Abstract
The effect of delayed failure phenomenon on fatigue crack initiation in water was investigated with notched specimen of high strength Ni-Cr-Mo steel (JIS: SNCM 8). The results obtained are as follows:
(1) The number of cycles at fatigue crack initiation (N) depends on the range of apparent stress intensity factor (ΔKa) regardless of the notch length, when the ratio of the mean value of repeating apparent stress intensity factor (Kam) to ΔKa and the notch root radius (ρ) are constant.
(2) When Kam⁄ΔKa and ρ are constant, the number of cycles at fatigue crack initiation (N) in water is less than that in air as the frequency or ΔKa decreases. The shape of ΔKa-N curve in water varies with Kam⁄ΔKa and frequency. Sometimes two bulged parts are observed on the ΔKa-N curves in water, and the upper one at short fatigue life suggests the existence of a strong effect of the delayed failure phenomenon on the fatigue crack initiation in water.
