Stribeck and Traction Curves Under Moderate Contact Pressure: From Friction to Interfacial Rheology

Friction in the full-fluid-film regime is generally attributed to the shear response of the lubricated interface under pressure. However, the associated rheological law remains under debate. Stribeck and traction experiments were carried out for model fluids and complex aged fully formulated fluids using the IRIS tribometer, which allows simultaneous measurement of film thickness and friction force under controlled contact kinematics. This leads to the establishment of rheograms that collapse over a wide range of shear rate for moderate contact pressure. A theoretical methodology is then proposed to determine the rheology of the confined interfacial film in a unique way, the latter being discussed in terms of the Eyring and Cross physical non-Newtonian models.