Life evaluation method for nickel-based directionally solidified turbine blade-like specimens under near-service conditions

Abstract

Life assessment of turbine blades is a challenging issue due to the complexity of their structural designs and operational loads. To address the issue, a life evaluation method for turbine blade-like specimens under near-service conditions was investigated. First, creep and creep-fatigue tests were conducted on these specimens to replicate operational environments, with the nominal load of the critical section set at 950 °C/273 MPa. Next, the coupled-damage Norton-Bailey model was used to simulate the creep behavior at 760 °C, 850 °C and 980 °C. Electromagnetic-thermal coupling simulations were then carried out in COMSOL with a 120A alternating current, yielding the temperature distribution for the blade-like specimen. The mechanical response of these specimens under creep and creep-fatigue conditions was simulated based on the Norton-Bailey model. Finally, a life prediction model was developed by introducing a weight function into the critical distance method. The results indicated that the introduction of film-cooling holes and cyclic loading reduced the specimens’ life by 43 % and 42 %, respectively. Elevated temperatures (942–965 °C) at the leading edge caused crack initiation in non-holed specimens, while high stress (maximum stress of 1103 MPa) around the holes led to crack initiation in holed specimens. A comparative analysis with traditional cross-sectional averaging methods demonstrated that the proposed model achieves higher predictive accuracy, with all predictions falling within a twofold scatter band.