Effect of Mean Stress on Fatigue Strength of Type 316 Stainless Steel
Masahiro KAWAKUBO and Masayuki KAMAYA
Abstract:The reduction in fatigue life due to mean stress is considered in fatigue design of nuclear power plant components. However, for stainless steel, it was pointed out that fatigue life did not decrease due to the mean stress. In this study, the effect of the mean stress on fatigue life and fatigue limit was investigated in detail for Type 316 stainless steel. Axial fatigue tests were conducted in ambient air and room temperature. In order to assess the influence of change in strain by applying the mean stress and its effect on fatigue life, the strain range was measured during the fatigue tests. Furthermore, crack closure due to the mean stress was identified by using the digital image correlation (DIC) technique. It was shown that fatigue life and fatigue limit were not reduced by applying the mean stress because the mean stress caused plastic shakedown and that reduced the strain amplitude under the same stress amplitude. It was found that fatigue limit as well as fatigue life correlated better with the strain amplitude than the stress amplitude. Fatigue life was well correlated with effective strain range ƒ¢ƒÃeff, which corresponded to the crack opening range. Since the mean stress did not reduce the ƒ¢ƒÃeff, the fatigue life was extended. It was concluded that consideration of the reduction in fatigue life and fatigue limit due to the mean stress is not necessary in the fatigue design of stainless steel components. Key Words:Mean stress, Plastic shakedown, Crack closure, Effective strain range, Stainless steel, Fatigue life, Fatigue limit