On the Mechanical Behavior of Entrained Materials in Concentrated Contacts

Abstract

A quantitative discussion is presented that suggests the solid-like mechanical properties of liquids control the low sliding speed tractive behaviors of highly loaded elastohydrodynamic contacts. A new method to calculate transient density and viscosity response of a material is proposed. This response model is used in a simulation of isothermal-pure rolling line contacts with load, speed, and material parameters similar to those utilized by Trachman, et al. It is shown, using accepted linear viscoelastic arguments, that solid-like behavior is obtained except at low load and speed conditions. The tensile and shear mechanical properties of grossly deformed and compressed solids as a function of hydrostatic pressure and shear rate are reviewed: it is shown that at low sliding speed, shear modulus and yield stress mechanical properties of lubricants in highly loaded, high speed elastohydrodynamic contacts have the same functional dependencies. A viscoelastic model of the time dependent shear stress transmission capability of a liquid is proposed that predicts the inverse dependence of effective viscosity on rolling speed. Estimates of the shear stress transmitted under isothermal conditions are high and it is proposed that inclusion of irreversible compressional heating effects will improve the predictions but will allow retention of the solid-like character of the material.