Prediction of Fatigue Crack Initiation Life in Notched Cylindrical Bars Under Multiaxial Cycling Loading

This paper addresses the determination of fatigue crack initiation lifetime in notched round bars under multiaxial loading on the basis of a total strain energy density approach. The modus operandi consists of developing a fatigue master curve relating the total strain energy density and the number of cycles to failure from the outcomes of a set of standard strain-controlled fatigue tests. In a second stage, the total strain energy density of the notched sample is computed from representative hysteresis loops obtained via linear-elastic finite-element models. The proposed methodology is tested in cylindrical bars with lateral U-shaped notches and cylindrical bars with blind transverse holes subjected to different constant-amplitude proportional bending-torsion loading. After fatigue testing, specimen surfaces are examined by scanning electron microscopy to identify the main failure micro-mechanisms.