Numerical and experimental analysis of buckling of hemisphere shell made by spinning forming method subjected to uniform external pressure

Due to its buckling resistance, the spherical shell is an ideal geometry for use in pressure vessels under uniform external pressure. The collapse pressure of these types of shells is much lower than its theoretical value due to the high sensitivity to imperfections and the yield stress of the material. Unlike cylindrical shells, the collapse pressure of spherical shells is not only dependent on the size of the imperfection, but is also dependent on the shape of the imperfection. Since the imperfection depends on the sheet metal forming method, it is necessary to investigate the effect of the fabrication method on the collapse pressure. This article is focused on experimental and numerical study of buckling of hemispherical shell made by spinning forming method. The most important problem of this method is the lack of control over the thickness. In this method, the imperfections are axially symmetrical, which is one of the advantages of this method. In this article, buckling analysis due to both diameter and thickness variations are done separately and simultaneously. It has been shown that thickness variations in rotational forming should be considered in the analysis of shell collapse. Also, by comparing the numerical and experimental results shown with the help of quadratic volume elements, thickness changes and boundary conditions can be applied with higher reliability compared to the shell element.