A unified treatment of the fatigue limit of components weakened by stress raisers, subject to multiaxial mode I, II, and III loading

This paper discusses the dependency of the fatigue limit ∆σg,th of components on the size of stress raisers, such as cracks, defects, and U- or V-notches, under mode I, II, and III loading conditions in Constant Amplitude (CA) fatigue. As summarized in the Atzori-Lazzarin-Meneghetti (ALM) diagram, depending on the size and acuity of the stress raiser and the material fatigue properties, three different fatigue limit regimes can be identified: (i) for short cracks, ∆σg,th approaches the plain fatigue limit ∆σ0, (ii) for long cracks or sharp notches, ∆σg,th is governed by the long crack fatigue propagation threshold ∆Kth,LC, and (iii) for blunt notches, ∆σg,th is governed by the theoretical stress concentration factor Kt. In this work, the ALM diagram is extended to include mode II and III loading conditions by proposing a single design curve for any stress raiser subjected to any loading condition by employing the averaged Strain Energy Density criterion. The averaged SED is a fatigue m...