Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session V2: Continuum and Multiscale Modeling III |
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Chair: David Benson, University of California, San Diego Room: Fairmont Orchid Hotel Amphitheater |
Friday, June 29, 2007 10:30AM - 10:45AM |
V2.00001: Void Growth and Coalescence Nanocrystalline Metals: Molecular Dynamics Modeling, Continuum Modeling, and Experiments David Benson, Sirirat Traiviratana, Marc Meyers, Parag Dixit, Alice Koniges, Dan Kalantar Fragmentation of the support structures in ICF experiments, leading to the damage of instrumentation and optics, is currently a concern as new research facilities are brought on line. The current research focuses on understanding the void formation and growth mechanisms. MD simulations in single and poly-crystalline nano-materials have been carried out with LAMMPS. Void growth occurred by the emission of shear dislocation loops. Continuum finite difference calculations of the same Vornoi-generated microstructure were also performed using ALE-AMR. The results of the calculations are compared to each other and to laser shock experiments in thin vanadium films. This research was supported by LLNL grant B558558. [Preview Abstract] |
Friday, June 29, 2007 10:45AM - 11:00AM |
V2.00002: Numerical simulation of interaction of hypervelocity particle stream with a target Ilya Lomov, Benjamin Liu, Vlad Georgevich, Tarabay Antoun We present results of direct numerical simulations of impact of hypervelocity particle stream with a target. The stream of interest consists of submillimeter (30-300 micron) brittle ceramic particles. Current supercomputer capabilities make it possible to simulate a realistic size of streams (up to 20 mm in diameter and 500 mm in length) while resolving each particle individually. Such simulations make possible to study the damage of the target from synergistic effects of individual impacts. In our research we fixed the velocity distribution along the axis of the stream (1-4 km/s) and volume fraction of the solid material (1-10\%) and study effects of particle size variation, particle and target material properties and surrounding air properties. We ran 3D calibration simulations with up to 10 million individual particles and conducted sensitivity studies with 2D cylindrically symmetric simulations. We used an Eulerian Godunov hydrocode with adaptive mesh refinement. The particles, target material and air are represented with volume-of-fluid approach. Brittle particle and target material has been simulated with pressure-dependent yield strength and Steinberg model has been used for metal targets. Simulations demonstrated penetration depth and a hole diameter similar to experimental observations and can explain the influence of parameters of the stream on the character of the penetration. [Preview Abstract] |
Friday, June 29, 2007 11:00AM - 11:15AM |
V2.00003: An extended finite element formulation for modeling the response of polycrystalline materials to shock loading Joshua Robbins, Thomas Voth The eXtended Finite Element Method (X-FEM) is a finite element based discretization technique developed originally to model dynamic crack propagation [1]. Since that time the method has been used for modeling physics ranging from static mesoscale material failure to dendrite growth. Here we adapt the recent advances of Benson et al. [2] and Belytchko et al. [3] to model shock loading of polycrystalline material. Through several demonstration problems we evaluate the method for modeling the shock response of polycrystalline materials at the mesoscale. Specifically, we use the X-FEM to model grain boundaries. This approach allows us to i) eliminate ad-hoc mixture rules for multi-material elements and ii) avoid explicitly meshing grain boundaries. ([1] N. Moes, J. Dolbow, J and T. Belytschko, 1999,``A finite element method for crack growth without remeshing,'' International Journal for Numerical Methods in Engineering, 46, 131-150. [2] E. Vitali, and D. J. Benson, 2006, ``An extended finite element formulation for contact in multi-material arbitrary Lagrangian-Eulerian calculations,'' International Journal for Numerical Methods in Engineering, 67, 1420-1444. [3] J-H Song, P. M. A. Areias and T. Belytschko, 2006, ``A method for dynamic crack and shear band propagation with phantom nodes,'' International Journal for Numerical Methods in Engineering, 67, 868-893.) [Preview Abstract] |
Friday, June 29, 2007 11:15AM - 11:30AM |
V2.00004: Simulation of Comet Impact and Survivability of Organic Compounds Benjamin Liu, Ilya Lomov, Jennifer Blank, Tarabay Antoun Comets have been proposed as a mechanism for the transport of complex organic compounds to Earth. For this to occur, a significant fraction of organic compounds must survive the shock loading, in particular the high temperatures, due to impact. 2D and 3D numerical simulations were performed to study the thermodynamic states due to a comet impact. The comet was modeled as a 1-km diameter icy sphere traveling at the Earth's escape velocity (11 km/s) impacting a half-space of basalt. Simulations were performed with GEODYN, a parallel, multi-material, Godunov-based Eulerian code employing adaptive mesh refinement. A constitutive model calibrated for hard rock was used for basalt. Tabular equations of state were used to account for the extreme conditions present upon shock loading. A major focus of the study was tracking the thermodynamic state of the comet material. Both the maximum temperature experienced and the phase were tracked for each point in the comet Temperature histories in the comet were also recorded. These quantities were used to estimate viability of organic compounds upon impact. This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
