Effect of aging on the reinforcement efficiency of carbon nanotubes in epoxy matrix

TL;DR

This study investigates how aging affects the reinforcement efficiency of carbon nanotubes in epoxy composites under cyclic tensile loading, revealing that aging diminishes reinforcement effectiveness especially at higher strains.

Contribution

It provides new insights into the impact of aging on CNT reinforcement efficiency in epoxy, highlighting the influence of cyclic strain and thermal post-curing.

Findings

Reinforcement efficiency follows a mean field mixture rule.

Aging reduces reinforcement efficiency, especially at higher strains.

Elastic modulus decreases with increasing cyclic maximum strain, similar to the Payne effect.

Abstract

The reinforcement efficiency of carbon nanotubes (CNTs) in epoxy matrix was investigated in the elastic regime. Cyclic uniaxial tensile tests were performed at constant strain amplitude and increasing maximum strain. Post-curing of the epoxy and its composite at a temperature close to the glass transition temperature allowed us to explore the effect of aging on the reinforcement efficiency of CNT. It is found that the reinforcement efficiency is compatible with a mean field mixture rule of stress reinforcement by random inclusions. It also diminishes when the maximum strain increased and this effect is amplified by aging. The decrease of elastic modulus with increasing cyclic maximum strain is quite similar to the one observed for filled elastomers with increasing strain amplitude, a phenomenon often referred as the Payne effect.