An Investigation Of Molding Mechanism And Constitutive Relationship Of Spherical Shell Of Big Petal Of High Strength Steel

With the development of petroleum, chemical industry, metallurgy and city gas industry, spherical tank as storage container has got extensive application and quick development. At present, the technique of manufacturing spherical tank is developing to get large capacity, diverse structure and high parameter, which requires the petals to become big, to reduce the length of welding line, to cut down the cost and increase the safety of spherical tank. Since 1980s, a class of high strength steel with σb = 610 MPa was produced in our country. But the board width was too narrow to meet the requirement of large spherical tank. Till the beginning of this century, broad board with high strength steel is produced in large quantities, which makes it possible to manufacture large spherical tank with domestic high strength steel. So with the application of domestic high strength steel in large spherical tank, it becomes imperative to study the formation mechanism and constitutive relationship of large petals.In this paper, we analyzed the stress and deformation of spherical tank shell in the process of punching, conducted stress test and analysis, deduced the elastic and plastic incremental constitutive relationship in the state of multi-dimensional stress and strain. Also, we analyzed the structure of high spherical shell made of high strength steel with FEM, discussed the stress and deformation strain during the plastic deformation of board, and produced a basis for the design of punching of high-strength steel spherical shell so that we may improve the manufacturing accuracy, the quality of products, and the engineering level of spherical shell installation. The concrete work of the thesis is as follows:1 By investigating the stress model of geometrical coupled and physical nonlinear circular plate, the plate's stress and deformation during stamping forming of spherical tank shell is analyzed. The structural problem in the process of deformation for plate and shell is discussed. The effect and resilience rule of the plate's plastic deformation and membrane force both of the stress state and the deformation state are discussed. The process of deformation for plate accords with the theory of linear strengthening. When the membrane stress is removed, circle elasticity deformation end radial shorten elasticity deformation make for resilience.2 We tested and analyzed the stress in the process of formation of big petal high strength steel spherical shell. On the basis of analyzing the characteristic of formation and mechanics of the shell, a new method of stress test has been created,and an accurate measurement of stress distribution and variation rules in the particular state of punching process has been obtained. During the punching process, when the model is punched to the right place, the biggest strain and stress appear in the center district of the model, while the strain and stress in other area don't exceed it, which is beneficial to the shell. So during the process of rolling, if we control the deformation of punching and make sure the stress in central areas is lower than the strength limit of the material, there will be no craft crack in the material and disadvantage mechanic factor in the central area.3 It is very import to study the incremental constitutive relationship of the material so that we can make non-linear analysis for the spherical tank shell made of high strength steel. After getting the experimental data of simple tension, torsion and shear, we analyzed the yielding behavior of high strength steel board with the elastic and plastic theory in continuum mechanics. With the abundant data of simple tension of high strength steel board, we deduced the plastic incremental constitutive relationship of high strength steel board in complex stress state. Also, with the data of torsion shearing of high strength steel board and using numerical simulation, we deduced another expression of the plastic incremental constitutive relationship. Considering the relationship of material parameters, we verif...