Effects of cold rolling on the tensile response of glassy polymers: Experiments and modeling

Cold rolling can significantly affect the mechanical response of amorphous glassy polymers. Traditionally, uniaxial compression tests are commonly used to evaluate the mechanical response of oriented polymers. In contrast, the tensile response of predeformed polymers is still not well characterized since the specimens typically do not exhibit a homogenous deformation in the subsequent reloading process. To address this limitation, in this work we first perform cold rolling on poly(ethylene terephthalate)-glycol (PETG), an amorphous glassy polymer, followed by a subsequent reloading test in uniaxial tension mode. Based on the digital image correlation technique, we are able to extract the stress–strain relationship of rolled specimens. The influence of rolling ratio and direction on stress response is then obtained, which shows a significant increase of hardening response for specimens rolled in the length direction while much less pronounced strain hardening for polymers rolled in the width direction. The yield strength and strain softening also depend on the rolling conditions. We then apply a viscoplastic model to predict the above experiments. The results show that the model can capture the hardening response of cold rolled specimens, while it fails to describe the yield strength. This indicates that the constitutive model needs to be improved for the future study. Overall, our work can deepen the fundamental understanding on the effects of cold rolling on mechanical properties of amorphous glassy polymers.