Thermal elastohydrodynamic lubrication characteristics of couple stress fluids in rolling/sliding line contacts

Abstract

A mathematical model is developed to analyse the effect of polymer additives on thermal elastohydrodynamic lubrication (EHL) behaviour under heavily-loaded rolling/sliding line contacts. The lubricant is assumed to be couple stress fluid and a non-dimensional couple stress parameter represents the molecular length of the additives. The Reynolds and mean temperature equations for the couple stress fluid (CSF) are derived using the rheological relationship presented by Stokes. The thermal EHL characteristics computed for polymer modified oils are found to have a strong dependence on the couple stress parameter. Polymer additives are shown to cause a significant increase in fluid-film thickness along with a noteworthy reduction in the coefficient of friction without any rise in fluid pressure. In addition, the polymer additives are found to cause a minimization of the thermal reduction in the fluid-film thickness as a well as decrease in fluid temperature, particularly under low speed-high load conditions, where fluid films are quite thin. These improvements are desirable in situations involving continuously varying slide to roll ratios, e.g. in gears.

Characterization of lubrication of asymmetric rollers including thermal effects

“…The mean temperature T m has been shown in Figures 4 and 5, as a function of n and U . It may be observed that the qualitative behavior of T m versus x is very similar to the temperature profile obtained by Prasad et al (1991), Saini et al (2007). Further, for a fixed value of n, T m increases with U , which indicates that the sliding temperature is higher than that of pure rolling (Ghosh and Hamrock, 1985;Sadeghi and Dow, 1987).…”

A novel numerical scheme for the analysis of effects of surface roughness on EHL line contact with couple stress fluid as lubricant

“…Accurate empirical formula for the film thickness of EHL elliptical contacts using couple stress lubricant [34] is a good substitute to earlier ones. The influence of couple stress on steady state thermal EHL line contact problem and, later investigation of compressible EHL line contact problem to demonstrate the combined influence of couple stress lubricant with wavy surface roughness on lubrication characteristics are presented in [35,36] respectively. For point contact problem [37] the effects of surface roughness and couple stress lubricant on EHL characteristics using average flow model equation are obtained.…”

A theoretical analysis of roll-over-web coating of couple stress fluid

“…This antisymmetric part of stress tensor manifests itself in the momentum equation by raising its order from two to four. Couple stress theory is used to model many industrial fluid flows, such as lubricants with additives, polymeric fluids with suspensions, colloidal fluids, paints, liquid crystals, magmas, molten alloy, [10][11][12][13][14][15][16] etc. According to Stokes, 9 one could expect couple stresses to appear in noticeable magnitudes in a liquid with very large molecules or with additives.…”

“…9 Several researchers have exploited this idea and studied various problems related to industry, physiology, and mechanical engineering. [10][11][12][13][14][15][16] In view of the above discussion, couple stress fluid model is best suited to study the coating of materials with suspended particles or having high molecular weight, for example, ultra-high-molecular-weight polyethylene. Motivated by this fact the aim of this work is to provide the results for this process employing the couple stress fluid constitutive equation.…”