Effects of independent pad displacement on fretting fatigue behavior of Ti-6Al-4V

A fretting test setup was developed which was capable of applying independent pad movement under a normal force and stress amplitude condition. The independent control of pad movement was achieved by dual actuators in a servohydraulic test frame where one of the two actuators was directly connected to the fretting fixture. This setup could perform both fretting fatigue (stick and stick-slip) and fretting wear (gross slip) tests. Cylinder-on-flat contact configuration was used to characterize the effects of pad displacement on the fretting fatigue behavior of a titanium alloy, Ti-6Al-4V. Several tests, at different pad displacements, were conducted at two normal forces but at one stress amplitude. For both normal forces, the fretting fatigue life decreased initially as the relative slip range increased. A minimum fretting fatigue life was observed at relative slip range of 50-60 mum, and then it increased with the increase of relative slip range. When the relative slip range was greater than 60 mum, the gross sliding occurred and the specimen did not fail. The fretting life versus relative slip range relationship was independent of the normal force used in this study. Fretting regimes (stick, partial slip, mixed, gross slip) were identified using the evolution, not the shape, of fretting loops (tangential force versus relative slip). (C) 2002 Elsevier Science B.V. All rights reserved.