A note on imperfection sensitivity of externally pressurized shells

The present paper extends the Hutchinson approach to consider the effect of the axisymmetric and nonaxisymmetric imperfections acting simultaneously. The solution is obtained using two interactive modes and the first variation of the potential energy. From this, two equilibrium equations result which contain a nonlinear relationship between the participating modes of deformation. Relationships for the critical pressure under the two mode participation are evaluated. These results are compared to specific numerical results developed from a computer program, NBALL, which is based upon Sanders' equations for the geometrically nonlinear analysis of arbitrary loaded shells of revolution. This comparison reveals the region of validity of Hutchinsons's results and the extension of his method presented herein. (orig.)