Reinforcement of CFRP single lap joints using metal laminates

Despite the recent increase in composite usage for structural applications, the susceptibility to delamination failure of these materials is still seen as a big limitation for a more widespread and efficient use of the materials. A technique aiming to reduce delamination by reinforcing composite adherends with aluminium laminates, inspired by the concept of Fibre Metal Laminates (FMLs), is proposed for single lap joints using two different epoxy-based adhesives. Unlike FMLs, the suggested reinforced joints, known as Composite Metal Laminates (CML), are not reinforced throughout the transverse direction but only at the adherends edges. An adequate performance is displayed for quasi-static (1 mm/min) and impact conditions (3 m/s). Delamination could not be avoided, but was delayed for the reinforced configurations, substantially increasing the failure loads. A numerical model using a finite element analysis is developed, and numerical and experimental results are compared. Additionally, since the performance of the technique is dependent on the mechanical properties of the adhesive used, a method is proposed to determine the minimum metal laminate thickness required for a positive performance of the reinforced joints when compared to a basic CFRP-only single lap joint (SLJ).