Abstract
Time dependent small angle x-ray scattering was conducted on poly (methyl methacrylate) (PMMA) at constant strains to study the micromechanism of the stress relaxation phenomenon. The application of strain induced a rapid nucleation of submicrocracks with lens-like shape (over 1000 Å in diameter and about 600 Å in thickness), and the correlation between the increase in submicrocrack concentration and the stress relaxation process was clarified quantitatively. These results suggest that in brittle polymers such as PMMA, the formation of submicrocracks plays a decisive role in the stress relaxation phenomenon.