High Temperature Low Cycle Fatigue Life Prediction Of Turbine Disk Using Critical Distance Theory

As one of the main fatigue critical components of aero engine,the high-pressure turbine disk suffers from the complicated coupling loads of cyclic temperature and mechanical loads,then result in various forms of failure,of which high temperature low cycle fatigue failure is one of the most important failure of the turbine disk.Once fatigue damage occurs in the turbine disk,it will give the engine or even the normal operation of the aircraft,which might cause great security risks,even leading to disastrous consequences.Moreover,due to the complexity of the roulette structure,stress concentration phenomenon usually exists in the disk structure.However,a complete system theory has not yet been established to solve such issues.In this regard,in-depth study of multiaxial fatigue failure mechanism of notch,damage accumulation mechanism and life prediction method is of great engineering and scientific significance.In this thesis,researches on the aero engine high pressure turbine disk have been drawn as follow:(1)Firstly,multiaxial fatigue analysis methods of two types of notched parts,namely,the field strength method and the critical distance method,are elaborated.Fatigue life of notched parts is predicted based on the evaluation results of the damage parameters and fatigue damage accumulation model.As a comparative study,several commonly-used methods were introduced to estimate the life of notched parts.Results show that the critical distance method has a higher prediction accuracy for fatigue analysis,and the computational cost is far less than the field strength method.(2)Finite element(FE)analysis and fatigue life prediction of a turbine disk.FE analysis was conducted according to the dangerous region of the turbine disk,such as the tongue and groove and the bolt holes.A new strain energy gradient model considering the notch effect is proposed.Fatigue life of the turbine disk was then evaluated.The proposed model not only considers the stress concentration phenomenon and the notch effect,but also has higher accuracy and more suitable for engineering applications,which provides a reference for life and reliability of turbine disks.(3)Combining the theory of critical distance with the strain energy gradient,a new critical distance-critical plane method is then proposed based on the critical plane method,which considers the notch effect and predicts the fatigue crack initiation position.Finally,GH4169 and TC4 notched fatigue test data are used for model validation and comparison.