On the localization of plastic flow in glassy polymers

The problem of strain localization in a tensile specimen is revisited in three dimensions for materials exhibiting rate-dependent behavior typical of amorphous glassy polymers. Finite element analysis is used to this end, employing a macromolecular constitutive model. Emphasis is laid on the effects of stress state on the onset and evolution of localization. Comparisons with previous analytical and numerical treatments for axisymmetric and plane-strain loadings, respectively, are made in terms of the nature of neck transition fronts and global response. New results are then obtained for three-dimensional specimens with a focus on specimen thickness effects. In particular, the interaction of one or multiple propagating necks with shear bands is studied in connection with global response and surface smoothness of the cold-drawn polymer. In thin specimens, it is shown that the kinetics of neck propagation is markedly different from what had been previously predicted. In thick specimens, analyzed in the plane strain limit, material softening is shown to affect the response and surface finish, in qualitative agreement with experimental reports but in contrast with previous simulations.

► We analyze strain localization in polymers under tensile loading.
► We examine changes in specimen thickness and material softening.
►  Decreasing thickness will increase propensity for shear banding if softening is mild.
► Increasing softening will trigger shear bands irrespective of thickness.
► Formation of multiple propagating necks affects quality of surface finish.