Observation of asymmetric explosive density evolution in the deflagration-to-detonation transition for porous explosives

Abstract

We report deflagration-to-detonation transition phenomena in cylindrical columns of porous explosives based on octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The HMX powder and LX-14 (95.5 wt. % HMX and 4.5 wt. % estane polyurethane) prills were observed with high-speed cameras and flash x rays under conditions that allow for precise scaling and registration of the recorded images. These experimental results test the conventional assumption of axisymmetric, effective one-dimensional burning. Polycarbonate confinement tubes allowed this direct imaging with steel spheres employed as radio-opaque fiducials. Spheres embedded in the explosive column revealed the displacement of the explosive prior to deflagration. X-ray and fast camera images show that a dense plug of compact explosive develops ahead of the deflagration front. The internal fiducials register both internal changes in the plug and changes in the position between successive x-ray images. Tantalum witness strips placed on the inner wall of the explosive channel revealed radial expansion of the tube bore at successive x-ray exposures, indicating the internal pressure of about 100 MPa just before detonation. Images indicate that the deflagration is not only asymmetric but also involves newly observed transient phenomena just before detonation. We typically see a brief but continuous increase in deflagration speed and the formation of a deflagration channel that bypasses the plug just prior to detonation. We hypothesize that these phenomena play an important role in the deflagration-to-detonation transition itself.