Stability Analysis and Experiment of Large-Scale Spherical Models Built by High Strength Steel

The spherical shell is a typical form of revolution shells which are used widely in engineering especially as underwater pressure hull. To disclose structural characteristics of the whole spherical shell with some initial imperfections and residual stresses, both material nonlinear and geometric nonlinear Finite Element Analysis (FEA) has been carried out in this paper. In the FE analysis, the elastic-plasticity stress-strain relations have been adopted and the initial deflection of spherical shell caused in manufacture was also taken into account in creating model. It is also shown that the nonlinear structural characteristics of the spherical shell vary from its different dimension parameters for initial imperfection. Compared with the exiting different rule’s methods, nonlinear FEM may exactly show sphere’s stability varying by initial imperfections. Then two groups of experiments of four spherical models, made by a high strength steel and with two kinds of same main sizes but with different initial deflection on them for manufacture, have been finished in model pressure tests. The experiment has been analyzed by comparing in different method while these results eventually indicate that the buckling stability of a spherical shell model varies by its initial imperfection and such materials sphere critical load could not be accounted for by current rules except nonlinear FEM or modified theoretical elastic-plasticity analysis method. Therefore it is essential to obtain the new analysis and design method for spherical shell made by high strength steel used to deep-sea vehicle or other ocean engineering.