Dynamics of a Rayleigh-step bearing: Generic Stribeck curve and rate-state models

The Stribeck curve forms the backbone of our understanding of frictional behavior. It has traditionally been associated with lubricated journal bearings and later on with EHL lubricated rough contacts. Still later, this behavior appeared to manifest itself also in dry rough contacts. While in this latter case, the Stribeck behavior has been simulated theoretically, in the lubricated case, the models have been confined to a few restricted cases.Here, I show that the Stribeck behavior emanates directly from the most basic/generic type of hydrodynamic bearing; namely the Rayleigh step bearing, without resort to the EHL/mixed-lubrication assumption. This bearing type can be taken in the macro sense, as a self-standing bearing; or in the micro sense, as an elemental roughness feature, which can be aggregated to understand rough lubricated sliding contacts.Furthermore, this simple model of a step bearing allows us to establish the dynamic behavior of the Stribeck curve; in particular, the friction lag phenomenon and the rate-state law. Main results show that the normalized CoF is universal function of the normalized Sommerfeld number reduced by the aspect ratio of the bearing and that the dynamic Stribeck effect cannot be decomposed into time-dependent Stribect effect combined with time-independent (instantaneous) viscous effect .