No description available.

No description available.

Aviation and aerospace structural components made of composite laminates due to their internal structure and manufacturing methods contain a number of inter- and intracomponent defects, which size, dispersion and interaction alter significantly the critical compression strain level. While there are a plethora of theoretical and experimental work on the problems stability loss and fracture of composites with internal defects in the scope of classic problems of fracture mechanics, there are few theoretical and numerical analyses available for the nonclassical problems of fracture mechanics of composites compressed along layers with interface cracks. These analyses usually have been considered the simplest problems, where the composite material with pronounced microstructure and interface defects (cracks, delaminations) have been analysed as two-dimensional (2-D) continuum in the condition of plane strain state. In the scope of these analyses only parallel defects have been considered, allowing for the interpenetration of the stress-free crack faces, or assuming so-called interfacial cracks with connected edges. This thesis broadens knowledge in the area of non-classical problems of fracture mechanics. It investigates the effect of interfacial cracks interaction on the critical buckling strain in layered and fibrous composite materials under compressive static loading. The behaviour of composite is analysed on several length-scales, starting from a ply and laminate levels (in 2-D approximation), down to a single-fibre level (a full 3-D model). The statements of the problems are based on the model of piecewise-homogeneous medium model, the most accurate within the framework of the mechanics of deformable bodies as applied to composite materials with pronounced microstructure. All composite constituents are modelled as linear-elastic material, where both isotropic and anisotropic materials are considered depending on the length-scale. It is assumed that the moment of stability loss in the microstructure of materials is treated as the onset of the fracture process. Besides that, the critical strain that corresponds to loss of stability in the microstructure of the composite, either surface or internal instability, must be smaller than the critical strain that corresponds to loss of stability of the entire composite. This project involves parameterised variables, such as the crack size, the crack spacing, the layer volume fraction and the fibre volume fraction. At each length-scale two types of cracks are analysed, namely, cracks with stress-free crack faces and cracks with frictionless Hertzian contact of the crack faces. A number of finite-element models for each length-scale are developed, and are validated analytically and numerically. The models' ability to simulate practical composite structures to a useful degree of accuracy with suitable material properties is discussed. A number of parameters, which quantifies the interfacial crack interaction and crack faces contact interaction phenomena, are introduced and discussed. Qualitative discussion on the crack faces contact zones, post-critical behaviour of composites and crack propagation are presented and discussed. Finally, the subject areas for the future work are outlined.

This thesis deals with the development and numerical modeling of Fiber Reinforced Polymer (FRP) wind turbine towers and luminaires. More specifically, this project is designed to capitalize on the technologies developed at the University of Manitoba to design FRP composite structures for use in remote communities where the costs of transportation and erection make the use of steel towers prohibitive. The work presented includes the analysis of a 50 m tall 750 kW wind turbine tower according to International Electrotechnical Commission (IEC) and Canadian Standard Association (CSA) standards using Glass Fiber Reinforced Polymer (GFRP), Carbon Fiber Reinforced Polymer (CFRP) and conventional steel. Standard luminaires, 6 m and 12 m, were also designed according to American Association of State Highway and Transportation Officials (AASHTO) standards for highway luminaires. The results showed that FRP can be effectively used as an alternative material for wind turbine towers and luminaires. Fiber Reinforced Polymer (FRP) composite wind turbine towers and luminaires studied in this project are lighter than similar structures fabricated using steel. Furthermore, these structures also meet the structural performance requirements set by AASHTO, IEC and CSA standards. / October 2016

