IMPACT INDUCED MICROSTRUCTURAL AND CRYSTAL ANISOTROPY EFFECTS ON THE PERFORMANCE OF HMX BASED ENERGETIC MATERIALS

This work presents findings in the combined experimental and computational study of the effects of anisotropy and microstructure on the behavior of HMX-based energetic materials. Large single crystal samples of β-HMX were meticulously created by solvent evaporation for experimental purposes, and respective orientations were identified via x-ray diffraction. Indentation modulus and hardness values were obtained for different orientations of β-HMX via nanoindentation experiments. Small-scale dynamic impact experiments were performed, and a viscoplastic power law model fit, to describe the anisotropic viscoplastic properties of the crystal. The anisotropic fracture toughness and surface energy of β-HMX were calculated by studying indentation-nucleated crack system formations and fitting the corresponding data to two different models, developed by Lawn and Laugier. It was found that the {011} and {110} planes had the highest and lowest fracture toughnesses, respectively. Drop hammer impact tests were performed to investigate effects of morphology on the impact-induced thermal response of HMX. Finally, the anisotropic properties obtained in this work were applied in a cohesive finite element simulation involving the impact of a sample of PBX containing HMX crystals with varying orientations. Cohesive finite element models were generated of separate microstructure containing either anisotropic (locally isotropic) or global isotropic properties of HMX particle. In comparison, the isotropic model appeared to be more deformation resistant.