Investigations on the Mechanical Properties of Composite T-Joints with Defects under Bending Loading

The composite T-joint, a typical structural element, is widely used in the fields of aerospace due to their excellent mechanical properties. However, several defects might occur in this material during manufacturing because of the application of co-curing and co-bonding technologies. The existence of the defects results in the reduction in the load bearing capacity, which negatively affects the safety of the structure. In this study, a finite element (FE) model of composite T-joints is established, which is verified by quasi-static tests to investigate the load bearing capacity and failure modes of composite T-joints under bending loadings with different types of defects, including core material defects, radius floating of the fillet, and debonding defects. It is indicated that the failure modes of T-joints with different kinds of defects under bending loadings are similar, i.e., the delamination occurs firstly at the interface between the filling area and the L-rib before expanding to both sides. Meanwhile, the types of defects exert great effects on the load bearing capacity of T-joints, and the debonding defects in the arc area represent the most dangerous one. Furthermore, the orthogonal test method was adopted to analyze the influence of combined defects on the load bearing capacity of T-joints, and the findings reveal that the most sensitive type of defect is the debonding defects, followed by the radius floating of the fillet, and then core material defects. This result indicates that combined defects have a coupling effect on the load bearing capacity of composite T-joints. This study provides theoretical guidance and technical support for the repair of the defects of composite T-joints.