Framework for deformation induced anisotropy in glassy polymers

In this paper a constitutive model for glassy polymers is developed. Glassy polymers consist of a number of polymer chains that at a microscopic level form a network. If the distribution of the polymer chains shows some preferred direction, the mechanical response at a global macroscopic level will be anisotropic. To incorporate the orientational distribution of the polymer chains, a homogenization procedure involving a chain orientation distribution function was undertaken. When polymers are exposed to external loading, the chains at the microscopic level orient in a certain manner, leading to an evolution of the macroscopic anisotropic properties. This phenomenon was modeled by use of evolution equations for the chains at a microscopic level and are then—by using the orientation distribution function—transformed to the macroscopic level. The theories involved are developed in a large strain setting in which a multiplicative split of the deformation gradient for the elastic-viscoplastic response is adopted. Various numerical experiments were conducted to evaluate the model that was developed.