Ultra High Performance Concrete (UHPC) is a class of cementitious materials that share similar characteristics including very large compressive strengths, tensile strength greater than conventional concrete and high durability. The material consists of finely graded cementitious particles and aggregates to develop a durable dense matrix. The addition of steel fibers increases ductility such that the material develops usable tensile strength. The durability and strength of UHPC makes it a desirable material for the production of highway bridge girders. However, UHPC's unique constitutive materials make it more expensive than conventional concrete. The cost and lack of appropriate design guidelines has limited its introduction into bridge products. The investigation presented in this thesis developed several optimization formulations to determine a suitable bridge girder shape for use with UHPC. The goal of this optimization was to develop a methodology of using UHPC in highway bridge designs that was cost competitive with conventional concrete solutions. Several surveys and field visits were performed to identify the important aspects of girder fabrication. Optimizations were formulated to develop optimized girder cross sections and full bridge design configurations that utilize UHPC. The results showed that for spans greater than 90 ft UHPC used in the proposed girder shape was more economical than conventional girders. The optimizations and surveys resulted in the development of a proposed method to utilize UHPC in highway bridges utilizing existing girder shapes and formwork. The proposed method consists of three simple calculations to transform an initial conventional design to an initial design using modified UHPC girders. / Master of Science

High dimensional data have been frequently collected in many fields of scientific research and technological development. The traditional idea of best subset selection methods, which use penalized L_0 regularization, is computationally too expensive for many modern statistical applications. A large number of variable selection approaches via various forms of penalized least squares or likelihood have been developed to select significant variables and estimate their effects simultaneously in high dimensional statistical inference. However, in modern applications in areas such as genomics and proteomics, ultra-high dimensional data are often collected, where the dimension of data may grow exponentially with the sample size. In such problems, the regularization methods can become computationally unstable or even infeasible. To deal with the ultra-high dimensionality, Fan and Lv (2008) proposed a variable screening procedure via correlation learning to reduce dimensionality in sparse ultra-high dimensional models. Since then many authors further developed the procedure and applied to various statistical models. However, they all focused on single type of predictors, that is, the predictors are either all continuous or all discrete. In practice, we often collect mixed type of data, which contains both continuous and discrete predictors. For example, in genetic studies, we can collect information on both gene expression profiles and single nucleotide polymorphism (SNP) genotypes. Furthermore, outliers are often present in the observations due to experimental errors and other reasons. And the true trend underlying the data might not follow the parametric models assumed in many existing screening procedures. Hence a robust screening procedure against outliers and model misspecification is desired. In my dissertation, I shall propose a robust feature screening procedure for mixed type of data. To gain insights on screening for individual types of data, I first studied feature screening procedures for single type of data in Chapter 2 based on marginal quantities. For each type of data, new feature screening procedures are proposed and simulation studies are performed to compare their performances with existing procedures. The aim is to identify a best robust screening procedure for each type of data. In Chapter 3, I combine these best screening procedures to form the robust feature screening procedure for mixed type of data. Its performance will be assessed by simulation studies. I shall further illustrate the proposed procedure by the analysis of a real example. / Ph. D.

This thesis presents results of an experimental investigation to characterize single straight steel fiber pullout in Ultra-High Performance Concrete (UHPC). Several parameters were explored including the distance of fibers to the edge of specimen, distance between fibers, and fiber volume in the matrix. The pullout load versus slip curve was recorded, from which the pullout work and maximum pullout load for each series of parameters were obtained. The curves were fitted to an existing fiber pullout model considering bond-fracture energy, Gd, bond frictional stress, 𝛕0, and slip hardening-softening coefficient, 𝜷. The representative load-slip curve characterizing the fiber pullout behavior will be implemented into a computational modeling protocol, for concrete structures, based on Lattice Discrete Particle Modeling (LDPM). The parametric study showed that distances over 12.7 mm from the edge of the specimen have no significant effect on the maximum pullout load and work. Edge distances of 3.2 mm decreased the average pullout work by 26% and the maximum pullout load by 24% for mixes with 0% fiber volume. The distance between fibers did not have a significant effect on the pullout behavior within this study. Slight differences in pullout behavior between the 2% and 4% fiber volumes were observed including slight increase in the maximum pullout load when increasing fiber volume. The suggested fitted parameters for modeling with 2% and 4% fiber volumes are a bond-fracture energy value of zero, a bond friction coefficient of 2.6 N/mm² and 2.9 N/mm² and a slip-hardening coefficient of 0.21 and 0.18 respectively. / Master of Science

