Traction Plateau and the Proper Evaluation of the Limiting Shear Stress for Friction Modelling in Elastohydrodynamic Lubrication

There is renewed interest in the phenomenon of limiting shear stress (LSS); an essential component of friction modelling in elastohydrodynamic lubrication (EHL), perhaps because it is thought to be detectable and measurable by a simple friction measurement. In a sense, this is true, but only with knowledge of the viscosity under the conditions of the friction data. The LSS dependence on pressure may be extracted from EHL traction only if the LSS is operating over nearly all the contact area. Otherwise, the value of the LSS will be understated. Recent attempts have utilized contact pressures that are insufficient to achieve the LSS over enough of the contact and the resulting pressure dependence erroneously appears to make the LSS go to zero at a large positive pressure. The current work discusses precautionary measures for a proper extraction of LSS from traction measurements, to be used in EHL friction modelling.