Damage-ignition mechanism of composite energetic materials with different densities under multi-pulse loading

Ignition of composite energetic materials (CEMs) may occur under multi-pulse loading, involving a complex interplay between damage and hotspot accumulation. The ignition mechanism is not clear due to the heterogeneous structure and complexity of the loading. In this study, multi-pulse dynamic compression tests were conducted on CEMs with different initial densities. The deformation, damage evolution, ignition behavior and temperature field were quantitatively characterized using a high-speed camera and an ultra-high-speed electro-optical framing camera. A coupled damage-ignition constitutive model for CEMs was established, including tensile failure, shear fracture and an ignition criterion governed by cumulative plastic dissipation. The results showed that ignition occurred during the third loading pulse. The ignition threshold and ignition delay time of CEMs are strongly dependent on the initial density and loading condition. The ignition and burning processes exhibited spatial heterogeneity. The hotspots first appeared near the outer region of the specimen, where shear strain rate was highly concentrated, and then rapidly propagated outward. Stress concentration and shear localization are more likely to occur in specimens with lower initial density, resulting in shorter ignition delay times and higher peak hotspot temperatures. The ignition mechanism of CEM samples with different densities under dynamic loading was revealed.