مطالعه‌ي عددي و تجربي عملكرد تريبولوژي تماس سطوح فلزي در حضور روانكار گريس

In this study, the tribological behavior of a pin on disk contact operating under mixed lubrication conditions with a focus on Lithium grease lubrication has been investigated. In this regime, the contact load is simultaneously carried by the elastohydrodynamic lubrication (EHL) film an‎d the asperity contacts, an‎d the prediction of film thickness, contact temperature, an‎d wear requires consideration of surface roughness effects, load sharing, an‎d lubricant film defect. For this purpose, the base EHL film thickness was first calculated using the classical Hamrock–Dowson relations while considering the effective contact modulus. Subsequently, the effect of grease on the film thickness was incorporated through an engineering correction factor based on experimentally reported results in the literature in order to account for the increase in film thickness due to the presence of grease thickener particles. Accurate wear prediction requires consideration of surface roughness, load sharing, contact temperature, an‎d lubricant film defect. Therefore, dry wear was first modeled as a reference condition using the continuum damage mechanics approach, an‎d the damage evolution in the contact region without lubrication was analyzed. This step was employed as a physical basis for modifying the wear model in the presence of lubrication. Next, based on the concept of mixed lubrication an‎d a micro-scale analytical–numerical framework for asperity contact, the load ratio carried by asperities was calculated using the elastic–plastic Kogut–Etsion model, which provides more accurate an‎d comprehensive relations compared to the Greenwood–Williamson model, together with the Greenwood–Johnson–Poon approach. Lubricant film defect, as a key parameter, was modeled with a direct dependence on the contact surface temperature. The contact surface temperature was determined by combining the steady-state bulk surface temperature an‎d the asperity flash temperature using a simplified thermal pin-on-disk model along with classical formulations. This temperature was then used as a primary input for modifying the wear coefficient. Finally, wear was predicted using Archard’s law while considering the actual load sharing in the contact an‎d correcting the wear coefficient based on film defect an‎d surface temperature. For model validation an‎d input parameter extraction, experimental tests including pin on disk wear tests, grease rheology tests, an‎d surface roughness measurements were conducted, an‎d the numerical results were compared with experimental data. The results indicate that the effects of load an‎d sliding speed on wear in grease-lubricated contacts are nonlinear an‎d are governed by the simultaneous variation of temperature, film thickness, an‎d asperity contact load share. Incorporating the grease film thickness correction an‎d accounting for surface temperature in the film defect model significantly improved the wear prediction accuracy. Comparison between the model predictions an‎d experimental data showed that the predicted wear volume under different operating conditions exhibited an error range of approximately 11% to 30%, with an average of about 25%, indicating the satisfactory capability of the proposed engineering framework in describing wear behavior under mixed lubrication conditions. The proposed framework enables an integrated analysis of lubricant film thickness, surface temperature, an‎d wear under mixed lubrication conditions.

صالح اكبرزاده , محمد سيلاني

محمدرضا فروزان , محسن اصفهانيان