Defect-controlled fatigue crack nucleation in additively manufactured Inconel 718: a peridynamic analysis of competing surface and subsurface defects

Mechanical components often exhibit surface roughness that is difficult to eliminate through post-processing. Surface roughness in additively manufactured metallic components acts as a primary crack nucleation site in the high cycle fatigue (HCF) regime. Therefore, reliable fatigue life prediction in the HCF regime requires an explicit representation of crack initiation driven by surface roughness. In this study, a bond-based peridynamic framework combined with a remaining-life fatigue model is used to investigate the HCF behavior of Inconel 718. The study focuses on crack-nucleation-dominated HCF life, since crack nucleation represents the dominant portion of fatigue life in this regime. The effect of the maximum surface valley depth on fatigue life is systematically investigated using a PD model, and the numerical results are validated against experimental data, demonstrating good agreement. Furthermore, the analysis is extended to examine the combined presence of surface roughness and porosity. The results indicate that both defects can serve as crack nucleation sites, and their relative dominance depends on the maximum surface valley depth and the pore to free-surface distance. These outcomes highlight the predictive capability of the PD fatigue framework in capturing the mechanistic role of different defect types and provide a new basis for evaluating the durability of AM components.