The Rheological Behavior of the Lubricant in the Contact Zone of a Rolling Contact System

Abstract

A technique has been developed for studying the rheological behavior of the lubricating film within the contact zone of rolling contact bodies. This is accomplished by rolling two contacting disks together with a small amount of sliding superimposed on a relatively high rolling velocity. By measuring the traction, slip-rate, and the lubricant film thickness in the elastically deformed contact, a plot of traction versus mean shear rate can be made. Data are presented for polyphenyl ether. The data depend on the disk temperature and contact pressure qualitatively as would be expected, but the observed dependencies on shear rate and rolling speed require explanation. Analysis of possible local thermal disturbances on the lubricating film assuming a Newtonian lubricant model indicates that, for the experiments described here, temperature changes only partially explain the observed nonlinear variations of traction with shear rate, and fall far short in accounting for variations with rolling speed. A study assuming isothermal conditions and a Ree-Eyring lubricant model provides a traction theory which is flexible enough to fit the variations with shear rate, if certain parameters have advantageous values, but which appears only partially able to correlate the variations with rolling speed. Thus additional analyses which consider, say, both non-Newtonian and thermal effects or perhaps other entities are necessary for interpreting the data.