Intrinsic fatigue resistance and the influence of material defects

CHAPETTI, M.D.

Hiroshima

Congreso; 13th International Fatigue Congress (FATIGUE 2022+1); 2023

The Society of Materials Science, Japan (JSMS) Committee on Fatigue of Materials

The demand for reliability and safety in mechanical components used in industrial applications has led to an increased focus on prediction approaches in the field of long-life fatigue. With the evolution of fracture mechanics tools, it has become possible to estimate the fatigue lives and limits associated with mechanical components that have small cracks or crack-like defects generated during manufacturing. Inherent defects in some manufacturing processes, such as additive manufacturing, can eliminate or minimize the initiation stage of fatigue cracks. As a result, the damage process primarily involves the propagation of a crack from the critical defect until it causes the component to fracture. Fracture mechanics is crucial in developing predictive models, and combined with the advancements in understanding the behavior of small cracks, the damage tolerance methodology has become the best tool for designing safe mechanical components. However, fracture mechanics analysis necessitates estimating the resistance curve of the material in the absence of defects. The intrinsic fatigue limit of the material, which represents the material's resistance without defects, is required to estimate the resistance curve if the defects are inherent to the manufacturing process. This work presents basic concepts and hypotheses related to fatigue limit and fracture mechanics models, as well as experimental evidence on the intrinsic fatigue limit and its association with naturally-nucleated non-propagating cracks. Two simple expressions are proposed for estimating the intrinsic fatigue resistance of metallic alloys.