Research On Fatigue Life Prediction And Reliability Assessment Of The Compressor Impeller

Impeller is the core component of the compressor which is as one kind of the large-scale mechanical equipment. Processing accurate life prediction and reliability assessment of it can not only improve the efficiency, reduce the costs and saving energy consumption; but also the research achievements can provide a support for the opportunity selection of "initiative remanufacturing". Nevertheless, due to the high manufacturing costs and complex running conditions, the data of degradation tests and running status aiming at studying the fatigue failure of the impeller are insufficient. Thus, in this dissertation, a large compressor impeller is selected for the study, based on the finite element analysis of the impeller model and the fatigue tests of the material, and through the combination of material parameters, running parameters and the stress-life model, the fatigue life prediction model and reliability assessment model of the impeller are established, and the fatigue lives as well as the reliability curves are therefore acquired.Firstly, the finite element model of the impeller is built. And the running condition is simulated by adding centrifugal load and aerodynamic load on the impeller, the stress concentration areas and their stress values are then obtained. After that, the crack models with different depths are built on the top of the blades, and with the same loading procedure, the stress values of the crack tips with different crack depths are obtained. Besides, the normal impeller and the impellers with cracks are all processed by modal analysis, the natural vibration frequencies are calculated.Secondly, the ultrasonic fatigue tests of the FV520B specimen are introduced. The experimental results of the material obtained by the tests are then converted into the experimental results of the impeller. After that, the material properties obtained by material analysis and the running parameters obtained by finite element analysis are substituted into the stress-life model, and the fatigue life calculating model of the impeller are therefore established. By comparing the calculating results and the experimental results of the fatigue lives, the accuracy of the calculating model is verified. In addition, the crack propagation life prediction model is applied to calculate the crack propagation lives of the impeller with different crack depths, which demonstrate that the fatigue degradation process of the impeller is high cycle fatigue failure.Finally, combining with the experimental data, the uncertain parameter in the life prediction model of the impeller is fitted with three parameters Weibull distribution by applying maximum likelihood estimation. The fatigue life probability distribution model of the impeller is then established as the reliability assessment model. By Monte Carlo method, the fatigue life values of the impeller are randomly sampled, and therefore the fatigue life probability distribution curves of the impeller are acquired and the Monte Carlo estimation values of the fatigue lives are calculated. The estimating values are then compared with the experimental values, so that the reliability assessment model is verified correct. Afterwards, based on the fatigue life probability distribution curves of the impeller, reliability curves of the impeller under different stress amplitudes are calculatedDepending on all above studies, in this dissertation, a method of fatigue life prediction and reliability assessment of the impeller by combining model analysis and material experiment is established, which provides a support for operation, maintenance and decision-making of remanufacturing of the larger compressor impeller under complicated running conditions.