Effect of a Very Small Number of Stress Cycles above Fatigue Limit on Crack Propagation Behavior under Variable Stress Amplitude

概要

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Two step-two fold, two step-three fold and two step multi-fold program fatigue tests were carried out by rotating bending loading. The material used was a plain carbon steel, JIS S35C, and the specimens were pre-cracked and stress relieved. The main results obtained were as follows. After application of a very small number of cycles n_1 at stress amplitude above fatigue limit, a non-propagating crack growth increment 21_2 by repetition of low stress level was dependent on n_1. As n_1 increased, 21_2 became longer. Crack retardation behavior under repetitions of high stress level was more prominent when 21_2 was longer and low stress level was higher. In two step multi-fold program fatigue tests, to attain the most critical condition, the number of cycles of high stress level had to be smaller and number of cycles of low stress level had not to be long enough to cause crack arresting.
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