Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session Q5: PM-1: Particulate Mechanics |
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Chair: David Chapman, University of Cambridge Room: Cheekwood GH |
Wednesday, July 1, 2009 9:30AM - 9:45AM |
Q5.00001: 2D Mesoscale Simulations: Insight into Projectile Instability Penetrating Dry Sand S.K. Dwivedi, C. Felice, J. Fernandes Continuing with our 2D mesoscale simulations, we present new results that provide insight into projectile instability during penetration into dry sand at impact velocities of 0.2 km/s to 2.0 km/s. The instability depends on the projectile nose shape with ogive nose being the most unstable and the flat nose being the most stable. In contrast to the loosely packed polyhedron grains or circular grains of any packing, the closely packed polyhedron grains with coincident edges cause maximum instability to the ogive nose projectile. Similarly, initial oblique impact results in more unstable behavior compared to the normal impact at any given impact velocity. Moreover, it is shown that (a) the deformation zone for a given sand body and projectile geometry depends on the friction between grains, but is otherwise independent of the impact velocity, and (b) there may exist a range of impact velocity for which the penetration of a given projectile into a given dry sand is stable. The results are presented in terms of the rotational momentum, angle of deviation, deformations zone dimensions, and the equivalent force on the projectile. [Preview Abstract] |
Wednesday, July 1, 2009 9:45AM - 10:00AM |
Q5.00002: Mesoscale simulations of powder compaction Ilya Lomov, Tarabay Antoun, Benjamin Liu Mesoscale 3D simulations of metal and ceramic powder compaction in shock waves have been performed with an Eulerian hydrocode GEODYN. The approach was validated by simulating shock compaction of porous well-characterized ductile metal using Steinberg material model. Results of the simulations with handbook values for parameters of solid 2024 aluminum have good agreement with experimental compaction curves and wave profiles. Brittle ceramic materials are not so well studied as metals, so material model for ceramic (tungsten carbide) has been fitted to shock compression experiments of non-porous samples and further calibrated to experimental match compaction curves. Direct simulations of gas gun experiments with ceramic powder have been performed and showed good agreement with experimental data. Numerical shock wave profile has same character and thickness as measured with VISAR. Numerical results show evidence of hard-to-explain reshock states above the single-shock Hugoniot line, which have also been observed in the experiments. We found that to receive good quantitative agreement with experiment it is essential to perform 3D simulations, since 2D results tend to underpredict stress levels for high-porosity powders regardless of material properties. We developed a process to extract macroscale information for the simulation which can be directly used in calibration of continuum model for heterogeneous media. [Preview Abstract] |
Wednesday, July 1, 2009 10:00AM - 10:30AM |
Q5.00003: A review of mesoscale simulations of granular materials Invited Speaker: With the advent of increased computing power, mesoscale simulations have been used to explore grain level phenomenology of dynamic compaction events of various heterogenous systems including foams, reactive materials and porous granular materials. This paper presents an overview of several mesoscale studies on a variety of materials include tungsten carbide and epoxy mixtures, wet and dry sand, and reactive materials (Al-MnO2-Epoxy mixtures). The simulations encompass a variety of geometries including one-dimensional planar and spherical shock configurations. This talk will focus on relating mesoscale modeling to experimental data and the role of material constitutive relations in this effort. In addition, lessons learning during these explorations, modeling techniques, strengths and weaknesses of hydrodynamic mesoscale simulations will also be presented. [Preview Abstract] |
Wednesday, July 1, 2009 10:30AM - 10:45AM |
Q5.00004: Shock-Less High Rate Compaction of Porous Brittle Materials Gregg Fenton, Terry Caipen, Glenn Daehn, Dennis Grady The dynamic behavior of granular materials such as granular silica (sand), technical ceramics, and porous geological substances has importance to a variety of engineering applications. Although the mechanical behaviors of sand and other granular ceramics have been studied extensively for several decades, the dynamic behavior of such materials remains poorly understood. This paper will describe how instrumented electromagnetic tube compression driven by capacitive discharge can be used to measure compaction of model materials at high and controlled strain rates. The technique relies on electromagnetically crushing a powder-filled conductive tube. By measuring the current as a function of time and the tube displacement through Photon Doppler Velocimetry (PDV) sufficient data can be obtained to reveal the behavior of the porous material. The method will be described in detail and example data will be shown for compaction of silica sand. [Preview Abstract] |
Wednesday, July 1, 2009 10:45AM - 11:00AM |
