| Neutrino physics is one of the most frontier research focus in the physics. Many countries have carried out a series of experiments on it, and a large number of detection facilities have been constructed, such as Super-Kamiokande neutrino detector in Japan and SNO neutrino experiment detector in Canada. China is also actively involved in the research of neutrinos, and has carried out Daya bay neutrino detection experiment, in which many achievements have been obtained. In 2013, Jiangmen Underground Neutrino Observatory (JUNO) project was proposed on the basis of Daya bay neutrino detection experiments, planning to build an acrylic sphere neutron detector with an inner diameter of 35.5m, in order to further explore the nature of neutrinos.In this thesis, the main goal is to design the structure of the acrylic sphere neutron detector. The preliminary design scheme, using a plurality of equatorial tangent column supports to support acrylic spherical vessel, cannot meet the design requirements because of high stress. According to the design technical requirements of the detector, the scheme of an equator flexible supported acrylic spherical vessel was proposed, whose strength and stability was analyzed by using the finite element method, and optimization design of the structure was determined. The main research work is as follows:(1) The artificial accelerated aging test for PMMA was carried out for studying the change of mechanical properties of PMMA aged in liquid scintillation. Based on the experimental data, the relationship between the change of mechanical properties and aging time was obtained, and the kinetic equation was extrapolated based on the aging mechanism. The kinetic equation was used to predict that the tensile strength degradation within PMMA,resulting in a reduction of 10% in 20 years within a liquid scintillation of 20℃.(2) The tensile strength of glued joints of the room-temperature bonding, quick bonding, UV light curing and UV curing with heat treatment were studied respectively. And the reliability of these four kinds of bonding methods are analyzed based on the Weibull distribution theory. The results show that the method of bonding at room temperature and quick bonding have higher reliability. Considering the adhesive speed, the quick bonding method was chosen for acrylic sphere neutron detector, and the joint strength weakening coefficient is 0.83.(3) Based on the data from joint tensile tests, aging tests and bulk tensile tests on PMMA, the allowable tensile stress of PMMA is 5MPa; Referring to EN13445 and the results of finite element analysis, the stability safety factor by eigenvalue analysis of ANSYS Workbench is 7.2.(4) The scheme of an equator flexible supported acrylic spherical vessel was proposed, and the strength and stability of which were analyzed with the finite element method. The results show that acrylic spherical vessel doesn’t meet the requirements of stability in the condition of working and filling with same level of both side medium, and the stability of acrylic spherical can be improved by increasing the wall thickness of the lower hemisphere or the difference of level between internal medium and external medium. Combined the condition of physical experiment, the difference of level between internal medium and external medium was increased to 3.5m for the purpose of improving the stability.(5) The influence of ellipse degree on the stability of acrylic spherical vessel and the effect of failure of one support on the strength of acrylic spherical vessel were analyzed with the finite element method. The results show that the influence of the degree of ellipse on the stability of acrylic spherical vessel and the effect of failure of one support on the strength of acrylic spherical vessel is negligible in a certain range. |
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