Publications

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Detonation corner turning describes the ability of a detonation wave to propagate into unreacted explosive that is not immediately in the path normal to the wave. The classic example of a corner turning test has a cylindrical geometry and involves a small diameter explosive propagating into a larger diameter explosive as described by Los Alamos' Mushroom test, where corner turning is inferred from optical breakout of the detonation wave. We present a complimentary method to study corner turning in millimeter-scale explosives through the use of vapor deposition to prepare the slab (quasi-2D) analog of the axisymmetric mushroom test. Because the samples are in a slab configuration, optical access to the explosive is excellent and direct imaging of the detonation wave and "dead zone" that results during corner turning is possible. Micromushroom test results are compared for two explosives that demonstrate different behaviors: pentaerythritol tetranitrate (PETN), which has corner turning properties that are nearly ideal; and hexanitroazobenzene (HNAB), which has corner turning properties that reveal a substantial dead zone.

The microstructure of pentaerythritol tetranitrate (PETN) films fabricated by physical vapor deposition can be altered substantially by changing the surface energy of the substrate on which they are deposited. High substrate surface energies lead to higher density, strongly textured films, while low substrate surface energies lead to lower density, more randomly oriented films. We take advantage of this behavior to create aluminum-confined PETN films with different microstructures depending on whether a vapor-deposited aluminum layer is exposed to atmosphere prior to PETN deposition. Detonation velocities are measured as a function of both PETN and aluminum thickness at near-failure conditions to elucidate the effects of microstructure on detonation behavior. The differences in microstructure produce distinct changes in detonation velocity but do not have a significant effect on failure geometry when confinement thicknesses are above the minimum effectively infinite condition.

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In this work, shock-induced reactions in high explosives and their chemical mechanisms were investigated using state-of-the-art experimental and theoretical techniques. Experimentally, ultrafast shock interrogation (USI, an ultrafast interferometry technique) and ultrafast absorption spectroscopy were used to interrogate shock compression and initiation of reaction on the picosecond timescale. The experiments yielded important new data that appear to indicate reaction of high explosives on the timescale of tens of picoseconds in response to shock compression, potentially setting new upper limits on the timescale of reaction. Theoretically, chemical mechanisms of shock-induced reactions were investigated using density functional theory. The calculations generated important insights regarding the ability of several hypothesized mechanisms to account for shock-induced reactions in explosive materials. The results of this work constitute significant advances in our understanding of the fundamental chemical reaction mechanisms that control explosive sensitivity and initiation of detonation.

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