Abnormal film shapes in sliding elastohydrodynamic contacts lubricated by fatty alcohols

This paper describes abnormal film shapes in point sliding contacts lubricated by fatty alcohols. The original film thickness features have appeared under moderate film thickness conditions using lauric alcohol and 1-dodecanol, which have a low viscosity and pressure-viscosity coefficient as lubricants. The film thickness is measured by white-light interferometry applied to glass disc-steel ball contacts. When the slide to roll ratio increases, the film thickness distribution changes. The thickness increase can lead to values several times higher than those measured under pure rolling conditions. Keeping the mean entrainment speed constant, despite the same absolute values of the slide to roll ratios, the film thickness distributions when the ball speed is higher differ from those when the disc speed is higher. The mechanisms that can explain such a new and unexpected EHL film behaviour are discussed using literature results and a simple thermal model that estimates the temperature increase at the solid surfaces and oil film. According to the results of the model, it is concluded that neither the temperature increase nor the temperature difference between the solid surfaces can explain the appearance of the abnormal film thickness features. However, the differences between the fluid responses suggest that the lubricant rheological behaviour contributes towards the observed phenomena.