Consideration on Low Cycle Fatigue Life Based on Cyclic Strain Behavior of Notched Specimen and Smooth Specimen

From the cyclic strains measured by strain gages during the low cycle fatigue test of notched specimens under the control of bending deflection, two types of cyclic strain behaviors near notch roots have been found : in one type named as IS, the strain near notches increases with an increasing cycles, and in other type named as CS, the strain near notches remains constant with an increasing cycles. Manson-Coffin rule may be applied to the relationships between the saturated strain range at a notch root and the number of cycles to the initiation of a edge crack at a notch root. It is discussed enough that the strain state at a notch root of a notched specimen is different from one of a smooth specimen and these differences induce the difference of the fatigue strength of both specimen. The comparison of the ε_R∿N_f of smooth round specimen with the ε_R∿N_c of notched specimen is also discussed. These experimental data and their discussions are shown