Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session E3: Grain Scale to Continuum Modeling II: Porous Explosives |
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Chair: Betsy Rice and Michael Sellers, Army Research Laboratory Room: Grand G |
Monday, June 15, 2015 3:30PM - 4:00PM |
E3.00001: Dynamic strength effects in shock-loaded metals and crystalline explosives Invited Speaker: Ryan Austin Multiscale methods show great promise for developing physically-based models of the dynamic behavior of solids under extreme loading conditions. In this approach, the material behavior on a fine scale is described in terms of the actual physical mechanisms/processes. This information is then passed along to descriptions situated at higher length scales, creating a hierarchy that may span from the atomistic level all the way up to the continuum level. Such an approach is appealing because it may lead to predictive modeling capabilities. However, models developed in this way tend to be very complex, involving numerous unknown parameters that are difficult to determine or calibrate from sparse experimental data. In this talk, recent developments pertaining to the dynamic strength of various metals and crystalline explosives will be reviewed, including multiscale model development and methods for extracting strength data from VISAR measurements. Selected calculations will then be presented to demonstrate the importance of strength effects when considering, for example, the temperature-dependence of elastic precursor wave decay, dynamic void growth in tensile waves, and the shear banding and chemical reaction of shock-loaded porous energetic crystals. [Preview Abstract] |
Monday, June 15, 2015 4:00PM - 4:15PM |
E3.00002: Examining the effects of microstructure and loading on the shock initiation of HMX with mesoscale simulations H. Keo Springer, Craig Tarver, Sorin Bastea We perform reactive mesoscale simulations to study shock initiation in HMX over a range of pore morphologies and sizes, porosities, and loading conditions in order to improve our understanding of structure-performance relationships. These relationships are important because they guide the development of advanced macroscale models incorporating hot spot mechanisms and the optimization of novel energetic material microstructures. Mesoscale simulations are performed using the multiphysics hydrocode, ALE3D. Spherical, elliptical, polygonal, and crack-like pore geometries 0.1, 1, 10, and 100 microns in size and 2, 5, 10, and 14{\%} porosity are explored. Loading conditions are realized with shock pressures of 6, 10, 20, 38, and 50 GPa. A Cheetah-based tabular model, including temperature-dependent heat capacity, is used for the unreacted and the product equation-of-state. Also, in-line Cheetah is used to probe chemical species evolution. The influence of microstructure and shock loading on shock-to-detonation-transition run distance, reaction rate and product gas species evolution are discussed. This work performed under the auspices of the U.S. DOE by LLNL under Contract DE-AC52-07NA27344. This work is funded by the Joint DoD-DOE Munitions Program. [Preview Abstract] |
Monday, June 15, 2015 4:15PM - 4:30PM |
E3.00003: A Two-Phase Model for Shocked Porous Explosive Brian Lambourn, Caroline Handley Mesoscale calculations of hotspots created by a shock wave in a porous explosive show that the hotspots do not cool in times of order at least a microsecond. This suggests that single phase models of porosity like the snowplough model, which assume that a shocked porous explosive jumps to a point on the Hugoniot that is instantaneously in thermodynamic equilibrium, are not correct. A two-phased model of shocked porous explosive has been developed in which a small fraction of the material, representing the hotspots, has a high temperature but the bulk of the material is cooler than the temperature calculated by, for example, the snowplough model. In terms of the mean state of the material, it is shown that the two-phase model only minimally affects the pressure - volume and shock velocity - particle velocity plot of the Hugoniot, but that the mean state lies slightly off the equation of state surface. The results of the model will be compared with two dimensional mesoscale calculations. [Preview Abstract] |
Monday, June 15, 2015 4:30PM - 4:45PM |
E3.00004: Microstructural Characterization of Pressed HMX Material Sets With Implications on Initiation Behavior Christopher Molek, Eric Welle, Yuki Horie, Ryan Wixom, Barry Ritchey, Philip Samuels The detonation physics community has embraced the idea that initiation of high explosives proceeds from an ignition event through subsequent growth to steady detonation. A weakness of all the commonly used ignition and growth models is that microstructural characteristics are not explicitly incorporated in their ignition and terms. This is the case in spite of a demonstrated, but not well-understood, empirical link between morphology and initiation of energetic materials. Morphological effects have been parametrically studied in many ways, with the majority of efforts focused on establishing a tie between bulk powder metrics and initiation of the pressed beds. More recently, there has been a shift toward characterizing the microstructure of pressed beds in order to understand the underlying mechanisms governing behavior. We have characterized the microstructures of several HMX materials using ion bombardment techniques that expose the microstructure of pellets studied in initiation experiments. We discuss our attempt to quantify microstructure and the impacts on continuum level initiation behavior. [Preview Abstract] |
Monday, June 15, 2015 4:45PM - 5:00PM |
E3.00005: Analysis of Compaction Shock Interactions During DDT of Low Density HMX Pratap Rao, Keith Gonthier Deflagration-to-Detonation Transition (DDT) within low density HMX often occurs by a complex mechanism that involves compaction shock interactions. Piston driven DDT experiments indicate that detonation can be abruptly triggered by the interaction of a strong combustion driven shock and a lead piston supported shock, where the nature of the interaction depends on initial density and lead shock strength. These shocks induce dissipation and thermomechanical fluctuations at the meso-scale due to pore collapse resulting in hot-spots. Inert meso-scale simulations of successive shock loading of low density HMX are performed to examine how dissipation and hot-spot formation are affected by initial density, and lead and trailing shock strength. Emphasis is placed on interpreting solutions in a phase space expressed in terms of effective pressure and dissipative work because of their relevance to hot-spot formation. Meso-scale predictions are shown to compare favorably to those given by a macro-scale theory. This information is being used to formulate a dissipation-dependent reactive burn model to describe shock desensitization and DDT. Preliminary redictions will be presented that illustrate how initial density and input shock strength can affect the transition mechanism. [Preview Abstract] |
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