An Improved Creep-Fatigue Life Model Involving the Cyclic Softening/Hardening and Stress Relaxation Effect

In this work, improved creep-fatigue life prediction models based on time fraction (TF) and ductility exhaustion (DE) rule are established for creep-fatigue life prediction of components at elevated temperatures. Cyclic softening/hardening and stress relaxation models for cyclic softening/hardening material are incorporated in the model. Materials data conducted by authors and collected from references are employed for validations. Results indicated that the improved models proposed could present more realistic evolution behavior of materials than the half-life models. The differences of the predicted lives based on the improved models and half-life models are dependent on cyclic behaviors of materials. The predicted life by the improved model is lower than that gained by the half-life model for cyclic softening steels, while it is higher than that by the half-life model for cyclic hardening steels. In addition, the DE rule could overcome the influence of cyclic softening/hardening on creep-fatigue life prediction more significantly than the TF rule.