Resumo O metacaulim é a principal matéria-prima utilizada na síntese de geopolímeros, embora a relação entre os teores de sílica e alumina não seja a ideal. Normalmente, o teor de SiO 2 é ajustado com o uso de silicatos presentes na solução ativadora. Uma opção ecoeficiente seria o uso de resíduos de vidro como fonte adicional de sílica. Este trabalho avalia a eficiência da ativação alcalina do metacaulim, utilizando hidróxido e silicato de potássio, com e sem substituição de 12,5% de metacaulim por micropartículas de vidro. A eficiência da ativação alcalina foi avaliada por difratometria de raios x, espectroscopia na região infravermelha com transformada de Fourier, espectroscopia de ressonância magnética nuclear do 27 Al e 29 Si, massa específica e resistência à compressão. Os resultados indicam a ocorrência de geopolimerização com e sem uso de resíduo de vidro. Observou-se que a substituição de 12,5% favorece o desempenho mecânico dos compósitos aos 28 dias, com aumentos de 37% e 47% da resistência mecânica do material com cura em estufa e na temperatura ambiente, respectivamente.

Abstract Metakaolinis the principal raw material utilized in the synthesis of geopolymers, although its ratio of silica and alumina contents is not ideal. Normally, the SiO2 content is adjusted with the use of silicates present in the activating solution. An eco-efficient alternative would be the use of glass waste as an additional source of silica.This work evaluates the efficiency of the alkaline activation of metakaolin, using potassium hydroxide and silicate, with and without the substitution of 12.5% of metakaolin by microparticles of glass. The efficiency of the alkaline activation was evaluated by X ray diffractometry, spectroscopy in the infrared region with the Fourier transform, nuclear magnetic resonance spectroscopy of 27Al and 29Si, specific mass and compressive strength. The results indicate the occurrence of geopolymerization with and without the use of glass waste. It was observed that the substitution of 12.5% favors the mechanical performance of the compounds at 28 days, with increases by 37% and 47% in the mechanical strength of the material with thermal curing and ambient temperature curing, respectively.

Severe plastic deformation (SPD) of metals leads to their strengthening and grain refinement, but to low uniform elongations. Low Strain Amplitude Multi Directional Forging (LSA-MDF) is an important method for increasing this low uniform elongation. The application of workpieces of SPD-processed materials requires that their distributions of mechanical properties, microstructures and deformation be as homogeneous as possible. Analyses of these distributions after LSA-MDF have not been found in the literature, and are presented in the current investigation utilizing microhardness measurements, optical and electronic microscopy and finite element simulations. LSA-MDF causes higher strains, mcrohardeness and structural distortions in the central regions of the specimens than at their edges and corners. In addition, LSA-MDF utilizing confined compressions seems to be the preferred processing route, due to its ease and to the more homogeneous microhardness, microstructure and strain distributions in relation to other experimental procedures.

Nodular cast irons (NCIs) involve the inoculation and nodulization of 0.03 to 0.06wt% Magnesium, as well as the addition of Molybdenum, Chromium, Nickel, Copper and Vanadium, although the presence of Niobium is not common. The literature reports that Niobium leads to better mechanical properties of the NCIs, and recent results indicate that 0.5wt% Niobium increases the strength and the Charpy notch toughness of NCIs, but decreases its hardness, in relation to a similar NCI without Niobium. The present report studies the addition of 0.23, 0.47, 0.67, and 0.85wt% Niobium to a NCI covering the effects on the microstructures, yield and tensile strengths, tensile elongations and Charpy toughness. The NCIs were prepared in a 120 kg medium frequency induction furnace, and samples were obtained following the ASTM A842 standard; the various test specimens were extracted from these samples according to specific standards for each test. Fracture analysis was performed in fractures specimens after the Charpy tests. It was shown that the volume fraction of pearlite increases as the Niobium content is raised, leading to increments in the yield and tensile strengths and hardness of these materials. Modest increment of tensile ductility and Charpy toughness are observed only for an addition of 0.23% Niobium. Fracture analysis revealed typical brittle cleavage surfaces and decohesion between grains and grain - graphite nodules interfaces, and very low porosity

Esse estudo avalia a influência das condições de queima do bagaço de cana-de-açúcar (BCA) nas características físico-química das cinzas geradas. A queima foi realizada nas temperaturas de 400, 600 e 800ºC com e sem circulação de ar no forno. As cinzas obtidas após a queima foram caracterizadas de acordo com o grau de cristalinidade, morfologia, análise granulométrica, ensaios de perda ao fogo e de reatividade em solução saturada de hidróxido de cálcio. Foi observado que a queima com circulação de ar desfaz as fibras, consome o material orgânico e produz partículas finas a uma temperatura de 600ºC. O material não orgânico observado nas cinzas apresenta alto grau de cristalinidade. Ensaios em material lavado em laboratório sugerem que a estrutura cristalina observada nas cinzas é areia proveniente da contaminação do solo. A redução na condutividade em uma solução de hidróxido de cálcio e a difração de raios X sugerem que a sílica amorfa é formada em temperaturas inferiores a 600ºC e a cristobalita é formada em temperaturas mais elevadas.

