摘要：为了从原子尺度了解BCC金属中晶界的状态与作用，以纯W为研究对象，基于分子动力学方法，实施了计算机模拟研究。文中简要叙述了分子动力学方法，经典的势函数模型，晶界的基本介绍及分类，同时简要介绍了晶界对材料的影响及国内外的研究情况。对模拟结果进行了分析，得到以下结论：1、晶粒尺寸的增大，屈服强度增大,并且随着晶粒的增加，晶粒尺寸减小，屈服强度减小。2、在二维拉伸模拟的过程中，可看出晶粒的微观变形机制有四种，分别是晶界发射位错；产生裂纹，然后裂纹扩展，；形成孪晶，孪晶和晶界迁移使晶界长大；晶粒扭转。3、取向差不同，晶界的微观机制仍和上述的一致。晶界能越大，屈服强度越大。且无论取向差如何，晶体内部都会产生断裂，切断裂方式为沿晶断裂。取向差越大，越容易产生晶粒扭转机制。取向差越小，孪生越容易产生，且发生变形所需的应变量越小，孪晶产生的启动应力越大。

关键字 晶界 分子动力学 取向差 屈服强度

Title Atomic Simulation of Tensile Process of  Polycrystalline  Tungsten 

Abstract:In order to understand the properties of grain boundaries in BCC metal from atomic scale, pure tungsten was used as the research object, and atomic simulation was carried out using molecular dynamics method. In this paper, the molecular dynamics method, the classical potential model, the basic introduction and classification of grain boundary are briefly described, then the influence of grain boundary on the material and the research results at other researchers are briefly introduced. The simulation results are analyzed and the following conclusions are obtained: 1. The yield strength increases with the increasing of the grain size, and with the increase of grain size, grain size decreases, yield strength decreases. 2, in the process of two-dimensional tensile simulation, we can see that there are four micro-deformation mechanism of grain：dislocation emission from GB ; crack propagation; the formation of twin, twin and grain boundary migration results in the growth of grain; grain twist. 3, with the different orientation, it is found that the microscopic mechanism of the grain boundary is still consistent with the above. The greater the grain boundary energy, the greater the yield strength. Regardless of the orientation difference, the intergranular fracture is always investigated in the crystal. The larger the orientation difference, the more likely grain twisting mechanism is found in the process of tensile. The smaller the orientation difference, the more prone to the twins, and the smaller the strain required for the deformation, the greater the initial stress produced by the twin. 

Keywords： grain boundary  molecular dynamics  orientation   yield strength

1绪论..1

1.1课题研究目的及意义.1

1.2晶体的晶界模型..2

1.3国内外研究情况..3

2分子动力学方法.5

2.1基本介绍..5

2.2边界条件..5

2.3基本方程式6

2.4势函数的选择.8

2.5初始条件和边界条件.9

3多晶模型建立..11

4分子动力学模拟多晶拉伸实验晶粒尺寸效应13

4.1应力应变曲线13

4.2多晶模型在拉伸过程中的结构分析15

5分子动力学模拟多晶拉伸实验取向差效应..25

5.1二维模型取向差分别取15°,45°,60°的应力应变曲线25

5.2二维模型取向差分别取15°,45°,60°的结构分析.26结论.32

致谢.33

参考文献34

1绪论

1.1课题研究目的及意义 多晶钨拉伸过程的原子模拟:http://www.chuibin.com/cailiao/lunwen_205158.html