La maîtrise du procédé séchage, étape essentielle dans la transformation du bois, est devenue incontournable pour la filière bois. Cette thèse propose l'utilisation de conduites de séchage oscillantes pour réduire les contraintes de séchage liées au retrait par l'activation du fluage mécanosorptif. A ce jour, la meilleure façon d'appliquer les conduites oscillantes représente un défi pour la communauté scientifique. Dans ce travail, nous avons choisi comme matériel d'étude une essence feuillue fortement utilisée dans la filière et très susceptible aux déformations lors du séchage : le hêtre (Fagus sylvatica). L'effet des conduites oscillantes sur les contraintes de séchage est étudié par une approche expérimentale et par une approche théorique, articulées en trois parties : - Un premier volet expérimental sur un séchoir semi – industriel pour saisir l'effet global des conduites oscillantes à l'échelle d'une pile de planches. L'amélioration de la qualité du bois séché s'est avérée par : une meilleure homogénéité de la teneur en eau finale inter et intra-planche, la diminution des déformations globales et la diminution des contraintes résiduelles exprimées par le gap du « slicing test ». - Ensuite, nous avons développé un volet théorique sur la base de modélisations analytique et numérique pour étudier l'évolution des champs de teneur en eau et de contraintes mécaniques au sein d'une planche lorsque les conditions climatiques oscillent. Une formulation analytique simple, adaptée aux conduites oscillantes, est proposée pour les utilisateurs de séchoirs n'ayant pas accès à un outil numérique sophistiqué. L'approche numérique effectuée avec l'outil de simulation TransPore permet une étude plus réaliste du séchage oscillant. Ainsi, le module mécanique de TransPore a été utilisé pour dégager des configurations pertinentes de séchage permettant d'étudier l'effet des conduites oscillantes sur la relaxation des contraintes. - Enfin, un second volet expérimental a été réalisé sur un séchoir de laboratoire, à l'échelle d'une planche, pour tester les informations issues du volet théorique. Un dispositif de séchage dissymétrique (flying wood) et deux dispositifs de séchage sous charge (poutre cantilever et flexion trois points) ont été utilisés pour étudier l'effet des oscillations. Toutefois, ces essais ne permettent pas de montrer clairement l'effet des oscillations sur la relaxation des contraintes. La confrontation entre les résultats expérimentaux à l'échelle d'une planche et la simulation numérique a mis en évidence l'effet conséquent des oscillations parasites de faibles période et amplitude sur les résultats expérimentaux, provoquées par la régulation du séchoir. Des modifications du modèle de comportement mécanique différé ont été proposées en perspectives de ce travail afin de mieux saisir le comportement observé expérimentalement. / Wood drying is an essential process in the wood industry. A perfect control of wood drying is nowadays very important for the wood industry. In this study, we propose the utilization of oscillating drying conditions to reduce the drying stresses induced by wood shrinkage by activating the mechanosorptive creep. The best way to apply this concept remains an open question in the scientific community. Beech wood (Fagus sylvatica), one of the most commonly used hardwood in France, was chosen for this study owing its elevated risk of drying defaults. The effect of oscillating conditions on drying stresses inside the boards was studied by both an experimental and a theoretical approach, structured in three parts: - A first experimental part realized with a semi – industrial kiln in order to study the global effect of oscillating conditions at the stack scale. Improvement of the quality of dried wood was showed by the best homogeneity of water content inside the board and among the boards and by the decrease of global deformations and residual stresses expressed by the gap measured by the slicing test. - The study was continued with a theoretical part based on analytical and numerical modeling to understand the development of internal heat and mass transfers inside the boards and the evolution of drying stresses during oscillating conditions. A simple analytical model adapted to the oscillating conditions was proposed, particularly for kiln users who don't have access to sophisticated numerical tools. The numerical approach used the simulation tool TransPore, able to simulate oscillating drying in more realistic conditions. Its mechanical module was used to set accurate drying schedules to study the effect of oscillating conditions on stresses relaxation. - Finally, a second experimental part was performed in a laboratory scale kiln, at the board scale, to test the information obtained theoretically. A non-symmetrical drying device (flying wood) and two different loaded drying devices (cantilever beam test and three points bending) were used to study the effect of oscillations. However, it is difficult to see the oscillating conditions effect on the stresses relaxation. The confrontation between experimental results at the board scale and the numerical simulation showed the significant effect produced on experimental results by parasite oscillations of small periods and intensities, originated by the kiln regulation. Further work should consider some modifications of the time dependent mechanical behavior model in order to capture the experimentally observed behavior.

