On the Intricate Relation between Contact Aspect Ratio, High-Pressure Rheology, and Minimum Film Thickness in Elastohydrodynamic Conjunctions

Until recently, it was believed that both central and minimum film thickness in elastohydrodynamic lubricated conjunctions are governed by the lubricant low-pressure rheology, in the contact inlet. A recent study by the authors has shown that minimum film thickness in circular contacts is also affected by the high-pressure rheology. It was shown that higher lubricant viscosity in the high-pressure central zone of the contact leads to lower minimum film thicknesses. This was linked to a reduction in lubricant outflow from the contact through the sides. That is why such effects would not be observed in infinitely long line contacts. It was then posited that minimum-film-thickness sensitivity to high-pressure rheology should be higher in circular contacts than wide elliptical ones and even higher in slender contacts. The current work aims to verify this assumption and elucidate the intricate relation between contact aspect ratio, high-pressure rheology, and minimum film thickness in elastohydrodynamic conjunctions. This is done through finite element simulations of elliptical contacts of variable ellipticity, lubricated with two hypothetical fluids having the exact same low-pressure viscosity response, but a different high-pressure one.