Effects of void size, density, and arrangement on deflagration and detonation sensitivity of a reactive empirical bond order high explosive

The shock response of two-dimensional model high explosive crystals with various arrangements of circular voids is explored. We simulate a piston impact using molecular-dynamics simulations with a reactive empirical bond order model potential for a submicron, subnanosecond exothermic reaction in a diatomic molecular solid. Voids of radius 10 nm reduce the minimum initiating velocity by a factor of 4; a single 2.5 nm void (per periodic image) reduces the minimum velocity for detonation by 10% and the exponent of the induction time's pressure dependence by about 4. In square lattices of voids all of one size, reducing that size or increasing the porosity while holding the other parameter fixed causes the hotspots to consume the material more quickly and detonation to occur sooner and at lower piston velocities. The early time behavior is seen to follow a very simple ignition and growth model. The hotspots collectively develop a broad pressure wave (a sonic, diffuse deflagration front) that, upon merging with the lead shock, transforms it into a detonation. The reaction yields produced by triangular lattices are not significantly different. With random void arrangements, the mean time to detonation is 15.5% larger than with the square lattice; the standard deviation of detonation delays is just 5.1%.