The properties of natural soil are inherently variable and influence design decisions in geotechnical engineering. Apart from the inherent variability of the soil, the variability may arise due to measurement of soil properties in the field or laboratory tests and model errors. These wide ranges of variability in soil are expressed in terms of mean, variance and autocorrelation function using probability/reliability based models. The most common term used in reliability based design is the reliability index, which is a probabilistic measure of assurance of performance of structure. The main objective of the reliability based design is to quantify probability of failure/reliability of a geotechnical system considering variability in the design parameters and associated safety. In foundation design, reliability based design is useful compared to deterministic factor of safety approach. Several design codes of practice recommend the use of limit state design concept based on probabilistic models, and suggest that, development of reliability based design methodologies for practical use are of immense value. The objective of the present study is to propose reliability based design methodologies for pile foundations under static and seismic loads. The work presented in this dissertation is subdivided into two parts, namely design of pile foundations under static vertical and lateral loading; and design of piles under seismic loading, embedded in non-liquefiable and liquefiable soil. The significance of consideration of variability in soil parameters in the design of pile foundation is highlighted. A brief review of literature is presented in Chapter 2 on current pile design methods under vertical, lateral and seismic loads. It also identifies the scope of the work. Chapter 3 discusses the methods of analysis which are subsequently used for the present study. Chapter 4 presents the reliability based design methodology for vertically and laterally loaded piles based on cone penetration test data for cohesive soil. CPT data from Konaseema area in India is used for analysis. Ultimate limit sate and serviceability limit state are considered for reliability based design using CPT data and load displacement curves. Chapter 5 presents the load resistance factor design (LRFD) of vertically and laterally loaded piles based on load test data. Reliability based code calibrated partial factors are determined considering bias in failure criteria, model bias and variability in load and resistance. Chapter 6 illustrates a comprehensive study on the effect of soil spatial variability on response of vertically and laterally loaded pile foundations in undrained clay. Two-dimensional finite difference program, FLAC2D (Itasca 2005) is used to model the soil and pile. The response of pile foundations due to the effect of variance and spatial correlation of undrained shear strength is studied using Monte Carlo simulation. The influence of spatial variability on the propagation and formation of failure near the pile foundation is also examined. Chapter 7 describes reliability based design methodology of piles in non-liquefiable soil. The seismic load on pile foundation is determined from code specified elastic design response spectrum using pseudo-static approach. Variability in seismic load and soil undrained shear strength are incorporated. The effects of soil relative densities, pile diameters, earthquake predominant frequencies and peak acceleration values on the two plausible failure mechanisms; bending and buckling are examined in Chapter 8. The two-dimensional finite difference analysis is used for dynamic analysis. A probabilistic approach is proposed to identify governing failure modes of piles in liquefiable soil in Chapter 9. The variability in the soil parameters namely SPT-N value, friction angle, shear modulus, bulk modulus, permeability and shear strain at 50% of modulus ratio is considered. Monte Carlo simulation is used to determine the probability of failure. A well documented case of the failed pile of Showa Bridge in 1964 Niigata earthquake is considered as case example. Based on the studies reported in this dissertation, it can be concluded that the reliability based design of pile foundations considering variability and spatial correlation of soil enables a rational choice of design loads. The variability in the seismic design load and soil shear strength can quantify the risk involved for pile design in a rational basis. The identification of depth of liquefiable soil layer is found to be most important to identify failure mechanisms of piles in liquefiable soil. Considerations of soil type, earthquake intensity, predominant frequency of earthquake, pile material, variability of soil are also significant.

