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 Z4: Continuum & Multiscale Modeling VII |
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Chair: Tracy Vogler, Sandia National Laboratories Room: Hyatt Regency Constellation E |
Friday, August 5, 2005 10:30AM - 10:45AM |
Z4.00001: Kinetic Approach for Shock Compressed Heterogeneous Medium Yuri Mescheryakov On the basis of experiments on shock loading of wide spectrum of materials, a criterion for changing the energy exchange regime between mesoscale and maroscale from evolutional to catastrophical is obtained. Intermediate regime of energy exchange is shown to be oscillating one. Two-level theoretical approach to uniaxial strain of heterogeneous medium is based on locking the momentum and mass balance equations (macroscopic scale level) with the kinetic equation for mesoparticle velocity distribution function (mesoscale). Constitutive equation $P =\rho D^2$ links the spherical component of pressure and particle velocity dispersion which plays a role ``granular temperature'' at the mesoscale. A coupling between mesoscale and macroscale levels results from current energy exchange by using the relationship between particle velocity dispersion and mean velocity loss $\Delta u =\frac{1}{2}\frac{\partial D^2}{\partial u}. $ It characterizes the losses of momentum at the macroscalel at the expense of outflow of the energy to mesoscale whereas dispersion $D^{2 }$characterizes the reversible energy of fluctuations at the mesoscale. The criterion for transition from homogeneous to heterogeneous straining is shown to be the ratio of rate of change of velocity dispersion and rate of change of mean particle velocity at the shock front of compressive pulse. [Preview Abstract] |
Friday, August 5, 2005 10:45AM - 11:00AM |
Z4.00002: Simplified Shock Conditions for Finite Elastoplasticity Bradley Plohr, JeeYeon N. Plohr In this talk, we consider shock loading of an elastoplastic material; the strain is not restricted to be small. We show how to reduce the Rankine-Hugoniot jump conditions to a simplified form analogous to that used in fluid dynamics. Just as for fluids, the shock conditions can be separated into a thermodynamic condition (the Hugoniot condition), a condition determining the velocity, and a condition determining the strain, which can be solved sequentially to determine the shock wave. [Preview Abstract] |
Friday, August 5, 2005 11:00AM - 11:15AM |
Z4.00003: Approximate Universal Relations Between Shock and Acceleration Waves Speeds for Oblique Plate Impact of Inelastic Solids Mike Scheidler We obtain some approximate universal relations between wave speeds in inelastic solids subject to oblique plate impact, i.e., a pressure-shear test. Attention is restricted to materials for which the fast wave is purely longitudinal. This includes isotropic solids as well as appropriately aligned orthotropic solids. For the case where the slower wave is a shear shock we derive approximate relations between this shock speed and the shear sound speeds (i.e., acceleration wave speeds) immediately ahead of and behind the shock. These relations are universally valid for a large class of materials which includes elastic solids as well as inelastic solids with instantaneous elastic response. [Preview Abstract] |
Friday, August 5, 2005 11:15AM - 11:30AM |
Z4.00004: Approximation of multifluid mixture response for simulation of sharp and diffuse material interfaces on an Eulerian grid Ilya Lomov, Ben Liu Multimaterial Eulerian and Arbitrary Lagragian-Eulerian (ALE) codes usually use volume fractions of materials to track individual components in mixed cells. Material advection usually is calculated by either interface capturing, when the high-order van Leer --like slope reconstruction technique is applied or interface tracking, when the normal reconstruction technique is applied. The former approach is more appropriate for gas-like substances, the latter is ideal for solids and liquids, since it does not smear out material interface. Wide range of problems involves both diffuse and sharp interfaces between substances and demand for combination of these techniques. It is possible to treat all substances which can diffuse into each other as a single material and only keep mass fractions of the individual components of the mixture. The material response can be determined based on the assumption of pressure and temperature equilibrium between components of the mixture. Unfortunately, it is extremely difficult to solve the corresponding system of equations. In order to avoid these problems one can introduce effective gamma and employ ideal gas approximation to calculate mixture response. The method provides reliable results, is able to compute strong shock waves, and deals with complex equations of state. Results from a number of simulations using this scheme will be presented [Preview Abstract] |
Friday, August 5, 2005 11:30AM - 11:45AM |
Z4.00005: Material failure modelling in metals at high strain rates Vili Panov, Rade Vignjevic, Neil Bourne Plate impact tests have been conducted on the OFHC Cu using single-stage gas gun. Using stress gauges, which were supported with PMMA blocks on the back of the target plates, stress-time histories have been recorded. After testing, micro structural observations of the softly recovered OFHC Cu spalled specimen were carried out and evolution of damage has been examined. To account for the physical mechanisms of failure, the concept that thermal activation in material separation during fracture processes has been adopted as basic mechanism for this material failure model development. With this basic assumption, the proposed model is compatible with the Mechanical Threshold Stress model and therefore in this development it was incorporated into the MTS material model in DYNA3D. In order to analyse proposed criterion a series of FE simulations have been performed for OFHC Cu. The numerical analysis results clearly demonstrate the ability of the model to predict the spall process and experimentally observed tensile damage and failure. It is possible to simulate high strain rate deformation processes and dynamic failure in tension for wide range of temperature. The proposed cumulative criterion, introduced in the DYNA3D code, is able to reproduce the ``pull-back'' stresses of the free surface caused by creation of the internal spalling, and enables one to analyse numerically the spalling over a wide range of impact velocities. [Preview Abstract] |
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