The high temperature BCC phase (b) of titanium undergoes a martensitic transformation to HCP phase (a) upon cooling, but can be stabilized at room temperature by alloying with BCC transition metals such as Mo. There exists a metastable composition range within which the alloyed b phase separates into a + b upon equilibrium cooling but not when rapidly quenched. Compositional partitioning of the stabilizing element in as-quenched b microstructure creates nanoscale precipitates of a new simple hexagonal w phase, which considerably reduces ductility. These phase transformation reactions have been extensively studied experimentally, yet several significant questions remain: (i) The mechanism by which the alloying element stabilizes the b phase, thwarts its transformation to w, and how these processes vary as a function of the concentration of the stabilizing element is unclear. (ii) What is the atomistic mechanism responsible for the non-Arrhenius, anomalous diffusion widely observed in experiments, and how does it extend to low temperatures? How does the concentration of the stabilizing elements alter this behavior? There are many other w forming alloys that such exhibit anomalous diffusion behavior. (iii) A lack of clarity remains on whether w can transform to a -phase in the crystal bulk or if it occurs only at high-energy regions such as grain boundaries. Furthermore, what is the nature of the a phase embryo? (iv) Although previous computational results discovered a new wa transformation mechanism in pure Ti with activation energy lower than the classical Silcock pathway, it is at odds with the a / b / w orientation relationship seen in experiments. First principles calculations based on density functional theory provide an accurate approach to study such nanoscale behavior with full atomistic resolution, allowing investigation of the complex structural and chemical effects inherent in the alloyed state. In the present work, a model Ti-Mo system is investigated to resolve these fundamental questions. Particular attention is paid to how Mo- (i) influences the bonding in Ti, (ii) distorts the local structure in the Ti lattice, (iii) impacts the point and interfacial defect formation and migration energies, and (iv) affects the mechanism and energetics of b w and wa transformations. Our results are correlated with appropriate experimental results of our collaborators and those in open literature. The modification of Ti bonding by Mo solutes and the attendant distortion of the lattice hold the key to answering the diverse questions listed above. The solutes enhance electron charge density in the <111> directions and, consequently, stiffen the lattice against the displacements necessary for b w transformation. However, Ti atoms uncoordinated by Mo remain relatively mobile, and locally displace towards w lattice positions. This effect was further studied in a metastable Ti-8.3 at.% Mo system with an alternate cell geometry which allows for either b w or $\betaa transformation, and it was found that after minimization Ti atoms possessed either a or w coordination environments. The creation of this microstructure is attributed to both the disruption of uniform b w transformation by the Mo atoms and the overlap of Ti-Mo bond contractions facilitating atomic displacements to the relatively stable a or w structures in Mo-free regions. The vacancy migration behavior in such a microstructure was then explored. Additionally, several minimized configurations were created with planar interfaces between Mo-stabilized b region and its adjacent a- or w- phases, and it was found that the positioning of Mo at the interface strongly dictates the structure of the adjacent Mo depleted region.

Ground granulated blast furnace slag is a by-product of the steel industry and is often used in combination with ordinary Portland cement as a binder in concrete. When concrete is exposed to high temperatures, physical and chemical transformations lead to significant loss of mechanical properties. This study aims to investigate the effect of high temperatures and rehydration on the mechanical properties, microstructure and phase composition of alkali activated slag. The results of the research could make an important contribution to decisions made concerning the reconstruction of structures affected by fire. In suitable cases it would be possible to regenerate parts of a structure instead of totally rebuilding it.

No description available.

