Micromechanical modelling of rubbery networks: discrete and continuum approaches

Thesis

Many soft materials consist of rubbery networks of polymer chains held together by crosslinks. These materials can undergo large elastic deformations, making them attractive to engineering, biomedical and consumer applications. Their mechanical response is intimately linked to the architecture of the underlying network. Consequently, understanding and predicting their behaviour requires models that account for their microstructure. This thesis contributes to this goal through the development of a comprehensive micromechanical modelling framework that combines discrete network (DN) simulations with continuum theories, enabling systematic investigations of elasticity, failure, and chemical degradation in rubber-like materials. In elasticity, we use DN simulations to link network structure to macroscopic mechanical properties, identifying the distribution of initial chain end-to-end distances as a key factor. Using DN results as a reference, we further show that many of the underlying assumptions of continuum micromechanics models do not hold. In modelling failure, the DN model augmented with deterministic chain scission reveals that damage is a localised process significantly impacted by local microstructural heterogeneities. Our results also show that classical semi-analytical estimates cannot predict failure in DNs. In chemical degradation, our DN model combined with stochastic chain scission shows that force-biased chain cleavage accelerates degradation, a feature captured by the continuum model we proposed. However, DN simulations reveal additional effects that cannot be reproduced by the continuum model, such as anisotropic damage and more severe deterioration of elastic properties as scissions become increasingly force-biased. Altogether, this thesis gives fresh insights into the mechanics of rubbery networks, important for the development of constitutive theories with improved predictive capabilities.

Authors: Mangas Araujo, L

• DOI: 10.5287/ora-g7vg4eeye
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: elastomers; microsphere model; hydrogels; failure; structure–property relationships; rubber elasticity; kinetic monte carlo; mechanophore; mechanochemistry; rubbery networks
• Subjects: Soft Materials; Solid Mechanics; Computational Mechanics; Mechancial Engineering