日本金属学会誌

J. Japan Inst. Metals, Vol. 36, No. 12 (1972),
pp. 1180-1188

The Fatigue Crack Propagation Law in Water of Ni-Cr-Mo Martensitic Steel

Keijiro Nakasa1, Hideo Takei1 and Tetsuhiro Asamoto2

1Faculty of Engineering, Hiroshima University, Hiroshima
2Graduate School, Hiroshima University, Hiroshima

Abstract:

The effect of delayed failure on the fatigue crack propagation rate in water of Ni-Cr-Mo martensitic steel was investigated. The results obtained are as follows:
(1) The relation between the fatigue crack propagation rate da/dN in air and the stress intensity factor range Δ K is expressed as da/dN=C1(Δ K)m1, and m1 increases with increase of Km/Δ K, where Km is the mean stress intensity factor.
(2) The relation between the crack propagation rate da/dt in delayed failure and the static stress intensity factor KD is expressed as da/dt=C2(KD)m2.
(3) The fatigue crack propagation rate (da/dN)w in water is expressed as the addition of both fatigue crack propagation rate in air and crack propagation rate in delayed failure, and the following equation holds:

(da/dN)w=da/dN+β(da/dt) · 1/f
where f is the frequency (cpm); β is a coefficient of addition and depends mainly on f and Km/Δ K. Under the condition in this experiment (f=55 ∼ 345 cpm, Km/Δ K=0.5 ∼ 4), β is 0.2 ∼ 0.4.
(4) Physical meaning of β is considered to be the ratio of the time in which the tri-axial tensile stress state region at the crack tip meet a cluster of hydrogen atoms during one cycle.


(Received 1972/7/17)

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