Rheological behavior of greases: Part I - Effects of composition and structure

The aim of this work is to show the correlation between grease rheological behavior and its composition and structure (base oil viscosity, soap nature , and concentration). A rheological investigation was carried out under the controlled stress mod e. The results, obtained over different time intervals, show that grease be haves like a non-Newtonian viscoelastic material, with a narrow linear doma in. The soap nature and concentration are the dominant parameters when grease i s submitted to low shearing. This was confirmed by TEM observations: the cl oser networks gave the highest rheological properties. Base oil viscosity i nfluenced grease behavior only under high strain rates. Some properties are discussed with respect to their influence on the contac t replenishment, which is a critical point for mechanism lifetime predictio n. Finally, the authors suggest using rheometry as an alternative technique to standardized methods. Yield stress varies in the same way as penetration d oes, but is further influenced by the sample macrostructure.