Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session S2: Detonations and Shock-Induced Chemistry V |
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Chair: Craig Tarver, Lawrence Livermore National Laboratory Room: Grand Ballroom IV-V |
Thursday, June 30, 2011 9:15AM - 9:30AM |
S2.00001: Shock Initiation of Hexanitrostilbene at Ultra-high Shock Pressures and Critical Energy Determination Mike Bowden, Matthew Maisey Hexanitrostilbene is a secondary explosive with attractive properties for detonator usage, including thermal stability, good safety properties and easy initiability. It is desirable to characterize the shock initiation of detonator explosives to enable optimization of system parameters. HNS is a suitable explosive for use in electrical and optical slapper detonators, where shock pressures generated by the flyer plates used can exceed 30 GPa. This extreme shock regime can be explored by initiating HNS with a variety of flyer thicknesses, from 3 to 25 microns at velocities of several km/s. Thresholds for optical and electrical slapper detonators were evaluated, and Photonic Doppler Velocimetery used to determine the flyer velocity at threshold. The flyer diameters are in excess of the critical diameter for HNS, allowing a one-dimensional treatment of the initiation. Calculated values for pressure and shock duration are used to evaluate the critical energy criteria P$^{n }\tau $. The calculated value of n is compared to published values and discussed for similar systems. The James Criterion is used to analyze the initiation, with values of E$_{c}$ and $\Sigma _{c}$ being determined from experimental data, providing a predictive capability to model other configurations such as different flyer thicknesses and materials. [Preview Abstract] |
Thursday, June 30, 2011 9:30AM - 9:45AM |
S2.00002: Shock Initiation of Powder Mixtures of Aluminum with Dense Metal Oxides Fran\c{c}ois-Xavier Jett\'e, Sam Goroshin, David Frost, Fan Zhang Strong and dense structural reactive materials may be produced by mixing aluminum powders with heavy metal-oxide powders (such as Bi2O3, PbO, Pb3O4, I2O5, etc.). The addition of certain additives to such mixtures, such as V2O5 and B2O3, can lower the softening point of the oxide mixture below the melting point of aluminum. This could lead to the fabrication of dense and non-porous aluminum-metal oxide structural materials. The shock sensitivity of aluminum-metal oxide mixtures was investigated in this work. The minimum shock initiating pressure was obtained for various porous and non-porous aluminum-metal oxide mixtures using the shock recovery technique. Since most reactions of Al-in metal oxide mixtures produce little pressure and material velocity changes but large increases in temperatures, thermocouples were used to observe the bulk reaction onset, which relates to the overall reaction rate, in those mixtures. The mixtures tested were found to be very sensitive to shock initiation and their reaction rates were found to be very fast, compared to other types of reactive powder mixtures. Finally, the addition V2O5 and B2O3 additives or the addition of liquid heptane (to fill the pores) did not lower the sensitivity or reaction rates of the mixtures investigated. [Preview Abstract] |
Thursday, June 30, 2011 9:45AM - 10:00AM |
S2.00003: ABSTRACT WITHDRAWN |
Thursday, June 30, 2011 10:00AM - 10:15AM |
S2.00004: Critical Hotspots and Flame Propagation in HMX-Based Explosives Caroline Handley Understanding reaction within hotspots (ignition) and its propagation into the bulk (growth) is key to the development of mesoscale models for shock initiation of heterogeneous explosives. An important concept is that of critical hotspots; a critical hotspot is just large and hot enough that it can itself react, and go on to spread reaction into the cooler surrounding explosive, before it is cooled by heat conduction. This paper will describe how previously-published hydrocode models for HMX and two binder materials were used to obtain critical hotspot criteria. The results compare well to those in the literature for HMX. In the simulations, which account for hydrodynamics, heat conduction and Arrhenius chemistry, reaction propagates outwards from hotspots via a flame driven by heat conduction. The flame propagation speed in the simulations has been compared to data for HMX from high- pressure diamond anvil cell experiments. Discrepancies between the hydrocode results and the data shed light on the mechanisms of reaction propagation in heterogeneous explosives. [Preview Abstract] |
Thursday, June 30, 2011 10:15AM - 10:30AM |
S2.00005: A Theoretical Exploration of the Differences between Prompt and Bow Shock Initiation of Explosives by Shaped Charge Jets Christopher Mellor, Hugh James, Michael Goff The use of the CREST reactive burn model in conjunction with results from the open literature demonstrates the differences between prompt and bow shock initiation, even when the diameter of the shaped charge jet is much larger than the failure diameter of the explosive. The burn model shows the need for the bow shock to build in strength before reaching an amplitude where significant reaction is triggered, and hence explains the observed very long runs to detonation required by this mechanism. While the compression of the explosive between the bow shock and the jet provides much greater pressures than those seen in the bow shock, the relative thermodynamic inefficiency of the compression process means that this region contributes little to the direct generation of reaction. [Preview Abstract] |
Thursday, June 30, 2011 10:30AM - 10:45AM |
S2.00006: The Effect of Failure Diameter on the Initiation of Explosives by Shaped Charge Jet. Hugh James, Christopher Mellor, Michael Goff Experiments on two explosives, where the shaped charge jet had a diameter that was much larger than the failure diameter for the HMX-based explosive, but much smaller than the failure diameter of the TATB-based explosive, show marked differences in the initiation behavior generated by the impact shock. In this ``prompt'' shock initiation regime the HMX-based explosive tended to run to detonation in a distance that was mainly comparable to its Pop Plot while the TATB took much longer despite the very high impact pressures. Theoretical investigations using the CREST reactive burn model showed that reaction started reasonably promptly across the diameter of the jet in both explosives, and the differences were due to the delay in corner turning out of this restricted diameter experienced by the detonation in the TATB. [Preview Abstract] |
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