Direction Dependent Mechanical Behavior of ETFE Foils

In recent decades, the use of ethylene-tetrafluoroethylene (ETFE) membranes has been increasing in the building industry for lightweight transparent structures. The nonlinear behavior of this material has garnered significant attention from researchers in recent years. However, there remains uncertainty regarding whether the material is orthotropic or isotropic, leading to conflicting conclusions in the literature. This work aims to clarify this question. To achieve this, uniaxial tensile tests were conducted on NOWOFLON ET 6235 foil at temperatures ranging from 16 °C to 32 °C, covering material orientations from –90° to 90° relative to the machine direction in increments of 15°. The results indicate that there is no significant difference in behavior based on cut orientation at small strains. However, a slight orthotropic behavior becomes evident after the initial inflection point on the engineering stress-strain curve, as confirmed by ANOVA analysis.