Wear characterization of titanium-aluminum-vanadium under fretting-reciprocating sliding.

摘要

Three main lines of experiments examined fretting wear and its interaction with fretting fatigue using cylindrical pads and flat specimens both machined from Ti-6Al-4V. Finite element analysis was used to simulate gross sliding to determine the stress state and micro-slip in a worn contact zone.;First, experiments were conducted to investigate the effect of slip regime on fretting fatigue life, which was found to increase with change in slip conditions from partial-slip regime to gross sliding. Evidence of the change in slip regime was determined by the Q-delta hysteresis loops, Q/P curves, and wear scar profiles. In tests with contact widths smaller than a critical width, finite element analysis showed that wear decreased the peak contact pressure enough to reduce static friction.;Second, experiments were conducted to investigate the fretting-reciprocating wear behavior of Ti-6Al-4V under cylinder-on-flat contact configuration with bulk cyclic loading. Four series of tests were conducted to characterize effects on wear behavior caused by relative slip, contact load, number of cycles, and bulk cyclic stress. The reciprocating wear produced "U-" and "W-shaped" scars on the specimen and pad. Optical and scanning electron microscopy of the scars revealed that the W-shaped scar "valleys" were covered by abrasive grooves, while scar "ridges" showed signs of adhesive wear. MATLAB-based computer programs determined wear volume using three-dimensional profilometry, calculated the product of contact load and relative slip, and computed energy dissipated per cycle. Wear volume amounts accurately conformed to Archard's equation and dissipated energy models.;Third, experiments were conducted to purposely cause fretting to switch back and forth between fretting fatigue and fretting wear modes. Results showed a synergy that lead to improvement in fretting life of specimens. Analysis suggested the benefit was not only due to fretting wear removing cracks nucleated by fretting fatigue, but also fluctuation of stress distributions due to gross sliding prevented reoccurrence of peak stresses at the same location.