Surholt Felix, Uhlemann Jörg, Stranghöner Natalie
Institute for Metal and Lightweight Structures, University of Duisburg-Essen, 45141 Essen, Germany.
Polymers (Basel). 2022 Aug 2;14(15):3156. doi: 10.3390/polym14153156.
With the first use of ETFE foils in building structures in the 1980s at the Burgers' Zoo in Arnhem, Netherlands, the implementation of ETFE foils in roof and façade systems in large-span structures has become steadily more prominent. To safely design ETFE foil structures, their mechanical behaviour has to be fundamentally understood. Until now, several research studies have been published investigating this material's behaviour. However, the parameters influencing these plastic's mechanical behaviour, such as the strain rate or the test temperature, have only been investigated separately but not simultaneously. In this contribution, an analytical model is presented which describes the mechanical behaviour of ETFE foils under varying test temperatures and strain rates simultaneously. The material model has been checked against experimental results achieved for materials from three different international producers and two different commonly used foil thicknesses with significant differences in their mechanical responses (so that it can be assumed that the international market is represented). In the first step, uniaxial tensile tests on strip specimens were performed to describe the nonlinear and viscoelastic temperature- and strain rate-dependent material behaviour under uniaxial tension. The achieved stress-strain curves exhibited, as expected, the two commonly so-called yield points, which can be taken as separators for three different material stages: viscoelastic, viscoelastic-plastic, and viscoplastic. In the second step, by separating the uniaxial tensile response into these three stages, two interdependent functions could be derived based on the well-known Ramberg-Osgood material model to simulate the viscoelastic and viscoelastic-plastic material behaviour of ETFE foils. For this purpose, analytical functions were developed to calculate the model parameters considering the influence of the test temperature and the test speed. It can be shown that the newly developed analytical material model fits well with the experimental results. With the use of the derived nonlinear material model, design engineers can predict the material's mechanical behaviour considering the environmental conditions on site while maintaining independence from the material's supplier.
20世纪80年代，荷兰阿纳姆的布尔格斯动物园首次在建筑结构中使用乙烯-四氟乙烯共聚物（ETFE）薄膜，此后ETFE薄膜在大跨度结构的屋顶和立面系统中的应用越来越普遍。为了安全地设计ETFE薄膜结构，必须从根本上了解其力学性能。到目前为止，已经发表了几项关于这种材料性能的研究。然而，影响这些塑料力学性能的参数，如应变率或试验温度，只是分别进行了研究，没有同时进行研究。在本论文中，提出了一个分析模型，该模型同时描述了ETFE薄膜在不同试验温度和应变率下的力学性能。该材料模型已与来自三个不同国际生产商、两种不同常用薄膜厚度且力学响应有显著差异的材料的实验结果进行了对比（从而可以认为代表了国际市场）。第一步，对条形试样进行单轴拉伸试验，以描述单轴拉伸下非线性、与温度和应变率相关的粘弹性材料行为。所得到的应力-应变曲线正如预期的那样，呈现出两个通常所说的屈服点，这两个屈服点可作为三个不同材料阶段的分隔点：粘弹性、粘弹性-塑性和粘塑性。第二步，通过将单轴拉伸响应分为这三个阶段，基于著名的兰伯格-奥斯古德材料模型，可以推导出两个相互依赖的函数，以模拟ETFE薄膜的粘弹性和粘弹性-塑性材料行为。为此，开发了分析函数来计算考虑试验温度和试验速度影响的模型参数。结果表明，新开发的分析材料模型与实验结果吻合良好。使用所推导的非线性材料模型，设计工程师可以在考虑现场环境条件的情况下预测材料的力学性能，同时保持与材料供应商无关。
