利用分子动力学在原子尺度模拟了单晶Cu (111)面纳构件的纳米加工过程和加工后纳构件的拉 伸过程, 分析了纳刻划过程的缺陷行为及加工缺陷对纳构件力学特性的影响. 结 果表明: 在纳刻划过程中, 在针尖的前方和下方形成加工变形区; 当刻划深度 较浅时, 位错仅在表面与亚表面繁殖; 随着刻划深度的增加, 加工后残留的缺 陷数量增加, 纳构件的有序度及首次屈服应力下降; 加工后的纳构件内部, 尤其在针尖退出处有较高的残余应力. 对加工后的纳构件施加拉伸载荷, 由于 存在残留加工缺陷和较高残余应力, 其应力--应变曲线在弹性上升阶段有局部下降; 在塑性阶段, 由于位错繁殖及位错塞积和中间部分原子的迁移重构使应力--应变曲 线呈锯齿状逐渐下降. 纳构件断裂失效前表现为单原子相连的纳 链. 纳构件的有序度随着刻划深度的增加而下降. 在应变为0.8处, 刻划较浅的 纳构件的有序度较首次屈服处的有序度略好.
Method of hybrid machining-tension simulations is proposed and applied to Cu (111) plane nanostructure basing on Molecular dynamics. The results show that atoms at frontage of and under tool deviate from their initial positions and form deformation zone in nanostructure. Dislocations only propagate in surface and subsurface when scratching depths are shallow, and some dislocations form dislocation loops as there exists stress gradient near tool. The number of residual defects increase and Order Degree of crystal structure decrease as scratching depths increase. There exist high residual stress in subsurface, especially near the position where tool withdraw nanostructure. After machining, tensile loads are applied to two ends of nanostructure. The response of initial loaded stage is elastic as a whole, while the stress-strain curves show local decrease as residual stress and defects from machining process result in movement of some atoms and onset of dislocations. The Yang's Modulus and yielding stress decrease as scratching depths increase. The initial plastic deformation of machined nanostructure are determined from dislocations slip and stacking faults, and conjugate slip planes ((1 1) and ( 1) slip planes) are formed at the two side of scratching groove. Dislocation slip results in the decreasing of stress, while pileup of dislocations and the forming of new slip plane result in the increasing of stress. As a result, the stress-strain curves decrease step by step. Order degree of nanostructure for first yielding and strain at 0.8 decreases as scratching depths increase, while Order degree of nanostructure for small scratching depths at the strain of 0.8 increase comparing to that of 0.045.
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