Understanding decay functions and their contribution in modeling of thermal-induced aging of cross-linked polymers

Abstract Different decay functions to describe the effects of homogeneous thermo-oxidative aging on the constitutive behavior of aged rubber-like materials for longer timescales is presented. Then, a suitable decay function has been introduced and implemented into a micro-mechanical model to study the effects of homogeneous thermo-oxidative aging on the quasi-static mechanical response of rubber-like materials 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 decomposition of original network and creation of a new one. Accordingly, in the course of aging, the strain energy of the polymer matrix is divided from two independent sources, (i) a decomposing original matrix (ii) a newly formed matrix. The model is validated with respect to a comprehensive set of own experimental data as well as data available in literature that were designed to capture thermal induced aging effects of constitutive behavior of polymers. Besides accuracy, the model is relatively simple and easy to fit.