<p>The properties and microstructure of Ti-5Al-5V-5Mo-3Cr were characterized under various stress states after the following heat treatments: 1) annealing above the β transus, followed by cooling at various rates and ageing for different times; 2) solution heat treatment in the α-β range, fan-cooling and ageing for various temperatures and times.</p> <p>Heat treatment above the ptransus temperature causes complete recrystallization of the as-forged microstructure. The as-cooled microstructure consists of equiaxed β grains with an average grain size of 200μm. Water quenching from above the β transus results in precipitation of a dispersion of nano-sized ω phase; while the fan-cooled microstructure contains nano-sized ω and α precipitates. Ageing of the fan-cooled microstructure at 790°C or 600°C precipitates sub micron acicular α throughout the β grains. The tensile properties of this condition could not be determined using standard tensile specimens due to brittle failure at the grips.</p> <p>Controlled cooling from above the β transus to the ageing temperature at slower rates produces a coarser α+β microstructure. Acicular α laths are produced with cooling rates of 1°C/min, while lamellar α develops at cooling rates of 3.4°C/min. The β annealed and fan-cooled condition is characterized by relatively low strength (~850MPa) and low ductility (~6% elong.).The fracture mode is by intensely localized slip and the creation of transgranular cracks. Localization of slip is attributed to shearing of the nano-scale ω precipitates by dislocations. A linear relationship between the grain size, d⁻¹/² , and the yield and fracture stresses was established, as described by the Hall-Petch relation. With controlled cooling, the strength and ductility improve by precipitation of lamellar α within the β matrix. Improvements in ductility and strength are achieved by reducing the slip length.</p> <p>Solution heat treatment below the β transus and fan-cooling results in complete dissolution of the as-forged acicular α phase. Solutionizing at 50°C below the ptransus yields a volume fraction of 16.5% primary α in a matrix of retained β. Low angle grain boundaries and globular primary α, each measuring 2-4μm average in diameter, are uniformly distributed throughout the retained β matrix. The tensile strength in this condition is relatively low, i.e. (900MPa) and the ductility relatively high (~16% elong.). With ageing in the 500°C to 600°C temperature range, precipitation of α within the retained β begins within 5 minutes of the start of ageing. Precipitating is heterogeneously nucleated at dislocations and grain boundaries. The yield and ultimate tensile strengths reach values of roughly 1200 and 1300MPa, respectively, and remain relatively constant for up 48 hours ageing</p> <p> The fracture stresses for the solution treated condition and for material subsequently aged at 500°C and 600°C are quite similar in magnitude. This similarity is due to the fact that the fracture mechanism, which controls the fracture stress, is the same for all these conditions. The fracture mechanism for all the solution treated conditions begins with shear decohesion of the primary α/β interfaces.</p> <p>For each condition, the damage mechanisms and final fracture modes were evaluated and rationalized on the basis of microstructural features. The yield and fracture stresses for the various conditions were calculated and plotted on a two-principal stress axis coordinate system, thus creating the failure envelope for Ti-5553. For the β annealed and fan cooled and for the α-β solution heat treated and aged conditions the yield and fracture envelopes are two concentric ellipses in good agreement with the shear strain energy (van Mises) model for failure.</p> <p>The fracture toughness and stress corrosion cracking behaviour for the STA condition were evaluated and compared against other β titanium alloys.</p> / Thesis / Doctor of Philosophy (PhD)

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Dry High speed and wet milling strategies have both been used to machine hardened die and mold H13 tool steel (HRC 45-58). The TiAlCrSiYN-based family of PVD coatings prepared with various architectures (mono-, multi- and multilayer with an TiAlCrN interlayer) were studied to evaluate the coating micro-mechanical properties that affect tool life during dry high-speed milling of H13 tool steel. A systematic design of varying TiAlCrN interlayer thickness within a multilayer coating structure was developed and its influence on coating properties and cutting performance was investigated. A comprehensive characterization of the coatings was performed using a transmission electron microscope (TEM), focused ion beam (FIB), scanning electron microscope (SEM), X-ray powder diffraction (XRD), room-temperature nanoindentation, a nano-impact, ramped load scratch and a repetitive load wear test. The incorporation of an interlayer into the multilayer coating structure was found to increase the crack propagation resistance (CPRs) to 5.8 compared to 1.9 for the multilayer and 1.6 for the monolayer coatings, which resulted in a 60% tool life increase. The wear test at a load of 1.5 N showed that although the 500nm interlayer exhibited the best coating adhesion, a decline in the H3/E2 ratio was observed to worsen the machining performance. An approximate 40% increase in the tool life was achieved with the 300 nm interlayer by obtaining a balance between mechanical and adhesion properties. To investigate the tool performance during the wet milling of hardened tool steels, the (AlCrN-TiAlN) bi-layer PVD coating was post-treated by WPC (Wide Peening Cleaning) at various pressures and times. Fatigue resistance of the coating following the application of post treatment was observed to improve as the micro-mechanical characteristics (such as H3/E2 ratio, yield stress) were increased. A deterioration in the coating’s adhesion with increasing WPC pressure was also observed as measured by wear test applying a load of 1 N. Through experimentation a balance between fatigue resistance and adhesion was found with tool life being improved by 35% at a WPC applied pressure of 0.2 MPa. / Dissertation / Doctor of Philosophy (PhD) / Over the last 50 years, PVD (physical vapor deposition) coatings have played an increasingly important role in manufacturing where tool cost takes up 3% of the total expenses of the production process. Optimization of these coatings can expedite production wherever machining is conducted under extreme cutting conditions and consequent high material removal rates. These considerations assert significant importance on conducting research on PVD coating development specifically for milling of H13 tool steel, the material widely used in the mold and die industry. This research work seeks to enhance the micro-mechanical and adhesion properties of PVD coatings through architectural design and careful process development while relating desired properties to the high-performance milling of H13 tool steel.

