Study On The Relationship Between Mechanical Properties And Constitutive Relationship Of Kapton Foil In Uniaxial Tension

Kapton foil material is a kind of PI(polyimide)foil produced by Du Pont in the United States.It is one of the main materials for inflatable deployable antennae.The clarity of its mechanical properties has a great influence on the structural design and the working performance orbit.However,the current existing researches on Kapton foils materials mainly focus on the physical molding and chemical preparation of materials.There are few researches on the basic mechanical properties of Kapton foils,especially the mechanical properties under high and low temperature environment have not been reported,so it is difficult to fulfill engineering applications.Therefore,this paper conducts experimental researches on the basic mechanical properties of Kapton foils.Firstly,uniaxial tensile tests of Kapton(polyimide)foils were conducted in this paper.Kapton foils with a thickness of 25?m were used and the strip specimens were manufactured according to the machine direction(MD)and the transverse direction(TD)of the foils.The stress-strain curves of the foils were obtained under five constant strain rates(10,25,50,100,200mm/min)at room temperature(20°C).By analyzing the stress-strain curve,the mechanical parameters such as tensile strength,elongation at break,equivalent yielding stress,equivalent yielding strain and elastic modulus of Kapton foil and their variation rule were obtained.By analyzing the mechanical parameters,the quadratic or linear fitting equations with the tensile rate as the variable are given,which can be used to predict the relevant mechanical parameters of Kapton foil at different tensile rates.Combined with the scanning observation results of the fracture electron microscope,the structural characterization of the Kapton foil material when it is destroyed is described,and its failure mode is summarized.Secondly,combined with the working environment of the inflatable antenna structure,and the tensile tests are conducted with the rate of 100mm/min at the high temperature(20?,50?,80?,110?,140?,170?)and low temperature(-70?,-40?,-10?,0?,20?).The stressstrain curves of foil material at different temperatures were obtained,and the internal mechanism of the curves varying with temperature was explained.Various mechanical properties are obtained by analyzing the curves under high and low temperature tension.On the basis of the high and low temperature tensile test,the temperature influence coefficient of the strength for Kapton foil material is proposed.the change rule of the mechanical properties with the temperature coefficient is analyzed,and the corresponding fitting formula is established.Finally,based on the stress-strain curve obtained from the uniaxial tensile test of Kapton foil,adopting the exponential function and quadratic function to fit the curves,the phenomenological constitutive equation of Kapton foils are obtained.By comparing obtained constitutive equations and the experimental curves,the results show that the constitutive equation selected in this paper can describe the tensile stress-strain curve of Kapton foils well.Subsequently,the relationships between the coefficients in the constitutive equation and the stretching rate and temperature coefficient are established,and the fitting formulas are given.