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Ignition Criterion for Heterogeneous Energetic Materials Based on Hotspot Size-Temperature Threshold

Min Zhou (Georgia Institute of Technolog), Ananda Barua (Georgia Institute of Technology), Seokpum Kim (Georgia Institute of Technology), Yasuyuki Horie (Air Force Research Lab)

Symposium in honor of Rod Clifton on the occasion of his 75th Birthday

Mon 10:45 - 12:15

Salomon 101

A criterion for the ignition of heterogeneous energetic materials under impact loading is developed. The criterion is based on integration of a quantification of the distributions of the sizes and locations of hotspots in loading events and a characterization of the critical size-temperature threshold of hotspots required for chemical ignition of solid explosives. The criterion, along with proper computational capability to quantify the thermal-mechanical response of energetic materials under dynamic loading, allows the critical impact velocity for ignition, time to ignition, and critical input energy at ignition to be determined as functions of material composition, microstructure and loading conditions. As an application, numerical studies are undertaken to evaluate the ignition threshold of granular HMX (GX) and HMX/Estane PBX under loading with impact velocities up to 350 ms-1 and strain rates up to 10^5 s-1. Results show that, for the GX, the time to criticality (tc) is strongly influenced by initial porosity, but is insensitive to grain size. Analyses also lead to a quantification of the differences between the responses of the GXs and PBXs in terms of critical impact velocity for ignition, time to ignition, and critical input energy at ignition. The applicability of the relation between the critical input energy (E) and impact velocity developed by James for shock loading is examined, leading to a modified interpretation which is sensitive to microstructure and loading condition.