In Situ Pressure and Film Thickness Measurements in Rolling/Sliding Lubricated Point Contacts

The physical conditions—pressure, temperature, shear stress—generated in an elastohydrodynamic contact govern the rheological behavior of the lubricant within the contact, and thus its tribological performance.This paper presents in situ measurements of pressure and film thickness in EHD point contacts using respectively Raman microspectrometry and differential colorimetric interferometry. A model lubricant—a polyphenylether oil (5P4E)—is used. The influence of load, temperature and sliding speed at different mean entrainment speeds on pressure and film thickness distributions is investigated. The analysis is based upon the relative values taken by the Moes dimensionless parameters M and L. In all cases, the pressure peak tends to increase and to move towards the center of the contact when the slide to roll ratio increases. When the sliding speed reaches large values (100 to 180%), several cases are encountered: When M > L, the pressure peak softens and moves towards the outlet; The Petrusevich peak disappears and the pressure profile remains almost constant as M and L are close to each other; When M < L, the peak disappears along with a strong modification of the pressure distribution. The maximum value is significantly reduced and the area of contact increases.Measured film thickness profiles confirm these tendencies. Increasing the slide to roll ratio leads to an important film thickness reduction and modifies the position of the constriction. Furthermore, film increase localized between the contact center and the constriction region is observed. This indicates the presence of important thermal effects within the contact and is discussed in the light of recently published papers.