Poly(lactic acid) is biodegradable polymer derived from renewable resources and non-toxic, which has become most interested polymer to substitute petroleum-based polymer. However, it has low glass transition temperature and poor gas barrier properties to restrict the application on hot contents packaging and long-term food packaging. The objectives of this research are: (a) to reduce coagulation of graphene oxide/single-walled carbon nanotube (GOCNT) nanocomposite in poly(lactic acid) matrix and (b) to improve mechanical strength and oxygen barrier property, which extend the application of poly(lactic acid). Graphene oxide has been found to have relatively even dispersion in poly(lactic acid) matrix while its own coagulation has become significant draw back for properties of nanocomposite such as gas barrier, mechanical properties and thermo stability as well as crystallinity. Here, single-walled carbon nanotube was hybrid with graphene oxide to reduce irreversible coagulation by preventing van der Waals of graphene oxide. Mass ratio of graphene oxide and carbon nanotube was determined as 3:1 at presenting greatest performance of preventing coagulation. Four different weight percentage of GOCNT nanocomposite, which are 0.05, 0.2, 0.3 and 0.4 weight percent, were composited with poly(lactic acid) by solution blending method. FESEM morphology determined minor coagulation of GOCNT nanocomopsite for different weight percentage composites. Insignificant crystallinity change was observed in DSC and XRD data. At 0.4 weight percent, it prevented most of UV-B light but was least transparent. GOCNT nanocomposite weight percent was linearly related to ultimate tensile strength of nanocomposite film. The greatest ultimate tensile strength was found at 0.4 weight percent which is 175% stronger than neat poly(lactic acid) film. Oxygen barrier property was improved as GOCNT weight percent increased. 66.57% of oxygen transmission rate was reduced at 0.4 weight percent compared to neat poly(lactic acid). The enhanced oxygen barrier property was ascribed to the outstanding impermeability of hybrid structure GOCNT as well as the strong interfacial adhesion of GOCNT and poly(lactic acid) rather than change of crystallinity. Such a small amount of GOCNT nanocomposite improved mechanical strength and oxygen barrier property while there were no significant change of crystallinity and thermal behavior found. / Master of Science

Yes / Considering the continuous development of sustainable development, energy saving, and emission reduction concepts, it is very important to reduce concrete's cement content in order to improve its environmental impact. Using reactive admixture to replace part of the cement in ultra-high performance concrete (UHPC) can effectively improve the overall performance of the concrete and reduce carbon dioxide emissions (CO2), which is an important aspect of environmental protection. Here, industrial waste residue (fly ash and slag), sea sand (SS), and manufactured sand (MS) were used to produce UHPC under standard curing condition, to reduce the material cost and make the it more environmentally friendly and sustainable. The effects of water-binder ratio, contents of cementitious materials, types of sands, and content of steel fibers on the mechanical performance of UHPC under standard curing were investigated experimentally. In addition, the effects of various factors on the depth under hydraulic pressure and electric flux of UHPC, mass loss, relative dynamic modulus of elasticity, flexural, and compressive strengths of UHPC specimens after freeze-thaw cycles were conducted to evaluate the impermeability, chloride, and freeze-thaw resistance of various UHPCs produced. The obtained experimental results show that the SS-UHPC and MS-UHPC prepared by standard curing exhibit high strength, excellent impermeability, and chloride resistance. The frost resistant grade of all groups of UHPCs prepared by standard curing are greater than F500 and had excellent freeze-thaw resistance, including those produced with local tap water or artificial seawater. The investigation presented in this paper could contribute to the production of new UHPCs of low cost and environmental-friendly and accelerate the application of UHPC in engineering structures.

