A lubrication theory that includes the coupled effects of surface roughness and anisotropic slips is proposed. The anisotropic-slip phenomena originate from the microscale roughness at the atomic scale (microtexture) and surface properties of the lubricating surfaces. The lubricant flow between rough surfaces (texture) is defined as the flow in nominal film thickness multiplied by the flow factors. A modified average Reynolds equation (modified ARE) as well as the related factors (pressure and shear flow factors, and shear stress factors) is then derived. The present model can be applied to squeeze film problems for anisotropic-slip conditions and to sliding lubrication problems with restrictions to symmetric anisotropic-slip conditions (the two lubricating surfaces have the same principal slip lengths, i.e., b1x=b2x and b1y=b2y). The performance of journal bearings is discussed by solving the modified ARE numerically. Different slenderness ratios 5, 1, and 0.2 are considered to discuss the coupled effects of anisotropic slip and surface roughness. The results show that the existence of boundary slip can dilute the effects of surface roughness. The boundary slip tends to “smoothen” the bearings, i.e., the derived flow factors with slip effects deviate lesser from the values at smooth cases (pressure flow factors φxxp,φyyp=1; shear flow factors φxxs=0; and shear stress factors φf,φfp=1 and φfs=0) than no-slip one. The load ratio increases as the dimensionless slip length (B) decreases exception case is also discussed or the slenderness ratio (b/d) increases. By controlling the surface texture and properties, a bearing with desired performance can be designed.
A lubrication theory, considering the coupled effects of anisotropic slips on both the solid/liquid interface and non-Newtonian power-law lubricant, is proposed for enhancing surface treatment and oil additives. A modified Reynolds equation as well as Poiseuille and Couette flow rate correctors are then derived by applying the rheology model and Navier-slip boundary conditions with orthogonal principal slip lengths( ix b , iy b ). Hence, the different slenderness ratios which leads different performance of journal bearings is used to highlight the coupling effects of anisotropic slips and flow rheology. Contours of constant load ratios are plotted and then the Downloaded by [Cambridge University Library] at 05:02 16 August 2015 ACCEPTED MANUSCRIPT 2 parameters in flow rheology and boundary slip can be located while designing functional surfaces in journal bearings.
By coupling the equations of the modified Reynolds equation with the anisotropic slip effect, the piezoviscosity and piezodensity relations, the elasticity deformation equation, and the load equilibrium equation are solved simultaneously using the finite element method (FEM) for the elastohydrodynamic lubrication (EHL) of circular contact problems under constant load conditions. Results show that the film thickness is more sensitive to the slip length in a sliding direction (x-direction) than to the slip length in a transverse direction (y-direction). A slip in the y-direction concentrates the pressure toward the center region, and the film collects toward the central region and possesses a deeper dimple. The central pressure and coefficient of friction (COF) increase as the slip length in the y-direction increases. On the contrary, the central pressure and COF decrease as the slip length in the x-direction increases. Detailed results and animations for film thicknesses and pressure distributions are available under the “Supplemental Data” tab for this paper on the ASME Digital Collection.
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