Detonation Failure Characterization of Homemade Explosives

Abstract

Typically characterizing home made explosives (HMEs) requires many large scale experiments, which is prohibitive given the large number of materials in use. A small scale experiment was developed to characterize HMEs such as ammonium nitrate‐fuel oil mixtures. A microwave interferometer is applied to small scale confined transient experiments, yielding time resolved characterization of a failing detonation that is initiated with an ideal explosive booster charge. Experiments were performed with ammonium nitrate and two fuel compositions (diesel fuel and mineral oil). It was observed that the failure dynamics were influenced by factors such as the chemical composition, confiner thickness, and applied shock wave strength. Thin steel walled confiners with 0.71 mm wall thickness experienced detonation failure and decoupling of the shock wave from the reaction zone. Confiners with a wall thickness of 34.9 mm showed a decrease in propagation speed and a steady reactive wave was achieved. Varying the applied shock strength by using an attenuator showed corresponding changes in the initial overdriven reactive wave velocity in the HMEs. The distance to detonation failure was also shown to depend on the attenuator length when thin wall confinement was used. This experimental method is shown to be repeatable and can be performed with little required material (about 2 g). The data obtained could be useful to model development and validation, as well as quantifying detonability of materials.

Using time-frequency analysis to determine time-resolved detonation velocity with microwave interferometry

“…A 35 GHz signal was generated using a custom microwave interferometer 11 and transmitted to the test article through a solid 0.635 cm diameter polytetrafluoroethylene (PTFE) waveguide. A quadrature mixer was used to produce twochannel output 90…”

“…The average material wavelength values for Primasheet 1000 and TATB were determined from the Landau-Lifschitz/Looyenga (LLL) mixture equation 1 and previous work. 11 The average wavelength for ANUR was estimated for the analysis because no previous data or mixture laws exist for this material at MI frequencies.…”

Reactive flow modeling of small scale detonation failure experiments for a baseline non-ideal explosive

“…2,13 In summary, a 35 GHz signal was generated using a custom microwave interferometer and transmitted to the test article through a solid 6.35 mm dia. polytetrafluoroethylene (PTFE) waveguide.…”

“…There exists a strong need for the screening, characterization, and modeling of nonideal explosives; both in the mining industry to tailor the fracture and heaving processes for rocks, 1 as well as national security to more adequately assess the threat from homemade explosives (HMEs). 2 Slight modifications to a nonideal explosive may have dramatic effects on the sensitivity to initiation and the detonation performance. For example, pre-compressing ANFO beyond $1.4 g/cm 3 may result in initiation failure, owing to the dead-pressing phenomenon.…”

“…In this work, a small scale characterization experiment utilizing a 35 GHz microwave interferometer (MI) is considered following the development by Janesheski et al 2 and Kittell et al 13 Microwave interferometry (MI) is a nonintrusive technique with a high temporal resolution, and is used to measure the instantaneous shock or detonation velocity in explosives. Specifically, this technique records the phase and amplitude of microwave signals that are transmitted through an unreacted explosive and reflected back at dielectric discontinuities, such as a shock wave or reaction front.…”