Investigation Of Fatigue Behavior And Damage Mechanism Of Compressor Blade Based On Continuous Damage Mechanics

Compressor blades are subjected to low-frequency centrifugal load,highfrequency aerodynamic load and bending load during operation,resulting in complex high-low cycle composite fatigue and bending fatigue behavior.At the same time,the blades will produce defects such as porosity and hardness when they are manufactured and repaired.Therefore,based on the continuous damage mechanics theory,this paper studied the effects of defect types(cavity,hard phases)and defect characteristics(size,location)on the high-low cycle composite fatigue performance of compressor blades and the effects of bending load on the bending fatigue performance of compressor blades.The main research contents are as follows:(1)Based on the continuum damage mechanics,considering the high-cycle fatigue,low-cycle fatigue and the interaction between them,the high-cycle and low-cycle composite fatigue damage model of compressor blades was developed.The high-low cycle composite fatigue damage model was used to study the fatigue performance of compressor blades at different cycle ratios from 20 to 2000.When the cycle ratio increased from 20 to 2000,the fatigue life decreased by 96%.It found that the fatigue crack initiated at the root of the blade,which was consistent with the peak stress position.The fatigue crack initiation mechanism of the stress-dominated compressor blade was revealed.(2)Based on finite element simulation,the effect of cavity on high and low cycle fatigue performance of blade was studied.When the high-low cycle ratio was 100 and the cavity diameter at the root was 1 mm,the peak stress of the blade was 1106 MPa.Compared with the non-defective blade,the stress increased by 23.9% and the fatigue life decreased by 74.8%.When the cavity diameter decreased from 1 mm to 0.05 mm,the peak stress decreased by 16 % and the fatigue life increased by 199%.Compared with the blade root,when the cavity was 20 mm away from the blade root,the peak stress of the blade was reduced to 906 MPa,the stress was reduced by 18.1%,and the fatigue life was increased by 195%.When the distance from the blade root was more than 20 mm,the cavity position had little effect on the fatigue life.(3)Hard phase was another main factor affecting fatigue performance of blade.Through finite element simulation,it found that when the high-low cycle ratio was 100 and the blade root contained 0.25 mm hard phase,the peak stress of the blade was 1023 MPa.Compared with the blade without defects,the stress was increased by 14.6 % and the fatigue life was reduced by 29.4 %.When the hard phase diameter decreased(0.25 mm – 0.05 mm),the peak stress of the blade decreased by 9.6%,and the fatigue life increased by 39.1%.Compared with the blade root,when the hard phase was 16 mm away from the blade root,the peak stress of the blade decreased by 10.5%,and the fatigue life increased by 43.7%.When the distance from blade root exceeded 16 mm,the position of hard phase had little effect on fatigue life.(4)The bending fatigue properties of blades were different under different bending amplitudes.When the bending amplitude increased from 10 mm to 15 mm,the fatigue life of plate bending fatigue specimen decreased by 85%,and that of blade bending fatigue specimen decreased by 88%.The bending fatigue cracks initiated from the outer surface of the sample and gradually expanded to the center of the sample.For the plate specimen,when the bending amplitude was less than 13 mm,the specimen was quasicleavage fracture.When the bending amplitude was greater than 13 mm,the fracture mode transformed into ductile fracture.For bending fatigue specimen of blade,fracture mode was cleavage fracture.