| For China lunar exploration project, the reliability of samples encapsulation was important to guarantee the scientific value of ground research. However, neither the US "Apollo" project nor the Soviet "Luna" project gave good solutions, and samples were contaminated in different levels, which made devices unable to maintain the lunar vacuum environment. Therefore, this study not only contributed to national major projects, but could be challenging as well.According to the requirements of reliability, automation and weight in China lunar exploration project, three different sealing schemes were proposed, including the explosive welding seal, the brazing seal and the redundant seal of O-type rubber ring and knife-edge indium. And the last one was selected when considering reliability. The leakage mechanism and mathematical models of the redundant seal were built for analysis, as well as the optimization of structures and processes. Then ground tests of leakage detection were carried out to validate this redundant seal’s preliminary feasibility. At last, the conclusions of this thesis gave the recommendable materials, structures and processes for the lunar sample return device.The main contents are as follows:In Chapter1, the significance of samples encapsulation techniques in lunar exploration programs was indicated, and then the literature review was given to analyze and compare different sealing materials and structures. At last, the study contents and difficulties were put forward.In Chapter2, the missions of the lunar sample return device were analyzed, as well as its working conditions. According to their requirements, three different sealing schemes were proposed, including the explosive welding seal, the brazing seal and the redundant seal of O-type rubber ring and knife-edge indium. And computational simulation, structures optimization and feasibility analysis were done for different prototypes respectively. At last, the redundant seal was chosen for the following theoretical and experimental studies.In Chapter3, the redundant seal for the lunar sample return device were discussed mainly in theory. For the O-type rubber seal, its leakage mathematics models were built based on Roth theory and empirical equations, and then the influence of rubber compression rate, temperature alternation, etc. were discussed to obtain better sealing performance; for the knife-edge indium seal, on one hand, its leakage models could be obtained based on Roth theory and finite element analysis, as well as the knife-edge optimization. On the other hand, new seal mechanism of cold-welding was explored to pursue better reliability. In addition to theoretical analysis, indium-silver alloy, which was the key material in this redundant seal, was studied by some tests, including the smelting process, the wettability on different metal coating surfaces, tensile strength measurement, the leak rate of welding interfaces by x-rays and image process, etc.In Chapter4, ground tests were conducted for the redundant seal based on theoretical analysis stated above, by means of helium-mass spectrometer technology. For the O-type rubber ring seal, three typical rubber and different installations were tested in alternative temperature. According to the results,"nitrile5080" was chosen when the elastic recovery and gas permeation were considered. Moreover, as rubber rings had different shrinkage directions, O-type rubber seal in axial installation had wider applicable temperature range, compared with that in radial installation; For the knife-edge indium seal, results showed that it could realize lower leak rate with lower pressing force, which contributed to lighter driving mechanism, besides, the addition of silver (9%) improved the alloy sealing performance in high temperature.In Chapter5, the main contents of this paper were concluded, as well as the study outcomes, from which recommendable sealing materials, structures and processes for the lunar sample return device were given. |
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