Abstract Strain accumulation was studied by digital image correlation technique (DIC) during microstructurally small fatigue crack propagation in polycrystalline 18%Cr ferritic stainless steel. Load-controlled fatigue testing was performed with R-ratio of 0.1 and frequency 10 Hz. The maximum applied stress was well below the yield stress of the studied material. The effect of the observed strain field on crack growth rate variation is discussed. Fracture surfaces were studied by scanning electron microscopy (SEM) evidencing the connection between the mechanism of the fatigue crack growth, accumulated strain and crack growth rate. Detailed study of fracture surface morphology was carried out by atomic force microscopy (AFM). Results indicate two processes of material damage accumulation and failure during cyclic loading: 1) local shear strain zones form successively ahead of the crack tip, and 2) fatigue crack growth occurs by both single- and multiple-slip mechanisms. The place and intensity of shear strain localization zones vary during the crack growth that is related closely to the local variation of crack growth rate.

中文翻译：

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bcc Fe-Cr铁素体不锈钢微观结构小疲劳裂纹扩展过程中的应变积累

摘要 采用数字图像相关技术(DIC) 研究了多晶18%Cr 铁素体不锈钢微观结构小疲劳裂纹扩展过程中的应变积累。负载控制疲劳测试是在 R 比为 0.1 和频率为 10 Hz 的情况下进行的。施加的最大应力远低于所研究材料的屈服应力。讨论了观察到的应变场对裂纹扩展速率变化的影响。通过扫描电子显微镜 (SEM) 研究了断裂表面，证明了疲劳裂纹扩展机制、累积应变和裂纹扩展速率之间的联系。通过原子力显微镜 (AFM) 对断裂表面形态进行了详细研究。结果表明循环加载期间材料损伤累积和失效的两个过程：1) 在裂纹尖端之前连续形成局部剪切应变区，和 2) 疲劳裂纹扩展发生在单滑移和多滑移机制中。裂纹扩展过程中剪切应变局部化区的位置和强度发生变化，这与裂纹扩展速率的局部变化密切相关。