Bulletin of the American Physical Society
20th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 62, Number 9
Sunday–Friday, July 9–14, 2017; St. Louis, Missouri
Session L2: Energetic and Reactive Materials: Hot Spots - Experiments |
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Chair: David Moore, Los Alamos National Laboratory Room: Grand Ballroom AB |
Tuesday, July 11, 2017 3:45PM - 4:15PM |
L2.00001: Shock Initiation of Explosives -- High Temperature Hot Spots Explained Invited Speaker: Will Bassett The pore-collapse mechanism for hot spot creation is currently one of the most intensely studied subjects in the initiation of energetic materials. In the present study, we use 1.5 -- 3.5 km s-1 laser-driven flyer plates to impact microgram charges of both polymer-bound and pure pentaerythritol tetranitrate (PETN) while recording the temperature and spatially-averaged emissivity with a high-speed optical pyrometer. The 32-color pyrometer has nanosecond time resolution and a high dynamic range with sensitivity to temperatures from \textasciitilde 7000 to 2000 K. Hot spot temperatures of 4000 K at impact are observed in the polymer-bound explosive charges where an elastomeric binder is used to fill void spaces. In pure PETN and more heterogeneous polymer-bound charges, in which significant void space is present, hot spot temperatures of 6000 K are observed, similar to previous reports with significant porosity. We attribute these high temperatures to gas-phase products formed in-situ being compressed under the driving shock. Experiments performed under various gas environments (air, butane, etc.) showed a strong influence on observed temperature upon impact. Control experiments where the PETN in the polymer-bound charges were replaced with sucrose and silica reinforce the result that hot spots are a result of in-situ gas formation from decomposition of organic molecules.\\ \\In collaboration with: Belinda Pacheco and Dana Dlott, University of Illinois at Urbana Champaign. [Preview Abstract] |
Tuesday, July 11, 2017 4:15PM - 4:30PM |
L2.00002: Correlation Between Hot Spots and 3-d Defect Structure in Single and Polycrystalline High-explosive Materials Cameron Hawkins, Oliver Tschuaner, Zachary Fussell, Jesse Smith A novel approach that spatially identifies inhomogeneities from microscale (defects, con-formational disorder) to mesoscale (voids, inclusions) is developed using synchrotron x-ray methods: tomography, Lang topography, and micro-diffraction mapping. These techniques pro-vide a non-destructive method for characterization of mm-sized samples prior to shock experiments. These characterization maps can be used to correlate continuum level measurements in shock compression experiments to the mesoscale and microscale structure. Specifically examined is a sample of C4. We show extensive conformational disorder in gamma-RDX, which is the main component. Further, we observe that the minor HMX-component in C4 contains at least two different phases: alpha- and beta-HMX. [Preview Abstract] |
Tuesday, July 11, 2017 4:30PM - 4:45PM |
L2.00003: Mechanical and chemical responses of low-velocity impacted RDX and HMX explosive powders. Yanqing Wu, Hongfu Guo, Fenglei Huang, Xiaowei Bao The experimental analyses of mechanical and chemical responses of RDX and HMX particles were performed based on the optimized drop-weight experimental system equipped with the High-Speed Camera (HSC). It has been found that Jetting phenomenon observed by HSC is the result of the energy released by gaseous products, which push the pulverized or melted explosives to splash radially. Jetting is the only and the most obvious difference between reactive and inert particles prior to combustion so that jetting can be regarded as the sign of ignition. Area expansion velocity, jetting velocity, and flame propagation velocity have been estimated via image processing, making it possible to characterize mechanical deformation and violence of reaction of each stage. Hot-spots coalescence promotes flame propagation whose velocity reflects the violence of deflagration reaction. Jetting appearance time can be used to determine time-to-ignition more accurately than other ways. For RDX, molten phase plays an important role to the formation of the hot-spots. Multiple particles experienced more severe burning reactions than an individual particle. [Preview Abstract] |
Tuesday, July 11, 2017 4:45PM - 5:00PM |
L2.00004: Particle Size Effects on CL-20 Initiation and Detonation Cole Valancius, Joe Bainbridge, Cody Love, Duane Richardson Particle size or specific surface area effects on explosives has been of interest to the explosives community for both application and modeling of initiation and detonation. Different particles sizes of CL-20 were used in detonator experiments to determine the effects of particle size on initiation, run-up to steady state detonation, and steady state detonation. Historical tests have demonstrated a direct relationship between particle size and initiation. However, historical tests inadvertently employed density gradients, making it difficult to discern the effects of particle size from the effects of density. Density gradients were removed from these tests using a larger diameter, shorter charge column, allowing for similar loading across different particle sizes. Without the density gradient, the effects of particle size on initiation and detonation are easier to determine. The results of which contrast with historical results, showing particle size does not directly affect initiation threshold. [Preview Abstract] |
Tuesday, July 11, 2017 5:00PM - 5:15PM |
L2.00005: Particle size and surface area effects on the thin-pulse shock initiation of Diaminoazoxyfurazan (DAAF). Rosemary Burritt, Elizabeth Francois, Gary Windler, David Chavez Diaminoazoxyfurazan (DAAF) has many of the safety characteristics of an insensitive high explosive (IHE): it is extremely insensitive to impact and friction and is comparable to triaminotrinitrobezene (TATB) in this way. Conversely, it demonstrates many performance characteristics of a Conventional High Explosive (CHE). DAAF has a small failure diameter of about 1.25 mm and can be sensitive to shock under the right conditions. Large particle sized DAAF will not initiate in a typical exploding foil initiator (EFI) configuration but smaller particle sizes will. Large particle sized DAAF, of 40 $\mu $m, was crash precipitated and ball milled into six distinct samples and pressed into pellets with a density of 1.60 g/cc (91{\%} TMD). To investigate the effect of particle size and surface area on the direct initiation on DAAF multiple threshold tests were preformed on each sample of DAAF in different EFI configurations, which varied in flyer thickness and/or bridge size. Comparative tests were performed examining threshold voltage and correlated to Photon Doppler Velocimetry (PDV) results. The samples with larger particle sizes and surface area required more energy to initiate while the smaller particle sizes required less energy and could be initiated with smaller diameter flyers. [Preview Abstract] |
Tuesday, July 11, 2017 5:15PM - 5:30PM |
L2.00006: Characterising shock propagation through inert beds James Edgeley, Christopher Braithwaite Optical velocimetry methods have been used extensively to measure the detonation wave velocity in explosives. The reaction zone length can subsequently be inferred using one of several methods, most involving transmitting the shock into an acceptor component made of another material and observing the wave's attenuation. The ultimate aim of this investigation is to develop a method optimised for characterising the reaction zone in low density PETN. The initial procedure involves a shock imparted by a gas gun into an inert bed in otherwise similar conditions. The design of the acceptor component is varied, and in each case an appropriate calculation is done to determine the size and profile of the shock. Laser interferometry is used to take velocity measurements where necessary. The results are compared against the input shock from the gun to assess the suitability of the apparatus. [Preview Abstract] |
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