Issue 49

B. El-Hadi et alii, Frattura ed Integrità Strutturale, 49 (2019) 547-556; DOI: 10.3221/IGF-ESIS.49.51 548 introducing a new hole or changing the microstructure of the material. In fact, there are two patch repair techniques, namely, simple patch repair (asymmetric repair) and double side patch repair (symmetric repair) [16-19]. Generally, it is the double patch that is preferable, because of the deflection effects that the simple patch introduces into the charged structure [20]. Regardless of the type of repair (symmetrical or asymmetrical), parameters such as thickness, surface area, number of layers, fiber orientation and patch shape remain the most studied for their interdependent influence on repair efficiency. In this context, Ramji & all carried out a comparative study in [16]. These authors studied several forms of patch and concluded that an extended octagonal patch has better performance for stress intensity factor reduction. Recently, Bachir Bouiadjra & all concluded in [7] that a trapezoidal form is more powerful than a rectangular form. Furthermore, in [10], it was concluded that a butterfly shape with a suitable dimensions is more efficient than the rectangular shape. For the number of layer and the thickness of the patch, H. Hosseini and colleagues in [21] concluded that the performance of the patch is proportionately improved by increasing the number of layers and reducing the thickness of the plate. Furthermore, [22] established that increasing the life of the repaired plate is related to increasing the thickness of the patch. Also for the type of composite used in the repair, H. Hosseini and co-workers in [23] found that, for a 45° inclined crack in a thick aluminum panel repaired by an asymmetric glass / epoxy patch, the lifetime during the crack propagation is significantly improved. Among the positive effects on the repair, [24] studied the effect of overload during the fatigue test. As a result, it was found that overloading extends the service life of the repaired structure. Despite a large number of published researches on this topic, to our knowledge, few of them consider the value of the stress intensity factor to be used for estimating the lifetime of repaired structures. Indeed, D. C. Seo and J. J. Lee in [25] experimentally proved that the crack front is not always a straight line when the crack is propagated. These latter concluded that the stress intensity factor of thick specimen showed a large variation through thickness direction. Moreover, Woo-Yong Lee and Jung-Ju Lee in [26] stated that the stress intensity factor (SIF) calculated at the crack tip is much influenced by crack front shape. Consequently, they proposed to predict the actual crack front shape evolution and take it into account for the accurate analysis of fatigue behavior. This was confirmed later by H. Hosseini et al. in [27] and recently in [28], where it was noted that the crack growths non-uniformly from its initial location through the thickness of the repaired panel and the maximum crack length occur at un-patched surface of the panels. In this study, for the accurate investigation of fatigue crack growth behavior, a consideration is taken for the crack front inclined in its plan from the patched toward un-patched side by various angles. This is done to simulate the experimental fatigue crack-growth behavior in mode-I failure and examine the SIF’s distribution along the crack front within centrally cracked aluminum panels. Moreover, trying to understand the physic of the crack growth difference between patched and un-patched side in two different panels thick and thin. Figure 1 Geometrical model of the repaired central cracked specimen . G EOMETRIES AND MECHANICAL PROPERTIES OF THE MODEL ig. 1 shows the basic geometry of the cracked structure considered in this study. This model is adapted from that proposed in [21]. The aluminum alloy plate 2014-T3 has dimensions of 100 x 50 mm2 with two different thicknesses, namely 2.29 and 6.35 mm. the plates contain an initial crack length of 2a = 10 mm and perpendicular to the loading axis (Fig. 1). Table 1 summarizes the dimensions of the plate, the patch and the adhesive. Mechanical F