High Pressure Viscosity and Shear Response of Oil using the Rotating Optical Micro-Viscometer

An optical impact micro-viscometer incorporating a rotational capability has been used to study the high pressure flow characteristics of a petroleum based lubricant, LVI 260. The rotation enables a wider range of shear rates to be investigated when compared to the basic impact technique. Accuracy has been enhanced by employing discrimination of the local intensity of the interference fringe images, measurements of which are used as a basis for the determination of true shear stress and true shear rate values. Oil trapped in the conjunction between a spherical elastic striker after impact with an elastic plane is subjected to simultaneous radial and circumferential shearing. Flow in the radial direction under a pressure gradient is affected by the rotational motion of the striker relative to the plane and the shape of the film varies with time. The oil was tested with five different rotational speeds. It exhibited non-Newtonian behaviour and a limiting shear stress. The effect of the rotation on the radial flow is to increase the apparent shear rate at the surfaces and to reduce the apparent viscosity. © 1995 Elsevier Science B.V. All rights reserved.