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对膜结构施工中由裁剪片拼接张拉形成的膜面进行应力松弛分析,考察膜面应力随时间逐渐减小的变化规律。考虑膜材材料和几何双重非线性,采用广义Maxwell黏弹性模型建立积分型本构方程,推导增量本构方程,编制非线性有限元程序实现成形曲面的应力松弛数值分析过程。对聚氯乙烯(PVC)膜材进行了不同初始应力水平下的单轴应力松弛试验和不同应力比下的双轴应力松弛试验,用5单元的广义Maxwell黏弹性模型对试验数据拟合,确定了膜材本构方程的黏弹性参数。进行十字形膜片的加载及应力松弛试验,对其试验过程进行数值分析,结果表明试验结果与数值分析结果基本一致,验证了成形曲面黏弹性数值分析方法的可行性。对PVC膜材马鞍形曲面算例进行黏弹性分析,结果表明,马鞍形曲面在张拉完成4 d后,膜面平均应力降低了44%。
During the construction of the membrane structure, the stress relaxation analysis was carried out on the membrane surface formed by the splicing of the cut pieces to investigate the variation of the membrane surface stress decreasing with time. Taking into account the dual nonlinearity of membrane material and geometry, the generalized Maxwell viscoelastic model is used to establish the integral constitutive equation, the incremental constitutive equation is deduced, and the nonlinear finite element program is used to realize the numerical analysis of the stress relaxation of the formed surface. The uniaxial stress relaxation tests of polyvinyl chloride (PVC) film under different initial stress levels and the biaxial stress relaxation tests under different stress ratios were performed. The experimental data were fitted by the general Maxwell viscoelastic model of 5 units, The viscoelastic parameters of membrane constitutive equation. The cross-shaped diaphragm was loaded and stress relaxation test was carried out, and the numerical analysis of the test process was carried out. The results show that the experimental results are in good agreement with the numerical results, which verifies the feasibility of the numerical analysis method of viscoelasticity of formed surface. The viscoelastic analysis of the saddle-shaped curved case of PVC membrane shows that the average stress of the saddle-shaped curved face decreases by 44% after 4 days.