Tensile performance of Fibre-Oriented scarf repair coupons for wing skin material

Bonded scarf repairs are attractive for large composite aerostructures due to their high performance and low weight compared with mechanical fastening methods. However, the scarfing process requires considerable time and expertise in the removal of undamaged parent material to which a repair patch is bonded. New portable and automated scarfing machines aim to address this issue while improving reliability and allowing for more complex and efficient repair designs. In this work, the tensile performance of novel fibre-oriented scarf repair coupons has been investigated. Non-destructive inspection and microscopy confirmed the viability and quality of a matched-ply approach for this type of complex repair design. Tensile testing revealed minor differences between the performance of size-optimised and strength-optimised fibre-oriented scarf repairs, which both behaved similarly to the conventional scarf design, reaching over 65% of the pristine laminate strength. However, analysis of the failure behaviour, loading curves, and fracture surfaces suggest that coupon failure initiates prematurely in the outermost parent plies rather than in the repair. This, and potential issues related to load application and the parent residual strength, are all discussed with recommendations for improved testing of repair joints in the future. © 2023 International Committee on Composite Materials. All rights reserved.