Abstract: Using a new proposed algorithm for the effective viscosity η^* of an Eyring fluid, a common assumption γ=△u/h is discussed in the analysis of lubricant rheology, the relations of the friction coefficient μ of heavily loaded line contact thermal elastohydrodynamic lubrication with the Newtonian viscosity η, the effective viscosity η^*, and the shear-strain rate γ of the Eyring fluid are studied theoretically through a strict numerical solution of a thermal elastohydrodynamic lubrication problem. Results show that, when the size of a contact is very small or in other similar cases with low temperatures, the traditional assumption of γ=△u/h can hold approximately, the friction coefficient, therefore, is dominated by the effective viscosity of the lubricant. However, when the size of the contact is very large or in other similar cases with high temperatures, γ=△u/h can no longer hold, the friction coefficient is mainly controlled not only by the effective viscosity but also by the change of the shear-strain rate, so the previous studies are inaccurate.

Key words: effective viscosity, friction coefficient, shear-strain rate, thermal elastohydrodynamic lubrication