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A study was made on the effects of stress rise time T1, maximum stress holding time T2, stress decreasing time T3 and minimum stress holding time T4 of a cycle on fatigue crack growth for a low alloy carbon steel in 3% NaCl solution. Measurements of the effective stress intensity range ratio U and observations of crack tip response were performed to clarify the causes of waveform effects. The results were summarized as follows; T1 had a strong accelerating effect due to corrosive dissolution of the fresh surfaces of the crack which were formed during T1. The crack growth rate was enhanced as T1 increased and reached a constant value (about 3 times that in air) after T1= 10s. The crack growth rate at low ΔK, however, decreased as T1 increased more than T1= 1 s. T2, T3 and T4 decreased the crack growth rate. The extent of decrease not only depended on the period of T2 (or T3, T4), but also on ΔK and T1. A previously derived crack growth law which considered waveform and frequency effects, is also valid to a first approximation for the present results.
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KAWAI et al. (1979) studied this question.
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