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

Abstract

In this work, improved creep-fatigue life prediction models based on time fraction and ductility exhaustion rule are established for creep-fatigue life prediction of components at elevated temperatures, with the cyclic softening/hardening and stress relaxation model for cyclic softening/hardening material incorporated. 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 ductility exhaustion rule could overcome the influence of cyclic softening/hardening on creep-fatigue life prediction more significantly than the time fraction rule.

Establishment of unified creep–fatigue life prediction under various temperatures and investigation of failure physical mechanism for Type 304 stainless steel

“…[2][3][4] Hence, the growing concern about creep-fatigue interaction, rather than single-driven fatigue or creep, has promoted the development of reliable damage and life assessment. [5][6][7] It is fairly common hypothesis for estimating the fatigue damage that can be determined by fatigue curves on the basis of cycle fraction concept. 8 Furthermore, the determination of creep damage performing on fatigue turn to the main argument on creep-fatigue damage assessments.…”