SIZE REDUCED COMPOSITE REPAIRS BY PLY WISE SCARFING

Scarf repairs of aerospace composite structures are today’s preferred technology. It is known that the shear stress distribution of the adhesive is inhomogeneous within the scarf. It depends on the stacking sequence and the scarf ratio. Main stress peaks are located at the interfaces of the 0 layers within the adhesive. A higher scarf ratio reduces these stress peaks at the cost of an increased joint size. A comprehensive study has been performed developing a methodology to reduce these shear stress peeks within state of the art composite scarf joints. The proposed method is a layer wise adaptation of the scarf ratio. Presented analytical calculations outline the concepts feasibility. An increased joint strength of layer wise scarfed coupons compared to constant ones is experimentally validated. Initial results show an increase in joint strength up to 50%. This improvement is a first step on the way towards size reduced composite repairs. The study’s results are relevant to increase the number of bonded repairs under current certification restrictions and to develop high strength composite scarf joints