الفهرس 
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Abstract
In the early 1990s, aluminum alloys applications have been rapidly expanded in the construction of high-speed commercial and military marine vessels because of their higher strength-to-weight ratio when compared to steel structures. Aluminum is marked by its ability to be extruded into custom profiles very economically. The extruding process is used to create a fixed cross section profile and it is performed by pressing an aluminum bar through a pre-manufactured die that creates the desired cross-section. This ability gives the designer the freedom to replace conventional plate and welded-stiffener panels with extrusions where the plate thickness may be varied, or where the plate and stiffener construction may be replaced by a sandwich-type structures. Such extrusions can be used economically on large flat deck structures such as cargo and passenger decks, cross-decks for multi-hull vessels, and the side shell above the waterline. They offer the possibility of weight savings, along with easier welding and reduced complexity of the resulting structure. Aluminum extrusions applied in practice are often thin walled with various cross-sectional shapes. Combined with the moderate value of elastic modulus (E), the structural stability of such thin-walled structures, when subjected to compressive loads, is a primary concern in the design of large naval and aeronautical structural parts. Longitudinal compressive strength is highly dependent on the buckling strength of the structure as a whole and of each structural member. Compared to steel, relatively little experience has been accumulated for large aluminum structures, and the existing design recommendations for aluminum panels are to a large extent based on experience from steel structures. This means that the design recommendations did not adequately consider the influence of improved tolerances and the possibility of more efficient stiffener designs. Moreover, the cross-sectional instability behavior (local and distortional buckling) of aluminum extrusions with arbitrary cross-sectional shapes is unknown, and the application of the current design rules may therefore be inefficient.
The aim of the present work is to investigate numerically the ultimate compressive strength of stiffened panels with aluminum extruded cross-sections in alloy 6082-T6, in order to attain the optimal geometrical characteristics for different aluminum extruded profiles based on the load carrying capacity and weight reduction. The stability of stiffened panels with a variety of aluminum extruded profiles under uni-axial compressive loading is investigated using a finite element model. The model was validated using published results of experimental tests on full-size stiffened aluminum panels with extrusions in alloy 6082-T6 and was subsequently used to perform the study with varying geometrical parameters. The parameters investigated are the extruded stiffener shape, plate slenderness, column slenderness, section modulus, attached plate thickness, web thickness and flange thickness. These geometrical parameters are varied according to specified design constraints, and their effect on the axial load carrying capacity and the mode of failure of stiffened panels is investigated both in the elastic and inelastic ranges. The presented benchmark study is made up of a total of 108 different shapes of extruded profiles classified into 3 series. The results obtained are compared with the design guidelines formulated in Eurocode 9, which is developed by the European Committee for Standardization and deals with the design of aluminum structures and ultimate strength of plates. The performed comparison indicates that Eurocode 9 guidelines are generally conservative. Based on the results obtained, a criterion is proposed and design guidelines for the appropriate selection of optimal geometrical characteristics for different aluminum extruded profiles based on the load carrying capacity and weight reduction are formulated. The comparative analysis resulted in several concluding remarks and recommendations which are beneficial for both design and repair strategies.