The measurement of the refractive index of a liquid lubricant at high pressure within an EHL impact dimple using a single optical interferogram

The optical film thickness, expressed as the product of the refractive index and the absolute film thickness, is often considered as a single parameter in optical elastohydrodynamic lubrication (EHL) studies. A theoretical study of the effect of refractive index upon the interference intensity has been carried out, providing a method for the evaluation of refractive index irrespective of the absolute film thickness. As a result, a simple and reliable method for measuring the refractive index of an oil in an optical EHL contact has been developed. The technique is applied to a highly pressurized liquid lubricant trapped inside an EHL dimple and its high pressure refractive index is determined.