Prediction Of Low Cycle Fatigue And Creep Life Of Turbine Blades

Turbine blades are prone to various failure behaviors,including fatigue failure,creep failure,creep/fatigue coupling failure,and may be damaged by external objects during operation.In addition,manufacturing process and material defects will also have a great impact on the blade service time.Accurate service life prediction of Aero-engine Turbine blade is of great significance to the structural safety,durability,combat readiness integrity and service cost reduction of aero-engine.In view of the complex failure behavior of blade,it is difficult to accurately predict its service life.In this paper,combined with CFD technology and finite element simulation technology,the gas,heat and solid multi field coupling simulation calculation of blade under typical working conditions is carried out,and the stress and strain distribution of blade is obtained.By comparing the characteristics of existing multiaxial low cycle fatigue life prediction models,the main causes of blade failure are analyzed,and the existing prediction models are improved by combining the advantages of critical surface method and SWT model.Based on the prediction of creep life of blade tip,a prediction method of creep life of blade tip after laser cladding repair is proposed.The specific research contents are as follows:Firstly,the cycle load spectrum of the single mission of turbine blade is obtained,and the physical field environment of aeroengine is analyzed.Three main loading forms are considered:aerodynamic load,centrifugal load and temperature load.After verifying the correctness of the aerodynamic simulation environment,the flow field of the blade is analyzed by CFX.On the basis of the simulation,the coupled simulation calculation of the gas,heat and solid fields of the blade under various working conditions is carried out by ANSYS Workbench.The stress,strain and deformation cloud chart of the turbine blade body at the maximum speed are obtained.The main factors causing the low cycle fatigue failure are analyzed,determine an assessment point A and B in the blade body and root respectively.The life of the evaluation point is taken as the low cycle fatigue life of the blade.The simulation method and calculation results can provide reference for the calculation of blade life and structural design.Then,the low cycle fatigue life of blade under typical working cycle is calculated.The prediction accuracy of Morrow correction model and SWT model is evaluated by using DD432 material fatigue test data in literature.Then the stress and strain distributions of blade under different working conditions are obtained by using finite element simulation method.Firstly,the fatigue parameters required by SWT model to calculate the low cycle fatigue life of assessment points A and B are obtained,and then the low cycle fatigue life of assessment points A and B are calculated respectively,point A is determined to be the point determining the low cycle fatigue life of blade.Finally,the prediction model is modified,and the low cycle fatigue life of point A is calculated by using the critical surface method combined with the characteristics of SWT model.The actual life range of blade is deduced by comparing the predicted data of SWT model with the actual data.The results show that the accuracy of the modified model is higher.Finally,the creep life of the remanufactured area of the tip is calculated.The temperature and stress level of the tip area at the maximum speed are obtained by using the finite element simulation results.The L-M parameters are fitted by the material creep test data of DD432 in the literature,and the creep life of the tip area is calculated by L-M parameter method.Then,the temperature field and stress field distribution characteristics are similar to the actual processing process.The simulation of laser cladding process of tip shows that the thermal impact zone is small.The mechanical properties of the micro sample are tested by using the cooperation mechanism,The modified parameters of remanufacturing creep life are defined as the ratio of minimum requirements between remanufactured micro sample and matrix durability.The creep life of tip region is modified by using this parameter to obtain creep life in remanufactured area of tip.