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 H2: Energetic Materials III |
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Chair: William Wilson, Defense Threat Reduction Agency Room: Hyatt Regency Constellation C |
Tuesday, August 2, 2005 9:00AM - 9:15AM |
H2.00001: An Ignition Model for Liquid-Solid Powder Hypergolic Reactions Raafat Guirguis, Vasant Joshi The thermal explosion theory is reformulated to describe the ignition of pulverized/finely divided solid explosives throughout which a hypergolic liquid has been dispersed. Although hypergolic in nature, the reaction at the interface between the two phases can be extinguished if the surface to volume ratio is outside a critical regime, or if the hypergolic liquid is quickly depleted because the injected amount was inadequate. The limitations on the particle size and mass fraction of the hypergolic liquid for successful ignition are derived in terms of the ambient temperature and heat of reaction, as well as the parameters controlling the rate of reaction and heat conduction of the solid explosive. [Preview Abstract] |
Tuesday, August 2, 2005 9:15AM - 9:30AM |
H2.00002: Measurement of temperature and ignition time during fast compression and flow in PBX 9501 Bryan Henson, Laura Smilowitz, Jerry Romero, Blaine Asay, Peter Dickson We have made radiometric temperature measurements on a microsecond time scale during the compression and flow of PBX 9501 subsequent to impact. A cylindrical sample was fired into a sapphire window normal to the cylinder axis at velocities on the order of several hundred meters per second. Cylindrically symmetric flow resulted which led to the classic circular ignition pattern at the outermost radial distance from the center at times of a few to tens of microseconds and temperatures on the order of 800 degrees Celsius. We also observed a difference in ignition pattern for samples of beta or delta PBX 9501. We report the times and temperatures of ignition and relate them to our model of PBX 9501 decomposition kinetics. We also discuss these results in the context of various other methods of thermally and mechanically heating PBX 9501 and note the invariance of the decomposition kinetics of HMX to the method of heating. [Preview Abstract] |
Tuesday, August 2, 2005 9:30AM - 10:00AM |
H2.00003: Explosively Driven Combustion of Shock-Dispersed Fuels Invited Speaker: Since the eighties our working group has been studying classical blast effects in small-scale experiments using custom-made miniature charges of 0.2 g to 1.5 g PETN. However, in the recent years the interest has shifted towards the performance of non-ideal explosives and the importance of secondary reactions such as after-burning. Thus we have designed an additional charge type, called Shock-Dispersed Fuel (SDF) charge. It consists of a lightweight, small paper cylinder filled with about one gram of a flammable powder (e.g., flake aluminum) surrounding a spherical PETN booster of 0.5 g. We have tested the SDF charges in a number of different environments, realized as closed steel vessels of simple geometry (barometric bombs). Three of the bombs vary in volume (6.6 l, 21.2 l and 40.5 l), while their aspect ratio L/D is kept constant at about 1. Two further bombs are comparable to the smallest bomb in volume (6.3 l), but provide different aspect ratios: L/D = 4.6 and 12.5. In addition, we have also performed tests in a tunnel-model with an L/D = 37.5. Our basic goal is to assess the performance of the charges by means of the combustion-related pressure built-up. Thus we contrast experiments on SDF charges in air with tests in nitrogen, to inhibit combustion, and with tests on conventional charges. Experiments and theoretical estimates on the expected overpressure allow one to formulate various indicators for the observed combustion performance. For SDF charges these indicate that the combustion efficiency decreases not only with increasing volume of the barometric bomb, but also with increasing aspect ratio at constant volume. This bears importance to the performance of SDF charges in tunnel environments. The performance losses reflect -- at least in part -- geometry-specific constraints on the mixing between fuel and air. [Preview Abstract] |
Tuesday, August 2, 2005 10:00AM - 10:15AM |
H2.00004: Flame Spread Across Surfaces of PBX 9501 Steven F. Son, H. Laine Berghout The safe use of energetic materials has been scientifically studied for over 100 years. Even with this long history of scientific inquiry, the level of understanding of the important deflagration phenomena in accidental initiations of high explosives remains inadequate to predict the response to possible thermal and mechanical (impact) scenarios. Currently, the most significant uncertainties are in the processes immediately following ignition. Flame spread across surfaces of explosives, such as PBX 9501, is of relevance to safety scenarios. We report the results of flame spread experiments in PBX 9501. Horizontal flame spread across the surface of PBX 9501 represents the limiting case of an infinitely wide crack. The flame spread rate for PBX 9501 as a function of pressure from 2 $\times $ 10$^{5}$ Pa -- 1.7 $\times $ 10$^{7}$ Pa obeys $r_\mbox{s} =0.253\,P^{0.545}\mbox{(cm/s)}$where $P$ is the dimensionless experimental pressure defined as $P$/$P_{0}$ with $P_{0}$ = 10$^{5}$ Pa. [Preview Abstract] |
Tuesday, August 2, 2005 10:15AM - 10:30AM |
H2.00005: Shockwave initiation of mixture liquid HE Alexey Men'shikh, A.V. Fedorov, A.L. Mikhaylov, D.V. Nazarov, S.A. Fenyushin, V.A. Davydov The authors performed studies of initiation of mixture liquid HE (of the ``oxidizer-fuel'' type) consisting of tetranitromethane with nitrobenzene (TNM/NB) having mass ratio of 74/26 by planar and spherically diverging shock waves with amplitudes of 10-25 GPa. Laser interferometry method was used to record profile of particle velocity at the HE-window interface. At initiation of HE detonation having thickness of 2-50 mm, the pulsing regime was recorded, maximum pressure of which reached 50 GPa in some parts of the front. Thickness of the layer of pulsing detonation wave was $\sim$150 mm. We recorded dispersion of particle velocity of wave. Different profiles and amplitudes of wave were recorded in one test at different interference lines. At HE thickness of 50 mm, in a series of tests, we recorded normal detonation wave with value of Neumann spike of 35 GPa, value of detonation pressure of 21 GPa. Pulsing detonation regime was also recorded at initiation of the other mixture liquid HE TNM/NB, where NB percentage was from 20 to 50\%. The paper presents hypotheses for explanation of the mechanism of detonation initiation in studied HE. [Preview Abstract] |
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