Multi-scale Contact Mechanics And Its Application In Sealing

Sealing device is a kind of very important machinery in spacecraft structure. The performance of the sealing device directly determine the overall performance and the service life of the spacecraft. In order to ensure the mission smoothly, it is necessary to study the sealing mechanism, the form of leakage and the optimization design of sealing device. Based on the sealing mechanism and process of fluid leakage, sealing is regarded as the coupling of initial morphology characterization of sealing surface, contact deformation, fluid flow characteristics and connecting features of leakage channel. This article has conducted these related research work, the main content includes the following several aspects.(1) The self-affine surface geometry morphology model is built according to the fractal geometry and the surface roughness power spectrum. The method to judge one surface whether has fractal characteristics and the measurement method of surface fractal dimension is presentation. Fourier series transformation method for isotropic self affine fractal surface has been carried on the numerical simulation.in order to simulate the complex, random, multi-scale and self-similar characteristics of the real surface.(2)The multi-scale contact mechanics model of sealing is built according to the Persson contact theory. The macroscopic contact parameters such as the distribution of surface stress, the real area of contact and the average separation distance of contact region are given. The effect of plastic deformation and surface adhesion on contact characteristics and distribution of micro leakage pore are considered. The sealing contact model established in this paper can correctly reflect the influence between the real contact area with the compaction force, surface roughness and surface defects.(3) The contact equation for rough surface contact numerical simulation is built according to the elastic half space theory. The contact equation is solved by Multilevel Matrix Multiplication algorithm(MLMS) and Conjugate Gradient method(C-G method). Results of simulation show the correctness of theoretical model.(4) The heterogeneous characters of leakage channel, such as scale related, disorder of topology, irregular of shape, are discussed using the theory of heterogeneous composite medium. Points out that the fluid equation is different in different size of the flow channel flow. When the leakage channels are mainly concentrated in small size, the effect of micro flows must be considered. The flow between rough surfaces with contacts between these surfaces, is analyzed through the volume averaging method and the Navier-Stokes equation. Two models of leakage of rubber seals are built, which is based on percolation theory and effective-medium theory respectively. The two models are compared in this paper.(5) Based on the seal model, this report designs a experiment system of leakage detection and vacuum sealing exoeriment environment. In usual pressure environment, the leak of seal are detected. The way of leak of seal in vacuum is very different to the way in usual pressure environment. Flash distillation happen in part of the leak fluid, the other part of fluid become to ice which grow along the surface of seal. In vacuum, there is a critical value of leak. When the leak outweigh this value, the seal will expiration at some time.