Effects of the Stress Amplitudes Below the Fatigue Limit on Fatigue Lives in the Cylindrical Specimens Having a V-shape Groove

Abstract

The effects of the stress amplitudes below the fatigue limit on the fatigue lives were investigated by the two steps multi-fold program fatigue tests in which the higher stress was above the fatigue limit and the lower stress was below the fatigue limit. Cylindrical specimens having V-shape groove of the structural carbon steel JIS S35C were used, and the stress concentration factors α of the specimens were selected as 2, 4 and 6. The test results revealed that the cumulative cycle ratios of the program fatigue tests were from 0.2 to 0.6 when α was 2, from 0.8 to 1.2 when α was 4, and from 0.9 to 1.4 when α was 6. The following behavior was also clarified : the fatigue crack was propagated even by the stress amplitude below the fatigue limit and in most cases the crack propagation was stopped as the number of cycles increased. Some discussions were made on the experimental results.