Titanium alloys are employed in many advanced engineering applications due to their exceptional properties, i.e., a high strength-to-weight ratio, corrosion resistance, and high temperature strength. The performance of titanium alloys is known to be strongly affected by its inherent microstructure, which forms as a result of its thermo-mechanical processing. These microstructures produce compromise relationships between beneficial and detrimental effects on the alloy's performance. To study these structure-property relationships, two distinct crystal plasticity algorithms have been calibrated to data acquired from cyclic deformation experiments performed on three different Ti microstructures: (1) Ti-6Al-4V beta-annealed , (2) Ti-18 solution-treated, age-hardened (STA), and (3) Ti-18 beta-annealed, slow-cooled, age-hardened (BASCA). The calibrated models have been utilized to simulate fatigue loading of variant microstructures to investigate the influence of mean grain size, crystallographic texture, and phase volume fraction. The driving force for fatigue crack nucleation and propagation is quantified through the calculation of relevant fatigue indicator parameters (FIPs) and radial correlation functions are employed to study the correlation between favorably oriented slip systems and the extreme value FIP locations. The computed results are utilized to observe fatigue performance trends associated with changes to key microstructural attributes.

A alvenaria estrutural é um sistema construtivo muito antigo no qual as paredes exercem função estrutural além da função de vedação. Este sistema construtivo é muito utilizado no Brasil, entretanto, poucas pesquisas foram realizadas sobre o seu comportamento em situação de incêndio e o país ainda não possui métodos normativos de dimensionamento de alvenaria estrutural em situação de incêndio. Assim, o objetivo deste trabalho foi verificar o desempenho da alvenaria estrutural com blocos de concreto submetida a elevadas temperaturas através da simulação de prismas. No software Abaqus foram simulados o comportamento do bloco e prisma sujeitos à compressão em temperatura ambiente e do prisma em situação de incêndio com diferentes condições de contorno. O comportamento do bloco e prisma sujeitos à compressão e em temperatura ambiente foi validado até a carga última. As elevações de temperatura das faces não expostas ao fogo ficaram bem representadas por meio das simulações térmicas. A perda de resistência dos materiais foi adotada conforme a literatura técnica nas simulações termomecânicas. Através do que foi analisado no trabalho observou-se que os prismas se comportam bem quanto ao isolamento térmico em situação de incêndio, principalmente aquele com revestimento em argamassa nas duas faces. Quanto ao critério de resistência mecânica os resultados numéricos não foram validados com experimentais, entretanto, foi possível representar a deterioração térmica dos materiais. / The structural masonry is a very old building system in which the walls have structural and partition function. The use of this building system is widely spread in Brazil, however, few research programs were carried out on their behavior under fire situation and the country has not yet developed standard normative methods for designing structural masonry subject to fire. Thus the purpose of this research was to verify the performance of concrete blockwork structural masonry submitted to high temperatures through the simulation of prisms. In the Abaqus software the behavior of block and prism subjected to compression at room temperature and of the prism under fire situation with different boundary conditions were simulated. The compression of the block and prism at room temperature was validated until ultimate loads. The temperature rises of the non-exposed faces were well represented through thermal simulations. The material\'s resistance loss was adopted according to the technical literature in the thermomechanical simulations. Based on the analyzed examples it was observed that the prisms behave well regarding the thermal insulation under fire situation, mainly when having mortar coating on both sides. Regarding the mechanical resistance criterion, the numeric results were not validated with experimental ones, however, it was possible to represent the thermal deterioration of the materials.

