This work investigates the effect on elastohydrodynamic\nlubrication of roughness ridges oriented along\nthe rollingââ?¬â??sliding direction, such as may be present on\nrolling bearing raceways. The roughness of the three specimens\ntested is characterised by the RMS of surface\nheights and a dominant wavelength. Optical interferometry\nand a ball-on-disc set-up were employed to map the oil film\nthickness. The paper first describes a novel procedure to\ncarry out optical interferometry measurements on rough\nsurfaces. Film thickness maps from the central part of the\ncontact were obtained for a range of speeds in pure rolling\nand rollingââ?¬â??sliding conditions. The evolution of the film\ndistribution with increasing speed along with the in-contact\nRMS and the real area of contact was calculated. The film\nmaps show that the lift-off speed increases when roughness\nis introduced compared with smooth surfaces, while the\naverage film thickness remains very close to the smooth\ncase. The general horseshoe film shape that becomes\nvisible at higher speeds is discussed. Using an inverse solution\napproach based on measured in-contact roughness,\nthe pressure distribution is estimated in a rough, lubricated\ncontact and its evolution with speed is explained. The\nfindings provide important insights into the transition from\nboundary, through mixed, to full EHL lubrication for longitudinal\nroughness.
Loading....