FeNiCu合金中位错对微裂纹扩展影响的分子动力学研究

Molecular dynamics study on effect of dislocation on micro-crack propagation of FeNiCu alloy

采用分子动力学方法研究了FeNiCu合金在单轴应力加载下的微裂纹扩展行为。分析了相对于裂纹不同角度位置的位错对微裂纹扩展的影响。结果表明,在微裂纹扩展过程中,裂纹在尖端主要的变形机制为滑移带和位错,裂纹尖端在滑移方向<110>发射位错。随着位错的连续增殖,位错密度逐渐增大,形成位错塞积,导致产生位错针扎,微裂纹沿此方向进行扩展。而预设不同滑移方向的位错对微裂纹扩展存在阻碍作用,在位错阻碍效果失效前,当位错相对位于裂纹30°时对裂纹的扩展运动阻碍效果最大,45°次之,60°最小。其中30°位错的滑移方向与裂纹的滑移方向垂直,且应力峰值最大,表示拉伸需要的外应力最大,表现出的阻碍效果最明显。这种抑制微裂纹扩展的效果越强,在裂纹尖端的应力集中现象越明显。而在抑制作用失效后,缺陷处会释放大量势能,使裂纹快速扩展,对材料造成破坏。

The micro-crack propagation behaviors of FeNiCu alloy under uniaxial stress load were studied by molecular dynamics method.The effects of dislocations at different angles relative to cracks on micro-crack propagation were analyzed.The results show that in the process of micro-crack propagation,the main deformation mechanism of crack tip is slip band and dislocation,and the crack tip emits dislocation in the slip direction of<110>.With the continuous proliferation of dislocation,the dislocation density gradually increases,resulting in dislocation plug,which leads to dislocation pinprick and microcrack propagation along this direction.However,the preset of dislocations with different slip directions can hinder the micro-crack growth.Before the failure of dislocation blocking effect,when the dislocations are located at 30°relative to the crack,the blocking effect on the crack growth is the largest,followed by 45°and the smallest at 60°.Among them,the slip direction of the 30°dislocation is perpendicular to the slip direction of the crack,and the stress peak value is the largest,which means that the external stress required for tension is the largest,and the blocking effect is the most obvious.The stronger the effect of restraining microcrack propagation is,the more obvious the stress concentration at the crack tip is.However,when the inhibition effect fails,a large amount of potential energy can be released from the defect,which makes the crack expand rapidly and damage the material.