| Summary |
This study aims at clarifyin the behaviour of ETFE film sheet using the FEM analysis. ETFE film exhibits both elasto-plastic and viscoelastic characteristics under stress. These characteristics have been discussed in the authorfs studies [3, 4]. In this paper, the viscoelastic characteristics under biaxial tension are described from the viewpoint of experimental tests and numerical simulations. First, the incremental constitutive equation under biaxial tension is proposed. It is based on the incremental nonlinear viscoelastic equation [4] under uniaxial condition. Then, it is developed in an applicable formula to biaxial stresses in the FEM analysis. The variation of temperature is included using a time-temperature changing equation. The parameters of constitutive equation are again estimated from results [1, 2] of dynamic viscoelastic experiment. Second, two types of experimental tests are performed. Then, the validity of constitutive equation is confirmed through comparison with results of numerical simulations. One experimental test is biaxial tension test. It is monotonic loading test with various stress ratios. The other one is biaxial creep test. It is two stress level test. |