A alvenaria estrutural é um sistema construtivo muito antigo no qual as paredes exercem função estrutural além da função de vedação. Este sistema construtivo é muito utilizado no Brasil, entretanto, poucas pesquisas foram realizadas sobre o seu comportamento em situação de incêndio e o país ainda não possui métodos normativos de dimensionamento de alvenaria estrutural em situação de incêndio. Assim, o objetivo deste trabalho foi verificar o desempenho da alvenaria estrutural com blocos de concreto submetida a elevadas temperaturas através da simulação de prismas. No software Abaqus foram simulados o comportamento do bloco e prisma sujeitos à compressão em temperatura ambiente e do prisma em situação de incêndio com diferentes condições de contorno. O comportamento do bloco e prisma sujeitos à compressão e em temperatura ambiente foi validado até a carga última. As elevações de temperatura das faces não expostas ao fogo ficaram bem representadas por meio das simulações térmicas. A perda de resistência dos materiais foi adotada conforme a literatura técnica nas simulações termomecânicas. Através do que foi analisado no trabalho observou-se que os prismas se comportam bem quanto ao isolamento térmico em situação de incêndio, principalmente aquele com revestimento em argamassa nas duas faces. Quanto ao critério de resistência mecânica os resultados numéricos não foram validados com experimentais, entretanto, foi possível representar a deterioração térmica dos materiais. / The structural masonry is a very old building system in which the walls have structural and partition function. The use of this building system is widely spread in Brazil, however, few research programs were carried out on their behavior under fire situation and the country has not yet developed standard normative methods for designing structural masonry subject to fire. Thus the purpose of this research was to verify the performance of concrete blockwork structural masonry submitted to high temperatures through the simulation of prisms. In the Abaqus software the behavior of block and prism subjected to compression at room temperature and of the prism under fire situation with different boundary conditions were simulated. The compression of the block and prism at room temperature was validated until ultimate loads. The temperature rises of the non-exposed faces were well represented through thermal simulations. The material\'s resistance loss was adopted according to the technical literature in the thermomechanical simulations. Based on the analyzed examples it was observed that the prisms behave well regarding the thermal insulation under fire situation, mainly when having mortar coating on both sides. Regarding the mechanical resistance criterion, the numeric results were not validated with experimental ones, however, it was possible to represent the thermal deterioration of the materials.

O concreto leve de alto desempenho (CLAD), com argila expandida nacional, é um material alternativo para as concentrações brasileiras, considerando as características climáticas do país e baixo custo do material. Mas atualmente, existe pouca informação disponível sobre a produção e aplicação deste concreto com agregados leves, adições e aditivos nacionais. O objetivo desta dissertação é analisar o comportamento estrutural, por intermédio de ensaios mecânicos (resistência à compressão, resistência à tração por compressão diametral e módulo de deformação) do CLAD, sob ação de altas temperaturas. Para tanto, realiza-se uma análise comparativa da resistência mecânica do concreto em estudo, constituído por agregados leves de argila expandida, com o concreto convencional CAD (concreto de alto desempenho), composto por agregados de brita basáltica, determinando-se assim as respectivas resistências mecânicas, após terem sido expostos a temperaturas externas de até 800 graus centígrados. Através da análise dos resultados obtidos experimentalmente, pode-se comprovar a viabilidade do CLAD, produzido com argila expandida, comparativamente ao CAD, sob à ação de altas temperaturas. / The high performance lightweight aggregate concrete (HPLC), with national expanded clay, is an alternative material for the Brazilian constructions, considering the climatic characteristics of the country and low cost of the material. But now, little available information exists about the production and application of this concrete with lightweight aggregate, additions and addictive national. The aim of this dissertation is to analyze the structural behavior, by mechanical tests (compressive strength, splitting tensile strength and deformation modulus) of HPLC, under action of high temperatures. For so much, it takes place a comparative analysis of the mechanical resistance of the concrete in study, constituted by lightweight aggregate of expanded clay, with the conventional concrete HPC (high performance concrete), composed by crushed basalt coarse aggregate, determining the respective mechanical strength, after they have been exposed to external temperatures of up to 800°C. Through the analysis of the results obtained experimentally, it can be proven the viability of HPLC, produced with expanded clay, comparatively to HPC, under to the action of high temperatures.

