The work is devoted into investigating the multiaxial low cycle fatigue behavior and constitutive model of 316L under various strain amplitudes, strain ratios, and phase angles at 550 °C. Experimental results show that both axial and shear stress amplitudes present three stages of cyclic hardening, softening and fracture. Internal stress analysis reveals that initial cyclic hardening is influenced by both friction and back stresses, while cyclic softening is primarily controlled by friction stress. Moreover, the Mises equivalent stress–strain relationship effectively accommodates different strain amplitudes and strain ratios, but cannot account for the non-proportional hardening arising from back stress. Pearson correlation analysis highlights a correlation between fatigue life and the equivalent stress amplitude and plastic strain energy density, and that elastic modulus is influenced by strain ratio and phase angle, not the strain amplitude. Based on the Chaboche unified viscoplastic constitutive theory, an improved constitutive model incorporating new hardening rules and Hooke’s law is proposed. In the proposed model, three classical loading path-dependent coefficients’ ability for description of non-proportional hardening and stiffness weakening behaviors are evaluated. Simulation results reveal that the proposed model can effectively capture the non-proportional hardening of back stress, stiffness weakening, non-masing effect, and varied softening rate.

中文翻译：

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316L 在高温下各种载荷路径下的多轴低周疲劳行为及本构模型


该工作致力于研究 316L 在 550 °C 下各种应变幅、应变比和相位角下的多轴低周疲劳行为和本构模型。 实验结果表明，轴向应力幅值和剪切应力幅值均呈现循环硬化、软化和断裂三个阶段。内部应力分析表明，初始循环硬化受摩擦应力和背应力的影响，而循环软化主要受摩擦应力控制。此外，Mises 等效应力-应变关系有效地适应了不同的应变幅值和应变比，但不能解释背应力引起的不成比例的硬化。Pearson 相关分析强调了疲劳寿命与等效应力幅值和塑性应变能密度之间的相关性，并且弹性模量受应变比和相位角的影响，而不是应变幅值。基于 Chaboche 统一粘塑性本构理论，提出了一种结合新硬化规则和 Hooke 定律的改进本构模型。在所提出的模型中，评估了三个经典的加载路径相关系数描述非比例硬化和刚度弱化行为的能力。仿真结果表明，所提模型能够有效捕捉背应力的非比例硬化、刚度减弱、非增乳效应和变化软化速率。