Micromechanics of oriented semi-crystalline polymers: from structure to properties*

The microstructure of semi-crystalline polymers, in terms of for example the degree of crystallinity, crystal type, size and orientation, may vary drastically depending on subtle details of the manner in which the polymer is shaped into the final product. For this material, often an oriented microstructure is formed, leading to anisotropic yield and failure kinetics.

To obtain a fundamental and quantitative understanding of how these anisotropic properties depend on the structure, a multiscale micromechanical model is developed. The modelling approach is based on a mean field framework, accounting for the crystalline phases, which are modelled by crystal plasticity and amorphous domains. The anisotropy of these amorphous regions is incorporated in the micromechanical model in the form of a pre-stretch of the amorphous network and anisotropic visco-plastic flow. Both aspects are found to be crucial for predicting the experimentally observed orientation dependence of the yield kinetics. With this combined experimental-modelling approach, new insight in the physical processes that govern the mechanics of semi-crystalline polymers are obtained.