Fractional Film Defect as a Measure of Lubricant Effectiveness

Abstract

This paper presents a mathematical model for predicting a critical temperature in boundary lubricated contacts, A starting point for the model is the concept of a fractional film defect which represents, in a physical sense, a ratio of the number of sites on the contact surface unoccupied by lubricant molecules to the total available number of sites on that surface. It can also be regarded as a measure of the probability of two bare asperity peaks coming into contact and initiating the process of lubricant film failure. It is postulated then that the critical point on the fractional film defect curve, corresponding to the critical temperature, is where the change in curvature first become a maximum.

It is shown that the critical temperature can be predicted reasonably accurately and that the predictions of the model compare well with published experimental data.