Under combined high and low cycle fatigue (CCF) loading, the multi-axial stress state induced by geometric discontinuities of different notch forms under the same stress amplitude can result in significant differences in fatigue performance of DD6 alloy. Therefore, it is of great importance to study the CCF behavior of Ni-base single-crystal alloy samples with differing notch geometries at the high temperatures. In order to obtain an approximate CCF lifespan, different stress amplitudes need to be applied to DD6 specimens with different notch forms. In this study, two kinds of notched DD6 plate specimens with [001] orientation were studied by CCF test at 760 °C, and the amplitudes of stresses were acquired under the same service life level. The effect of stress redistribution, in particular stress triaxiality, was evaluated on CCF lifetime of the DD6 specimens. A damage model with anisotropy considering stress triaxiality effect was suggested. The results indicated that the conventional stress–strain variables could not reflect the trend of CCF lifetime for different geometrical notched DD6 specimens, whereas the stress triaxiality at the CCF load peak could. A modified Basquin model was introduced for predicting CCF life according to the stress triaxiality at the peak loading. It can accurately and efficiently estimate the CCF life of two kinds of notched DD6 plate specimens, and the life prediction results fall within a scatter band of ±3 times of fatigue life.

中文翻译：

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DD6 不同缺口试件应力再分布对高温下高低周联合疲劳寿命的影响研究


在高低周疲劳 （CCF） 联合载荷下，在相同应力幅值下，不同缺口形式的几何不连续性引起的多轴应力状态会导致 DD6 合金的疲劳性能发生显著差异。因此，研究具有不同缺口几何形状的镍基单晶合金样品在高温下的 CCF 行为非常重要。为了获得近似的 CCF 寿命，需要对具有不同缺口形式的 DD6 试样施加不同的应力幅值。本研究在 760 °C 下通过 CCF 测试研究了两种具有 [001] 取向的缺口 DD6 板试件，并获得了相同使用寿命水平下的应力幅值。评估了应力再分布，特别是应力三轴性对 DD6 试样 CCF 寿命的影响。提出了一种考虑应力三轴效应的各向异性的损伤模型。结果表明，常规应力-应变变量不能反映不同几何缺口 DD6 试件的 CCF 寿命趋势，而 CCF 载荷峰值处的应力三轴性可以。引入了改进的 Basquin 模型，用于根据峰值载荷下的应力三轴性预测 CCF 寿命。该算法能够准确高效地估计两种带缺口的DD6板试件的CCF寿命，寿命预测结果落在疲劳寿命的±3倍的散射带内。