Quantitative elastohydrodynamic film thickness of mechanically degraded oil

The low-shear viscosities of new oil and used (degraded) oil were measured to moderately high pressure. Shear-thinning flow curves were generated over a range of shear stress important to EHL film forming. Mechanical shear degradation only affected the viscosity at low shear stress while the viscosity at high stress remained unchanged. A recently published film thickness equation for double-Newtonian shear-thinning, employing the measured rheology, predicts the surprising result that thickness of the EHL film was not changed by the degradation although the low-shear viscosities were reduced substantially. Colorimetric measurements of the film thicknesses validate the predictions. Concern over the permanent loss in viscosity due to degradation may be misplaced when addressing EHL films.

► Shear-dependent viscosity of new oil and degraded oil was measured under pressure.
► Shear degradation only affected the viscosity at low shear stress, not at high.
► A published formula predicts EHL film thickness was not changed by the degradation.
► Colorimetric measurements of the film thicknesses validate the predictions.
► Concern over permanent viscosity loss due to degradation may be misplaced in EHL.