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Physics-based constitutive equation for thermochemically aged elastomers based on crosslink density evolution

Maryam Shakiba and Aimane Najmeddine

Vol. 17 (2022), No. 3, 229–246
Abstract

This paper presents a physics-based constitutive equation to predict the mechanical responses of thermochemically aged elastomers. High-temperature oxidation in elastomers is a complex phenomenon. The macromolecular network of elastomers’ microstructures undergoes chain scission and crosslinking under high temperature and oxygen saturation conditions. In this work, we modify the network stiffness and the chain extensibility in the well-known Arruda–Boyce constitutive equation to incorporate network changes in the microstructures of elastomers during thermochemical aging. In particular, the effects of network evolution due to aging in changing the shear modulus and the number of Kuhn monomers are considered. The modification is based on chemical characterization tests measuring the crosslink density evolution. The developed constitutive equation predicts the mechanical responses of thermochemically aged elastomers independently of any mechanical tests on aged samples. The proposed constitutive equation is validated with respect to a comprehensive set of experimental data available in the literature that were designed to capture thermochemical aging effects in elastomers. The comparison showed that the developed constitutive equation can accurately predict the tensile tests conducted on aged samples based on crosslink density evolution input. The obtained constitutive equation is physics-based, simple, and includes minimal material parameters.

Keywords
thermochemical aging, crosslink density, large deformation, elastomer aging, oxidation
Milestones
Received: 15 October 2021
Revised: 4 January 2022
Accepted: 28 January 2022
Published: 22 January 2023
Authors
Maryam Shakiba
Department Civil and Environmental Engineering
Virginia Tech
Blacksburg, VA
United States
Macromolecules Innovation Institute (MII)
Virginia Tech
United States
Aimane Najmeddine
Department Civil and Environmental Engineering
Virginia Tech
Blacksburg, VA
United States