Some Observations of the Relationship Between Film Thickness and Load in High Hertz Pressure Sliding Elastohydrodynamic Contacts

Abstract

The dependence of film thickness on Hertz pressure at pressure levels typical of design applications has been investigated. The data presented by investigators at NASA and Battelle using an X-ray transmission technique showing a dependence much greater than that indicated by commonly accepted theories are substantiated by an independent study using an optical interference film thickness measurement technique. It is also shown that the minimum film thickness is influenced to a much greater extent by the Hertz pressure than the center line film thickness.

An Analysis of Elastohydrodynamic Lubrication with Limiting Shear Stress: Part II — Load Influence

“…When sliding dominates in the motion, the central and minimum film thicknesses are much more sensitive to load variations in the light to medium range than con- ventional theory predicts. This agrees with the experimental results of Lee et al (1973) for simple sliding elastohydrodynamic lubrication, which showed a stronger dependence of the central and minimum film thicknesses on the loads giving the maximum Hertzian pressures over 0.5 GPa as opposed to the conventional isothermal and thermal EHL theories. Gentle et al (1975) attributed the increased film thickness dependence to a reduction of the inlet viscosity by temperature.…”

“…The concepl of interfacial limiting shear stress is capable of interpreting the experimentally observed elastohydrodynamic film collapse and failure, which are poorly explained by present EHL theories. The collapse and failure of EHL film with increased load is not explained by conventional isothermal and thermal EHL theories (Lee et al, 1973;Czichos,1974). The lubrication law for collapsing EHL film is obviously distinct.…”

EHL Film Thickness Limitation Theory Under a Limiting Shear Stress

“…The present authors seriously wonder whether their theory is applicable to the case of heavy loads where severe film collapse occurs. Compared with others' similar experiments (Lee et al, 1973;Czichos, 1974), Kaneta's experimental results (1996) appear too particular. The reason for this may need to be examined.…”

“…First, the lubrication in their experiment easily deviates from conventional EHL theories, since their experiment is where film collopsc and failure eirsily occurs at modest loads (Lee et al, 1973;Czichos, 1974). Secondly, they showed abnormal interferograms of their experimental contacts compared with conventional ones, but were not aware that their observed phenomena may be the samc with the earlier findings by Lee et al (1973) for the similar case, which showed anomalous results of film thickness and its vrrricrtion with load in their experiment compared with conventional EHL theories indicating severe film collapse at relatively heavy loads. Surprisingly, Kaneta et al (1996) measured the film thickness higher than conventional EHL theory prediction indicating dimples of their contacts.…”

“…In an earlier study, Wen and Zhang (2000) predicted an inlet zone slip and much reduced film thickness cotnpirred to conventional EHL theory for pure rolling, and found the satlie phenomena of EHL film for large slide-roll ratios nnd heavy loads when using a lower interfacial limiting shear stress. Their rcsults are new for explaining experimentally observed EHL film collapse and failure (Lee et al, 1973;Czichos, 1974), which is not explained by conventional EHL theories. Ehret et al (1998) established an interfacial slip EHL theory for explaining the dimples of sliding EHL contacts experimentally observed by Kaneta et al (1992).…”