On the Optical Assessment of the Structural Degradation of Rheologically Stressed Lubricating Greases

Abstract

This work explores optical measurements' potential to better understand structural degradation due to the internal friction process of lubricating greases. The samples have been examined as closely as possible to their original state due to the specimen preparation protocol. Eleven model lubricating greases were evaluated for these purposes. Image analysis of transmitted light microscope, SEM and AFM measurements were used to evaluate the grease microstructure under stressed and unperturbed conditions. The results showed that the type of thickener could significantly influence the internal frictional energy due to the structural degradation of the lubricating grease. Thus, the structural skeletons of lithium and calcium greases can dissipate less mechanical energy during a shearing process than polyurea grease or isolated pure biogenic greases.