The High Pressure Impact Microviscometer

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Abstract
The apparent viscosities of liquid lubricants at high pressures measured using an impact viscometer have been reported in previous research to be time-dependent. In the work reported here, the impact microviscometer technique has been further developed to give measurements of true shear stress and true shear rate, allowing studies of the rheological behavior of liquid without any initial assumptions about flow properties. The temporal variation of viscosity is shown to be a shear-thinning effect. Under high pressures, the lubricants examined exhibited non-Newtonian behavior and a limiting shear stress. Their characteristics may be described by a shear-thinning power law model. A new viscosity-pressure relationship has been developed, which takes the form of a Barus Equation at low pressures and reaches a limiting viscosity at high pressures.

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