Mechanical and Microstructural Effects in Fretting Fatigue of Ti-6Al-4V

Fretting fatigue is the repetitive sliding of contacting surfaces at small displacements and can cause cracking that leads to failure in the presence of a bulk fatigue load. Dovetail joints in gas turbine engines are particularly susceptible to fretting fatigue and are the motivation for this study. Experiments are conducted in ambient air utilizing a sphere-on-flat contact geometry since its contact mechanics are well known. The effect of changing critical contact and bulk loading parameters are examined in depth for a mill annealed and solution treated overaged variants of Ti-6Al-4V. Parameters which are instrumented and controlled include the applied normal load, tangential load, and axial fatigue load. The fretting fatigue resistance of several other heat treated variants of Ti-6Al-4V are compared versus the two more common variants. Various stages of fretting fatigue crack growth are examined using a fracture mechanics approach. A multiaxial stress-based crack initiation criteria is developed and evaluated. The adhesion model of Giannakopoulos et al., is invoked to determine a contact fatigue threshold of 2 MPa square root of m for Ti-6Al-4V and forms the basis of a life-prediction methodology. Finally, the usefulness of various surface treatments and dovetail designs as palliatives to counter fretting fatigue is discussed.Air Force Inst of Tech Wright-Patterson AFB OH is the author of 'Mechanical and Microstructural Effects in Fretting Fatigue of Ti-6Al-4V', published 2000 under ISBN 9781423533801 and ISBN 1423533801.