ON DESIGN AND OPTIMIZATION OF CURVED COMPOSITE BEAMS

In curved beams of thin-walled construction secondary stresses such as crushing of the web and curling of the flanges occur due to the initial curvature of the beam. The presence of these stresses becomes more significant when advanced composite materials are used. Two parameters, accounting for material stiffness and geometric effects of the beam structure, characterize the flange stress redistribution. Using a simple "strength of materials"-based analytical solution for flange curling and web crushing, the design and optimization of curved composite I- and box beams under bending were examined. The ply orientations and stacking sequence of the flange have been found to drastically affect the nature of these stress redistributions and consequently the overall load carrying capability of the beam. Overall frame optimization was explored. To maximize load carrying capability, for a given amount of material, of a curved beam structure under bending in its own plane, the overall bending stiffness should be maximized and flange curling minimized. For composite beams, this is most effectively accomplished by minimizing web thickness and placing a large percentage of flange fibers perpendicular to the web. For the box beam, a low web bending stiffness seems beneficial in reducing flange curling moments. While web crushing needs to be considered, the curling of the flanges and its effect on the web is more critical.