Analysis of shock decomposition and sensitivity of energetic materials with reaxff molecular dynamics

Shock sensitivity of single crystal energetic materials (EM) can depend both on the shock pressure and on crystal direction. The initial response of EM to shock or high-strain loading can be related to such fundamental characteristics of EM as its shear response upon uniaxial compression. To study the influence of shock or impact/strain orientation on initiation and decomposition of energetic materials we have performed a series of molecular dynamics (MD) simulations using ReaxFF reactive force field. Our analysis shows that the sensitivity, pathways, and products of ReaxFF shock simulations in RDX and PETN single crystals are both dependent on compression ratio and the stress. We also found a correlation of PETN shock sensitivity with a behavior of the shear stress upon uniaxial compression. The shear stress in PETN under elastic uniaxial strain ε =1-V/V0 increases monotonically in the sensitive direction [110] up to ε ~ 0.3, while for the less sensitive [100] direction it has more complicated (non-monotonic) behavior for strains ε = 0.25 - 0.35.