On the Stribeck Curves for Lubricated Counterformal Contacts of Rough Surfaces

Abstract

The “Stribeck curve” is a well-known concept, describing the frictional behavior of a lubricated interface during the transition from boundary and mixed lubrication up to full-film hydrodynamic/elastohydrodynamic lubrication. It can be found in nearly every tribology textbook/handbook and many articles and technical papers. However, the majority of the published Stribeck curves are only conceptual without real data from either experiments or numerical solutions. The limited number of published ones with real data is often incomplete, covering only a portion of the entire transition. This is because generating a complete Stribeck curve requires experimental or numerical results in an extremely wide range of operating conditions, which has been a great challenge. Also, numerically calculating a Stribeck curve requires a unified model with robust algorithms that is capable of handling the entire spectrum of lubrication status. In the present study, numerical solutions in counterformal contacts of rough surfaces are obtained by using the unified deterministic mixed elastohydrodynamic lubrication (EHL) model recently developed. Stribeck curves are plotted in a wide range of speed and lubricant film thickness based on the simulation results with various types of contact geometry using machined rough surfaces of different orientations. Surface flash temperature is also analyzed during the friction calculation considering the mutual dependence between friction and interfacial temperature. Obtained results show that in lubricated concentrated contacts, friction continuously decreases as speed and film thickness increase even in the full-film regime until extremely high speeds are reached. This is mainly due to the reduction of lubricant limiting shear stress caused by flash temperature rise. The results also reveal that contact ellipticity and roughness orientation have limited influence on frictional behaviors, especially in the full-film and boundary lubrication regimes.

Investigation on the angular contact ball bearings under low speed and heavy load with coupled mixed lubrication and quasi‐dynamic analysis

“…The unified deterministic mixed EHL model is used for analysing the lubrication performance of the angular contact ball bearing, which has been proven to be capable of simulating a wide range of lubrication regimes. The pressure p (including both the “hydrodynamic” pressure and the “contact” pressure) is governed by the Reynolds equation, which has also been employed in some recent papers …”

“…In the contact areas, the shear stress is calculated by where f b is the frictional coefficient under boundary lubrication and its value is set as f b = 0.115 …”

“…Then, the dynamic characteristics of the bearing (such as the normal contact load, entraining velocity, relative sliding velocity, and contact angle) can be obtained through quasi‐dynamic analysis. Further, the lubrication performance of the bearings is calculated by using the mixed EHL model . The obtained minimum film thickness h m and friction coefficient f are then used for the quasi‐dynamic analysis.…”

“…In the present study, the dynamic behaviour and the mixed lubrication performance of angular contact ball bearings are analysed by combining the quasi‐dynamic method and mixed EHL method . The effects of the minimum film thickness and frictional coefficient on the dynamic characteristics of bearing are presented.…”

An experimental characterization of the friction coefficient of a wind turbine gearbox lubricant

“…In addition, the Benedict and Kelly's formula predicts low friction coefficients when S R is increased, a behavior that was not evident in the measurements presented in this paper. Other studies have used EHD lubrication theory to theoretically predict friction . However, this approach requires significant computational effort to predict gear tooth contact friction.…”