This paper reviews the electrical methods to evaluate lubrication, with the focus on elastohydrodynamic applications. The methods are based on the measurement of the electrical resistance and/or capacitance, and are used to determine the thickness of lubricating films as well as to detect asperity contact in the mixed lubrication regime. The experimental works are introduced in which these methods are used in conventional sliding and rolling/sliding tests and machine component tests including piston ring and cylinder liner, cam and follower, and gears. Also some works on the effect of electric field upon lubrication phenomena are introduced. Advantages and disadvantages of the electrical methods are discussed.

The lubrication of rough surfaces has been a focus of researchers in the field for many years now. A good deal of work has been carried out either on the experimental or on the theoretical sides of the research. From the experimental point of view it is obviously more convenient to study the lubrication of artificial roughness features such as ridges, bumps or dents rather than real, random roughness. The advantage of model roughness features is that they are well individualized, located, and characterized, thus a comparison of the surfaces geometry inside and outside an elastohydrodynamic contact can be made. The studies carried out so far have focused on the effect of the geometry of the features and that of the entrainment speed. No detailed experimental work on the effect of the lubricant properties on the behavior of the EHD films has been performed, to the authors’ knowledge. The present study uses the optical interferometry method to measure the EHD film thickness between a flat disc and a ball on which artificial ridges have been sputtered. Two lubricants, with different viscosity and pressure/viscosity coefficient are used in a range of pressures and entrainment speeds.