定荷重フラクトグラフィ試験によるK_<ISC>C,K_<IH>および割れ進展速度の評価

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The threshold stress intensity factor, K_<ISCC> for stress-corrosion cracking or K_<IH> for hydrogen assisted cracking, is generally determined by one of the cantilever constant-displacement test and rising-load test. In the present paper, problems encountered with these tests, especially on the accuracy, test duration, and/or measurement of crack growth rate, were discussed first. Then the holding-load and fractography test was proposed as a way to improve the existing procedures: An outline of the new testing procedure is as follows: Several precracked specimens exposed in test environments or precharged with hydrogen are loaded constantly at different K_I values for a relatively short predetermined test duration. The specimens are then unloaded and separated apart by cleavage fracture or fatigue loading. The amount of subcritical crack growth during the test. Δa_H, is measured by an electron microscopic observation of the fracture surface. The value of K_<ISCC> or K_<IH> at the onset of the crack growth and the growth rate are determined from the relation of Δ_aH and its rate per test duration to K_I value. The test procedure was used to predict the values of K_<IH> and growth rate for hydrogen assisted cracking of 1/2 Mo steel and 2-1/4Cr-lMo steel. The results indicate that the usual test procedure estimates higher K_<IH> than the proposed one. Thus, it is considered that the reexamination of the existing K_<ISCC> and K_<IH> data is required.
社団法人日本材料学会の論文
1987-03-15

定荷重フラクトグラフィ試験によるK_<ISC>C,K_<IH>および割れ進展速度の評価

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