Investigation of the structural strength of a carbon fiber reinforced spar in an UAV wing based on cross-section profile and ply orientations using the finite element method

Due to their high strength, low density, and fatigue resistance, carbon fiber reinforced composites are widely used in the aerospace industry. The use of these materials is increasing day by day, particularly in the wing and fuselage structures of lightweight aerial platforms. Numerous studies can be found in the literature on this topic. In this thesis, the structural behavior of carbon fiber reinforced composite beams used in wing structures which is one of the most critical components of air vehicles has been numerically investigated with respect to cross-sectional profiles and fiber lay-up angles. Within this scope, finite element models were developed for beam structures with I, C, and box cross-sections, using fiber orientations of 0˚ and ±45˚, under aerodynamic loading conditions. A wing design was created for a selected aircraft configuration, and the pressure loads obtained from CFD (Computational Fluid Dynamics) analyses conducted on this wing were transferred to the structural model using a one-way Fluid-Structure Interaction approach. Based on these loads, static structural analyses were performed. The results were then evaluated in relation to the cross-sectional profiles and lay-up angles of the beams. It was observed that the use of ±45˚ fiber layers led to sudden drops in IRF (Inverse Reserve Factor) values, whereas 0˚ fibers resulted in increased IRF values with noticeable fluctuations. These fluctuations became more pronounced as the ratio of ±45˚ layers in the stacking sequence increased. On the other hand, lay-ups consisting completely 0˚ fibers showed a highly consistent IRF distribution. Moreover, the use of ±45˚ layers was found to increase deformations in both the lift and drag directions. In terms of cross-section comparison, the box profile demonstrated superior strength, while the C profile proved more advantageous in terms of weight. Although the I profile was close to the C profile in terms of weight, it lagged behind both in strength and in terms of manufacturing complexity.