Fatigue And Creep Life Prediction Of Nickel-based Single Crystal Superalloy Turbine Blade At Multiple Scales

As one of the core components of aeroengine,turbine blade performance has an important influence on the overall performance of aeroengine.As the failure mechanism of high-pressure turbine blades is complicated due to the complex working environment,the establishment of a high-precision life assessment model of turbine blades is a key scientific and difficult problem in the design process of high-pressure turbine blades.Nickel-based single crystal superalloy has become the preferred material for high pressure turbine blades because of its excellent fatigue and creep resistance at high temperature.However,due to the anisotropy of single crystal materials,the fatigue and creep behavior of high-pressure turbine blades under multiaxial stress becomes more complex,and the accuracy of life prediction needs to be further improved.To develop a high precision and high efficiency life prediction method that reflects the fatigue and creep mechanism of nickel based single crystal turbine blades is an important guarantee for improving turbine blade performance.Based on this,the low-cycle fatigue life evaluation method,creep life evaluation method and life model under fatigue/creep interaction of nickel-based single crystal superalloy were studied from multi-scale perspective,which were further applied in life evaluation of high-pressure turbine blades.The main research contents are as follows:(1)A macro-scale multi-axis low-cycle fatigue life assessment model of nickelbased single crystal superalloy was proposed considering average stress modification.The blades were subjected to asymmetric cyclic loads during actual operation,and their low-cycle fatigue lives were not equal even under the same load amplitude.The influence of average stress on fatigue life could not be ignored.In this paper,Walker average stress model and energy method low cycle fatigue life evaluation model are studied.On this basis,a multi-axis low cycle fatigue life model of nickel-based single crystal superalloy is established considering the crystal orientation,average stress and sensitivity of average stress.The uniaxial/multiaxial fatigue life of DD3 nickel-based single crystal alloy at different temperatures and crystal orientations was evaluated by the model.The results of the fatigue life evaluation were compared with the experimental life to verify the validity of the model.(2)Establish a multi-axial fatigue life assessment method based on microscopic damage parameters of nickel-based single crystal superalloy: when the material is subjected to cyclic loading,the microscopic sliding system decomposes shear stress to cause alternate sliding of dislocation,thus forming initial fatigue cracks in the slip system.A more reasonable fatigue life evaluation model can be established by studying the fatigue mechanism of nickel-based single crystal alloy from the microscopic point of view.Therefore,based on the microscopic scales combine theory of crystal slip and critical plane method,according to the fatigue damage mechanism to determine the maximum shear stress in the decomposition of slip system as the critical plane,on this basis to the critical slip surface larger effects on the fatigue damage parameter was built in the form of power function model of the low cycle fatigue life.The fatigue life of nickel-based single crystal materials PWA1480 and DD3 was evaluated by using this model,and the feasibility and accuracy of the proposed method were verified.(3)Creep life evaluation of nickel-based single crystal superalloy based on microscopic damage parameters: The creep behavior of nickel-based single crystal at high temperature is also related to crystal orientation.Considering the influence of crystal orientation,this paper uses the maximum decomposition shear stress of slip system to replace the macro stress parameters in Lemaitre creep damage model,and uses this model to evaluate the creep damage and life of high-pressure turbine blades,and verifies the accuracy of the model.(4)the interaction between fatigue and creep under the influence of high pressure turbine blade life assessment model: high pressure turbine blade high-speed rotating at high temperature,easy to produce low cycle fatigue,creep and fatigue/creep interaction damage,based on macroscopic and microscopic fatigue and creep life evaluation model,the fatigue/creep interaction nickel-based superalloy were studied.On this basis,a model of the blade was established,and the fluid-thermal-solid coupling analysis of the blade was carried out by using the finite element simulation method to obtain the stress/strain of the blade under centrifugal load,aerodynamic load and temperature load,and the life of the high-pressure turbine blade was analyzed.