An Approach to Determining Non-Linear Lubricant Viscoelastic Properties

By using empirical and semi-empirical relationships previously reported in the literature, non-linear viscoelastic properties of a number of lubricants have been determined from their linear viscoelastic behaviour, as measured by an oscillatory rheometer. Similarly to polymeric viscosity index improved (VII) lubricants, non-polymeric mineral blends were also shown to display viscoelastic behaviour.

A general equation is suggested that allows the first normal stress difference which characterises the viscoelastic behaviour of lubricants to be expressed as a function of the shear viscosity.