Issue 50

A. Benzaama et alii, Frattura ed Integrità Strutturale, 50 (2019) 184-193; DOI: 10.3221/IGF-ESIS.50.16 185 K EYWORDS . Failure load; Damage; Notch; XFEM. Copyright: © 2019 This is an open access article under the terms of the CC-BY 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. I NTRODUCTION tructures used in aeronautical, aerospace and aircraft are often exposed to extreme operating conditions, overload, fatigue and other reasons in service or because of internal defects [1]. This type of structure are always suffering quick damage and failures starting with local microcracks and defaults that make their service life limited [2]. Geometric discontinuities (a notch or abrupt change in structural geometry) are causes of the reduction of the load bearing section and the local amplification of stress near the discontinuity. Patch repair of damaged composite parts bonded with an adhesive film [3] and one of the techniques that significantly extend the service life of these damaged structures [4,5]. The present work uses numerical validation framework of the research works experimentally carried out by Madani et al. [6] who analyzed five different forms of notches in aluminum plates repaired by composite patches. They compared with unrepaired plates and they found that the reduced repair mean of 20% damage for all models. At first Kirsh studied in 1898 [7] the distribution of stress around a hole, Later several researchers have focused their research on increasingly complex geometries such as Neuber [8] and Peterson [9]. The research aims to understand the phenomenon of initiation and propagation of cracks to predict the life of aeronautical structures. Torbani [10] investigated the damage of an O, U, V-shaped slotted plate where he used the point stress criterion combined with the equivalent material concept, he concluded that the accuracy of each failure criterion depends on essentially the characteristic of the notch and therefore the distribution of stresses around the edge of the notch. Other researchers such as berto and all [11] have worked on uniaxial and multiaxial fatigue for different types of notches. The approach is based on strain energy density (SED) of a steel and aluminum alloys structure to tension, torsion and combined tension and torsion. They demonstrated that a linear elastic analysis allows to summarize all the high phases of the given cycle of fatigue resistance using a single SED value. Torabi's other works with Mohammad Hosseini [12] have experimentally and theoretically studied U-slotted Al 7075-T6 plates under the mixed loading mode (I / II). The concept of equivalent material (EMC) is used in conjunction with the criterion of maximum tangential stress (UMTS) and mean stress UMS. They showed that the experimental failure loads are well predicted using the UMTS-EMC calculation and UMS-EMC criteria. Also, the work of Mohammad Rez [13] on the resistance of friction malaxed welded joints containing notches at right angles in the interface of the joints of welded plates and tested under a three-point bending in order to study the resistance to interface rupture of Al - Cu joints. They also showed that the highest breaking loads were obtained at low spindle speeds. One of the most important parameters is the stress intensity factor for estimating the life of the cracked structure; the Paris model describes the growth rate of fatigue cracks, the integral J technique and the extended finite element method [14] can all be realized using theoretical or numerical techniques. Researchers are still trying to understand the phenomenon of crack initiation and propagation, which terminates the lifespan of aeronautical structures. The advantage of the XFEM technique is that initiation and propagation are not chosen, but other criteria such as the cohesive element and the VCCT criterion require a choice to locate the separation surfaces. Even more, the mesh does not need to be updated to follow the crack path. This path creates partitions in the elements as they can take adjacent elements hence the importance of mesh optimization. This is why other researchers are using this technique to numerically analyze damage to structures where it can be used to repair patches. XFEM crack modeling was introduced by Sukumar et al [15], who solved several problems of planar crack mode-I. They showed that this method compares with analytical solutions. XFEM is used to perform crack propagation analysis, which is not feasible in practice by conventional FEM that often requires remeshing procedures [16- 17-18]. The objective of this study is to evaluate by numerical simulation the effect of dimension and localization of notch on resistance of a plate type Aluminum under damage behavior by tensile load. Four geometrical notches have been selected with different dimensions in order to see their effect on the failure load of the plate. We also put into consideration the augmentation of résistance by reinforcing the plate around the notch. The analysis of the numerical results show that the failure load increases as the notched plate has reinforced geometric around the notch. S