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Models for explosives containing metal particles must consider the complex gas-particle flow that is generated following detonation of the explosive. Previous experimental studies have shown that when a layer of solid particles is explosively dispersed, the particles often develop a non-uniform spatial distribution. The instabilities within the particles and at the particle layer interface likely form on the timescale of the detonation propagation through the particles. The mesoscale perturbations are manifested at later times in experiments by the formation of clusters of particles or coherent jet-like particle structures which persist for some distance during the dispersal process. These particle jets influence the particle-gas mixing and hence particle reaction rates at the macro scale. The particle instabilities that occur in explosively dispersed particles are investigated with a mesh-free computational method (smoothed-particle hydrodynamics). The simulations are compared with experimental results for the dispersal of a cylindrical packed bed of particles surrounding a central explosive charge. Of particular interest is the effect of the particle density and charge/particle mass ratio on the susceptibility of the particles to form jets. [ABSTRACT FROM AUTHOR]

A new experimental technique was developed to directly observe the onset of shock initiation in powder mixtures contained in recovery capsules over time scales ranging from hundreds of nanoseconds to at least hundreds of milliseconds. Simultaneously with a thermocouple embedded in the test mixture to monitor bulk temperature changes, a photomultiplier tube detected light emissions produced by the reacting sample. A window/optic fiber system was developed that remained intact and did not move during the experiment. A polycarbonate window was placed into a steel recovery capsule, which was held solidly in place in a steel anvil designed to protect the fiber optic and to prevent motion of the window. Samples of as-blended 5Ti+3Si powders and ball-milled mixtures 5Ti+3Si were tested in this setup. In all experiments, a weak light emission peak was observed upon shock passage followed by much more intense light beginning a few milliseconds to a few hundreds of milliseconds later. The intense light emissions occurred at approximately the same time as a bulk temperature increase measured with the thermocouple. These results suggest that only a very small fraction of the sample was initiated by the shock. [ABSTRACT FROM AUTHOR]

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 significantly lower the sensitivity or reaction rates of the mixtures investigated. [ABSTRACT FROM AUTHOR]

Archival front curvature data from two studies of nitromethane detonating in Pyrex tubes are re-read from the original films to obtain detonation wave shapes. Each data set is fit with an analytic form, for which the fitting parameters are tabulated. The wavefront fits are also plotted in normal velocity-curvature (D[SUBn][κ]) space in which, according to the simplest detonation shock dynamics model, they should follow a common curve. All D[SUBn][κ] curves do overlay for sufficiently small curvatures, but diverge at larger curvatures. A single best D[SUBn][κ] function is obtained by a global optimization scheme that considers both the diameter effect curve and each shock shape. The effect of a concentration χ of diethylenetriamine sensitizer is estimated by scaling this calibration function for pure nitromethane in a manner consistent with sensitized rate stick data, giving a calibration surface D[UBn][κ, χ]. [ABSTRACT FROM AUTHOR]