<p> The room-temperature fracture behaviour of calcia partially stabilized zirconia (PSZ) was investigated. Fracture energy measurements were made using the standard stress intensity calibration and work to fracture techniques. The detailed nature of the PSZ microstructure was studied using scanning electron microscopy, qualitative X-ray analysis and T.E.M, surface replication. The grain structure was detenninod to be bimodal with small grains of pure zirconia dispersed along the boundaries of large grains. These large grains consist of a binary pure-zirconia/stabilized zirconia mixture. An attempt was made to relate the fracture properties to the nature of the inherent flaws present in the material. </p> <p> The strength of calcia partially stabilised zirconia was observed to depend on the size and distribution of the grain boundary precipitate of pure zirconia. It is postulated that this grain boundary precipitate causes decohesion and weakening of some of the grain boundaries due to the large internal stresses associated with its martensitic phase transformation. This phenomena of grain boundary decohesion leads to elastic nonlinearity and hysteresis. Crack propagation was always observed to proceed in a slow controlled fashion in this material. A model is proposed to explain theses observations based on the formation of a microcrack zone at the tip of a propagation crack. The occurrence of continued stable crack propagation is believed associated with increasing microcrack zone size with increasing crack length. Evidence supporting this model is presented. </p> / Thesis / Master of Science (MSc)

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Proton exchange membrane fuel cells (PEMFCs) have been extensively studied as clean, sustainable and efficient power sources for electric vehicles, and portable and residential power sources. As one of the key components in PEMFC system, proton exchange membranes (PEMs) act as the electrolyte that transfers protons from the anode to the cathode. The state-of-art commercial PEM materials are typically based on perfluorinated sulfonic acid containing ionomers (PFSAs), represented by DuPont's Nafion®. Despite their good chemical stability and proton conductivity at high relative humidity (RH) and low temperature, several major drawbacks have been observed on PFSAs, such as high cost, high fuel permeability, insufficient thermo-mechanical properties above 80°C, and low proton conductivity at low RH levels. Therefore the challenge lies in developing alternative PEMs which feature associated ionic domains at low hydration levels. Nanophase separated hydrophilic-hydrophobic block copolymer ionomers are believed to be desirable for this purpose Three series of hydrophobic/hydrophillic, partially fluorinated/sulfonated multiblock copolymers were synthesized and characterized in this thesis. The hydrophilic blocks were based upon the nucleophilic step polymerization of 3, 3′-disulfonated, 4, 4′-dichlorodiphenyl sulfone (SDCDPS) with an excess 4, 4′-biphenol (BP) to afford phenoxide endgroups. The partially fluorinated hydrophobic blocks were largely based on 4, 4′-hexafluoroisopropylidenediphenol (6F-BPA) and various difluoro monomers (excess). These copolymers were obtained through moderate temperature (~130-150°C) coupling reactions, which minimize the ether-ether interchanges between hydrophobic and hydrophilic telechelic oligomers via a nucleophilic aromatic substitution mechanism. The copolymers were obtained in high molecular weights and were solvent cast into tough membranes, which had nanophase separated hydrophilic and hydrophobic regions. The performance and structure-property relationships of these materials were studied and compared to random copolymer systems. NMR results supported that the multiblock sequence had been achieved. They displayed superior proton conductivity, due to ionic, proton conducting channels formed through the self-assembly of the sulfonated blocks. The nano-phase separated morphologies of the copolymer membranes were studied and confirmed by transmission electron microscopy (TEM) and small angle X-ray scattering (SAXS). Through control of a variety of parameters, including ion exchange capacity and sequence lengths, performances as high, or even higher than those of the state-of-the-art PEM, Nafion®, were achieved. Another series of semi-crystalline hydrophobic poly(ether ether ketone)-hydrophilic sulfonated poly(arylene ether sulfone) (PEEK-BPSH100) multiblock copolymers was first synthesized and characterized. However due to their semi-crystalline structure, PEEK blocks are insoluble in most organic solvents at relatively low reaction temperatures, which prevents the coupling reaction between PEEK and BPS100. In order to facilitate the synthesis and processing, removable bulky ketimine was introduced to synthesize amorphous pre-oligomers poly(ether ether ketimine) (PEEKt). The synthetic procedure first involves the synthesis of hydrophobic poly(ether ether ketimine)-hydrophilic sulfonated poly(arylene ether sulfone) (PEEKt-BPS100) multiblock pre-copolymers via coupling reactions between phenoxide terminated hydrophilic BPS100 and fluorine terminated hydrophobic PEEKt blocks. The membranes cast from PEEKt-BPS100 were boiled in 0.5M sulfuric acid water solution to hydrolyze the amorphous PEEKt blocks to semi-crystalline PEEK blocks and acidify BPS100 blocks to BPSH100 blocks simultaneously. FT-IR spectra clearly showed the successful hydrolysis and acidification. The proton conductivity, water uptake and other membrane properties of the acidified semi-crystalline PEEK-BPSH100 membranes were then evaluated and compared with those of the state-of-the-art PEM, Nafion®. / Ph. D.

