Abstract
We measured the complex shear modulus, G*=G'+iG", of glassy poly (methyl methacrylate) (PMMA) during its stop-start stretching processes to investigate the relationship between change in mechanical properties due to aging under a finite strain and relaxation of strain-induced nonequilibrium structures. The yield stress as well as the tensile modulus at the beginning of the re-stretching increased with aging time beyond their initial values in the undeformed state, showing the effect of strain aging appeared in these quantities. The storage shear modulus G' also increased with time elapsed in the stress relaxation period. The development of tensile modulus was observed to be much faster than that of the storage shear modulus. As time scales used for the dynamic measurement is much shorter than that for the macroscopic straining, evolution of tensile modulus due to aging under a finite strain is not ascribable only to the relaxation of nonequilibrium glassy structures induced by large deformation.
