Dual experimental-numerical study of oil film thickness and friction in a wide elliptical TEHL contact: From pure rolling to opposite sliding

This study presents a dual experimental-numerical approach to simultaneously investigate oil film thickness and friction in a wide elliptical thermo-elastohydrodynamic (TEHL) contact over sliding conditions ranging from pure rolling to opposite sliding (slide-to-roll ratio SRR between 0 and 4). Experiments are performed on a barrel-on-disk tribometer instrumented for friction and optical oil film thickness measurements. In addition, a TEHL numerical model based on the full system approach is used to predict film thickness and friction response variation with sliding. The trends of film thickness variation with SRR are different for SRR lower and higher than 2 because of the genesis of the thermal viscosity wedge effect at opposite sliding. The friction coefficient measured experimentally increases with increasing SRR and then stabilizes at high SRR. The numerical model can accurately predict the film thickness over a wide range of sliding conditions. Also, the model predicts friction with a good accuracy for SRR>2. In contrast, for SRR<2, numerical results overestimate friction coefficient. In addition, a numerical parametric investigation is realized to understand the effect of varying ambient temperature, normal load, and entrainment velocity on film thickness and friction over a wide range of sliding conditions. Numerical results are then used to create a simple formula for an accurate estimation of the minimum film thickness based on classical dimensionless parameters and SRR for a wide range of sliding conditions (0≤SRR≤4).