Delineating nature of stress responses during ductile uniaxial extension of polycarbonate glass

Abstract

We carry out simultaneous mechanical and IR-thermal-imaging-based temperature measurements of tensile extension on untreated, milled (mechanically “rejuvenated”) and melt-stretched bisphenol A-polycarbonate (PC). The extension is found to cause significant buildup of both excess internal energy u2 and plastic dissipation. The magnitude of u2 is one to two orders of magnitude higher than the energy involved in rubbery elastic deformation. While the ratio of u2 to the mechanical work w decreases with increasing rate of extension for untreated PC, milled PC is found to be more dissipative at lower rates. Homogeneous extension of melt-stretched PC in the post-yield regime including strain hardening behavior reveals largely non-dissipative responses, emphasizing the plastic deformation of glassy polymer may not be fully dissipative. The experimental results clearly indicate that a significant component of stress can be intrasegmental leading to the observed buildup of internal energy by distortions of covalent bonds. The glassy polymer physics at the chain level complements the more familiar idea of inter-segmental dissipation as the dominant event during plastic deformation.