Forough Sohrabizadeh

Grade:  Master

Thesis Title:

Implementation of a Constitutive Model for Thermoplastic Polymers Coupling Viscoplasticity, Thermal effect and Damage

Year: Sept. 2019 - Sept. 2022.

Abstract:

The mechanical response of polymers depends significantly on the strain rate and the temperature. The present study is aimed to provide a thermomechanical constitutive model derived based on viscoplasticity and continuum damage mechanics, to simulate the mechanical behavior of the thermoplastic polymers. First, the “Eindhoven Glassy Polymer (EGP)” constitutive model is developed by considering the thermal effects within the framework of continuum damage mechanics. Second, the modified EGP model is evaluated using the mechanical properties of the polymer and experimental results in the literature. For this purpose, the modified EGP model is implemented in MATLAB as well as Abaqus through a UMAT subroutine. The predictions of the nonlinear elastic, viscoplastic, and damage behaviors of polymer are then compared with experimentally measured values, within different loading conditions, including tension and compression tests with various strain rates and temperatures, when a single element with one integration point is used. In addition, the numerical results of damage progression caused by consecutive reduction of elastic modulus in loading-unloading cycles are compared with experimental ones. Finally, three-dimensional simulations of a tensile test (with dumbbell-shaped specimens), as well as a uniaxial compression test of a cylinder, are conducted, and the model is validated by comparing the numerical and experimental results. These results reveal the excellent accuracy of the model for predicting the damage progression caused by accumulated plastic strain at any specified strain rate and temperature.

Keywords:  Thermoplastic polymers, Continuum damage mechanics, Viscoelasticity, Viscoplasticity, Eindhoven glassy polymer (EGP) model.