The Fundamental Chemistry and Physics of Munitions under Extreme Conditions

We developed the ReaxFF first-principles based reactive molecular dynamics RMD modeling approach to determine the nanoscale phenomena underlying shock detonation processes of energetic materials EM. Using the ReaxFF approach, we proposed Compressive Shear Reactive Dynamics CS-RD simulation methodology to predict sensitivity of explosive crystals under combined shock and shear load. We also developed empirical van der Waals correction to Density Functional Theory for calculating accurate equation of states EOS of EM. We implemented ReaxFF in parallel multiprocessor software to carry out large-scale simulations of initiation chemistry in homogeneous and heterogeneous HE under mechanical shock and shear on supercomputers. We discovered that sensitivity is dominated by a combination of shear and compression, with the rate of decomposition and temperature increase correlating with the experimental differences in sensitivity. The second major focus was on the development of multiscale modeling of HE detonation using novel finite elements method with explicit generation of slip lines in the subgrain microstructure and inclusion of thermochemical constitutive parameters obtained from RD modeling to predict the hot spot formation and reaction initiation at the subgrain scale in polycrystalline explosives. The methodologies were successfully tested and validated by computational prediction of anisotropic sensitivity of PETN, as well as the formation of hot spots and chemical initiation in polycrystalline PETN.