Study On The Vibration Character And The High Cycle Fatigue Life Of Turbine Blade For Turbocharger

Turbine wheel,as a key component of turbocharger on engine,operates in an environment of fluctuating temperature,pressure and rotation speed.High frequency vibration caused by aerodynamic force on turbine blades is a key contribution to the blade failure of high cycle fatigue.Therefore this is important to understand the vibration characteristic of turbocharger turbine blades.This Ph D work focuse on one single blade of turbine wheel to study the vibration characteristics by combining theoretical analysis and experimental testing.A new reliability method has been developed to calculate the high cycle fatigue life of turbine wheel.The main research contents and achievements of this work are as follows:-The current research status of the high cycle fatigue of turbine wheel is discussed in the first chapter.It includes the experimental techniques studies,the simulation methodology studies and the failure mechanism studies.Also an energy statistical analysis method is introduced into the study of the high cycle fatigue of turbine wheels.Some existing issues are highlighted.Considering the testing cell condition of the author's company and engineering requirements,a research strategy and a research methodology for the high cycle fatigue of the turbine wheel are put forward for this Ph D program.Within the remit of linear vibration theory,a turbocharger turbine wheel is simplified as a linear vibration system model in the second chapter.According to the vibration characteristics of turbine blades under the single mode excitation,turbine wheel is further simplified into a single blade viration system model.From this single blade linear vibration system model,the theoretical solution of blade vibration is obtained by theoretical analysis which obtains the blade strain through introduction of an energy analysis method into vibration analysis.This provides a theoretical foundation for the next experimental study.In Chapter Three,experimental method is described.On the basis of the theoretical analysis,a strain collection system was added onto the existing experimental platform,and blade strain signal collected.Based on the analysis of the experimental results,it is found that the blade strain agrees with the linear theory in the frequency domain,but not in the time domain.Due to the fluctuation of the predicted strain in the time domain,other factors such as nonlinear effect need to be further considered.This is covered in Chapter Four.Through the study of blade strain under different acceleration conditions,it was found that the strain response of the turbine blade had a nonlinear characteristic.Therefore,acceleration was considered a nonlinear parameter which was introduced into the single blade vibration model.As a result from experimental verification,the nonlinear strain response model can predict strain well not only in the frequency domain but also in time domain.Furthermore,the influence of the key parameters on the nonlinear model was studied,which provided reliable input parameters for the life prediction of the high cycle fatigue of the turbine wheel.In Chapter Five,a new reliability life prediction model had been propsed for the high cycle fatigue of turbine wheel based on the nonlinear single blade vibration model.This model uses engine duty cycle data and measured strain data as key input to work out strain distribution of turbine blades from the nonlinear prediction model.By applying the cumulative damage theory,the high cycle fatigue life can be calculated by combining the S-N curve of material and the strain distribution of turbine wheel in time domain.This reliability model,when used in engineering practice,can not only evaluate the life of turbocharger turbine blades but also can calibrate the S-N curve of turbine materials from historic blade failure data.Meanwhile,Chapter Six also proposed a durability testing method for turbine wheel based on this nonlinear vibration model.In summary,a nonlinear prediction model for the strain response of the turbine wheel blade was proposed by the theoretical analysis and the experimental study.Based on this model,a new reliability model of the high cycle fatigue for turbine blade was proposed.