不同温度下HMX和RDX晶体的感度判别和力学性能预估分子动力学比较研究

为探讨和比较炸药黑索金(RDX)和奥克托今(HMX)晶体的结构、 能量和力学性质随温度的递变规律, 在COMPASS力场和NPT系综下, 对其合适的等原子数超晶胞模型分别进行5个温度(195, 245, 295, 345和395 K)下的分子动力学(MD)周期性模拟研究. 结果表明, 随着温度的升高, RDX和HMX晶体引发键N-NO₂的最大键长(L_max)的逐渐增大以及引发键连双原子作用能(E_N-N)和内聚能密度(CED)的逐渐减小均与感度随温度升高而增大的实验结果一致; 且在各温度下, RDX晶体的L_max均大于HMX晶体的L_max, 与HMX相比, RDX的E_N-N和CED均较小, 上述结果与RDX比HMX感度大的实验结果相符. 由此表明, 在一定条件下, L_max, E_N-N和CED可用于高能物质的热和撞击感度的相对大小的判别. 基于MD模拟原子运动轨迹, 用静态法求得2种晶体的弹性力学性能, 发现拉伸、 体积和剪切模量均随温度的升高而递减, 与实验结果一致.

Sensitivity Criterion and Mechanical Properties Prediction of HMX and RDX Crystals at Different Temperatures Comparative Study with Molecular Dymamics Simulation

In order to explore and compare the progressive changes of structure, energetic and mechanical properties of RDX(cyclotrimethylene trinitramine) and HMX(cyclotetramethylene tetranitramine) crystals with temperature, molecular dynamics simulation was conducted for their suitable models containing the same number of atoms. COMPASS force field was applied in the simulation in NPT ensemble. Five different temperatures, i.e., 195, 245, 295, 345 and 395 K, were considered. The simulation results show that the maximum bond length(L_max) of their N-N trigger bond increases, the interaction energy(E_N-N) between two N atoms of the N-N trigger bond decreases and the cohesive energy density(CED)decreases as the temperature increases. These results agree with the experimental fact that both RDX and HMX become more sensitive as the temperature increases. Moreover, the L_max value of RDX is larger than that of HMX, and the values of E_N-N and CEDof RDX are lower than those of HMX at all temperatures. These also agree with the fact that RDX is more sensitive than HMX. It is thus suggested that the L_max, E_N-N and CED indeed can be used as theoretical criteria to predict the relative degree of heat and impact sensitivity of high energy materials under certain conditions. The mechanical properties were obtained with static analysis method. The results show that the engineering modulus such as tensile modulus, bulk modulus and shear modulus decrease with the increasing temperature, which agrees with the experimental results.