Rate-dependent mechanical properties and elastic modulus of ETFE foils used in inflated forming of transparency air-inflated cushion membrane structures

Abstract ETFE (ethylene tetrafluoroethylene) air-inflated cushion structure has become one of the primary choices for being roofs and facades of large-span structures. Prior to the load bearing stages, it is required to firstly inflate the ETFE cushion envelope to gain the desired initial geometrical height and structural stiffness. This paper thus proposes a combination of analytical, experimental, and numerical methods to evaluate the rate-dependent mechanical properties and elastic modulus of ETFE foils used in the inflated forming processes of ETFE cushion structures. Starting from the typical uniaxial tensile stress-strain curve, the existing geometrical and mathematical method and a new proposed equivalent energy method are utilized to determine the mechanical parameters of ETFE foils together. Subsequently, a series of uniaxial tensile tests at the strain rates of 0.1–1000%/min were conducted on the dumbbell specimens of ETFE foils in order to acquire the yield strength and strain, the tangent, secant and equivalent moduli. Such results can be used to uncover the rate-dependent mechanical properties of ETFE foils and analyze the structural behaviors of ETFE cushions. Finally, numerical simulations of inflated forming were completed on four flat-patterning ETFE cushion models with considering the nonlinear material model of Perzyna model and the linear material properties of tangent, secant and equivalent moduli, respectively. As such, this research provides a new opportunity to elucidate the most appropriate choice of elastic moduli in design, analysis and optimization of ETFE membrane structures.