Notch Effect in Low Cycle Fatigue : 1st Report, Some Considerations on Fatigue Strength Reduction Factor by Round-Bar Specimens with Circumferential Notches

Abstract

The present paper describes experiments and some considerations on notch effect characteristics in low cycle fatigue. The experiments are strain-controlled and stress-controlled push-pull low cycle fatigue tests on unnotched round-bar steel specimens and stress-controlled fatigue tests on round-bar specimens with several types of circumferential notches. Considerations on the test results show that in order to clarify the notch effect in low cycle fatigue, it is necessary to distinguish the fatigue lives for crack initiation and for fracture. The fatigue life for crack initiation can be regarded as a function of the peak value of effective strain range at the notch, but the crack propagation after the crack initiation is almost independent of the notch. The so-called fatigue notch factor K_f, i.e. the fatigue strength reduction factor due to notch effect is discussed in various aspects of fatigue curves at low cycle region.