Uniaxial tensile properties of pre-stretched ethylene-tetrafluoroethylene (ETFE) foil

The ETFE foil is a type of good cladding material in the field of architecture and its uniaxial tensile properties are important considerations in the design analysis. In engineering application, the stress of ETFE foil may exceed the first and second yield stress under external load and the large plastic deformation is usually observed. Previous studies mainly focus on its uniaxial tensile properties along the uniaxial pre-stretching direction after the uniaxial pre-stretching stress is over the yield stress. Uniaxial pre-stretch will cause the ETFE film to compress in the other direction due to Poisson's ratio, while the uniaxial tensile properties perpendicular to the uniaxial pre-stretching direction is still unknown. Besides, the study on its uniaxial tensile properties along the biaxial pre-stretching direction after the biaxial pre-stretching stress is over the yield stress is also quite limited. In order to investigate this issue, the uniaxial pre-stretching tests, the asynchronous biaxial pre -stretching tests and the synchronous biaxial pre-stretching tests were performed to make the uniaxial stress and the biaxial stress reach over the first and second yield stress respectively. Square specimens for subsequent uniaxial tensile tests were prepared from these pre-stretching tests and the uniaxial tensile stress-strain curves of specimens of different pre-stretching tests were obtained. The uniaxial tensile test results demonstrate that in some cases the bearing capacity of ETFE foil was strengthened after pre-stretching tests while in many cases both the uniaxial pre-stretching and the biaxial pre-stretching lowered the bearing capacity of ETFE foil. Additionally, the pre-stretching strain correlates strongly with the bearing capacity of pre-stretched ETFE foil and the relationship between them is discussed.