Study On The Mechanism And Shear Characteristics Of Boundary Slip Under High Pressure And Shear Rate Condition

Boundary slip may occur readily when lubricating oil film is working under highpressure and shear rate. After that, the velocity boundary condition of film is changedand the velocity of film adjacent the wall doesn’t equal to the velocity of the wall. Thefilm thickness, bearing capacity and fractional force would change as well. Thus,boundary slip has great effect on the dynamic characteristics of lubricating oil film. Inthis research, molecular dynamic theory was applied to establish molecular shearmodel in microcosmic which was also called Couette flow model. Then, the dynamicresponse, velocity and shear stress of oil film molecular were analyzed and themechanism and transient process of boundary slip phenomenon was been explored.Moreover, a boundary slip rate and limiting shear stress calculating equation was beenfitted with abundant data.Based on the molecular structure of basic elements of “Santotrac50” traction oilwhich was widely used in engineering, a visible oil film molecular model was built.Combined with the Fe atom model and force field parameters, a molecular shearmodel in microcosmic was established. Then this model was solved by moleculardynamic theory. The dynamic response and its change law under different pressure,shear rate, wettability of the wall and temperature. Besides, according to the velocityprofile along film thickness direction and its change law under different influencingfactors, such as pressure, shear rate, wettability of the wall and temperature, the maxvalue of boundary slip rate equation was fitted and a boundary slip rate model wasestablished. In addition, the shear stress distribution along film thickness directionwas researched both under no slip condition and boundary slip condition. The resultsrevealed that a stress peak adjacent to the wall would occur under boundary slipcondition, which was the force mechanism of boundary slip phenomenon.Furthermore, limiting shear stress equation was fitted with plenty of data underdifferent condition and its change law was researched under different influencingfactors. In the end, the shear stress distribution law under initial slip point wasanalyzed and the transient process of boundary slip phenomenon was announced.