Mechanical behavior of PBX with different HMX crystal size during die pressing: Experimental study and DEM simulation

The effects of crystal size on the mechanical properties and meso-mechanical behavior of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) based polymer bonded explosives (PBX) during die pressing were systematically studied based on experiments and Discrete Element Method (DEM) simulations. The experimental results show that under the same pressure, larger crystal size will show higher relative breakage (B_r), and further lead to the increase of density and the decrease of mechanical strength. By using DEM simulations which considered the realistic particle shape and microstructure of component crystals and binder, a comprehensive understanding of meso-mechanical behavior of PBX powder during die pressing has been achieved. Under the same stress, the maximum contact force between particles increases along with the crystal size. Tensile micro-cracks dominated the crystal breakage during the loading process. Energy dissipation results indicate crystal breakage plays a key role in promoting crystal displacement and enhancing the interparticle friction dissipation. Particularly, at small strains, crystal breakage disrupts the strain energy build-up. At large strains, particle breakage is greatly reduced, steady energy dissipation by elastic potential energy build-up and interparticle friction can be observed.