A new perspective of damage-induced shear strain localization is proposed to elucidate the formation mechanism of fine granular area (FGA) generated in a high-strength steel under very-high-cycle fatigue (VHCF). The development of local shear strain, effective resolved shear stress, and damage evolution at the vicinity of an inclusion has been predicted by crystal plasticity finite element method (CPFEM) coupled with damage at stress ratios of R = −1, 0.1, and 0.5. The microstructure of FGA is characterized by using scanning electron microscopy, transmission electron microscopy, and transmission Kikuchi diffraction. The experimental results show that the FGA consists of high-density dislocations, subgrains, and fine grains with high-angle grain boundaries. The simulation results find that the negative local effective stress ratio is compulsory to FGA formation in VHCF. Finally, the tendency of decreasing FGA formation with increasing global stress ratio is explained, and the conventional FGA formation mechanism is extended.

中文翻译：

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超高周疲劳损伤诱导剪切应变局部化形成细颗粒区

提出了损伤诱导剪切应变局部化的新视角，以阐明在超高周疲劳 (VHCF) 下高强度钢中产生的细颗粒区 (FGA) 的形成机制。通过晶体塑性有限元方法 (CPFEM) 结合应力比为R = -1、0.1 和 0.5。FGA 的微观结构通过使用扫描电子显微镜、透射电子显微镜和透射菊池衍射进行表征。实验结果表明，FGA 由高密度位错、亚晶粒和具有大角度晶界的细晶粒组成。模拟结果发现负局部有效应力比对 VHCF 中的 FGA 形成是强制性的。最后，解释了随着整体应力比的增加 FGA 形成减少的趋势，并扩展了传统的 FGA 形成机制。