Secondary hardening ultra-high strength (SHUHS) steels possess a unique combination of strength, fracture toughness and stress corrosion cracking resistance, which makes them candidate materials for aircraft landing gear and armour applications. There is a sustained drive to develop stronger and tougher materials for such applications. The objectives of this thesis are two-fold: first, to develop a new SHUHS alloy that is stronger than the existing SHUHS steel developed at Defence Metallurgical Research Laboratory (DMRL), Hyderabad and second, to establish processing-structure-property correlations for the new alloy. Empirical design and development of these complex steels involves enormous effort, cost, time and materials resources. To avoid this, a semi-empirical approach was espoused in this thesis wherein thermodynamic calculations using ThermoCalc were conducted to computationally design a series of alloys with varying levels of Cr and Mo. The design space was constrained by two objectives related to M2C carbides which are the primary cause of secondary hardening in these alloys. The first objective was to increase the amount of M2C to increase the peak strength, while the second objective was to lower the Cr/Mo ratio of the M2C to control its over-ageing behavior. Two new alloys C23 (with 2Cr-3Mo, wt. %) and C55 (with 5Cr-5Mo, wt. %) and a base alloy akin to the DMRL SHUHS steel, C21 were selected for experimental validation. These alloys were melted, rolled and subjected to a battery of heat treatments. Austenitization studies revealed that the new alloys required higher austenitization temperatures to dissolve primary carbides. However such a treatment also resulted in an austenite composition that was not conducive for obtaining a fully martensitic microstructure on quenching. Based on these studies, the design space was modified to include additional criteria related to the Ms and precipitate dissolution temperatures. C55 failed to clear either criteria, while C23 cleared both, and so tempering studies were limited to C23. Isochronal tempering studies revealed that C23 in the peak aged condition was >10% stronger than C21 indicating that the alloy design objective of strength enhancement was achieved successfully. Microstructural characterization revealed that the strength enhancement was due to the higher number density and volume fraction of the M2C-like solute clusters in C23, which resist shearing in the under-aged condition and strengthen by Orowan mechanism in the over-aged condition. This thesis has successfully demonstrated that the design paradigm of enhancing strength by increasing the amount of M2C is justified and that ThermoCalc can be used to as an objective-oriented alloy design tool in this class of the steels.

