This paper presents the results of a numerical investigation for applying a combination of buckling mode shapes as an initial imperfection to shell geometries under external pressure. The effect that imposed imperfections had on the critical buckling pressure was found to be dependent upon both the shell geometry and the characteristics of the imposed imperfection. Imperfections were generated via linear combinations of the linear elastic buckling mode shapes, with the fundamental mode having the greatest influence. For a number of tests, inclusion of higher order modes into the initial imperfection caused an increase in the critical buckling pressure. This behaviour was observed for both elastic and plastic material models.

For the purpose of limiting the extent of the analysis, the magnitudes of imposed imperfections were maintained within the industry required fabrication tolerances and in particular, acceptable out-of-roundness. The purpose of this paper is to present the methodology and results from this imperfection investigation. Additional testing and discussion may allow a design methodology to be developed that addresses the application of initial imperfections in shells under external pressure.

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