Le comportement rhéologique de suspensions magmatiques synthétiques hydratées a été expérimentalement étudié en déformation coaxiale et en torsion à haute température et haute pression à l’aide d’une presse de type Paterson. Les résultats obtenus illustrent l’influence de la fraction cristalline et de la forme des cristaux sur la rhéologie et le développement des Orientations Préférentielles de Forme (OPF) des particules au sein des suspensions magmatiques. La formation d’une charpente cristalline, associée à une forte hausse de la viscosité, intervient pour des fractions solides comprises entre fs = 0,20 et 0,38 en relation avec le développement de fabriques de type pénétratif. En augmentant la fraction solide (fs = 0,50), le développement d’une fabrique pénétrative, couplé à des bandes de cisaillement bordées de gradients de déformation, engendre un adoucissement de la réponse rhéologique et une hausse moins importante de la viscosité. Pour fs = 0,58, des bandes de cisaillement de type cassant sans gradient de déformation, recoupant une suspension non déformée, apparaissent et contrôlent le fort adoucissement de la réponse rhéologique. La viscosité de la suspension n’augmente plus alors que légèrement. Au-delà de cette fraction cristalline, les suspensions étudiées montrent une forte réduction de la taille et du rapport de forme des cristaux se traduisant par une stabilisation de la réponse rhéologique en fonction de la déformation. Aucune OPF n’a pu être déterminée et une quasistabilisation de la viscosité est observée (comportement mécanique de solide). Toutes les suspensions étudiées se caractérisent par un comportement rhéologique non-Newtonien de type rhéofluidifiant. La dépendance entre le comportement rhéologique des suspensions magmatiques et le développement des microstructures doit être intégrée dans la modélisation de la mécanique des suspensions magmatiques. / The rheological behaviour of synthetic hydrous magmatic suspensions has been experimentally investigated in compression and torsion at high temperatures and pressures in a Paterson press. The results illustrate the influence of the crystal fraction and of the shape of the crystals on the rheology and the Shape Preferred Orientation (SPO) of the particles. A solid particle network, associated with a strong increase of the viscosity, is generated between crystal fractions (fs) of 0.20 and 0.38, with the development of pervasive fabrics. With increasing the crystal fraction (fs = 0.50), shear bands bordered by symmetrical deformation gradients crosscut the pervasive fabric, resulting in a weakening in the rheological behaviour of the suspension. The increase of the viscosity with increasing cristallinity of the suspension becomes less important. At fs = 0.58, brittle shear bands without deformation gradients crosscut an undeformed suspension and lead to a strong weakening of the rheological behaviour which explains the small increase of the viscosity of the suspension with increasing crystal fraction. Above this crystal fraction, suspensions show a strong reduction of the crystal size and shape ratio. No SPO has been determined but the near-stabilisation of the viscosity, coupled with a stabilisation of the stress with strain, is consistent with a solid-like mechanical behaviour at these high crystallinities. All studied suspensions are characterized by a non-Newtonian, shear thinning rheological behaviour. Our results and, in particular, the dependence between the rheological behaviour and the development of crystal microstructures, need to be integrated in mechanical models of magmatic suspensions.

"The fire resistance of structural building elements has become an increasing concern after the terrorist attacks on September 11th, 2001. This concern has pushed for changes in the building codes and standards to incorporate a performance-based approach to design. Performance-based design is a process where fire safety solutions are determined using a representation of the actual fire stages that may occur in a structure during a fire event. The American Institute of Steel Construction (AISC) has added Appendix 4 in the Specification for Structural Steel Buildings to the current edition of the Steel Construction Manual to provide engineers with guidance in designing steel structures and components for fire conditions. The performance-based approach outlined in Appendix 4 is designed to prevent loss of life, structural collapse, and the outbreak of fires through elimination of ignition sources. Adopting this approach, requires structural engineers to have a better understanding of the behavior of steel connections under fire conditions as well as the tools, techniques and judgment for analysis. The focus of this thesis is to study the strength behavior of steel connections under fire conditions with the assistance of the finite element software, ALGOR. Connections of varying thickness and bolt patterns are constructed using the ALGOR pre-processing software. A time-temperature fire curve is combined with external loads, applied to the models and then analyzed in the program. Stress-strain diagrams are created using the results and yield loads are determined for the various connections at normal and elevated temperatures. These yield loads are compared to values found from a mathematical analysis of the limit state equations in Chapter J of the Specifications. The elevated models are created with temperature-dependent material properties, therefore the yield loads are associated with critical temperatures within the connection models. It is found that the capacity and governing temperature of the connections is determined by the limit state of bearing at the bolt hole. At elevated temperatures, the finite element analysis produces capacities significantly lower than the analysis at normal temperatures. "

