Soutenance de thèse Augusto EMMEL SELKE – “Variational models of thermo-viscoelastic damage at finite strains: local and nonlocal approaches applied to polymer behavior”

RÉSUMÉ:

The development of material models dedicated to the description of polymer behavior has long been and remains a subject of interest, as their use grows in many realms of application. Their microstructural features are responsible for challenges that must be addressed for accurate constitutive modeling, including thermomechanical coupling, large strain phenomena, viscosity effects and particular degradation behavior, among others.

This thesis aims to tackle this problem within the framework of variationally-formulated constitutive modeling of dissipative phenomena. This type of energy-based approach allows for an efficient treatment of multiphysics coupling, while accounting for dissipation in a thermodynamically sound manner.

Formulations for a wide range of thermo-viscoelasticity phenomena in finite strains are presented, with an emphasis on the coupling mechanisms and on the chosen parametrization of all dissipation sources.

Similar variational approaches can be extended to the problem of degrading material properties, an essentially dissipative issue. With the microstructural features of polymers in mind, a formulation for a class of coupled thermo-viscoelastic damage is then proposed. The model hinges on hypotheses relating all physical phenomena to the same damaging function, leading to a naturally separable structure between an equivalent undamaged state where thermo-viscoelasticity is solved and a damage evolution problem.

Although capable of encompassing various aspects of polymer-like material behavior, the proposed models remain subject to the limitations of local damage modeling, namely, spurious localization. The recent Thick Level Set approach to nonlocal damage, providing an efficient level-set based bridge between damage and fracture, is explored as a way to circumvent this issue.

JURY:

Rapporteurs :

Philippe DEVLOO, Professeur, Universidade Estadual de Campinas – UNICAMP
Dominique EYHERAMENDY, Professeur, Centrale Marseille

Examinateurs :

Eduardo DE SOUZA NETO, Professeur, Swansea University
Ludovic NOELS, Professeur, Université de Liège

Directeur de thèse :

Laurent STAINIER, Professeur, Centrale Nantes

Co-directeur de thèse :

Eduardo Alberto FANCELLO, Professeur, Universidade Federal de Santa Catarina – UFSC