Bi-layered materials are a reduced weight derivative of the sandwich structure and are comprised of one thin skin face reinforced by a thick layer of low density material. Bi-layered materials are characterized by high flexural stiffness and are a viable alternative to conventional sandwich materials in applications where the functional requirements can be met without the second face sheet of the sandwich. For structural applications bi-layered materials are required to have oil canning and buckling resistance. This work addresses the buckling of shallow bi-layered arches using numerical and analytical approaches. A numerical, finite element model is developed to simulate the buckling phenomenon and the results were compared with known experimental data. An analytical model was developed using the energy method analysis and the buckling load was predicted from the minimum energy criterion. Comparison of the numerical and analytical results yielded fairly good agreement. An imperfection analysis conducted by means of the numerical model indicated that the load carrying capacity of bi-layered structures is reduced by up to 40% due to the presence of material and geometric imperfections. A parametric study conducted using the analytical model has been described to setup design guidelines for shallow bi-layered arches. It was found that the use of bi-layered structures can result in weight reduction of around 70% when compared with equivalent single layered structure.

Bi-layered materials are a reduced weight derivative of the sandwich structure and are comprised of one thin skin face reinforced by a thick layer of low density material. Bi-layered materials are characterized by high flexural stiffness and are a viable alternative to conventional sandwich materials in applications where the functional requirements can be met without the second face sheet of the sandwich. For structural applications bi-layered materials are required to have oil canning and buckling resistance. This work addresses the buckling of shallow bi-layered arches using numerical and analytical approaches. A numerical, finite element model is developed to simulate the buckling phenomenon and the results were compared with known experimental data. An analytical model was developed using the energy method analysis and the buckling load was predicted from the minimum energy criterion. Comparison of the numerical and analytical results yielded fairly good agreement. An imperfection analysis conducted by means of the numerical model indicated that the load carrying capacity of bi-layered structures is reduced by up to 40% due to the presence of material and geometric imperfections. A parametric study conducted using the analytical model has been described to setup design guidelines for shallow bi-layered arches. It was found that the use of bi-layered structures can result in weight reduction of around 70% when compared with equivalent single layered structure.

Das hygroskopische Verhalten von Holz wird im Kontext zahlreicher Anwendungen des Materials zumeist negativ interpretiert. Durch einen grundlegenden Perspektivwechsel werden Potenziale und Lösungsansätze sichtbar, die interessante Zukunftsperspektiven für das reaktive Phänomen des Werkstoffes eröffnen. Im Rahmen einer Masterthesis im Studiengang Architektur wurde ein Konzept entwickelt, welches das Quell- und Schwindverhalten zur Realisierung klimasensitiver Verschattungselemente aus Bi-Layer-Holzfurnieren nutzen möchte. Die feuchte- und temperaturbedingten Formänderungen von Holz sind vom Maß der Feuchtezufuhr, vom Schnittbereich des Holzes und von dessen Struktur abhängig. Vor dem Hintergrund des natürlichen Ursprungs des Materials resultiert daraus ein kaum vorhersagbares Verformungsverhalten. Das Projekt folgt der Idee, die Formänderung durch die Kombination von zwei Furnierarten maßgeblich zu beeinflussen. Durch eine schubsteife Verklebung der Furniere eröffnet sich ein weites Feld an Kombinationsmöglichkeiten von Parametern (Furnierdicke, Faserausrichtung, Dimension), um zunächst deutlich weniger streuende Ergebnisse zu erzielen. Um das Krümmungsverhalten der Bi-Layer zu untersuchen, wurde eine Versuchsserie von sechs Kombinationsvarianten mit jeweils zwei Proben pro Variante konzipiert und in einem Klimaschrank mit drei Versuchsarten durchgeführt. Im Ergebnis der Versuche konnte die Eingangsthese plausibilisiert werden. Die gewonnenen Erkenntnisse zeigen erhebliche Potenziale das Materialverhalten kalkulierbar und skalierbar zu machen. Auf der Basis der Messwerte und der per 3D-Scan aufgenommenen Biegeverhalten wurde ein parametrisches Simulationsmodell erzeugt und genutzt, um den Anwendungsansatz als Verschattungspaneele in der Architektur an einer Musterfassade zu veranschaulichen.