An der TU Dresden wurde eine Forschungsarbeit zur experimentell-theoretischen Analyse des Tragverhaltens von Verankerungen durchgeführt, die hauptsächlich zur oberflächenparallelen Einleitung großer Schubkräfte in einen Betongrund ausgelegt sind. Diese Verankerungen ermöglichen die Übertragung einer großen Querkraftbe¬anspruchung mit geringer Exzentrizität zur Oberfläche, die mit einer Normalbean¬spruchung in Zug- oder Druckrichtung kombiniert werden kann. Die wesentlichen Grundelemente sind zumindest ein Schubdübel, ein Zuganker und eine Grundplatte, mehrere Schubdübel oder Anker können vorhanden sein. Der quaderförmige Schub¬dübel überträgt die Kraft in den Beton. Die angreifenden Lastmomente und das Moment aus der exzentrischen Einleitung der Schublast werden in ein vor und hinter dem Dübel wirkendes Kräftepaar zerlegt. Die Zugkomponente wird dem Zuganker in Form eines Kopfbolzendübels zugewiesen. Die Grundplatte verbindet die lastseitige Befestigungskonstruktion mit den lastübertragenden Bauteilen Schubdübel und Zug¬anker. Gleichzeitig kann die Grundplatte in den Beton eingelassen sein und überträgt dann ebenfalls Schublasten. Die Lastabtragung und das Verhalten der Einbauteile im Versuch wurden analysiert. Von besonderer Bedeutung ist hierbei die Last-Verschiebungslinie, die die Lastüber¬tragung charakterisiert. Ziel war es, ein Bemessungskonzept zur Dimensionierung der Schubdübel zu erarbeiten. Um die im Versuch erkennbare maßgebende Beein¬flussung der Lastübertragungskapazität durch den sich einstellenden Verformungs¬zustand eingehender untersuchen zu können, wurde der Versuch mit finiten Elemen¬ten abgebildet. So war es möglich, in einem ersten Schritt Lastübertragungskapazitä¬ten für unverformte Systeme zu ermitteln, die praktisch im Versuch nicht oder nur extrem aufwändig realisiert werden könnten. In einem zweiten Schritt kann dann der Einfluss der Verformung berücksichtigt werden. Hierbei können die Parameter ge¬nauer und vielschichtiger variiert werden als dies bei den relativ aufwändigen Versu¬chen rein quantitativ möglich war. Das in dieser Arbeit vorgestellte Berechnungsver¬fahren liefert neben der maximal aufnehmbaren Schubbeanspruchung geometrisch beliebiger Einbauteile auch die Beanspruchbarkeit einzelner Baugruppen und erlaubt es zu beurteilen, inwieweit die einzelnen Lastübertragungsmechanismen additiv oder alternativ wirksam sind. Das Verfahren gibt Auskunft über das zu erwartende lastabhängige Verhalten der Einbauteile inklusive der Vorhersage von Teilversagens¬zuständen. Das Potential der Befestigungssysteme zur Übertragung großer Schublasten ist durch die Aufsplittung der Lastkomponenten und Übertragung durch spezialisierte Bauteile begründet. Diese können in ihrer Beschaffenheit den Erfordernissen optimal angepasst werden. Einsatzgebiete für diese Befestigungen sind alle konzentrierten Lasteinleitungen oder Montagestöße zwischen Betonbauteilen oder Stahl-Holz-Kon¬struktionen auf der einen und Betonelementen auf der anderen Seite. Neben der Auflagerung von Trägern oder Fassadenelementen ist vor allem auch an die Ertüchti¬gung und Verstärkung bestehender Betonbauteile durch zusätzliche Stahlkonstrukti¬onen zu denken. / An experimental and theoretical analysis of the behaviour of complex shear loaded fastenings was carried out at Dresden University of Technology. The main focus was on applications which introduce a great amount of shear load value parallel to the surface into a concrete base using a stell shear lug. The behaviour of these special fixings is presented as the result of the finished research program. Structures, as shown in the opposite figure, are able to transmit high values of shear loads to the anchor ground. An additional loading of normal force und bending moment is suitable, but will only be supposed to cover the necessary tolerance and off centre condition of the fixture parts. The advantage of fastening with shear lugs is based on the splitting of the load transfer into different components. The shear lug/lugs caries/carry the shear load, and the tie bar itself only balances the system by tension load due to moment loading and normal loading. Thusall loads are transferred by highly specialized components. If the base plate is embedded, there will be a shear load transferred in front of the base plate, too. The load carrying behaviour of the fastenings in the experiments is analyzed. Here, the load-displacement relationship is of special importance . This thesis aims at elaborating a dimensioning concept for the design of shear lugs. The tests show a decisive influence of the movements – displacements as well as rotations – of the fastenings to the load carrying capacity. In order to to be able to examine this behaviour, the experiment is redesigned by finite elements. In a first step it is therefore possible to examine fastenings without movements based on the anchor bolt stiffness. In a second step, the influence of the deformation can be explored. Here, the parameters can be varied more exactly and in a more complex way than this is possible in terms of quantity with the comparetively extensive test setup. The calculation method being introduced here does not only supply the maximum shear load transfer capacity of the hole fastening system, a system with free geometries, but also shows the partial shear load transfer capacity of the individual parts of the unit. This method is a means of predicting the load-related behaviour of the fastenings to be expected, including the forecast of partial failure states. As a result, a suggestion for the design of the fittings is shown. This design can be applied to all fittings by splitting the different load components to especially provided anchor elements. The design resistance and behaviour of the fastenings is estimated, depending on different geometries and stiffness conditions of the lug. Different strength classes of the concrete as well as different load combinations are taken into consideration. First examples from building sites are also available.

