Impact damage of composite scarf bonded repair structure for aircraft

The high efficiency load transferred scarf joints have been applied widely in composite junctions and repairs. However, the damage resistance and damage tolerance were not considered in aircraft structure design. The mechanical and fracture properties of composite scarf repair under low velocity impact were investigated. In the bonded zone, different impact locations were set to found the most sensitive location. Then at this position the variation of impact energy was studied. Low impact energy level and high energy level studies imply that the central position has the lowest impact resistance. Impact responses of impact load reveal that four typical phases exist during impact procedure. The impact load has double peak forces phenomenon. The first peak keeps constant while the second one rises with the increase of impact energy. From the failure investigating on the central section, it is found that there are two damage modes of the composites laminates and the adhesive. Composite damage contains the matrix crack on 90ånd 45° plies and the delamination between 0° and 90° plies. Adhesive damage appears at the backside of specimen opposite to the impact location. Further study of simulation reveals the whole impact behavior of the composite scarf repair. The composite damage leads to impact load dropping at PhaseⅡ, and adhesive damage causes the impact load dropping again at the beginning of phase Ⅳ.