Research on Strength Evaluation of Crystalline Metal Based on Molecular Dynamics Simulation

采用原子模型和连续介质模型对多晶金属断裂过程的基本现象进行了计算机模拟研究。得到的主要结果总结如下：(1)对fcc-Cu和bcc-Fe单晶进行了分子动力学模拟，考察了以下控制材料强度性能的基本现象；a)位错与变形孪晶相互作用激活的裂纹起裂机制；b) I、II和III模式加载下近片区原子结构的动力学特征，特别是晶体取向和温度对导致韧性断裂的位错发射的依赖关系；c)晶界与晶格缺陷的相互作用；d)晶界区自扩散特性及其温度依赖关系。(2)利用晶体塑性理论导出的连续介质模型，对延性裂纹进行了有限元分析，并将原子模型的模拟结果作为细观断裂过程的实质性数据，考察了细观应力的意义和剪切带形成的微观机理。(3)为了评价其适用性和有效性的局限性，分别采用超细胞法和/或分子轨道法进行了从头算分析。

Fundamental phenomena governing the fracture processes appearing in a polycrystalline metal are studied by means of computer simulation using both atomic and continuum models. The main results obtained are summarized as follows :(1) Molecular dynamics simulations are performed for fcc-Cu and bcc-Fe single crystals and the following fundamental phenomena governing the material strength properties are examined ; a) crack initiation mechanisms activated by interaction of the dislocation and deformation twin, b) dynamical characters of the atomic structure in near-chip region under the modes I,II and III loading, especially dependence of the crystal orientation and temperature on the dislocation emission leading to the ductile fracture,c) interaction between the grain boundary and lattice defects, and d) the self-diffusion properties and its temperature dependence in the grain boundary region.(2) Using the continuum model derived from the crystal plasticity theory, the finite element analysis of the ductile crack is carried on and meaning of microscopic stress and micro-mechanism of shear-band formation is examined, regarding the simulation results obtain from the atomic model as a substantial data for the microscopic fracture process.(3) In order to evaluate the appropriateness and limit of its validity, ab initio analysis based on super-cell method and/or molecular orbital method are performed.