A thermodynamically-based constitutive model for thermoplastic polymers coupling viscoelasticity, viscoplasticity and ductile damage

• A constitutive model for isotropic homogeneous thermoplastic polymers (TPs).
• Coupling viscoelasticity viscoplasticity and ductile damage.
• The viscoplastic response combines isotropic and nonlinear kinematic hardenings.
• Ductile damage evolution is linked to that of viscoplastic strains.
• Numerical predictions are validated against experiments on different TPs.

A thermodynamically-based constitutive model is proposed for isotropic homogeneous thermoplastic polymers under arbitrary multiaxial and non-monotonic loadings. The model couples viscoelasticity, viscoplasticity and ductile damage. The total strain is decomposed into viscoelastic and viscoplastic parts. The undamaged Cauchy stress depends on the history of viscoelastic strains through Boltzmann’s integral. Viscoelastic bulk and relaxation moduli follow general Prony series. The viscoplastic response combines isotropic and nonlinear kinematic hardenings. Ductile damage evolution is linked to that of viscoplastic strains. Constitutive equations are developed within the framework of thermodynamics of irreversible processes. Numerical predictions are validated against experimental tests on different polymers under various loadings.