Gaseous Cavitation and Wear in Lubricated Fretting Contacts

Fretting phenomena operating in the presence of grease was investigated experimentally and analytically. A fretting test rig was designed, developed, and equipped with a microscope and high-speed video camera to observe the effects of the lubricant entrainment within the contact during the fretting phenomena. A mixed elastohydrodynamic lubrication model was used to analytically investigate lubricated fretting and corroborate with experimental results. An analytical approach is also presented to determine the amount of lubrication entrained within the fretting contact. The results of fretting wear operating in the presence of grease are presented for case-hardened steel in the crossed cylinder configuration and hardened steel ball-on-sapphire flat configuration. The roles of lubrication, oscillation amplitude, and cavitation in fretting are presented and discussed. Lubrication was found to mitigate the effect of fretting on a surface while the effect of oscillation amplitude on fretting was more complex. The results indicate that frequency increases the amount of material transfer between fretting surfaces. Gaseous cavitation was observed to occur in the trailing edge of the fretting contact and increased with speed. A closed form equation was derived to approximate the volume of the lubricant entering the fretting contact area during the fretting motion and explain the effect of test conditions on fretting wear.