3:30PM - 3:45PM |
U5.00002: A volume-filtered description of shock-particle interactions Gregory Shallcross, Jesse Capecelatro This study presents a volume-filtered formulation and consistent numerical discretization to simulate particle-shock interactions. When a shock passes through a dense suspension of solid particles, the surrounding gas accelerates to supersonic speeds, referred to as choking. While this phenomenon is captured in fully resolved simulations of shock-particle interactions, it remains a challenge to reproduce using coarse-grained models, such as Euler-Euler and Euler-Lagrange methods. Volume filtering the viscous compressible Navier-Stokes equations reveals sub-filtered terms that require closure but are typically neglected. A-priori filtering the flow fields generated from particle-resolved direct numerical simulations is performed to evaluate the relative contributions of these unclosed terms. Results are reported for different values of filter size and particle loadings. Of particular interest is the pseudo-turbulent kinetic energy (PTKE), which appears in conservation of momentum, energy, and the equation of state. This term systematically acts to reduce the local gas-phase pressure and increase the Mach number. We present a transport equation for PTKE within a high-order Eulerian-Lagrangian framework and validate it against direct numerical simulations. [Preview Abstract] |
Thursday, June 20, 2019 3:45PM - 4:00PM |
U5.00003: Rate Effects on Shear Strength in Granular Compaction Michael Homel, Eric Herbold For shock loaded granular materials, it is difficult to experimentally distinguish between effects of compaction vs. shear strength. This presents a challenge when parameterizing continuum models for use in generalized dynamic loading. Mesoscale simulations reveal that the shear stress behind the shock front in a fully compacted granular material can be well below the shear strength of the solid phase—inconsistent with many continuum models for porous strength. The strength of the solid material itself may depend on rate, temperature, pressure, damage, etc., but even without these complications, there are dynamic effects that significantly reduce the apparent shear strength of the granular material in shock loading. Dynamic relaxation occurs from local unloading of material due to impact and release at pore surfaces during compaction. Additionally, there is significant effect of “shear heterogeneity”, the spatial variability in the alignment of the deviatoric stress tensor immediately behind the compaction front, which produces a non-equilibrium state and subsequent relaxation in the compacted material. Implications on continuum modeling and methods for experimental validation are discussed. [Preview Abstract] |
Thursday, June 20, 2019 4:00PM - 4:15PM |
U5.00004: Cylindrical Driven Shocks in Ceria T J Voorhees, M S Freeman, C L Rousculp, D A Fredenburg, J T Bradley, P M Donovan, Frank Fiero, J R Griego, J C Lamar, F G Mariam, Levi P Neukirch, D M Oro, A R Patten, R B Randolph, W A Reass, R E Reinovsky, A Saunders, S Sjue, Z Tang, P J Turchi Shock compression of granular ceria was studied in converging cylindrical geometry using LANL Proton Radiography driven by the PHELIX magnetic implosion system in which a 1 mm thick liner-impactor was accelerated it to ~0.8 mm/$\mu s$. The impactor launched a shock in the cylindrical Al outer wall of the target assembly containing equiaxed, 63 $\mu$m-mean diameter ceria powder initially compacted to a static density of ~4 g/cc. The cylindrically converging shock in the ceria was observed with a series of 31 proton-radiographic frames down the axis of the cylinder. Results indicate that significant shock energy was expended in compacting the porous ceria, as the wave velocity markedly decreases during convergence, and a clear shock reflected from the axis was not observed. These observations are inconsistent with pre-shot modeling, and highlight the need for an improved understanding of the physics of compaction under non-ideal loading. [Preview Abstract] |
Thursday, June 20, 2019 4:15PM - 4:45PM |
U5.00005: Progress toward development of a predictive dynamic compaction model framework Invited Speaker: D Fredenburg The shock densification of initially porous materials is a complex process that is influenced by properties of the bulk material, as well as characteristics of the grains and pores. However, modeling and simulation of the densification process is often required at the continuum level, which by definition, treats both the grains and pores as a single component. As such, the multi-scale nature of the densification process presents challenges in the development of a predictive continuum-level compaction model. In the present work, the authors present an examination of several continuum compaction models within the context of their ability to be predictive. A single model form is selected as having the requisite characteristics, and is explored further with respect to its ability to capture various aspects of initially porous systems. Finally, a predictive dynamic compaction model framework is presented, within a set of bounds, and is applied to several data sets. [Preview Abstract] |
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