Joined application of a multiaxial critical plane criterion and a strain energy density criterion in low-cycle fatigue

In the present paper, the multiaxial fatigue life assessment ofnotched structural components is performed by employing a strain-basedmultiaxial fatigue criterion. Such a criterion, depending on the critical planeconcept, is extended by implementing the control volume concept reated tothe Strain Energy Density (SED) approach: a material point located at acertain distance from the notch tip is assumed to be the verification pointwhere to perform the above assessment. Such a distance, measured along thenotch bisector, is a function of both the biaxiality ratio (defined as the ratiobetween the applied shear stress amplitude and the normal stress amplitude)and the control volume radii under Mode I and Mode III. Once the positionof the verification point is determined, the fatigue lifetime is assessed throughan equivalent strain amplitude, acting on the critical plane, together with aunique material reference curve (i.e. the Manson-Coffin curve). Some uniaxialand multiaxial fatigue data related to V-notched round bars made of titaniumgrade 5 alloy (Ti-6Al-4V) are examined to validate the present criterion.