Detonation mechanisms in a condensed-phase porous explosive

In the present study, we experimentally investigate detonation mechanisms in heterogeneous media using a model explosive in which the physical and chemical properties can be easily varied. The model explosive is composed of a packed bed of solid inert beads with a liquid explosive completely filling the voids between the beads. The liquid explosive consists of NM chemically sensitized with diethylenetriamine (DETA), and glass beads ranging in size from 66 mum to 2.4 mm.; By changing the bead size in a mixture of NM with 15% DETA in glass beads, we have found two very different types of critical diameter behavior for small and large beads. For beads smaller than 1 mm in diameter (regime II), the critical diameter of the mixture increases with increasing bead size. For beads larger than 1 mm (regime I), the trend is reversed. Velocity measurements in the three regimes of propagation show a weak diameter-effect for regimes I and II and unstable velocities in regime III. Hence we have found three distinct regimes of detonation propagation that depend on the local physical and chemical length-scales of the heterogeneous explosive. Reducing the amount of DETA was found to cause a sharp increase in the critical diameter in regime I and a slight decrease in the critical diameter in regime II, further emphasizing the difference in the propagation mechanisms.; To interpret the observed regimes of detonation behavior, we propose two competing propagation mechanisms within the explosive. In regime I, the global detonation front is controlled by local detonation wavelets that propagate in the pores between the beads. Here, the local diffraction and reinitiation of the wavelets is assumed to play an important role in the macroscopic detonation properties. In regime II, the global detonation is controlled by a sympathetic mechanism of shock initiation of isolated explosive pockets in the porous bead bed.; A simple qualitative model was developed based on hot spot generation from both particles and natural detonation-front instabilities. The competition between these two types of hot spots is found to play a crucial role in the transition from one detonation propagation regime to the other. Natural hot spots dominate the detonation propagation in the regime I while particle-generated hot spots dominate the regime II. The model agrees qualitatively with the experimental results, and hence provides a promising approach to modeling the two propagation regimes in the present packed-bead explosive. The present study thus lends insight into two types of micro-mechanisms in heterogeneous condensed phase explosives and provides a qualitative model capable describing the detonation properties caused by multiple-regime behavior. (Abstract shortened by UMI.)...