Abstract:

Through biaxial cyclic tensile tests of PVC membrane materials at seven different ratios between warp and weft stress, which are 0∶1, 1∶5, 1∶2, 1∶1, 2∶1, 5∶1 and 1∶0 respectively, tensile performances of the samples under biaxial tensile loads are analyzed. The tests indicate that after three cyclic loading, the experimental properties of membrane materials agree well with actual properties of membrane materials used in structures. The test results show that the behavior of membrane material is highly nonlinear and orthotropic under biaxial tensile loads. During the cyclic loading test, the residual strain is obvious at the end of first unloading. With the increase of loading cycles (usually after three cycles), the total residual strain is nearly unchangeable and the hysteresis curve becomes stable. The generalized Poisson’s ratio is measured using the results of biaxial tensile tests of PVCmembrane materials, which verifies the nonlinear characteristics of generalized Poisson’s ratio. It is illustrated in the test that the strain in warp direction is positive when C≥1, while for C≤0.5, the generalized Poisson’s ratio turns to negative. When the stress ratio is 1∶0 or 0∶1, the biaxial test turns to uniaxial test, and the determination of the generalized Poisson’s ratio becomes routine Poisson’s ratio test. Both the theory and test results indicate that under the condition of C=1, both warp and weft directions have the biggest elastic moduli.

Key words:  architectural membrane materials; biaxial tensile test; orthotropic; nonlinear; generalized Poisson’s ratio; elastic modulus