In this work the finite element method was used to analyse the composite patch shape effect of the repair performance. Unlike all the works done conducted so far in this domain, this work proposed here, takes into account the reducing both, the stress intensity factor in repairing crack heads and the maximum shear stresses in the adhesive layer. This is the originality of this work. In function of the surface and the volume of the rectangular patch, three cases were taken into consideration: with conservation of the patches surface and its volume, with a reduction of the patches surface and its volumes, and in the end, with a reduction of the patches surface and conservation of its volume. The obtained results show that in the first case, the patch shape have no effect on the SIF, the sharp edges (obtuse, right and acute) of oblique shapes generate high shear stresses, in the second case, the reduced surfaces lead to significant mass gain with the same SIF values. and to an increase in the maximum shear stresses, in the latter case the patches shapes lead to a reduction of the SIF and the shear stresses.

In this work the finite element method (FEM) was used to analyze the mechanical behavior of the composite materials subjected to the mechanical loading. This behavior is studied in terms of stress intensity factor variation as a function of the applied stress intensity. The residual stresses induced in the composites, during the elaboration of these composites are taken into consideration in this study. The superimposition of these types of stresses (residuals and commissioning) is simulated here by thermomechanical stresses. The results obtained show that in the vicinity very close to the fibermatrix interface and under the effect of this loading type, the matrix cracks propagate in modes I, II and III, and far from the interface, in mode I. The propagation kinetics is slowed down by the interface-crack interaction. The effects of the crack size, the orientation and propagation of the crack, commissioning stresses, the elaboration temperature, fiber physical properties, matrix stiffness and thermomechanical stresses have been highlighted in this work.

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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