Theoretical And Experimental Study Of Helium Leakage Mechanism Of Aerostat Envelope Materials

The stratospheric aerostat permanently stayed in the complex space environment with thin air and strong effect of ultraviolet radiation and ozone. Excellent properties like lightweight, high strength, tear resistance, high sealing and anti-aging are the key technical requirements of envelope material. Ordinary single-component material is difficult to meet these requirements, to achieve the standards of aerostat's practical application the envelope materials must be formed of laminated film composite with different special functions. On the basis of ensuring the strength, reducing mass and enhancing the helium barrier ability are the main trends of the future development of envelope materials.The dissertation studies the microstructure of each layer and discusses different helium penetration mechanism of all three parts of the envelope material. For the protective layer Tedlar film and helium barrier layer Mylar polyester film, the solution-diffusion model was used to describe the behavior of helium penetration. For the load layer which consists of a plain fabric Polyarylate Vectran fiber, helium penetration includes both the porous media viscous flow model and the solution-diffusion model. By the multi-layer penetration model, the helium permeance of the envelope material was obtained Theoretically and which was only 22.4 percent higher than the value from experiment tests. At the same time, the influence of each layer with different thickness on helium permeability of the whole skin was analyzed, which points out that the protective layer and the helium barrier layer contribute near 90% to the helium sealing performance.By the simulated space environment experiments of temperature cycling, ozone oxidation and ultraviolet radiation, the helium permeability and the tensile modulus of post-treated envelope samples were obtained; meanwhile by fitting the experimental data, the function relationship between helium permeability and the elastic modulus were established.On the damage induced helium leak mechanism, the influence of three different types of damage on helium penetration properties of envelope material were analyzed based on the microscopic damage mechanics, and the functional relationship between helium permeability and crack density and crack thickness was established theoretically. An identical form of function relationship between helium penetrability and damage variables was found by the result mentioned above and by continuum damage mechanics model in relative literatures. It also showed the same trend between experiment test results and the theoretical prediction with respect to the change of helium permeability after damage induced in the envelope material, which confirming the valid of theoretical model of damage induced helium permeability of envelope material.