Rheology meets tribology: Updated Stribeck curve for the lubrication between smooth surfaces

抄録

The Stribeck curve is a fundamental concept to characterize the shear behavior in the entire range of lubrication, including hydrodynamic, mixed, and boundary lubrication regime. This concept covers both rheological and tribological aspects, and is widely used to grasp the shear behavior of many practical systems. However, the Stribeck curve has at least two quantitative problems: (i) baseless assumption that the effect of increasing sliding velocity on lubricant film thickness (and resulting friction force) is quantitatively equivalent to that of decreasing load; and (ii) the viscosity of lubricant is regarded as constant, which is incorrect. The surface forces apparatus (SFA) is very suitable to approach this issue; the SFA enables the direct measurement of film thickness using optical technique simultaneously with friction measurements, and boundary lubrication is quantitatively described using effective viscosity. According to this approach, bulk rheological properties and thin film tribological properties have been quantitatively connected, which leads to the updated Stribeck curve for smooth surfaces.