Study On Uniaxial Tensile Properties And Constitutive Model Of ETFE Films

ETFE(ethylene-tetra-fluoro-ethylene)is a new type of copolymer which is widely used in the greenhouse plants,swimming pool,stadium and other large buildings after 1980 due to the light(1.7-1.77g/cm~3),the high transmittance(95%),self-clean,durable and anti-aging characteristics.From the point of view of the current status of the research,there are more studies on the mechanical properties of ETFE material test,but fewer for the nonlinear time-variant constitutive model of ETFE fims relatively.The approximate elastic model is difficult to accurately reveal the ETFE membrane structure real mechanical behavior characteristics,leading to irrational structure and performance evaluation.First of all,the uniaxial tensile tests of 250?m strip ETFE film samples are carried out in eight speeds(drawing speed by 1mm/min to500mm/min).The stress strain curves,yield strength,elastic modulus and other parameters with the variation law of the tensile rate are obtained from the uniaxial tests above.The results show that the yield strength and yield strain of ETFE films increase with the increase of tensile rate;the tangent,secant modulus and the equivalent elastic modulus based on strain energy and strain complementary energy increases with the increase of tensile rate.Secondly,according to the data of uniaxial tensile test and the viscoplastic mechanics,the constitutive equation of ETFE films which is based on Peirce model is established.Then,the numerical simulation analysis of the loading process of ETFE films is conducted in the finite element software ANSYS,the results of which are compared with the results of uniaxial tensile test.On the basis of Peirce model of ETFE constitutive equation,the numerical simulation of the loading process of the positive triangle ETFE cushion which has a length of 2.5m is conducted in ANSYS,the results of which is compared with the testing results of actual observation and the numerical simulation results of the linear model.The results show that the Peirce model can describe the deformation characteristics of ETFE membrane very well in the first 10%mechanical strain.Finally,according to the uniaxial tensile test data,the constitutive equation was established based on the Maxwell model.Then,the results of the numerical simulation of the loading process of the strip-shaped films is also given and compared with that of the uniaxial test data.Further more,based on the constitutive model of Maxwell model,the loading process of triangle cushion with 2.5m length is numerically simulated,the results of which are contrasted with the actual experimental observations and the Peirce constitutive simulation results.The results show that the Maxwell model of ETFE constitution can't describe the mechanical properties of ETFE films as better as the Peirce model before 10%strain,but after the second yield strain the mechanical characteristics and test data fit well.