Pressure tubes of Zr-2.5Nb alloy in Pressurized Heavy Water Reactors experience low cycle fatigue (LCF) due to cooling water flow and power fluctuations, which could be a factor destroying their structural integrity. Therefore, it is essential to systematically investigate their LCF properties and develop accurate life prediction models. Existing research primarily focuses on single-phase Zr alloys, leaving a gap in understanding the fatigue behavior and microstructural evolution of the dual-phase Zr-2.5Nb alloy. This study addressed these gaps by conducting LCF tests on the Zr-2.5Nb alloy under strain amplitudes ranging from ± 0.50 % to ± 1.5 % at room temperature. The results indicated that the cyclic response can be divided into three stages (Ⅰ, Ⅱ, Ⅲ) based on the relative number of cycles. Cyclic softening/hardening originated from microstructural changes such as dislocation sub-structure, grain rotation, and texture evolution. A novel fatigue life prediction model was proposed based on the plastic work of back stress. For non-Masing materials, this model overcame the limitations of traditional plastic strain energy models and demonstrated higher prediction accuracy. This work contributes to a more accurate prediction of fatigue life in Zr alloys and provides new insights into their fatigue behavior and microstructure evolution under LCF conditions.

中文翻译：

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基于 Zr-2.5Nb 合金中背应力塑性功的低周疲劳性能和寿命预测


加压重水反应器中的 Zr-2.5Nb 合金压力管由于冷却水流量和功率波动而经历低周疲劳 （LCF），这可能是破坏其结构完整性的一个因素。因此，必须系统地研究它们的 LCF 特性并开发准确的寿命预测模型。现有的研究主要集中在单相 Zr 合金上，在理解双相 Zr-2.5Nb 合金的疲劳行为和微观结构演变方面存在空白。本研究通过在室温下± 0.50 % 至 ± 1.5 % 的应变幅值对 Zr-2.5Nb 合金进行 LCF 测试来解决这些差距。结果表明，根据相对循环次数，循环响应可分为 I.、II.、III.三个阶段。循环软化/硬化源于微观结构变化，例如位错子结构、晶粒旋转和织构演变。提出了一种基于背应力塑性功的新型疲劳寿命预测模型。对于非 Masing 材料，该模型克服了传统塑性应变能模型的局限性，并表现出更高的预测精度。这项工作有助于更准确地预测 Zr 合金的疲劳寿命，并为它们在 LCF 条件下的疲劳行为和微观结构演变提供了新的见解。