Research On Fatigue Damage Model Under Multi-load Effect And Life Prediction Of Compressor Blade

Compressor blades are the key rotating components of aero-engine.During the engine operation,the high-speed rotating blades are subjected to the complex centrifugal and aerodynamic loads.Hence,the blades are prone to local stress concentration and cause fatigue failure,which affects the normal operation of the aeroengine.Therefore,the research on fatigue damage model under multi-load effect,life prediction of compressor blade and improving the engine reliability has the high scientific value and engineering significance.The predicion models of fatigue damage are studied to analyze the models for theoretical foundation,computational accuracy and application characteristics.Besides,the damage evolution equation of high cycle fatigue is established.Combined with the fatigue test resarch of Ti-6Al-4V titanium alloy,the load parameters affecting the fatigue behavior of the material are analyzed.Based on the elastoplastic stress-strain relationship,a fatigue correction factor considering the elastoplastic strain weighting effect is established,which describes the change of damage with the material local plastic deformation.The elastoplastic fatigue factor is introduced into the stress term of the nonlinear continuum damage model,and the fatigue damage model considering asymmetric loading effect is established to correct the high cycle fatigue life prediction,which the relative errors between predicted lives and experimental lives are reduced by 20 %.In addition,the nonlinear fatigue damage model under variable amplitude loading conditions is also established to consider the loading sequence effect on damage behavior.Finally,the modified model is verified with the fatigue test.Considering the different initial damage parameters to analyze the cumulative damage behavior under low amplitude loads,it is found that the loads below fatigue limit not only strengthens the fatigue life,but also causes the deterioration effect on the damage accumulation.Therefore,the fatigue load is divided into high amplitude load above fatigue limit and low amplitude load below fatigue limit.Moreover,the low amplitude load is classified into the load with and without strengthening effect.Based on the theory of continuum damage mechanics,the strengthening effect is introduced by an exponential function and the cumulative damage is calculated by fuzzy method with membership functions.A modified nonlinear model is proposed to take into account the loads below fatigue limit with its strengthening effect.Based on the research of fatigue damage prediction theory and model,the material parameters of the modified model are analyzed based on the method of Optimal Latin Hypercube Design.With the discussion of the contribution of model parameters to the calculation accuracy and the interaction between the model parameters,the sensitivity analysis of the model parameters is carried out.Combined with the sensitivity calculation results,the model prediction life error is taken as the optimization target,and the model parameters are optimized to determine the fatigue model parameters for further calculaitons.The three-dimensional model,the structural finite element model and the flow field model of the compressor blade are established.According to the blade force conditions,the complex centrifugal and aerodynamic loads are comprehensively considered and the stress distribution of the compressor blade is calculated to determine the fatigue failure critical position.The fatigue analysis loading spectrum is compiled in combination with the QAR data.Finally,the fatigue life of the compressor blade under actual operating conditions is predicted by the modified fatigue damage model.