FATIGUE LIFETIME EVALUATION OF NOTCHED COMPONENTS: IMPLEMENTATION OF THE CONTROL VOLUME CONCEPT IN A STRAIN-BASED LCF CRITERION

The goal of the present paper is to discuss the reliability of a strain-based multiaxial Low-Cycle Fatigue (LCF) criterion, recently proposed by some of the present authors, in estimating the fatigue lifetime of metallic structural components weakened by sharp notches.  Such a criterion, based on the critical plane approach, is formulated according to the control volume concept related to the Strain Energy Density (SED) criterion: a material point located at a certain distance from the notch tip is assumed to be the verification point where to perform the fatigue assessment.  The above distance is assumed to be a function of both the biaxiality ratio (applied shear stress amplitude over normal stress amplitude) and the control volume radii under pure Mode I and pure Mode III loading conditions.  Once the position of the verification point and the orientation of the critical plane are determined, the fatigue lifetime is theoretically evaluated through an equivalent normal strain amplitude acting on the critical plane, together with the tensile Manson-Coffin curve.  Some uniaxial and multiaxial LCF data, recently published in the literature for V-notched round bars made of Ti-6Al-4V titanium alloy, are analysed through the present criterion.