Small‐Scale Characterization of Shock Sensitivity for Non‐Ideal Explosives Based on Imaging of Detonation Failure Behavior

Abstract

The plethora of potential homemade explosive (HME) formulations combined with the fact they often exhibit large critical diameters make them expensive to characterize with traditional large-scale tests. A relatively new method for small-scale characterization was investigated using non-ideal explosive charges consisting of ammonium nitrate (AN) and various fuels. Here, we extend this method using an optical characterization technique that utilizes the decay rate of the reaction wave velocity in failing detonations of sub-critical diameter charges as a metric for the shock sensitivity of an explosive. The conditions required for successful detonation initiation and failure have long been used to investigate shock sensitivity (critical diameter, gap tests, run-to-detonation experiments); however, the failure regime still remains largely unexplored. The utility of this small-scale characterization technique lies in its ability to determine the relative shock sensitivity of explosive with minimal material and experiments while simultaneously providing transient velocity data for potential use in modeling efforts. In this work, high speed imaging was used and analyzed to determine rates of reaction wave velocity decay in the AN-fuel samples. Among the fuels tested with AN were diesel (ANFO), nitromethane (ANNM), and aluminum (ANÀ Al). It was found that nitromethane was the most effective at sensitizing the AN of the systems considered. In both ANNM and ANÀ Al, maximum shock sensitivity (here measured as the minimum reactive wave velocity decay rate) occurred at fuel percentages below stoichiometric mixtures. This was interpreted to be due to the competing effects of stoichiometry and hot spot criticality. Sensitivity results were compared to run-to-failure (RTF) distances and published critical diameter trends which showed good correlation.

Urea‐Hydrogen Peroxide (UHP): Comparative study on the experimental detonation pressure of a non‐ideal explosive

“…First, at large scale, using an optical system, we looked at the Attenuated Shock Velocity (ASV) in different inert materials. Secondly, in an attempt to study large-scale behaviour from lab-scale experiments [2,16,17] and avoid time-consuming, expensive and potentially hazardous large-scale experimental campaigns, we used Photonic Doppler Velocimetry (PDV) in combination with a Polymethylmethacrylate (PMMA) impedance window (IW). One of the key advantages of this method, compared for example to the flyer plate method [15,18], is the potential ability to capture the whole particle velocity history of an explosive/inert material interface from one single shot.…”

“…Carbamide Peroxide, an adduct of Urea and Hydrogen Peroxide (UHP), is industrially used as a solid source of hydrogen peroxide. Like other oxidisers such as ammonium nitrate (AN) [1], or AN‐based explosive compositions [2], it exhibits significant non‐ideal detonation properties at the 10‐cm scale. To the best of our knowledge, the explosive behaviour of UHP was rather recently studied in the literature and a detailed characterisation of UHP detonation performance parameters is still lacking.…”