Crack behavior of Ti-6Al-4V alloy combined conformal contact fretting, non-conformal contact fretting and simple fatigue

This paper presents the results of fatigue tests combined with conformal contact, non-conformal contact and simple fatigue carried out on Ti-6Al-4V sheet specimens under externally remote bending load. A special fretting fatigue test rig was proposed to focus on two different fretting modes fatigue test simultaneously between non-conformal contact and conformal contact. The test results showed that all the specimens failed at the conformal contact area under external bending load, although the contact stress was lower, residual stress was higher than that with non-conformal contact area. The reason for failure was radial fretting induced fatigue depending upon the nature of conformal geometry. The conformal geometric nature reversed the contact shear stress, accelerated the debris accumulation, redistributed the contact loading and exacerbated the crack nucleation conditions. The mechanisms of fretting fatigue crack formation, including crack nucleation and the three stages of crack propagation were discussed. Furthermore, among the four regions (fretting region, protrusion region, dark inner friction region and fracture region) on fractography, the protrusion region and dark inner friction region were special, rarely reported before. To explain the formation of the protrusion region, dark inner friction region, internal crack and stripped material on the fractography, a friction-based press-push-separate procedure interpretation was proposed. In addition, crack arresting effect exists in the propagation of fretting fatigue cracks due to compression loading on the contact surface with non-conformal contact.