ABSTRACT Fatigue crack growth (FCG) and creep-fatigue crack growth (CFCG) in austenitic stainless-steel Fe-25Ni-20Cr (Alloy 709) were measured experimentally and simulated using the finite element method. Temperature conditions investigated were 550°C, 600°C and 700°C, with load hold times of 0 s, 60 s and 600 s. Fracture surface was investigated using scanning electron microscopy and optical imaging. Experiments indicated that crack growth exhibits minimal sensitivity to the various loading conditions evaluated. At 600°C, crack growth rates were independent of hold time or loading frequency. At 700°C, there was a small increase in crack growth rate as a function of hold time, with a 600s hold time causing a factor of 2 increase in crack growth rate over FCG. Finite element simulations were performed to compute plasticity-induced crack closure in the presence of creep deformations at the crack tip. The simulations produced FCG and CFCG rates similar to the experimental results.

中文翻译：

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高温下 709 合金的疲劳和蠕变疲劳裂纹扩展

摘要 奥氏体不锈钢 Fe-25Ni-20Cr（合金 709）中的疲劳裂纹扩展 (FCG) 和蠕变疲劳裂纹扩展 (CFCG) 通过实验测量并使用有限元方法进行模拟。研究的温度条件为 550°C、600°C 和 700°C，负载保持时间为 0 秒、60 秒和 600 秒。使用扫描电子显微镜和光学成像研究断裂表面。实验表明，裂纹扩展对所评估的各种加载条件的敏感性最低。在 600°C 时，裂纹扩展速率与保持时间或加载频率无关。在 700°C 时，裂纹扩展速率随保持时间略有增加，600 秒的保持时间导致裂纹扩展速率比 FCG 增加 2 倍。在裂纹尖端存在蠕变变形的情况下，进行了有限元模拟以计算塑性诱导的裂纹闭合。模拟产生的 FCG 和 CFCG 率与实验结果相似。