The variation with sliding speed of the traction transmitted by E.H.L. oil films has been measured in a rolling contact disc machine, at contact pressures up to 260,000 lbf/in2 and at various rolling speeds and disc temperatures. From the traction measurements at very low sliding speeds, under isothermal conditions, the variation in apparent viscosity of the oil with pressure and temperature has been found. The variation with temperature at high pressure was exponential with an index similar to that at low pressure. The variation with pressure showed a striking reduction in the rate of increase with pressure in the high pressure region (> 105 lbf/in2). At high sliding speeds the traction coefficient was found to approach a common ‘ceiling’, which was largely independent of contact pressure, rolling speed and disc temperature. The ceiling appears to be a function of sliding speed only; it falls from 0.07 at 5 in/s to 0.04 at 60 in/s. Using the measurements of apparent viscosity obtained at low rolling speed, it has been shown conclusively that the limitation (or ceiling) in traction at intermediate sliding speeds cannot be explained by Crook's theory of a reduction in Newtonian viscosity by frictional heating. Alternative explanations based upon plastic shear of the lubricant when a critical shear stress is reached are much more consistent with the observations. But further work is necessary to elucidate fully the behaviour of E.H.L. films in sliding.

The magnitude of mechanical vibration and noise generated within machinery depends on damping. However, little is understood about how damping is distributed among the various possible damping sources. The results given in this paper isolate and quantify lubrication film damping between rolling discs and show that damping within the lubrication film contributes significantly to the total damping. A comparison of laboratory measurements with computer calculations shows that lubrication film damping is greatest under conditions of contact separation and thus indicates that fluid film damping is generated primarily by the squeeze film mechanism.

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