Flexible polyvinyl chloride (PVC)-coated woven fabric is one of the architectural materials used for lightweight tension structure. The tensile stiffness and strength of coated fabrics are essential mechanical properties for the design of tension structure, a typical membrane structure for roofs. A lack of understanding of the tensile performance of flexible coated fabrics leads to the practice of high safety factor, typically larger than five even as great as ten, which is twice to four times that for the supporting cables, rods and webbing [1]. 1 Reinforced by woven fabric, which is interwoven by two perpendicularly oriented yarn systems (termed as warp and fill yarns) to form a quosi-orthogonal fibrous architecture, coated fabrics are, therefore, characterized highly anisotropic. In addition, as a result of crimped yarn configuration Abstract The aim of this study was to provide a practical approach towards discovering the anisotropic behaviors of polyvinyl chloride (PVC)-coated fabrics under low tensile stresses, as well as those at the tensile failure stage. Test specimens were PVC-coated polyester woven fabrics. One group of bias tensile experiments, with off-axial angles of 0°, 15°, 30°, 45°, 60°, 75° and 90°, was conducted under low tensile stresses. The anisotropic behaviors on elastic constants of coated fabrics were analyzed with the application of offaxial constitutive response of orthotropic and elastic materials. The experiment data agreed well with the prediction of the off-axial constitutive response. It was proved that coated fabrics can be regarded as orthotropic and elastic materials within 20 % of the ultimate tensile stress. To analyze the anisotropic behaviors at the tensile failure stage, another group of bias tensile experiments with the same off-axial angles was carried out. Three types of failure mechanisms, pure tensile failure, pure shear failure and a mixed failure of tensile and shear, were observed by analyzing the fracture configuration of the specimens under each bias tensile loading. For the prediction of the anisotropic failure strength of coated fabrics, Tsai-Hill strength criterion was used and the results analyzed.

Tensile characteristics are the most significant mechanical properties for coated woven fabrics as membrane materials used in lightweight constructions. Factors that might affect test results of the material under uni-and biaxial tensile loads are examined. After series of tensile tests on PVC-coated membrane materials, it is demonstrated that (1) to measure the strains in the two perpendicular directions, the contact method by the needle extensometer does not interfere the correct data recording; (2) the positions where the strains are measured on specimens have a great influence on the test results of the stiffness and Poisson's ratio in warp direction under uni-axial load; (3) to perform bi-axial tensile tests the size of the cruciform specimen in bi-axial tensile test can be much smaller than those suggested in the literature. The tensile behavior of coated membrane materials under biaxial loads are affected dramatically by the stress ratio in the warp and fill directions. Besides the residual strains of coated membrane materials are affected not only by the properties of the constituent yarns and woven structure but also by loading conditions during the coating process.

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ABSTRACT:The tensile performance of coated woven fabrics under multiaxial loads is examined in the present study. Two groups of experiments were conducted to investigate the influences of the configuration of the fabric specimen and the loading speed on the multiaxial tensile properties of the fabrics. The configuration of the specimen for the multiaxial tensile tests is identified as gear-shape with large arm widths. A loading speed of lower than 20 mm/min is suggested to obtain the tensile properties of the coated woven fabrics under multiaxial loads. The tensile performances of coated woven fabrics under uni-, bi-, and multiaxial loads were compared. We found that the tensile performances under bi-and multiaxial loads are much better than those under uniaxial loads. Therefore, for the application of the coated woven fabrics in lightweight structures, biaxial or multiaxial loading conditions will be necessary. Experiments on the specimens with an initial crack in the center under multiaxial loads show that, by comparison with other loading directions, the tensile properties in warp direction of the coated woven fabrics play an important role in the failure performance and crack propagation under multiaxial loads. To eliminate the dependence on the mechanical properties in warp direction, the balance of the two principle directions of coated woven fabrics should be improved.