A limited number of studies have been conducted in the literature to examine the effect of stacking sequence and fiber orientation on the compressive behavior of fiber reinforced polymer (FRP) confined concrete. This thesis presents the results of an experimental investigation examining the effect of parameters such as fiber orientation, amount of confinement, and specimen size on the behavior of FRP-confined concrete. As part of the experimental study, a large set of concrete cylinders having two different sizes (100 mm x 200 mm and 150 mm x 300 mm) were jacketed with carbon fiber reinforced polymer (CFRP) sheets having various orientations and tested under pure axial compressive loading. The specimens were confined using various CFRP stacking sequences, with fibers oriented at 0⁰, 90⁰, and ±45⁰ (both unidirectional and woven). Furthermore, within each stacking sequence, the numbers of layers was varied between 4, 6, and 8 to examine the impact of number of plies on the behavior of the FRP-confined concrete cylinders. In addition, the research program included a large number of CFRP coupons made from CFRP laminates having the same properties as the CFRP jackets used in the strengthening of the cylinder series. The analytical program assesses the accuracy and suitability of using various FRP confinement models in the literature to predict the stress-strain response of the confined cylinders tested in the experimental program. The results indicate that parameters such as fiber orientation, stacking sequence, number of confinement layers and specimen size have a direct impact on the strength, ductility and stress-strain behavior of CFRP confined concrete. However, the level of influence varies from one parameter to the other, with the results demonstrating that fiber orientation has a more noticeable effect when compared to the other parameters. The results of the analytical program demonstrate the need to develop reliable confinement models which can take into account the effects of fiber orientation.

Le graphène est un plan unique d'atomes de carbone formant une structure en nid d'abeilles. Dans le cas idéal, le graphène possède des propriétés physiques étonnantes résultant de sa structure électronique en « cône de Dirac ». En particulier, la mobilité électronique dans le graphène est exceptionnelle ce qui ouvre des perspectives pour les transistors futurs. Dans cette thèse notre objectif est de tester les propriétés et les performances de transistors réalisés sur graphène à l'aide d'une technologie compatible CMOS. Depuis 2004, il est connu qu'on peut obtenir ce matériau bidimensionnel à partir de la graphitisation du carbure de silicium (SiC). C'est cette technique qui a été utilisée ici. Parmi les résultats obtenus, nous présenterons en particulier une méthode innovante pour déterminer le nombre de couches de graphène. Nous détaillerons la technologie d'intégration mise au point, avec la réalisation de transistors à canal court et étroit. Nous montrerons les caractéristiques obtenues. La mobilité électronique mesurée est à l’état de l’art international. Nous analyserons également le rôle du diélectrique de grille sur la qualité des performances. / Graphene consists of a single atoms plane reorganized in honeycomb lattice. Ideal graphene has astonishing properties coming from his electronic structure in Dirac cone. One of these properties is an exceptional mobility indispensable for future transistors. In this work, our objective is to evaluate properties and performance of transistors based on graphene. These transistors are fabricated by using a CMOS-like integration. Since 2004, graphene can be obtained via sublimation of silicon carbide substrate. We used this technique to study graphene. We will present a particular method to enumerate the number of layer obtained in surface and the integration choosen to obtain short and thin transistors. We will show electrical characteristic obtained. The charge carrier mobility measured is similar to the state of the art. An analysis of the gate dielectric is also presented.