Mechanism-Based Modeling for Low Cycle Fatigue of Cast Austenitic Steel

A mechanism-based approach-the integrated creep-fatigue theory (ICFT)-is used to model low cycle fatigue behavior of 1.4848 cast austenitic steel over the temperature range from room temperature (RT) to 1173 K (900 A degrees C) and the strain rate range from of 2 x 10(-4) to 2 x 10(-2) s(-1). The ICFT formulates the material's constitutive equation based on the physical strain decomposition into mechanism strains, and the associated damage accumulation consisting of crack nucleation and propagation in coalescence with internally distributed damage. At room temperature, the material behavior is controlled by plasticity, resulting in a rate-independent and cyclically stable behavior. The material exhibits significant cyclic hardening at intermediate temperatures, 673 K to 873 K (400 A degrees C to 600 A degrees C), with negative strain rate sensitivity, due to dynamic strain aging. At high temperatures > 1073 K (800 A degrees C), time-dependent deformation is manifested with positive rate sensitivity as commonly seen in metallic materials at high temperature. The ICFT quantitatively delineates the contribution of each mechanism in damage accumulation, and predicts the fatigue life as a result of synergistic interaction of the above identified mechanisms. The model descriptions agree well with the experimental and fractographic observations.