Reducing the friction of lubricated nonconformal point contacts by transverse shallow micro-grooves

Abstract

This study focuses on the effects of transverse shallow micro-grooves on the film thickness and friction of nonconformal contacts under relative motion. Experiments were conducted using a ball-on-disc tribometer equipped with high speed camera and torque sensor. The lubricated contact between the steel ball and glass disc represents a nonconformal point contact with elastohydrodynamic lubrication. The measurements of the film thickness were carried out using the optical interferometry technique while the friction was measured by a torque sensor on the ball shaft. The results reveal that the rubbing surfaces with transverse shallow micro-grooves with a length less than the diameter of the Hertzian contact have an improved tribological performance in comparison with smooth surfaces in the elastohydrodynamic lubrication regime. Indeed, a significant enhancement of film thickness has been observed using such design of micro-grooves. On the other hand, the transverse deep and shallow micro-grooves with a length larger than the diameter of the Hertzian contact suffer from the side leakage and the lubricant is ejected out of the contact by sideways leading to a pressure drop and film thickness collapse. Moreover, the measured friction of surfaces textured with shallow micro-grooves without intersection with the outer Hertzian circle is less than the friction of smooth surfaces in sliding and reversal motion.