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本文采用多尺度准连续介质法(quasi-continuum method, QC)模拟体心立方(body-centered-cubic, bcc)金属钽(Ta)Ⅱ型裂纹尖端位错的形核与发射过程,获得位错发射位置与应力强度因子关系曲线,分析裂纹尖端缺陷萌生过程,研究全位错分解以及扩展位错形成机理. 位错活动在不同阶段表现出不一致的特征,新位错的发射对于位错运动具有促进作用. 研究表明,裂纹扩展初始阶段首先萌生点缺陷,点缺陷随着加载强度增加会萌生新的点缺陷,点缺陷最终运动到边界,导致Ⅱ型断裂破坏. 在全位错发射之前有不全位错的形核与发射表明全位错的分解分步进行,从势能曲线上来看,也就是两个极小值点的形成机理不同.The quasi-continuum method (QC), a multiscale method, is used to analyze body-centered-cubic (bcc) metal tantalum (tantalum, Ta) type Ⅱ crack-tip dislocation nucleation. Based on the relationship curves between dislocations emission position and stress intensity factor, the processes of dislocation defect initiation and development are investigated. Dislocation travels forward with different characteristics in different stages and the new nucleated dislocations expedite the already nucleated dislocation to move away from the crack tip. The analysis of initiation of the crack tip defects shows that they are the local defects that first appear, and with loading, more local defects emerge, which eventually move to the boundary, and lead to the type Ⅱ fracture. Furthermore, dislocation dissociation as well as extended dislocation is discussed. The partial dislocation nucleating before the perfect dislocation nucleation and emission is full proof that the dissociation of perfect dislocation takes place step by step, which means that the two minimum points on the energy curve have different formation mechanisms.
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