The dynamic characteristics of hydrogen and ionic bonding contributes to the reversible properties of acrylic polymers, opening new avenues for designing materials with mechanical strength and processability. These non-covalent interactions function as physical crosslinks, which provide enhanced structural and mechanical integrity to acrylic block copolymers. The strong hydrogen bonding or ionic interaction also directs self-assembly to hierarchical microstructures, which enables many applications including thermoplastic elastomers and energy storage devices. Inspired by complementary hydrogen bonding interactions between nucleobase pairs in DNA, a series of bioinspired nucleobase-acrylate monomers such as adenine acrylate (AdA), thymine acrylate (ThA), cytosine acrylate (CyA) were designed, whose synthesis were afforded by aza-Michael addition. Among those nucleobases, cytosine arises as a unique category. It is not only able to self-associate via weak hydrogen bonds, but also forms quadruple hydrogen-bond bearing units (ureido-cytosine) when functionalized with isocyanates. Reversible addition-fragmentation chain transfer polymerization (RAFT) yielded acrylic ABA triblock copolymers with CyA external hard blocks. A subsequent post-functionalization using hexyl-isocyanate generated the corresponding ureido-cytosine acrylate(UCyA)-containing triblock copolymers. The self-complementary quadruple hydrogen bonding in the UCyA polymers achieved a broader service temperature window, while the alkyl chain ends of UCyA units allowed tunability of the mechanical strength to apply as thermoplastic elastomers. In addition, quadruple hydrogen bonding induced stronger propensity of self-assembly and denser packing of the polymers, which contributed to a well-defined ordered morphology and enhanced resistance to moisture uptake. A facile 2-step synthesis provided doubly-charged styrenic DABCO salt monomer(VBDC₁₈BrCl) containing an octadecyl tail. RAFT polymerization allowed the preparation of DABCO ABA block copolymers with defined molecular weights and low polydispersity. Thermal analysis revealed a melting transition of the VBDC₁₈BrCl block copolymer resulting from the side-chain crystallization of the long alkyl tail. Systematic mechanical comparisons between DABCO salt-containing copolymers and the corresponding singly-charged polymer controls demonstrated superior mechanical properties attributable to a stronger ionic interaction between the doubly-charged groups. Morphological characterizations revealed a well-ordered lamellar microstructure and a unique three-phase morphology of the DABCO block copolymers, which involve a soft phase, a hard phase, and an ionic aggregates domain dispersed within the hard domain. / Master of Science

Os ligamentos são estruturas estabilizadoras estáticas das articulações e desempenham um papel importante na junção mecânica. Podem ser influenciadas por fatores de diversas naturezas, inclusive adaptações sofridas durante o período puerperal. Na gravidez existem grandes modificações hormonais que preparam o organismo materno para o desenvolvimento do embrião e feto, bem como para a parturição. Assim, sob ação hormonal os ligamentos e a sínfise púbica têm suas características mecânicas alteradas preparando a mãe para o parto. Este trabalho teve por objetivo caracterizar mecanicamente as modificações sofridas na sínfise púbica e no ligamento cruzado anterior do joelho, durante a gestação e na fase final. Para o estudo foram utilizadas 44 ratas da raça Wistar, com massa corporal inicial média de 301.1 / 8,1g e idade aproximada de 100 dias. Os animais foram divididos em três grupos experimentais: o grupo controle, grupo prenhez I e o grupo prenhez II. Para constituição do grupo prenhez I e II, fêmeas férteis foram acasaladas com machos e o coito foi comprovado pela presença de espermatozóides no lavado vaginal obtido da fêmea. Confirmando a prenhez, os animais foram mantidos em gaiolas até o décimo sexto dia para o grupo prenhez I e sacrificados, para o grupo prenhez II foi esperado até o vigésimo dia de gestação e sacrificados, sendo coletados a pelve e os joelhos de ambos os grupos. Após preparo, a sínfise púbica e o ligamento cruzado anterior do joelho foram ensaiados mecanicamente em tração, com obtenção dos seguintes parâmetros: carga no limite máximo e rigidez. Os resultados comparados com as fêmeas controles não prenhes mostraram que para a sínfise púbica houve aumento da rigidez e diminuição da carga no limite máximo. Para o ligamento cruzado anterior não houve diferença significativa entre os grupos / Ligaments are static stabilizer structures of the joints and play an important role in the mechanical junction. They may be influenced by factors of several natures, including adaptations suffered during the puerperal period. There are in pregnancy big hormonal modifications