EHL of Coated Surfaces: Part II—Non-Newtonian Results

1994 ◽  
Vol 116 (4) ◽  
pp. 786-793 ◽  
Author(s):  
A. A. Elsharkawy ◽  
B. J. Hamrock
Keyword(s):  
Newtonian Fluid ◽  
Reynolds Equation ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Elastic Half Space ◽  
Hard Coatings ◽  
Surface Shear Stress ◽  
Coating Materials ◽  
Surface Shear ◽  
Pressure Profiles

A complete non-Newtonian elastohydrodynamic lubrication solution for multilayered elastic solids is introduced in this paper. A modified form for the Reynolds equation was derived by incorporating the circular non-Newtonian fluid model associated with a limiting shear strength directly into the momentum equations that govern the instantaneous equilibrium of a fluid element inside the lubricated conjunction. The modified Reynolds equation, the elasticity equations of multilayered elastic half-space, the lubricant pressure-viscosity equation, the lubricant pressure-density equation, and the load equilibrium equation were solved simultaneously by using the system approach. The effects of the surface coating on pressure profiles, film shapes, and surface shear stress profiles are shown. Furthermore, the effects of coating thickness on the minimum film thickness and on the coefficient of friction are presented for different coating materials. The results show that for hard coatings non-Newtonian fluid effects on the pressure profiles and film shapes are significant because of the increase in the contact pressure.

EHL of Coated Surfaces: Part I—Newtonian Results

1994 ◽  
Vol 116 (1) ◽  
pp. 29-36 ◽  
Author(s):  
A. A. Elsharkawy ◽  
B. J. Hamrock
Keyword(s):  
Coating Thickness ◽  
Numerical Solutions ◽  
Complete Solution ◽  
Elastohydrodynamic Lubrication ◽  
Elastic Half Space ◽  
Hard Coatings ◽  
Coating Materials ◽  
Pressure Profiles ◽  
Pressure Spike ◽  
Coated Surfaces

A complete solution for the Newtonian elastohydrodynamic lubrication of coated surfaces in line contact is introduced in this paper. The formulation is based mainly on solving the Reynolds equation coupled with the elasticity equations of the multilayered elastic half space. The effects of pressure inside the lubricated conjunction on the lubricant viscosity and density are considered. The mathematical model for this problem is a nonlinear one, and an iterative Newton-Raphson scheme is used for numerical solutions. The effects of coating material and coating thickness on the pressure profiles and the film shapes are presented. Two different coating materials (molybdenum disulfide as a soft coating and titanium nitride as a hard coating) are considered. The results show that the pressure spike is higher for hard coatings than for uncoated surfaces but that the pressure spike disappears for soft coatings. Furthermore, the coating thickness has a significant influence on the minimum film thickness and the maximum contact pressure for both soft and hard coatings.

A Circular Non-Newtonian Fluid Model: Part I—Used in Elastohydrodynamic Lubrication

1990 ◽  
Vol 112 (3) ◽  
pp. 486-495 ◽  
Author(s):  
Rong-Tsong Lee ◽  
B. J. Hamrock
Keyword(s):  
Shear Strength ◽  
Newtonian Fluid ◽  
Reynolds Equation ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Load Parameter ◽  
Viscosity Term ◽  
Pure Rolling ◽  
The Coefficient Of Friction

A circular non-Newtonian fluid model associated with the limiting shear strength was considered. Using this model a modified Reynolds equation was developed which is almost the same as the classical Reynolds equation except for the viscosity term. Results show that the calculation of the central and minimum film thicknesses from the classical Reynolds equation is still valid for pure rolling conditions. The effects on performance of dimensionless load parameter, dimensionless speed parameter, slide/roll ratio, different oils, the limiting shear strength proportionality constant were studied. Such parameters as the pressure profile, the film shape, the coefficient of friction, the dimensionless shear stress at surface a, and the velocitiy contour in the conjunction were considered.

scholarly journals Oscillatory Free Convection about a Horizontal Circular Cylinder in the Presence of Heat Generation

