Low cycle fatigue properties and life prediction based on plastic work of back stress in a Zr-2.5Nb alloy

Abstract

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.