En presente trabajo se estudian las condiciones de servicio, así como el proceso que ocurre al producirse la rotura del suelo en cargas rápidas sobre arcillas: a) Elaboración de un modelo elasto-plástico, en el cual se reproduzca la plastificación progresiva del material, definiendo un nuevo criterio de rotura que pueda incluir los factores más representativos del comportamiento de la arcilla, incluso la anisotropía y la heterogeneidad de la misma que no eran considerados anteriormente. b) Introducción de este modelo reológico en un nuevo modelo de elementos finitos. De entre las diferentes posibilidades se ha elegido un modelo híbrido en tensiones y deformaciones, para lo cual partiendo del principio variacional de REISSNER, se ha generalizado para estudiar la fase plástica. La discretización se ha efectuado con los elementos triangulares y cuadrangulares híbridos. c) Se aplica el modelo en una zapata en faja indefinida actuando sobre una capa de arcilla deformable sobre una base rocosa rígida con interfaz lisa, variándose todos los parámetros que en él intervienen y deducción de una serie de conclusiones sobre la influencia de los factores estudiados en el comportamiento de la arcilla. / In this paper we study the conditions of service, and the process that occurs at ground breaking in fast load on clays: a) Development of elastic-plastic model in which to play the pushover of the material, defining a new failure criterion which may include factors represent the behavior of the clay, including the anisotropy and heterogeneity of the same were not considered previously. b) Introduction of the rheological model in a new finite element model. Among the different possibilities we have chosen a hybrid model stresses and strains for which starting from the Reissner variational principle has been generalized to study the plastic phase. The discretization was made with triangular and quadrangular elements hybrids. c) Model was applied in a strip footing on indefinite acting on a layer of deformable clay on a rock hard smooth interface, by varying all the parameters involved in it and deduction of a number of conclusions about the influence of the factors studied the behavior of the clay.

Cette thèse s’ajoute aux différents travaux de recherche qui traitent des alliages d’aluminium fortement utilisés dans l’industrie aéronautique et contribue fortement à comprendre le comportement élastoplastique en chargement cyclique à contrainte imposée du 2017A. L’apport essentiel de ce travail est l’étude de l’anisotropie propre du matériau utilisé à travers le suivi de l’évolution des différents paramètres caractérisant la plasticité cyclique de notre matériau. En effet, nous avons caractérisé cette anisotropie en comparant le comportement du matériau en traction-compression avec celui de la torsion alternée selon l’évolution cyclique de la réponse contrainte-déformation, l’évolution de l’état stabilisé, l’évolution des variables d’écrouissages cinématique et isotrope ainsi que l’anisotropie selon le comportement en fatigue et endommagement. Pour mieux affiner la partie expérimentale de ce travail, des investigations microstructurales des faciès de rupture de toutes les éprouvettes utilisées ont été effectuées afin de mieux comprendre les mécanismes d’endommagement cyclique dans notre matériau. Dans la partie numérique de cette thèse, nous avons réalisé des simulations numériques en utilisant la dernière version du modèle multimécanismes qui tient compte de l’anisotropie du matériau. Les résultats de ces simulations, réalisées en considérant les mêmes conditions de nos essais expérimentaux, confirment les capacités de cette nouvelle version à estimer le comportement élastoplastique d’un matériau anisotrope. / The present work is devoted to study the anisotropic behavior of an extruded aluminum alloy under cyclic loading in axial and shear directions. In the first part, we have studied its elastoplastic behavior through the evolution of stress–strain loops, isotropic and kinematic hardening and we have associated this behavior with the evolution of its elastic adaptation (shakedown). We have studied the behavior of the material in fatigue damage using the evolution of stiffness. Microstructural investigations were performed on fractured surfaces using scanning electron microscope (SEM) in orderto understand the evolution of fatigue damage during cyclic loading. In the second part, we have simulated all the tests performed in the experimental part using the new version of multimechanisms model. The obtained results show that this version is able to take into account the anisotropic behavior of the materials under stress controlled tests.

