Abstract
The nonlinear stability analysis of a structure with initial geometric imperfections is very complex, difficult, and unsolved yet in designing. At present, there are no unified design guidelines for imperfection sensitive metal shells (spherical, cylindrical, conical, and so forth), and the study about composite shell structures is often for a specific ply parameter and therefore less adaptable. In this paper, the imperfection sensitivity analysis of orthotropic conical shells with and without cutouts under compression is investigated numerically. The eigenmode-shape imperfections and dimple-shape imperfections are introduced to conical shells with different cutout sizes. In order to find the worst imperfections that can reduce the buckling load as far as possible, an optimization framework based on the multiple perturbation load approach is developed by the present authors to search the possible positions of dimple-shape imperfections; the effectiveness of the algorithm has been proved by comparing with other conventional approaches.Mid-surface imperfections, a type of realistic imperfection, transferred from a cylinder are considered for a conical shell with a cutout at last. This work can provide a reference value for conical shell design for practical engineering applications.
Highlights
There is no doubt that the buckling behavior of thin-walled structures is inevitably affected by initial imperfections such as geometric deviations, load eccentricities, and different boundaries
Tafreshi29 investigated the buckling response of composite cylinders with cutouts, and the results showed that the buckling load decreases with the increase in cutout size; the analysis value could agree well with reference data by introducing initial geometric imperfections to the perfect geometry
Błachut et al conducted a series of experiments to investigate the buckling of conical shells under different types of external pressure, and the results showed that the predicted value provides a safety margin of about 100% against the experimental collapse due to the existence of initial geometric imperfections
Summary
There is no doubt that the buckling behavior of thin-walled structures is inevitably affected by initial imperfections such as geometric deviations, load eccentricities, and different boundaries. Speicher and Saal suggested to use the first eigenmode shape as a type of geometric imperfection, and the maximum amplitude of the imperfections is based on the manufacturing tolerance of the structure.8 This approach has been widely used by researchers to predict the buckling behavior of ideally buckled structures. Tafreshi investigated the buckling response of composite cylinders with cutouts, and the results showed that the buckling load decreases with the increase in cutout size; the analysis value could agree well with reference data by introducing initial geometric imperfections to the perfect geometry. Błachut et al conducted a series of experiments to investigate the buckling of conical shells under different types of external pressure, and the results showed that the predicted value provides a safety margin of about 100% against the experimental collapse due to the existence of initial geometric imperfections.. Mid-surface imperfections (MSIs), a type of realistic imperfection, transferred from a cylinder are introduced to the conical shell with a cutout
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