Abstract
The mean stress effect on the fatigue life of 304L austenitic steel was evaluated at 300 °C in air and pressurized water reactor (PWR) environments. Uniaxial tests were performed in strain-control and load-control modes, with zero mean stress and a positive mean stress of 50 MPa. A specific procedure was used for the strain-controlled experiments to maintain the strain amplitude and mean stress constant. The strain-controlled data indicate that the application of positive mean stress decreases the fatigue life for a given strain amplitude in air and PWR environments. The data also show that the life reduction is independent of the environments, suggesting that no synergistic effects between the mean stress and the LWR environment occur. The load-controlled experiments confirm that the application of positive mean stress increases fatigue due to cyclic hardening processes. This observation is much less pronounced in the PWR environment. All data were analyzed using the Smith–Watson–Topper (SWT) stress–strain function, which was shown to correlate well with all strain- and load-controlled data with and without mean stress in each environment. In the SWT–life curve representation, the life reduction in the PWR environment was found fully consistent with the NUREG-CR6909 predictions.
Highlights
Austenitic stainless steels are extensively used as structural materials in light water reactor (LWR) environments where high temperature, irradiation and complex thermomechanical loading conditions exist [1]
The analysis shows that converting the standard NUREG/CR-6909 strain–life curve into a SWT–life appears as a powerful method to account for the mean stress effect in air and pressurized water reactor (PWR) environments
The analysis shows that converting the standard NUREG/CR-6909 strain–life curve into a SWT–life appears as a powerful method to account for the mean stress effect in air and factor with these
Summary
Austenitic stainless steels are extensively used as structural materials in light water reactor (LWR) environments where high temperature, irradiation and complex thermomechanical loading conditions exist [1]. Temperature variations associated with start-ups and shutdowns, power adjustments, thermal stratification and striping are responsible for thermomechanical fatigue [2,3]. While a great deal of work has been performed on the fatigue life of austenitic stainless steels, many issues remain to be addressed in the field of environmentally assisted fatigue (EAF) in LWR environments. It is well established that the fatigue life in such environments is shorter than in air, depending in particular on the temperature, strain rate and water chemistry [3]. EAF was not explicitly considered at the time of the construction of the currently operated nuclear power plants. Following the comprehensive NUREG-CR-6909 report [4], LWR environmental effects on fatigue are quantified by an environmental factor, Fen , initially proposed by Kanasaki et al [5] and defined as: Nf,air,RT
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