It has long been established that in polymer melts and solutions the viscosity is a non-linear function of shear rate, the value falling from the ‘Newtonian’ or low-shear-rate limiting value as the shear rate is increased. Attempts to observe directly the non-Newtonian behaviour of simple liquids and lubricants in continuous shear at room temperature have met with little success, however, due principly to the considerable heat generated even in a very thin fluid film at the high shear rates required. Non-Newtonian effects have been observed in oil films under elastohydrodynamic conditions, where the fluid is subject to high pressures, and it has been deduced that these effects occur above a critical shear-stress level of between 1 and 100 MPa, depending on the pressure and the molecular weight of the liquid (Hirst and Moore, 1978).
KeywordsShear Stress Shear Rate Glass Transition Temperature Apparent Viscosity High Shear Rate
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- Plazek, D.J., 1968, J.Polymer Sci. A-2, 6: 621–638.Google Scholar