Ultimate local strength of a submarine structure considering the influence of localized reduction of thickness

Abstract

Commonly, failures that occur in a submarine's structure could be caused by the high external hydrostatic pressure which may first take it to an unstable condition influenced by its geometry. In these vessels, reduction of thickness can develop because of corrosion or similar causes, which leads to reduction of structure's strength. The objective of this work is to determine the ultimate load that a cylindrical part of a submarine structure can support, considering the influence of localized thickness reduction. For this purpose, firstly the ultimate response of a 50 cm steel square plate of 3 mm in thickness, intact and considering local thickness reduction was analyzed using experimental tests and numerical approach. Then, the ultimate response of a high strength steel cylinder is numerically analyzed, intact condition and with localized thickness reduction. For this analysis typical submarine hull segment including three circular frames is modelled with solid finite elements subjected to external pressure and axial load, simultaneously. Buckling occurs in the elastic range of the material and the circular plate thickness reduction considering a diameter of 78% of the space between frames and 30% of the thickness, reduces only in 6% the collapse external load on the cylinder.