Buckling of near-perfect thick-walled circular cylinders under-external Hydrostatic pressure

The aim of this study was to produce design charts to predict inelastic collapse pressures for thick-walled circular cylinders under uniform external pressure because the existing charts were out of the range for shorter and thicker vessels. Both theoretical and experimental investigations were carried out on 15 stainless steel models, which were tested to destruction and reported for the first time. A theoretical investigation was also carried on other models, tested by previous researchers, to give more points and more credibility to the design chart. The theoretical investigation was based on an analytical method because previous work proved that, in general, it was superior to numerical methods for this particular problem. It was hoped that the details from the current series of models, together with the new design chart, would enable some smaller submarines to descend to the bottom of the Mariana’s Trench (11.52 km or 7.16 mi); one of the models collapsed at a pressure of about 1000 bar, which was equivalent to a submarine diving to a depth of about 10 km (6.2 mi). The analytical solution adopted the von Mises buckling analysis via a home produced computer program called MisesNP, which also calculated the Windenburg thinness ratio (λ). By plotting the reciprocal thinness ratio against the plastic knockdown factor (PKD), where the PKD was obtained by dividing the theoretical buckling pressure by the corresponding experimentally obtained buckling pressure for each vessel, a useful design chart was produced.