Design optimization of composite I-beam wing spars with corrugated web

Abstract

The main goal of this study is to develop a methodology for optimum structural design of composite I-beam wing spars with wavy corrugated web to minimize mass and investigate their mechanical behaviors under aerodynamic loading conditions. For this purpose, Hu¨rku¸s Advanced Training Plane is selected as the plane model for which the spar is optimally designed. Accordingly, the wing dimensions are selected and the loads on the spar are evaluated. The lift as a non-uniformly distributed transverse load is calculated considering aircraft mass and directly applied to the spar. IM7/8552 carbon-fiber reinforced composite material is selected for the model because of its high strength with low density. Buckling analysis is carried out to determine the failure load levels considering that the most critical failure mode in I-beam spars is web buckling due to shear loads. Tsai-Wu criterion is used to predict static failure. By using ANSYS Parametric Design Language (APDL), codes are developed to implement the optimization algorithms and carry out structural analyses to determine the maximum load capacity of the spar. The web is designed like a multi-period wave with four parameters. These are the initial wavelength, the wavelength increment rate, the initial amplitude and the final amplitude. The shape of the web is defined by spline curves passing through key points having coordinates determined by the above-mentioned four parameters. The objective function to be minimized is chosen as the mass of the spar with the buckling strength constraint. The optimum shape of the web is found using modified simulated annealing algorithm, which is a stochastic global search algorithm. A considerable improvement is obtained in mechanical strength with much less use of material compared to the conventional wing spars.