Estudou-se a polimerização do álcool furfurílico líquido na interface nonômero-catalisador delimitada pelo interior de um tubo de vidro capilar. A superfície do álcool furfurílico líquido contido em um tubo de vidro de diâmetro interno inferior a 5.4mm foi exposta aos vapores de ácido clorídrico concentrado, o catalisador. Observou-se a formação de uma película auto-organizada e colorida na interface que, sob a ação da gravidade, cai para o interior do tubo com velocidade constante. O espectro de absorção óptica identificou a formação de oligômeros com picos de absorção em 570nm, 650nm, 770nm e 930nm, sendo a de 650nm a mais de peso molecular dos oligômeros difere fortemente daqueles formados por catálise homogênea. A condutância dessas películas foi observada medindo-se a resistência elétrica de películas formadas sobre uma placa invertida de vidro plano / The polymerization of furfuryl alcohol in the interface alcohol-concentrated hydrochloric acid vapor was studied inside glass tubes whose internal diameter were smaller than 5.4mm. Shortly after exposition of furfuryl alcohol to the acid vapor an auto organized bluish pellicle is generated that under gravity falls inside the tube with constant velocity. The observed optical absorption spectrum peaks at 570nm, 650nm, 770nm and 930nm were attributed to oligomers with 3, 5, 7 and 9 mers, respectively. The optical absorption band at 650nm being the stronger. The oligomers molecular weight distribution so formed was found to strongly differ of the ones formed by homogeneous catalysis. The electrical conductivity of these pellicles, made of conjugated oligomers, were observed measuring the electrical resistance of pellicles specially made on the flat inverted glass plate

At the present work the UO2 fuel production process was extensively studied and analyzed. The objectives of such investigation were to understand and analyze the influence of different additives and the variation of the production process steps on the microstructure and consequently in the mechanical strength of the nuclear fuel pellet. Moreover, an improvement of the qualitative characteristics of the ceramic fuel pellets was also aimed. For this purpose UO2 pellets without additives, the so-called standard pellets, pellets containing as additive for example AZB (Azodicarbonamid), black U3O8 (Oxidized uranium pellet scrap - OS), green U3O8 (Oxidized uranium powder - OP), keratin fibers (a non conventional additive) were produced. The introduction of these additives to the UO2 powder mixture prior or after the granulation production step and in different concentrations produced several microstructure configurations. As it would not be possible to analyze all of them here so during the investigation pre-tests some of them were separated to be studied in more detail. Pellets with AZB added after the granulation presented larger grains and larger pores than those with AZB added before granulation, also porosity free grains and a granulate structure instead of a homogeneous one. Pellets with OS present fine porosity distributed all over the pellet matrix with some porosity clusters whereas pellets containing OP show in its matrix porosity agglomerated in form of hooks. As for the grain size, a more uniform grain size distribution can be observed in pellets OS than in pellets with OP. The variations in the amount of keratin fibers added, sintering dwell time and green density resulted indeed in different microstructures. Nevertheless, some common characteristics among them were observed such as the presence of elongated pores, porosity clusters and larger grains located at the pellets borders while the smaller ones were concentrated more in the central part of the pellet. This distribution of grains was identified as bi-modal structure. The mentioned microstructure aspects certainly influence on the mechanical properties of the fuel pellet. However, the sintering parameters, the green and final pellet density and the pellet dimensions also have an influence on the mechanical characteristics of the pellets. For studying the influence of all these parameters on the pellet mechanical properties four testing procedures were utilized the so-called squirrel-cage where the mechanical resistance of the not sintered pellets against mechanical shocks was tested, the diametrical compression test (Brazilian Test) where the strength of sintered and not sintered pellets was studied, the Vickers indentation technique and the creep test where the pellet plasticity respectively at room and at elevated temperatures was analyzed. The squirrel-cage results showed that the pellets with keratin fibers were much more mechanically resistant than those pellets without it, which means that the keratin fibers acted, prior sintering, as a powder binder increasing the cohesion among the powder granules proportionating the green pellets higher mechanical resistance against impacts. The Brazilian test evaluated the influence of the pellet length to the pellet diameter (L/D ratio), the influence of different additives mixed to the UO2 powder and the different pellet production processes. The L/D influence analysis showed that if one fixes the pellet diameter and increase the pellet length the Weibull modulus (here a measure of the pellet lot reliability) will also increase. By comparing pellets with OS, OP and 0.3% keratin fibers it was observed that pellets with OS presented the highest volume of pores smaller than 10 mm while pellets with OP and keratin presented the highest volume of pores larger than 20 mm. It seems that this relevant characteristic favored to the highest Weibull strength value for pellets with OS. In the indentation test standard pellets, pellets with OS and pellets with keratin fibers were tested. The results showed that the calculated hardness for the standard pellets is slightly lower when compared to the values obtained by the pellets with keratin fibers. Also the pellets containing OS when compared to the keratin fibers pellets have in most of the cases a lower hardness. The calculated fracture toughness and fracture surface energy values show also a better mechanical behavior for the keratin fibre pellets than in the standard pellets. Standard pellets, pellets with 30%OP, which had the smallest grain size, pellets with keratin fibers, having the bi-modal structure and pellets with chromium oxide, which had the largest grain size, were tested in the creep furnace. The results showed that all pellets with additives presented a better creep behavior than the standard pellets. Among the pellets prepared with additives the comparison clearly showed that under lower stresses pellets with smaller grains have a better creep rate. By increasing the applied stresses we observe an improvement of the creep rate of the pellets with chromium oxide and keratin fibre even slightly overcoming the pellets with 30%OP at the highest applied stress. / Sacramento Santana, HH. (2014). Improving mechanical properties and microstructure development of fiber reinforced ceramic nuclear fuel [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/37199 / TESIS

