Probabilistic Creep-Fatigue Life Prediction Of Engine Turbine Discs

As one of fatigue critical components of the aero engine,turbine disc is subjected to complex cyclic heat loads and mechanical loads,then result in various forms of failure.Among them,high temperature low cycle fatigue is the main failure mode of the turbine disc.Once the fatigue failure of turbine disc occurs,the normal operation of engine even aircraft will have great security risks,and then result in catastrophic consequences and significant losses.Therefore,probabilistic fatigue life prediction of turbine disc and its reliability analysis under random loadings have great scientific significance and engineering application value.In this thesis,a series of researches on a high pressure turbine disc have been drawn as follow:(1)Fatigue life prediction by considering both the effects of mean stress and ratcheting.Turbine disc operates at high temperatures,endures large mean stresses,the region of tongue and groove and bolt hole produce greater stress and strain.Due to the turbine disc subjected to asymmetric cyclic loading and cyclic softening of the material under high temperatures,based on the damage modeling by using dynamic viscosity and the failure criterion of ductility dissipation,this thesis proposed a fatigue life prediction model considering both of mean stress and ratcheting effects.In order to verify the proposed fatigue life prediction model,several data sets of experimental fatigue data from the literature have been used to assess the capability and accuracy of the proposed model.(2)Finite element analysis and fatigue life prediction of turbine disc.The finite element analysis of the groove and bolt hole in the turbine disc are carried out to obtain the stress and strain states under different working conditions.Fatigue life of a turbine disc is evaluated by using the proposed model.The relationship between mean stress,stress amplitude and mean ratcheting strain rate is studied.Finally,based on the fatigue cumulative damage theory,the turbine disc life is calculated.(3)Probabilistic fatigue life prediction of a turbine disc under random loadings.Due to the variability in the service,speed,temperature,structure size,material properties of the turbine disc,the loads of turbine disc are random.The P-S-N curve of turbine disc under typical operating conditions is plotted against the P-S-N curve of the disc material,a fatigue cumulative damage calculation method under stochastic loads is proposed based on the P-S-N curve,and then the fatigue life of the turbine disc is estimated.Finally,the influence of the random load dispersion on the life of turbine disc is analyzed.(4)Reliability analysis of a turbine disc under random loads.Based on the P-S-N curve of turbine disc under typical operating conditions and stress-intensity interference theory,reliability analysis of a turbine disc has been carried out.The influence of the two variables of random loads on the reliability of the turbine disc is analyzed.Then,a trend graph of the reliability curve and method for selecting the safety factor of the turbine disc under random loads are provided in this thesis.