Abstract: Carbon fiber composite Skin/Stringer is a typical component of aircraft structure. However, the manufacturing process of laminated composite structure can lead to the existence of defects in the bonds. The pre-existing defects have a great effect on the ultimate bearing capacity and failure behavior of Skin/Stringer. Therefore, it is important to assess structural integrity. In this paper, the specimens were subjected to three-point bending. To evaluate the debonding mechanisms between the skin and the stringer, different sizes and locations of defects were taken into consideration. First, a three-dimensional finite element model based on Abaqus/Standard was established, and the bilinear cohesive zone model (CZM) was used to simulate the interface failure between the skin and the stringer; Then, the validity of the model were verified through the experimental data of the literatures. Finally based on the finite element model, the influence of the sizes and locations of the defects on the failure modes and the load-carrying capacity of the structure were investigated. The result indicats that the calculated results show good agreement with those of experiments. The load capacity of the structure is found to decrease with increasing defect size, and Skin-Stringer is very sensitive to defects at the middle of the interface; The failure modes of the Skin/Stringer changes because of the pre-existing defects. But the initial crack always occurs in the matrix near the interface area.

Key words: composite, stiffener, defects, cohesive zone model, carrying capacity