The measurement of shear compliances for oriented polyethylene terephthalate sheet

Two techniques have been used to measure the shear compliances of one-way drawn uniplanar-axially-oriented polyethylene terephthalate (PET) sheet, draw ratio 51; a torsional method for all three compliancesS₄₄,S₅₅ andS₆₆, and a recently-developed simple-shear method forS₄₄ andS₆₆. The two techniques gave values for the compliances in common which agreed very well. An examination of end effects in torsion has also been made. The determination of the three shear compliances complete the determination of all nine independent compliances for this PET sheet. The overall mechanical anisotropy has been considered in the light of existing structural information, and comparison made with the elastic constants of isotropic PET and a highly oriented PET fibre on the basis of the single-phase aggregate model.