双晶Fe拉伸性能及裂纹扩展的原子模拟
毕业论文关键词 晶界 分子动力学 拉伸 裂纹扩展
Title Molecular dynamic simulation of tension and crackpropagation in bicrystal iron
Abstract BCC iron were taken as the research object.Different kinds of grain boundary ofBicrystal iron model was built to caculate the stastic GB energies .Moleculardynamics simulations was applied to the tensile deformation and crack propagationsimulations. The mechanisms of crack propagation as well as the effect from testingtemperature,the loading velocity are analyzed on several typical kinds ofbicrystal iron.(1) 42 GB energies were summarized in table3.1,table 3.2 and table 3.3. [100]Σ5(36.87˚),[110]Σ3 (112)and[111]Σ21(21.8˚) with low Σ value local minimumpoints in ergetic carves has the lowest GB engry in all the simulation results.(2) When GB engry is lower,the BCC iron transform to FCC/HCP iron.While GB engryis higher,the bicrystal iron is completely separated near cracking tips.(3) During fatigue crack propagation ,the BCC iron transform to FCC/HCP iron withlower GB engry.Twinning strips or sub crack are observed in higher GB engry.HighestGB engry can emit dislocation on the grain boundary.(4) With the elevating of temperature or the decrease of the loading velocity ,theformation of twinning strips become easier.
Keywords grain boundary molecular dynamics tension crack propagation
目次
1绪论1
1.1课题研究目的及意义1
1.2晶体的界面结构1
1.3重合位置点阵模型（CSL）2
1.4微裂纹萌生与扩展机理3
1.4.1微裂纹的萌生阶段3
1.4.2裂纹扩展阶段4
1.4.3减少微裂纹的措施4
2分子动力学模拟方法6
2.1基本思想6
2.2实际应用6
2.3周期性边界条件7
2.4MD模拟的基本步骤7
2.5Fe的势函数模型8
2.6位错提取算法（DXA）的应用8
2.7中心对称系数8
3双晶Fe晶界模型的建立以及晶界能计算9
3.1国内外研究晶界的进展9
3.2双晶Fe几何模型的建立11
3.3双晶Fe系统的弛豫过程14
3.4双晶Fe静态晶界能计算结果与分析15
4具有不同晶界的双晶Fe拉伸过程模拟17
4.1双晶Fe模拟拉伸过程的模型建立17
4.2模拟结果与分析18
4.3应力应变以及断裂强度的统计29
4.4本章总结29
5具有不同晶界的双晶Fe裂纹扩展过程模拟33
5.1双晶Fe裂纹扩展过程模型建立33
5.2双晶Fe裂纹扩展过程的分析34
5.3本章总结44
6其他条件对双晶Fe的[110]Σ3（112）晶界断裂破坏机理的影响45
6.1有无晶界对[110]Σ3（112）晶界断裂机制的影响45
6.2温度对[110]Σ3（112）晶界断裂机制的影响46
6.3应变速率对[110]Σ3（112）晶界断裂机制的影响47