2014 ◽  
Vol 2014 ◽  
pp. 1-8
Author(s):  
Najahulfazliah Zainuddin ◽  
Muhaimin Ismoen ◽  
Rozaini Roslan ◽  
Ishak Hashim
Keyword(s):  
Circular Cylinder ◽  
Free Convection ◽  
Newtonian Fluid ◽  
Heat Generation ◽  
Surrounding Medium ◽  
Surface Shear Stress ◽  
Surface Shear ◽  
Local Skin ◽  
Local Skin Friction ◽  
Horizontal Circular Cylinder

The oscillatory free convection about a horizontal circular cylinder in a Newtonian fluid in the presence of heat generation is investigated numerically by using the finite difference method. The surface temperature of the cylinder oscillates harmonically about the temperature of the surrounding medium. Heat is generated internally within the Newtonian fluid at a rate proportional to a power of the temperature difference. It is found that the presence of heat generation significantly increases the temperature and velocity distribution. The effects of the heat generation parameter and the Prandtl number on the surface rate of heat transfer, in terms of the local Nusselt number, and the surface shear stress, in terms of the local skin friction, are shown graphically from the stagnation point of the circular cylinder.

scholarly journals Non-Newtonian Fluid Model Incorporated Into Elastohydrodynamic Lubrication of Rectangular Contacts

1984 ◽  
Vol 106 (2) ◽  
pp. 275-282 ◽  
Author(s):  
B. O. Jacobson ◽  
B. J. Hamrock
Keyword(s):  
Shear Stress ◽  
Shear Strength ◽  
Film Thickness ◽  
Numerical Solution ◽  
Newtonian Fluid ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Sliding Velocity ◽  
Minimum Film Thickness ◽  
Limiting Value

A procedure is outlined for the numerical solution of the complete elastohydrodynamic lubrication of rectangular contacts incorporating a non-Newtonian fluid model. The approach uses a Newtonian model as long as the shear stress is less than a limiting shear stress. If the shear stress exceeds the limiting value, the shear stress is set equal to the limiting value. The numerical solution requires the coupled solution of the pressure, film shape, and fluid rheology equations from the inlet to the outlet. Isothermal and no-side-leakage assumptions were imposed in the analysis. The influence of dimensionless speed U, load W, materials G, and sliding velocity U* and limiting-shear-strength proportionality constant γ on dimensionless minimum film thickness Hmin was investigated. Fourteen cases were investigated for an elastohydrodynamically lubricated rectangular contact incorporating a non-Newtonian fluid model. The influence of sliding velocity (U*) and limiting shear strength (γ) on minimum film thickness was observed to be small. Hence the film thickness equation obtained for a Newtonian fluid is sufficient for calculations considering non-Newtonian effects. Computer plots are also presented that indicate in detail pressure distribution, film shape, shear stress at the surfaces, and flow throughout the conjunction.

A Circular Non-Newtonian Fluid Model: Part II—Used in Microelastohydrodynamic Lubrication

1990 ◽  
Vol 112 (3) ◽  
pp. 497-505 ◽  
Author(s):  
Rong-Tsong Lee ◽  
B. J. Hamrock
Keyword(s):  
Newtonian Fluid ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Hertzian Contact ◽  
Surface Irregularity ◽  
Good Prediction ◽  
Moving Surface ◽  
Stationary Surface ◽  
Lubrication Performance ◽  
Line Contacts

A circular non-Newtonian fluid model and system approach is used in this paper to study the effect of a stationary surface irregularity where the film shape has been modified in the conjunctions of line contacts. A modified transient Reynolds equation is developed in this paper and is used to study the effect of a moving surface irregularity in the problem of microelastohydrodynamic lubrication. Lubrication performance factors such as pressure and film profiles were studied for both a stationary and a moving surface irregularity in a lubricated conjunction. The shear stress and traction coefficient for various height of the surface irregularity were also studied for a stationary surface irregularity. Results show that the film shape obtained from full-film elastohydrodynamic lubrication theory still gave a good prediction except when the surface irregularity occurred at inlet (Xp = − 1.0), but it failed to explain the high pressure and film fluctuations around the surface irregularity which was in the Hertzian contact zone. A bump or a groove occurring in the outlet around (Xp = 1.0) significantly affected the location of the outlet boundary, and the depth of the nip film thickness in the outlet caused by the surface irregularity profoundly affected the pressure spike for both a stationary and a moving surface irregularity.

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