In this work, a model based on the combination of two approaches XFEM and CZM, has been used to predict the damage of repairs by composite patch (patch/adhesive/plate assembly). This degradation is analyzed in terms of adhesive damage considering both initiation and propagation of interfacial debonding. The interfacial cohesive zone of the patch/adhesive/plate system is defined by its cohesive properties and its resistance to debonding estimated from the displacement-load curves.This study highlights, as a function of the adhesive properties of the plate/patch interface, the competition between two degradation mechanisms: adhesive damage (through a mechanism of initiation and propagation of patch debonding from the plate) and plate damage (through a phenomenon of crack initiation and propagation emanating from notch). It also highlights, depending on the nature of the interface, four physical parameters: the bending deflection of the repaired plate, the displacement path of the patch-reinforced plate, the debonding resistance and the interfacial shear stresses, characteristic of the adhesive joint damage and their interactions with the interface. This is the originality of this study. Results show that XFEM simulations based on the CZM model allow adequate prediction of the damage of the patch/adhesive/plate assemblies.

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The repair technique has presented its effectiveness in the reduction of the stresses at the level of stresses concentration areas. The search for a patch and suitable adhesive for a good transfer of load has pushed researchers to develop many ideas, which relate the form, the nature, the stacking sequence of the patch and the adhesive type to give a better combination of choice between the patch and the adhesive. Our work fits in this context; the objective is to analyze by the method of finite elements the behavior in the rupture of a damaged plate in the presence of defect of bonding. The analysis of J-Integral and stresses in the tow substrates adhesive and patch shows clearly that their values depends strongly on the position of the default essentially when it's located close to the free edge of the free edge of the adhesive or the crack.

The adhesive bonding technique is employed from the aeronautical/aerospace industry to current house products. To comply with the requirements of distinct applications, different joint configurations are available to the designer. While single-lap joints (SLJ) are the most common in application and research, double-lap joints, scarf joints and T-joints find specific applications. T-joints are seldom studied in the literature, but these are used, for instance, in aircraft to bond the stiffener beams to the skin, or in the cars between the B-pillar and the rocker. Due to the high stress concentrations, T-joints often fail under average stresses much lower than the adhesive strengths, giving rise to the necessity for proper design and strength improvement methodologies. This work initially aims to validate the cohesive zone modelling (CZM) technique with experiments, and then use it to numerically evaluate and optimize the performance of T-joints subjected to peel loads. CZM is nowadays regarded as the most powerful strength prediction tool for adhesive joints, and can be a valuable tool to improve T-joints. Different features are addressed for a complete analysis: adhesive type, geometrical parameters, dual-adhesive technique for strength improvement, and composite joints. The evaluated geometrical parameters are the base adherend thickness (a), T-part thickness (t), overlap or bonding length (l) and curvature radius (r). As a result of this work, the model was successfully validated, and clear design guidelines were provided to define the ideal geometric and material (adhesive) conditions for best performance.

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