Aerospace manufacturers increasingly rely on composite materials for the most advanced aircraft, due to their superior performance and tailorability. As the adoption of such structures grows, so does the occurrence of various kind of damages throughout their service life. Therefore, there is the necessity to develop robust, reliable and repeatable procedures to fully restore the structural integrity of composite components. An additional challenge is posed by composite structures that include functional inserts: the functionality of such inserts needs to be re-instated on top of the integrity of the overall structure, while ensuring a seamless repair finish. This thesis considered two damage scenarios in a CFRP fuselage access panel whose edges are wrapped with a functional material, and defined the most suited repair procedure to tackle them.
The first scenario is represented by damages located in the CFRP structural part of the fuselage access panel. The scarf repair method was identified as the optimal one for this instance, research effort was therefore directed towards its improvement. Indeed, such technique does not currently allow to achieve a fully flush surface, as a mismatch between the repaired area and the undamaged one remains noticeable. Eliminating such unevenness is crucial for stealth and eventually aerodynamic reasons, and therefore needs to be investigated. Two repair configurations were implemented: the first one consists of re-milling the surface once the repair is completed, while the second one relies on a thinner repair patch that — once properly aligned — allows for a flush surface. The first option allowed for an improvement of over 80\%, reducing the surface unevenness from more than 1/2 of a millimeter to less than a 1/10, while ensuring a smooth, continuous surface finish. At the same time, it proved capable of meeting all the mechanical requirements, performing closely to a reference repair configuration in several tests. On the other hand, the second option only partially improved the surface finish, but fell short of the fatigue life requirement by a large margin and also showed a significantly poorer mechanical performance compared to the reference repair and the other configuration.
The second scenario is represented by small, cosmetic damages located in the functional edge of the fuselage access panel. It was identified that such damages are best addressed with repair procedures based on a filler compound. Guidelines to define such repair compounds were defined. Then, two repair procedures based on the use of these compounds were thought out: the first one is similar to conventional filling repair processes, while the second one relies on a bespoke tool to inject the repair compound. The former was implemented and produced promising results: it allowed to precisely restore the original profile and achieve a seamless surface finish. Damages affecting both the structural and functional parts were also briefly addressed, paving the way for future developments.