Investigation on the High‐Cycle Fatigue Behavior of Domestic Zr‐2.5Nb Alloy in Consideration of Notch Effects

ABSTRACT The Zr‐2.5Nb alloy used for pressure tubes in heavy‐water reactors was utilized to investigate its high‐cycle fatigue (HCF) behavior at room temperature using both smooth and notched specimens. Based on the Theory of Critical Distance (TCD), the influence of notch geometry on fatigue behavior and life prediction was systematically examined. The fatigue failure mechanisms were further elucidated through micrographic observation. The results indicate that the main factors of fatigue life differ substantially between smooth and notched specimens, as well as crack initiation and propagation characteristics. For Zr‐2.5Nb with smaller grain sizes, typical spalling‐like stepped morphologies are observed on the fracture surface under high stress levels. Stress concentration significantly affects both the number and distribution of fatigue crack initiation sites. The TCD was employed to predict the fatigue life of two types of specimens with different notch sizes, and the results indicate that TCD provides a high prediction accuracy. The present results provide a reliable fatigue database for the assessment of domestic Zr‐2.5Nb pressure tube materials and support the applicability of TCD‐based design methodologies in nuclear engineering components.