Unforeseen, negative interaction-effect of adjacent circumferential notches on the fatigue limit of Ni-based superalloy 718

Abstract Investigations were conducted on the interaction-effects of adjacent, circumferential V-notches on the fatigue limit of Alloy 718, with the aid of fully-reversed, tension–compression fatigue tests. Contrary to expectation, specimen with seven adjacent circumferential notches had lower fatigue limit than that with a single circumferential notch. This phenomenon was attributed to the increased stress intensity factor (SIF) range of shear-mode fatigue cracks at notch-roots, resulting from competition between two factors: (i) stress mitigation through the mechanistic interaction of notches (decreased SIF) and (ii) the orderly, spatial alignment of crack-planes, due to the asymmetric stress-fields in the vicinity of notch-roots (increased SIF).