Size and load effects on the biaxial fatigue resistance of holed structural components

. A high-cycle multiaxial fatigue criterion, based on a combined critical point-critical plane approach, is used to estimate the multiaxial endurance limit in notched metal structural components. Accordingly, the position of the critical point and the orientation of the critical plane at such a point (plane where fatigue strength assessment has to be performed) are determined on the basis of some pseudo-isostatic lines related to the stress fields experiencing, at each material point, the maximum principal stress in the loading cycle. Some experimental results related to holed steel specimens subjected to in-phase and out-of-phase axial and torsional loading are analysed. The comparison is instrumental in highlighting the notch size-effect (as the hole diameter varies) under uniaxial and biaxial far-field stress conditions as well as the effect of the loading phase