A Quantitative Determination of Minimum Film Thickness in Elastohydrodynamic Circular Contacts

Wassim Habchi,Philippe Vergne

doi:10.1007/s11249-021-01512-z

Abstract

The current work presents a quantitative approach for the prediction of minimum film thickness in elastohydrodynamic-lubricated (EHL) circular contacts. In contrast to central film thickness, minimum film thickness can be hard to accurately measure, and it is usually poorly estimated by classical film thickness formulae. For this, an advanced finite element-based numerical model is used to quantify variations of the central-to-minimum film thickness ratio with operating conditions, under isothermal Newtonian pure-rolling conditions. An ensuing analytical expression is then derived and compared to classical film thickness formulae and to more recent similar expressions. The comparisons confirmed the inability of the former to predict the minimum film thickness, and the limitations of the latter, which tend to overestimate the ratio of central-to-minimum film thickness. The proposed approach is validated against numerical results as well as experimental data from the literature, revealing an excellent agreement with both. This framework can be used to predict minimum film thickness in circular elastohydrodynamic contacts from knowledge of central film thickness, which can be either accurately measured or rather well estimated using classical film thickness formulae.

Highlights

Introduction and backgroundMinimum film thickness in circular elastohydrodynamic (EHD) contacts has been significantly less studied than central film thickness and the mechanisms behind the former certainly less understood.Experimentally, rational explanations can be found for this contrasting situation
It is interesting to consider the variations of the central to minimum thickness ratio because i) it has the advantage of not being dependent on the non-dimensioning convention and ii) it provides a quick way of correctly estimating the minimum thickness from knowledge of a central thickness value that is easier to obtain experimentally or analytically, using film thickness formulae
This work presents a quantitative analysis of the prediction of minimum film thickness in elastohydrodynamic circular contacts

Summary

Quantitative minimum film thickness predictions

Brief description of the numerical model Quantitative minimum film thickness predictions are carried out in this work using the full-system finite element approach [24]. It consists in a simultaneous resolution of all governing equations of the isothermal Newtonian EHL problem. The last equation ensures that the correct external load is applied to the contact, by balancing it with the integral of the pressure field generated within the lubricating film. This is achieved through a monitoring of the rigid-body separation of the contacting solids. The interested reader is referred to [24]

Conditions

Comparisons and validation

Summary