Combined Cycle Fatigue Life Prediction And Reliability Analysis Of Turbine Blades

As one of fatigue critical components of an aero engine,failure of turbine blade is disastrous for the engine safety and reliability.Thus,life prediction and reliability analysis of gas turbine blades has become the most highlighted link of quality problems for aero engines.Since the operation environment of turbine blades are critical with complex loadings at high temperatures.Among them,low cycle fatigue(LCF)loads result from the ground-air-ground cycling of the engine,high cycle fatigue(HCF)loads result from in-flight vibrations.LCF loads have shown large stress amplitudes with low frequency,whereas HCF loads have small stress amplitudes with high frequency.Thus,turbine blade is subjected to a complex interaction of LCF loads superimposed with HCF loads simultaneity during its operation,which usually induces failures of combined high and low cycle fatigue(CCF)in turbine blades.In order to guarantee reliability and maintainability of aero engines,it is necessary to estimate the fatigue lifetime under CCF conditions.During life prediction of an aero engine,this thesis tends to predict the CCF life based on finite element(FE)analysis of a high pressure turbine blade under CCF loadings.Until now,life prediction under CCF has been paid more attentions in recent years.Among them,researches on CCF life predictions based on fatigue damage accumulation methods are increasing for CCF life predictions.This thesis analyzed the combined damage mechanisms using four loading parameters and proposed a life prediction model by coupling the high and low cycle fatigue damages.The proposed model was compared with existing models of combined high and low cycle fatigue to verify its accuracy.It provides a reference for the maintenance of turbine blades.Secondly,FE analysis of a turbine blade was conducted using ANSYS Workbench.During its static strength analysis,load constraints and loads are introduced according to the real operating condition of the turbine blade.Through modal analyzing and gaining the dynamic frequency and static frequency,the vibration performance of the turbine blade is evaluated.The equivalent stress distribution under the high cycle excitation of turbine blade is obtained based on the analysis of harmonic response to ensure the critical location of the turbine blade.Finally,the stress and strain analysis of a turbine blade was carried out according to the load spectrum of an aero engine.Fatigue life and reliability of this turbine blade was estimated by using the proposed model and linear damage rule.Results show that researches on CCF life prediction based on coupling damage in this thesis can offer certain reference for estimating the operational life and reliability of turbine blades.