The impact of crack closure and environmental effects on the experimental determination of the fatigue crack propagation threshold is a major problem for the assessment of cyclically loaded components, especially at low stress ratios $R$. In this work, the influence of the experimental procedure and air humidity on $\mathrm{d}a/\mathrm{d}N-\Delta K$ data at different $R$ is discussed. Unlike the results at $R=-1$, the threshold values obtained at $R\approx 0.8$, i.e. under negligible crack closure levels, show a very small scatter band regardless of the variation of the test parameters and environmental conditions.

中文翻译：

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确定疲劳裂纹扩展阈值的最新进展

裂纹闭合和环境影响对疲劳裂纹扩展阈值的实验确定的影响是评估循环加载部件的主要问题，特别是在低应力比下$R$. 在这项工作中，实验程序和空气湿度对$\mathrm{d}\mathrm{一个}/\mathrm{d}ñ-\Delta ķ$不同的数据$R$被讨论。与结果不同$R=-1$, 在获得的阈值$R\approx 0.8$，即在可忽略的裂纹闭合水平下，无论测试参数和环境条件如何变化，都显示出非常小的散射带。