Maximization of buckling strength of sandwich- structured composite panels subjected to in-plane compression loadings

Sandwich composites are versatile and developable materials that are generally used in many industrial and structural applications. Among the reasons for its use in many areas are its superior properties such as low weight, high strength, good thermal and acoustic insulation, high rigidity, design flexibility and corrosion resistance. In this thesis, it is aimed to obtain sandwich structured composites with maximum buckling strength for various geometric and in- plane loading scenarios. There are two separate studies in the thesis. In line with this goal, sandwich structure composite with graphite/epoxy faces and aluminum honeycomb core was selected from the literature for the first study. Afterwards, the program codes to be used in the optimization procedure were verified with the buckling problems previously solved in the literature. In this study, critical buckling load values very close to those in the reference study were obtained. Then, a pre-optimization study was carried out using the problems considered in code validation to investigate whether greater buckling strength of sandwich-structured composites is possible. As a result of this study, it has been seen that larger critical buckling loads in sandwich panels can be obtained by the optimum fiber orientations of the composite laminate faces under the symmetrical boundary condition using genetic algorithm (GA) in the MATLAB program. In the second study of the thesis, the critical buckling loads of sandwich composite panels considering the same materials from the literature were maximized. Optimization studies were carried out under the Tsai-Wu failure criterion by considering two types of cores and loading for various plate aspect ratios and in-plane loading ratios for optimum fiber orientation designs using conventional −45°, 0°, 45°, 90° fiber angles on the graphite/epoxy faces of sandwich panels. The specified problems were solved using GA/SQPA hybrid algorithm constituted with the MATLAB program. The results show that optimum designs are obtained having maximum buckling strength and not having the first ply failure under Nx = 100 N/mm and 200 N/mm loads for the most of the considered plate aspect ratios (a/b) and loading ratios (Ny/Nx) in both core types.