Application of a large deformation nonlinear-viscoelastic viscoplastic viscodamage constitutive model to polymers and their composites

Based on the effective stress concept in continuum damage mechanics and the large deformation theory, a viscodamage model, coupled with Schapery-type nonlinear-viscoelasticity and Perzyna-type viscoplasticity constitutive models, is used in order to simulate and predict the inelastic and time-dependent damage behavior of polymeric materials and their composites. The thermo-viscodamage model is presented as a function of temperature, total effective strain, damage history, and a damage-driving force expressed in terms of the deviatoric stress invariants in the undamaged configuration. This expression for the damage force allows for the distinction between the influence of compression and extension loading conditions on damage nucleation and growth. Also, the ability of the constitutive model for predicting the tertiary creep, which shows the nonlinear behavior of polymers during damage growth and nucleation, is presented. The numerical algorithm for integrating the coupled constitutive model is implemented in the finite element software Abaqus via the user-material subroutine UMAT. The model capability in predicting the nonlinear-viscoelastic, viscoplastic, and damage behavior of polymers is demonstrated through comparison of model predictions with experimental measurements in different loading conditions including creep tests and constant strain rate tests over a range of stress levels, strain rates, and temperatures. Also, a general thermodynamic framework for deriving a coupled viscoelastic–viscoplastic–viscodamage constitutive model is presented.