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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Resultados da Pesquisa

Agora exibindo 1 - 10 de 27

The Bauschinger effect magnitude control in ultra-low carbon steel wires.
(2023) David, Felipe Farage; Cordeiro, Rafael de Oliveira; Vasconcelos, Luan Marcel Costa; Batista, Ben Dêivide de Oliveira; Liberato, Frank de Mello; Costa, Adilson Rodrigues da
The cold roller die process increases the tensile strength and decreases the ductility of steel wire. Annealing heat treatment is applied to restore mechanical properties, but this is a costly process. This research shows that it is possible to control the mechanical properties of ultra-low carbon steel wire inducing the Bauschinger effect and relieving residual steel stresses. The present study uses several pulleys to promote and control the Bauschinger effect magnitude through alternated cyclic bending. A Completely Randomized Design, a regression study, and the Akaike Information Criterion were used to understand the relationship between the quantity and diameter of pulleys and the influence on the magnitude of the Bauschinger effect. Statistical models showed that it is possible to have a maximum increase of 103% in uniform elongation and a maximum decrease of 14% in yield strength. An interaction between the factors studied in controlling the Bauschinger effect magnitude was confirmed.
Abrasiveness of iron ores : analysis of service-worn conveyor belts and laboratory Dry Sand/Rubber Wheel tests.
(2022) Nins, Barbara; Penagos, Jose Jimmy; Carneiro, Leandro Moreira; Münch, Daiane; Falqueto, Patrick Amaral; Viáfara, Cristian Camilo; Costa, Adilson Rodrigues da
Belt conveyors are currently one of the most commonly used technologies for transporting iron ore. Of the components of the conveyor system, the belt is the most expensive and susceptible to damage. Failures due to wear of the rubber cover lead to downtime for corrective maintenance, greater operational risks and performance and economic losses. To improve the tribological performance of conveyor belts, it is necessary to know the main parameters that influence their wear. As wear behavior is not an intrinsic property of a material, the most reliable results are obtained when the wear mechanisms produced in laboratory tests are similar to those in service. In this work, two types were investigated of belt rubber, one new and one worn in service, and four types of iron ore in two class sizes. Loose abrasive wear tests were carried out using the Dry Sand/Rubber Wheel apparatus with belt rubber test pieces and iron ores as abrasives. This work characterized the wear mechanisms that occur in service and in laboratory tests. The predominant wear mechanism found was the formation of Schallamach waves. In the wear tests, Friable Hematite samples presented the highest abrasiveness. In addition, the chemical, mineralogical and morphological features of the iron ore samples were characterized. The high abrasiveness of Friable Hematite was possibly due to the mineral assembly.
Conventional hammering of a Fe-7.2%Ni alloy sample from Itutinga meteorite : an evaluation of its formability and functionality.
(2020) Nunes, Gilson Antônio; Silva, Gilberto Henrique Tavares Álvares da; Costa, Adilson Rodrigues da
Using a mechanical forming process used in the beginning of metallurgy, the samples from the iron meteorite Itutinga were heated and plastically deformed by hammering. Two sharp pieces, similar to small arrowheads, were produced and characterized microstructurally by optical microscopy and scanning electron microscopy (SEM/EDS/EBSD), complemented with Vickers hardness. As expected, the observations pointed to the presence of α2 phase, cracks, oxidation and deformed taenite lamellae. To assess the performance of the arrowheads a penetration test was done on a leather sample. The results demonstrated the possibility of making a useful rudimentary arrowhead from of iron meteorite.
Development and characterization of titanium dioxide ceramic substrates with high dielectric permittivities.
(2020) Freitas, Antonio Evangelista de; Manhabosco, Taíse Matte; Batista, Ronaldo Junio Campos; Rêgo Segundo, Alan Kardek; Araujo, Humberto Xavier de; Araujo, Fernando Gabriel da Silva; Costa, Adilson Rodrigues da
Titanium dioxide substrates have been synthesized by means of solid-state reactions with sintering temperatures varying from 1150 ◦C up to 1350 ◦C. X-ray diffraction and scanning electron microscopy (SEM) where employed to investigate the crystal structure, grain size and porosity of the resulting samples. The obtained ceramics are tetragonal (rutile phase) with average grain sizes varying from 2.94 µm up to 5.81 µm. The average grain size of samples increases with increasing temperature, while the porosity decreases. The effect of microstructure on the dielectric properties has been also studied. The reduction of porosity of samples significantly improves the dielectric parameters (relative dielectric permittivity and loss tangent) in comparison to those of commercial substrates, indicating that the obtained ceramic substrates could be useful in the miniaturization of telecommunication devices.
