Modeling the irreversible time-dependent rheological behavior of complex materials

A number of relevant materials undergo irreversible processes of either a chemical or physical nature and present a complex transient rheological behavior, which cannot be properly described by existing constitutive models. Two important examples are cement slurries and waxy crude oils. Cement slurries undergo solidification as a result of hydration reactions, while waxy crude oils are subjected to irreversible shear degradation under flow at low temperatures. In this talk, a recently proposed time-dependent constitutive model, which takes into account elasticity, viscoplasticity, thixotropy, and irreversible effects, is discussed in detail. The model is based on a single scalar structure parameter and composed of one differential equation describing the evolution of the material's structure, one equation relating the shear rate to the shear stress, and one equation describing the progress of the irreversible process. The predictions of the model are compared to rheometric experiments performed with a cement slurry and a gelled waxy crude oil and the parameters of the model are estimated from experimental data. Interesting phenomena are observed and described by the model, including bifurcation, shear banding, stress overshoots, effects of chemical reactions, and irreversible shear degradation. It is argued that the ideas employed in the present model can be used to incorporate irreversible effects into other thixotropic models, giving rise to the possibility of describing the transient rheological behavior of complex materials in an unprecedented fashion.

Publication year:2019

Accessibility:Open