Molecular Dynamics Simulation Of Energetic Materials With Crystal Defects

Crystal defects have important influence on the mechanical properties,explosive properties,sensitivity and reaction mechanism of energetic materials.It is of great significance to study the crystal defects of energetic materials.The COMPASS force field is adopted to conduct the simulation.Cutting surface,establishing the defective crystal and injecting the F₂₃₁₁311 polymer are operated to investigate the influence of dislocation,vacancies,holes and doping crystal defects on the mechanical properties,trigger bond lengths and the molecular banding energies of nitromethane?NM?,2,2-dinitroethene-1,1-diamine?FOX-7?,2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazatetracyclo[5.5.0.0.0]dodecane?CL-20?,FOX-7-based polymer bonded explosives FOX-7/F₂₃₁₁,HMX-based polymer bonded explosives HMX/F₂₃₁₁311 and HMX/FOX-7 co-crystal explosives.In this process,it is the equilibrium criterion that temperature and energy fluctuate over time in 5%¹0%.Firstly,the unit cell model was constructed by neutron diffraction or X-ray diffraction data,and three different crystal surfaces of?001??010?and?100?were constructed by cutting the surface method,then different crystal defects are established on the specific crystal surfaces.Then the molecular dynamics simulation is conducted with the total time of 200ps under COMPASS force field,which is applied to judge the mechanical properties of the perfect system and the defective system by the values of tensile modulus,bulk modulus,shear modulus,Poisson's ratio and Cauchy pressure.The results show that the 2.08%⁴.17%crystal defects can reduce the tensile modulus,bulk modulus,shear modulus and increase Cauchy pressure and K/G of NM,FOX-7,CL-20,FOX-7/F₂₃₁₁,HMX/F₂₃₁₁311 and HMX/FOX-7co-crystal explosives,engineering modulus changing in the range of 0.3%⁴7.3%,which fully explains that the crystal defects can improve the flexibility and ductility of explosives,and reduce the rigidity.The trigger bond length of PBX with crystal defects is increased of0.1%³.01%,while the bond energy is decreased of 2.0%¹3.6%,which indicates that the crystal defects can increase the activation degree and the sensitivity of the system and make a bad compatibility of polymer chain.The change of the modulus and Cauchy pressure in the dislocation 2 columns is more obvious comparing with those in dislocation 1,which shows that the concentration of the crystal defects are positively correlated with the change of mechanical properties.The molecular dynamics method is used to simulate the elastic coefficient and mechanical properties of FOX-7 with defects at different temperatures.At different temperatures,the effect of different crystal defects on the single explosive is consistent.The modulus of defective system were smaller than perfect crystal,which shows that the rigidity of energetic materials is reduced under any temperature.And tensile modulus,bulk modulus and shear modulus decreased with the increase of temperature,showing that crystal defects decrease the hardness and improve the flexibility of energetic materials.It is important to predict the temperature influence on the thermal decomposition mechanism of explosives.