Buckling of axially compressed cylindrical shells with local imperfections

Thin cylindrical shells in axial compression are known to be highly sensitive to geometric imperfections. Previous theoretical and experimental investigations have mostly concentrated on imperfections of small amplitude extending over the whole surface or at least over the whole circumference of the cylinder. Local imperfections occurring naturally are often found to be similar in form to the diamond-shaped facets of the buckle pattern of the collapsed cylinder. The current study is aimed at investigating experimentally the effect of such facet-shaped dimples on the load bearing capacity of the axially loaded circular cylindrical shell and evaluating the applicability of the space frame theory in predicting the same. The space frame theory predicts the secondary collapses observed in cylindrical shells under axial compression in terms of the buckling strengths of the diagonal members of an equivalent space frame having the geometry of the Yoshimura pattern. The proposed application of the space frame model to estimate the load carrying capacity of shells with diamond-shaped defects is based on the hypothesis that the effect of such a defect is similar to that of a facet of the same size in a buckled cylinder. Central to this model is the effective width of the flanges of the diagonal members of the space frame. In the present work modifications are introduced in the space frame theory to accommodate an analytical determination of the effective width of the flanges. Geometric constraints on the buckled configuration of the axially loaded cylinder are also investigated.