Empirical constitutive equations - from monotonous to non-monotonous flow curves

摘要

A number of parameters appearing in the 'classical' empirical constitutive equations (rheological equations of state) describing viscosity behaviour of non-Newtonian fluids usually oscillate between two (power-law or Bingham model) and five (as e.g. Carreau-Yasuda model). With the onset of new Theologically more complex materials exhibiting non-monotonous behaviour of flow curves this range (2-5) is no longer tenable and more additional parameters are required for a proper description of the flow curves. The present contribution summarises basic classical monotonous models, and analyses a non-monotonous problem for the cases: shear viscosity vs. shear rate and shear viscosity vs. shear stress.