Q5.00005: Meso-Scale Simulation of the Shock Compression Response of Equiaxed and Needle Morphology 6061 Aluminum Powders D. Anthony Fredenburg, Tracy J. Vogler, Naresh N. Thadhani Particle level simulations on equiaxed and needle morphology 6061 Al powders are carried out on real microstructures to determine the shock densification response of powder compacts pre-pressed to 68{\%} theoretical density. Two particle configurations are investigated, homogeneous particles with properties of bulk 6061 Al, and 6061 Al particles with a 2 micron thick high strength outer shell, representative of a nanocrystalline surface layer. A linear shock velocity-particle velocity relationship is observed for the homogeneous particle configuration over the particle velocity range 200-850 m/s. Deviation in shock velocity-particle velocity linearity is observed at lower particle velocities for the layered particles with material behavior approaching linearity as particle velocity increases. In addition, a novel scheme for determining vorticity in interparticle contact areas is presented for the purpose of elucidating the effect of particle morphology on compaction characteristics. Research funded through Sandia Contract {\#} 521274. [Preview Abstract] |
Wednesday, July 1, 2009 11:00AM - 11:15AM |
Q5.00006: Particle size effect in granular composite aluminum/tungsten Po-Hsun Chiu, Sophia Wang, Eric Herbold, David Benson, Vitali Nesterenko Compressive dynamic strength and fracture pattern of high density Al-W granular composites with an identical weight ratio between Al (23.8 wt{\%}) and W (76.2 wt{\%}) and with different porosities, size and shape of W component were investigated at strain rate 0.001 1/s. Samples were fabricated by Cold Isostatic Pressing. It was shown that dynamic strength (107 MPa) of composites with fine W particles ($<$1 micron) was significantly larger than strength (73 MPa) of composite with the course W particles (-325 mesh) at the same porosity 26{\%}. More dense samples (porosity 15{\%}) with course W particles exhibited higher strength of 175 MPa. Morphology of W inclusions had a strong effect on dynamic strength. Samples with W wires arranged in axial direction (diameter 100 microns) and porosity of the sample 16{\%} with the same volume content of components demonstrated dynamic strength of 350 MPa. Dynamic strength and fracture pattern of composites was numerically simulated using computer code Raven. [Preview Abstract] |
Wednesday, July 1, 2009 11:15AM - 11:30AM |
Q5.00007: Computational Analysis of Compaction Wave Interactions with Non-Planar Boundaries Anirban Mandal, Rohan Panchadhar, Keith Gonthier The interaction of initially planar, piston supported compaction waves with a stationary, convex rigid boundary is computationally examined at both the bulk and meso-scales. The bulk-scale model accounts for elastic and inelastic volumetric deformation of the granular material, and hot-spots formed at the grain scale are estimated based on a simple bulk energy localization strategy. The meso-scale model combines conservation principles with an elastic-viscoplastic and friction constitutive theory to predict thermomechanical fields within grains, and accounts for interaction between grains using an efficient penalty based technique. Particular emphasis is placed on characterizing the variation in spatial wave structure and hot-spot mass fraction in the vicinity of the boundary with piston speed (100-500~m/s). Meso-scale fields are locally averaged and compared to those predicted by the bulk model; good agreement exists. Predictions indicate that maximum heating occurs near the boundary away from the stagnation region. [Preview Abstract] |
Wednesday, July 1, 2009 11:30AM - 11:45AM |
Q5.00008: Numeric techniques for viscoelastic or highly porous heterogeneous materials Kenneth Jordan, John Borg Since the advent of computer simulations, the dynamic shock compaction of homogeneous ductile engineering materials has enjoyed a long history of success. The shock compaction of materials which demonstrate more complicated constitutive relations, such as extremely porous heterogeneous materials or viscoelastic materials, has proven more challenging. This talk focuses on the implementation of constitutive relations and numeric techniques for resolving the shock compaction of either highly porous or viscoelastic materials in a Lagrangian hydrocode configuration. For both materials, results are compared to experimental data obtained in a one-dimensional shock configuration. [Preview Abstract] |
Wednesday, July 1, 2009 11:45AM - 12:00PM |
Q5.00009: Investigation of the rate dependence of long-rod penetration of granular media using an improved Digital Speckle Radiography program John Addiss, Adam Collins, William Proud Digital Speckle Radiography (DSR) is a technique allowing full field displacement maps in a plane within an opaque material to be determined. The displacements are determined by tracking the motions of small sub-sections of a deforming speckle pattern, produced by seeding an internal layer of lead and taking flash x-ray images. Using a digital image cross correlation program, written and optimised for DSR experiments, the temporal progression of a long-rod (100 mm long, 10 mm diameter) penetrating a granular sample at a variety of rates is investigated. Quasi-static rates of 1.5 mm per min are achieved using an Instron machine, 5 m/s is achieved using a drop-weight and 200 m/s is achieved using a gas gun. These experiments are carried out using a series of time delayed flash x-ray images. The subsequent data sheds considerable light on the response of granular materials to penetration at a variety of rates. [Preview Abstract] |
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