Experimental and numerical analysis of bonded composite patch repair in aluminum alloy 7075 T6

• The fatigue life of structures repaired by non-aged patches may be increased up to fifteen times.
• Water absorption increases the ductility of the adhesive and reduces the repair efficiency.
• The SIF at the crack tip is highly reduced by the composite patch.

In this study, the performances of aged bonded composite repair of aircraft structures have been evaluated by conducting experimental and numerical investigations. The accelerating aging of the patch was realized by immersion in water for 120 days. The performance of aged and non-aged bonded composite patches in the repair of cracked structures was evaluated. The experimental results showed that the fatigue life of the aircraft structures can be significantly improved with the patch repair. The patch aging reduces the repair performances because of the reduction of the composite rigidity by humidity absorption. Numerical results show that the stress intensity factor at the crack tip is significantly reduced by the presence of the patch. The humidity absorption increases the stress intensity factor at the crack tip and decreases the adhesive stresses. Nevertheless, the repair durability cannot be improved by the humidity absorption because it leads to a reduction of the mechanical resistance of the adhesive.