Orientador: José de Assis Fonseca Faria / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos / Made available in DSpace on 2018-08-18T02:06:39Z (GMT). No. of bitstreams: 1 Cardoso_ClaudioFernandes_D.pdf: 26277698 bytes, checksum: d17c520e85b9389e672d2641e795333d (MD5) Previous issue date: 2011 / Resumo: Esta pesquisa teve como objetivo avaliar o desempenho de um sistema asséptico piloto para a produção de leite UHT (Ultra Hight-Temperature), com capacidade de 1.000 L/h, em embalagens flexíveis institucionais do tipo Bag-in-box (BIB). As embalagens estudadas eram compostas de um filme de polietileno de baixa densidade (PEBD) e um filme de polietileno tereftalato metalizado (PETmet), com volume de 2.000 mL, desenvolvido especialmente para o envase asséptico de produtos lácteos. Leite cru refrigerado tipo A foi utilizado como matéria-prima. O envase do leite UHT foi realizado através de uma dosadeira semi-automática dentro de uma Sala Limpa ISO posicionada sobre o bocal de enchimento das embalagens. O sistema foi avaliado através da identificação e monitoramento de pontos de controle do processo, testes de esterilidade comercial, análises sensorial e físico-química do produto, bem como avaliações da embalagem. O desempenho das embalagens BIB foi avaliado através de ensaios de caracterização, integridade do sistema e estudos de estabilidade microbiana e testes de efetividade de esterilização. As embalagens foram esterilizadas com o uso de radiação ionizante (gama), com dose de 15 kGy. Os ensaios foram conduzidos através da produção de 4 lotes experimentais de leite UHT, obtido em trocador de calor a placas (140 °C por 5 s). A taxa de defeito encontrada nos testes de esterilidade comercial variou entre 0 e 6,7%, sendo que a principal causa de defeitos foi associada aos problemas inerentes a operacionalidade da linha, como falhas nas vedações das junções de tubulações e bombas centrífugas. Os resultados da avaliação dos pontos de controle do processo e embalagem indicaram um bom desempenho do sistema, justificado pela ausência de microorganismos viáveis. O leite UHT acondicionado nas embalagens BIB teve sua vida de prateleira estimada em até 27 semanas de estocagem, valor este muito superior quando comparado às amostras controle de leite UHT comercial, acondicionado em embalagens laminadas cartonadas, que teve sua vida de prateleira estimada em 19 semanas. A diferença de estabilidade físico-química, microbiológica e sensorial entre as amostras processadas e a comercial foi associada às propriedades de barreira das estruturas das embalagens à luz e ao oxigênio, bem como pela qualidade da matéria-prima utilizada. O sistema asséptico piloto avaliado correspondeu às expectativas de desempenho e atendeu aos requisitos estabelecidos pelo Codex Alimentarius. Concluiu-se que o sistema apresenta potencial para utilização por indústrias de laticínios visando atender o mercado institucional de leite longa vida / Abstract: The aim of this research was to evaluate the performance of an aseptic pilot system for the production of Ultra High Temperature (UHT) milk, with 1.000 L/h capacity, filled in flexible institutional packages Bag-in-box (BIB) type. The BIB packages were constructed with one layer of low density polyethylene film (LDPE) and another one of metalized polyethylene terephthalate film (PETmet), with 2.000 mL capacity, specially developed for the aseptic filling of dairy products. Type-A milk was used as raw material and the UHT milk filling was made by a semiautomatic machine located inside a ISO Clean room. The system was evaluated by the identification and monitoring of the control points during the process and also by commercial sterility tests, sensorial and physical-chemistry analysis and packages evaluations. The BIB packages were sterilized by gamma radiation with minimum doses of 15 kGy. The assays were conducted by the production of 4 experimental batches processed in a plate heat exchanger (140 °C/5 s). The defect rates founded were between 0 and 6.7% and these values can be explained by problems linked to the pilot plant operation, like failures in the connections of pipes and centrifugal pumps. The results of the control points evaluation and also BIB packages showed a good performance of the entire process, justified by the absence of viable microorganisms. The milk filled in BIB packages targeted until 27 weeks of shelf life, a superior value when it was compared to the commercial UHT samples, which targeted just 19 weeks. The difference of physical-chemistry, microbiology and sensory stability between the processed samples and the commercial one was associated to the oxygen and light barriers properties and also to the raw milk quality used during the processes. The pilot aseptic system evaluated attended to the Codex Alimentarius requirements and it could be concluded that the system showed potential for application in dairy industry in view of the long life milk institutional market / Doutorado / Tecnologia de Alimentos / Doutor em Tecnologia de Alimentos

Atlas Copco Secoroc AB are searching after new bulk materials for drill heads that are used in percussive drilling in order to improve their strength and durability. The aim of this project is to assist Atlas Copco in this search and provide them with further information regarding material properties, alloying elements, suppliers, etc. A literary study was carried out in order to identify materials that had UTS and KIC more than or equal to 1700 MPa and 70 MPa*m^1/2, respectively. Materials that fulfilled these criteria were T250 grade maraging steel, Cobalt free maraging steel, High cobalt maraging steel, 300 grade maraging steel, AerMet 100, AF1410, S53, M54, 300M, 4340M and PremoMet. These were categorized into maraging steels, high alloy secondary hardened steels, and low alloy steels, and were then further researched. The material with the highest combination of UTS and KIC was M54 followed by AerMet 100; while AF1410 had the highest KIC but a low UTS, and PremoMet had the highest UTS but a low KIC. Maraging steels and HASH steels have a similar price range, while low alloy steels are much cheaper.