Lipid bi-layers are ubiquitous components of biological cells and are found in a variety of cell components. In biological membranes, lipid bi-layer membranes carry membrane proteins, which control transport of material and communication of signals in and out the cell. There are several disadvantages involved with patch clamping method as a way of studying biological membranes and protein interactions. Hence, artificial synthesis of bi-layer has been of great interest in basic biophysical studies, drug discoveries in pharmaceutical studies and study of protein nanopores for precise engineering applications. However, conventional lipid bi-layer synthesis techniques require skilled operators, have low repeatability (reliability), have portability restrictions and result in unstable bi-layers having a short lifetime. In this investigation a novel microfluidic device and a method for artificial synthesis of lipid bi-layer in-situ are explored. In the proposed method, lipid trapped at an aperture on a Teflon sheet, is thinned to form a lipid bi-layer by a continuous flow of buffer solution on both sides of the aperture in the microfluidic device. The microfluidic device is expected to have advantages from its compact design. Further, the new approach is expected to be repetitive and good for automation removing the requirement of a skilled operator. The microfluidic device was fabricated using two glass substrates. Two channels of ? ? shape were etched and through holes were fabricated at all four terminal ends of the microchannels on each glass substrate. A thin Teflon sheet carrying a 100?m diameter hole was sandwiched between the two glass wafers forming two sets of microchannels on both sides of the aperture. An analytical microfluid model of the microchannels was developed to investigate the nature of the flow and to select microchannel parameters. Experiments using the proposed device were performed to verify the feasibility of the novel approach for lipid bi-layer synthesis. Experimental results suggest formation of a lipid bi-layer at an aperture on the Teflon sheet but further investigation might be necessary for verification. Life time of the bi-layer is short mainly due to low quality of the used aperture.

A crescente preocupação com o desenvolvimento sustentável, aliada com uma maior conscientização com relação à preservação do meio ambiente, tem incentivado pesquisas com a finalidade de encontrar substitutos ambientalmente amigáveis para os eficientes sistemas à base de cromo hexavalente (Cr6+), que são empregados como pré-tratamento em ligas de alumínio de alta resistência utilizadas na indústria aeronáutica. Neste trabalho, o desempenho do silano BTSE (Bis-1,2-(trietoxisilil) etano) como método de proteção contra a corrosão da liga de alumínio 2024-T3 foi investigado utilizando técnicas de caracterização eletroquímicas, microestruturais e químicas. Para melhorar as propriedades anticorrosivas do sistema, a camada de silano foi modificada pela introdução de aditivos, tendo sido estudados também sistemas em bi-camada. Efeitos das condições de cura (tempo e temperatura) do BTSE e da quantidade de modificantes sobre as propriedades dos substratos revestidos também foram avaliados. Para os estudos eletroquímicos, realizados em solução de NaCl 0,1 M, foram empregadas a espectroscopia de impedância eletroquímica (EIS) e curvas de polarização potenciodinâmica anódica e catódica. As técnicas de caracterização morfológica e microestrutural foram microscopia de força atômica (AFM), microscopia eletrônica de varredura (SEM) e medidas de ângulo de contato. A caracterização da composição e do estado químico da camada foi realizada usando as espectroscopias por energia dispersiva de Raios-X (EDS), de infravermelho (IR) e de fotoelétrons excitados (XPS). Os resultados dos ensaios de corrosão mostraram que a adição dos modificantes à camada de BTSE melhora o desempenho anticorrosivo do sistema, o qual também teve seu comportamento melhorado quando utilizado em forma de bi-camada. Verificou-se que um excesso de aditivos tende a deteriorar as propriedades protetoras do silano, e que o aumento do tempo e da temperatura de cura é benéfico para as propriedades anticorrosivas dos diferentes sistemas. Os resultados dos ensaios de caracterização química e microestrutural também detectaram que os modificantes contribuem para uma melhor cobertura do substrato pela camada de silano, assim como para uma maior reticulação da mesma, sem, no entanto, modificar sua estrutura química e física. / The increasing concern with sustainable development, allied with a stronger awareness with environmental preservation, has stimulated researches in order to find environmentally friendly substitutes to replace the efficient hexavalent chromium-based pre-treatment systems (Cr6+) used to protect high-strength aluminium alloys employed in the aircraft industry. In this work, the performance of BTSE (bis-1, 2-(triethoxysilyl) ethane) as a protection method against corrosion of aluminium alloy 2024-T3 was investigated using electrochemical, microstructural and chemical characterization techniques. In order to improve the system anticorrosion properties, modifiers were added to the silane layer, and bi-layers systems were also tested. The effects of the silane curing conditions (time and temperature) and of the modifiers amounts on the properties of the layers were also evaluated. Electrochemical impedance spectroscopy (EIS) and anodic and cathodic potentiodynamic polarization curves were employed for the electrochemical studies, which were performed in 0.1 M NaCl solution. For microstructural and morphological characterization, atomic force microscopy (AFM), scanning electron microscopy (SEM) and contact angle measurements were used. The chemical state and the composition of the different layers were evaluated using X-ray photoelectrons (XPS), infrared (IR) and X-ray dispersive energy (EDS) spectroscopy. The results of the corrosion studies have shown that the addition of modifiers to the BTSE layer improves its anticorrosion performance, which was also improved in the bi-layers systems. It was also verified that addition of modifiers excess hinders the performance of the layers, as well as that increasing curing time and temperature are beneficial to the anticorrosion properties of the systems. The results of the different chemical and microstructural analyses showed that the modifiers contribute to better substrate coverage by the silane layer, as well as to a more complete reticulation. However, this does not imply in modifications of the chemical and physical structure of the layer.

