Design Optimization for Hydrostatic Pressure in Hybrid Composite Cylinders

Abstract This study explores an optimization system to achieve the highest collapse pressure on glass-carbon hybrid composite cylinders under hydrostatic loading conditions. This work evaluates and validates previously established composite buckling solutions for cylindrical composite structures under hydrostatic pressure with experimental results of hybrid composite shells. It utilizes the validated analytical solution to optimize the buckling pressure by varying layup configuration, optimum layup angle, material content, and thickness of each lamina. The optimization is performed on asymmetric and symmetric layup cases to evaluate the influence of the hybrid layup construction on the buckling performance of the structure. Results show that the thicker glass fiber plies are preferred for inner layers and the stiffer carbon fiber plies for the outermost layers to achieve maximum buckling collapse pressure for all the optimization cases, as this configuration provides superior flexural rigidity. For hybrid composite structures with asymmetric configurations, the collapse pressure can be higher when most layers are made of glass fiber if the glass layers are at least twice as thick as the carbon layers. Similarly, axial-load-resistant layers (0°) should be located around the geometric center of the laminate with the hoop-load-resistant layers (90°) on or near the outermost layers and shear-resistant layers (45°) between these layers for both symmetric and asymmetric hybrid structures. Moreover, long tubes with small diameters (L/D > 10) favor hoop bending stiffnesses (90°) for all layers in the laminate due to less influence of boundary conditions at endcap locations.