High pressure rheology of lubricants using the rotating optical micro-viscometer

An optical impact micro-viscometer incorporating a rotational capability has been used to study high pressure flow characteristics of the tested lubricant: Polyphenyl ether 5P4E which has been used in many experiments in lubricant rheology investigation by various researchers. Accuracy of the impact technique is enhanced by employing discrimination of the local intensity of interference fringe images. Knowing the changing of the true shape of dimple and pressure distribution leads flow in the radial direction under a pressure gradient to be obtained and then the true shear stress and shear rate are determined by the experimental analysis. Variations of the shear stress with shear rate at different pressures provide further evidence of the existence of a limiting shear stress. The results also show that the limiting shear stress increases linearly with pressure.