Interactions of Inert Confiners with Explosives

Abstract

Abstract. The deformation of an inert confiner by a steady detonation wave in an adjacent explosive is investigated for cases where the confiner is sufficiently strong (or the explosive sufficiently weak) such that the overall change in the sound speed of the inert is small. A coupling condition which relates the pressure to the deflection angle along the explosive-inert interface is determined. This includes its dependence on the thickness of the inert, for cases where the initial sound speed of the inert is less than or greater than the detonation speed in the explosive (supersonic and subsonic inert flows, respectively). The deformation of the inert is then solved by prescribing the pressure along the interface. In the supersonic case, the detonation drives a shock into the inert, subsequent to which the flow in the inert consists of alternating regions of compression and tension. In this case reverberations or 'ringing' occurs along both the deflected interface and outer edge of the inert. For the subsonic case, the flow in the interior of the inert is smooth and shockless. The detonation in the explosive initially deflects the smooth interface towards the explosive. For sufficiently thick inerts in such cases, it appears that the deflection of the confiner would either drive the detonation speed in the explosive up to the sound speed of the inert or drive a precursor wave ahead of the detonation in the explosive. Transonic cases, where the inert sound speed is close to the detonation speed, are also considered. It is shown that the confinement affect of the inert on the detonation is enhanced as sonic conditions are approached from either side.

Experimental observations of detonation in ammonium-nitrate-fuel-oil (ANFO) surrounded by a high-sound-speed, shockless, aluminum confiner

“…It is apparent that increasing the wall thickness not only increases the detonation velocity, but also results in a detonation profile with less overall curvature. Such behavior agrees well with theory [4]. The velocity-curvature relationship for these data are presented in a separate study [9].…”

“…Detonation and aluminum stress wave velocities were recorded with shorting, ionization, and piezoelectric pins embedded in the tube wall. In all cases, increasing the tube wall thickness led to higher detonation velocities and less wavefront 11 Preprint of http://dx.doi.org/10.1016/j.proci.2010.07.084 curvature, as predicted by prior work [4]. Double-shock structure was also observed in some tests and attributed to separation of the imaging window from the explosive.…”

“…As mentioned, this trend was expected due to the extended length of the ANFO reaction zone and the subsonic confinement condition. No inert shocks were present to limit the entire confiner thickness from acting on the reaction zone [4].…”

“…The arrival of the detonation shock near 250 µs then rapidly increases the wall velocity up to 1.0 mm/µs as the wall is driven outwards by the expanding detonation products. Sharpe and Bdzil [4] predicted that the precursor motion would be first inwards, followed by outward motion due to the detonation arrival. This is similar to the current results but does not recover the initial outwards motion observed, which may be an initiation transient.…”

“…The precursor energy can also cause loss of confinement ahead of the detonation, which can also result in detonation failure [3]. Finally, the large reaction zone lengths of NIHEs coupled with the subsonic confinement allow for a much greater dependence of confiner thickness on detonation velocity [4].…”