Rotational Rheometry of a Fumed Silica Lubricating Grease

Abstract

The rheological properties of lubricating greases are the governing properties for performance assessment in lubrication applications. These properties can be determined under both controlled stress and strain rheometry. Moreover, studying the effect of temperature on these properties is of great importance. This study investigates the differences between rheological characterizations performed under both controlled stress and strain modes on fumed silica greases. The results of steady-state viscometry under controlled strain mode revealed a non-monotonic temperature-dependent behavior. This non-monotonic behavior, attributed to the shear banding, was also observed in up and down stress ramp data. The results of the controlled stress and controlled strain rheometry modes coincided well at high values of stress and shear rates due to the reduced effect of stick-slip phenomenon and elastic deformation. A two-step yielding flow curve observed in the steady flow curves was justified by bond and cage breakage mechanisms in fumed silica suspensions.