Granular bright facets (GBFs) are frequently observed adjacent to inclusions and within fish-eye areas in the fatigue fractures of high-strength steels under very-high-cycle fatigue (VHCF), considered as a characteristic fracture feature of VHCF. Previous understanding on GBF formation emphasizes the occurrence of nanocystallization in microstructure. In this study, however, the same morphology can also be observed under high-cycle fatigue (HCF). GBF, although closer to fatigue crack initiator and experiencing more stress cycles than the peripheral part of fish-eye (PPFE), exhibits rougher surface morphology in the absence of accumulated plastic strain in microstructure, manifesting relieved crack surface wear. This indicates that the traditional theories on GBF formation for VHCF becomes invalid for HCF. The root cause for GBF formation under HCF is analyzed to be the presence of residual stress around inclusions, which reduces the contact pressure of fatigue crack surfaces inducing wear relief. Accordingly, an analytical model capable of predicting GBF thickness with the effects of HCF conditions and steel properties taken into consideration is established. The model yields accurate predictions of GBF thickness with various loading stresses and inclusion diameters, validated by experimental observations. This study provides theoretical guidance for HCF fracture analysis and fatigue life prediction.

中文翻译：

---

高周疲劳下高强度钢夹杂物周围残余应力诱导的粒状光亮面


在超高周疲劳（VHCF）下高强度钢的疲劳断裂中，在夹杂物附近和鱼眼区域内经常观察到粒状光亮面（GBF），被认为是VHCF的特征断裂特征。先前对GBF形成的理解强调微观结构中纳米晶化的发生。然而，在这项研究中，在高周疲劳（HCF）下也可以观察到相同的形态。 GBF虽然比鱼眼周边部分（PPFE）更接近疲劳裂纹引发源并经历更多的应力循环，但在微观结构中没有累积塑性应变的情况下表现出更粗糙的表面形态，表现出减轻的裂纹表面磨损。这表明关于VHCF的GBF形成的传统理论对于HCF来说变得无效。分析HCF下GBF形成的根本原因是夹杂物周围存在残余应力，这降低了疲劳裂纹表面的接触压力，从而导致磨损减轻。因此，建立了一个能够预测GBF厚度并考虑HCF条件和钢性能影响的分析模型。该模型可准确预测不同负载应力和夹杂物直径下的 GBF 厚度，并通过实验观察进行验证。该研究为HCF断裂分析和疲劳寿命预测提供理论指导。