Hybrid approaches for aircraft primary structure repairs

Currently bonded repairs can only be permitted on those aircraft primary structures suffering cracks/damages having a residual strength well exceeding the design limit load prior to application of the bonded repairs. This paper focuses on the approaches to meet the certification requirement by combining a bonded patch with other methods that enhance residual strength of the damaged structures. An overview of the recent research in this area conducted by Defence Science and Technology Group and its research partner organisations is presented. The outcomes from six individual research programs indicated the hybrid repair methods are promising for primary structure repair applications. Significant residual strength increases were achieved through optimum damage removal and/or inclusion of alternative load paths. These methods also provide significant additional fatigue life post premature bond failure that would allow any possible bond-line defect/damage to be identified by NDI means long before a catastrophic failure. The adhesive bond in the hybrid repairs was proven to provide significant benefit in enhancing the static strength and fatigue resistance. Key issues for the application of these hybrid repair methods and future research directions are also discussed.