Research On Interface Modeling And Leakage Mechanism Of Spacecraft Contact Seal

The sealing device is an important part to ensure the reliable operation of spacecraft and the life safety of astronauts.In this paper,the contacting sealing structure of spacecraft is selected as the research object.Based on the fractal theory,the contacting theory and the hydrodynamics theory,the interface modeling and the leakage mechanism of contacting sealing structure are studied.The specific research contents are shown as follows:(1)The characterization of sealing surface topography based on the fractal theory.Based on the fractal theory,the representation forms of contour function and statistical parameters are obtained for the fractal surface topography.Moreover,the calculation method and the accuracy of fractal parameters for the fractal surface topography characterization are discussed according to the fractal contour function.The numerical simulation results show that the structural function method can be used to calculate the fractal parameters of contour lines,which has the best calculation accuracy and stability.In addition,the feasibility of fractal contour function is applied to the characterization of surface topography and verified by experiments.According to the self-similarity of fractal theory,the reference plane is introduced into the fractal surface,which is represented by the fractal contour function.Also,the complex fractal surface is divided into several independent asperities and pores.Thus,the fractal surface is proposed.The discrete model can transform the complex surface into the asperities and the pores,which lays a foundation for the future studies of the surface contacting model and the interface flow model.(2)The study on the contacting process of sealing surface.According to G-T equivalent theory,the contacting equivalent model is deduced based on the discrete model of fractal surface.The contacting problem of double rough surfaces can be equivalent to that of single rough surface and rigid plane.The contacting process between asperity and rigid plane is discussed.Moreover,the difference between elastic deformation,elastic-plastic deformation and plastic deformation of asperity is considered.In the deformation state,the influence of the difference between contacting force and area on the surface contacting process is studied.The discriminant function of deformation state for the asperity is established,and the deformation state interval of asperity is obtained by solving the discriminant function.By means of calculating the integration sum of contacting model and distribution function for the asperity in the phase-strain state interval,the deformation state interval based on the above models,the influence of surface morphology parameters and material parameters on the contact process are analyzed according to the numerical calculation.(3)The flow process of sealing interface.Based on the discrete model of fractal surface,the calculation methods of fractal dimension,maximum capillary diameter and tortuosity for the sealing interface are deduced.Moreover,the structural characteristics of sealing interface are characterized by the above parameters.By means of combining with the flow model of capillary,the liquid driven by pressure in the sealing interface is established.Based on the above models,the effects of contacting distance and surface morphology on the the flow process of sealing interface are analyzed by the numerical calculation.(4)The prediction model for the leakage rate of spacecraft surface contacting sealing structure.According to the combination of the surface contacting model with the flow model,the prediction model for the leakage rate of sealing structure is established for the conditions of pressure driving and non-pressure driving.According to the numerical calculation,the effects of the model pressure,the surface morphology,the material properties,the difference of internal and external pressure as well as the sealing structure size on the leakage rate of sealing structure are analyzed.(5)The experimental study on the leakage mechanism of spacecraft surface contacting sealing.The experimental system of leak rate for the surface sealing structure is constructed.The system has the simple structure and the high accuracy,which can adjust the liquid pressure difference,the contacting pressure and the structure size within a certain range.Based on the experimental system,the leakage rate measurement experiment of different experimental samples and working conditions are conducted.The experimental results show that this model is accurate for predicting the leakage rate of metal surface sealing structure with the fractal characteristics,and the model accuracy is verified.