The Research Of Combined High And Low Cycle Fatigue Damage Of Ti-6Al-4V Titanium Alloy Based On The Continuum Damage Mechanics

In real work,compressor blades are mainly subjected to loads in two directions,one is the low cycle load with low frequency and high stress which is caused by the high speed rotation of compressor blades,and the other is the vibration load with high frequency and low stress which is caused by the unevenness and instability of flow field in environment.Therefore,the fatigue of the compressor blade is actually the composite fatigue problem of the low cycle load superimposed with the high cycle vibration load,and the fatigue failure of the compressor blade is caused by combined high and low cycle fatigue load.Ti-6Al-4V titanium alloy has been the main material used in the compressor blades due to its high strength,low density and good corrosion resistance.Therefore,it is of great significance to study and build the model of combined high and low cycle fatigue damage life prediction for Ti-6Al-4V titanium alloy and use this model to predict the combined high and low cycle fatigue damage life of the compressor blade.First of all,a low cycle fatigue damage model,a high cycle damage model and a combined high and low cycle fatigue damage model considering high and low cycle fatigue interaction were established based on the continuum damage mechanics and the irreversible thermodynamics framework.The combined hardening model mixed with Chaboche nonlinear kinematic hardening and nonlinear isotropic hardening was selected and used to describe the elastic and plastic behavior.The combined high and low cycle fatigue damage model and the combined hardening model together constitute the finite element prediction model for the combined high and low cycle fatigue damage life of Ti-6Al-4V titanium alloy.Then,uniaxial tensile tests,low cycle fatigue tests and high cycle fatigue tests were conducted.The parameters of the finite element prediction model for the combined high and low cycle fatigue damage life of Ti-6Al-4V titanium alloy were determined through fitting the data and results of these tests,then a complete prediction mode was established.The combined high and low cycle fatigue damage model was compiled into USDFLD subroutine,then this USDFLD subroutine was coupled into ABAQUS software.The low cycle fatigue damage model and the high cycle fatigue damage model were verified and analyzed respectively.Comparing the results of experiments and simulations,the prediction life based on the damage model is in good agreement with the experimental life.The average error of the low cycle fatigue damage model is 3.878%,and the average error of the high cycle fatigue damage model is 7.55%.A three-dimensional model of the compressor blade was constructed by reverse modeling.The high and low cycle fatigue damage evolution processes of different high and low cycle fatigue load cycle ratios under the load conditions of maximum speed 1440 rpm and high cycle fatigue load amplitude 0.5MPa perpendicular to the blade surface were simulated.The simulation results show that the crack starts initially from the root position of the blade surface and the crack initiation life decreases rapidly with the increase of the high and low cycle fatigue cycle ratio h.