Implicit type constitutive relations for elastic solids and their use in the development of mathematical models for viscoelastic fluids

TL;DR

This paper introduces a novel approach to modeling viscoelastic fluids using implicit constitutive relations inspired by recent developments in elastic solid models, emphasizing thermodynamic consistency and generalizability.

Contribution

It applies implicit constitutive relations, particularly stress-dependent left Cauchy-Green tensors, to develop new mathematical models for viscoelastic fluids, offering a flexible alternative to classical methods.

Findings

Demonstrates the use of Gibbs free energy in model formulation

Shows compatibility with Giesekus/Oldroyd-B models

Provides a pathway for modeling complex viscoelastic fluids

Abstract

Viscoelastic fluids are non-Newtonian fluids that exhibit both "viscous" and "elastic" characteristics in virtue of mechanisms to store energy and produce entropy. Usually the energy storage properties of such fluids are modelled using the same concepts as in the classical theory of nonlinear solids. Recently new models for elastic solids have been successfully developed by appealing to implicit constitutive relations, and these new models offer a different perspective to the old topic of elastic response of materials. In particular, a sub-class of implicit constitutive relations, namely relations wherein the left Cauchy-Green tensor is expressed as a function of stress is of interest. We show how to use this new perspective it the development of mathematical models for viscoelastic fluids, and we provide a discussion of the thermodynamic underpinnings of such models. We focus on the use of Gibbs free energy instead of the Helmholtz free energy, and using the standard Giesekus/Oldroyd-B models, we show how the alternative approach works in the case of well-known models. The proposed approach is straightforward to generalise to more complex setting wherein the classical approach might be impractical of even inapplicable.