Anisotropic structural evolution in poly(methyl methacrylate) aged under inelastic strain

Cylindrical specimens of fully annealed poly(methyl methacrylate) (PMMA) were simply sheared by twisting, up to an inelastic strain and left under the sheared condition for various periods. Subsequently, the specimens were sheared by twisting in the same direction or opposite to that of the inelastic pre-strain. The elastic modulus and yield stress for the aged specimens evaluated by twisting them in the same direction with the pre-strain increased monotonously with aging time, and their values were significantly higher than those of fully annealed specimens. Yet, when the specimens were twisted in the opposite direction to the pre-strain, their modulus and yield stress decreased with increasing time of aging at short aging time, and subsequently increased at long aging times. These results revealed a specific anisotropic structural evolution in PMMA aged under inelastic strain.