Ignition Desensitization of PBX via Aluminization
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TRODUCTION
SOME modern high explosive mixtures contain aluminum particles for enhanced performance.[1] Historically, the initial purpose of using Al, at least for some explosive formulators, was to improve the mixing of explosive crystals in binders,[2] as it is known that the inclusion of aluminum decreases the viscosity of PBX.[3,4] Studies have been conducted on not only the mechanism through which Al particles affect the performance, but also on desired timing for the addition of the particles and how they affect the microstructure of the materials. However, there has been little basic scientific research on the influence of aluminum addition on explosive ignition and ignition sensitivity, be it in the context of accidental insults or design loads. A few exceptions to this statement are the papers that have reported a desensitizing effect of Al particle addition in drop weight test.[4,5] In this paper, we report a first attempt to analyze this issue computationally by focusing on one configuration of a HMX/Estane PBX. The approach we use is based on a cohesive finite element method (CFEM) we developed in the last few years for PBXs and granular explosives.[6–10] This framework accounts for finite elasticity, viscoelasticity, viscoplasticity, internal fracture, contact, friction, frictional heating, and heat conduction. The overall analyses also entail the use of a hotspot-based ignition criterion and a scheme to quantify the size-temperature states of hotspots in the SEOKPUM KIM, Graduate Student, and MIN ZHOU, Professor, are with The George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30318. Contact e-mail: [email protected] YASUYUKI HORIE is recently retired from Munitions Directorate, Air Force Research Lab, Eglin AFB, FL 32542. Manuscript submitted on April 13, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
overall microstructures and in the energetic phase of the microstructures more specifically.[8] The extension here in this paper beyond the previous studies is to add Al to the constituents considered. The calculations quantify the response of the PBX and identify trends which can be used for future, more systematic studies on the behavior of aluminized PBXs. In particular, the calculations presented in this paper are limited to the addition of one population of mono-sized Al particles. The microstructures are designed in a way to keep the total solid (Al and HMX) fraction constant, while the fraction of the HMX is adjusted accordingly as the Al fraction is increased. We adopted this methodology following the practice in the publically available literature on the effect of Al addition.[4,5,11–13] The goal here is to identify a possible desensitizing effect of Al in low velocity impact loading that is beyond the effect of reduced fractions of solid explosive crystals in an overall PBX. As will become clear, the trend identified by numerical simulations is in qualitative agreement with available experimental data in the literature.
II.
FRAMEWORK OF ANALYSIS
A. Material
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