Carbon nanotubes (CNTs) have been the subject of intensive research for nearly two decades, and this is due to their exceptional lightness, large aspect ratio, extraordinary mechanical, electrical, thermal properties and additional multi-functional characteristics. Ceramics have high stiffness and good thermal stability with a relatively low density, and they are an important constituent in the fabrication of advanced composites where high thermal and chemical stability are important. However, brittleness has limited their application in many structural applications. The combination of ceramic (alumina in particular) and CNTs, endeavouring to develop functional composites, offers a very attractive system for research and development. The fabrication of such alumina-CNT composites at bulk scale is therefore highly desirable for industrial applications. However, the synthesis of such composites possesses many technical challenges which need to be addressed. Poor synergy between the matrix and CNTs, potential damage to CNTs, obtaining a uniform and agglomeration-free distribution of CNTs within the matrix, and high cost of CNTs and processes involved in their composite fabrication have proved to be the significant challenges. In this thesis, the focuses are laid on addressing these issues and on the fabrication of specially engineered composites for particular applications such as filter and composites with improved mechanical properties. In this regard, it has been tried to directly fabricate CNTs in different ceramic matrices based on the application requirements. After that, the critical issues and challenges in the fabrication of these functional materials have been clearly investigated and by introducing novel methods and approaches, it has been tried to solve these problems. Also, a new polymer-ceramic-CNT composite has been fabricated by using two different thermoset (epoxy resin) and thermoplastic (polyamide 12) matrices. In this regard, good interfacial bonding between the composite elements along with good wettability of ceramic and CNTs with polymer had to be addressed as critical issues and challenges in the fabrication process. If the adherence at the interface is not strong enough, the material will tear and fail easier. In contrary, a tailored functionalization of CNTs can lead to an improved wettability and as the results, strong interfacial adhesion and bonding between the composite elements. These dominating factors will improve the degree of filling which results in existence of fewer voids inside the composite. These voids will act later as stress points and reduce the composite strength. At the end, the mechanical properties of the fabricated samples have been assessed. The CNT filters have been tested in the removal of bioorganic (yeast cells) and inorganic (heavy metal ions) contaminants from water, and of particulates from air, and they all showed very promising results. More than 99.6% of the air particles (size ranges from 0.3 to 10 µm) were filtered using 300 mm long CNT filter. A complete removal of heavy metal ions from water was reported particularly for single ion. 98% of the yeast cells were filtered. Different factors involved in the filtration efficiency such as ceramic pore size, length of filters, CNT loading and injection rates have also been discussed. Furthermore, the mechanical properties (compression test, hardness and impact test) of the composite materials (including ceramic-CNT, epoxy resin-ceramic-CNT and polyamide-ceramic-CNT composites) have been assessed. During impact test, the epoxy resin-ceramic-CNT composite absorbed 117.2% and 32.7% more energy compared to the pure epoxy resin and epoxy resin-ceramic composite, respectively. The epoxy resin-ceramic-CNT composite sustained 40% more elastic deformation before breakage compared to the epoxy resin-ceramic composite as a result of the CNT reinforcement. The addition of CNTs to the polyamide12-ceramic composite increased its yield stress by 41%. All of these results represent a big leap towards practical applications for the composite reported in the thesis, which may open up new opportunities for CNT engineering at industrial scales, due to the easy fabrication methods introduced and the promising performance they have exhibited.

Les composites organiques-inorganiques avec la zéolithe comme matrice hôte sont de plus en plus étudiés dans le but de concevoir des matériaux multifonctionnels conjuguant les propriétés de la molécule organique et celle de la zéolithe (ex. : élaboration de commutateurs magnétiques/optiques, doubleurs de fréquence). Les propriétés macroscopiques recherchées (SHG, transition de spin) dépendent des interactions entre les espèces organiques invitées et la zéolithe (charpente, cations compensateurs de charge), qui sont encore mal connue, en particulier en raison de l'absence de structures cristallographiques précises. Cette thèse s'est intéressée à deux types de composites principalement : (Co2+(bpy)3-zéolithe X) réputé présenter une transition de spin en température et dmpNA-MORdénite), à propriété potentielle de génération de second harmonique. Dans l’étude du composite magnétique, nous nous sommes particulièrement penché sur l'évolution de la structure de la zéolithe précurseur Na,Co-X dans différents état d’hydratation. Des études complémentaires par diffraction des rayons X sur monocristal, EXAFS et simulations Monte-Carlo ont mis en évidence la forte interaction entre cations cobalt et charpente aluminosilicatée ainsi que la migration des cations Co2+ accompagnant l'hydratation progressive de la zéolithe Na,Co-X. L’étude structurale du composite dmpNA-mordénite par diffraction des rayons X sur poudre (synchrotron SPring-8, Japon) a montré que les canaux droits de la mordénite sont presque totalement occupés par les molécules de dmpNA, qui adoptent un empilement quasi linéaire favorable à la Génération de Seconde Harmonique. / The organic-inorganic composites with zeolite as host matrix are mostly studied to produce performing materials for non-linear optics, optoelectronics, optical/magnetic memories. The performances of these new materials are driven by the coupling between the guest and host properties, in particular, by the molecularframework, molecular-cation interactions. Actually, only few accurate crystallographic structures of such composite are available in literature, so the guest-host interactions are still little known. In this work, I’m interested in the crystallographic structures of two composites: temperature induced spin crossover Co2+(bpy)3-zeolite X and dmpNA-mordenite that have to produce the Second Harmonic Generation signal. In the case of magnetic composite, I have particularly studied the composite precursor, zeolite Na,Co-X, in the different hydration states in order to follow an insight on structural modifications induced by water molecules desorption. Because of desorder, the structural studies are difficult. Nevertheless, the complementarities of the experimental (X-ray Diffraction and Absorption) and simulations (Monte-Carlo) approaches were fruitful to obtain the accurate partially/completely hydrated and dehydrated structures. These structures clearly show the cell volume contraction and cation migrations over dehydration that where caused by the strong cobalt –framework interactions. The crystal structure of dmpNA-mordenite has been determined from high resolution synchrotron powder diffraction and showed that zeolite straight channels are completely loaded with dmpNA molecules with a moderate tilt angle relative to the channel axe which is favourable to frequency doubling signal.

