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This and the next 3 images are from:
Jeroen Mennink, “Cross-sectional stability of aluminium extrusions”, Ph.D. dissertation Eindhoven University of Technology, The Netherlands, 2002
SUMMARY: Aluminium extrusions applied in daily practice are often thin-walled with complex cross- sectional shapes. These shapes are based on a variety of demands that are in general non-structural. As a result, several types of instability may occur, including overall and cross-sectional instability modes as well as mode interactions. Research on overall buckling is usually based on simple and symmetrical cross-sections, whereas cross-sectional instability is simplified to buckling of individual plates. It is therefore highly unlikely that these design rules provide an accurate description of the actual buckling behaviour of arbitrary cross-sections. As predicted failure modes not necessarily agree with actual ones, the outcome of the results may be overly conservative but could be unsafe as well. In order to investigate the actual cross-sectional stability behaviour of aluminium extrusions, a large experimental program is executed at Eindhoven University of Technology. This program consists of aluminium extrusions under uniform axial compression. Test specimens with rectangular hollows (SHS), U-sections (US), as well as very complex cross-sectional shapes (CS) have been tested. A detailed investigation is made into the influence of the test set-up, initial imperfections, as well as the material characteristic. This results in is a large set of test data on the actual buckling behaviour of aluminium extrusions, including local, distortional, flexural and flexural-torsional buckling, as well as mode interaction. To support the findings of the experiments, a numerical program using the finite element (FE) method is executed. Most experiments are simulated using the actual geometry, material, and imperfections. Comparison of the experimental and numerical results shows that an accurate prediction is achieved. Furthermore, the FE-analyses allow a detailed investigation of specific aspects like the bifurcation load, the influence of imperfections and materials, the test set-up, and mode interaction. The FE-results enable the development of a new and general prediction model for the local buckling behaviour of aluminium extrusions. Based on the actual local buckling behaviour of cross-sections, it is derived for uniformly compressed aluminium extrusions with arbitrary cross-sections consisting of flat plates. As such, it allows an accurate and conservative prediction of the strength and stiffness of a large range of commercial extrusions. The promising results of this model may result in design rules that enable more economical designs and are able to include distortional buckling and mode interaction. This combination of experimental, numerical (FE), and analytical work results in a thorough investigation on the actual local buckling behaviour of aluminium extrusions with arbitrary and complex cross-sections.
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