On the Choice of Initial Geometric Imperfections in Externally Pressurized Shells

Localized and global, of eigenmode type, initial geometric imperfections were superimposed on perfect torispherical, ellipsoidal, and toroidal shells of circular and elliptical cross section. Reduction of the load-carrying capacity was then calculated numerically for various geometries and the yield point of material which was assumed to be mild steel. Results show that the buckling strength of torispheres and ellipsoids could be strongly affected by imperfections, but reduction of its magnitude was dependent on the choice of imperfection shape and, more importantly, on the imperfection’s location. Calculations carried out for closed toroids of circular cross section show that these shells are not sensitive to eigenmode-type imperfections, while toroids with elliptical cross sections are sensitive to eigen-imperfections.