Research On Fretting Fatigue Life Of Dovetail Joint In Aero-Engine

Fretting damage known as "industry cancer", widely occurs to the junction between twomechanical components. Fretting fatigue failure in dovetail joints is one of main causes in aero-enginefailure. However, the experimental and theoretical research is not mature currently because of somany influence factors on fretting fatigue. Therefore, systematical research on fretting fatigueexperiments and life technology of dovetail joints are required and will contribute significant valuesin theoretical study and practical engineering applications.The fretting fatigue experiments were conducted by the combination of theoretical andexperimental methods. According to the latest research of current fretting fatigue theories, in-depthresearch has been explored in this paper in order to solve the fretting damage and life technologyproblems.First, a new fretting damage parameter CSE（considering the multi-factor in the calculating ofthe Strain Energy） was introduced and the quantitative research on a new fretting fatigue lifeprediction model was carried out, based on the critical plane theory and the damage mechanism, thefretting induced crack initiation and early propagation. The fretting damage parameter CSE considersmany factors including geometry characteristic, material characteristics, load characteristics, surfacecondition and so on，which can represent the energy loss in the fretting damage and explain thephenomenon of stress concentration in the fretting fatigue. The fretting fatigue life prediction modelof CSE contains general fatigue properties and less undetermined parameter, which is suitable for thelife prediction of a link structure of an alloy material.Second, employing the concept of the overall balance framework in the structure design, aunique fretting fatigue test apparatus based on a fatigue testing machine has been designed andfabricated to characterize the fretting fatigue damage process with a facility to observe the crackwhich is being initiated in and around the contact zone during the test. There are three types ofcontacting pair among the fretting specimen and the pad including titanium alloy TC11and TC11,single crystal nickel DD3and powder metallurgy superalloy FGH95, directionally solidifiedsuperalloy DZ125and FGH95, and a relevant fretting fatigue law is obtained. The result shows goodloading stability of the normal load, high success rate and strong test maneuverability, and theequipment works well. Fretting fatigue significantly reduces fatigue performance and fatigue life ofthe material. The fretting fatigue life is affected by the normal load and the axial load, and the axialload is the most important influencing factor for the fretting fatigue life. Finally, numerical analysis was carried out by the combination of theoretical and experimentalresearch on fretting fatigue life. The initiation location and orientation of the fretting fatigue crack andthe life prediction model for isotropic and anisotropic materials were validated and compared. Thefretting damage laws and damage mechanisms of different materials were also discussed. The resultof the CSE prediction model shows good agreement with experimental results. The CSE critical planeapproach is appropriate for predicting the initiation location and growth orientation of the frettingfatigue crack. The anisotropic material shows better resistance in fretting fatigue than the isotropicmaterial.