abstract: Hydrogel polymers have been the subject of many studies, due to their fascinating ability to alternate between being hydrophilic and hydrophobic, upon the application of appropriate stimuli. In particular, thermo-responsive hydrogels such as N-Isopropylacrylamide (NIPAM), which possess a unique lower critical solution temperature (LCST) of 32°C, have been leveraged for membrane-based processes such as using NIPAM as a draw agent for forward osmosis (FO) desalination. The low LCST temperature of NIPAM ensures that fresh water can be recovered, at a modest energy cost as compared to other thermally based desalination processes which require water recovery at higher temperatures. This work studies by experimentation, key process parameters involved in desalination by FO using NIPAM and a copolymer of NIPAM and Sodium Acrylate (NIPAM-SA). It encompasses synthesis of the hydrogels, development of experiments to effectively characterize synthesized products, and the measuring of FO performance for the individual hydrogels. FO performance was measured using single layers of NIPAM and NIPAM-SA respectively. The values of permeation flux obtained were compared to relevant published literature and it was found to be within reasonable range. Furthermore, a conceptual design for future large-scale implementation of this technology is proposed. It is proposed that perhaps more effort should focus on physical processes that have the ability to increase the low permeation flux of hydrogel driven FO desalination systems, rather than development of novel classes of hydrogels / Dissertation/Thesis / Masters Thesis Mechanical Engineering 2019

A crescente preocupação com o desenvolvimento sustentável, aliada com uma maior conscientização com relação à preservação do meio ambiente, tem incentivado pesquisas com a finalidade de encontrar substitutos ambientalmente amigáveis para os eficientes sistemas à base de cromo hexavalente (Cr6+), que são empregados como pré-tratamento em ligas de alumínio de alta resistência utilizadas na indústria aeronáutica. Neste trabalho, o desempenho do silano BTSE (Bis-1,2-(trietoxisilil) etano) como método de proteção contra a corrosão da liga de alumínio 2024-T3 foi investigado utilizando técnicas de caracterização eletroquímicas, microestruturais e químicas. Para melhorar as propriedades anticorrosivas do sistema, a camada de silano foi modificada pela introdução de aditivos, tendo sido estudados também sistemas em bi-camada. Efeitos das condições de cura (tempo e temperatura) do BTSE e da quantidade de modificantes sobre as propriedades dos substratos revestidos também foram avaliados. Para os estudos eletroquímicos, realizados em solução de NaCl 0,1 M, foram empregadas a espectroscopia de impedância eletroquímica (EIS) e curvas de polarização potenciodinâmica anódica e catódica. As técnicas de caracterização morfológica e microestrutural foram microscopia de força atômica (AFM), microscopia eletrônica de varredura (SEM) e medidas de ângulo de contato. A caracterização da composição e do estado químico da camada foi realizada usando as espectroscopias por energia dispersiva de Raios-X (EDS), de infravermelho (IR) e de fotoelétrons excitados (XPS). Os resultados dos ensaios de corrosão mostraram que a adição dos modificantes à camada de BTSE melhora o desempenho anticorrosivo do sistema, o qual também teve seu comportamento melhorado quando utilizado em forma de bi-camada. Verificou-se que um excesso de aditivos tende a deteriorar as propriedades protetoras do silano, e que o aumento do tempo e da temperatura de cura é benéfico para as propriedades anticorrosivas dos diferentes sistemas. Os resultados dos ensaios de caracterização química e microestrutural também detectaram que os modificantes contribuem para uma melhor cobertura do substrato pela camada de silano, assim como para uma maior reticulação da mesma, sem, no entanto, modificar sua estrutura química e física. / The increasing concern with sustainable development, allied with a stronger awareness with environmental preservation, has stimulated researches in order to find environmentally friendly substitutes to replace the efficient hexavalent chromium-based pre-treatment systems (Cr6+) used to protect high-strength aluminium alloys employed in the aircraft industry. In this work, the performance of BTSE (bis-1, 2-(triethoxysilyl) ethane) as a protection method against corrosion of aluminium alloy 2024-T3 was investigated using electrochemical, microstructural and chemical characterization techniques. In order to improve the system anticorrosion properties, modifiers were added to the silane layer, and bi-layers systems were also tested. The effects of the silane curing conditions (time and temperature) and of the modifiers amounts on the properties of the layers were also evaluated. Electrochemical impedance spectroscopy (EIS) and anodic and cathodic potentiodynamic polarization curves were employed for the electrochemical studies, which were performed in 0.1 M NaCl solution. For microstructural and morphological characterization, atomic force microscopy (AFM), scanning electron microscopy (SEM) and contact angle measurements were used. The chemical state and the composition of the different layers were evaluated using X-ray photoelectrons (XPS), infrared (IR) and X-ray dispersive energy (EDS) spectroscopy. The results of the corrosion studies have shown that the addition of modifiers to the BTSE layer improves its anticorrosion performance, which was also improved in the bi-layers systems. It was also verified that addition of modifiers excess hinders the performance of the layers, as well as that increasing curing time and temperature are beneficial to the anticorrosion properties of the systems. The results of the different chemical and microstructural analyses showed that the modifiers contribute to better substrate coverage by the silane layer, as well as to a more complete reticulation. However, this does not imply in modifications of the chemical and physical structure of the layer.

