Buckling strength of welded HY-80 spherical shells

Introduction Spherical shell structures are commonly used in submarine application. Examples include submarines for deep sea research, submarines for military application or manned divers units. Buckling Strength ofWelded HY-80 Spherical Shells The pressure hull of this submarine is in the form of a complete sphere, being a typical example for a spherical shell structure in submarine application. HY-80 steel is often used for the construction of pressure hulls of submarines. It was developed in the 1950's, having a high yield strength of over 550N/mm2 and an ultimate strength of over 770 N/mm2. The hull structure of a submarine is mainly constructed by welding preformed plates. Figure 1.2 shows a picture of an end-dome of a submarine's pressure hull with a radius of 3.2 m and a wall-thickness of 32 mm, made from preformed shell segments. Preformed HY-80 shell segments are welded using multi-pass welds to form the final shell structure. The welding process causes residual stress and deformations in the structure. Resistance against buckling caused by the hydrostatic pressure of the water is an important factor to consider when designing the pressure hull of a submarine. The buckling strength of a shell is greatly influenced by its geometrical and structural imperfections Ce. g. residual stress), which are not known during the design process. A „knock-down“ factor based on lab-scale buckling tests and the geometrical imperfection of the shell is therefore used at present to render a secure buckling load of the structure. Due to improvements in the manufacturing process, like hot forming of the shell segments, geometrical imperfections are getting smaller and the only influencing imperfection arises from welding. The influence of the welding residual stress and deformation on the buckling strength of spherical shell structures far submarine application is currently not known.