THE HIGH-PRESSURE HIGH SHEAR-STRESS RHEOLOGY OF LIQUID LUBRICANTS

A limiting shear stress model of liquid lubricant shear rheology is offered which accurately represents all available primary data. The model is of the nonlinear Maxwell type with shear modulus taken into the time derivative and broadening of the viscous-plastic transition with pressure. Property relations for viscosity, limiting stress and shear modulus are refined for a polyphenyl ether in particular. The model, with simplifying assumptions, is compared with disk machine results. This model, with change of yield criterion, may be applicable to some shear thinning liquids at low pressure. Limiting shear stress varies with pressure in the same manner as the ultimate shear strength of solid polymers.