Fretting Fatigue Strength Analysis of Ti-6Al-4V in Air

Abstract

The influence of fretting damage on fatigue strength has been investigated using Ti-6Al-4V alloy. Axial fatigue loading was applied at frequencies of 20 Hz and 0.5 Hz in a laboratory environment with the fretting applied to the specimen central section through a fretting pad made of the same material as the fatigue specimen.
The reduction in fatigue strength due to the fretting damage depended on the contact pressure, p. When the value of p is about 20 MPa, the fatigue life exhibited a minimum. The fretting fatigue crack initiated at the center of the fretted surface. Many micro cracks existed prior to main crack initiation. However, when the value of p is more than 30 MPa, the fretting fatigue crack initiated at the edge of the fretted surface. Few micro cracks existed prior to main crack initiation.
Fretting fatigue cycles more than 90 % of the total life in the interrupted fretting fatigue test are required in order to continue crack propagation after the removal of the fretting pad, although the crack already initiated at cycles less than 50 %.