Volume 8, Issue 8 (September 2011)
Effect of Creep and Oxidation on the Isothermal and Thermomechanical Fatigue Behavior of an Austenitic Stainless Steel
Austenitic stainless steels are often used for high-temperature applications under conditions where fatigue loading occurs in combination with varying temperatures, superimposed mean stresses or dwell times and environmental effects. In order to characterize and separate the various damage contributions on the deformation behavior and the damage evolution of AISI304L, isothermal and thermomechanical fatigue tests were carried out at temperatures ranging from room temperature to 800°C. The test results in combination with microstructural observations were used for an adaption and application of a simple multi-component model to predict the stress-strain response under thermomechanical fatigue conditions solely from isothermal data. A very reasonable predictive accuracy was obtained and the cyclic stress-strain calculation was directly incorporated in fatigue life assessment models. Two models, which were found to be suitable for isothermal fatigue conditions, are presented. These models were extended and applied to non-isothermal conditions. A comparison of the experimentally observed fatigue life data with the predicted values revealed that thermomechanical fatigue life can reasonably be assessed from isothermal test results, if environmental effects are correctly taken into account. Thermomechanical fatigue tests employing dwell periods indicate that the life prediction models developed are robust and conservative.