A viscoelastic-viscoplastic constitutive model and its finite element implementation of amorphous polymers

The amorphous polymers present remarkable temperature- and rate-dependent deformation behaviors. Based on a combination of the multiple relaxation viscoelastic-viscoplastic model and the three-element viscoelastic model, a constitutive model was constructed to describe the changes in mechanical properties of amorphous polymers from below to above glass transition temperature (θg). In this model, an exponential evolution equation of volume fraction was constructed to reflect the changes in glassy and rubbery phases at different temperatures. The proposed model was implemented into ABAQUS using the user-defined material subroutine (VUMAT). The strain-softening after yield and rate-dependent behaviors above and below θg were reasonably captured by the present model. Meanwhile, the creep and relaxation behaviors of the material were described. Finally, the processes of the tensile deformation of a dumbbell plate with a circular hole and the rate-dependent pressed film molding were simulated by the VUMAT. The results show that the implemented model can reasonably predict the structural responses of amorphous polymers.