Issue 49

N. Kaddouri et alii, Frattura ed Integrità Strutturale, 49 (2019) 331-340; DOI: 10.3221/IGF-ESIS49.33 332 The patch of composite material bonded on the outside face has been recognized as an effective method for repairing cracks, and consequently extend the service life of structures cracked. Considerable research has been done in recent years to develop the technology for bonding composite patches in aeronautical structures. Several authors have searched to optimize the composite and the adhesive by the search for mechanical properties that are suitable to absorb as at the crack point is one of the approaches used in the performance analysis of composite material patches. Experimental studies, numerical and even analytical, were conducted to study the behavior of cracks repaired by patch in composite. They showed that the crack point stress field, fatigue life and the stress intensity factor depend on several parameters, namely, the mechanical and geometrical properties, the number and thickness of the patch layers, the volume fraction and the orientation of the fibers, the shear modulus of the adhesive, its thickness and its temperature of elaboration and service, the size of much as possible the stresses of the damaged area. Other authors have searched to optimize the geometric shape of the patch in order to transfer more and more stress at the crack head or the damaged area [4]. Numerical analysis is an important tool for determining the stresses distribution in different substrates. Several authors have proposed many methods to model the repaired structure taking into account the mechanical parameters of the adhesive and the composite [5, 6]. The analysis of the stresses in the adhesive layer is important since this latter is the weakest link in the structure or its mechanical properties are the weakest and therefore rapid damage to the latter. However, little research has been devoted to studying the presence of bonding defects. [7,8]. The voids in the adhesive layer are produced during the treatment by the enclosed air or by gas products of the adhesive or adherents. The gas typically forms a bubble in the liquid adhesive and when the adhesive cross-links and solidifies, the bubble remains a void. In other hand, during the realization of a bonded assembly, many types of defects are likely to be created. The nature of the defects that can meet in the bonded assemblies varies according to the phenomena having caused these defects. The concentrations of porosities can lead to the creation of holes or cavities. When they are located in the close vicinity of the interface. The cavities create places of interfaces not related or geometric discontinuities. These may evolve and give birth to preferential sites of initiation of cracking or detachment leading to the rupture of the junction. Little research has been done in this area. The objective of our study is to analyze by the finite element method the effect of the presence of a defect of square geometrical shape whose position is variable according to the surface of the adhesive on the value of the J-Integral and the different stress in the patch and the adhesive. G EOMETRICAL MODEL AND MECHANICAL PROPERTIES et consider a 2024-T3 Aluminum plate with the presence of a lateral crack repaired by a composite carbon / epoxy patch. This patch is bonded on the damaged area using an adhesive type ADEKIT A-140 as shown in Fig. 1. The dimensions of the different substrates are shown in Tab. 1. In order to analyze the effect of the presence of defect of bonding on the stresses transfer from the plate to the patch and therefore on the quality of the repair and the value of the J-Integral at the level of the crack tip, we have tried to model the presence of a defect in the adhesive layer. It was assumed a defect of Square shape of dimension (1*1 mm 2 ) which its position is random. The most defect positions are chosen close to the crack, at the level of the crack and at the level of the adhesive free edges (Fig. 2). Length (mm) width (mm) Thickness (mm) Plate H=250 W= 125 e p = 2 Adhesif h= 80 w=80 e a =0.2 Patch h=80 w=80 e r =2 Table 1 : Dimensions of the different substrates. The mechanical properties of the plate (2024-T3 Aluminum) and the adhesive (Adekit A-140) (Tab. 2) are drawn directly of traction tests performed in the laboratory LASIE (Laboratory of the Engineering sciences for the Environment) in France [9]. However, for the composite patch, the mechanical properties have been determined by calculation of L