Made available in DSpace on 2016-06-02T20:30:59Z (GMT). No. of bitstreams: 1 6757.pdf: 1103934 bytes, checksum: 1e243bc6fc800e7f55079679a98ba983 (MD5) Previous issue date: 2015-03-09 / Financiadora de Estudos e Projetos / Research upon attitude s formation and change using the stimulus equivalence paradigm has shown, at the same time, a potential for the formation of new classes, and a difficulty with respect to teaching new relationships when the stimuli used are familiar and socially loaded. As racial prejudice is a problem worldwide, and stimulus equivalence paradigm has proven to be useful when studying attitude s formation and change, the aim of this study was to verify, from a systematic replication, if teaching new relations to children who showed a negative racial bias towards black people could revert the pre-existing classes. The level of 54 children s bias was assessed by the Self-Assessment Manikin (SAM), an instrument that measures the affective experience of individuals on pictures or events. The 22 participants who had attributed to black people s pictures lower levels of pleasure compared to white people s pictures also performed a second test aimed to confirm the bias shown. The 13 participants whose negative bias towards black people was confirmed were trained to match indirectly black people s pictures with positive attributes in a matching-to-sample task. Two experimenters, a black and a white one conducted the research with different children, to evaluate possible differences in the participants performance. The performances of these children were compared in two conditions: using simultaneous or delayed matching-to-sample, analyzing 1) How many children formed the expected equivalence classes; 2) in which of the two conditions the results were more robust; and 3) if the presence of white faces as a third comparison-stimuli in a modified equivalence test caused changes in the previous responses given by the participants who responded in accord with stimulus equivalence. Two instruments, a self-report and a implicit measure were used as complementary measures of transfer of functions, to evaluate the meaning of the stimuli. Results showed no differences between delayed and simultaneous matching-to-sample, or between the experimenters in the formation of the equivalence classes. All 13 participants who demonstrated a negative racial bias showed formation of the equivalence classes experimentally planned. Of those 13 children, nine have maintained their responses on the modified equivalence test, and the group data showed transfer of function, evidenced by SAM. Although there was a statistically significant difference between the pleasure levels of white and black faces before the class formation, post-test data revealed no statistically significant differences; this was also confirmed by the results of another instrument, called Implicit Relational Assessment Procedure (IRAP). Future research should recruit a larger number of participants and systematically change variables such as the use of mixed training of trained relations and the review of baseline relations, in order to identify which of them may be responsible for the positive results of equivalence. / Pesquisas sobre formação e mudança de atitudes utilizando o paradigma de equivalência de estímulos têm mostrado, ao mesmo tempo, um potencial para a formação de novas classes, e a dificuldade com relação ao ensino de novas relações, quando os estímulos utilizados são familiares e socialmente carregados. Como o preconceito racial é um problema presente no mundo todo, e o paradigma de equivalência de estímulos tem se mostrado útil no estudo da formação e mudança de atitudes, o objetivo dessa pesquisa foi verificar, a partir de uma replicação sistemática, se o ensino de novas relações de equivalência a crianças que demonstrassem ter viés negativo para faces negras reverteria as classes pré-existentes. O nível de viés racial de 54 crianças foi avaliado pela Auto-Avaliação Manikin (SAM), instrumento que mede a experiência afetiva dos indivíduos diante de imagens ou eventos. As 22 crianças que avaliaram fotos de negros com níveis de prazer inferiores aos atribuídos nas fotos de brancos realizaram um segundo teste com o intuito de confirmar o viés apresentado. Os 13 participantes cujo viés racial negativo foi confirmado foram treinados a emparelhar, de maneira indireta, fotos de negros com um símbolo positivo, a partir de tarefas de emparelhamento de acordo com o modelo. Duas experimentadoras, uma negra e outra branca conduziram a pesquisa com diferentes crianças, para avaliar possíveis diferenças no desempenho dos participantes. O desempenho dos participantes foi comparado em duas condições: com o uso de emparelhamento ao modelo simultâneo versus com atraso, analisando 1) quantas crianças formariam as classes de equivalência esperadas; 2) em qual das duas condições os resultados obtidos foram mais robustos; e 