On the propagation pressure of long cylindrical shells under external pressure

Abstract

Local imperfections induced in long tubes subjected to high external pressures can lead to local collapse, from which a propagating buckle can be initiated. This can result in catastrophic collapse of large sections of the structure. The propagation pressure is the lowest pressure at which such a buckle will propagate. For common structural metal tubes with diameter-to-thickness ratios of less than 100, the propagation pressure is typically half an order of magnitude lower than the collapse pressure of the intact tubes. As a result, the design of several tubular structures with external pressure loading requires that the collapse and propagation pressures be accurately known. This paper deals with the experimental and analytical challenges of establishing the propagation pressure. A special purpose three-dimensional analysis, in combination with experimental observations and results, is used to demonstrate a mechanism of initiation of propagating buckles in long tubes, to study the parametric dependence of the propagation pressure and to illustrate the effect of axial tension on the propagation pressure. Propagation pressures predicted with this analysis are used to evaluate the strengths and weaknesses of simpler models developed in the past.