A study of the mechanical anisotropy in shear of high-draw,low-draw,and voided poly(vinylidene fluoride)

The mechanical anisotropy in shear of oriented from I poly(vinylidene fluoride) sheet has been studied, completing the measurement of all nine independent compliances for this material. The morphology is parallel-crystallite; however, the crystalline regions are not lamellar in shape, but take the form of blocks with a bricklike shape oriented along the draw direction. The results have been analyzed in terms of a three-dimensional generalization of the Takayanagi model. First, modelling of the three principal extensional compliances based on previous measurements indicates that the gaps between the crystalline units are smaller in the transverse directions than in the draw direction. A voided sample shows a marked increase in the transverse compliances of the amorphous regions and considerable anisotropy owing to the voids. Secondly, a novel development of the Takayanagi model has been made to analyze the shear behavior. This has enabled the calculation of the shear compliances of the amorphous regions and indicates that the larger magnitude of the shear compliance in the plane normal to the draw direction is due to the large magnitude of the corresponding amorphous shear compliance, and that this is not affected by increased draw ratio or by the voids.