The mean strain effect on AISI 304 stainless steel was examined through strain-controlled low-cycle fatigue tests under uniaxial and non-proportional random loading. Under uniaxial loading, cyclic stress responses showed initial hardening followed by continuous softening, typical of austenitic stainless steel. In contrast, non-proportional loading resulted in consistent hardening. Mean strain primarily influenced fatigue life by altering the stress range: a reduced stress range generally led to extended life. Mean stress relaxation was observed and analyzed under various mean strains. An improved Itoh–Sakane (IS) method was developed, incorporating the calculation of mean strain coordinates and a new coordinate system. This enhancement allows accurate calculation of principal strain and stress under mean strain conditions, significantly improving life evaluation accuracy, with results typically within a factor of 2. Based on this, a new life evaluation method was established, applicable to strain-based models and their modifications, as well as energy-based models. The advantages and disadvantages of different models were compared.

中文翻译：

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非比例随机载荷下 AISI 304 奥氏体不锈钢低周疲劳的平均应变效应：实验和寿命评价方法


通过在单轴和非比例随机载荷下的应变控制低周疲劳试验检查了对 AISI 304 不锈钢的平均应变效应。在单轴载荷下，循环应力响应表现为初始硬化，然后是持续软化，这是奥氏体不锈钢的典型特征。相比之下，非比例载荷导致一致的硬化。平均应变主要通过改变应力范围来影响疲劳寿命：应力范围的减小通常会导致寿命延长。在各种平均应变下观察和分析平均应力松弛。开发了一种改进的 Itoh-Sakane （IS） 方法，该方法结合了平均应变坐标的计算和新的坐标系。这种增强功能允许在平均应变条件下准确计算主应变和应力，显著提高寿命评估精度，结果通常在 2 倍以内。基于此，建立了一种新的寿命评估方法，适用于基于应变的模型及其修改，以及基于能量的模型。比较了不同模型的优缺点。