Shock-induced energy localization and reaction growth considering chemical-inclusions effects for crystalline explosives

Abstract

Chemical inclusions significantly alter shock responses of crystalline explosives in macroscale gap experiments but their microscale dynamics origin remains unclear. Herein shock-induced energy localization, overall physical responses, and reactions in α-1,3,5-trinitro-1,3,5-triazinane (α-RDX) crystal entrained various chemical inclusions were investigated by the multi-scale shock technique implemented in the reactive molecular dynamics method. Results indicated that energy localization and shock reaction were affected by the intrinsic factors within chemical inclusions, i.e., phase states, chemical compositions, and concentrations. The atomic origin of chemical-inclusions effects on energy localization is dependent on the dynamics mechanism of interfacial molecules with free space volume, which includes homogeneous intermolecular compression, interfacial impact and shear, and void collapse and jet. As introducing various chemical inclusions, the initiation of those dynamics mechanisms triggers diverse decay rates of bulk RDX molecules and hereby impacts on growth speeds of final reactions. Adding chemical inclusions can reduce the effectiveness of the void during the shock impacting. Under the shockwave velocity of 9 km/s, the parent RDX decay rate in RDX entrained amorphous carbon decreases the most and is about one fourth of that in RDX with a vacuum void, and solid HMX and TATB inclusions are more reactive than amorphous carbon but less reactive than dry air or acetone inclusions. The less-dense shocking system denotes the greater increases in local temperature and stress, the faster energy liberation, and the earlier final reaction into equilibrium, revealing more pronounced responses to the present intense shockwave. The quantitative models associated with the relative system density (RDsys) were proposed for indicating energy-localization mechanisms and evaluating initiation safety in the shocked crystalline explosive. RDsys is defined by the density ratio of defective RDX to perfect crystal after dynamics relaxation and reveals the global density characteristic in shocked systems filled with chemical inclusions. When RDsys is below 0.9, local hydrodynamic jet initiated by void collapse dominates upon energy localization instead of interfacial impact. This study sheds light on novel insights for understanding the shock chemistry and physical-based atomic origin in crystalline explosives considering chemical-inclusions effects.