Abstract
To further extend knowledge about fluid film friction in elastohydrodynamic contact, it is important to examine how lubricant flows. In this paper, several film thickness results obtained by interferometry technique for different kinds of experiments were analyzed and discussed based on lubricant flow continuity. Results of two steady-state and two transient experiments are presented. Possible speed profiles that can explain observed film thickness distributions were suggested. It is shown that major part of present experiments can be explained by a single speed profile known as a plug flow. This finding is in contradiction to usual linear speed profile predicted by Reynolds equation.
Highlights
Elastohydrodynamic lubricant (EHL) is a regime of non-conformal contact lubrication that enables low friction and long life operation of machine elements
The most lubricants change its viscosity with pressure approximately exponentially, it is surprising that EHL contact exhibits low coefficient of friction
It was already well recognized that the shape of film thickness profile inside contact is given by density change
Summary
Elastohydrodynamic lubricant (EHL) is a regime of non-conformal contact lubrication that enables low friction and long life operation of machine elements. Lubricant rheology undergoes a significant change inside contact under loading by pressure and shear rate. The most lubricants change its viscosity with pressure approximately exponentially, it is surprising that EHL contact exhibits low coefficient of friction. This question has been recognized for many years [1], but it was not sufficiently answered yet. This equation consists of so-called Poiseuille, Couette and squeeze terms, respectively. If there is no change of film thickness profile over the time, the squeeze term will be zero and transient problem converts to stationary.
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