A Damage Evolution Method for Estimating Low Cycle Fatigue Life of GH4169 Alloy Based on Thermodynamic Entropy Generation at Elevated Temperature

Hot-section components made by nickel-based superalloy for areo-engines always experience a long-term elevated temperature operating environment. Mechanical load caused more serious low cycle fatigue (LCF) at elevated temperature due to the reduction of mechanical properties. It is essential to investigate LCF under elevated temperature, especially LCF behavior and fatigue life. This paper considered the isothermal LCF for disc superalloy GH4169 at elevated temperature from the perspective of irreversible thermodynamics and degradation. A strain-controlled LCF behavior simulation program coded in MATLAB program based on Chaboche plastic constitutive model to simulate cyclic stress–strain responses and entropy generation. According to the results of accumulation of entropy generation in LCF process, a proposed model utilizing Belehradek law to fit fatigue fracture entropy generation under different loading conditions. A defined damage factor based on degradation-theorem and entropy generation was proposed to describe the evolution of fatigue damage in LCF. A damage evolution method utilized the entropy generation are adopted to estimate fatigue life. Compared with the experiment lives and predicted results from classic life prediction model, such as Ostergren and SWT models, this method can estimate the fatigue life for LCF at elevated temperature reasonably. Finally, the damage evolution method provided a suitable approach to monitor remaining life for elevated temperature LCF for GH4169.