日本金属学会誌

J. Japan Inst. Metals, Vol. 39, No. 4 (1975),
pp. 327-333

Initiation of Fatigue Crack in Notched Specimen of High Strength Steel in Water

Keijiro Nakasa1, Hideo Takei1 and Tetsuhiro Asamoto2

1Faculty of Engineering, Hiroshima University, Hiroshima
2Graduate School, Hiroshima University, Hiroshima. Present address: Mitsubishi Electric Co., Ltd., Nagoya

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 ( Δ Ka) regardless of the notch length, when the ratio of the mean value of repeating apparent stress intensity factor (Kam) to Δ Ka and the notch root radius ( ρ ) are constant.
(2) When Kam/Δ Ka 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 Δ Ka decreases. The shape of Δ Ka-N curve in water varies with Kam/Δ Ka and frequency. Sometimes two bulged parts are observed on the Δ Ka-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.


(Received 1973/08/11)

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