The shock-induced pore collapsing and hot spot formation processes of plastic bonded explosives are simulated by molecular dynamics. After shock loading, the temperature field, pressure field, particle velocity field, energy field, plastic work field, and plastic temperature field are calculated by using the virtual grid method. A set of microscopic parameters about the hot spot are evaluated, including the pore collapsing time, pore collapsing speed, plastic work, and hot spot radius. The physical models to describe the energy dissipation and temperature relaxation behaviors of the hot spot are developed. We find that the hot spot formation consists of three steps: pore collapsing, work-heat transition, and temperature relaxation. The pore collapsing speed is proportional to the piston speed, and the temperature relaxation time is proportional to the square of the hot spot radius.

In recent years, cyclo-N₅^– has attracted extensive attention because all-nitrogen high-energy-density materials (HEDMs) have been expected to reach a TNT equivalent of over 3.0. However, for cyclo-N₅^–-containing HEDMs, the stabilization mechanism has remained enigmatic. In this study, two typical cyclo-N₅^–-containing metal hydrates, [Na(H₂O)(N₅)]·2H₂O (Na-cyclo-N₅^–) and [Mg(H₂O)₆(N₅)₂]·4H₂O (Mg-cyclo-N₅^–), are selected to gain insights into the factors affecting their stability by the first-principles method. Both binding/lattice energy calculations and density of states analysis show that Mg-cyclo-N₅^– is more stable than Na-cyclo-N₅^–. Hydrogen bonding is the main stabilization mechanism for stabilizing crystals and cyclo-N₅^–. Two types of hydrogen bonds, O–H···O and O–H···N, are clarified, which construct a 3D hydrogen bond network in Mg-cyclo-N₅^– and an intralayer 2D hydrogen bond network in Na-cyclo-N₅^–. Moreover, nonuniform stress causes distortion of cyclo-N₅^–. Comparing the two samples, the distortion degree of cyclo-N₅^– is higher in Na-cyclo-N₅^–, which indicates that cyclo-N₅^– decomposition is easier. These findings will enhance the future prospects for the design and synthesis of cyclo-N₅^–-containing HEDMs.

We simulate the shock loading process of $\beta$ -octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine by molecular dynamics and calculate the isoentropic curve, Hugoniot curve, temperature field, velocity field, stress field, and density field. Based on the simulation results, we develop a physical model to describe the pore collapse, crack expansion, and hot spot formation mechanisms and calculate a set of key parameters, such as pore collapsing speed, rarefaction wave speed, and crack expansion speed. A microscopic physical picture for defect evolution at the early time of shock loading is obtained.