Issue 46

N. C. M. Ibrahim et alii, Frattura ed Integrità Strutturale, 46 (2018) 140-149; DOI: 10.3221/IGF-ESIS.46.14 141 mechanical properties of the patch, the adhesive and of the structure itself, and have shown that, after repair, the stress intensity factor exhibits asymptotic behavior when the length of the crack increases as Fekirini and al.[14], Belhouari and al.[15] et Bachir Bouiadjra [16] Which also showed that an adhesive with a high shear modulus gives a low stress intensity factor at the end of the repaired cracks. Therefore, they recommend the use of these types of adhesives to increase the performance of the repair. However, the higher the adhesive shear modulus leads to higher adhesive stresses, which increases the risk of adhesive failure. They also analyzed the thickness importance of the adhesive and concluded that the adhesive properties should be optimized to improve repair performance and avoid adhesive breaking. Ouinas and al. [17] made a comparison between the boron / epoxy patch and the graphite / epoxy patch for repairing aircraft structures. They indicated that the reduction of the stress intensity factor at the crack tip is more important for the boron / epoxy patch. Ouinas and al. [18,19], Mhamdia and al. [20] they analyzed the effect of the shape of the composite patch on the repair of aircraft structures. These authors analysed the performance of the repair is related to the patch shape, where they showed that the effectiveness of the rectangular shape of the plate can be greatly improved if this shape is modified in "H" or arrow shapes. The latter shape reduces: the stress intensity factor at the tip of the crack, the mass of the composite patch and therefore the repair cost, the adhesive stresses what improves the durability of the repair. The repair of doubly cracked structures is the objective of this study, where the interconnection of these cracks leads to the ruin of the structure. Thus, the presence of a crack in the vicinity close to another leads to an increase in the probability of instability of these cracks by an intensification of the FIC. The subcritical size of this narrow crack is about 3 times when the cracks are close to each other. Such a fissure arrangement can be fatal to the structures, thus leading to their break. In order to delay this interconnection during commissioning and consequently to improve the service life. The latter is analyzed in terms of stress intensity factor, which depends on the stress applied, the size of the cracks, and their interdistance. Figure: 1 Geometrical models containing , (a) central crack of size "a", (b) Two parallel cracks, (c) two parallel central fissures distant from (dx) and (dy).