Review on ultra-low cycle fatigue of metallic materials: performance, damage, and life evaluation

In the structural safety of construction, aerospace, and marine engineering, etc., the ultra-low cycle fatigue (ULCF) performance of metallic materials is critical. This paper aims to provide a comprehensive review of the research on ULCF of metallic materials in recent years, including basic characteristics, micro-nano damage mechanism, life prediction model, etc. Current research shows a significant imbalance: macrostructural studies prevail, while explorations on micro-deformation mechanism remain inadequate. Under ULCF, materials exhibit fuller hysteresis curves and prominent kinematic hardening. Their damage mechanism involves synergistically ductile fracture and fatigue fracture, which is influenced by stress triaxiality, load amplitude, and material composition, etc. Despite accuracy improvements via stress triaxiality and void evolution, existing prediction models face challenges of complex parameter calibration, insufficient universality, and high computational costs. More efforts need to be invested in research methods such as machine learning and in-situ characterization in the future, and deepening explorations into damage mechanisms under extreme environments (such as high temperature, and corrosion, etc.), to advance ULCF research from macroscopic empirical modeling to micro-mechanism guided design.