A theoretical study on crystal defect of HMX and HMX/HTPB PBX

Based on the established models with vacancy and doping point defects, molecular dynamics (MD) simulation has been used to explore the effects of crystal defects on mechanical and detonation properties of perfect β-HMX crystal and β-HMX based polymer-bonded explosives (PBX), in which the hydroxyl terminated polybutadiene (HTPB) is used as a binder. The mechanical properties were obtained by analyzing MD simulation trajectories and the detonation properties were calculated using a corrected Kamlet-J equation. It was found that compared to the elastic coefficients and modulus (tensile, bulk and share) of perfect HMX crystal (1), those of the defect crystals (2 and 3) were decreased and the values of Cauchy pressure and K/G were increased gradually. These account for rigidity weakening comparatively, ductibility and tenacity strengthening comparatively step by step. The mechanical properties of their corresponding three PBXs follow the same changing trends. In addition, detonation property depends on the constitutes and structures of systems. Owing to the inert polymer, the detonation properties of three PBXs decrease comparatively to those of the corresponding three based HMX crystals, that is, crystal(1)≤PBX(1), crystal(2)≤PBX(2) and crystal(3)≤PBX(3). The order of detonation velocity and pressure of PBXs 1, PBXs 2 and PBXs 3 is PBX(1)≤PBX(2)≤PBX(3), coinciding with the one of base explosives (1, 2 and 3), crystal(1)≤ crystal(2)≤crystal(3). All these results and rules can provide guidance to the design of PBX formulations.