Molecular Dynamics Simulation Study On The Structure And Performace Of CL-20/TNT Cocrystal、RDX Defective Crystal And Their Composite Materials

In this paper, the structure and performance of CL-20/TNT cocrystal-based polymer bonded explosive (PBX) was first reported by molecular dynamics (MD) simulation. The relationship between cocrystal explosive and external factors, such as polymer concentration, temperature and binder types was discussed. Besides, MD simulation was employed to investigate RDX and RDX/paraffin composite cotaining different voids, and explore the relationship between the sensitivity and the aperture from the aspect of energy.First, PBXs (CL-20/TNT/F2311) coated with different concentration of polymer F2311(2.5%,9.2%,14.9%,19.9%) were chosen to investigate by using MD. With the increase of F2311 polymer concentration, the sensitivity of PBXs system which correlate with the maximum trigger bond length [Lmax(N-NO2)] decreases first, and then stabilizes in the concentration of 9.2%; At the same time, the cohesive energy density (CED), detonation pressure and detonation velocity gradually decrease, and the binding energy and ductility gradually increase when polymer concentration rises. Then, the appropriate PBX model was chosen to simulate at different temperature (195K-395K). MD results indicate that Lmax(N-NO2), the interaction energy(EN-N) between two N atoms in the trigger bond and CED were related with heat and impact sensitivity. These results are more consistent with the experiment fact that the crystal becomes more sensitive with the temperature enhancing gradually. The mechanical properties of PBX system regularly varied with the change of the temperature, however, the binding energy (Ebind) presents complex changes, suggesting that Ebind was not related with sensitivity. Finally, four polymers (F2311, F2314, PVAc, PS) as binders were chosen and MD simulation was applied to study CL-20/TNT cocrystal-based PBXs. It is found that both F2311 and F2314 not only improve the ductility of PBXs effectively, but also reduce detonation pressure and detonation velocity of PBXs in small increment. The order of the binding energies between cocrystal explosive and four binders are CL-20/TNT/PVAc>CL-20/TNT/F2311> CL-20/TNT/PS> CL-20/TNT/F2314, and it is found that moleculars or atoms close to the (010) surface had weakest interaction with binders among three surfaces[(100), (010), (001)]. The pair function correlation [g(r)] was applied to analyze the interaction between CL-20/TNT cocrystal explosive and binders.MD simulation is also employed for RDX and RDX/paraffin composite systems. It is found that the sensitivity of the two systems both increase with increasing aperture when the aperture wasnot more than the diagonal of RDX cell; in terms of the same aperture, RDX system is easier to form the void defects than RDX/paraffin composite system, and thus RDX is more sensitive than RDX/paraffin composte system. The results are in consistent with experiment fact that the paraffin can desensitize explosives. And five RDX models and RDX/paraffin composites whose apertures are six, were investigated. The restults suggested these two systems have the same order of sensitivity, which were anaysized by Ebind and PCF. In addtion, molecular diffusion in RDX and RDX/paraffin composite systems was investigated, and it is found that both void defects and paraffin are helpful to accelerate the molecular diffusion.