The influence of circumferential thickness variations on the buckling of cylindrical shells under external pressure

Imperfection sensitivity of thin shells of constant thickness was widely studied during the last 50 years (J.G. Teng, Appl. Mech. Rev. 1996:49(4)). Recently, Koiter et al. (Int. J. Solids Struct. 1994:31(6):797–805) investigated the influence of axisymmetric modal thickness variation on the buckling load of an axially compressed shell. In this paper, the influence of harmonic thickness variation in the circumferential direction on thin cylindrical shell buckling under external pressure is analysed by means of FE bifurcation analysis. Two different FE codes were used, one with quasi-axisymmetrical multimodal Fourier analysis (A. Combescure, Etude de la stabilité des coques minces sous chargements complexes dans INCA. Rapport DMT/94-460, in French, 1994; Modélisation des coques axisymétriques avec imperfection quelconque: L’élément COMI (in French). Rapport DMT/97-189, 1997; Schauder B. Flambage des Coques Cylindriques en Fléxion. Thèse de doctorat, INSA de Lyon, in French, 1997), and the second one with 3D shell elements. A new quasi-axisymmetric element (COMI) is presented. It uses Fourier series expansion in the circumferential direction coupled with a full numerical integration around the circumference, which allows any variation of thickness or of initial imperfections.