3D printing is a revolutionary manufacturing method that allows the productions of engineering parts almost directly from modeling software on a computer. With 3D printing technology, future manufacturing could become vastly efficient. However, it is observed that the procedures used in 3D printing differ substantially among the printers and from those used in conventional manufacturing. In this thesis, the mechanical properties of engineering products fabricated by 3D printing were comprehensively evaluated and then compared with those made by conventional manufacturing. Three open-source 3D printers, i.e., the Flash Forge Dreamer, the Tevo Tornado, and the Prusa, were used to fabricate the identical parts out of the same material (acrylonitrile butadiene styrene). The parts were printed at various positions on the printer platforms and then tested in bending. Results indicate that there exist substantial differences in mechanical responses among the parts by different 3D printers. Specimens from the Prusa printer exhibit the best elastic properties while specimens from the Flash Forge printer exhibit the greatest post-yield responses. There further exist noticeable variations in mechanical properties among the parts that were fabricated by the same printer. Depending on the positions that the parts were placed on a printer platform, the properties of resultant parts can vary greatly. For comparison, identical parts were fabricated using a conventional manufacturing method, i.e., compression molding. Results show that compression molded parts exhibit more robust and more homogeneous properties than those from 3D printing. During 3D printing, the machine code (e.g., the Gcode) would provide the processing instructions (the x, y, and z coordinates and the linear movements) to the printer head to construct the physical parts. Often times the default processing instructions used by commercial 3D printers may not yield the optimal mechanical properties of the parts. In the second part of this thesis, the orientation-dependent properties of 3D printed parts were examined. The multi-layered composite theory was used to design the directions of printing so that the properties of 3D printed objects can be optimized. Such method can potentially be used to design and optimize the 3D printing of complex engineering products. In the last part of this thesis, the printing process of an actual automobile A-pillar structure was designed and optimized. The finite element software (ANSYS) was used to design and optimize the filament orientations of the A-pillar. Actual parts from the proposed designs were fabricated using 3D printer and then tested. Consistent results have been observed between computational designs and experimental testing. It is recommended that the filament orientations in 3D-printing be “designed” or “tailored” by using laminate composite theory. The method would allow 3D printers to produce parts with optimal microstructure and mechanical properties to better satisfy the specific needs.

Two new three-dimensional rock mass strength criteria are developed in this dissertation by extending an existing rock mass strength criterion. These criteria incorporate the effects of the intermediate principal stress, minimum principal stress and the anisotropy resulting from these stresses acting on the fracture system. In addition, these criteria have the capability of capturing the anisotropic and scale dependent behavior of the jointed rock mass strength by incorporating the effect of fracture geometry through the fracture tensor components. Another significant feature of the new rock mass strength criterion which has the exponential functions (equation 6.7) is having only four empirical coefficients compared to the existing strength criterion which has five empirical coefficients; if the joint sets have the same isotropic mechanical behavior, the number of the empirical coefficients reduces to two in this new strength criterion (equation 6.10). The new criteria were proposed after analyzing 452 numerical modeling results of the triaxial, polyaxial and biaxial compression tests conducted on the jointed rock blocks having one or two joint sets by the PFC3D software version 5. In this research to have several samples with the same properties a synthetic rock material that is made out of a mixture of gypsum, sand and water was used. In total, 20 joint systems were chosen and joint sets have different dip angles varying from 15 to 60 at an interval of 15 with dip directions of 30 and 75 for the two joint sets. Each joint set also has 3 persistent joints with the joint spacing of 42 mm in a cubic sample of size 160 mm and the joints have the same isotropic mechanical behavior. The confining stress combination values were chosen based on the uniaxial compressive strength (UCS) value of the modeled intact synthetic rock. The minimum principal stress values were chosen as 0, 20, 40 and 60 percent of the UCS. For each minimum principal stress value, the intermediate principal stress value varies starting at the minimum principal stress value and increasing at an interval of 20 percent of the UCS until it is lower than the strength of the sample under the biaxial loading condition with the same minimum principal stress value. The new rock mass failure criteria were developed from the PFC3D modeling data. However, since the joint sets having the dip angle of 60 intersect the top and bottom boundaries of the sample simultaneously, the joint systems with at least one of the joint sets having the dip angle of 60 were removed from the database. Thus, 284 data points from 12 joint systems were used to find the best values of the empirical coefficients for the new rock mass strength criteria. λ, p and q were found to be 0.675, 3.16 and 0.6, respectively, through a conducted grid analysis with a high R2 (coefficient of determination) value of 0.94 for the new criterion given by equation 6.9 and a and b were found to be 0.404 and 0.972, respectively, through a conducted grid analysis with a high R2 value of 0.92 for the new criterion given by equation 6.10. The research results clearly illustrate how increase of the minimum and intermediate principal stresses and decrease of the joint dip angle, increase the jointed rock block strength. This dissertation also illustrates how different confining stress combinations and joint set dip angles result in different jointed rock mass failure modes such as sliding on the joints, failure through the intact rock and a combination of the intact rock and joint failures. To express the new rock mass strength failure criteria, it was necessary to determine the intact rock strengths under the same