Mechanistic modeling of roughness–notch effects on fatigue life of Hastelloy X fabricated via laser powder bed fusion

Understanding how strain redistributes in geometrically complex components with rough surfaces is essential for predicting fatigue performance, particularly in components fabricated via additive manufacturing (AM), where surface morphology is inherently tied to build orientation. In AM components, the presence of notches and surface roughness localizes strains, driving heterogeneous plastic deformation under cyclic loading. These strain localization effects are especially pronounced under low-cycle fatigue (LCF) conditions, where cyclic plasticity dominates material response. To investigate these coupled effects, this work developed and implemented a high-fidelity finite element model (FEM) that incorporated as-built surface topography to realistically capture geometrical detail and localized strain accumulation. A plastic strain energy-based fatigue damage model was employed to estimate crack initiation life, complemented by a strain–life approach for overall fatigue life prediction. The model explicitly quantified the influence of surface roughness and macro-scale notches on fatigue behavior through detailed analysis of localized strain fields. The framework was validated using experimental data for laser powder bed fusion (L-PBF) Hastelloy X specimens, demonstrating strong predictive accuracy, achieving approximately 85 % agreement with measured crack initiation lives, particularly at low strain amplitudes where crack initiation dominates failure. Furthermore, the interaction between notches and surface roughness was investigated via the numerical modeling framework, and the results showed that the evaluation of an effective plastic strain was required to predict the fatigue life of notched specimens with 96 % accuracy. This strain-centric approach offers new insight into the role of surface morphology and geometric discontinuities in controlling fatigue performance and paves the way for an improved mechanistic understanding of damage evolution in AM components.