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 S1: Detonations & Shock-Induced Chemistry V |
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Chair: Hugh James, AWE, Aldermaston, UK Room: Hyatt Regency Constellation B |
Thursday, August 4, 2005 9:30AM - 9:45AM |
S1.00001: Detonation in Pre-Compressed Nitromethane Akio Yoshinaka, Andrew J. Higgins, Oren E. Petel, Vincent Tanguay, Fan Zhang Detonation propagation in liquid nitromethane (NM) that has been pre-compressed by multiple shock waves was investigated experimentally. An explosively driven flyer plate is allowed to impact a thin NM sample encapsulated between two higher impedance metallic plates. Resulting multiple shock reverberations between the two plates quasi-isentropically compresses the NM to densities 1.5 times its initial value, with pressure plateaus typically ranging between 5 and 8 GPa. A secondary event then initiates detonation in a direction perpendicular to that of the reverberating shock wave. Light emitted from the detonation front is recorded through the use of photodiodes monitoring discrete locations along the detonation path. The results are compared with previous investigations of incident and reflected shock initiation of detonation to explore the detonation initiation mechanism of liquid explosives. [Preview Abstract] |
Thursday, August 4, 2005 9:45AM - 10:00AM |
S1.00002: Shock-Induced Chemical Reaction in Organic and Silicon-Based Liquids Stephen Sheffield, Dana Dattelbaum, David Robbins, Rick Alcon, Richard Gustavsen Shock-induced chemical reactions remain an area that needs to be closely studied to determine the influence of pressure, temperature, and chemical structure on reactivity. Several studies have been performed in the past that indicate dimerization, polymerization, and decomposition take place in different shock-produced pressure and temperature regimes depending on chemical functionality. We present results obtained from single-shock experiments on several organic and silicon-based liquids, which used embedded multiple magnetic gauges to measure the shock profile as a function of Lagrangian position in the liquid. A comparison will be made between reactivity in carbon vs. silicon-based materials. A discussion of the relationship between free energy and the input shock parameters producing chemical reaction will also be presented. [Preview Abstract] |
Thursday, August 4, 2005 10:00AM - 10:15AM |
S1.00003: Effect of Shock Precompression on the Critical Diameter of Liquid Explosives Oren E. Petel, Andrew J. Higgins, Akio Yoshinaka, Fan Zhang The critical diameter of both ambient and shock precompressed liquid explosives confined in PVC tubing are measured experimentally. In the precompression experiments, the explosive is compressed by a strong shock wave generated by a donor explosive and reflected from a high impedance anvil prior to being detonated by a secondary event. The final pressure in the test section reaches approximately 6.8 GPa before the detonation enters the test section. The results demonstrate a 20{\%} decrease in the critical diameter for the shock compressed explosive. This critical diameter decrease is observed despite a significant decrease in the predicted Von Neumann temperature of the detonation in the precompressed explosive. The results are discussed in the context of theoretical predictions based on thermal ignition theory and previous critical diameter measurements. [Preview Abstract] |
Thursday, August 4, 2005 10:15AM - 10:30AM |
S1.00004: Modelling temperatures of reacting nitromethane Roberta Mulford, Damian Swift Detonations are chemical reactions and as such may appropriately be modelled using a temperature-dependent rate model. We test the predictions of such a model against temperatures reported for shock-loaded and reacting nitromethane liquid. Liquid nitromethane has the advantage of being largely free of pores, and thus reacting homogeneously to produce a single uniform temperature, rather than exhibiting ``hot-spots.'' The liquid is also transparent, allowing observation of emission from the shocked and reacting state rather than the surface. A thermodynamically complete EOS is necessary in order to apply a temperature- dependent rate model within a hydrocode. A quasiharmonic EOS is used to determine an adequately reliable temperature for a given state in pressure and energy. The temperature is determined by assuming that available energy is distributed over vibrational modes for the reactant molecule. The model has previously been shown to reproduce measured particle velocity profiles that compare well with published reactive behavior. [Preview Abstract] |
