Study on Fatigue Life Prediction of Notched Specimen under Intermittent Stress

On the blades of gas turbines and blowers, the vibrating stress superposes on the centrifugal stress which is repeated with the start-stop of machine. This combined stress wave is called the intermittent stress wave, and number of studies have been conducted under this stress wave. However, some unclarified problems are left regarding the intermittent stress fatigue. The present report aims at the fatigue life prediction of a notched specimen made of carbon steel (S35C) under the condition of superposed stress cycles 102-104. The following conclusions were obtained from this experimental study. (1) Miner's rule does not predict the fatigue life under the intermittent stress. (2) The experimental life is a little shorter than the life predicted by the modified Miner's rule. (3) The proposed life prediction method may well predict the crack initiation life by using the interaction coefficient C of 0.2-0.4.