FRETTING FATIGUE OF AN AUSTENITIC STAINLESS-STEEL IN SEAWATER

Fretting fatigue tests of an austenitic stainless steel used for a propeller tail shaft were carried out in seawater and in air. In seawater, fretting significantly reduced the fatigue strength, however, the fretting fatigue lives at higher levels of stress were longer than those in air. The tangential force coefficient (defined as the ratio of the frictional force amplitude and the contact load) in seawater was much lower than that in air and varied in the range from 0.3 to 0.5 during the fretting fatigue tests. The lower tangential force coefficient in seawater seems to be the main reason for the longer fretting fatigue life in seawater. The prediction of fretting fatigue life was made on the basis of elastic-plastic fracture mechanics, where the frictional force between the specimen and the contact pad was taken into consideration. The predicted fatigue lives agreed well with the experimental results in both air and seawater.