Hot spot formation and initial chemical reaction of PETN containing nanoscale spherical voids under high shock loading

Abstract

The initial response process of PETN containing nanoscale spherical cavities under impact loading was investigated using the ReaxFF-lg force field combined with the molecular dynamic method. The impact-induced void collapse process, hot spot formation and growth, and chemical reaction processes were determined. The hot spot formation goes through four stages: (1) overall temperature rise due to initial impact compression; (2) temperature rise on the upper surface of the void caused by local plastic deformation; (3) rapid temperature rise caused by molecules entering the interior of the void colliding with the downstream surface of the void; and (4) thermal diffusion between the hot spot and the surrounding region, resulting in a decrease in the temperature of the center of the hot spot and a slow increase in the temperature of the neighboring region. With weak impact, the void shape remains basically symmetric during the void collapse, and the void collapse is mainly caused by local plastic deformation. A strong impact will lead to a more intense material focusing. The void collapse caused by strong impact has a greater effect on the heating of the surrounding material, and the secondary compression formed by the collision between particles makes the hot spot area expand and the central region of the hot spot evolve into an approximate triangular cone. NO₂ is produced in large quantities as the initial product during the void collapse to form the hot spot, indicating that the void activates the chemical reactivity of the PETN crystal.