An Analysis of Surface Crack Growth in Circumferentially Grooved Components under Low-Cycle Fatigue

Abstract

Circumferentially grooved specimens were low - cycle fatigued, and the local stress-strain relation was calculated at the notch root by F.E.M. (finite-element method). The fatigue lives for crack initiation and final failure were satisfactorily evaluated by both the axial and equivalent plastic strain ranges existing at the notch root, and Coffin-Manson law held for the notched specimens as well as for the smooth specimen. The growth behavior of surface cracks at the notch root was examined in association with the growth rates of the surface crack in the smooth specimen and of the long through-crack. The fatigue crack growth rates, da/dN, were successfully plotted against the cyclic J-integral range, ΔJ, and the strain intensity factor range, ΔK_ε, which were estimated using the stress-strain hysteresis loop analyzed at the notch roots by F.E.M: The plots of log da/dN versus log ΔJ and log da/dN versus log ΔK_ε for the notched specimens were expressed by linear lines which were nearly in accord with these relations for the surface crack in the smooth specimen.