Numerical Simulation Of The Crack Initiation Behavior Of Compressor Blades Under Combined High And Low Cycle Fatigue

Compressor blade in the engine inlet side,in the work,in addition to affected by large amplitude and low frequency centrifugal load,but also subjected to a small amplitude and high frequency vibration load.During in the working,low-cycle fatigue is caused by the centrifugal load and high-cycle fatigue is caused by the vibration load.Therefore,the compressor blades are subjected to both high-cycle fatigue and low-cycle fatigue.Combined high and low cycle fatigue is not only a simple low cycle fatigue,but also not a simple high cycle fatigue,but a complex form of fatigue.At present,the research on fatigue crack initiation,fatigue damage mechanism and fatigue life prediction model under high and low cycle combined loads is still not enough.The main work of this paper is to simulate the crack initiation behavior of compressor blades under combined high and low cycle fatigue.The main contents and conclusions are as follows:(1)Based on the continuum damage mechanics(CMD)and irreversible thermodynamics framework,the high cycle fatigue damage evolution equation and the low cycle fatigue damage evolution equation are fully studied,then a new damage model has been developed for high-low cycle fatigue.Based on the model,a user defined material subroutine(UMAT)was compiled and the crack initiation life of the compressor blade under combined high and low cycle fatigue was simulated by the finite element method using ABAQUS codes.(2)The study found that the crack initiation occurs at the place of stress concentration in the root of the compressor blade.The higher the amplitude of the high cycle stress,the shorter the initiation time of the crack.Under the conditions of 932 MPa maximum stress and 500 cycle ratio,when the high stress amplitude is 198 MPa,the crack initiation life is 9503 cycles,when it increased to 706 MPa,the crack initiation life is shortened to 54 cycles.With the increase of the maximum stress,the initiation life of crack is reduced from 9503 cycles at 932 MPa to 3026 cycles at 954 MPa.The ratios of high cycle and low cycle is another factor that affects the initiation life of crack.When the cycle ratios increase from 500 to 5000,the initiation life of cracks decreases from 9503 cycles to 1978 cycles.(3)The influence of different notch forms on the combined high and low fatigue crack initiation life of the compressor blade is also simulated.Under the conditions of 198 MPa high stress amplitude and 1000 cycle ratio,founding that the radius of the gap is different,the crack initiation life is different,with the increase of the radius,the initiation life of the crack is increased from 1 cycles of 0.02 mm to 187531 cycles at 0.09 mm.The notch is far away from the bottom of the blade,the crack initiation life is long.The notch depth will also affect the initiation life of crack,the deeper the notch depth,the shorter the crack initiation life.