confining stress combinations mentioned earlier. Therefore, the intact rock was also modeled for all three compression tests and the intact rock strengths were found for 33 different confining stress combinations. Suitability of six major intact rock failure criteria: Mohr-Coulomb, Hoek-Brown, Modified Lade, Modified Wiebols and Cook, Mogi and Drucker-Prager in representing the intact rock strength was examined through fitting them using the aforementioned 33 PFC3D data points. Among these criteria, Modified Lade, Modified Mogi with power function and Modified Wiebols and Cook were found to be the best failure criteria producing lower Root Mean Square Error (RMSE) values of 0.272, 0.301 and 0.307, respectively. Thus, these three failure criteria are recommended for the prediction of the intact rock strength under the polyaxial stress condition. In PFC unlike the other methods, macro mechanical parameters are not directly used in the model and micro mechanical parameter values applicable between the particles should be calibrated using the macro mechanical properties. Accurate calibration is a difficult or challenging task. This dissertation emphasized the importance of studying the effects of all micro parameter values on the macro mechanical properties before one goes through calibration of the micro parameters in PFC modeling. Important effects of two micro parameters, which have received very little attention, the particle size distribution and the cov of the normal and shear strengths, on the macro properties are clearly illustrated before conducting the said calibration. The intact rock macro mechanical parameter values for the Young’s modulus, uniaxial compression strength (UCS), internal friction angle, cohesion and Poisson's ratio were found by performing 3 uniaxial tests, 3 triaxial tests and 5 Brazilian tests on a synthetic material made out of a mixture of gypsum, sand and water and the joint macro mechanical parameter values were found by conducting 4 uniaxial compression tests and 4 direct shear tests on jointed synthetic rocks with a horizontal joint. Then the micro mechanical properties of the Linear Parallel Bond Model (LPMB) and Modified Smooth Joint Contact Model (MSJCM) were calibrated to represent the intact rock and joints respectively, through the specific procedures explained in this research. The similar results obtained between the 2 polyaxial experiments tests of the intact rock and 11 polyaxial experimental tests of the jointed rock blocks having one joint set and the numerical modeling verified the calibrated micro mechanical properties and further modification of these properties was not necessary. This dissertation also proposes a modification to the Smooth Joint Contact Model (SJCM) to overcome the shortcoming of the SJCM to capture the non-linear behavior of the joint closure varying with the joint normal stress. Modified Smooth Joint Contact Model (MSJCM) uses a linear relation between the joint normal stiffness and the normal contact stress to model the non-linear relation between the joint normal deformation and the joint normal stress observed in the compression joint normal stiffness test. A good agreement obtained between the results from the experimental tests and the numerical modeling of the compression joint normal test shows the accuracy of this new model. Moreover, another shortcoming associated with the SJCM application known as the interlocking problem was solved through this research by proposing a new joint contact implementation algorithm called joint sides checking (JSC) approach. The interlocking problem occurs due to a shortcoming of the updating procedure in the PFC software related to the contact conditions of the particles that lie around the intended joint plane during high shear displacements. This problem increases the joint strength and dilation angle and creates unwanted fractures around the intended joint plane.

L’augmentation de la puissance électrique des composants électroniques pose le problème de la dissipation de la chaleur générée. Les boîtiers électriques doivent permettre la dissipation de cette chaleur en conservant une isolation électrique. La solution retenue pour évacuer la chaleur par transfert thermique consiste en matériaux composites dont les renforts par leur structuration vont améliorer la conductivité thermique. Des composites à matrice polymère ont été choisis pour leur aptitude de mise en forme. La conductivité thermique et l’isolation électrique sont assurées par des charges céramiques. Les méthodes d’homogénéisation donnent des pistes d’amélioration du comportement de composites en fonction des propriétés de leurs constituants, de leur géométrie et de leur distribution. Elles fournissent ainsi une formulation optimisée de matériaux répondant à certaines caractéristiques issues de cahiers des charges émanant du partenaire industriel (Institut de Soudure). La conductivité thermique attendue des composites impose une forte fraction volumique de charges pour compenser le caractère isolant de la matrice polymère. Des méthodes d’homogénéisation ont été développées pour prédire la conductivité thermique effective pour de forts taux de charges (supérieur à 20%) et des contrastes élevés de conductivité thermique. La présence d’une interphase provenant d’incompatibilités fortes entre les composants doit également être modélisée / The increase of electronic components in the integrated circuits and the required electrical power set the question of the dissipation of the heat generated. The electrical box must favor the heat dissipation while maintaining electrical insulation. The solution chosen to transfer the heat is to develop composite materials whose reinforcements by their structure will improve the thermal conductivity. Polymer-based composite materials were chosen for their building ability. Thermal conductivity and electrical insulation are insured by ceramic reinforcements. The homogenization methods allow to improve the composites’ design according to the properties of their constituents, their geometry and their distribution. They thus provide an optimized formulation of materials satisfying the characteristics emanating from the industrial partner (‘Institut de Soudure’). The expected thermal conductivity of the composites imposes a high volume fraction of reinforcements to counterbalance the insulating polymer matrix. Homogenization methods have been developed to provide predictions of effective thermal conductivity for high (greater than 20%) reinforcement rates and high thermal conductivity contrasts. The presence of an interphase resulting from strong physico-chemical incompatibilities between the components must also be modeled