Semi‐crystalline polymers at finite strains: A thermo‐coupled constitutive model for varying degrees of crystallinity and temperatures

Abstract

AbstractThermoplastics are gaining interest for various industrial applications, since they can be widely used for thermoforming and injection moulding processes due to their thermostable material behavior. In combination with the material's low density and high strength to mass ratio, they are especially of interest in times where an improved environmental balance is more and more important. Hence, why they are for example frequently used in the automotive industry to reduce the weight of automotive components.Semi‐crystalline polymers as a subcategory of thermoplastics, partly crystallize after cool‐down from the molten state. During the thermoforming process, they are subjected to large deformations as well as thermal loads and show strong thermo‐mechanical coupling effects in addition to the influence of the evolution of the crystalline phase on the macroscopic material behavior. Therefore, computational models are needed to predict the complex material response reliably and minimize production errors.This work presents a thermomechanically consistent material formulation at finite strains. In order to account for the highly nonlinear material behavior, elasto‐plastic and visco‐elastic contributions are combined in the Helmholtz free energy and a dependency on temperature as well as the degree of cristallinity (DOC) is incorporated. Special attention is devoted to the choice of yield function and hardening behavior.A comparison of the simulation results to experiments at varying degrees of crystallinity and temperatures is presented to review the changes in the formulation. Therefore a special blending technique is used to ensure stable crystallinity conditions in the test samples.