| Porous materials have been developed rapidly in recent years,among which porous graphite is widely used in mechanical seals,electrode materials and biological environmental protection because of its excellent physical chemistry properties.In the field of mechanical seals,the strength and hardness of materials are required to be high,but the mechanical properties of porous graphite,such as strength and hardness,can not meet the requirements of working conditions because of its too many pores,at present,the properties of porous graphite are often improved by means of impregnation.Because of the heterogeneity of the pores of the samples and the fact that the experiments are usually carried out in a high pressure and closed environment,the impregnation process is difficult to follow and the research is less,so the numerical simulation method is considered to be adopted to study the process,however,the oversimplification of the model leads to its poor universality.In this thesis,the threedimensional structure of porous graphite is obtained by experiments,and the threedimensional reconstruction technique is used to establish the model which can be used in the finite element simulation,the related infiltration laws of pressure,velocity,inlet and outlet modes and different media are studied through the porous media seepage mechanics,which provides certain support and reference for the porous media infiltration flow.The main research contents and conclusions are as follows:(1)The porous graphite samples are characterized by metallographic scanning,scanning electron microscopy and computed tomography scanning.The pore structure and solid skeleton structure are analyzed.The Electron Probe X-ray Micro-Analyzer is used to obtain the high power electron micrograph and the characteristic elements are extracted,so that the sample quality of impregnated graphite can be better observed.(2)Based on Avizo technology,contrast adjustment,slice selection and filter noise reduction are preprocessed on the CT slices,and the pore structure is extracted after threshold segmentation.The error between the calculated results and the real CT scanning results is 1.37% and 1.79% respectively,which proves the rationality and feasibility of 3D reconstruction.In order to save computing resources,the models are simplified properly.The size of 200 × 200 × 200 voxels is determined and the threedimensional structures are derived.The models are meshed in ICEM,and the grid reliabilities are ensured by the grid-independent verification.The sample 1 model has664544 nodes and 3812061 tetrahedral meshes,while the sample 2 model has 467986 nodes and 2641524 tetrahedral meshes.(3)Through the finite element simulation,the influence of pressure,velocity and inlet and outlet mode on the seepage flow of molten metal antimony is analyzed.The results show that the optimum inlet pressure range is 7.0 MPa-10.0 MPa under oneinlet-one-outlet mode,the optimal inlet pressure range is 3.0 MPa-4.0 MPa under twoinlet-two-outlet mode,and the optimal inlet pressure range is 2.5MPa-3.5MPa under four-inlet-two-outlet mode.According to the pressure and velocity distribution,the best impregnation effect is obtained under the four-inlet-two-outlet impregnation mode.(4)Through the finite element simulation,the influence of pressure,velocity and inlet and outlet mode on the seepage flow of epoxy is analyzed.The results showed that the optimal inlet pressure range is 1.0MPa-2.0MPa under one-inlet-one-outlet mode,through the pressure and velocity distribution,the best impregnation effect is four-inlettwo-outlet mode,but the internal velocity is too high to damage the sample solid skeleton.Due to the narrow pore channel in the middle of the sample,two-inlet-twooutlet mode shows poor impregnation effect.For two-inlet-four-outlet mode,the best impregnation effect is obtained when the porosity of the inlet is large,and the optimum inlet pressure range is 1.0 MPa-1.5 MPa.The thesis has 64 figures,14 tables,and 89 references. |
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