Co-authors​ :

 Zikai ZHOU , Chao YOU (CHINA), Xiguang GAO , Yingdong SONG  

Ceramic matrix composites (CMCs) have advantages in excellent high-temperature mechanical properties. Its rapid development is significant to improving the thrust-to-weight ratio of aeroengines. By far, CMCs have been successfully applied to static hot components of aeroengines such as turbines, combustion chambers, nozzles, etc., but their application in turbine rotor blades is still at early stage of research. As one of the most important components of the engine, turbine rotor blades experience significant risk of fatigue failure due to the coupling effects of various loads under service conditions. However, at present, research on the fatigue failure mechanisms of CMCs under complex working conditions is still very limited. There is also a lack of associated fatigue life prediction methods applicable to CMCs, which significantly delays the application of CMCs in turbine rotor blades.
Based on this background, this study conducted an in-depth study on the fatigue failure mechanisms of 2.5D CMCs under creep-fatigue combined with high-low cycle fatigue loading at high temperature environment, and developed an associated fatigue life prediction method. Firstly, the sine-wave loading fatigue behavior of 2.5D CMCs was studied, and the effects of test temperatures and loading levels on the fatigue damage of CMCs were clarified by comparing the trends in the accumulation of hysteresis dissipation energy, stiffness degradation and fracture surface characteristics. Furthermore, the effects of loading dwell time, high stress ratio and combined high-low cycle fatigue loading on the fatigue life of CMCs were studied respectively. The results showed that the dwell time and mean stress levels were key factors affecting the fatigue life of CMCs, in addition to the hysteresis dissipation energy caused by friction between yarns during fatigue loading. It also showed that the combined effects of high-low cycle fatigue loading have limited effects on the overall fatigue life based on the selected loading schemes. Based on the above mechanisms, a fatigue life prediction method for CMCs considering the influence of loading dwell time and mean stress levels was developed. Finally, an airfoil sub-component of the 2.5D CMC rotor blade was designed based on the root cross-section of the airfoil, which was a risky area during service. Its failure modes resulting from combined fatigue loading were then investigated experimentally. Numerical analysis was also carried out to help clarify the fatigue failure modes and to predict the fatigue life of the 2.5D CMC airfoil sub-component, demonstrating the effectiveness of the proposed lifing method for CMCs under combined fatigue loading.