O refinamento dos poros, associado à reação pozolânica e ao efeito filer, reduz a permeabilidade do concreto com cinza de casca de arroz (CCA), o que pode antecipar a sua degradação em altas temperaturas. A literatura mostra que o concreto reidratado em água pode recuperar substancialmente a sua resistência inicial, porém, os estudos sobre a reidratação ao ar e sobre a influência do modo de resfriamento na reidratação são escassos. A pesquisa desenvolvida teve como principal objetivo avançar na análise experimental de concretos convencional e com CCA em altas temperaturas e na reidratação. Na etapa exploratória se avaliou a influência da temperatura de exposição, da adição mineral, do ambiente de acondicionamento, da taxa de aquecimento e do tempo de exposição na resistência à compressão e módulo de elasticidade. Na etapa principal se avaliou a influência do modo de resfriamento, da adição e da idade de reidratação na resistência residual. Complementarmente se utilizou o ensaio de velocidade de pulso ultrassônico (VPU) para avaliar o grau de microfissuração e correlacionar a VPU com as propriedades mecânicas residuais. Na etapa exploratória concluiu-se que a adição, a temperatura, a taxa de aquecimento e o tempo de exposição influenciaram significativamente os resultados. O concreto com CCA cristalina apresentou pior desempenho em altas temperaturas. O concreto com CCA amorfa apresentou desempenho ligeiramente inferior ao concreto convencional em 200°C, devido ao efeito da poro-pressão. No entanto, ambas as CCA podem ser alternativas viáveis considerando sustentabilidade. Na etapa principal, o resfriamento brusco com água provocou maior redução na resistência devido aos gradientes térmicos, porém, permitiu maior recuperação logo nos primeiros sete dias de reidratação. Apesar da recuperação parcial, a resistência ao fim de 154 dias foi inferior a 40% do valor inicial. Nas análises térmicas e de DRX foi possível observar nos concretos resfriados com água a recristalização dos aluminatos de cálcio, do C-S-H e da portlandita, em maior grau no concreto convencional. Foi possível observar correlações fortes entre as variáveis de resposta na etapa exploratória, porém, o mesmo não ocorreu na etapa principal, devido à fissuração e presença de água nos poros. / The pore refinement, associated with the pozzolanic reaction and the filler effect, reduces the permeability of blended concrete with rice husk ash (RHA), which can anticipate its degradation at high temperatures. The literature shows that concrete rehydrated with water can recover substantially its initial strength, but studies on rehydration in air and on the influence of the cooling method on rehydration are scarce. The main objective of this research was to evaluate the performance at high temperatures and in rehydration of conventional and blended concretes with RHA. In the exploratory stage, the influence of exposure temperature, mineral admixture, conditioning environment, heating rate and exposure time on residual strength and modulus of elasticity of heated concrete was evaluated. In the main stage, the influence of cooling method, mineral admixture and time of rehydration in an unsaturated environment on residual strength of concrete was evaluated. The ultrasonic pulse velocity test (UPV) was used to evaluate the degree of micro cracking of concrete and to correlate the UPV with residual strength and modulus. In the exploratory stage it was concluded that mineral admixture, temperature, heating rate and time of exposure significantly influenced the results. In general, concrete with partially crystalline RHA presented the worst performance at high temperatures. Concrete with amorphous RHA presented worse performance than conventional concrete only at 200°C, due to the pore-pressure effect. Despite these results, RHA can be a viable option considering sustainability and high temperatures performance. In the main stage, the rapid cooling with water caused a greater reduction in strength, due to thermal gradients, however, caused a greater strength recovery in the first seven days of rehydration. Despite this partial recovery, the final strength of both concretes after 154 days of rehydration was less than 40% of the initial value. In water-cooled concretes thermal and XRD analyzes show recrystallization of the calcium aluminates, C-S-H and portlandite, to a greater degree in conventional concrete. In the exploratory stage it was possible to observe strong correlations between the independent variables; however, the same did not occur in the main stage, due to cracking and to the presence of water in the pores.