3) se a presença das faces brancas como 3º. estímulocomparação em um teste de equivalência modificado ocasionaria mudanças nas respostas prévias dadas pelos participantes que demonstraram a formação das classes de equivalência. Dois instrumentos, um de autorrelato, e outro de medidas implícitas foram utilizados como medidas complementares de transferência de função, para verificar o significado dos estímulos. Os resultados mostraram não haver diferenças entre o uso de emparelhamento de acordo com o modelo simultâneo ou atrasado, ou entre as duas experimentadoras na formação das classes de equivalência. Todos os 13 participantes com viés negativo para faces negras demonstraram a formação das classes de equivalência planejadas experimentalmente. Desses 13, nove mantiveram suas respostas no teste de equivalência modificado, e os dados de grupo evidenciaram transferência de função obtida pelo SAM. Apesar de haver diferença estatisticamente significativa entre os níveis de prazer das faces brancas e negras antes da formação das classes, os dados de pós-teste com o SAM revelaram não haver diferenças estatisticamente significativas, dado confirmado pelos resultados de outro instrumento, chamado Procedimento de Avaliação Relacional Implícita (IRAP). Pesquisas futuras devem recrutar um número maior de participantes, além de alternar sistematicamente variáveis como o uso de treino misto das relações treinadas e a revisão das relações de linha de base, de modo a identificar quais delas podem ser responsáveis pelos resultados positivos de equivalência.

Rotating and non-rotating beams are widely used to model important engineering struc-tures. Hence, the vibration analyses of these beams are an important problem from a structural dynamics point of view. Depending on the beam dimensions, they are mod-eled using different beam theories. In most cases, the governing differential equations of these types of beams do not yield any simple closed-form solutions; hence we look for the inverse problem approach in determining the beam property variations given certain solutions. The long and slender beams are generally modeled using the Euler-Bernoulli beam theory. Under the premise of this theory, we study (i) the second mode tailoring of non-rotating beams having six different boundary conditions, (ii) closed-form solutions for free vibration analysis of free-free beams, (iii) closed-form solutions for free vibration analysis for gravity-loaded cantilever beams, (iv) closed-form solutions for free vibration analysis of rotating cantilever and pinned-free beams and (v) beams with shared eigen-pair. Short and thick beams are generally modeled using the Timoshenko beam theory. Here, we provide analytical closed-form solutions for the free vibration analysis of ro-tating non-homogeneous Timoshenko beams. The Rayleigh beam provides a marginal improvement over the Euler-Bernoulli beam theory without venturing into the math-ematical complexities of the Timoshenko beam theory. Under this theory, we provide closed-form solutions for the free vibration analysis of cantilever Rayleigh beams under three different axial loading conditions - uniform loading, gravity-loading and centrifu-gally loaded. We assume simple polynomial mode shapes which satisfy the different boundary conditions of a particular beam, and derive the corresponding beam property variations. In case of the shared eigenpair, we use the mode shape of a uniform beam which has a closed-form solution and use it to derive the stiffness distribution of a corresponding axially loaded beam having same length, mass variation and boundary condition. For the Timoshenko beam, we assume polynomial functions for the bending displacement and the rotation due to bending. The derived properties are demonstrated as benchmark analytical solutions for approximate and numerical methods used for the free vibration analysis of beams. They can also aid in designing actual beams for a pre-specified frequency or nodal locations in some cases. The effect of different parameters in the derived property variations and the bounds on the pre-specified frequencies and nodal locations are also studied for certain cases. The derived analytical solutions can also serve as a benchmark solution for different statistical simulation tools to find the probabilistic nature of the derived stiffness distri-bution for known probability distributions of the pre-specified frequencies. In presence of uncertainty, this flexural stiffness is treated as a spatial random field. For known probability distributions of the natural frequencies, the corresponding distribution of this field is determined analytically for the rotating cantilever Euler-Bernoulli beams. The derived analytical solutions are also used to derive the coefficient of variation of the stiffness distribution, which is further used to optimize the beam profile to maximize the allowable tolerances during manufacturing.

