Modelling of cyclic stress-strain behavior under thermomechanical fatigue conditions — A new approach based upon a multi-component model

Abstract

Operating conditions of many high temperature components involve thermal transients in combination with mechanical strain cycles. For lifetime prediction, an accurate knowledge of the cyclic stress-strain behavior of the material is required. Ideally, in laboratory thermomechanical fatigue (TMF) tests the cyclic stress-strain behavior should be determined under conditions which resemble those experienced by the actual component as closely as possible. However, thermomechanical fatigue tests require expensive test equipment and are often time-consuming. Therefore, the majority of tests are performed under isothermal conditions at the maximum service temperature experienced by the component during service. It is assumed that this test method leads to a conservative lifetime prediction. However, cyclic stress-strain response and crack initiation and fatigue crack growth are often reported to be significantly different in tests performed under isothermal and under TMF conditions, respectively. This can lead to a non-conservative lifetime prediction, if isothermal data are used. In this paper the cyclic stress-strain behavior of an AISI 304L-type steel under TMF conditions is modeled as cyclic deformation behavior of this material has been characterized extensively both under isothermal and TMF conditions.