The Study Of The Fatigue Property Of The Compressor Blade With The Consideration Of Surface Defect And Internal Defect

The high strength metal FV520B-I is employed to manufacture the key components of the large-scale machinery equipment, such as the blade of the centrifugal compressor. According to the production requirement and the actual working condition, the fatigue life of the blade should be 10 to 20 years, so the "giga-fatigue" level. With the comprehensive study for the fatigue failure, it is found that the defect is the most significant factor affecting the material fatigue property, including the surface roughness and the internal inclusion, which can cause the fatigue failure easily. The defect can weaken the fatigue property and this procedure is also accompanied with the comprehensive influence of stress ratio, actual stress amplitude and some other factors. There is no current comprehensive fatigue property analysis of FV520B-I is conducted. Not only that, the relevant experimental data is still lack, no definite fatigue strength model or material parameter has ever been proposed.In this paper, a summary about the study of the fatigue strength and fatigue life is made firstly, so the importance and innovation of this study are proposed clearly and the summary also lays a theoretical foundation for the further study.Then the ultrasonic fatigue experiment for FV520B-I is carried out. The experimental data show that giga-fatigue failure is affected by the hydrogen significantly and it can't be neglected in the fatigue strength analysis process. The finite element analysis is presented with the consideration of fatigue crack to simulate the actual failure and the actual stress amplitude is obtained.In chapter three, the influences of stress state and geometric on the fatigue strength are analyzed detailed. It includes the mean stress, stress ratio and the size coefficient. The analysis makes clear the influence mechanism of these factors and the modified formulas of stress ratio are established based on the classic fatigue theory.In the fourth and fifth chapters, the surface roughness and the internal inclusion are the main subjects, and the fatigue strength models with the consideration of surface roughness the internal inclusion are obtained. The additional experiment is carried to prove the accuracy of the model with the consideration of surface roughness. The model factors, including stress ratio, hydrogen and size coefficient are determined according to the actual engineering. Substituting the fatigue strength model into the classic fatigue life model, and the theoretic strength and life are calculated. By comparing the theoretic life and experimental data, the accuracy of the fatigue strength model are proved.