Shock Induced Ignition of Porous HMX-Computational Examination of Hot-Spot Formation Rates

摘要

Experiments have shown that shock induced initiation of porous explosives is in- fluenced by the effective packing density and the size and shape of the particles. Character- izing ignition behind compaction shocks is important for describing the initiation and fail- ure of detonation which establishes the material’s sensitivity. The ignition time behind the wave, which represents the onset of measurable vigorous combustion due to growth and co- alescence of reactive hot-spots, is controlled by distributions in the intensity, size, and spa- tial proximity of hot-spots which depend on mesostructure and wave strength. Mesoscale simulations of planar shock propagation in porous HMX are performed to characterize how initial packing density affects the formation rate of reactive hot-spots by steady waves. It is shown that the distribution of formation times relative to the wave is exponential which is indicative of a time invariant Poisson process. The effective formation rate, established by the formation time distribution, is related to wave strength using 1) an Arrhenius descrip- tion that leads to a kinetic interpretation of reactive hot-spot formation and 2) a conventional power law description in terms of wave pressure. A simple "P~nτ -type" relation for the ig- nition induction time behind a wave is proposed based on a cumulative ignition function that depends on mesostructure through the effective reactive hot-spot formation rate.