Micromeritic Analysis of the Rheology and Mechanics of Castable Plastic Bonded Energetic Materials

The risks of uncontrolled explosions in sensitive energetic materials used in ammunition are high due to formation of heat from friction or pressure build-up as a result of an impact. Polymer bonded explosives (PBX) composed of energetic powders dispersed in an inert polymer matrix ensure insensitivity and are used in modern ammunition. The initial viscosity of the uncured explosive right after mixing is critical as the formation of air gaps that may initiate energetic reactions locally due to adiabatic compression must be prevented during casting into warheads. In this study, we used cyclotetramethylene tetranitramine (HMX), as the solid energetic material. We found the optimum initial viscosity of the HMX-based PBX before casting and curing depending on physical factors, such as solid filler loading (wt/wt), mean particle size, and modality, i.e. fine-to-coarse ratio of energetic fillers. We used HMX mixtures with varying fine-to-coarse ratios in monomodal, bimodal, and trimodal forms.