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The interfaces of plastic components are often operated as self-lubricating or lubricated with greases close to the piezoviscous-elastic lubrication regime. However, current basic tribological knowledge about grease-lubricated compliant contacts is still very limited. This experimental study provides insight into relations between film thicknesses of grease and its base oil in compliant polymethylmethacrylate–steel and stiff glass–steel point contacts at different speeds and loads. The results are compared with predictions. The ratio between grease and its base oil film thickness was found to be significantly influenced by the interplay of load and the non-Newtonian response of grease, especially for the compliant contact, while the effect of speed and the slide-to-roll ratio was considerably lower. The role of viscoelasticity and grease thickener concentration is discussed.

In the first paper of this series, a new formula for central film thickness of slender contacts has been proposed. In this paper, interferometry measurement of the film thickness in slender elliptic contacts is performed for comparison with film thickness distribution of EHL simulation. The new film thickness formula presented in part I of this paper series is successfully validated by comparison with the experimental data. State-of-the-art minimum film thickness formulas are compared with the experimental results and results obtained through a multilevel EHL solver. Significant deviation of the analytical minimum film thickness formulas regarding both numerical and experimental results is given. Therefore, an alternative approach for calculation of minimum film thickness via the film thickness ratio with central film thickness is proposed, which yields promising results for moderately slender elliptic EHL contacts.

Rolling element bearings lubricated by greases represent the most used mechanical components in industry, thus the total volume of energy required to overcome their friction is enormous. Even small improvements can provide considerable savings. To reach these improvements, it is necessary to understand all the processes in the bearing, and especially those that take place in contacts of rolling elements. So far, most of the research was done on tribometers employing a ball-on-disc configuration. Tests on such devices are easy to perform but differ from conditions of actual bearings in some important aspects such as a contact geometry, presence of cage, number of contacts, spin motion of rolling elements, or action of centrifugal and capillary forces. The aim of this experimental study is to refer about film thickness during the initial running phase of simulated thrust rolling bearing and to reveal some patterns of lubricant behaviour for different conditions and greases. Measurements were carried out on unique apparatus of simulated thrust rolling bearing using optical methods with high speed camera. Results showed that the ball-on-disc configuration does not completely correspond to behaviour of actual bearings, mostly in terms of starvation and replenishment of grease. Multiple contacts in succession of simulated bearing do not tend to starve so rapidly and seriously during experiments as is presented in literature for ball-on disc configuration under similar conditions.