Fracture energy for repaired cracks with bonded composite patch having two adhesive bands in aircraft structures

Adhesive in bonded composite repair plays two opposite roles. The first consists in ensuring the transfer of load between the composite patch and the cracked aluminium component. The second role is to ensure the connection between these two structures in order to avoid the adhesive failure. In this study, a method of repair is proposed; it consists in dividing the adhesive layer into two bands with different properties. The first band is used on the crack region to ensure the stress transfer and the second band is used beyond the crack region to avoid the adhesive failure. The energy release rate at the crack tip is computed for this repair configuration using the finite element method. The obtained results show that the energy release rate at the crack tips is highly reduce by the difference of properties between the two adhesive bands, what can involve the improvement of fatigue life of cracked structure.