Study On Nickel-base Single Crystal Alloy Yield Criterion And Blade Fatigue Life

Nickel-base single crystal alloy is a new type of high-temperature alloys. It is widelyused in some of the ships engine blades, aero-engine blades in filed of high temperaturebecause it can work under high temperature and pressure environment. At the same time,blades are the most important part of the engine, its safety and service life directly impact onthe application of advanced engine. Therefore, the study of nickel-base single crystal alloyblade has a very important significance. Since the advent of this new material, considerableresearches involving blades have been done by domestic and foreign scholars, but researchesin nickel-base single crystal alloy blades are still rare. Therefore, in this study, nickel-basesingle crystal blades were taken as research object. Low cycle fatigue life of the blades wasstudied, the modification of yield criterion used in the analysis is discussed and elastic-plasticconstitutive equation is derived. Details are as follows:1. According to the basic parameters of blades and the working conditions, a simplethermal coupling simulation is done for nickel-base single crystal blades in the work state byusing finite element software ANSYS. The stress and strain contours of blade are drawn andthe position of danger point for the preparation of low-cycle fatigue life prediction is foundout.2. Considering the material characteristics and mechanical properties of nickel-basesingle crystal blades, the energy law used in multiaxial low-cycle fatigue life prediction ismodified. The parameters of the fatigue life’s modified formula are sured by making use ofthe experimental data of nickel-base single crystal low-cycle fatigue life. According to theresults of the blade’s stress and strain contours and the position of danger point, verify thecorrectness of the modified formula with comparing the experimental results with thecalculation result of low cycle fatigue life.3. According to the defects of orthotropic materials yield criterion in the analysis, theHill yield criterion was modified by creasing the coupling term considering the tensile-shearand the shear-shear coupling. Second, the precision of modified hill formula is discussed bycomparing the calculation results of yield stress in different directions with the experimentaldata. Finally, according to the anisotropic material constitutive equations derived method, wecan derive the constitutive equations of single crystal nickel-base alloy with the application of drucker postulate.