The effect of calcination temperature and air flow on the content of organic material, morphology of particles, degree of crystallinity and the reactivity with lime solution of the sugar cane bagasse ash is evaluated. The results show that the long fibers of the bagasse and organic material are retained when calcination occurs without sufficient air flow. Calcining with forced air-flow breaks the fibers, removes organic material and produces fine particles at a temperature of 600ºC. The non-organic material observed in the ash displays a high degree of crystallinity. Experiments show that the crystalline structure observed in the ashes is due to adhered sand which was not previously washed away. The reduction on the conductivity in lime solution and X-rays diffraction pattern suggest that amorphous silica is formed at temperatures lower than 600ºC and cristobalite is formed at higher temperatures.

Os compósitos cimentícios, comumente, são avaliados em função de sua trabalhabilidade, do teor de ar incorporado, do seu módulo de elasticidade e de resistência à compressão. Essa resistência é determinada através de ensaios de compressão axial de corpos-de-prova moldados especialmente para essa finalidade. Na execução do ensaio de compressão, é necessário que as superfícies, onde se aplicam as cargas, sejam planas, paralelas e lisas, de modo que o carregamento seja uniformemente distribuído. Para isso são utilizadas diversas técnicas e materiais, como capeamentos aderentes, não aderentes, sistemas de desgaste mecânico ou moldes especiais. Atualmente, os capeamentos mais utilizados são os que utilizam argamassas de enxofre ou almofadas de neoprene. O presente trabalho avalia, experimentalmente, a interferência de diferentes tipos de regularização das bases dos corpos-de-prova para compósitos cimentícios de diferentes classes de resistência.

Cementitious composites are commonly evaluated considering their workability, level of incorporated air, elasticity modulus and compression strength. Data from compression testing commonly present a high dispersion, which has been attributed to effects of the specimen geometry, dimensions and of the degree of material compaction, as well as to problems in the specimen end-faces, such as their parallelism, orthogonality in relation to the compression axis and surface regularity. Specimen end-face regularization has been achieved through various techniques, such as adhering or non-adhering capping with various materials, mechanical grinding and systems involving special moulds. The regularization methods utilized more frequently employ sulfur mortar capping, neoprene cushions and surface grinding. The present work covers the experimental compression tests of cementitious composites of different classes of strength employing sulfur mortar capping and neoprene cushions. It was concluded that there is a strong influence of the chosen regularization technique on the measured compression strengths.

Grain refinement in magnesium is evaluated in the present paper. Equal Channel Angular Pressing is used to process commercially pure magnesium. Processing was carried out at 523 K which is lower than the temperature used in other papers on the literature. The grain structure was evaluated throughout the deformation zone. The low processing temperature prevents significant grain growth. The evolution of the grain structure is compared to a recent model for mechanism of grain refinement in magnesium. The present results confirm the validity of the model.

Os laminadores a frio da Aperam South America são equipados com mandris que têm a função de sustentar o peso da bobina e de transmitir torque proveniente do acionamento. Os mandris são dotados de mecanismos chamados mordente, cuja função é prender a ponta da tira no início do processo de enrolamento e, assim, permitir a aplicação da tração de bobinamento. A prática atual de bobinamento considera que a aplicação da tração somente pode ser iniciada após, pelo menos, 1,5 voltas de tira no mandril, o que gera perda de rendimento físico nos laminadores. Foi desenvolvida uma metodologia para medição do atrito entre a tira e a superfície do mandril, numa aproximação das condições industriais, tendo em vista estudos posteriores para avaliação da capacidade dos mordentes dos mandris, a fim de se aplicar a tração com menos de uma volta de tira enrolada no mandril. Desenvolveu-se um modelo físico que foi construído próximo da escala real, o qual foi submetido a ensaios experimentais envolvendo segmentos dos mandris de dois laminadores. Os resultados do atrito médio na interface tira e mandril estão coerentes com os usados na literatura.

