Analysis of Deformation Mechanism with Re-stretching of Stretched Polymer Film

The re-orientation of the molecular chain axis under plastic deformation was investigated for the off-axis angle stretching of biaxially stretched poly (ethylene terephthalate) (PET) and isotactic polypropylene (it-PP) films using a linear representation of the molecular chain vectors and the extinction direction. The strain changes caused by the re-stretching were further analyzed using a local coordinate system. The re-stretching deformation of PET and it-PP films does not lead to a change in thickness and is caused by a pure shear stress in the plane parallel to the restretching and width directions. This same tendency was observed in HDPE film.