M.Tech. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / To replace the conventional wastewater treatment technology, photocatalysis has the best potential due to its utilization of visible light to photodegrade organic and inorganic contaminants. However, agglomeration of nanoparticles leads to serious decrease in photocatalytic performance when applied in slurry form, due to hindrance effect. TiO2 semiconductor photocatalyst mediated advanced oxidation process is referred to as one of the most efficient technologies to degrade organic pollutants in water. However, TiO2 semiconductor for water purification hinders large scale applicability due to poor activity under visible light and the recombination of photogenerated electron and hole pairs. The modification of TiO2 semiconductor photocatalyst with carbon dots (CDs) is of high importance due to low toxicity, aqueous stability, enhanced surface area, economic feasibility, good biocompatibility and chemical inertness of CDs. Herein, strategies are highlighted to improve the activity of TiO2 semiconductor photocatalyst by coupling it with CDs and Fe2O3. In this study, we study the morphological influence of TiO2 nanostructures on photocatalytic degradation of tetracycline hydrochloride present in industrial wastewater. TiO2 nanostructures, nanotubes, nanospheres and nanofibers were Synthesized using the hydrothermal technique. TiO2 nanotubes, nanofibers and nanospheres were prepared by the hydrothermal treatment of TiO2 nanoparticles with different NaOH concentrations (5, 10 and 12 N) at 120 and 140 ˚C; afterwards, HCl was added until it reached pH 2. Both the crystalline phase and coordination of the TiO2 nanotubes, nanofibers and nanospheres were composed principally. Likewise, the surface area, pore volume and pore size of the TiO2 nanotubes, nanofibers and nanospheres changed with the NaOH rinsing treatment. The photocatalytic activity for tetracycline degradation were strongly enhanced by the nanofibers and nanotubes in the basic and acid media, respectively, showing a relationship between their structure and the medium. TiO2 nanostructures and the composite material were characterized by scanning electron microscope\SEM), X-Ray Diffraction (XRD), transmission electron microscope (TEM) and Fourier transform infrared (FTIR). BET surface area analysis was carried out using nitrogen adsorption desorption curves. The results show that TiO2 morphology had great influence on photocatalytic degradation of tetracycline hydrochloride due to difference in specific surface area and pore volume of nanostructures. The photocatalytic degradation experiments were carried out for three hours under visible-LED light. TiO2 nanofibers show better degradation performance than nanotubes and nanospheres due to presence of large surface area for reaction, higher porosity with dispersion of active sites at different length scales of pores and presence of oxygen vacancies. Agricultural biomass pine bark serves as a carbon source and was doped into TiO2-nanofibers (TNF) to fabricate the composite material (CD-TNF). CD-TNF composite nanofibers were prepared via a facile hydrothermal method. This study revealed that the photocatalytic efficiency of tetracycline (TC) under visible light irradiation of the composite nanofiber is higher than that of pure TiO2-nanofiber. The anchored CDs can both enhance the light absorption and suppress photogenerated electron hole recombination which results in the enhancement of catalytic and antibacterial properties. The CDs can better capture and transfer photogenerated electrons through the Ti-O-C and Fe-O-C bonds. Moreover, CDs can improve the utilization of photogenerated electrons and the electrons in CDs are captured by O2 to produce O2•- radicals and the role of O2•- radicals in the photocatalytic process is significantly improved. A new efficient photocatalyst consisting of TiO2/CD/Fe2O3 composite material was Synthesized by the hydrothermal treatment and applied in the photodegradation of 5 mg/L tetracycline hydrochloride (TC) under visible-LED light. The CDs/TiO2/Fe2O3 composite showed enhanced photocatalytic performance for tetracycline photodegradation when compared with TiO2/CDs and pure TiO2 under the visible light irradiation. The mechanism of the improved photocatalytic activity over CDs/TiO2/Fe2O3 was also investigated. The influence of the interface formation between Fe2O3 and TiO2/CDs affects severely the charges separation efficiency and enhances the electron transfer to keep on the existence of Fe3+/Fe2+ moieties that take significant role in the reaction mechanism.

