  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.
