Bulletin of the American Physical Society
21st Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 64, Number 8
Sunday–Friday, June 16–21, 2019; Portland, Oregon
Session 1A: Energetic Materials |
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Room: Broadway I/II |
Sunday, June 16, 2019 9:15AM - 9:30AM |
1A.00001: Measurements of shock sensitivity in a damaged explosive using a small-scale gap test Nick Cummock, Chris Molek, Chad Rumchik, Steven Son The shock sensitivity of an explosive is often given in terms of the input pressure versus the corresponding run-distance to complete detonation. Plotted in log-log space, these are known as Pop-plots. In this work, small cylindrical samples of less than 0.5 g of explosive are used in a small-scale gap test to determine the run-distance as a function of pressure in PBX 9501 at varying initial densities, which are compared to thermally damaged samples. In this set of experiments, the L50, or pressure input at which 50\% of the samples will initiate is determined for pellets of length equal to 6 mm and 3 mm, where the pellet length is taken as the run distance for the L50 pressure. Differences in shock sensitivity as shown by Pop-plots are shown. Further work involving isolation of the mechanisms influencing the change in shock sensitivity, such as porosity shifts, changes in particle size, and solid phase changes is considered. [Preview Abstract] |
Sunday, June 16, 2019 9:30AM - 9:45AM |
1A.00002: Anisotropic Thermomechanical Response to Shock Wave Loading in TATB (symp) Puhan Zhao, Matthew Kroonblawd, Nithin Mathew, Tommy Sewell Molecular dynamics simulations were used to study shock loading in oriented crystalline TATB. The crystal structure consists of planar hydrogen-bonded sheets of individually planar TATB molecules that stack into graphitic-like layers. Shocks were studied for seven crystal orientations, with limiting cases that correspond to propagation exactly perpendicular and exactly parallel to the molecular layers. The simulations were performed for initially pristine crystals using a reverse-ballistic configuration with an impact speed of 1 km/s. Orientation-dependent properties are reported including pressures, temperatures, compression ratios, shock speeds, and local strain rates. Analysis of temperature, stress, material flow, and molecular orientations reveal complicated processes that arise for specific shock directions. The shock response is highly sensitive to crystal orientation, with significant qualitative differences for the evolution of stress and temperature, elastic/inelastic compression response, defect formation and growth, and strain rates. Several inelastic deformation mechanisms are identified, ranging from twinning to dislocation-mediated plasticity to intense shear strain localization. [Preview Abstract] |
Sunday, June 16, 2019 9:45AM - 10:00AM |
1A.00003: Effects of Inert Additives on Cyclotrimethylene-Trinitramine (RDX)/Trinitrotoluene (TNT) Detonation Parameters to Predict Detonation Synthesis Phase Production Martin Langenderfer, Catherine Johnson, William Fahrenholtz The following methodology was developed to predict temperature and pressure regimes achieved during detonation of RDX/TNT compositions as they relate to the formation of solid carbon-based phases precipitating from the detonation process. This study computationally assesses the effects of inert material additives on explosive compositions used in detonation synthesis experiments. Thermomechanical and thermochemical models are used to evaluate detonation parameters starting with an explosive base composition of 50 wt.{\%} RDX and 50 wt.{\%} TNT. The effects of mesoscale inclusions and porosity created by inert additives on the sensitivity of the explosive composition to undergo a shock-to-detonation transition are estimated using a limited scope approach regarding hotspot formation and collapse. On the continuum scale, the effect of inert additives on pressure and temperature generated behind the detonation wave and within the reaction zone are parameterized through reactive burn modeling using the Becker-Kistiakowsky-Wilson (BKW) equation of state (EOS). The Jones-Wilkins-Lee (JWL) EOS is compared to the post reacted BKW model, and predicted state variables are input into thermochemical equilibrium modeling software to evaluate the state of the detonation products at various levels of expansion. [Preview Abstract] |
Sunday, June 16, 2019 10:00AM - 10:15AM |
1A.00004: Spectroscopy in Deflagrating High Explosives Suzanne Sheehe, Scott Jackson Physically based kinetic models are desirable to enhance the predictive capability of reaction zone (RZ) models for high explosives (HEs). Current models use only a 1- or 2-step reaction mechanism, which may not fully capture all relevant kinetic effects on deflagrative and detonative performance. The development of more physically accurate multi-step reaction models (containing both endothermic and exothermic steps) for HEs could dramatically improve the predictive range of models. Despite significant efforts to spectroscopically characterize detonating HE flows, progress has been limited due to the extremely temporally (20 ns) and spatially (200 micron) short detonation RZ scales, and high optical opacity. Deflagrations have significantly larger reaction zone scales (mm-sized), pressure-dependent burn rates (on the order of mm/s) and lower opacity at pressures in the MPa range. This readily enables spectroscopic characterization of key transient species critical in late-stage energy release. This work presents and discusses new results of emission spectroscopy and burn rate measurements in deflagrating HE (such as PBX 9407 and PBX 9502). [Preview Abstract] |
Sunday, June 16, 2019 10:15AM - 10:30AM |
1A.00005: SYMP Ultrafast Shock Induced Mid-Infrared Vibrational Changes in Thin Film Explosives Michael Powell, Pamela Bowlan, Steven Son, Cynthia Bolme, Kathryn Brown, David Moore, Marc Cawkwell, Alejandro Strachan, Shawn McGrane There are many chemical reactions and pathways predicted to occur during shock loading of explosive materials. Direct experimental evidence of intermediate formation from shock induced chemistry is very limited. Reactive models can provide insight into the chemistry and physics that occur during shock; however, experiments have typically been on orders of magnitude longer time and length scales resulting in limited direct experimental comparison. This work aims to bridge that gap using ultrafast laser spectroscopies to probe electronic and vibrational functional group changes at comparable scales. Broadband mid-infrared (MIR) and visible (VIS) absorption spectroscopy were performed on shocked thin films of explosives materials. Strong absorbance changes were measured in the MIR with peak disappearance as well as a broad absorptive feature in time. VIS absorbance also showed strong absorbance changes indicating electronic structure changes under shocked loading conditions. These results were compared to reactive molecular dynamics and accelerated chemistry models [Preview Abstract] |
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