Experimentation and cohesive zone model validation of adhesively-bonded repair strategies for carbon fibre reinforcement polymers

The demand for the use of advanced composite materials in the aerospace industry has significantly increased in recent years due to their specific mechanical properties. Repairing of damaged aerospace composite parts has, therefore, become necessary to seek environmental sustainability and cost reduction by preventing scrapping the parts. To promote the best practices in composite repairing and propose a numerical design approach, this study aims to investigate the restitution capacity of repair methods for high-performance composite materials, such as carbon fibre prepregs with an epoxy matrix, after the identification of surface cracks. Two different adhesive repair techniques were chosen, namely composite filling (CF) and composite skin replacement (CSR). Tensile and 3-point bending (3PB) tests were performed, and the maximum load ( P m ), failure energy ( E f ), and failure modes evaluated. The experiments were numerically replicated using cohesive zone models (CZM) for the adhesive failure and the Tsai-Wu criterion for composite fracture prediction. Beforehand, peel ( σ y ) and shear ( τ xy ) stresses in the adhesive film were analysed in the elastic regime. The numerical results accurately replicated the experiments. Overall, this analysis showed that the CSR repair method restores over 80% of the original composite strength, under both tensile and flexural loads. On the other hand, the CF repair method was ineffective and revealed worse results than the CSR repair, also resulting in a significantly smaller strength restitution compared to the original structure (below 20%).