Research On Prediction Method Of Fretting Fatigue Life At Elevated Temperature

Fatigue failure caused by fretting is a major problem in the field of aviation.Compared to normal fatigue,it typically results in a significant reduction in the life of the structural components.In aeroengine,the location of fretting damage usually occurs on the dovetail of the compressor blade and the disk.Since the internal temperature of the aero-engine compressor is as high as 500?,it is very important to study the fretting fatigue behavior of engine titanium alloy blades and disks under the working temperature in order to ensure the safety of the engine.Therefore,this paper carried out elevated temperature and low cycle fretting fatigue test of the dovetail structure,and established a prediction model of low-fretting fretting fatigue life of the dovetail structure at different temperatures.The main research work and conclusions are as follows:Firstly,a kind of elevated temperature dovetail fretting fatigue test device was designed for the compressor fan/disk connection structure of aviation turbofan engine.The fretting fatigue test of TC11 titanium alloy at 200?and 500?was carried out.It is proposed to monitor the fretting fatigue life of dovetail structure by dynamic strain and dynamic displacement method.It is found that the fretting cracks are at the lower edge of the contact area of the dovetail and a large amount of abrasive scrap appear on the contact surface,which belongs to the typical fretting fatigue failure.The test results show that the effect of temperature environment on fretting fatigue life is obvious.With the increase of the test temperature,the fatigue life of the test specimen would gradually decrease.Secondly,based on the Walker formula,a temperature equivalent damage parameter is proposed,and the damage parameters are used to modify the Farris life prediction model,and a fretting fatigue life prediction model considering temperature is established.In addition,the finite element analysis of the dovetail structures at different temperatures was conducted,and the material parameters of the life model were fitted and the correlation analysis of the life prediction model was carried out.The results show that there is a good correlation between the three temperature equivalent damage parameters and the fretting fatigue life at different temperatures.Finally,the life prediction model described by the temperature equivalent damage parameters is used to predict the fretting fatigue life of the second type dovetail structure.Compared with the test life,it can be concluded that the predicted results are within the error band of 3.Lastly,based on the finite element software ANSYS,the main influential factors of fretting fatigue are analyzed:the changes of relative slip amplitude,contact pressure,tangential stress,Von Mises equivalent stress and C_eq temperature equivalent damage parameters under different temperature,friction coefficient and geometric contact and their Effect on fretting fatigue life.The results show that the fretting fatigue life of dovetail structures at different temperatures gradually decreases with the increase of the maximum contact pressure,the relative slip amplitude and the maximum tangential stress.The crack initiation position of the dovetail structure does not change with the change of the temperature and the friction coefficient,and all occur at the lower edge of the fan and disk contact area.