Experimental and modeling study of the viscoelastic-viscoplastic deformation behavior of amorphous polymers over a wide temperature range

The deformation behavior of amorphous polymers in the post-yield region is viscoelastic-viscoplastic (VE-VP) as it exhibits both viscoelastic and viscoplastic characteristics. However, a systematic experimental and modeling study for it is lacking. In this paper, the VE-VP deformation behavior of an amorphous polymer was experi-mentally investigated over a wide temperature range. It was found that some of the observed deformation be-haviors cannot be reasonably explained by the common assumptions of the thermally-activated segmental motions and the formation of a topologically-entangled rubbery network. With the assumption that there is a glassy network formed from weak linkages in the polymer, the observed deformation behaviors over a wide temperature range can be well explained by considering the stretch and relaxation of the glassy network. The glassy network assumption was first proposed by one of our coauthors and employed for modeling the VE-VP deformation behavior of amorphous polymers at room temperature. In this paper, the glassy network assump-tion was further examined at different temperatures and employed to establish a constitutive model for simu-lating the VE-VP deformation behavior of amorphous polymers over a wide temperature range. The model was validated by corroboration with experiments. It was demonstrated that a constitutive model based on the glassy network assumption is capable of representing the loading, strain recovery, and stress relaxation behaviors simultaneously, in contrast to most of the existing constitutive models. Hence, this work not only proposes a reasonable physical picture for understanding but also provides a robust constitutive model for simulating the VE-VP deformation behavior of amorphous polymers and its temperature dependence.