Closure to “Discussions of ‘Non-Newtonian Fluid Model Incorporated Into Elastohydrodynamic Lubrication of Rectangular Contacts’” (1984, ASME J. Tribol., 106, pp. 282–284)

1984 ◽  
Vol 106 (2) ◽  
pp. 284-284
Author(s):  
B. O. Jacobson ◽  
B. J. Hamrock
1984 ◽  
Vol 106 (2) ◽  
pp. 275-282 ◽  
Author(s):  
B. O. Jacobson ◽  
B. J. Hamrock

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.


1990 ◽  
Vol 112 (3) ◽  
pp. 497-505 ◽  
Author(s):  
Rong-Tsong Lee ◽  
B. J. Hamrock

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.


1994 ◽  
Vol 116 (4) ◽  
pp. 786-793 ◽  
Author(s):  
A. A. Elsharkawy ◽  
B. J. Hamrock

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.


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