A unified life prediction model for 316L austenitic stainless steel under isothermal, thermomechanical fatigue and creep-thermomechanical fatigue loadings

Thermomechanical fatigue (TMF) life prediction is crucial for the structural design and reliability assessment of high-temperature components. Based on the test results and damage mechanisms analysis, a unified liner damage accumulation model for predicting isothermal fatigue (IF), TMF and creep-TMF (CTMF) life of 316L under various loading conditions is proposed. The developed model introduces a mechanical property impairment factor based on uniform tensile plastic strain energy at different temperature to characterize the progressive degradation of material properties under elevated temperature. By incorporating thermal plastic strain energy and the mechanical property impairment factor, the model accurately describes the fatigue damage across different temperature ranges. Additionally, a modified time fraction method is developed to separately assess creep damage during cycling loading and strain holding. The oxidation damage modeling takes into account the process of repeated formation and rupture of oxides at the crack tip. The results show that the linear summation of damage components provides a uniform and accurate description of fatigue life for different strain amplitudes, phase angles, temperature ranges, and strain-holding conditions. Finally, the validity of the proposed model in characterizing the damage mechanism is substantiated by analyzing the percentage distribution of damage component percentage and the fracture mechanism.