Keywords: torsion, combined loading, buckling, piping, elastic-plastic, temperature.

Torsional buckling of cylindrical shells has been studied for a wide range of geometries, initial geometric imperfections and boundary conditions, but only for thin-walled shells where buckling remains elastic. Elastic-plastic buckling of cylindrical shells subjected to torsion, on the other hand, has received much less attention. Experimental results are rare here and they are scattered over a long timescale.

Motivation for this contribution comes from recent developments in metallic materials which can withstand extreme environments. One particular path of research activity has looked into the manipulation of a grain structure in order to increase the strength of a structural component. To this end it has been shown that twisted bars develop a permanent helical grain structure. By analogy, it has been felt that by twisting cylindrical shells or tubes one can obtain similar effects in them. If so, this would instantly lead to an increase of the tube's strength, e.g. in tubes subjected to internal pressure.

Hence the application of torsion has suddenly become one of the possible routes for the above mentioned structural enhancement of thick tubes. But, as expected, torsional buckling could limit this process and there appears to be a very limited amount of available information on buckling performance of mandrel free 'thick tubes' within the elastic-plastic range.

The current paper briefly reviews the field of torsional buckling of cylinders for the radius-to-wall-thickness ratio, R/t, in the range from 100 to 10. The finite element predictions of torsional buckling, and based on proprietory finite element code, are benchmarked against known experimental data and other available numerical predictions of static buckling. Some fresh results are obtained for combined static stability of cylinders, e.g. for torsion-tension, axial tension/compression-external pressure. Both the elastic and elastic-plastic buckling range, are discussed.

Next, the paper moves to torsional buckling of metallic tubes which are differentially heated along the axial direction. This results in inhomogenous material properties: variable Young's modulus, the yield point, and post-yield behaviour of material.

The finite element results are provided for a specific case study, i.e. for a steel tube from PM2000 alloy with the length-to-radius ratio, L/R = 13.88, and the ratio, R/t = 7.55. The soft segment of the tube had 750°C, and the influence of its length, and transition to cool ('stiff') segments, on buckling has been assessed. Other relevant details are provided in the manuscript together with the proposed extensions of the scope in the future computations driven by this specific application.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £140 +P&P)