Improving the performance of Scarf and Step adhesive repairs with external reinforcements in composite structures

In recent years, the development of adhesive repair in composites has been considered as crucial, as it not only prolongs the service life and fortifies structural resilience but also addresses environmental concerns by restoring and reinforcing composite components across diverse sectors, such as the aeronautic and automotive industries. This study presents a numerical analysis with cohesive zone modelling of adhesively bonded repairs of carbon fibre reinforced polymers with overplies using an epoxy adhesive and provides insights into optimising repairs for such components. The study focuses on two repair geometries: Scarf and Two-Stepped, considering variables such as overlap and reinforcement lengths, and its position when subjected to tensile and three-point bending loading. The results show that the introduction of external reinforcements (overplies) significantly increases the mechanical strength of the repaired joints, resulting in substantial improvements in the failure load for both geometries and both loading conditions. Under tension conditions, the Stepped repair generally obtained better strength than the Scarf geometry. On the other hand, when subject to bending, Scarf repair strength increases considerably in comparison to the Stepped geometry. The failure analysis provides further insights into the failure paths of Scarf and Step repairs.