Two carbon-fiber-reinforced composite cylinders were tested in bending. One cylinder, the baseline cylinder, consisted of 0º, 90º and ±45º plies, whereas the other cylinder, called the variable-stiffness cylinder, contained plies with fiber orientations that varied in the circumferential direction, which caused a variation in laminate stiffness. The cylinders were optimized for maximum buckling load carrying capability under bending. Simulations showed that the variable-stiffness cylinder was able to redistribute the applied loads around the circumference, resulting in lower strain values at both the tension and the compression side of the cylinder and an improvement of the buckling load by 18 percent compared to the baseline cylinder. The purpose of the bending test was to show that the improvements obtained in the analytical results could also be achieved experimentally. The baseline cylinder was tested first to serve as a benchmark for the variable-stiffness cylinder. The finite element model was adjusted based on the baseline cylinder tests to represent the experimental conditions correctly. The model took into account the flexible connection between the cylinder and the test fixture, the test mechanism and geometric imperfections present in the cylinder and showed good agreement with the experimental results. The variable-stiffness cylinder was tested twice: first oriented in the direction it was designed for and later rotated 180 degrees about the cylinder axis, such that the loading direction on the cylinder was reversed. The predicted global response and strain distributions for both configurations corresponded well with the experimental data. The flexible boundary conditions and the geometric imperfections affected the load and strain distributions of the baseline and the variable-stiffness cylinders, but the relative improvements of the variablestiffness cylinder in the preferred orientation with respect to the baseline cylinder were not affected. Follow-up tests of the cylinders including cutouts or induced damage are planned in the future.
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