Film thickness predictions for elastohydrodynamic elliptical contacts over a wide range of radius ratios with consideration of side starvation

Abstract

The paper presents numerical solutions obtained for a wide range of elliptical elastohydrodynamic lubrication (EHL) problems. The conditions considered encompass relative principal radii of curvature ratios from 20:1 with entrainment in the minor axis direction, to 50:1 with entrainment in the major axis direction. The problems considered derive from investigations of practical machine elements where the width of contact (perpendicular to entrainment) is limited by the extent of the metal surfaces on either side. Two sets of results have been obtained: one with the width of the lubricated contact approximately twice that of the Hertzian dry contact, and the other where the ratio of these widths is 1:2. Taken as a whole the results present a complete range of conditions obtained using the same numerical model throughout. The film thickness predictions are compared with those given by well-known published formulae and design charts.

The Influence of Longitudinal Roughness in Thin-Film, Mixed Elastohydrodynamic Lubrication

“…Sharif, et al (44) have performed the most recent study on the effect of ellipticity of an EHD contact on film thickness. The range of ratio of principal curvatures considered in their work is the most extensive to date but still does not encompass the value of the present study, although its limit is closer to that of the present study than that of Eq.…”

“…13, it appears that the minimum film thickness for the longitudinally rough surface (defined by the film at the peak of the asperity) can be accurately predicted from the corresponding smooth elliptical micro-contact by (44) 0.02 < R y / R x < 20 Dowson and Hamrock (38) 0.955 <R y / R x < ∞ allowing for the effect of the ridge geometry, R y , in the inlet and for the ridge load. Finally, it is important to note that this micro-EHD film thickness prediction technique for longitudinal roughness will be valid only at extremely low lambda ratios as in the present study, within the mixed lubrication regime, since it assumes that the ridges are independent and that there is no hydrodynamic lift from lubricant in the valleys.…”

Revisiting film thickness in slender elasto-hydrodynamically lubricated contacts

“…This is illustrated by comparing the authors results with the results for narrow contacts presented in reference [17], see Tables 1 to 3. To reduce the effects of the size of the domain only results are presented for load conditions which are sufficiently well in the (piezoviscous)-elastic regime (i.e.…”

“…Therefore, all contact results of a given curve are for contacts with the same maximum Hertzian pressure. It can be observed that for each [17] for narrow elliptic contacts, and references therein. It is also clearly shown in Fig.…”

“…For each value of M c , the value of h c /h m increases linearly with 1/κ. Following Hooke's suggestion in reference [29] in references [17], and [28] the behaviour of the ratio h c /h m is plotted as a function of the ratio of the elastic deformation and the minimum film thickness represented by the dimensionless parameter = a 2 /(Rh m ), which was originally introduced by Archard and Cowking [30]. The results showed that to a good approximation, the ratio h c /h m is a function of only.…”