Mechanical properties of ETFE foils in form-developing of inflated cushion through flat-patterning

This present paper focuses the main effort on the mechanical properties of ETFE (ethylene tetrafluoroethylene) foils during the form-developing process of inflated cushion structure through the forming design method of flat-patterning. To this end, an equilateral triangle ETFE cushion model with the side length of 2.5 m was designed and developed through flat-patterning. A multidisciplinary approach, combining the automatic pressure control, photogrammetry, laser measurement and graphics processing, was utilized to realize the form-developing process of the ETFE cushion model. The whole form-developing process included the inflating phase from 0 kPa to 4 kPa, the viscoelastic-plastic creep phase under 4 kPa within 25 min and the creep-recovery phase under 0.5 kPa within 24 h. Some original experimental data, such as the values of the internal pressure, shapes of the upper layer and rises of the lower layer, were obtained from the forming test of ETFE cushion model. Based on the measurement results, the stress distributions and strain distributions under different conditions were calculated by using the force finding method and triangular element method, respectively. Some profound material mechanical properties and structural behavior, such as the elastic deformation, viscoelastic creep, creep-recovery and strengthening, were revealed via the analysis of experimental results. These results demonstrate the applicability of the flat-patterning method, which will improve the popularization of ETFE cushion structure.