Computational fluid dynamics and experimental analysis of a coated stainless steel gas turbine blade.
(2019) Souza, Leandro Augusto; Leal, Elisângela Martins; Costa, Adilson Rodrigues da; Lima, Milton Sérgio Fernandes de
This work Aims to analyze, through computational fluid dynamics (Cfd) with the concept of conjugate heat transfer (Cht), the effect of the Thermal Barrier coating and the cooling systemon an Austenitic Stainless steel blade in order to Evaluate the Temperature Behavior of the Material. Although this Steel has a Lower cost compared to Super ALLOYS, it has Similar Properties, Such as the Thermal Expansion Coefficient, chemical Affinity and Melting point. this Evaluation used Ansys® Cfx Software ot Solve the Numerical Problem. the Systemis Validated by Comparing the computational Results to an Experiment. Gas Turbine Blades have a low weight and an Elevated cost. this cost came Mainly form both the Material used and the Sophisticated coating and cooling Method. Thermal Barrier Coatings Associated to a cooling System are Employed on gas Turbine Blades to Increase the Lifetime of the Blade and the gas Turbine Performance. the study Indicates that the Thermal Barrier coating and ahe cooling System were Efficient At Reducing the Temperature of the Metallic Substrate By 160°C. this can Indicated that Stainless steel Blades can be used in gas turbines where the Metallic Temperature limit was not be reached.
Influência da microestrutura na resistência ao desgaste microabrasivo de ligas de F-Cr-C e Fe-Cr-C-Nb.
(2019) Oliveira, Tatiane Gabi de; Costa, Adilson Rodrigues da
Neste trabalho é feita uma avaliação da influência do teor de cromo e da combinação do cromo e nióbio em ligas de revestimento duro do tipo Fe-Cr-C, na microestrutura e propriedades que envolvam a resistência ao desgaste microabrasivo. Vários estudos têm sido realizados em busca de informações conclusivas sobre este sistema em condições de desgaste, devido às distintas fases e propriedades apresentadas por estas ligas. As ligas de Fe-Cr-C associam fases duras (carbonetos), com uma matriz metálica, o que lhes proporciona elevada dureza e resistência mecânica. Para realização dos experimentos, foram utilizadas as ligas de Fe-Cr-C comerciais, em forma de consumíveis (eletrodos e arame) e aplicadas em aço carbono ASTM A36 por meio de processos de soldagem SMAW e GMAW, respectivamente, como revestimentos. Neste caso, foram utilizados dois eletrodos com adição de 25 e 45% em peso de cromo e um arame com 20 e 5% em peso de cromo e nióbio, respectivamente. O ensaio de desgaste por microabrasão foi realizado utilizando o teste por esfera rotativa fixa e, como abrasivo, uma suspensão de diamante de granulação 3µm. Para o qual, foram utilizados 4 corpos de prova referentes à cada liga. Para determinar o coeficiente de desgaste foi obtida a perda média de volume de material, em intervalos de tempo de ensaio pré-estabelecidos, relacionando o resultado com a distância de deslizamento. Ao analisar os resultados obtidos, verificou-se que a liga que apresentou combinação de cromo e nióbio em sua composição exibiu melhores resultados de resistência ao desgaste, embora apresentasse menores valores de dureza e percentual de carbonetos em relação às outras duas ligas. Tal fato evidencia a possibilidade de se utilizar tais ligas em aplicações que requerem alto desempenho em relação à resistência ao desgaste.
A comparative study of the heat input during laser welding of aeronautical aluminum alloy AA6013-T4.
(2018) Coelho, Bruno Nazário; Lima, Milton Sérgio Fernandes de; Carvalho, Sheila Medeiros de; Costa, Adilson Rodrigues da
The heat input is the amount of energy supplied per unit length of the welded workpiece. In this study, the effect of two different heat inputs in laser beam welding of a high strength aluminum alloy AA6013-T4 was evaluated from macrostructural and microstructural points of view. The experiments were performed using a continuous wave 2 kW Yb-fiber laser with 100 μm spot size on the upper surface of the workpiece. Keeping the heat input at a given level, 13 or 30 J/mm, the laser power was changed from 650 W to 2 kW and the welding speed from 33 to 150 mm/s. In the condition of higher heat input 30 J/mm it was possible to obtain both cutting and welding processes. For 13 J/mm, welding processes were obtained in conduction and keyhole modes. The equiaxed grain fraction changed with changing speed for the same heat input. The laser processing induced a decrease in the hardness of the weld bead of about 25% due to the solubilization of the precipitates. The estimated absorptivities of the laser beam in the liquid aluminum changed largely with experimental conditions, from 4.6% to 10.5%, being the most significant source of error in measuring the real amount of energy absorbed in the process. For the same heat input the macrostructure of the welded surfaces, i.e., humps and dropouts, changed as well. All these facts indicate that the heat input is not a convenient method to parameterize the laser beam welding parameters aiming the same weld features.