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The official recommendations in geotechnical engineering are according to Swedish practice to install inclined driven piles in order to resist external horizontal loads, which usually consist of windloads. These loads gets counteracted by utilizing the pile's axial load-bearing capacity, however when designing a foundation the use of inclined piles has proven to be problematic from a number of different perspectives. This has made both engineers as well as contractors long for a solution where the piles instead are allowed to be installed vertically, which could be made possible by utilizing the lateral bearing capacity of the pile which occurs in connection with lateral resistance during pile-soil interaction. The present day knowledge about such an engineering procedure in Sweden has proven to be limited and consists mainly of one governing document, namely report 101 published by the Commission on Pile Research. The aim of our study is to test and evaluate the method in report 101 based on a number of different load cases related to lateral load effects during pile-soil interaction. An analytical method reproduced from the Commission on Pile Research's report has been implemented with help of Mathcad, a computer software for reuse of mathematical calculations. Decisive parameters that distinguish the different load cases have included external load impact in pile head, mechanical strength properties of friction or cohesive soil, along with cross-sectional dimensions and reinforcement content of piles etc. The results differed significantly depending on the loadcase, a majority of the given answers were also perceived as unreliable and in a number of load cases the method also failed to obtain an analytical solution. Our conclusion is that it is doubtful whether the elastoplastic method presented in report 101 in the end in practice benefits the engineer tasked with designing, this stands in stark contrast to an increasing demand for easily accessible knowledge within its field. / Pålar i samband med grundläggning har sedan en tid tillbaka enligt svensk praxis installerats snedslagna, detta för att med hjälp av pålens axiella bärförmåga motstå yttre horisontell lastpåverkan till följd av exempelvis vindlaster. Att snedställa pålar har visat sig vara problematiskt ur ett flertal olika perspektiv, en lösning som både konstruktörer och entreprenörer efterlängtat är att pålarna istället tillåts installeras rakställda. Detta skulle vara möjligt genom att nyttja pålens transversella bärförmåga som uppstår i samband med sidomotstånd vid interaktion påle-jord. Kunskap kring ett sådant dimensioneringsförfarande i Sverige idag har visat sig vara begränsad och till stor del bestå av ett styrande dokument, nämligen rapport 101 utgiven av Pålkommissionen. I denna studie har en analytisk handberäkningsmetod som återges ur Pålkommissionens rapport implementerats i beräkningsprogrammet Mathcad, detta i syfte att testa och utvärdera metoden utifrån ett flertal olika belastningsfall relaterade till transversell lastpåverkan vid interaktion påle-jord. Avgörande parametrar som skiljt de olika belastningsfallen åt har bl.a. utgjorts av hållfasthetsegenskaper hos friktion- eller kohesionsjord, tvärsnittsdimensioner och armeringsinnehåll hos påle, yttre lastpåverkan i påltopp. Resultaten skiljde sig åt markant beroende på typ av belastningsfall där en majoritet av svaren upplevdes som icke tillförlitliga och till ett flertal olika fall, utifrån vårt försök till implementering, klarade metoden heller inte av att erhålla någon analytisk lösning. Vi finner det därför svårt att tro att den elastoplastiska metoden som återges i rapport 101 i slutändan kommer till någon direkt praktisk nytta, vilket står i tvär kontrast mot ett uppenbart behov där lättillgänglig kunskap inom området efterfrågas.

