Keywords: circular cylinders, thick-walled, buckling, external pressure, design chart, finite elements, ANSYS.

The aim of this study was to produce a design chart to predict inelastic collapse pressures for thick-walled circular cylinders under uniform external pressure. Both theoretical and experimental investigations were carried out on fifteen stainless steel models, for the first time, which were tested to destruction. Theoretical investigations were also carried on other models, tested by previous researchers to give more points and more credibility to the design chart.

One of the theoretical investigations was based on an analytical method while the other theoretical analysis was based on a finite element method, using the well-known commercial computer package, namely ANSYS. 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 miles).

The analytical solution adopted the von Mises buckling analysis, using a computer program , written by the authors, called MisesNP, which also calculated the Windenburg thinness ratio (lambda). 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, useful design charts were produced.

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