Description: In a Newtonian fluid the relation between the shear stress and the shear strain rate is linear with the constant of proportionality based on the coefficient of viscosity, which can be a function of only temperature. Many fluids of industrial interest are non-Newtonian: they exhibit flow properties that cannot be described by a constant viscosity. Instead, the relation between the shear stress and the shear strain rate is nonlinear. Some common non-Newtonian fluids include blood, paint, shampoo, and many molten polymer solutions. In a non-Newtonian fluid the relation between the shear stress and the shear strain rate is nonlinear. Non-Newtonian fluids can be classified as shear-thinning (or pseudoplastic)—when the apparent viscosity decreases with increasing shear rate—and shear-thickening (or dilatant)—when the viscosity increases with strain rate.

Abaqus/Explicit now supports the following models of nonlinear viscosity to describe non-Newtonian fluids: power law, Carreau-Yasuda, Cross, Herschel-Bulkey, Powell-Eyring, and Ellis-Meter. In addition to these models, other functional forms of the viscosity can be specified in tabular format or in user subroutine VUVISCOSITY. These models can be used to describe the deviatoric behavior of the equation of state models already available in Abaqus/Explicit.

The temperature dependence of the viscosity of many polymer materials of industrial interest obeys a time-temperature shift relationship, which is usually referred to as thermo-rheologically simple (TRS) temperature dependence. Abaqus/Explicit supports the following forms of the shift function to define the temperature dependence of the non-Newtonian viscosity: the Williams-Landell-Ferry (WLF) form, the Arrhenius form, and user-defined forms via user subroutine VUTRS.