A Survey of Boundary Lubrication Effect in Elastohydrodynamic Lubrication

Boundary lubrication effect is investigated in isothermal line contact elastohydrodynamic lubrication (EHL) by using the inlet zone analysis method and taking the nanometer-scale thin film lubrication analytical approach proposed by the author.(1) Calculation of the load carried by the EHL contact is made for the film thickness in the Hertzian contact zone ranging from 2 nm to 20 nm when the dimensionless material parameter G is 4500, the dimensionless rolling speed U is 1.0E-12, and the compound curvature radius of the contact surfaces R is 10 mm. Calculation is also made for different contact-lubricant interaction strengths represented by the critical thickness parameter h(cr) of boundary film. Results show that when the film thickness in the Hertzian contact zone is on the 1 nm scale (or lower), the load carried by the EHL contact can be considerably increased when the boundary lubrication in the EHL contact is considered; Otherwise, the change of the carried load by the EHL contact because of boundary lubrication consideration is negligible, and conventional EHL model can cover the whole EHL contact. Results also show that the compressibility of the lubricant due to the contact-lubricant interaction considerably reduces the load-carrying capacity of the EHL contact when the Hertzian contact zone is in boundary lubrication.