A multi-objective green UAV routing problem.
(2017) Coelho, Bruno Nazário; Coelho, Vitor Nazário; Coelho, Igor Machado; Ochi, Luiz Satoru; Koochaksaraei, Roozbeh Haghnazar; Zuidema, Demetrius; Lima, Milton Sérgio Fernandes de; Costa, Adilson Rodrigues da
This paper introduces an Unmanned Aerial Vehicle (UAV) heterogeneous fleet routing problem, dealing with vehicles limited autonomy by considering multiple charging stations and respecting operational re- quirements. A green routing problem is designed for overcoming difficulties that exist as a result of lim- ited vehicle driving range. Due to the large amount of drones emerging in the society, UAVs use and efficiency should be optimized. In particular, these kinds of vehicles have been recently used for deliver- ing and collecting products. Here, we design a new real-time routing problem, in which different types of drones can collect and deliver packages. These aerial vehicles are able to collect more than one deliver- able at the same time if it fits their maximum capacity. Inspired by a multi-criteria view of real systems, seven different objective functions are considered and sought to be minimized using a Mixed-Integer Lin- ear Programming (MILP) model solved by a matheuristic algorithm. The latter filters the non-dominated solutions from the pool of solutions found in the branch-and-bound optimization tree, using a black-box dynamic search algorithm. A case of study, considering a bi-layer scenario, is presented in order to val- idate the proposal, which showed to be able to provide good quality solutions for supporting decision making.
Discontinuity detection in the shield metal arc welding process.
(2017) Cocota Júnior, José Alberto Naves; Garcia, Gabriel Carvalho; Costa, Adilson Rodrigues da; Lima, Milton Sérgio Fernandes de; Rocha, Filipe Augusto Santos; Freitas, Gustavo Medeiros
This work proposes a new methodology for the detection of discontinuities in the weld bead applied in Shielded Metal ArcWelding (SMAW) processes. The detection system is based on two sensors—a microphone and piezoelectric—that acquire acoustic emissions generated during the welding. The feature vectors extracted from the sensor dataset are used to construct classifier models. The approaches based on Artificial Neural Network (ANN) and Support Vector Machine (SVM) classifiers are able to identify with a high accuracy the three proposed weld bead classes: desirable weld bead, shrinkage cavity and burn through discontinuities. Experimental results illustrate the system’s high accuracy, greater than 90% for each class. A novel Hierarchical Support Vector Machine (HSVM) structure is proposed to make feasible the use of this system in industrial environments. This approach presented 96.6% overall accuracy. Given the simplicity of the equipment involved, this system can be applied in the metal transformation industries.
Laser surface treatment for enhanced titanium to carbon fiber‑reinforced polymer adhesion.
(2017) Palavra, Armin; Coelho, Bruno Nazário; Hosso, Jeff Th. M. de; Lima, Milton Sérgio Fernandes de; Carvalho, Sheila Medeiros de; Costa, Adilson Rodrigues da
The adhesion between carbon fiber-reinforced polymer (CFRP) and titanium parts can be improved by laser surface texturing before gluing them together. Here, a pulsed Nd:YAG laser was employed before bonding of the textured surfaces using an epoxy paste adhesive. To investigate the influence of the laser parameters, the roughness of the surfaces were characterized and correlated to the wettability, by measuring the contact angles of water droplets. Scanning electron microscope (SEM) characterization was also performed showing that under careful conditions, the fiber structure could be maintained. Tensile tests were performed to evaluate the influence of the laser treatment parameters on the joining efficiency. The lap-joint tensile strength tests presented the best results when the titanium surfaces were treated using 5.03 × 10−3 J pulses and the CFRP sample treated with 5.03 × 10−4 or 5.03 × 10−3 J or even using a virginal CFRP surface. Using a virginal CFRP surface, the critical load of fiber delamination was increased and as a consequence the tensile strength attains the highest level of 8.2 MPa.

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