Effect of large deformation on the linear viscoelastic response of a glassy polymer

The state of a glassy material changes as a result of a loading-unloading cycle, provided the loading is sufficiently large to take the material past yield. This is evidenced by the well-known observation that the DSC trace upon heating following a load-unload cyclel exhibits a broad exothermic sub-Tg peak not present in a reference material not subjected to deformation. We now report that the loading-unloading cycle also significantly changes the viscoelastic spectrum of a PMMA-PBMA co-polymer deformed at Tg-35°C. The large deformation has been performed in uniaxial extension and the frequency dependent linear viscoelastic behavior has been obtained in shear. The implications of the observed effect of deformation on the viscoelastic spectrum for fundamental understanding of the glassy state as well as the constitutive modeling of glassy polymers will be discussed.