Micro-mechanical modelling of anisotropic behaviour of oriented semi-crystalline polymers

Journal article, 2019

Some manufacturing processes of polymeric materials, such as injection moulding or film blowing, cause the final product to be highly anisotropic. In this study, the mechanical behaviour of drawn Polyethylene (PE) tapes is investigated via micro-mechanical modelling. An elastoviscoplastic micro-mechanical model, developed within the framework of the so-called composite inclusion model, is presented to capture the anisotropic behaviour of oriented semi-crystalline Polyethylene. Two different phases namely, amorphous and crystalline (both described by elasto-viscoplastic constitutive models), are considered at the micro-structural level. The initial oriented crystallographic structure of the drawn tapes is taken into account. It was previously shown  that by only considering the oriented crystallographic structure, it is not possible to capture the macroscopic anisotropic behaviour of drawn tapes. The main contribution of this study is the development of an anisotropic model for the amorphous phase within the micro-mechanical framework. An EGP (Eindhoven Glassy Polymer) based model including different sources of anisotropy namely, anisotropic elasticity, internal stress in the elastic network and anisotropic viscoplasticity, is developed for the amorphous phase and incorporated into the micro-mechanical model. Comparisons against experimental results reveal remarkable improvements of the model predictions (compared to micro-mechanical model predictions including isotropic amorphous domains) and thus the signicance of the amorphous phase anisotropy on the overall behavior of drawn PE tapes.