Modeling and simulation of stimuli-responsive viscoelastic polymers

The development of a physics-based approach and of a numerical model for the study of the mechanical behavior of advanced polymeric materials is motivated by several real-world applications. The description of the energy state of polymeric materials through their network’s chains configuration allows to model the problem, by accounting for the main involved mechanisms (such as rate-dependence, damage, swelling, etc.) and is suitable for developing a continuous approach, readily usable for the Finite Element implementation. The models proposed in the literature already present singularly some of the above mentioned features, nevertheless a comprehensive and physics-based approach is particularly desired for the development of new polymer-like materials and for the so-called advanced «responsive polymers». The aim of this thesis is to develop a comprehensive theoretical formulation, deeply rooted in the physics of the involved phenomena, and also its Finite Element implementation, for the simulation of real problems requiring to determine quantitatively the mechanical response of such a class of materials. Particular attention has been paid to the rate-dependent response of polymers, as well as to the chains failure (damage mechanism); the mixing with a fluid phase inducing the swelling of the material and the presence of the so-called mechanophore molecules - inducing mechanical effects to the network - has also been taken into account. For each of the above listed features, a detailed explanation is provided and the proposed theoretical model is illustrated; moreover, numerical examples are provided in order to underline the effects of the involved physical parameters and to prove the reliability of the proposed solution. Subsequently, the Finite Element implementation of the proposed theoretical model is illustrated and some numerical parametric tests are illustrated. Finally, some real experimental cases are presented and the mechanical response is numerically simulated through the developed theory, implemented in a nonlinear Finite Element code.