Effect of pore morphology and multiple hotspot formation mechanisms in high energetic materials

The detonation sensitivity of energetic materials depends strongly on the localization of energy in hotspots. Hotspots with temperatures above a critical value can form self-sustained deflagration waves, which subsequently can turn into a detonation. Shock-induced pore collapse is one of the most important hotspot formation mechanisms. Defects or pores in HE materials are complicated and usually have much different morphologies. Although numerous studies have reached the general conclusion of higher porosity results in higher shock sensitivity, the detailed hotspot formation mechanism or mechanisms for complex pore morphology has not been well understood.

Recently, we conducted a series of large-scale atomistic simulations on the collapse of pore with high aspect ratios under shock condition. We find that multiple hotspot formation mechanisms coexist for this kind of pores. The hotspot formation mechanism also depends on shock strength. Under the shock condition of particle velocity over 750 m/s, there are three main hotspot formation mechanisms, i.e., zipping of pore boundaries, recompression of a molecule jet, and impact of molecule on downstream void surface. If the particle velocity below 750 m/s, the mechanisms reduce to shear band or shear band accompanied with zipping of pore boundaries. Another important finding is that the molecule jet is accelerated inside the void and the acceleration rate as well as the maximum molecule velocity, as well as resulted hotspot temperature, are strongly depending on both pore curvature and aspect ratio.