that prepare the maternal organism for the embryo and fetus development, as well to parturition. Thus, under hormonal actions the ligaments and the pubic sinfisis have their mechanical features shifted preparing the mother for the labor. This paper aimed to point out the shifts occurred by the pubic sinfisis and by the knee anterior cruciate ligament during pregnancy and in the final phase. For the study were used 44 mice Wistar breed, corporal average mass of 301,1 / 8,1g and approximated age of 100 days. They were divided into 3 experimental groups: control group, pregnancy I group and pregnancy II group. For the disposition of the control group, the animals were expected to complete 120 days, then sacrificed and collected the pelvis and the knees. For pregnancy group I and II, fertile females were mated with males and the coitus was proved with the presence of spermatozoids in the vaginal washed obtained from the female. Once confirmed pregnancy, the animals were kept in cages until the 16th day for pregnancy group I and so only collected the animal’s pelvis. For pregnancy group II was expected until the 23rd day of pregnancy and sacrificed, being collected the pelvis and the knees. After preparing, the pubic sinfisis and the anterior cruciate ligament of the knee were mechanically tested in traction, obtaining the following parameters: load in maximum border line and stiffness. The results compared with non pregnant females showed that to the pubic sinfisis there was an increase of stiffness and a load in maximum border line decrease. For the anterior cruciate ligament there was no significant difference between the groups

Made available in DSpace on 2017-07-21T20:42:45Z (GMT). No. of bitstreams: 1 Karine Coelho Correa.pdf: 9563905 bytes, checksum: 8a65961fdf0ee9c5473b25bbc4f19942 (MD5) Previous issue date: 2007-05-31 / The knowledge of the microstructures and final properties of ceramic masses allow to determine the advantages and limitations of its application in specific conditions. This work had for objective to study the microstructural development of a known mass of porcelainized stoneware formulated with raw materials from south Brazil, especially the formation of the phase mulita, and its influence on the mechanical properties. For so many different amounts of kaolin were added (it already leaves constituent of the mass), to obtain a variation of the amount of phase mulita, and each obtained composition was sintering in 4 different times (30, 60, 120, 240 minutes), being compared the mechanical properties and microstructures obtained in each case. It was verified that as larger the burning time, larger the resistance of the stoneware ceramic. With the kaolin addition the resistance increases to certain point, producing inverse effect for larger amounts than 24% in the ceramic mass in the temperatures of sintering from 120 to 240 minutes. The largest resistance value was 67,54 MPa, obtained in the composition with addition of 24% of kaolin and sintered for 240 minutes. It was observed that the porosity and the absorption of the samples decrease significantly with the increase of the kaolin contents and increase of the temperature. The compositions were analyzed by X ray diffractometry, Scanning Electronic Microscopy, rupture module and physical characterization of samples. / O conhecimento das microestruturas e propriedades finais de massas cerâmicas permite determinar as vantagens e limitações de seu emprego em condições específicas. Este trabalho teve por objetivo estudar o desenvolvimento microestrutural de uma massa conhecida de grês porcelanato formulada com matérias-primas da região, em especial a formação da fase mulita, e sua influência nas propriedades mecânicas. Para tanto foram adicionadas diferentes quantidades de caulim (parte já constituinte da massa), para se obter uma variação da quantidade de fase mulita, e cada composição foi sinterizada em 4 tempos diferentes (30, 60, 120, 240 minutos), sendo comparadas as propriedades mecânicas e microestruturais obtidas em cada caso. Verificou-se que quanto maior o tempo de queima, maior a resistência do grês porcelanato. Com a adição de caulim a resistência aumenta até certo ponto, produzindo efeito inverso para quantidades maiores de 24% na massa cerâmica nos tempos de sinterização de 120 e 240 minutos. O maior valor de resistência foi de 67,54 MPa, obtida na composição com adição de 24% de caulim e sinterizado durante 240 minutos. Observou-se que a porosidade e a absorção das amostras diminuem significativamente com o aumento do teor de caulim e aumento da temperatura. As composições foram analisadas por microscopia eletrônica de varredura (MEV), microanálise por energia dispersiva (EDS), análise qualitativa das fases presentes por difração de raio-X, módulo de ruptura por flexão em três pontos e caracterização física das amostras.