Key factors governing bending fatigue behavior and its evaluation methods in metal additive manufacturing: a review

Bending fatigue is one of the key issues in evaluating the service reliability of metal additively manufactured components. Unlike conventional wrought materials, metal additive manufacturing processes introduce materials with a complex thermal history, microstructural heterogeneity, build-orientation-dependent anisotropy, and multiscale defect distributions during fabrication. These characteristics make such materials particularly sensitive to surface roughness, near-surface porosity, and residual stress–factors exacerbated by the surface-concentrated cyclic stress gradients inherent in bending. Consequently, damage mechanisms in bending differ significantly from axial fatigue, directly reflecting surface-dominated crack initiation. From this perspective, this review examines the effects of processing conditions, build orientation, post-processing treatments, and life assessment methods on the bending fatigue behavior of metal additively manufactured materials, with particular emphasis on how these factors govern crack initiation and early crack propagation by altering surface condition, defect morphology and spatial location, and local stress response. In addition, the major limitations of current research in terms of test comparability, standardized evaluation, and bending-specific fatigue life models are discussed. This work aims to provide a framework for reliable design, performance optimization, and engineering application of metal additively manufactured components.