Sequential biaxial stretching of polycarbonate‐films for characterization of strain‐induced anisotropy

Abstract

Amorphous polymers consist of polymer‐chains whose alignment is a well‐known microstructural evolution effect due to stretching of polymers. This so‐called morphology‐development is investigated in the literature, where for thin films simultaneous biaxial stretching is distinguished from sequential biaxial stretching. Both procedures have a strong influence on the macroscopic properties of an initially isotropic material, resulting in induced anisotropy. This work concentrates on sequential biaxial stretching of cold forming realized by tensile testing. To this end, thin polycarbonate films are examined in 2 loading phases: In the first preloading phase anisotropy is induced and in the consecutive second reloading phase, the material direction is varied. Optical measurements support the analysis of highly inhomogenous strain fields. As a main result two‐dimensional strain contours are obtained from test data which will set a basis for parameter identification of constitutive equations for strain‐induced anisotropy in the future.