GaAsBi is a relatively unexplored alloy with interesting features such as a large bandgap reduction for a given lattice mismatch with GaAs substrates and good photoluminescence which make it promising for long wavelength light detection and emission applications. In this research, the molecular beam epitaxy (MBE) method was used to grow epi-layers and hetero-structures. A Vertical-external-cavity surface-emitting-laser (VECSEL) was grown as a part of collaboration with Tampere University in Finland. The process of laser growth promoted the writer’s skills in the growth of hetero-structures and led into an investigation of the effect of growth conditions on GaAsBi optical properties with important results. For instance, when the substrate temperature during growth was reduced from 400°C to 300°C and all other growth conditions were fixed, the Bi concentration in the deposited films increased from 1% to 5% and the photoluminescence (PL) intensity decreased by more than a factor of 1000. This is an indication of the importance of growth temperature in GaAsBi crystal quality. n+/p junctions were grown for the deep level transient spectroscopy (DLTS) experiments in collaboration with Simon Fraser University. The DLTS measurements showed that lowering the GaAsBi growth temperature increases the deep level density by a factor of 10. These deep levels are the source of non-radiative recombination and decrease the PL intensity. The structural properties of GaAsBi were investigated by high resolution x-ray diffraction and polarized PL and revealed long distance atomic arrangement (Cu-Pt ordering) in GaAsBi. The measurements showed that the ordering is more probable at high growth temperature. This can be due to the larger mobility of the atoms on the surface at high growth temperatures that allows them to find the ordered low energy sites. / Graduate

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ASTRACT: The very high strength, enhanced ductility and long-term durability of ultra-high performance concrete (UHPC) makes it an ideal material to be used for building structures in the future. The non-heat treated UHPC requires less quality control than heat treated UHPC, which makes it more relevant to be applied in South Africa. This research focuses on developing non-heat treated UHPC with locally available materials, with the exception of short, straight, high strength steel fibre. While UHPC mix design guidelines have been proposed, ingredient materials available locally, but which do not necessarily comply with recommended property ranges, may be compensated for by particular strategies. The local ingredient materials are compared based on their mineralogy, specific surface area, particle size and grading by researchers who successful developed non-heat treat UHPC. The majority of local materials were found not that ideal for UHPC. Under such circumstances, following the general UHPC mix design, it is difficult to reach the same designated strength as those achieved by the other researchers. One of the problems for non-heat treated UHPC is its large shrinkage caused by very low water to cement ratio. A new mix design philosophy is developed for UHPC by making use of steel fibre to improve its compressive strength. Instead of avoiding the large shrinkage, this method uses shrinkage to improve the bond between steel fibre and matrix through the mechanism of shrinkage induced clamping pressure. Subsequently, the mechanism of bridging effect of steel fibre is used to confine shrinkage evolvement in UHPC. Through such a mix design philosophy, the steel fibres are pre-stressed inside UHPC so that it both improves the compressive strength and ductility. A UHPC strength of 168 MPa is achieve in this research. After the UHPC has successfully been developed, factors that can affect UHPC strength are tested. It is found that the environmental temperature of UHPC, cement composition and specimen cover during the moulded period significantly influence UHPC strength by approximately 24%. It is also found that after two days of de-moulding, the UHPC exposed to the air, achieved similar strength as that cured in water, which is helpful for future industrial application.