No description available.

This thesis discusses the effect of cryogenic temperatures on composite materials. The work includes estimating the shear strength of carbon/epoxy and glass/polyester composites at low temperatures and finding the rate of generation of microcracks in composites at cryogenic temperatures by acoustic emission technique. Microcracks increase the permeability of composites. So to study the permeability growth with microcracks, equipment is also designed to measure the permeability of composite to low temperature fluids. With short beam shear testing it was observed that the shear strength of composites increases with decreasing temperatures. Also carbon/epoxy composites were found to be much stronger than glass/polyester composites. Cryogenic temperatures improve the strength of composites but also generate microcracks in the structure due to the thermal expansion mismatch between the matrix and fiber. With acoustic emission testing from room to –150ºC, it was found that the rate of generation of microcracks increases with reducing temperatures. The work is extended to design a permeability equipment.

In recent years, steel components manufactured through additive manufacturing have increased their popularity and commercial importance and carbon fiber reinforced polymers are widely used in today’s society. Yet there is no composite material combining the properties of steel and carbon fibers. This thesis work is a part of the World Class Material-project at Swerim AB where different methods for manufacturing a steel matrix carbon fiber composite are researched upon. Two methods for additive manufacturing: selective laser melting and electron beam melting were used to evaluate the possibility of creating a steel matrix carbon fiber composite. The experiment with electron beam melting was conducted without powder and the two selective laser melting experiments were conducted with powder using fibers with organic and metal coating respectively. The main aspect evaluated was the survival of carbon fibers during processing. The results showed no intact carbon fibers after processing organically sized fibers in either of the processes. In the selective laser melting experiment with organic coating, big voids were found where the fiber bundles had been placed, showing no infiltration of powder or molten metal into the bundle prior to fiber breakdown. The metal-coated fibers survived partially but showed poor infiltration of matrix material into the carbon fiber bundle. The methods used in this report were not found suitable for the manufacturing of steel matrix carbon fiber composites. / De senaste åren har additiv tillverkning av stålkomponenter blivit alltmer populärt och kolfiberarmerade polymerer används i stor utsträckning i dagens samhälle. Trots det finns det i nuläget inget kompositmaterial som kombinerar stål och kolfiber. Detta kandidatexamensarbete har varit en del av World Class Material-projektet på Swerim AB, där olika metoder för tillverkning av en kolfiberkomposit med stålmatris undersöks. Två additiva tillverkningsmetoder, selective laser melting (SLM) och electron beam melting (EBM), användes för att utvärdera möjligheten att med dessa tillverka en stål-och kolfiberkomposit. Testet i EBM genomfördes utan pulver och i testerna SLM med pulver där fibrerna i ena försöket hade kvar sin organiska ytbeläggning och en metallbeläggning i det andra försöket. Den huvudsakliga aspekten som undersöktes var kolfibrernas förmåga att klara tillverkningsmiljön. Det förekom inga intakta kolfiber efter processen i försöken med EBM och SLM med den organiska ytbeläggningen. Beträffande SLM-försöket, påträffades även stora håligheter där kolfiber befunnit sig, vilket visade på en bristfällig impregnering av fibrerna innan deras nedbrytning. Fibrerna som var belagda med en metall överlevde framställningsprocessen i en större utsträckning, men impregnationen var fortfarande bristfällig. Metoderna som undersöktes i denna rapport var sålunda inte lämpliga för att tillverka en kolfiberkomposit med stålmatris.

Este trabalho apresenta uma abordagem abrangente das estruturas mistas aço-concreto, com ênfase em edifícios, e dos principais elementos que compõem esse sistema: as vigas mistas, simplesmente apoiadas e contínuas, as lajes mistas e os pilares mistos. São abordados os aspectos construtivos, o comportamento estrutural e os procedimentos para dimensionamento recomendados pelas principais normas aplicáveis, enfatizando a norma norte-americana do AISC e o EUROCODE 4. O projeto em situação de incêndio também é analisado, considerando o comportamento e o dimensionamento de elementos mistos frente à ação do fogo. No final, são desenvolvidos exemplos de dimensionamento, onde procura-se comparar e discutir os resultados obtidos pelas principais normas / This study consists of a broad analysis of composite structures, with particular emphasis on buildings, and the principal elements that make up this system, i.e., continuous and simply supported composite beams, composite slabs and composite columns. Several aspects of construction are broached, as well as structural behavior and the procedures for design recommended by the main codes, mainly the American AISC and the EUROCODE 4 codes. Fire design is also analyzed, considering the behavior and design of composite elements under fire conditions. The study concludes with some examples of design, comparing and discussing the results achieved by the principal codes