A constitutive model for strain hardening behavior of predeformed amorphous polymers: Incorporating dissipative dynamics of molecular orientation

摘要

A series of uniaxial compression tests are performed on amorphous thermoplastics poly (ethylene terephthalate)-glycol (PETG). The stress response shows a dramatic change with temperature and strain rate, including the modulus, yield strength and strain hardening. The strain hardening behavior also shows a strong dependence on predeformation, representing as a less pronounced hardening response during the reloading process with increasing the predeformation temperature and decreasing the predeformation rate. This phenomenon cannot be described by the models assuming a temperature-dependent hardening modulus. In this work, we develop a thermodynamic consistent model, which employs a dissipative back-stress tensor for molecular orientation. With increasing temperature, a stronger relaxation occurs, resulting in less molecular orientation and hardening response. A numerical scheme is also constructed to determine the model parameters. Comparison with experiments shows that the model is able to reproduce all the main features of the stress response at various strain rates spanning the glass transition region. The model can also accurately capture the strain hardening response of polymers predeformed to a strain of 30% or 60% at various temperatures and rates. (C) 2019 Elsevier Ltd. All rights reserved.