Experimental investigation of transient and thermal effects on lubricated non‐conformal contacts

Thermal and transient effects in lubricated point contacts are investigated through experimental analyses using the optical interferometry technique. Experiments between a ball and a plane surface of a disc are described. To include effects due to different thermal properties, experiments are carried out for different slide-to-roll-ratios with a steel-on-steel and a glass-on-steel contact. A paraffin base mineral oil is used as a lubricant. Friction coefficients and film thicknesses are measured (the film thickness only for the the glass-on-steel-contact). Under transient conditions the entraining velocity is varied with a sinusoidal law. It is found that the film thickness and the friction coefficient are influenced a lot by the slideto-roll ratio and the thermal properties of the contacting materials. Under transient conditions film thicknesses and friction coefficients are influenced by thermal effects and not only by transient effects like squeeze. Squeeze effects explain “loops” of friction- and film thickness found also in previous works. The formation of friction loops are related to the measured film thickness differences. Thermal effects could explain differences in film thickness and friction loops for different slide-to-roll-ratios and surface materials.