Molecular Dynamics Simulation Study On The Structure And Properties Of HMX And PETN And Their Composite Materials

Both HMX (octahydro-1,3.5,7-tetranitro-1,3,5,7-tetrazocane) and PETN (pentaerythritol tetranitrate) are single compound explosives with high chemical stability and excellent explosive performance. Molecular dynamics (MD) simulation was employed to explore HMX and PETN and their composite materials with COMPASS force field. The relationship between structure and properties were discussed particularly associated with sensitivity and safety performance.In this thesis, firstly, the influence of different HMX models for MD simulation was studied. The results show that the larger cutting models are suitable for MD simulation. Secondly, the appropriate models for HMX and HMX/paraffin composite system were simulated at five different temperatures, i.e.,245K,295K,345K,395K and445K. The relationships of structure, energy and mechanical properties with sensitivity were studied. And the desensitization mechanism for paraffin was revealed. The maximum bond length (Lmax), the interaction energy (EN-N) of the N-N trigger bond and the cohesive energy density (CED) were related to the heat and impact sensitivity. Finally, three HMX/hydroxyl-terminated polymer PBXs were investigated by MD simulation whose three binding materials are hydrogenated hydroxyl-terminated polyisoprene (HHTPI), hydroxyl-terminated polybutadiene (HTPB) and hydroxy-terminated polyether (HTPE). It has found that HTPB is the best binder of the three binders in consideration of the three basic properties:compatibility, safety and mechanical properties. By these researches, reference or instruction for the PBXs formulations can be provided.With regard to MD simulation of PETN and PETN-based composite materials, the influence of models and temperatures were studied firstly. It has also found that the cutting model can obtain stable and better results. Then, MD simulation was conducted for PETN/TNT composite explosive at four different temperatures, i.e.,195K,245K,295K and345K. The structure, energy, mechanical properties and temperature effects were discussed. The micro-structure theoretical criteria of sensitivity for composite explosives were checked and verified. In addition, it has also found that the Lmax value of PETN/TNT is smaller than that of PETN, the value of EN-N of PETN/TNT is higher than that of PETN, and mechanical properties of PETN/TNT are better than those of PETN at all temperatures. It is thus suggested that the comprehensive performance of the composite explosive is better than the single compound explosives, which agrees with the experimental fact. In conclusion, studying on the influences of models of HMX and PETN is benefit for taking suitable models for subsequent MD simulations. Investigating the relationship between structure and properties of HMX, PETN and their composite systems by MD simulations reveals the desensitization mechanism of paraffin and provids different kinds of data for the PBXs formulations and comparatives for the single compound explosives and composite explosive.