Giga-Fatigue Life Research Of Centrifugal Compressor Impeller Material FV520B-I

The most important core component of Centrifugal compressor is impeller vane, which is manufactured with high strength material FV520B-Ⅰ and it is also the common position of fatigue failure. In practical engineering, the most dangerous failure form of impeller vane is fatigue failure. Fatigue crack initiate in the position of internal inclusions then propagate under the cyclic loading, this will lead to the decline of the fatigue property of FV520B-I until failure. There is no omen before the failure, it happens instantaneously and it is also irreversible, it will cause great harm to the mechanical system even threaten the security of the staff. However the test for the fatigue property of FV520B-I has not been carried out widely, lack enough experimental data about its fatigue life and property, analyses the fatigue property of FV510B-I, especially the fatigue strength, then establish the specific fatigue life prediction model for FV520B-I.In this paper, the qualitative simulation analysis is carried out in the Ansys Workbench and stress distribution of impeller vane is simulated, from the result of analysis, it is clear that the stress concentration exists at the contact position between the blade and cover where is the dangerous site for fatigue failure.The fatigue experiment for FV520B-Ⅰ is conducted in UFTS (Ultrasonic Fatigue Test System) to, fatigue life, S-N curve and some other experimental data are recorded. Using the SEM (scanning electron microscope) and OM (optical microscope) to observe the fracture surface of the specimen and measure the inclusion size. GBF (Granular Bright Facet) and "fish-eye" can be obviously observed which prove that the internal inclusions and hydrogen have a significant influence on the fatigue life of FV520B-I. All these fatigue data and phenomenon of FV520B-I make a contribution to the establishment of the specific life prediction model.In chapter Four, based on the theory of fracture mechanics, internal inclusion size are considered to be equal to the fatigue crack size, and the formula describing the inclusion size and fatigue strength is established according to the relationship between stress intensity factor and amplitude of stress intensity factor., then the fatigue strength formula is modified with the consideration of hydrogen and stress ratio, as they will have a significant influences on the fatigue strength.In the last chapter, the basic life prediction model is obtained based on the energy theory and Paris formula. The empirical fatigue life prediction model is identified by employing a fitting algorithm and determining the model unknown parameters, based on the fatigue data including life and inclusion size. Model validation is performed through the analysis of errors between the model and experimental data, which are shown within an accepted tolerance for its engineering applicability. So this model can be used to predict the fatigue life of FV520B-Ⅰ with internal inclusion.FV520B-I fatigue life prediction is difficult in theory, but useful in practical engineering. It has a high value in the study of remanufacturing and also the remanufacturing engineering.