Analysis of fluid film formation between contacting compliant solids

Abstract

Industrial compliant surface bearings and dynamic seals sometimes suffer severe damage during start up after long rest, and a similar problem is predicted for joint prostheses with compliant artificial articular cartilage. In this study, fluid film developing between compliant solids by sliding is analyzed numerically using a modified elasto-hydrodynamic lubrication theory which permits direct contact and cavitation. The result shows that the forefront of the fluid film moves in the same direction with sliding while direct contact remains until the fluid film takes the place of the entire contacting region. With an increase of compliance and the Stribeck number, the velocity of fluid film formation increases and approaches half of the sliding speed but never exceeds it. In other words, the minimum sliding distance for non-contacting condition is twice the initial contact width. Therefore, when a heavy load is applied to compliant surface bearings, the contact width will be large and the unlubricated region will remain long. Since a compliant material is not as strong as hard materials, it may be damaged during start up after a long rest. As the study has thus clarified the mechanism of damage which compliant surfaces experience during start up, effective methods to protect surfaces from damage will be found according to the theoretical backgrounds.