Void Reduction Strategies for Improved Strength Recovery in Co-Bonded Composite Scarf Repairs M. Préau, M. Brodel, and P. Hubert Department of Mechanical Engineering, McGill University 817 Rue Sherbrooke Ouest, Montreal, H3A 0C3, Canada pascal.hubert@mcgill.ca SUMMARY An ‘air breathable’ film adhesive was used to improve repair patch and bondline quality of in situ bonded scarf repairs. The method led to a significant reduction in void content in both the repair patch and the bondline. Controlled low-porosity scarf repairs were tested in tension and exhibited higher strength recovery and a change in failure mode. Keywords: Repairs, out-of-autoclave, adhesive bonding, X-ray, porosity, failure mechanism BACKGROUND Co-bonded scarf repairs are a high property recovery solution for damaged composite components. The process involves co-bonding a stack of prepreg plies with an adhesive film over the repair cavity. Repairs are performed directly on the damaged component under atmospheric pressure only. As no additional consolidation pressure is available in repair conditions, any entrapped air is likely to generate unacceptable level of voidage. This study examined the use of semi-impregnated prepregs and an engineered film adhesive. REPAIR PROCESSING The semi-impregnated material selected for this work was Cytec’s Cycom ® 5320 with plain-weave and 8-harness satin fibre bed architectures. Low temperature cure adhesive FM ® 300-2 was modified to allow air passing through. An angle of 3° was used to prepare the parent laminate, and all repairs were conducted in a convection oven after a room-temperature vacuum hold under ambient pressure. VOID REDUCTION AND IMPROVED STRENGTH RECOVERY X-ray radiography was employed to assess the content, distribution, and morphology of voids within the bondline. Optical microscopy was used to visualize repair patch quality. When the adhesive film was not modified, large voids were found in the step resin-rich regions of the bondline in large quantities. When using an ‘air breathable’ adhesive, almost no voids were found in the bondline. Uni-axial tensile test results suggested that reducing porosity in the bondline improves the strength recovery of the repair. The figure below displays representative X-ray images of the adhesive void morphology and distribution along with the ultimate tensile strength recovery of the respective repair configurations.