| Summary |
ETFE film is the material which has a large elongation under tensile stress, and it has been proposed by stretching to make higher strength. After unloading the tensile stress, it is important to predict the residual strain and stress in the plastic region. ETFE film has a viscous property such as creep and relaxation, and it is depended on strain rate. Especially, to show the yield stress depended on strain rate and the stress-strain relationships on the elasto-plastic constitutive equation, the material constant must be changed according to the strain rate. In this reason, visco-plastic constitutive equation is needed. In this paper, visco-plastic constitutive equation is formulated by combining the kinematic hardening creep theory and the nonlinear kinematic hardening theory to investigate the visco-plastic behavior of ETFE film. And, the material constant is determined by the strain velocity dependence. Also, the validity of the visco-plastic constitutive equation isduction of tensile force are executed. These experiments are mainly the uniaxial extension test and the biaxial extension test. Based on the results of these tests, “stable strain” is evaluated and the authors propose the stress-strain model for the design.
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