Non-linear and time-dependent viscoplastic material properties of ETFE films as membrane elements with multiaxial stress states in civil engineering

土木工程中具有多轴应力状态的 ETFE 薄膜作为膜元件的非线性和时间依赖性粘塑性材料特性

• 批准号: 527832586
• 负责人: Professorin Dr.-Ing. Natalie Stranghöner
• 金额: --
• 依托单位: Institut für Metall- und Leichtbau
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/527832586?language=en
• 关键词: Non; linear; time; dependent; viscoplastic

In membrane structures, foils made of ethylene tetrafluoroethylene (ETFE) are mostly used on prestigious buildings as roof or façade systems, whereby they impress with their high translucency and low dead weight, enabling large, column-free spans. In the design of ETFE foil structures, the multi-axial stresses in the ETFE foils due to the applied loads are simplified into biaxially aligned orthogonal main stresses. Although the multiaxial load bearing behaviour is decisive, the design is based on monoaxially determined material properties. This leads to deficient approaches with respect to the material properties and the load bearing behaviour of the structure. To counteract this situation, the material and load bearing behaviour of ETFE foils in multiaxial stress conditions needs to be investigated. Currently, only the biaxial material behaviour is determined by means of cross-shaped specimens, whereby due to the slotted cross-shaped specimen geometry always a specimen and no material failure occurs and the actual overall biaxial material behaviour cannot be determined. In STR 482/6-1, the applicant was able to show that the multiaxial, non-linear viscoelastic to viscoplastic material behaviour of ETFE foils cannot be determined by biaxial test rigs, but must be investigated in multiaxial test rigs. In preliminary multiaxial tests it could be shown that in the multiaxial stress state, compared to the monoaxial stress state, non-negligible material-strengthening and -stiffening effects occur. The aim of this project is to analyse and characterise the viscoplastic material behaviour of ETFE foils as well as the strengthening and stiffening behaviour in multiaxial simple and cyclic loading. Material reserves are to be identified in order to expand the fields of application of ETFE foils in membrane structures of the building industry and to be able to design these foil structures more safely and at the same time more economically. In this context, the current structural forms - anticlastic and synclastic - as well as influences from varying strain rates, varying test temperatures, different foil thicknesses and foil products on the multiaxial load bearing behaviour of ETFE foils are to be investigated. The analytical models, correlations and methods for the description of the mono- and biaxial material behaviour established in STR 482/6-1 are to be further developed on the basis of multiaxial tests to be carried out and numerical parameter studies, so that the multiaxial, visco-plastic material behaviour can be modelled analytically and material hardening, material strengthening and saturation effects due to cyclic loads can be taken into account.

在膜结构中，由乙烯四氟乙烯 (ETFE) 制成的箔片主要用于著名的建筑作为屋顶或外墙系统，因此它们以其高半透明度和低自重而令人印象深刻，在 ETFE 箔片的设计中实现了大的无柱跨度。在结构中，由于施加的载荷而导致的 ETFE 箔中的多轴应力被简化为双轴排列的正交主应力，尽管多轴承载行为是决定性的，但设计是基于单轴确定的材料特性。导致材料性能和结构承载行为方面的方法存在缺陷。为了解决这种情况，需要研究 ETFE 箔在多轴应力条件下的材料和承载行为，目前仅研究双轴材料行为。通过十字形样本确定，因此由于开槽十字形样本几何形状始终是样本并且不会发生材料失效，并且在STR 482/6-1中，申请人能够确定实际的整体双轴材料行为。来表明ETFE 箔片的多轴、非线性粘弹性到粘塑性材料行为无法通过双轴试验装置确定，但必须在多轴试验装置中进行研究，在初步多轴试验中，可以表明在多轴应力状态下，与单轴应力相比。状态下，会发生不可忽略的材料强化和硬化效应，该项目的目的是分析和表征 ETFE 箔的粘塑性材料行为以及确定材料储备，以扩大 ETFE 箔在建筑行业膜结构中的应用领域，并能够更安全地设计这些箔结构。在这种情况下，需要研究当前的结构形式（抗弹和同弹）以及不同的应变率、不同的测试温度、不同的箔厚度和箔产品对 ETFE 箔的多轴承载行为的影响。分析模型，在即将进行的多轴试验和数值参数研究的基础上，将进一步开发 STR 482/6-1 中建立的单轴和双轴材料行为描述的相关性和方法，以便多轴、粘塑性可以对材料行为进行分析建模，并且可以考虑循环载荷引起的材料硬化、材料强化和饱和效应。