Research On Fatigue Life Prediction And Reliability Analysis Method Of Aero-engine Turbine Shaft

With the continuous development of aviation,the aero-engine determines the ability of a country to guarantee air control.In order to ensure the smooth operation of the flight mission,the aero-engine must overcome a series of problems brought by the service in the harsh environment,such as high temperature and high load.Due to the complex structure of aero-engine,the fatigue problem of its hot end parts is more serious in the service process.Many researchers at home and abroad focus on the fatigue life and reliability of the key parts of the engine,aiming to improve the performance and service life of aeroengine.Turbine shaft is a key component in the engine assembly of aero-engine,which mainly plays the role of power transmission and support.Its failure is fatal to the aircraft in flight mission.Because the turbine shaft has the characteristics of small sample size,long life and high cost,it is difficult to obtain a large number of failure data and test data.Therefore,it is necessary to combine the material test data and simulation data effectively when carrying out the research on the turbine shaft life and reliability.In this thesis,the fatigue failure mechanism and load condition of an aero-engine turbine shaft are investigated.On this basis,the fatigue life prediction and reliability analysis of the turbine shaft are carried out.The research content of this thesis includes the following three parts:(1)Low cycle fatigue life prediction of turbine shaft.According to the characteristics of low cycle fatigue failure of the turbine shaft,the low cycle load of the turbine shaft was analyzed firstly,and a three-dimensional model was established.Then,based on the existing critical surface model,an improved SWT critical surface model was proposed to predict the low cycle fatigue life of the turbine shaft.Then,considering the uncertain factors of the turbine shaft,the material parameters and load parameters of the turbine shaft were regarded as random variables,and the least square support vector machine model was introduced.Combined with the simulation data obtained from the finite element simulation and the improved critical surface model,the relationship between the life of the turbine shaft and the random variables was established.Finally,the low-cycle fatigue life distribution of the turbine shaft was calculated by Monte Carlo method combined with the established support vector machine model,and the probability low cycle fatigue life prediction of the turbine shaft was realized.(2)High cycle fatigue life prediction of turbine shaft.Because the fatigue data of the turbine shaft material are few,a Bayesian method based P-S-N curve estimation method under small sample is firstly studied.By using the collected fatigue test data of the turbine shaft material GH4169 and combining with the expert information,the unknown parameters of P-S-N curve are estimated.Then,the finite element simulation analysis of the turbine shaft under high cycle loading was carried out to obtain the stress information of the dangerous position,and the high cycle fatigue life of the turbine shaft was predicted by the nominal stress method.Finally,Monte Carlo method and least squares support vector machine model were used to calculate the high cycle fatigue life distribution of the turbine shaft,and the probability high cycle fatigue life prediction of the turbine shaft was realized.(3)Reliability analysis of high and low cycle composite fatigue of turbine shaft.Aiming at the high and low cycle composite fatigue failure problem of turbine shaft,a composite fatigue reliability analysis method of turbine shaft based on cumulative damage was proposed.Firstly,the nonlinear cumulative damage model of Ye Duyi was introduced,and then the load correction factor was introduced.Then,a cumulative damage model for high and low cycle composite fatigue problem was proposed.Then,the composite fatigue cumulative damage model was used to calculate the composite fatigue damage of the turbine shaft.Finally,combined with the fatigue damage threshold of the turbine shaft,the functional function of the turbine shaft was established,and the reliability model of the turbine shaft was further established.Finally,the composite fatigue reliability of the turbine shaft was solved by Monte Carlo method,and the combined fatigue reliability analysis of the high and low cycle of the turbine shaft was completed.