In the doctoral thesis, the bi-layer ceramic bodies with core-shell geometry were prepared by thermoplastic co-extrusion method and for these composite bodies the mechanical properties were studied. For study of co-extrusion and mechanical properties were designed two composite systems. First system ZTA-A combined the dense core ZTA (zirconia-toughened alumina) and the dense shell Al2O3. Second system ZST-Z consisted of porous core and dense shell made from ZrO2 for both cases. In the thesis, the rheology of ceramic thermoplastic suspensions and their mutual influence during co-extrusion was studied. Subsequently, the debinding process and sintering were studied, and based on the optimization of all process steps were obtained defect-free bodies with core-shell geometry. The mechanical properties (elastic modulus, hardness and bending strength) were determined for sintered bodies. To estimate the stress path in the core shell bodies loaded in bending, the relationship considering different elastic moduli of the core and the shell was used. For bodies of ZTA-A system was increased the strength in comparison with monolithic bodies of the individual components. Thus, bodies with high surface hardness of shell from Al2O3 and moreover having high fracture strength in bending were obtained. The effective elastic modulus was decreased for bodies of ZST-Z system up to 25 % in comparison with the elastic modulus of dense monolithic samples. The same effective modulus of elasticity was possible to achieve with core-shell bodies while maintaining significantly higher fracture strength than monolithic porous bodies or pipes.

No description available.

The motivation of this study is to investigate the size dependent properties of Gadolinium silicide nanoparticles and their potential applications in Biomedicine. We use two approaches in our investigation - size dependence and possible exchange interaction in a core-shell structure. Past results showed Gd5Si4 NPs exhibit significantly reduced echo time compared to superparamagnetic iron oxide nanoparticles (SPION) when measured in a 7 T magnetic resonance imaging (MRI) system. This indicates potential use of Gd5Si4 ferromagnetic nanoparticles as T2 contrast agents for MRI. Until recently most contrast agents (CA) that are used in Magnetic Resonance Imaging (MRI) studies have been paramagnetic. However, ferromagnetic CAs are potentially more sensitive as T2 CAs than T1 paramagnetic compounds due to their large magnetic moments. Furthermore, the need for better MRI images without the need of upgrading to the higher magnetic field strength can be achieved using better CA such as Gd5Si4 NP. The quality of the image contrast in MRI is improved by shortening T1 and T2 relaxation times at the site or close proximity to the CA. In this study, effect of Gd5Si4 NP of varying sizes and with different concentrations are investigated on T1, T2 and T2* (effective/observed T2) relaxations times. Further study was carried out on possible exchange interaction between Fe3O4 and Gd5Si4 to enhance the magnetic properties of the Gd5Si4 which could be later used to synthesize core-shell structures. Exchange interaction / bias is a phenomena associated with the exchange anisotropy created at the interface between the two magnetic materials. Therefore, thin films of varying thickness was deposited and studied for their magnetic properties.