Experimental Study And Simulation Of ETFE Cushion Based On Flat-patterning Forming Method

ETFE(ethylene-tetra-fluoro-ethylene),transparent membrane material with lightweight,high light transmission,self-cleaning and recyclability,has been widely used in large-scale membrane structures in combination with steel or aluminum alloy structures.From the current research status,studies on temperature and rate effects of mechanical properties and creep properties of ETFE,and flat-patterning design of ETFE cushion based on nonlinear properties are still insufficient,and further research and experiments are needed.In this paper,ETFE foil and ETFE cushion were studied,experiment method and FEM method were performed to investigate mechanical properties under temperature effects.Main content of this paper includes uniaxial tensile test and creep test under different temperature,and the experimental study and simulation of ETFE cushion based on flatpatterning forming method were also conducted.Firstly,uniaxial tensile tests on 15 groups of ETFE foil of 250?m thick were conducted under temperatures of 40?,60? and 80? and loading strain rates of 1%/min,10%/min,50%/min,100%/min and 200%/min based on practical temperature and stress level of ETFE membrane structures.The corresponding yeild strengths of ETFE foils were determined by area method,while the variation law of the yeild strength was obtained by curve fitting,which are helpful to practical engineering application.Secondly,creep tests on 12 groups of ETFE foil samples were carried out under considering different temperatures and stresses.The logarithmic fitting of time and creep strain is employed and analysed the changing regularity of fit parameters under different test conditions.The relationship between creep strain,stress and temperature was obtained,which can describe creep properties of ETFE foils under different temperature and stress.It is found that large creep strain starts under high temperature or large stress,and the relationship between strain,stress and temperature is nonlinear.Moreover,the creep strain keeps small at temperature under 40? and the stress under 6 MPa,while large creep strain is observed in the case of high temperature or large stress.Subsequently,a creep model of ETFE foils at different temperatures was established based on Modified Time Hardening Theory model,which can consider the relationship between true creep strain,stress and creep time at different temperatures.The model parameters were determined by fitting 24 h creep results.In addition,the use of ANSYS to simulate the creep results shows that Modified Time Hardening model is successful to describe creep properties of ETFE foils.Finally,three rectangular ETFE cushions were designed and fabricated based on the flat-patterning forming method.The three cushion models experienced different loading processes at 24?,40? and 60? in order to study the effects of different temperature on flat patterning method.The whole process includes inflation phase and 24 h creep phase.The experimental results show that the ETFE foils experienced inconsistent creep process under the increasing shape,and larger creep deformation happened at higher temperatures.The inflated-forming processes of the three cushion models were simulated on the basis of Multilinear Isotropic Hardening model and Modified Time Hardening model to verify the applicability of the simulation method.Structural properties of ETFE cushions under different conditions were investigated to understand the flatpatterning forming process of ETFE cushions under different temperatures,especially for practical engineering application.