Browsing by Author "Madani, K."
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- Impact of bonding defect on the tensile response of a composite patch-repaired structure: Effect of the defect position and sizePublication . Kaddouri, N.; Madani, K.; Djebbar, S.CH.; Belhouari, M.; Campilho, R.D.S.G.Adhesive bonding has seen rapid development in recent years, with emphasis to composite patch repairing processes of geometric defects in aeronautical structures. However, its use is still limited given its low resistance to climatic conditions and requirement of specialized labor to avoid fabrication induced defects, such as air bubbles, cracks, and cavities. This work aims to numerically analyze, by the finite element method, the failure behavior of a damaged plate, in the form of a bonding defect, and repaired by an adhesively bonded composite patch. The position and size of the defect were studied. The results of the numerical analysis clearly showed that the position of the defect in the adhesive layer has a large effect on the value of J-Integral. The reduction in the value of J-Integral is also related to the composite stacking sequence which, according to the mechanical properties of the ply, provides better load transfer from the plate to the repair piece through the adhesive. In addition, the increase in the applied load significantly affects the value of the J-Integral at the crack tip in the presence of a bonding defect, even for small dimensions, by reducing the load transfer.
- Numerical analysis of the combined aging and fillet effect of the adhesive on the mechanical behavior of a single lap joint of type Aluminum/AluminumPublication . Medjdoub, S.M.; Madani, K.; Rezgani, L.; Mallarino, S.; Touzain, S.; Campilho, R.D.S.G.Bonded joints have proven their performance against conventional joining processes such as welding, riveting and bolting. The single-lap joint is the most widely used to characterize adhesive joints in tensile-shear loadings. However, the high stress concentrations in the adhesive joint due to the non-linearity of the applied loads generate a bending moment in the joint, resulting in high stresses at the adhesive edges. Geometric optimization of the bonded joint to reduce this high stress concentration prompted various researchers to perform geometric modifications of the adhesive and adherends at their free edges. Modifying both edges of the adhesive (spew) and the adherends (bevel) has proven to be an effective solution to reduce stresses at both edges and improve stress transfer at the inner part of the adhesive layer. The majority of research aimed at improving the geometry of the plate and adhesive edges has not considered the effect of temperature and water absorption in evaluating the strength of the joint. The objective of this work is to analyze, by the finite element method, the stress distribution in an adhesive joint between two 2024-T3 aluminum plates. The effects of the adhesive fillet and adherend bevel on the bonded joint stresses were taken into account. On the other hand, degradation of the mechanical properties of the adhesive following its exposure to moisture and temperature was found. The results clearly showed that the modification of the edges of the adhesive and of the bonding agent have an important role in the durability of the bond. Although the modification of the adhesive and bonding edges significantly improves the joint strength, the simultaneous exposure of the joint to temperature and moisture generates high stress concentrations in the adhesive joint that, in most cases, can easily reach the failure point of the material even at low applied stresses.
- Substrate geometry effect on the strength of repaired plates: Combined XFEM and CZM approachPublication . Djebbar, S. Ch.; Madani, K.; El Ajrami, M.; Houari, A.; Kaddouri, N.; Mokhtari, M.; Feaugas, X.; Campilho, R.D.S.G.Aluminum alloys are commonly used in aeronautical applications because of their specific strength and improved corrosion resistance. These structures, during their service, are exposed to various loading cycles, eventually leading to failure at the loci of geometric discontinuities. Repairing by metal or composite patch bonding is widespread to extend the structures’ life by limiting stress concentrations and delaying crack initiation. This work consists of a numerical study, validated by experimental test data, to assess the effect of a central circular notch in an aluminum plate, either reinforced or not by an adhesively bonded composite patch, on the global tensile response of the structure. The constitutive law of the aluminum and adhesive is assumed nonlinear and follows Von Mises equivalent stress flow theory with a hardening variable in incremental form. Damage initiation in the aluminum alloy is modeled by the XFEM (eXtended Finite Element Method), using the maximum principal stress criterion (MAXPS) for damage initiation prediction. Damage evolution is based on the energy approach. The adhesive layer was modeled by CZM (Cohesive Zone Model). A good agreement was found between the experimental results of the tensile curves of the repaired and unrepaired plates with those resulting from numerical modeling. Once the numerical model was validated, several parameters werenumerically studied, namely the shape of the composite patch, the size of the notch, the nature of the adhesive and repair mode by single and double patch, to reduce maximum stress of the damaged area and provide maximum repair efficiency.