Fracture mechanics approaches for material defect assessment and fatigue design

The increasing demand for reliability and safety in industrial mechanical components has heightened the focus on predictive methods in long-life fatigue analysis. Advances in fracture mechanics now enable accurate estimation of fatigue life and limits in components with small cracks or crack-like defects, often introduced during manufacturing. In processes like additive manufacturing, inherent defects may bypass the crack initiation phase, accelerating the fatigue process. Consequently, the damage mechanism primarily involves crack propagation from critical defects until component failure occurs. However, the statistical variation in the size of inherent defects in certain materials or components results in significant dispersion in fatigue life under similar stress levels, making it difficult to identify and quantify the intrinsic strengths involved, and particularly challenging to compare different configurations. This work advances the understanding of the essential structure of traditional S-N curves and the limitations they display in describing results. Proposed alternatives, as documented in the literature, are critically analyzed, and a new alternative is proposed, based on fracture mechanics methodologies that allow the entire propagation process to be quantified and the deficiencies of previous proposals to be explained.