Local buckling of shear-deformable composite laminated beams with flanges and webs made of unsymmetrically layered laminates

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Composite structures in the form of thin laminated plates or shells have found an increasing use in many different branches of engineering science, e.g. in aerospace or automotive engineering, but also in civil engineering applications over the last few decades. Due to their excellent specific strength and stiffness properties, composite laminates or shells are prominently found in lightweight engineering applications. Generally, composite laminates are layered plates or shells consisting of anisotropic and unidirectionally fiber-reinforced layers, e.g. carbon or glass fibers in a plastic matrix.In civil engineering applications, the most basic structural elements are prismatic beams under axial and bending load. Due to their slenderness and their overall thin-walled nature, stability problems such as global buckling (i.e. flexural buckling, flexural-torsional buckling and lateral buckling) as well as local buckling need to be taken into account. The current research project is devoted to the investigation of local buckling problems, i.e. the local buckling of flanges and webs of thin-walled composite laminated beams. For this purpose, discrete plate models shall be used in which webs and flanges are considered as being separate plates considering elastic clampings at those locations where adjacent beam segments intersect. Besides purely closed-form analytical solutions using the Rayleigh quotient employing adequate shape functions for all relevant buckling degrees of freedom, series expansions in conjunction with the Ritz method will enable the analysis and investigation of the local buckling behavior of composite laminated beams under consideration of transverse shear deformations and typical coupling effects as they occur in composite laminates. Specifically, bending-extension coupling in the case of unsymmetric laminates as well as bending-twisting coupling in the case of non-orthotropic laminate layups shall be taken into account explicitly. To this day, no investigations are available that would treat these effects in a systematic manner so that a significant requirement for research exists. Once adequate methods for the local buckling analysis have been developed, the buckling problem will be transformed into an optimization problem. By means of mathematical programming and nonlinear optimization, beam designs will be determined which exhibit the highest possible buckling resistance which is an important factor for any practical application where composite laminated beams are employed. Lastly, all developed analysis methods and the main buckling characteristics will be validated by sys-tematic buckling experiments.