Theoretical And Experimental Study On Elastohydrodynamic Lubrication Film Failure Of Non-Newtonian Lubricants

An early validation of the classical Newtonian elastohydrodynamic lubrication (EHL) film thickness formula found it to be accurate for mineral oils in normal operating conditions but not to be accurate for mineral oils in harsh operating conditions or mineral oil/polymer blends and some synthetic oils. In such condition, the real EHL oil film is much thinner than classical Newtonian EHL theory predicts or even disappears. It was assumed that non-Newtonian rheological properties of lubricants were responsible for films being thinner than predicted by Newtonian theory. Currently theoretical studies on non-Newtonian EHL film failure mainly focus on the effects of operating parameters on EHL characteristics, but results still can not coincide with experimental results. Therefore, the current non-Newtonian EHL theories are still not applicable to lubrication design.The current paper focuses on the study of non-Newtonian EHL. The influence of shear-thinning and viscoplastic non-Newtonian properties of lubricants on EHL characteristics was mainly studied. The film failure mechanisms of non-Newtonian EHL were studied through theory and experiment, and the relationship of EHL film load-carrying capacity with the lubricant non-Newtonian properties was also studied.The current paper improves the non-Newtonian fluid EHL analytical approach, and establishes a new kind of theory of isothermal line contact non-Newtonian EHL. The non-Newtonian EHL theory shows that lubricant non-Newtonian rheological properties can directly cause EHL film instability and failure. On the other hand, this paper also put forward new kinds of non-Newtonian EHL experimental approaches. Non-Newtonian EHL theory established in this paper was verified by experiments. It shows that EHL film failure has the relationship with the lubricant non-Newtonian rheological properties. The main research contents are as following:(1) The current paper put forwards a new non-Newtonian rheological model. The new model includes the following lubricant properties: viscoelastic property, shear-thinning property and plastic property. Whether the new rheological model can reflect lubricant flow properties under EHL operating condition will be verified.(2) A full numerical analysis for the isothermal line contact EHL is studied based on the new non-Newtonian rheological model.(3) Influence of non-Newtonian properties on pressure distribution and film shape distribution of EHL is analysized theoretically and compared with classical Newtonian EHL theory.(4) Influence of non-Newtonian properties on relationship between EHL film thickness and rolling speed is analysized theoretically.(5) Influence of non-Newtonian properties on relationship between EHL film thickness and load is analysized theoretically.(6) Correction factor formula to predict EHL film thickness for non-Newtonian lubricants is developed. In practical engineering applications, the film thickness can be easily obtained through the corresponding Newtonian film thickness multiplied by the correction factor.(7) Special experiments are designed to verify the theoretical results.