Keywords: conical shells, external pressure, axial compression, buckling, combined stability.

The literature review shows that there have been more than 600 experimental buckling tests on truncated, and non-reinforced, conical shells since 1960. Nearly all of them were within the elastic regime. Experimental test results on elastic-plastic buckling have only become available within the last decade, and in addition, all of them were on cones being subjected to a single loading. Elastic-plastic buckling tests on cones subjected to the simultaneous action of two or more loads appear not to exist in the open literature. The background to the current contribution can be found in the following references [1,2].

The paper concentrates on combined stability of mild steel conical shells subjected to quasi-static external pressure and axial compression. The envelope of the load bearing capacity is established numerically together with forms of stability loss (asymmetric bifurcation, axisymmetric collapse). In addition, for all computed configurations the first yielding of the wall has been identified. This allowed the first-yield envelope to be drawn, in addition to the ultimate failure envelope. The split of total stability domain into the elastic and elastic-plastic parts becomes very important issue, both from theoretical and practical perspective, since the loading path within the elastic-plastic region is path-dependent (non-potential loading). A related feature of the combined stability plot is its convexity. In practice it means that any internal point of the domain can be reached through, for example, proportional loading [2]. Results provided in the current paper confirm the convexity of the combined stability plot.

The paper also addresses the concept of the equivalent cylinder. Due to similarities in behaviour of cones and cylinders, it has been postulated that the design of cones be based on the design of 'equivalent cylinders'. In the past this concept has been used for slender cones subjected to axial compression and within the elastic range. Its applicability to shorter and thicker cones has not been studied at all.

This paper provides theoretical and experimental results addressing not only axially compressed but also externally pressurised cones and derived from them equivalent cylinders. The equivalent cylinders of approximately 200 mm diameter, were CNC-machined and collapsed by axial compression and by external hydrostatic pressure.

Both the numerical and experimental results given in the current paper indicate that the concept of equivalent cylinders is not applicable to short and relatively thick metallic conical shells. As the above concept is being successfully used for slender cones with primarily elastic behaviour, it would be interesting to establish the range of its applicability.

1

J. Blachut, O. Ifayefunmi, "Plastic buckling of conical shells", Journal of Offshore Mechanics and Arctic Engineering, Transactions of the ASME, 132(4), in print, 2010. doi:10.1115/1.4001437

2

J. Blachut, O. Ifayefunmi, "Buckling of unstiffened steel cones subjected to axial compression and external pressure", in "Proceedings of the 29th International Conference on Ocean, Offshore and Arctic Engineering OMAE2010-20518", Shanghai, China, June 6-11, 2010. doi:10.1115/OMAE2010-20518

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