Issue 50

M. Baghdadi et alii, Frattura ed Integrità Strutturale, 50 (2019) 68-85; DOI: 10.3221/IGF-ESIS.50.08 69 the crack tip and minimise the shear stresses in the adhesive layer. Mhamdia and all [5], proceeding at conception of a new patch shape, named patch double arrow, show that, compared with the conventional rectangular shape, this shape, resulting in a more performing and more efficient repair in terms of the normal tension stresses relaxation, highly concentrated in the crack heads. Chung K.H and al [6, 7], Jeong Gi-Hyeon and all [8], by analysing the efficiency of patch geometry, from a point of view, fracture mechanics and disbonding of the patch, proceeded with the development of a composite patch geometry leading to the maximum reduction of the SIF. Ramji and Srilakshmi [9], by analysing the repair of the structure solicited in mixed mode with composite patch, have shown that the SIF in repairing crack is insensitive to the patch shapes. In another study, Ramji and al [10], studying the effect of the circular, square, rectangular, elliptical and octagonal shapes of the patch on the crack repair efficiency in mixed mode, they concluded that, the rectangular and octagonal shapes are the performances, in terms of the SIF reducing. Kashfuddoja and all. [11] developed this analysis by adding the elliptical shape, they studied the effects of these shapes on the repair quality in terms of reducing of the stress concentration factor "SCF" in the circular notch vicinity located in a plate centre, repaired with a composite patch unidirectional, by comparing the values of these parameter resulting from these different shapes, these authors have shown that the octagonal patch elongated perpendicular to the traction direction, is the most effective shape. Fekih and al [12], analysed the patch shapes effect on the durability and reliability of the repair, in term of “J” integral reducing, shown that the patch shaped star is the most effective. Mahadesh Kumar and all. [13] analysed the values of the SIF resulting from the repair using four principal regular patches geometries, square, rectangular, circular and elliptical. They show as well, from a point of view a reduction of this parameter, that the classic rectangular shape with important elongation in the direction parallel to the crack, is the most effective. Based on these findings, these authors have developed a new patch shape, called "skewed patch", They concluded that, this last, leads to a mass gain around 28% in practically the same value of the SIF. Or it reduces this value of 10% for the same volume of the patch. Mohamed Ibrahim and all [14], analysed the effect of a rectangular patch on the repair performance of the two cracks interaction. This analysis is done in terms of reducing the stress intensity factor in mode I. This work fits into this context and aims to analyse the effect of the patch composite shapes on the efficiency and performance of the repair, in terms of reduction of the stress intensity factor in cracks heads and the shear stresses in all the adhesive layer. A finite element method was used for this analysis. For this purpose, a geometric model has been developed. Figure 1 : Geometric model of the structure. G EOMETRIC M ODEL he geometric model developed consists of a 2024-T3 aluminium alloy plate of an aircraft structure, this plate is characterized by its height H = 250 mm, its width W= 125 mm and its thickness ep = 2 mm. This plate is subjected to uniaxial tension stresses of varying amplitude, allowing the crack propagation in opening mode, the T