Uniaxial tensile creep properties of ETFE foils at a wide range of loading stresses subjected to long-term loading

Abstract

As a typical fluorine-based copolymer with excellent chemical, thermal, electrical and physical properties, ETFE (ethylene tetrafluoroethylene) is usually produced into thin films as an essential building and construction material especially for constructing the permanent membrane structures in civil engineering. This paper is thus aimed to investigate the uniaxial tensile time-dependent behaviors of ETFE foils with applying long loading period and various creep stresses experimentally. To this end, 30-day and 1-day uniaxial tensile creep tests were accomplished for the dumbbell specimens of the original ETFE foils by employing a new method and the traditional method, respectively. High efficiency, feasibility and precision of the selected new method could be firstly confirmed while comparing the 1-day creep curves of the original ETFE foils between two results from different methods. The experimental results of creep tests demonstrate that the creep curves of the original ETFE foils are strongly nonlinear with the faster strain during the initial stage and the slower strain during the final stage, and also prove that the creep stress is an essential factor in influencing the time-dependent behaviors. Meanwhile, it could be found that the ETFE foils subjected to the larger creep stresses were still deformed slowly even after the 30-day creep test. Additionally, uniaxial tensile stress-strain test was performed on the deformed ETFE foils that have undergone the 30-day creep test to evaluate the post-deforming mechanical properties. The experimental result of the additional stress-strain test shows that the elastic modulus of the deformed ETFE foils would increase with enlarging the creep stress. These findings would be significant in understanding the time-dependent behaviors of ETFE foils and especially for estimating the structural safety of ETFE membrane structure during the long-term service condition.