Viscous Characteristics of ETFE Film Sheet under Equal Biaxial Tensions

ETFE membrane film structures are often realized in construction. Because ETFE film is a kind of polymer materials, it shows both elasto-plastic and visco-elastic characteristics. Using FEM and experimental results of ETFE film, the authors developed the constitutive equation.First to investigate the elasto-plastic characteristics of ETFE, a biaxial tensile test was carried out. The elasto-plastic characteristics are formulated adopting the von Mises criterion under biaxial stresses. FEM analysis of the test of rectangular ETFE cushion under pressure showed the validity in presenting ETFE behaviour based on the proposed constitutive equation.Then to investigate the viscoelastic properties, an incremental formula of the constitutive equation was extended and introduced to FEM analysis. The test showed that uniaxial creep properties can be presented using the proposed constitutive equation.Furthermore, to present biaxial creep properties, the incremental form of the constitutive equation was extended and the confirmation was given for its validityIn this paper, also to investigate temperature dependency of the elasto-plastic characteristic, the following points are focused on:1.Under multiple temperature conditions, uniaxial and biaxial tensile tests as well as creep testes are carried out.2.To include these properties, an incremental form of the constitutive equation is presented.3.Confirmation of the validity of the proposed constitutive equation is given.