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.

Friction-induced vibration has been studied in a system consisting of an elastically suspended, damped slider which is loaded against a surface moving at a constant velocity. Exact analysis reveals a critical velocity which limits the incidence of vibration. The critical velocity depends on damping, load, stiffness, and friction characteristics which vary with time and velocity. Approximations in the theory yield an amplitude-velocity equation and another critical velocity relationship. Reasonable agreement is found to exist between the exact and approximate theories for critical velocity. Experimental results for several systems illustrate amplitude-velocity relationships and the existence of critical velocities. The correlation between the experimental results and the approximate theory indicates that the analytical method could be used to predict the vibration behavior of actual systems.

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A variable magnetic reluctance technique has been developed and used to measure the thickness of oil films between smooth rolling discs under various conditions of load, speed, and temperature using two different lubricants. In repeating the experimental conditions of other workers who measured the capacitance of oil films between discs, good correlation is demonstrated between the results of capacitance and reluctance measurements. Since it is unlikely that the two methods suffer from the same uncertainties this correlation can be considered as a recommendation to future users of either method. The main predictions of the Dowson and Higginson theory are verified by the experimental results, apart from a discrepancy in the dependence of h0 upon the dimensionless parameter U0·7 when thick films are developed. In this region observations are qualitatively more in keeping with the thermal theory of Cheng An application of the reluctance technique to the measurements of oil film thickness in gearing is proposed.