Mean Stress Effect on Fatigue Properties of Type 316 Stainless Steel: Part I — In High-Temperature Air Environment

The mean stress effect on the fatigue life of Type 316 stainless steel was investigated at 325°C in air. It was shown that the fatigue life was extended by applying the mean stress under the same stress amplitude. Increase in the maximum peak stress by applying the mean stress induced additional plastic strain and this hardened the material. The strain range of the hardened material was relatively small for the same stress amplitude, and this extended the fatigue life for a given stress amplitude. On the other hand, the fatigue life was shortened by the mean stress for the same strain range. The mean stress increased the effective strain range due to an increase in the minimum peak stress. Also, the mean stress induced ratcheting strain during the fatigue test and this accelerated crack mouth opening. The enhanced crack mouth opening accelerated the crack growth and shortened the fatigue life for a given strain range.