Abstract The effects of inclusion size and stress ratio (R) on the very-high-cycle fatigue (VHCF) behavior of pearlitic steel were experimentally assessed. The S–N curve under rotating bending loading exhibited a horizontal asymptote shape and a clear fatigue limit. In contrast, the S–N curve under ultrasonic axial loading exhibited a continuously descending shape, and the fatigue limit disappeared at a fatigue life of 107 cycles. The fine granular area (FGA) within nanograins formed in the crack initiation region only for the samples subjected to VHCF at R = −1. All instances of interior crack initiation were caused by the MnS inclusions.

中文翻译：

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夹杂物尺寸和应力比对珠光体钢超高周疲劳行为的影响

摘要 通过实验评估了夹杂物尺寸和应力比 (R) 对珠光体钢超高周疲劳 (VHCF) 行为的影响。旋转弯曲载荷下的 S-N 曲线表现出水平渐近线形状和明确的疲劳极限。相比之下，超声轴向载荷下的 S-N 曲线呈现连续下降的形状，疲劳极限在 107 次循环时消失。纳米颗粒内的细颗粒区域 (FGA) 形成于裂纹萌生区域，仅适用于在 R = -1 下经受 VHCF 的样品。所有内部裂纹萌生都是由 MnS 夹杂物引起的。