Repair modeling and finite element analysis on composite wing structures

Carbon fiber reinforced polymers (CFRP) are widely used in the aviation industry. These materials have properties such as high strength-to-weight ratio, fatigue resistance, lightweight, and corrosion resistance. However, a significant disadvantage of these composite structures is their susceptibility to damage due to low impact toughness. It is known that when such damage occurs, it may necessitate the repair or replacement of the structure. Repair designs of composite structures can provide strength repair and enable relatively cost-effective repair of damaged parts by creating aerodynamically smooth surfaces. Therefore, parameters such as layer orientation, thickness, shape, extra layer count, and repair area size should be selected according to requirements. In this thesis, repair designs on a full-scale composite wing structure were modeled and the structural integrity of the structure was evaluated under realistic loading conditions. Repair modeling and analyses were performed using the shell method on the composite structure. To validate the shell method, tensile tests were conducted at the specimen level according to ASTM-3039D standards. The results obtained from the tests conducted at the specimen level corroborated the structural analysis results. Structural analyses were performed using ABAQUS software. In the continuation of the thesis study, computational fluid dynamics (CFD) analyses of a new wing model developed based on the NACA wing profiles and designed according to determined requirements were performed using ANSYS Fluent software. CFD analyses were conducted considering angles of attack of 0°-5°-10°-15°-20°-25°-30° on the designed wing profile. The pressure values obtained at the most critical angle of attack from the CFD analyses were determined using the load distribution function for use in structural analyses. In addition to aerodynamic forces, forces such as gravity, ammunition weight, and fuel weight were applied as boundary conditions to the full scale wing model. Various repair scenarios were identified, and structural analyses of repairs were performed on the most critical region of the full-scale wing shell structure. The repair scenarios applied in the determined region were compared with strain values using the Hashin method, and the repair works were validated. The results obtained showed that factors such as the number of damaged areas in the structure, the number of damaged layers, the number and orientation of extra layers applied to the repair area, and the shape of the repair design affect the load-carrying capacity and load path of the structure. The conducted numerical analysis studies showed that repair modeling using the shell method provided accurate results and provided important information about the method to be followed in case of possible damage.