Rapid modern technological changes and improvements bring great motivations in advanced material designs and fabrications. In this context, metal matrix composites, as an emerging material category, have undergone great developments over the past 50 years. Their primary applications, such as automotive, aerospace and military industries, require materials with increasingly strict specifications, especially high stiffness, lightweight and superior strength. For these advanced applications, carbon fiber reinforced aluminum matrix composites have proven their enormous potential where outstanding machinability, engineering reliability and economy efficiency are vital priorities. To contribute in the understanding and development of carbon fiber reinforced aluminum matrix composites, this study focuses on composite fabrication, mechanical testing and physical property modelling. The composites are fabricated by squeeze casting. Plain weave carbon fiber (AS4 Hexcel) is used as reinforcement, while aluminum alloy 6061 is used as matrix. The improvement of the squeeze casting fabrication process is focused on reducing leakage while combining thermal expansion pressure with post-processing pressing. Three different fiber volume fractions are investigated to achieve optimum mechanical properties. Piston-on-ring (POR) bend tests are used to measure the biaxial flexural stiffness and fracture strength on disc samples. The stress-strain curves and fracture surfaces reveal the effect of fiber-matrix interface bonding on composite bend behaviour. The composites achieved up to 11.6%, 248.3% and 90.1% increase in flexural modulus, strain hardening modulus and yield strength as compared with the unreinforced aluminum alloy control group, respectively. Analytical modelling and finite element modelling are used to comparatively characterise and verify the composite effective flexural modulus and strength. Specifically, they allowed iii evaluating how far the experimental results deviate from idealized assumptions of the models, which provides an insight into the composite sample quality, particularly at fiber-matrix interfaces. Overall, the models agree well with experimental results in identifying an improvement in flexural modulus up to a carbon fiber volume fraction of 4.81vol%. However, beyond a fiber content of 3.74vol%, there is risk of deterioration of mechanical properties, particularly the strength. This is because higher carbon fiber volume fractions restrict the infiltration and wetting of carbon fibre by the liquid, potentially leading to poor fiber-matrix interface bonding. It is shown that higher thermal expansion pressures and subsequent post-processing pressing can overcome this challenge at higher carbon fiber volume contents by reducing fiber-aluminum contact angle, improving infiltration, reducing defects such as porosity, and overall improving fiber-matrix bonding.

Dans le cadre d'un projet de modélisation multi-échelle des propriétés mécaniques des polymères semi-cristallins, nous avons entrepris au cours de cette thèse une étude à l'échelle moléculaire. Les polymères semi-cristallins se caractérisent par la coexistence de phases cristalline et amorphe et la modélisation à l'échelle moléculaire de ces matériaux est un défi scientifique. En effet, l'observation expérimentale d'une interface entre le cristal et l'amorphe est encore impossible. Il est donc nécessaire de réaliser des hypothèses pour la construction de cette interface. Par ailleurs, les dimensions des molécules étudiées, les temps de relaxation associés à leur dynamique et la différence de structure entre les phases constituent des difficultés supplémentaires pour la représentation aux échelles de taille et de temps de la modélisation moléculaire. Ce travail a été structuré selon deux axes de recherche : la construction d'un modèle moléculaire de polymère semi-cristallin et la validation de différentes méthodes de calcul des constantes élastiques à l'aide de la simulation moléculaire. L'originalité de ce travail a été, d'une part, la réalisation d'une étude comparative des différentes méthodes de calcul utilisées, et d'autre part, la construction d'un modèle prenant explicitement en compte l'interface entre les phases cristalline et amorphe. / As part of a project aiming to predict mechanical properties of semicrystalline polymers using multi-scale models, we did a numerical study at the molecular level during this thesis. Semicrystalline polymers are special in that they contain two phases: one crystalline and one amorphous. This makes their molecular modelling an actual scientific challenge. The interface between the phases is still not directly observable through experiment and in order to build a model of this interface, many assumptions and hypotheses are to be done. Furthermore, the length of the molecules, relaxation times associated with their dynamics and the difference of internal structure between the phases are parameters that have to be taken into consideration because of the typical scales of time and space in molecular simulation. This work is built along two axes: the construction of a molecular model for semicrystalline polymer and a review of the methods that are proposed to compute mechanical properties at the molecular scale. The originality of this work is, on the one hand, the comparative benchmark of the different computation methods, and, on the other hand, the making of a molecular model which takes explicitly in account the interface between amorphous and crystalline phases.

