Composite Repair Techniques for J-Stiffened Composite Fuselage Structures,

The next generation of lightweight military aircrafts will feature an essentially increased application of CFRP to primary structure including fuselage side skins. Mainly for cost and weight reasons they will be large size integrally stiffened components cocured in a single shot operation. In order to avoid a costly replacement of the entire side skin in case of damage adjusted repair techniques are required. Basic repair philosophies for field and depot level repairs using composite materials were defined and proved by two different types of test specimen so far. Specially designed flat panels with a 50 mm diameter hole penetrating skin and stiffener were followed by single curved side skin elements damaged by a destructive qualification test. Both types were repaired using different methods and finally destructive tested. The test results showed that the restoration of part stiffness and sufficient strength after repair can successfully be realized. Manufacturing problems were recognized concerning material choice and cure cycles at elevated temperatures and regarding the non destructive inspection of applied repair patches.