A micro-mechanical approach to model thermal induced aging in elastomers

Abstract This paper presents a micro-mechanical approach to describe the effects of thermal induced aging on the constitutive behavior of aged elastomers for long-range timescales. In particular, this model focuses on the effects of thermal induced aging on the quasi-static mechanical response of elastomers and their inelastic responses such as Mullins effect and permanent set over time. The model describes the aging induced damage with respect to experimental studies on the process of chemical aging which suggests high detachment of original covalent bonds and formation of new bonds. Accordingly, in the course of aging, the strain energy of the polymer matrix is divided from two independent sources, (i) a decomposing original matrix cross-linked by a small number of strong original bonds, (ii) a newly formed matrix cross-linked by a high number of weak reformed bonds. Each network has its own damage mechanisms which are induced based on the applied deformation and time. The proposed mechanism satisfies the Clausius–Planck inequality and is thus physically feasible. The model is validated with respect to a comprehensive set of experimental data designed by Johlitz et al. [38]. to capture thermal induced aging effect on constitutive behavior of elastomers. Besides accuracy, the model is relatively simple and easy to fit. It requires ten material parameters, all with clear physical meaning, which can be identified from only one set of experiment.