In this work, microstructure dependent impact-induced failure of hydroxyl-terminated polybutadiene (HTPB)–cyclo-tetra-methylene-tetra-nitramine (HMX) energetic material samples is studied using the cohesive finite element method (CFEM). The CFEM model incorporates experimentally measured viscoplastic constitutive behavior, experimentally measured interface level separation properties, and phenomenological temperature increase due to mechanical impact based on viscoplastic and frictional energy dissipation. Nanoscale dynamic impact experiments were used to obtain parameters for a strain-rate dependent power law viscoplastic constitutive model in the case of bulk HTPB and HMX as well as the HTPB–HMX interfaces. An in situ mechanical Raman spectroscopy (MRS) setup was used to obtain bilinear cohesive zone model parameters to simulate interface separation. During analyses, the impact-induced viscoplastic energy dissipation and the frictional contact dissipation at the failed HTPB–HMX interfaces is found to have a significant contribution toward local temperature rise. Microstructures having circular HMX particles show a higher local temperature rise as compared to those with diamond or irregularly shaped HMX particles with sharp edges indicating that the specific particle surface area has a higher role in temperature rise than particle shape and sharp edges. Regions within the analyzed microstructures near the HTPB–HMX interfaces with a high-volume fraction of HMX particles were found to have the maximum temperature increase.
For energetic crystals such as HMX, the sensitivity of the material to shock, the possibility of initiation, and the subsequent reaction is known to be controlled by processes occurring at the crystal level. The anisotropic nature of β-HMX can be critical in determining the performance of HMX based polymer bonded explosives, which are widely used across multiple industries as propellant or explosives. In this work, we experimentally obtain constitutive parameters for characterizing the response of multiple crystalline planes of β-HMX crystals to external loading. Nanoindentation and small-scale dynamic impact experiments were performed on multiple planes of β-HMX crystals to comparatively measure the indentation moduli in multiple orientation directions. Anisotropic material behavior, involving constitutive elastic and non-elastic parameters, was measured and studied. Findings regarding material properties for the (100), (010), (001), {110}, and {011} planes of β-HMX are presented and compared with literature data.
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