EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
Notícias
A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.
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6 resultados
Resultados da Pesquisa
Item Study of mechanical, durability and microstructural properties of cementitious composite with addition of different iron ore tailings from Brazil.(2022) Almada, Bruna Silva; Melo, Henrique da Silva Silveira; Duarte, Marlo Souza; Aguilar, Maria Teresa Paulino de; Garcia, Dayana Cristina Silva; Silva, Guilherme Jorge Brigolini; Santos, White José dosBrazil is the second-largest global iron ore producer in the world. Consequently, a large volume of iron ore tailings (IOTs) is generated, which is associated with environmental impacts. IOTs present potential to be used as an addition in cementitious compounds, however, few studies assess how the heterogeneity of this waste can limit its utilization as a building material. Thus, the present study aims to assess whether the heterogeneity of IOTs influences mechanical, durability, and microstructural properties when added to the cementitious composite. Four IOTs samples from different origins were collected and added to cementitious composite at 40% addition content. Composites’ mechanical (compressive strength and modulus of elasticity) and durability properties (water absorption, porosity, electrical resistivity, carbonation, and pH pore solution) were correlated to the microstructure of the IOTs. Results showed that the IOTs from different mines exhibited different physical properties and chemical/mineralogical compositions. Moreover, the higher the degree of ore processing, the lower the heterogeneity, iron content, and specific gravity. Although the IOT samples are heterogeneous, this type of tailing can be used as a filler addition in structural mortars. IOT addition tends to improve the mechanical and durability properties. Heterogeneity most significantly influenced the properties in the fresh state, durability, and microstructural properties. The microstructure of the cement matrix tends to be denser in the IOT-added with higher SSA and silica content. Was observed higher-porosity in regions close to the interfacial transition zone in the samples with coarser IOT.Item Effect of thermal aging on the microstructure and mechanical properties of stainless steel UNS S31803.(2020) Costa, Junia Maria Gândara; Lacerda, José Carlos de; Godefroid, Leonardo Barbosa; Cândido, Luiz CláudioDuplex stainless steel UNS S31803 exhibits high mechanical strength with high corrosion properties, due to its microstructure composed of ferrite and austenite phases, in equal proportion. When the UNS S31803 steel is submitted to high temperatures, some precipitations can occur, such as nitrites, carbides, and third phases (e.g. sigma phase -σ, and alpha prime - α'). These phases are deleterious in relation to the mechanical properties and corrosion resistance, and their effects are analyzed regarding the properties of the steel. In order to evaluate the precipitation of this deleterious phase, isothermal treatment was done at 500°C for 144 hours (α' phase) and at 850ºC for 80 minutes (σ phase). The results were obtained through the microstructural analysis and tensile tests. The presence of sigma phase was verified in the grain boundary, an increase in the mechanical resistance with a loss of toughness. There was as well as an increase in mechanical resistance with the precipitation of α', with less loss of ductility than that observed in the experiments involving the presence of sigma phase.Item Effect of niobium on microstructure and mechanical properties of a hypereutectoid steel.(2022) Pessoa, Ricardo Amorim; Porcaro, Rodrigo Rangel; Cândido, Luiz Cláudio; Pereda, Beatriz; Lopez, BeatrizHigh-carbon steels have been used to high-strength steel wire and strands for prestressing concrete. The necessity of high-strength levels at increasingly larger diameters of wire rods is a technological challenge. Two steels with and without Nb were obtained in a steel mill, submitted to detailed microstructural (previous austenitic grain size, pearlite interlamellar spacing and colony size) and mechanical characterization through tensile tests and hardness. Hot torsion and dilatometry tests were performed to simulate steels processing and to verify the influence of Nb on phase transformation. Adding Nb to steel resulted in a refinement in austenitic grain size and pearlite colonies but had no effect on pearlitic interlamellar spacing. There was a decrease at the start transformation temperature austenite/pearlite and therefore an increase in the hardenability of the Nb-added steel. Finally, Nb addition proved to be a technical and economical way to increase tensile strength and to reduce the variability of the mechanical properties.Item Microstructure evolution and mechanical behavior of a lean duplex stainless steel aged at 475o C.(2021) Reis, Thompson Júnior Ávila; Santos, Henrique Meckler; Almeida, Eliza Wilk Reis de; Godefroid, Leonardo BarbosaIn this research, the effects of isothermal treatments at 475 ◦C on the microstructure and mechanical properties of a UNS S32304 lean duplex stainless steel were investigated. Samples of the alloy under as received and aged conditions were analyzed by atomic force microscopy and magnetic force microscopy in order to evaluate the ability of these techniques to identify important aspects that characterize microstructural changes caused by aging. The mechanical behavior was evaluated by tensile tests, hardness tests, Charpy impact tests, crack extension resistance tests, force controlled axial fatigue tests and fatigue crack growth rate tests. The fracture surfaces of all tested specimens were analyzed by scanning electron microscopy. The results indicate that the α-phase spinodal decomposition occurred, with a tendency to saturation for a not too long aging time. The analysis by atomic/magnetic force microscopy allowed to identify characteristics regarding the preferential phase dissolution of the α phase that distinguish the alloy in the as received condition from the aged alloy. As a consequence of the formation of the α’ phase, the absorbed impact energy and the fracture toughness of the alloy decreased substantially. On the other hand, the tensile strength and the fatigue resistance increased significantly.Item Investigation on mechanical and microstructural properties of alkali-activated materials made of wood biomass ash and glass powder.(2021) Silva, Guilherme Jorge Brigolini; Santana, Vanessa Pereira; Wójcik, MartaThe possibility of the application of biomass fly ash (BFA) as a precursor material for the synthesis of alkaliactivated materials (AAM) is presented in this paper. Glass powder (GP) was tested as an additional substrate in a synthesis process. Different mixtures of samples were produced: four mixtures using only BFA for different NaOH concentrations and nine mixtures where BFA was partially replaced by the GP. Three different NaOH concentrations were applied here. Compressive and flexural strength after 7 and 14 days were performed. The microstructure and the chemical composition of samples were obtained. The results show that the compressive and flexural strength of materials increased with the increase of NaOH concentration and the decrease of the GP content in a mixture. The samples were also characterized by the high porosity with some voids and microcracks. The poorly dissolved BFA particles were also noted in a matrix.Item Assessment of the mechanical parameters of resin composites with the addition of various types of fibres.(2020) Dębska, Bernardeta; Lichołai, Lech; Silva, Guilherme Jorge Brigolini; Caetano, Marina AltoéThe article describes tests of epoxy mortars after the addition of fibres. The fibres were a substitute for sand in the amount of 0, 1, 2, 3, 4 and 5% by volume, respectively. Three types of mortar were obtained, containing polypropylene, glass and carbon fibres, respectively. Statistical analyses (ANOVA) were carried out to assess the impact of fibre content on the mechanical properties of mortars. Brittle fracture toughness was also tested using the Cracked Straight Through Brazilian Disc method. The addition of each type of fibre improved the assessed parameters. Based on the obtained research results, and also due to availability and price, the most advantageous seems to be the production of composites containing the addition of polypropylene fibres.