STRUCTURAL CHANGES DURING PLASTIC DEFORMATION AT CRACK TIPS OF PVDF FILMS - A SEMI-QUANTITATIVE ANALYSIS

摘要

On 200μm thick α-Poly(vinylidene fluoride) (PVDF) films double edge notched tension tests have been performed and the structural properties of the deformation zone were investigated using scanning small angle X-ray scattering (sSAXS) and scanning wide angle X-ray scattering (sWAXS) methods. PVDF is a semi-crystalline polymer exhibiting different polymorphous states, which can be transformed into each other. The polymorphs of highest interest are the most commonly observed α-phase and the piezoelectric β-phase. Scanning scattering methods allow the correlation of morphological properties of a specimen with the position on the sample. The crack tip region was scanned in two directions perpendicular to the X-ray beam with a spatial resolution of 0.2 mm. Changes in non-crystalline features (e.g. void formation, craze fibril formation and orientation) and the crystalline morphology and fine structure (e.g. phase transformation) in the crack tip plastic zone region were investigated in detail. It was found that the plastic zone ahead of the crack could be divided into 3 areas: the outer zone, characterized by the presence of cavities, a transition state with very strong cavitation and the mid-rip zone with β-PVDF fibers bridging a low density α-PVDF matrix.