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On the growth of nanoscale fatigue cracks

机译：关于纳米疲劳裂纹的生长

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摘要

We identify nanoscale mechanisms of fatigue-crack growth in copper single crystals using molecular dynamics. By quantifying the nanoscale fatigue-crack growth rates, we can compare the growth rates for fatigue cracks on microstructural and macrostructural length scales. Computed crack growth rates in the nanometer range are shown to be very similar to those experimentally measured for small cracks ( micron range), and at stress-intensity-factor ranges lower than the threshold for long cracks (millimeter range). Molecular dynamics simulations indicate that reversible plastic slip along the active crystallographic directions at the crack tip is responsible for advancing the crack during a fatigue cycle. In the case of single or double plastic slip localization at the crack tip, a typical Mode I fatigue crack deviates along a slip band, resulting in a mixed Mode I+Mode II crack-growth mechanism. For crystal orientations characterized by multiple slip systems concomitantly active at the crack tip, the crack advance mechanism is characterized by nanovoid nucleation in the high-density nucleation region ahead of the crack tip and linkage with the main crack leading to crack extension.
机译：我们使用分子动力学确定铜单晶体疲劳裂纹生长的纳米尺度机制。通过量化纳米级疲劳裂纹的增长率，我们可以在微观结构和宏观结构长度尺度上比较疲劳裂纹的增长率。纳米计算的裂纹扩展率与小裂纹（微米范围）的实验测量值非常相似，应力强度因子范围低于长裂纹的阈值（毫米范围）。分子动力学模拟表明，沿裂纹尖端的有效晶体学方向的可逆塑性滑动是造成疲劳循环中裂纹发展的原因。在裂纹尖端出现单个或两个塑性滑移局部的情况下，典型的I型疲劳裂纹会沿着滑移带发生偏移，从而导致I +模式II混合裂纹扩展机制。对于以在裂纹尖端处同时起作用的多个滑动系统为特征的晶体取向，裂纹发展机理的特征在于在裂纹尖端之前的高密度成核区域中的纳米空隙形核以及与主裂纹的连接导致裂纹扩展。

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