Next generation aerospace vehicles require thermal protection system (TPS) materials that are capable of withstanding the extreme aerothermal environment during hypersonic flight (>Mach 5 [>1700 m/s]). Ultra-high temperature ceramics (UHTC) such as zirconium diboride (ZrB₂) are candidate TPS materials due to their high-temperature thermal and mechanical properties and are often the basis for advanced composites for enhanced oxidation resistance. However, ZrB₂ matrix impurities in the form of boron trioxide (B₂O₃) and zirconium dioxide (ZrO₂) limit the high-temperature capabilities. Electric based sintering techniques, such as spark plasma sintering (SPS), that use joule heating have become the preferred densification method to process advanced ceramics due to its ability to produce high density parts with reduced densification times and limit grain growth. This study focuses on a combined experimental and thermodynamic assisted processing approach to enhance powder purity through a carbo- and borocarbo-thermal reduction of oxides using carbon (C) and boron carbide (B₄C). The amount of oxides on the powder surface are measured, the amount of additive required to remove oxides is calculated, and processing conditions (temperature, pressure, environment) are controlled to promote favorable thermodynamic reactions both during thermal processing in a tube furnace and SPS. Untreated ZrB₂ contains 0.18 wt%O after SPS. Additions of 0.75 wt%C is found to reduce powder surface oxides to 0.12 wt%O. A preliminary Zr-C-O computational thermodynamic model shows limited efficiency of carbon additions to completely remove oxygen due to the solubility of oxygen in zirconium carbide (ZrC) forming a zirconium oxycarbide (ZrCₓOᵧ). Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) with atomic scale elemental spectroscopy shows reduced oxygen content with amorphous Zr-B oxides and discreet ZrO₂ particle impurities in the microstructure. Processing ZrB₂ with minimal additions of B₄C (0.25 wt%) produces high purity parts after SPS with only 0.06 wt%O. STEM identifies unique “trash collector” oxides composed of manufacturer powder impurities of calcium, silver, and yttrium. A preliminary Zr-B-C-O thermodynamic model is used to show the potential reaction paths using B₄C that promotes oxide removal to produce high-purity ZrB₂ with fine grains (3.3 𝜇m) and superior mechanical properties (flexural strength of 660MPa) than the current state-of-the-art ZrB₂ ceramics. Due to the desirable properties produced using SPS, there is growing interest to advance processing techniques from lab-scale (20 mm discs) to large-scale (>100 mm). The advancement of SPS technologies has been stunted due to the limited power and load delivery of lab-scale furnaces. We use a large scale direct current sintering furnace (DCS) to address the challenges of producing industrially relevant sized parts. However, current-assisted sintering techniques, like SPS and DCS, are highly dependent on tooling resistances and the electrical conductivity of the sample, which influences the part uniformity through localized heating spots that are strongly dependent on the current flow path. We develop a coupled thermal-electrical finite element analysis model to investigate the development and effects of tooling and current density manipulation on an electrical conductor (ZrB₂) and an electrical insulator, silicon nitride (Si₃N₄), at the steady-state where material properties, temperature gradients and current/voltage input are constant. The model is built based on experimentally measured temperature gradients in the tooling for 20 mm discs and validated by producing 30 mm discs with similar temperature gradients and grain size uniformity across the part. The model aids in developing tooling to manipulate localize current density in specific regions to produce uniform 100 mm discs of ZrB₂ and Si₃N₄.

The hydrogenation of β-ketoesters over chirally modified Ni catalysts is a celebrated and thoroughly researched example of an enantioselective heterogeneous catalytic reaction. Enantioselective heterogeneous processes, although extremely attractive in terms of fewer complications in the separation of products from the catalyst, are hindered in their viability as industrial applications due to the lack of detailed knowledge on how chirality is conferred to the metal surface. Surface science techniques have afforded substantial progress into determining mechanisms between modifier, reactant and catalyst to explain the source of enantioselectivity of the system. In this study, a combination of solution and ultra-high vacuum (UHV)-based experiments allow a more realistic interpretation of the surface chemistry underpinning the catalytic reaction as the key step in achieving enantioselective performance is the adsorption of chiral modifiers from solution. The behaviour of (S)-aspartic acid and (S)-lysine on Ni{111} and their interaction with the prochiral β-ketoester methylacetoacetate is investigated in this study to understand their potential as chiral modifiers for the system. In UHV, scanning tunnelling microscopy (STM), reflection absorption infrared spectroscopy (RAIRS), and temperature programmed desorption (TPD) are used to analyse the conformation and order of the amino acids on the metal, and their thermal stability. Additionally, liquid-solid interface RAIRS and X-ray photoelectron spectroscopy (XPS) are used to examine the modified Ni surface, prepared under aqueous conditions, to give an accurate representation of the catalytic studies. It has been found highly likely that, for (S)-aspartic acid modified Ni{111}, enantioselective sites exist at step or step/kink defects, formed by corrosive leaching of the Ni substrate. Conversely, lysine appears to bind with a high sticking probability to Ni, in the form of lysine islands, and does not appear to etch the Ni chirally. Finally, similar experiments have been carried out on Au{111}, where lysine was found to chiral restructure the surface and form nanofingers, and 2D Ni clusters grown on Au{111} in order to investigate the formation of possible metal-organic frameworks.