Is Elastohydrodynamic Minimum Film Thickness Truly Governed by Inlet Rheology?

This work investigates the governing mechanisms of minimum film thickness in elastohydrodynamic lubricated contacts. Up until now, it was thought to be governed by lubricant rheology in the low-pressure contact inlet. Through numerical simulations of EHL line and circular contacts, lubricated with fluids having the same low-pressure viscosity, but a very different response at high-pressure, minimum film thickness is shown to be governed by lubricant inlet rheology only in the theoretical line contact configuration. In real contacts however, it is not only governed by inlet rheology, but also by the high-pressure viscosity response of the lubricant. It is observed that the greater the viscosity at high pressure, the lower the minimum film thickness would be, as a result of reduced lateral flow out of the contact. Conservation of mass requires then that a higher minimum film thickness would be attained along the central line of the contact, in the entrainment direction. These findings corroborate well with experimental observations.