Shear force effects on fretting fatigue behavior of Ti-6Al-4V

The present study examined the role of shear force on fretting fatigue behavior as well as its interdependence on other test variables, such as bulk stress, normal load, relative slip, and coefficient of friction, by using a fretting test system where shear force was controlled independent of other applied loads. Two contact geometries were used: cylinder-on-flat and flat-on-flat. For a given applied bulk stress and normal load condition, there is a simple relationship between shear force and relative slip up to a maximum value of shear force where contact condition changes from partial slip to gross slip. The effects of shear force and relative slip therefore can be combined together to characterize fretting behavior such as in a fretting map. Under a prescribed loading condition, fretting fatigue life decreases as shear force increases in partial slip condition. Further, the inter-relationships between shear force and other variables appear to be independent of contact geometry. In the tests where shear force is not applied independently rather when generated indirectly through the compliance of fretting setup, it is affected by the applied bulk stress and normal load, which in turn affect the relative slip range. Therefore, there is a complex interaction among various variables, and it is difficult to isolate their effects on fretting behavior in such test conditions. An independent control of relative slip in the fretting test thus provides an alternate means to characterize the variables’ effects and their interdependence.