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, sigma(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 degrees 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.