Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session D4: Continuum & Multiscale Modeling II |
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Chair: John Clayton, US Army Research Laboratory Room: Hyatt Regency Constellation E |
Monday, August 1, 2005 1:30PM - 1:45PM |
D4.00001: Multi-scale simulations of shock-induced plasticity M. Shehadeh, E. Bringa, H. Zbib, B. Remington, J. McNaney A multi-scale model of plasticity that couples discrete dislocation dynamics and finite element continuum analyses is used to investigate shock-induced dislocation nucleation in copper single crystals. We include a model for homogeneous nucleation of dislocations based on large-scale atomistic simulations of shock loading. The resulting huge rate of dislocation production takes the uniaxialy compressed material to a hydrostatically compressed state (1D to 3D) after a few tens of ps, as observed experimentally. The density of dislocations produced in a sample with pre-existing dislocation sources decreases with shock wave rise time, implying relatively lower densities for isentropic loading conditions, as suggested by recent experiments. The work at LLNL was performed under the auspices of the U.S. Department of Energy and Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [Preview Abstract] |
Monday, August 1, 2005 1:45PM - 2:00PM |
D4.00002: Atomistic dynamics and the evolution of the Richtmyer-Meshkov instability in solids and liquids. V.V. Zhakhovskii, S.V. Zybin, S.I. Abarzhi, K. Nishihara For the first time the molecular dynamics (MD) approach is applied to study the evolution of the shock-driven Richtmyer- Meshkov instability (RMI), which develops at the corrugated interface separating two Lennard-Jones (LJ) liquids or two solids with different densities. Compared to traditional hydrodynamic simulations, MD has a number of fundamental advantages. It accounts for strong gradients of the pressure and temperature, and captures accurately the heat transfer and the viscous or plastic flow at early (shock passage) as well as late (turbulent mixing) stages of the instability evolution. MD has no limitations for the spatial resolution and does not require the assumption of thermodynamic equilibrium. We analyze the influence of the critical parameters, energy and mass transfer, and the governing stresses on the growth of the interface perturbations, and compare the cases of LJ liquids and solids. In liquids, RMI is driven by the non-uniform velocity shear and vorticity production. In solids, the development of visco-plastic flow, shear stresses, and elastic anisotropy influences significantly the evolution of initial perturbations. [Preview Abstract] |
Monday, August 1, 2005 2:00PM - 2:15PM |
D4.00003: Comparison of Mesomechanical and Continuum Granular Flow Models for Ceramics Donald Curran Constitutive models for the shear strength of ceramics undergoing fracture are needed for modeling long rod and shaped-charge jet penetration events in ceramic armor. The ceramic material ahead of the penetrator has been observed to be finely comminuted material that flows around the nose of the eroding penetrator [Shockey at al, 1990]. The most-used continuum models are of the Drucker-Prager type with an upper cutoff [Walker, 2002], or of the Mohr-Coulomb type with strain rate dependence and strain- softening [Johnson and Holmquist, 1992, 1993, 2002]. A disadvantage of such models is that they have an unclear connection to the actual microscopic processes of granular flow and comminution. An alternate approach is to use mesomechanical models that describe the dynamics of the granular flow, as well as containing a description of the granular comminution and resultant material softening. However, a disadvantage of the mesomechanical models is that they are computationally more burdensome to apply. In the present paper, we compare the behaviors of a mesomechanical model, FRAGBED2 [Curran and Cooper, 2003], with the Walker and Johnson-Holmquist continuum models, where the granular material is subjected to simple strain histories under various confining pressures and strain rates. We conclude that the mesomechanical model can provide valuable input to the continuum models, both in interpretation of the continuum models' parameters, and in suggesting the range of applicability. [Preview Abstract] |
Monday, August 1, 2005 2:15PM - 2:30PM |
D4.00004: Shock Interaction of Metal Particles in Condensed Explosive Detonation Robert Ripley, Fan Zhang, Fue-Sang Lien For detonation propagation in a condensed explosive with metal particles, a macro-scale physical model describing the momentum transfer between the explosive and particles has yet to be completely established. Previous 1D and 2D meso-scale modeling studies indicated that significant momentum transfer from the explosive to the particles occurs as the leading shock front crosses the particles, thus influencing the initiation and detonation structure. In this work, 3D meso-scale modeling is conducted to further study the two-phase momentum transfer during the shock diffraction and subsequent detonation in liquid nitromethane containing packed metal particles. Detonation of the condensed explosive is computed using an Arrhenius reaction model and a hybrid EOS model that combines the Mie-Gruneisen equation for reactants and the JWL equation for products. The compressible particles are modeled using the Tait EOS, where the material strength is negligible. The effect of particle packing configuration and inter-particle spacing is shown by parametric studies. Finally, a physical description of the momentum transfer is discussed. [Preview Abstract] |
Monday, August 1, 2005 2:30PM - 2:45PM |
D4.00005: Coupling Grain Scale and Bulk Mechanical Response for PBXs using Numerical Simulations of Real Microstructures Scott Bardenhagen, Andrew Brydon, Todd Williams, Christelle Boutry PBXs are complex composites geometrically (irregularly shaped grains vary greatly in size), and constitutively (grains are anisotropic, twin and fracture). Heterogeneity at the grain scale results in localized damage and the creation of hot spots. To develop accurate, quantitative and predictive models it is imperative to develop a sound physical understanding of the grain scale material response. Numerical simulation is a useful tool to further model development. Here an inherent advantage of a particle method in discretizing geometrically complex materials is exploited to import three-dimensional material configurations from x-ray microtomography data, i.e. ``real'' microstructures. Numerical simulations determine representative volume element size and generate statistics on grain scale strain heterogeneity. These statistics calibrate the Stochastic Transformation Field Analysis bulk constitutive model. [Preview Abstract] |
Monday, August 1, 2005 2:45PM - 3:00PM |
D4.00006: Finite Element Method Calculations on Statistically Consistent Microstructures of PBX 9501. Eric Mas, Brad Clements, Axinte Ionita We have used data from image analysis to guide us in creating a finite element mesh of PBX 9501. Information about the binder concentration at different length scales taken from micrographs allow us to create a mesh which naturally incorporates inhomogeneities of the microstructure in a manner which is statistically consistent with the observed microstructure. We then apply constitutive models which are consistent with the different binder concentrations and run finite element simulations. We will present our technique for incorporating the image analysis information into the mesh, our mechanical models, and results of the simulations. [Preview Abstract] |
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