Physical aging of epoxy networks after quenching and/or plastic cycling

Shear experiments were performed on epoxy network specimens aged at different temperatures and strain rates. The experiments showed an increase of yield stress, σ_y, versus the aging time in the glassy state. Two aging regimes, with a fast and slow kinetics, were exhibited in the case of temperatures between glass transition temperature, T_g, and T_g - 10°C. Other experiments were carried out to analyze the evolution of the yield stress for samples which were subjected to a prior plastic cycle, i.e., plastically deformed and then returned to zero strain. The comparison of cycled to non-cycled samples showed that the yield stress evolves similarly in both cases. However, the yield stress of cycled samples was always lower than that measured for the non-cycled specimens.