Joints in structures always cause strength reduction. The percentage of strength reduction depends upon the selection of several factors such as: type of joint (i.e. adhesive or mechanical), technique of joint (i.e. lap joint, butt joint etc.), geometry of joint, mode of load application etc. Here in this research, the strength of adhesively bonded butt joints with several geometries, later referred as joint angles, is investigated under uniaxial tension loading. Adhesively bonded simple butt joints, where joints are placed perpendicular to the loading direction are in common practice mainly because of ease in manufacturing process. But when the joint is fabricated with an angle respective to the loading direction, the geometry of the joint itself affects the strength of the joint significantly. Without going too deep into other factors that affects the joint strength such as manufacturing techniques, manufacturing defects, material behavior etc. only the geometry of the joint is considered and it is evaluated whether it is worth to change the joint geometry or not. The significant issue in adhesive joint technology is the prediction of joint strength. However, an approach similar to plastic yield criterion later referred as elastic limit offset method (attempted for 0.025% offset) is considered to estimate the linear elastic limit. Since RUAG Space AB (the industry for which this project is performed) is only interested in the linear elastic regime of the stress-strain curve, therefore the elastic limit offset method is considered to be the suitable one. The present work is concerned with the study of adhesively bonded angled butt joint vs. strength behavior. The strength of adhesively bonded butt joints is examined for several butt joint angles under uniaxial tensile loading. The employed butt joint angles are: 0°, 30°, 45°, 60° and 75°. The main objective of the current investigation is to find the joint angle that has the highest strength or the highest capability of load transfer. In addition to the above, the influence of the joint on the stress field, joint strength and type of failure is also evaluated using DSP (Digital Speckle Photography) technique and simulated using well known finite element tool, ABAQUS. It is observed that specific strength of the joint is greatly influenced with joint angle. The 45° joint showed the highest elasticity and failed like ductile behavior whereas 75° joint showed the lowest elasticity and failure was purely brittle. Moreover, post-failure inspection of fractured surfaces showed cohesive failure (failure within adhesive layers) for 0°, 30°, 45° and 60°whereas 75° showed composite or adherend failure. The simulation is performed for each joint angle. However to validate the model only 45° and 75° joints results are compared with experimental results and plotted in the report. The simulation results of these angles showed good agreement with the experimental ones. Moreover, the stress fields for each joint angle are captured (from ABAQUS), showing that all joints are susceptible to inter-laminar shear. Besides, the relative slip between the top and middle adherends is also calculated, the results show that, the 45° joint has higher tendency of relative slip than others.

Ce travail de thèse porte sur la déformation bi-axiale contrôlée de nano-composites W/Cu en couches minces déposées sur des substrats polyimides. La nano-structuration est obtenue par stratification de deux matériaux immiscibles (W et Cu) par pulvérisation ionique avec contrôle de la taille des grains au sein du film mince par contrôle de l'épaisseur selon la direction decroissance du film. Nous avons développé une procédure permettant de caractériser le comportement mécanique des échantillons à deux échelles différentes. L'essai de traction biaxial est couplé à la diffraction des rayons X (déformation microscopique) et à la corrélation d'images numériques (déformation macroscopique). Nous avons utilisé une machine de tractionbi-axiale développée dans le cadre d’un projet ANR sur la ligne de lumière DiffAbs du synchrotron SOLEIL. Elle permet de contrôler les contraintes dans des films minces supportés par des substrats polyimides. La confrontation des résultats obtenus par ces deux techniques dans le domaine d'élasticité a montré que la déformation est intégralement transmise via l’interfacefilm - substrat. La seconde étape de notre travail a consisté à étudier les déformations du nanocomposite W/Cu au-delà du domaine d’élasticité. Nous avons mis en évidence trois domaines de déformation associés à différents mécanismes de déformation. La limite d'élasticité du nanocomposite W/Cu a été déterminée en comparant la déformation élastique du film mince à la déformation macroscopique du substrat. Enfin, l'étude de la limite d'élasticité du nanocomposite W/Cu pour différents ratios de force a révélé un comportement fragile du nanocomposite W/Cu. / This thesis focuses on the biaxial deformation of W/Cu nanocomposite thin films deposited on polyimide substrates. The grain size in the thin film is controlled by stratification of two immiscible materials (W and Cu) employing sputtering techniques. We developed a procedure to characterize the mechanical behavior of samples at two different scales. A biaxial tensile test is coupled to X-ray diffraction (microscopic deformation) and digital image correlation (macroscopic deformation) techniques. We used a biaxial tensile setup developed in the framework of an ANR project on the DiffAbs beamline at synchrotron SOLEIL allowing forthe control of stresses in thin films supported by polyimide substrates. By comparing the strains obtained by these two techniques, the applied strain is determined to be transmitted unchanged in the elastic domain through the film - substrate interface. The second part of our work was to study the deformation of W/Cu nanocomposite beyond the elastic range. We have highlighted three domains of deformation associated with different deformation mechanisms. The elastic limit of the W/Cu nanocomposite was determined by comparing the elastic deformation of the thin film to the macroscopic deformation of the substrate. Finally, the elastic limit of W/Cu nanocomposite was studied for different load ratios. The overall results emphasized the brittle behavior of these nanocomposites.

This thesis deals with stress, strain and reliability analysis of synchronous generator stator including an inhomogeneous temperature field. Using the finite element method, stress and strain are calculated, and from these values safety against yield strength is determined, which is followed by the life calculation of the most stressed weld joint and the determination of its possible damage during the period required by the customer.