Thursday, August 4, 2005 10:30AM - 11:00AM |
S1.00005: Development of Optical Diagnostics to Probe Post-Detonation Processes Invited Speaker: Recent developments have spurred a need to recognize processes that occur after the detonation of energetic materials. Understanding enhanced explosive effects whereby substantial energy releasing steps happen nanoseconds to milliseconds after a detonation is a critical need. Optical diagnostic methods are promising because they can meet stringent requirements inherent in detonation events. Optical sensors can monitor fast events and can be remotely placed to be immune from the heat and pressure inherent in a detonation. They thus complement electrical gauges currently in use. We have applied time-resolved emission spectroscopy in monitoring the transient chemical processes in several detonating formulations. Gauges using refractive index to measure pressure have also been developed. Optical fibers have also been tremendously useful in determining shock velocities. These measurements of transient chemistry, pressure and particle flow are essential in unraveling these complex post detonation processes. Other optical techniques in development will be discussed. The scope of applications for these gauges and their limitations will be presented. [Preview Abstract] |
Thursday, August 4, 2005 11:00AM - 11:15AM |
S1.00006: Proton Radiography Observations of the Failure of a Detonation Wave to Propagate to the End of a Conical Explosive Charge Eric N. Ferm, Fesseha G. Mariam Failure diameter is a well-known property of explosive materials, being the critical diameter below which a steady detonation wave will not be able to support itself and ultimately fails to propagate. A detonation wave traveling down a uniform cylindrical charge larger than its critical diameter will reach a steady detonation velocity which is a function of the diameter of the explosive as well as other material properties, notably density and temperature. In this work, we use proton radiography to study the propagation of detonations down conical PBX 9502 charges beginning at diameters larger than failure diameter and ending at diameters much smaller than failure diameter. Experiments show cases where complete detonation of the cone occurs as well as cases where failure is observed significantly before the end of the cone and significant portions of the charge remain unreacted. Wave velocities and densities are obtained from the multiple image proton radiography experiments and compared with failure diameter effect curves for PBX 9502. [Preview Abstract] |
Thursday, August 4, 2005 11:15AM - 11:30AM |
S1.00007: Study of detonation wave structure in solid and liquid tetranitromethane Dmitry Nazarov, Anatoly Mikhailov, Alexey Fedorov, Alexey Men'shikh, Stanislav Finushin, Valery Davydov, Tatiana Govorunova Investigations of detonation front structure and parameters in solid and liquid tetranitromethane were done using Doppler Fabry-Perot velocimeter. We recorded the particle velocity of explosion products, braking on the HE/window interface. Smooth front of the detonation wave and concave negative-going mass velocity profile were recorded for liquid TNM, i.e. breaks of registration on the interferograms and mass velocity fluctuations on an unloading wave were not observed. The evaluated Neumann spike value was Ð$_{N}^{liq}_{TNM}$=21.6 GPa, U$_{N}^{liq}_{TNM}$=2.07 mm/$\mu $sec. Solid TNM becomes heterogeneous, obtains polycrystalline structure and its density grows from $\rho _{0}^{liq}$=1.64~g/cm$^{3}$ up to $\rho _{0}^{sol}$=1.82~g/cm$^{3}$ ($\rho _{0}^{sol (TMD)}$=2.00 g/cm$^{3})$. The experimental records indicates, that because of solid TNM heterogeneity flow turbulization occurs behind detonation wave front. Fluctuation on the particle velocity U(t) profile appears with amplitude $\Delta $U=20{\ldots}220 m/s duration - $\Delta $t= 40{\ldots}180nsec. The registered Neumann spike value in solid TNM P$_{N}^{sol}_{TNM}$=28.7 GPa and U$_{N}^{sol}_{TNM}$=2.27~mm/$\mu $sec exceeds C-J value in solid TNM in 1.33 times. [Preview Abstract] |
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