Characterization and modelling of the nonlinear material behaviour of coated fabrics for architectural membrane structures II

由涂层织物制成的纺织薄膜结构是当今土木工程中一种根深蒂固的构造形式，特别是用于大面积无支承屋面。充分考虑材料刚度是在有限元模型中对膜进行预测性建模的基础，从而也是计算膜和子结构中的机械载荷和位移的基础，从而确保无损结构、安全和盈利。涂层织物薄膜在双向拉伸试验中表现出各向异性和高度非线性的应力-应变行为。作为外部载荷的结果，观察到材料的软化导致永久应变，该永久应变随着循环载荷的增加而增加，并且在固定的最大载荷下呈现饱和行为。在确定膜结构的尺寸时，这种预处理产生的附加应变是必须考虑的，然而，由于缺乏合适的模型，在当今的实践中并非如此。此外，目前用线弹性公式来近似非线性应力-应变行为，在预测应力和位移时精度不够高。这表明，在非线性材料响应的表征和建模方面存在着基本的知识差距，这是本研究项目计划要弥合的。该项目的中心目标是开发用于膜结构的结构计算的概念，用于结合纺织膜的与载荷和结构相关的非线性材料特性。主要创新点和研究目标如下：1.开发了一种双向拉伸试验程序，以确定纺织薄膜的结构和载荷相关的材料性能，该程序适应于实际载荷情况，并考虑了外部载荷下的预应力和预适应过程。2.发展了两种考虑纺织薄膜非线性材料性质的有限元计算方法：a.与载荷和结构有关的虚拟弹性常数；b.描述非线性非弹性材料性质的连续介质-力学材料模型。3.验证文[2]中提出的方法的有效性。基于大型结构试验，主要针对两种结构类型(平面型和马鞍型)来评估真实膜结构的位移和应力。4.通过与非线性模型的对比分析，将虚拟弹性常数法推广到进一步的结构形状(如高点膜和四点帆)。

Textile membrane structures made of coated fabrics are nowadays a firmly established constructive form in civil engineering, in particular for the unsupported roofing of large areas. The adequate incorporation of material stiffness forms the basis for a predictive modeling of the membrane in Finite Element models and thus for the calculation of mechanical load and displacement in the membrane and in the substructure, ensuring damage-free constructions, safety and profitability. Coated fabric membranes show an anisotropic and highly nonlinear stress-strain-behaviour in biaxial tension tests. As a result of external loading, softening of the material is observed leading to permanent strains which increase with cyclic loading and which show a saturating behaviour under fixed maximum load. The additional strains resulting from this preconditioning are essential to be considered when dimensioning a membrane structure, which, however, is not the case in nowadays practice due to a lack of suitable models. Moreover, the nonlinear stress-strain-behaviour is currently approximated by linear elastic formulations which yield an insufficient accuracy in the prediction of stresses and displacements. This shows that there is a fundamental knowledge gap with respect to the characterization and modeling of the nonlinear material response, which is planned to be closed in this research project. Central goal of this project is to develop concepts for the incorporation of load- and structure-dependent nonlinear material properties of textile membranes for the structural computation of membrane constructions. The main innovations and thus research goals are as follows: 1. Development of a procedure for biaxial tension tests to identify structure- and load-dependent material behaviour of textile membranes, which is adapted to the real load situation and which account for the prestress and preconditioning process under external loading. 2. Development of two methods for finite element calculations for the consideration of the nonlinear material properties of textile membranes base on: a. Load- and structure-dependent fictitious elastic constants and b. Continuum-mechanical material model for the description of the nonlinear inelastic material properties. 3. Validation of the methods developed in 2. based on experimental large-construction experiments mainly focusing on two structure types (plane and saddle-shaped form) for the assessment of displacements and stresses in real membrane structures. 4. Extension of the method using fictitious elastic constants to further structural shapes (e.g. high point membrane and 4-point sail) by comparative analysis with the nonlinear model.