中文摘要：

为研究聚合物力学和电学性能变化的微观机理,利用Materials Studio（MS）软件建立了聚乙烯分子结构模型。通过施加预直流电场作用,研究了分子链段运动产生的能量和自由体积变化对微观结构、力学性能和击穿性能的影响。模拟结果表明：在预直流电场作用下,聚合物分子链段出现局部有序排列现象,并且随着电场强度（简称场强）由5.20×102 MV/m增加到5.00×10~3 MV/m,自由体积出现先降低再升高的变化趋势,在场强为5.20×102MV/m处出现0.95 nm3的极小值;而当场强增加至2.60×10~3 MV/m时,化学键C—H键断裂,并产生新的化学键C=C键,进而形成低密度劣化区。材料内自由体积和化学键的变化从根本上改变了聚合物的微观结构,影响其力学性能和电学性能,进而使杨氏模量和击穿场强在场强为5.20×10~2 MV/m处分别出现7.50 GPa和11.52×10~3 MV/m的极大值,与未经预直流处理的聚合物相比,分别增长了66%和29%。研究成果可为高压电缆的绝缘设计提供参考,也同为在预电应力作用下聚合物的击穿性能模拟提供借鉴。

英文摘要：

To understand the microscopic mechanism associated with performance changes in mechanical and electrical properties of the polymer, the molecular structure of polyethylene was modeled by means of the Materials Studio（MS） simulation software. Moreover, DC pre-electrical stress was applied, and the effects of the changes in energy and free volume due to the chain segment motion of polyethylene on microstructure, mechanical properties, and electrical breakdown properties were investigated. The simulation results show that the local ordered arrangement of the molecular chain segment in polymers under DC pre-electrical stress can be observed. As the electrical field strength enhances from 5.20×102 MV/m to 5.00×10~3 MV/m, the free volume of polyethylene gradually increases. The minimum value of free volume is 0.95 nm3 at the pre-electrical stress of 5.20×102 MV/m. The breakage of chemical bond C—H appears,and the new chemical bond C=C and low density region emerge at 2.60×10~3 MV/m. The changes of free volume and chemical bonds transform fundamentally the microstructure of polymer, further causing the changes of mechanical and electrical properties of polyethylene. Thus the Young＇s Modulus and electrical breakdown strength are up to 7.50 GPa and 11.52×10~3 MV/m respectively at the electrical field of 5.20×102 MV/m, and increase, respectively, by 66% and 29% compared those in the absence of DC pre-electrical stress. The research results can provide references for the insulation design of high voltage cables, as well as the simulation of breakdown property in polymeric materials under the DC pre-electric stress.