Study On The Large Deformation Of Thin-Wall Hemispherical Shells And The Dynamic Behavior Of The Internally Nested Spherical Shell System

Thin-walled spherical shells have been widely applied in engineering field because of their light weight, high bearing capacity and energy absorption, such as, aerospace, boat etc. But because the undevelopable geometric property of hemispherical shell surface, the deformation mode will changed, from axial symmetric dimpling to non axial symmetric dimpling, and the non axial symmetric dimpling mode is composed of plastic hinge lines. However, no appropriate theory gives the position and amount of plastic hinge lines.In this paper, the hemispherical shells are regarded as the research object, the large deformation of them and the non axial symmetric are analyzed by use of the universal testing machine SUMSCMT 5105 A and FEM. And the dynamic behavior of the internally nested spherical shell system was researched by the drop-testing machine DHR-9401. The main works are as follows:Two different deformation modes were observed based on the experimental results, that quasi-static response of hemispherical shell in different boundary condition. The deformation mode was hexagon when grooved boundary, but pentagon when free boundary. By utilizing the finite element method, the internal mechanism of effect of different boundary conditions on quasi-static response of hemispherical shell is researched, and the load deformation curves, transformation of deformation contour map and the relation between top displacement of hemispherical shell and loading plate displacement are compared. The result shows: the compression process of hemisphere shell can be divided into four stages: local flattening, axial symmetric dimpling, non axial symmetric dimpling and local flattening again when the friction coefficient between shell and baseplate is 0.1 or 0.2. However, when the friction coefficient is 0.5, the compression process can be divided into three stages: local flattening, axial symmetric dimpling and peripheral buckling of the shells.The compression progress of hemispherical shell between two plates can be divided into seven stages: local flattening, axial symmetric dimpling, non axial symmetric dimpling, strengthen, peripheral buckling, the second strengthen and overall collapse. And the reason for strengthen is the transition from the move of rolling hinge to peripheral buckling, not the vertex of shell reaches the baseplate.Based on the application of least energy consumption principle in structural analysis, the energy absorbed by the plastic hinge lines is obtained, then combining with the model of mirror reflection, the governing equation of polygonal model of thin spherical shells under impact loading is established. By comparing the numerical solution with the experimental results, we can obtain that the governing equation of polygonal model when considering the energy dissipation of plastic hinge lines is able to better predict the residual deformation of polygon collapse mode. According to the result about the deformation mode of hemisphere shells under different impact energy and different size of shells by finite element method, the transition from axial-symmetry collapse mode to the polygon collapse mode is observed when the impact energy increases. And the thickness of a thin spherical shell is more sensitive for the transition than the radius.The dynamic behavior of three different systems of the internally nested spherical shell was researched by the drop-testing machine DHR-9401. The result shows: the peak force of system will increase as the height of drop increases when the dimension of hemispherical shells is the same, but the response time doesn’t change. The peak force will decrease and the response time will lengthen when the stiffness of the outer shell is smaller than the inner shell, that will be useful for the energy absorbed.