Nonlinear buckling of cylinders under external pressure with nonaxisymmetric thickness imperfections using the COMI axisymmetric shell element

This paper concerns the influence of thickness imperfections on the nonlinear buckling of cylinders under uniform external pressure. The material is assumed to behave elastically. A parametric study is performed using the COMI finite element, which allows to perform nonlinear analyses of shells of revolution with any kind of nonaxisymmetric initial imperfection. Let us assume that the perfect shell buckles with a Fourier mode m and that the initial thickness imperfection is on Fourier mode 1, m or 2m. As shown in a previous study on linear buckling of cylinders with thickness imperfections, 1 and 2m are the most harmful thickness imperfections. We show that the nonlinear pre-buckling does not affect the buckling pressures very much. We then study the coupling with geometrical imperfections. We show that the geometry and thickness imperfections have a multiplicative effect on the decrease in buckling load in the nonlinear range. Finally, we show that if one uses only the measured outer radius of a shell to input initial imperfections, very different nonlinear buckling pressures can be obtained under the assumptions that the imperfection is purely geometric, purely thickness, or a combination of both. (C) 2001 Elsevier Science Ltd. All rights reserved.