Application of Elastic/Plastic Rheological Model in Characteristics Analysis of Elastohydrodynamic Lubrication of Grease

A modified ball-on-disc test rig was performed to measure the traction forces of a bi-ester type domestic lithium grease No.7007. Two equations for calculating the average limiting shear stress and shear elastic modulus of the grease in elestohydrodynamic (EHD) lubrication condition were derivated. The method to calculate the traction forces of the grease was presented based on the elastic/plastic rheological model introduced by Johnson and Tevaarwerk. One example calculation was then made for grease No.7007 and its rheological properties were analyzed. The results showed that the lithium grease behaved elastic and plastic throughout the experimental conditions and the calculated traction force agreed well with the measured one. The semi-empirical equations for calculating the traction force of the grease in EHD condition could be used to guide the lubrication analysis in engineering computing.