2025 Volume 74 Issue 12 Pages 741-748
It was shown that the fatigue life of an elbow pipe made of carbon steel was shorter than that obtained under uniaxial loading conditions, while an elbow pipe made of stainless steel did not exhibit a reduction in fatigue life. To investigate the influence of stress triaxiality on the fatigue life reduction in the elbow pipe, fatigue life under equi-biaxial loading conditions was examined using disc bending fatigue testing equipment. A 15C carbon steel and Type 316 stainless steel were used for the fatigue tests. It was found that the fatigue life obtained from the disc bending fatigue test was longer than that obtained from the uniaxial fatigue tests for the same equivalent strain range, which was used as the driving force for fatigue damage in the design of nuclear power plant components. Therefore, it was concluded that the reduction in fatigue life of the elbow pipe was not caused by stress triaxiality. Although a reduction in fatigue life was observed only for the carbon elbow steel, the degree of change in the fatigue life due to stress triaxiality was comparable for both the carbon steel and stainless steel. This implies that stress triaxiality plays a minor role in the reduction of fatigue life in the elbow pipe.