The deterioration of the surfaces of the constructions made with mortar C/A 1: 5 of Portland cement, are produced by being exposed to the emission of toxic gases emanating from the growing automobile fleet, this problem causes alternatives to be sought in order to counteract its effect on buildings and the environment. A new method to deal this problem is the incorporation of the titanium dioxide photocatalyst (TiO2) into the Portland cement mortar, which can develop self-cleaning and air purification properties to be in contact with sunlight. This work seeks to introduce this organic component to the Portland cement mortar, used for the facade charging and structural elements, for this purpose, different percentages (5%, 7.5% and 10%) of titanium dioxide (TiO2) are added and the properties of the modified mortars making use of [1] compression tests, [2] fluidity tests, [3] absorption tests and [4] photocatalytic activity tests with which the self-cleaning capacity was verified. This study concludes that the best percentage of titanium dioxide addition is 5%, with which the Portland cement mortar is granted self-cleaning property without substantially damaging its mechanical properties.

This experiment investigated the effect of infill pattern shape on structural stiffness for 3D printed components made out of carbon fiber reinforced nylon. In order to determine the natural frequency of each specimen, nondestructive vibrational testing was conducted and processed using data acquisition software. After obtaining the acceleration information of each component, in response to ambient vibrational conditions and excitation, frequency response functions were generated. These functions provided the natural frequency of each component, making it possible to calculate their respective stiffness values. The four infill patterns investigated in this experiment were: Zig Zag, Tri-Hex, Triangle, and Concentric. Results of the experiment showed that changing the infill pattern of a 3D printed component, while maintaining a constant geometry and density, could increase mechanical stiffness properties by a factor of two. Comprehensively, the experiment showed that infill pattern geometry directly attributes to the mechanical stiffness of 3D printed components. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

No description available.

Diverse fiber-forming proteins are found in nature that accomplish a wide range of functions including signaling, cell adhesion, and mechanical support. Unique sequence characteristics of these proteins often lead to their specialized roles. However, these proteins also share a common organizational hierarchy in primary and secondary structures that strongly influence both their intramolecular folding and intermolecular interactions. Based on what is known regarding protein fiber assembly of silk peptides, shear-induced elongation of the molecular strands drives interchain secondary structure crystallization via anisotropic alignment, which creates a molecular superstructure that forms the basis a fiber network. In this work, the hypothesis is this type of protein fiber assembly is not unique to silk sequences and that other proteins can be spun into fibers in similar fashion while maintaining unique functionality given by their specialized amino acid sequences such as RGD, GX1X2, and so forth. This was investigated by modeling the manner in which hydrophobic and hydrophilic blocks of amino acids create interacting secondary structures at the chain level when exposed to shear. It was determined computationally and then verified experimentally that fiber spinning success is most likely to occur after shear processing if the protein sequence exhibits a balance of hydrophobic and hydrophilic content and has sufficient length. Applied to the biological scale, both pure and mixed solutions of proteins such as fibronectin, laminin, and silk fibroin were spun into fibers. In particular, alloy protein fibers of silk fibroin mixed with fibronectin exhibited the characteristic mechanical integrity of silk and the bioactivity of fibronectin. This simple method of creating protein fibers with hybrid characteristics is significantly faster, less expensive, and less technically intensive than chimeric protein production, which purports to do the same. This finding also provides insight into a fundamental means by which protein fibers may be assembled in vivo by taking advantage of the thermodynamically favorable assembly of peptide sequences at the chain level under proper molecular orientation. Taken together, a high throughput means of producing a wide-range of pure and hybrid protein fibers has been developed for various biological applications and research investigations into the fibrous elements of biology.

Application of composite materials to structures has presented the need for engineering analysis and modeling to understand the failure mechanisms. Unfortunately, composite materials, especially in a tubular geometry, present a situation where it is difficult to generate simple stress states that allow for the characterization of the ply-level properties. The present work focuses on calculating the mechanical characteristics, both on a global and local level, for composite laminate tubes. Global responses to axisymmetric test conditions (axial tension, torsion, and internal pressure) are measured on sections of the material. New analysis techniques are developed to use the global responses to calculate the ply level properties for tubular composite structures. Error analyses are performed to illustrate the sensitivity of the nonlinear regression methods to error in the experimental data. Ideal test matrices are proposed to provide the best data sets for improved accuracy of the property estimates. With these values, the stress and strain states can be calculated through the thickness of the material, enabling the application of failure criteria, and the calculation of failure envelopes. / Ph. D.

The aim of this thesis is influence of precipitation hardening regime, specifically quench rate, on mechanical properties of aluminium alloy A356 (AlSi7Mg0.3). Samples were after solution treatment quenched into water with different temperatures and age hardened. Tensile strength tests, hardness tests and microstructure observations were done after heat tretment.