Three testing methods are proposed to characterize properties of fuel cell materials that affect the mechanical durability of proton exchange membranes (PEMs). The first two methods involved measuring the in-plane biaxial strength of PEMs and the biaxial hygrothermal stresses that occur in PEMs during hygrothermal cycles. The third method investigated the nonuniform thickness and compressibility of gas diffusion media which can lead to concentrated compressive stresses in the PEM in the through-plane direction. Fatigue and creep to leak tests using multi-cell pressure-loaded blister fixtures were conducted to obtain the lifetimes of PEMs before reaching a threshold value of gas leakage. These tests are believed to be more relevant than quasi-static uniaxial tensile to rupture tests because of the introduction of biaxial cyclic and sustained loading and the use of gas leakage as the failure criterion. They also have advantages over relative humidity cycling test because of the controllable mechanical loading. Nafion® NRE-211 membrane was tested at three different temperatures and the time-temperature superposition principle was used to construct a stress-lifetime master curve. Tested at 90°C, extruded Ion Power® N111-IP membrane was found to have longer lifetime than Gore™-Select® 57 and Nafion NRE-211 membranes under the same blister pressure profiles. Bimaterial specimens fabricated by bonding a piece of PEM to a substrate material were used to measure the hygral stresses, compressive and tensile, in the PEM during relative humidity cycles. The substrate material and its thickness were carefully chosen so that stresses in the PEM could be obtained directly from the curvature of the bimaterial specimen without knowing the constitutive properties of the PEM. Three commercial PEMs were tested at 80°C by cycling the relative humidity between 90% and 0% and by drying the membrane to 0%RH after submersion in liquid water. Stress histories for all three membranes show strong time-dependencies and Nafion® NRE-211 exhibited the largest tensile stress upon drying. Besides in-plane stresses, hard spots in gas diffusion media (GDM) can locally overcompress PEMs in the out-of-plane direction and cause electrical shorting. In this study, GDM samples sealed with an impermeable Kapton® film on the surface were compressed with uniform air pressure and the nonuniform displacement field was measured with a three-dimensional digital image correlation technique. Hard spots as a result of the nonuniform thickness and compressibility of the GDM were found and their severities as stress risers are evident. Locally, a nominal platen compression (similar to bipolar plate land compression) of 0.68 MPa can lead to compressive stress as large as 2.30 MPa in various hard spots that are in the order of 100s µm to 1 mm in size. / Ph. D.

Diese Dissertation befasst sich mit der industrienahen Herstellung von Katalysatorschichten für Polymer-Elektrolyt-Membran-Brennstoffzellen mit Hilfe des Tiefdrucks als Fertigungsverfahren. Um die Anforderungen an die Katalysatorschicht hinsichtlich der Schichtdicke zu erreichen, wird ein Linienraster für den Tiefdruck entwickelt. Das patentierte und verifizierte Designkonzept des Linienrasters ermöglicht es, trotz Tinten mit geringem Feststoffgehalt hohe Trockenschichtdicken zu erzeugen. Aufgrund des verwendeten Tiefdruckrasters sind Optimierungsschritte an der Fertigungsanlage notwendig, um eine hohe Schichtqualität zu erreichen. Schließlich werden kontinuierlich und industrienah Katalysatorschichten gefertigt, die als Membran-Elektroden-Einheit in einer Polymer-Elektrolyt-Membran-Brennstoffzelle erfolgreich eingesetzt werden. / This work presents an industrial close manufacturing process of active electrodes for Polymer Electrolyte Fuel Cells utilizing an adapted gravure printing process. To meet the requirements of the electrodes regarding the layer thickness (weight) and quality a novel line screen with maximized dipping volume for gravure printing was developed and investigated. A design rule for this kind of screens was realized and verified by a successful manufacturing of electrodes with different dried layer thicknesses. Due to the rough structure and the high dipping volumes of these line screens an adaption and optimization of the machinery and the whole process was necessary to achieve high quality electrodes. Finally, it is shown that it is possible to manufacture continuiously in an industrial close roll-to-roll process platinum loaded electrodes, working successful as cathode in a Membran-Electrode-Assembly.