Abstract
The ignition of aluminized HMX-based polymer-bonded explosives (PBXs) under shock loading is studied via mesoscale simulations. The conditions analyzed concern loading pulses of 20 nanoseconds to 0.8 microseconds in duration and impact piston velocities on the order of 400-1000 m/s or loading stresses on the order of 3-14 GPa. The sets of samples studied have stochastically similar microstructures consisting of a bimodal distribution of HMX grains, an Estane binder, and aluminum particles 50-100 µm in diameter. The computational model accounts for constituent elasto-viscoplasticity, viscoelasticity, bulk compressibility, fracture, interfacial debonding, internal contact, bulk and frictional heating, and heat conduction. The analysis focuses on the development of hotspots under different material settings and loading conditions. In particular, the ignition thresholds in the forms of the James relation and the Walker-Wasley relation and the corresponding ignition probability are calculated and expressed as functions of the aluminum volume fraction for the PBXs analyzed. It is found that the addition of aluminum raises the ignition thresholds, causing the materials to be less sensitive. Dissipation and heating mechanism changes responsible for this trend are delineated.
Highlights
Understanding the physical mechanisms governing the ignition behavior of high explosives (HEs) is a critical challenge when designing insensitive munitions
We focus on the ignition behavior of aluminized HMX-based polymer-bonded explosives (PBXs) under shock pulse loading
The 50% ignition threshold for each Al concentration are mapped as a function of the power flux and energy fluence which are measures for loading condition
Summary
Understanding the physical mechanisms governing the ignition behavior of high explosives (HEs) is a critical challenge when designing insensitive munitions. One of the predominant theories regarding detonation correlates ignition with the development of critical hotspots in an energetic sample under loading.. Microstructure plays a dominant role in the formation of hotspots. Material attributes, including defects, porosity, grain size distribution, can all play a role in localized energy dissipation under shock loading.. The mechanisms behind the development of these critical hotspots, and resulting ignition, is an important topic of research in the field of energetic materials, and currently requires theoretical/simulation approaches to study effectively, as direct experimental measurement of localized heating at the level of individual hotspots remains largely elusive and is only in its infancy Material attributes, including defects, porosity, grain size distribution, can all play a role in localized energy dissipation under shock loading. The mechanisms behind the development of these critical hotspots, and resulting ignition, is an important topic of research in the field of energetic materials, and currently requires theoretical/simulation approaches to study effectively, as direct experimental measurement of localized heating at the level of individual hotspots remains largely elusive and is only in its infancy
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