Transient effects in EHL point and line contacts having rough transverse surface finish

Abstract

The paper presents transient point contact elastohydrodynamic lubrication (EHL) results obtained with a formulation that couples the elastic and hydrodynamic equations. Results are presented for elliptical point contacts with the entrainment direction corresponding to the minor contact dimension so that the roughness/entrainment configuration of ground involute gears is replicated. Results are shown that compare the film thickness and pressure distributions obtained along the entrainment centreline with calculations for an equivalent line contact. These indicate that there is no significant difference between transient rough surface results for these two cases, for low Λ (film, thickness/composite surface roughness) conditions, and that a line contact analysis is sufficient to identify the transient EHL response of such gear tooth contacts over most of their face width. Results for the transient variation of von-Mises equivalent stress at surface asperities are presented. These indicate that micro-EHL can cause severe stress cycling close to the material surface and that the cycle rates can be obtained from kinematic calculation of asperity collisions. Further results consider side leakage effects at the transverse limits of the elliptical point contact. These show that side leakage from the valley features of the rough surfaces can seriously undermine the entrainment mechanism and lead to a high incidence of direct asperity/asperity contact. The contact pattern is explored for a range of surface profiles and is seen to correlate qualitatively with the location of scuffing failure in the experimental contacts being replicated.