【摘要】 通过对PVC膜材进行7种应力比下的双轴正交拉伸循环试验,经纬向应力比值分别为0∶1,1∶5,1∶2,1∶1,2∶1,5∶1和1∶0,对膜材在双轴拉伸作用下的拉伸特性进行了研究.试验表明,经过3次循环作用后,膜材的力学试验性能更接近工程实际情况,且材料具有非线性和正交各向异性.在循环荷载作用下,初次循环后残余应变较大.随着循环次数的增加(一般3次后),残余应变趋于常数,滞回曲线形状趋于稳定.采用双轴拉伸试验方法测定了PVC膜材的广义泊松比,验证了广义泊松比的非线性特征.试验证明,当经纬向应力比C≥1时,经向应变为正值;当C≥0.5时,广义泊松比变为负值;当应力比C为1∶0或0∶1时,双轴变成单轴试验,广义泊松比测定变成常规泊松比试验.理论和试验均证明当C=1时,膜材的经向和纬向同时具有最大的弹性模量.更多还原

【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 PVC membrane 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.更多还原