摘要：本文通过分子动力学方法模拟多晶bcc－Fe的拉伸过程，考察不同条件下拉伸过程中的原子尺度结构变化，用图表分析总结相关计算结果。研究结果表明：晶粒尺寸对多晶铁拉伸过程中发生的应变机制影响不大；晶粒尺寸越大，多晶铁拉伸过程中越容易产生裂纹；随着晶粒尺寸的减小，纳米多晶铁的屈服强度逐渐减小，纳米多晶铁的抗拉强度随晶粒尺寸的减小而减小,显示出反常的Hall-Pethch效应；温度对多晶铁的二维拉伸过程中的应变机制影响不大，拉伸变形过程中都有晶界处发射位错、晶界迁移、晶粒扭转以及孪晶等机制；温度主要影响拉伸过程产生孪生变形的启动应力，温度越高，发生孪生变形的临界应变量越小，发生孪生变形的启动应力越小；随着拉伸温度的升高，应力最大值减小，多晶铁的抗拉强度随温度的升高而减小。

关键词：铁 分子动力学 拉伸 晶界 裂纹

毕业设计说明书外文摘要

Title Molecular dynamic simulation of stretching process in polycrystalline iron

Abstract：In this paper, a simulation of polycrystalline BCC - Fe stretching process was carried out based on molecular dynamics method. We studied the process under the different condition and summarized the related chart and results. From the simulation results，the following results are obtained: The size of grain has little effect on the strain mechanism of the polycrystalline iron’s tensile process ; The larger the grain size, the more likely it is to crack in the process; With the decrease of the grain size, the yield strength of polycrystalline iron decreases, nano-polycrystalline iron’s tensile strength decreases with the decrease of the grain size, showing abnormal Hall - Pethch effect; The temperature has little effect on the strain mechanism of the polycrystalline iron’s two-dimensional model in the tensile process; The higher the temperature, the critical strain of the twin deformation is smaller; As the tensile temperature increases, the maximum stress decreases, and the tensile strength of the polycrystalline iron decreases with the increase of temperature.

Keywords     iron   molecular dynamics   tension   grain boundary   crack

目 次

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 1

1.3 分子动力学 5

1.4数据处理技术 7

1.5国内外研究现状 8

2 晶界模型的建立 10

3 晶粒尺寸对多晶铁拉伸的影响 12

3.1多晶铁的二维模型拉伸模拟 12

3.2 多晶铁的三维模型拉伸模拟 19

4 温度对多晶铁拉伸的影响 27

4.1温度为150K时的拉伸模拟 27

4.2温度为300K时的拉伸模拟 28

4.3温度为450K时的拉伸模拟 30