| Due to the combining mechanical features, e.g. high specific strength and specific stiffness, and specially engineering functions, e.g. fatigue resistance and well designability, resin-matrix fiber composites appear to be promising and have been widely used in aerospace, transportation and civil construction applications. Herein, according to the characteristic of composite materialss, this thesis investigates the pre-buckling and post-buckling process for AGS structures under compressional load by analytical and FE methods. In addition, the effects of cutouts and reinforcement on AGS shells are studied. This study is a sub-part of the project of National Basic Research Program of China (973 Project) "Study on multi-functional innovation construction of extra-waighted and porous materials & structures" (No.2006CB601205), National Science Foundation in China (No.90816025 & No.10702012) and Doctor Startup Fund in Liaoning Province (No.20071093). The main research work can be summarized as follows:1. Analytical method for stability of geometrically perfect AGS periodic symmetry shellsGeometrically perfect AGS periodic symmetry shells consist of numerous periodic symmetry unit cells. Thus, equivalent stiffness model, which smears the grided panel as a flat panel or analyze the force and moment effect of the panel on a unit cell, is simple and efficient for the prediction of global mechanical behavior of AGS structures which consist high density of grid, therefore it is widely applied in the preliminary design of AGS structures. In this thesis, equivalent stiffness model for the AGS shells is developed based on structural mechanics, considering non-uniform distribution of grids. Then the expressions of global and local critical load under uniform external transverse pressure and compression are deduced. Finally, the author employ FEM results indicate the reliability of present analytical method2. Optimal design for geometrically perfect AGS periodic symmetry shellsThe various parameters influence the buckling behavior of the AGS shells, making it difficult to achieve a general conclusion. Meanwhile, the highly statically indeterminate and nonlinear characters of the structures, which caused by the distribution of ribs on the skin, raise the analytical cost. Besides, the design variables are taken on mixed discrete-continuous values. The author employed the Multi-Island genetic algorithm, which could transforms continuous design variables into discrete values, to proceed the optimal design of AGS shells. Finally, the results indicate that the iso-grid is the best grid patterns of AGS shells under axial or lateral load, based on typical numerical results for the minimum weights of AGS shells with ortho-grid, iso-grid and 45°angle-grid patterns under the same loads.3. Buckling behavior of compression-loaded AGS cylindrical shells with reinforced cutoutsTo meet the practical application requirements that serve as doors, windows, or access ports, there is necessity of cutouts in AGS cylindrical shells. Nevertheless, the cutouts will interrupt the continuity of stress and deformation distribution of AGS structures, reduce the equivalent cross-section of the structures and block the load transmission. Thus, the critical load carry capacity will reduce. In this thesis, the pre-buckling and post-buckling behavior of an typical AGS cylindrical shell with a rectangular cutout is investigated using FEM. The reinforced effects of a series of cutout reinforcements with different orientation, thickness and size were investigated. It suggests that there is an optimal reinforcement size for reinforcements of AGS cylindrical shells with cutouts.
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