The cold rolling mills of Aperam South America are equipped with mandrels which have the function of sustaining the coil load and torque transmission from the motor. The mandrels are equipped with mechanisms called grippers, whose function is to grip the tail of the strip at the beginning of the wrapping process and thus permit the winding tension application. The current winding practice considers that tension application can only be started after the wrapping up of at least 1.5 turns of the strip onto the mandrel, which generates a decline in the physical performance of the rolling mills. A methodology was developed to measure the friction between the strip and the surface of the mandrel, under approximate industrial conditions in order to further studies for evaluating madrel gripper capacity under an applied tension of less than one turn of the strip around the mandrel. A near-scale physical model was built, which was subjected to experimental tests involving segments of mandrels from two mills. The results of the average friction at the interface strip and mandrel are consistent with those found in literature.

O presente trabalho tem por objetivo analisar a formação de bandas cisalhantes em chapas metálicas de aço baixo carbono (SAE 1006) submetidas à tração uniaxial. Essa verificação foi feita através de análise numérica utilizando o software Deform2D, bem como a realização dos testes físicos por meio de corpos-de-prova de tração entalhados com geometrias variadas. Foram levantadas a curva de fluxo e a anisotropia do material utilizado para a realização da simulação numérica. A partir dessa simulação, foram feitas análises da formação das bandas, utilizando-se vários passos em cada corpo-de-prova e, posteriormente, comparando essa mesma formação entre os corpos-de-prova com geometrias de entalhes diferentes. Por fim, foi verificado que, tanto a formação de bandas de cisalhamento, quanto às características da fratura no material estudado, estão diretamente relacionadas com a forma geométrica do entalhe.

The present study had as main purpose to analyze the formation of shear bands in metallic sheets of low-carbon steel (SAE 1006) submitted to uniaxial tension test. This verification has been made through numerical analysis using the software Deform2D, and the performance of physical tests with the tension's test specimen being notched with varied geometries. The flow curve and the anisotropy of the material used for the realization of numerical simulation have been designed. After this simulation, band formation analysis was performed using varios steps for each sample, and compared with the test specimen of the same formation with different geometrical notches. Finally, it was verified that both the shear band formation and the fracture characteristics of the studied material are directly related with the geometrical shape of the notch.

Cold forming is usually associated with the "work hardening" of the material being formed. The work hardening behavior of metals subject to complex processing paths is different from that in monotonic deformation. The results show that, after some initial hardening, there is a possibility that further deformation will cause softening in the material ("work softening"). Recent work showed that cyclic torsion applied to drawn products causes changes in the subsequent tensile behavior of low carbon steel, and that the effect will depend on the previous "history" of the material. For annealed samples, the cyclic torsion leads to an increase in the yield strength, but does not affect the tensile strength and elongation. For the case of previously drawn bars, the cyclic deformation caused a decrease in the yield and tensile strength and an increase in the total elongation. The present paper discusses the dislocation structure changes associated with different strain paths in mild steel.

Equal Channel Angular Pressing (ECAP) is the most prominent SPD (Severe Plastic Deformation) method for the production of ultrafine and nanostructured metals, and has been extensively employed and analyzed. This technique was applied to a Pb-4%Sb alloy at room temperature, in order to study its effect on a low melting point and multiphase metallic material. The material was subjected to effective strains higher than 9, after 8 passes of processing, where dynamic and static recrystallization are expected during and after each pass. This eliminates any grain refinement and allows the analysis only of the microstructural effects associated with second phase redistribution and eventual precipitate dissolution. ECAP followed route C, which eliminates structural alignment after each even ECAP pass, facilitating the study of the microstructural evolution. It is shown that three ECAP passes are necessary to completely break the lamellar structure of the as cast strucure and that antimony dissolves into the lead rich matrix. Dynamic recrystallization and structural changes reduce the material strength and change the flow curve format.

The work hardening of metals subjected to complex processing paths is different from that in monotonic deformation. Changes in the deformation mode can promote transients in the strain-hardening rate, leading to anomalous softening or hardening of the material. This paper investigates the influence of strain path changes on the tensile behavior of drawn 0.12% steel rods. Annealed or predrawn specimens were submitted to cyclic twisting and then tested in tension. The results show that the cyclic deformation causes changes in the mechanical behavior of the metal, and the effect will depend on the previous "history" of the material. Cyclic twisting causes hardening in annealed samples, but leads to softening of the drawn bars. These phenomena are in line with the corresponding substructural aspects.