Study On Creep Mechanical Properties Of Kapton Film

Kapton film is a kind of polymer aerospace film material,and creep will occur in long-term use.Creep will lead to prestress loss of membrane material,wrinkles,morphological changes,even damage and loss of structural function,which will seriously affect the on-orbit safety and mission completion of spacecraft.In the design of membrane structure,the influence of creep properties of membrane materials on the forming process of structure should be fully considered to maintain the morphology of membrane structure and better play its structural function.As an important part of inflatable antenna structure,the creep effect of Kapton membrane is particularly important to the structure.Therefore,this paper studies the creep mechanical properties of Kapton membrane:Firstly,this paper studies the creep variation of polyimide（Kapton）film with a thickness of 25μm under different stress levels（35%,50%,65%,80%of ultimate tensile strength）and different temperatures（23°C,50°C,80°C,110°C,140°C and 170°C）.The creep constitutive model based on viscoelasticity（classical Kelvin,classical Maxwell,Burgers,three-parameter generalized Kelvin and five-parameter generalized Kelvin）is used to fit the experimental data,and the fitting effect of each model is compared and analyzed.The results show that the Kapton membrane exhibits obvious viscoelastic properties,and its creep properties are significantly affected by initial stress and temperature.The determination coefficient of the five-parameter generalized Kelvin model is more than 0.98,which can predict the creep behavior of the film well,followed by the Burgers model.The coefficients of determination of classical Kelvin,three-parameter generalized Kelvin and classical Maxwell models are above 0.7,and the fitting effect can also meet the needs of practical engineering applications.Secondly,the time-temperature equivalence of Kapton film is studied,and the creep master curves in MD and TD directions are drawn to predict the creep behavior of Kapton film.The creep boundary point is discussed,the critical creep condition of Kapton film is determined,and the service life and reliability of the material are evaluated.This study can save a lot of test time and cost.The results show that under the initial stress of 50%ultimate tensile strength,the creep compliance master curve time is much longer than 12 h of the test,and the MD direction lgt extends to 90854837.47×10^-7,MD direction lgt extends to 88554837.47×10^-7.Moreover,with the increase of temperature,the time for Kapton film to reach the steady-state creep stage gradually decreases,and the MD and TD directions reach the steady-state creep stage within 8 h and 6 h,respectively.According to the creep demarcation point,the creep curve is divided into nonlinear and linear segments,which can better describe the creep behavior of Kapton film before failure.Finally,considering the nonlinear,time-dependent and temperature-dependent characteristics of Kapton film,the time-hardening model is used to simulate the creep process of the film under different stress and temperature by using ABAQUS finite element analysis software.The simulation process is consistent with the actual test process and the characteristics of the film.Through the total strain cloud diagram,creep strain cloud diagram and stress cloud diagram obtained by numerical simulation results,the internal mechanism of film creep behavior is analyzed,and its creep performance is further explored.The difference between the creep strain and the total strain between the test data and the finite element results is compared to verify the rationality of the simulation process to predict the long-term performance of the film.