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 K4: Continuum & Multiscale Modeling IV |
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Chair: Larry Libersky, Los Alamos National Laboratory Room: Hyatt Regency Constellation E |
Tuesday, August 2, 2005 1:30PM - 2:00PM |
K4.00001: Anisotropic Modeling of Shocked Single Crystals with Application to Energetic Materials Invited Speaker: A continuum, anisotropic modeling framework has been developed for simulating shock wave propagation in single crystals of arbitrary orientation. Our modeling approach incorporates nonlinear elasticity and crystal plasticity in a thermodynamically consistent tensor formulation. Crystal plasticity is described using a model that considers dislocation motion along specified slip planes. Shear cracking along specified crystal planes is also considered. Numerical simulations, using a finite-difference code, for large amplitude wave propagation in single crystals are presented. From these simulations, issues related to pure mode propagation for nonlinear elastic waves are discussed. Also, the effects of plasticity on wave propagation in single crystals are explored by comparing simulations to wave profile data for copper (Jones and Mote, 1969) and for LiF (Asay, et al., 1972). For copper, a single dislocation model for slip on {\{}111{\}} planes provides good agreement with quartz gauge data for shocks along the [100], [110], and [111] directions. For LiF, slip occurs on {\{}110{\}} planes, and good agreement with data is obtained for shocks along the [100] direction. Using the same dislocation model, simulated shock wave propagation along the low symmetry [310] direction of LiF is also examined. In addition, simulations are compared to transmitted wave profiles (Dick and Ritchie, 1994; Dick, 1997) for various orientations of shocked pentaerythritol tetranitrate (PETN) single crystals. For shocks along the insensitive [100] orientation of PETN, dislocation slip is unhindered and a dislocation dynamics model provides good fits to the wave profile data. For shocks along the sensitive [110] orientation, in which steric hindrance impedes the motion of dislocations, evidence of strain-softening behavior is observed and a shear cracking model fits the data well. Work supported by DOE and ONR. [Preview Abstract] |
Tuesday, August 2, 2005 2:00PM - 2:15PM |
K4.00002: Modeling the Asymmetical Burning of Ultrafine Particles Clinton Richmond A model has been developed that accounts for asymmetrical combustion effects due to oxide caps and/or other surface contaminants of burning ultrafine metal particles. The burning rate law of a particle is modified to include the effects of surface contamination. The modifications are then used in solving the Shvab-Zeldovich differential equations for diffusion of energy and chemical species within the mixing region and reaction zone. The model is validated by comparing its predictions to experiments in which asymmetrical particle combustion was observed. The model accounts for different pathological aspects of particles combustion attributed to asymmetrical burning, such as the deviation from the ``D$^{2}$ law.'' [Preview Abstract] |
Tuesday, August 2, 2005 2:15PM - 2:30PM |
K4.00003: Experimental Validation of Detonation Shock Dynamics in Condensed Explosives D. Scott Stewart, David E. Lambert, Sunhee Yoo, Bradley L. Wescott Experiments in the HMX-based, condensed explosive PBX-9501 were carried out to validate a reduced, asymptotically derived description of detonation shock dynamics (DSD) where it is assumed that the normal detonation shock speed is determined by the total shock curvature. The passover experiment has a lead disk embedded in a right circular cylindrical charge of PBX-9501 and is initiated from the bottom. A range of dynamic detonation states with both diverging (convex) and converging (concave) shock shapes are realized as the detonation shock passes over the disk. The time of arrival of the detonation shock at the top surface of the charge is recorded and compared against DSD simulation and direct multi-material simulation. A new wide-ranging equation of state (EOS) and rate law is used to describe the explosive and is employed in both theory and multi-material simulation. The experiment and theory and simulation are found to be in excellent agreement. [Preview Abstract] |
Tuesday, August 2, 2005 2:30PM - 2:45PM |
K4.00004: Hydro-Reactive Calculations of Detonation in Ribs. Yehuda Partom We use our Surface Burn (SB) reactive flow model with Temperature Dependent Reaction Rate (TDRR) to calculate detonation in explosives in the shape of cylindrical ribs. The main purpose is to check the assumptions of the Detonation Shock Dynamics (DSD) model which are: 1) the normal detonation velocity (D$_{n})$ depends on the local curvature (k), and this dependence is unique and single valued; 2) there is a limiting angle boundary condition at the boundaries; and sometimes also 3) there is a failure curvature beyond which quasi-steady detonation cannot propagate. Usually D$_{n}$(k) is calibrated from breakout curves obtained from rate stick tests. Such tests cover only part of the curvature range, and they sometimes indicate that D$_{n}$(k) may be non unique. Running hydro-reactive calculations for ribs we found that it is possible to extend substantially the range of curvature being monitored. Performing these calculations for PBX-9502 we found the following: 1) after a short travel in the rib the front reaches steady state in terms of shape and angular velocity; 2) the D$_{n}$(k) relation obtained is not unique, but varies with rib geometry; 3) the D$_{n}$(k) relation obtained is not single valued, but becomes double valued at low and high curvatures; 4) the limiting angle at the boundary is only approximately constant; and 5) there is no indication of a failure curvature. It seems that, the in view of the calculations, one needs to take another look at the DSD model assumptions. [Preview Abstract] |
Tuesday, August 2, 2005 2:45PM - 3:00PM |
K4.00005: Shock-Induced Chemical Reaction in Structural Energetic Materials Vindhya Narayanan, Xia Lu, Sathya Hanagud Various powder mixtures like intermetallic mixtures and mixtures of metals and metal oxides have potential applications as structural energetic materials (SEMs). Technologies of varying the compositions and the powder sizes and their synthesis are being investigated to provide multiple desirable characteristics, like high strength and high energy content. One of applications of SEMs requires assuring the absence of chemical reaction when only strength is needed in applications that involve shock effects. In this paper, we formulate a model for SEMs for their application in shock conditions, in the framework of nonequilibrium thermodynamics model and continuum mechanics. A mixture of Al and KClO$_{3}$ and binders is selected as the example for SEMs. A mixture model, pore collapse, and plasticity model are included. By adapting energy barriers for reaction as a function of temperature, particle size, pressure and pressure gradient and introducing a relaxation mechanism in the reaction model, shock-induced chemical reaction model is developed. The variation of the relaxation mechanism with pressure and other effects is also modeled. Numerical tools are formulated to simulate gas-gun tests of energetic intermetallic nanocomposites. The initiation and propagation of chemical reactions are studied. The time and spatial dependency of chemical reaction on the shock wave conditions are investigated. [Preview Abstract] |
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