Friday, June 29, 2007 11:30AM - 11:45AM |
V2.00005: Implementation of the TEPLA Damage Model in a 3D Eulerian Hydrocode Kathleen S. Holian, Sean P. Clancy, Paul J. Maudlin A sophisticated damage model (TEPLA) has been implemented into a three-dimensional (Cartesian) computer code (Pagosa) used here at Los Alamos National Laboratory.~ TEPLA was originally an isotropic damage model based upon the Gurson flow surface (a potential function used in conjunction with the associated flow law) that models damage due to both porosity growth and plastic strain.~~ It has since been modified to model anisotropic elastoplastic material strength as well.~ Pagosa is an Eulerian hydrodynamics code that has the following special features:~ a predictor-corrector Lagrangian step that advances the state variables in time,~ a high-order advection algorithm that remaps the problem back to the original mesh every time step, and a material interface tracking scheme with van Leer monotonic advection.~ It also includes a variety of equation of state, strength, fracture, and high explosive burn models.~ We will describe the physics of the TEPLA model (that models both strength and damage) and will show preliminary results of test problems that are used to validate the model.~ The four test problems (simple shear, stretching rod, Taylor anvil, and plate impact) can be compared with either analytic solutions or with experimental data. [Preview Abstract] |
Friday, June 29, 2007 11:45AM - 12:00PM |
V2.00006: Numerical Simulation of high velocity impact phenomenon by the Distinct Element Method (DEM) Yoko Tsukahara, Akiko Matsuo, Katsumi Tanaka The Distinct Element Method (DEM) is one of the particle methods and is generally applied to granular materials and incompressible elastic materials. DEM with elastic-plastic deformation is developed for simulations of shock loading phenomenon in condensed media, and is applied to problems with large deformations. DEM gives more stable results than Lagrangian Finite Difference or Finite Element Method. Numerical oscillations are reduced by the consideration of artificial viscosity. The hydrodynamic constitutive law is introduced to the DEM, and the dynamic behaviors of materials, such as metals and concretes, under high velocity impact phenomenon are well compared with experimental and other computational results. [Preview Abstract] |
Friday, June 29, 2007 12:00PM - 12:15PM |
V2.00007: Numerical Studies on the Explosive Welding by Smoothed Particle Hydrodynamics (SPH) Katsumi Tanaka A particular characteristic of an explosively produced weld is that the profile of the weld interface often has a regular wavy appearance. An effect of detached shock wave and jetting on the metal interface of explosive welding has been shown by SPH (Smoothed particle hydrodynamics). Numerical results show wavy interface which is observed in several experiments. High speed jet between interface and Karman vortex after oblique impact of a flyer plate to a parent plate were major mechanism of explosive welding. [Preview Abstract] |
Friday, June 29, 2007 12:15PM - 12:30PM |
V2.00008: Structural-Scaling Transitions in Microshear Ensembles and Self-Similarity of Wave Fronts and Failure in Shocked Materials Oleg Naimark Statistical theory of mesodefects allowed establishment of new type of critical phenomena--structural-scaling transitions, to develop thermodynamics and phenomenology in terms of defect density tensor and structural scaling parameter, which reflects scaling transition and generation of collective modes of defects: shear transformation zones (STZ) and damage transformation zone (DTZ), which provide plastic relaxation and damage-failure transition. Shock wave experiments and structural study supported linkage of these modes with material responses in large range of load intensity and allowed interpretation: (i) mechanisms of failure wave generation and propagation that has the nature of delayed failure needed for excitation time of blow-up collective modes. Experimental study of failure wave generation and propagation was analyzed for Taylor test in fused quartz rod using high-speed framing and supported ``delayed'' mechanism of failure wave generation; (ii) self-similarity of wave fronts under reloading and unloading, fourth power universality of steady-state plastic was confirmed both theoretically and experimentally in plate impact test for copper and using NEW VIEW scaling analysis of STZ distribution in recovered specimen; (ii) transition from thermo-activation kinetics of plastic relaxation to steady-state relaxation and overdriven shock regime. [Preview Abstract] |
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