Concrete filled steel tubes are regarded as ideal frame members in seismic resisting systems, as they combine large axial and flexural capacity with ductility. The combination of the two materials increases the strength of the confined concrete and avoids premature local buckling of the steel tube. These benefits are more prominent for circular than for rectangular concrete filled steel tubes. However, most common connection configurations for circular concrete filled tubes are not economic in the US market due to (a) the desire of designers to use only fully restrained connections and its associated (b) high cost of fabrication and field welding. Research indicates that well designed partially restrained connections can supply equal or even better cyclic behavior. Partially restrained connections also possess potential capability to develop self-centering system, which has many merits in seismic design. The goal of this research is to develop a new connection configuration between circular concrete filled steel columns and conventional W steel beams. The new connection configuration is intended to provide another option for rapid assembling on site with low erection costs. The proposed connection is based on an extended stiffened end plate that utilizes through rods. The rods are a combination of conventional steel and shape memory alloy that provide both energy dissipation and self-centering capacity. The new connection configuration should be workable for large beam sizes and can be easily expanded to a biaxial bending moment connection. / Ph. D.

There are many issues and challenges to deal with when designing a curved I-girder bridge. These challenges primarily deal with the many performance stages that curved I-girder bridges have such as the erection, construction, and in-service stages. When design engineers assess the stability of a bridge system, they typically evaluate the system in its final configuration with all cross frames attached and the hardened concrete deck placed. The evaluation of girder stability during erection and early stages of construction stages is difficult because of the limited presence of bracing in the system. Due to a lack of readily available analytical tools, many contractors do not conduct detailed analytical evaluations of the bridge behavior during early stages of the construction when stability is often critical. Instead, many contractors use rules of thumb and experience to ensure stability during erection. Erection and construction practices typically vary among contractors and consistent erection methods are a rarity. Although some rules of thumb may be quite conservative, others are much less so. Therefore, coming up with design guidelines based on parametric studies rather than rules of thumb are desirable to help allow the contractor and the designer to work together to prevent issues that may occur due to the lack of communication between the two professions. Lastly, many challenges arise due to the complex geometry of curved I-girders. To prevent excessive rotation in erected girders, three points of vertical support are often provided. Two of these points usually consist of permanent supports in the form of bridge piers or abutments. The third point of support may consist of a temporary support in the form of a shore tower or holding crane. Cases where a holding crane may be satisfactory over a shore tower are also not well understood. To improve the understanding of lifting practices and temporary support requirements, parametric studies were conducted using the finite element program ANSYS. Field data consisting of displacement, stress, and girder rotations gathered from two tests were used to validate both the linear and geometric non-linear three-dimensional FEA models. Upon validation, the finite element model was used to conduct linear and geometric non-linear analyses to determine critical factors in curved I-girder bridges during construction. Specifically, serviceability limit states were studied for the lifting of curved girders. For partially constructed states, parametric studies were conducted to determine optimal locations to place temporary supports as well as to investigate stability differences between using a shore tower and a holding crane. Recommendations are presented to provide guidance for the lifting of curved I-girders as well as to maximize stability of partially constructed bridges. / text

Cette thèse s'intéresse à la définition de mécanismes, aussi bien au niveau logiciel que matériel, facilitant la gestion des systèmes-sur-puce hétérogènes et dynamiquement reconfigurable (HRSoC). L'hétérogénéité de ses architectures se manifeste par la présence à la fois de processeurs de calcul généralistes et de modules matériels reconfigurables. L'objectif de cette thèse est de permettre à un développeur d'application de s'abstraire de cette hétérogénéité en ce qui concerne l'allocation des tâches sur les différentes unités de calcul disponibles. Cette abstraction passe par une première phase d'homogénéisation des interfaces utilisateurs (API) et la définition d'un modèle de thread matériel, au même titre qu'il existe des threads logiciels. Cette homogénéisation se poursuit ensuite dans la gestion de ces threads matériels. Nous avons implémenté des services au niveau du système d'exploitation permettant de sauvegarder, préempter, et restaurer le contexte d'un thread matériel. Des outils de conception ont également été développés afin de surpasser le problème de la relocation d'un thread matériel au sein d'un FPGA. Enfin, la dernière étape a été d'étendre l'accès aux services offerts par tous les systèmes d'exploitation distribués au sein de la plateforme à tous les threads s'exécutant sur celle-ci, indépendamment de leur localisation. Ceci a été réalisé via une implémentation originale de l'API MRAPI. Avec ces trois étapes, nous avons apporté une base solide afin, dans le futur, de proposer au développeur un flot de conception dédié aux architectures HRSoC lui permettant de procéder à une exploration architecturale précise de son système. Finalement, afin d'éprouver le fonctionnement de ces mécanismes, nous avons réalisé une plateforme de démonstration sur FPGA Virtex 5 mettant en scène une application de suivi de cibles dynamique. / This thesis aims to define software and hardware mechanisms helping in the management the Heterogeneous and dynamically Reconfigurable Systems-on-Chip (HRSoC). The heterogeneity is due to the presence of general processing units and reconfigurable IPs. Our objective is to provide to an application developer an abstracted view of this heterogeneity, regarding the task mapping on the available processing elements. First, we homogenize the user interface defining a hardware thread model. Then, we pursue with the homogenization of the hardware threads management. We implemented OS services permitting to save and restore a hardware thread context. Conception tools have also been developed in order to overcome the relocation issue. The last step consisted in extending the access to the distributed OS services to every thread running on the platform. This access is provided independently from the thread location and is is realized implementing the MRAPI API. With these three steps, we build a solid basis to, in future work, provide to the developer, a conception flow dedicated to HRSoC allowing to perform precise architectural space explorations. Finally, to validate these mechanisms, we realize a demonstration platform on a Virtex 5 FPGA running a dynamic tracking application.