Multiaxial Fatigue Life Prediction And Reliability Analysis Of Engine Blade-Disk Attachment

Due to China's continuous development in the aviation field,people constantly put forward higher requirements for the efficiency and reliability of aero-engines.As an important connecting form of turbine blade and turbine disk in modern aero-engine rotor structure,the fir-tree tenon structure is often subjected to the cycle action of high temperature,high pressure and complex loads in the actual operation process.Once a destructive mechanical failure occurs,it will lead to extremely serious consequences.Therefore,it is of great engineering value to focus on the fatigue life prediction and reliability analysis of the fir-tree tenon structure.In this thesis,the fir-tree tenon structure of an aero-engine is studied as follows:(1)Development of a multiaxial fatigue critical plane-damage parameter based on the FS damage parameter.Since the FS model provides conservative fatigue life predictions for GH4169 alloys,a new multiaxial fatigue critical plane-damage parameter is proposed.Combining with FE simulations,fatigue life of a high-pressure turbine disk is predicted,and results are compared and analyzed with several multiaxial fatigue models.This proposed model gives more accurate life predictions than others,which provides a reference for the subsequent model research.(2)Proposal of an energy-based model considering virtual shear strain energy for multiaxial fatigue life prediction.The commonly-used multiaxial fatigue life prediction models are briefly classified and analyzed,and the relationship between virtual shear strain energy and fatigue life is studied.Based on this,a multiaxial fatigue life prediction model combining strain energy and critical plane method is proposed without any additional material constants.Then,Experimental results of GH4169 and TC4 alloys are utilized for model comparison.Compared with the existing models,the results show that the proposed model has a significant advantage for the application range and life prediction accuracy.(3)Development of stress-strain calculation and fatigue life prediction for notched specimens.The strain energy of elasto-plastic body under cyclic loading is analyzed.In order to obtain more accurate stress-strain response of notch root,based on the Neuber criterion,the stress-strain analysis of notched parts is performed by considering the dissipated heat energy.The calculations are compared with the results of elastic-plastic finite element analysis(FEA).The proposed criterion has higher calculation accuracy than the existing criteria.In addition,the traditional energy model is modified by considering the notch support effect to further improve the prediction accuracy of fatigue life for the notched parts.(4)Analysis of fatigue reliability for the turbine disk.In order to reflect the real performance of the high-pressure turbine disk in the actual working conditions more reasonably,the P-S-N curve is drawn according to the fatigue test data of the aviation material GH4169.At the same time,fatigue damage of turbine disk under typical conditions is calculated with FE simulation results of tenon groove,and the proposed multiaxial fatigue life model is used to predict the fatigue life of turbine disc.Finally,considering the influence of uncertain factors such as material properties,structure geometry and rotational speed on the fatigue life dispersion of turbine disk,the reliability of the turbine disk is estimated based on the Miner rule and the P-S-N curve of turbine disk under various working conditions.