Mestrado em Engenharia Mecânica
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- ItemEstudo do comportamento em desgaste microabrasivo da liga Nb-Ni-WC-Cu sinterizada a plasma pulsado(Universidade Federal do Espírito Santo, 2024-11-11) Souza, Juliana Prates; Bozzi, Antônio Cesar ; https://orcid.org/0000-0003-4857-0216; http://lattes.cnpq.br/3017292130810807; https://orcid.org/0009-0001-4353-5991; http://lattes.cnpq.br/7583082369760297; Orlando, Marcos Tadeu D´Azeredo ; https://orcid.org/0000-0002-8387-6504; http://lattes.cnpq.br/3562894103432242; Franco Júnior, Adonias Ribeiro ; https://orcid.org/0000-0003-0511-1052; http://lattes.cnpq.br/6677652514776940There is an increasing demand in the industry for alloys with increasingly enhanced mechanical properties. Aiming at high-temperature applications, the Nb-Ni-WC-Cu alloy was developed in a previous study by spark plasma sintering (SPS) in three different nickel compositions (5%, 10%, and 15%) and sintered at three distinct temperatures (1000°C, 1100°C, and 1200°C). The objective of this work was to investigate the micro-abrasive wear behavior of this alloy. For this, Vickers hardness tests and micro-abrasion tests were carried out using three abrasives: alumina (Al₂O₃), silicon carbide (SiC), and silica (SiO₂). The results indicated that increasing the sintering temperature led to an increase in the hardness of the samples. The composition with 10% nickel sintered at 1100°C (M2 1100) showed the highest hardness (1345.80 HV). The micro-abrasion test was conducted in a fixed-ball configuration, with a load of 0.3 N and a rotation speed of 20 rpm, using an abrasive suspension with a concentration of 0.1 g/cm³ for Al₂O₃ and SiC, and 0.35 g/cm³ for SiO₂. The best results regarding abrasive wear were obtained for the samples sintered at 1100°C, for all compositions. Through scanning electron microscopy (SEM), it was observed that the predominant wear mechanism was grooving for the Al₂O₃ and SiO₂ abrasives, and rolling and mixed mechanisms for the SiC abrasive
- ItemInterfaces e estratégias de controle baseadas em machine learning aplicadas a um exoesqueleto de braço para reabilitação motora(Universidade Federal do Espírito Santo, 2024-09-17) Dias, Eduardo Antonio Fragoso; Andrade, Rafhael Milanezi de; https://orcid.org/0000-0002-2839-3649; Bastos Filho, Teodiano Freire; Vimieiro, Claysson Bruno SantosStroke is one of the leading causes of acquired disability worldwide, with approximately 80% of survivors living with permanent disabilities. Recovery of upper limb functionality is particularly challenging, with only about 50% of patients regaining some functional use after the event. In this context, physiotherapy and occupational therapy are essential, but robotic rehabilitation emerges as a promising alternative to enhance therapeutic outcomes. However, the effectiveness of these new therapies is directly linked to the control interfaces and strategies applied in the patient’s interaction with the robotic device. Thus, this work investigates the development and application of control strategies and interfaces in an arm exoskeleton designed for neuromotor rehabilitation of post-stroke patients. We explore different strategies using surface electromyography (sEMG) to identify the patient’s movement intention and strategies operated by the physiotherapist, applied to an upper limb exoskeleton. Additionally, a rehabilitation protocol was implemented using an interface based on assistive trajectory control. The results indicate significant improvements in rehabilitation, highlighting the efficacy of incorporating advanced robotic technologies in the neuromotor recovery process, providing a more effective and individually tailored approach to patient needs.
- ItemUma comparação entre elementos de contorno contínuos e descontínuos na solução de problemas de Laplace(Universidade Federal do Espírito Santo, 2024-09-09) Cruzeiro, Filipe Lopes; Loeffler Neto, Carlos Friedrich; https://orcid.org/0000-0002-5754-6368; Lara, Luciano de Oliveira Castro; https://orcid.org/0000-0003-1329-2957; https://orcid.org/0009-0003-8857-6951; Campos, Lucas Silveira; Bulcão, AndréThe Boundary Element Method (BEM) is one of the most powerful techniques for solving continuum mechanics problems and, along with the Finite Element Method (FEM) and the Finite Difference Method (FDM), has completely transformed engineering. The Boundary Element Method emerged as a powerful alternative among other numerical methods, particularly for problems requiring high precision, such as stress concentration problems and problems with infinite domains. The main characteristic of the Boundary Element Method is the integration only at the boundaries of the problem, meaning the elements are located solely on the boundary. In some cases, it is necessary to place source points within the domain, either to introduce degrees of freedom, as in problems related to membrane vibrations, or to obtain specific properties at that point, such as a heat source. However, in self-adjoint equations, such as the Laplace equation, it is not necessary to place points within the domain, with only the boundary being discretized. For this type of problem, the quality of the solution will depend on how the elements are constructed. In its simplest form, BEM has an element with only one source point at its center, and the properties of this point are adopted for the entire element. Another formulation involves continuous linear elements, which have two functional points positioned on geometric points, and these functional points are shared with neighboring elements. This formulation evolved to include high-order elements, with quadratic and cubic elements being quite common. These elements have some deficiencies, such as the need for special treatment at corners, as well as the difficulty of generating meshes for the subdomain technique. These problems led to the creation of a type of element called discontinuous. This type of element is characterized by discontinuity between element i and the adjacent elements, meaning there is no sharing of functional points between elements. The use of this element is a specific feature of BEM, and it cannot be applied in other classical methods. This work will analyze the efficiency of the discontinuous Boundary Element Method in solving the Laplace equation, evaluating the quality and the order of convergence of this formulation compared to the continuous formulation.
- ItemSliding wear of microalloyed wheel steel and high-strength rail steel under very high normal load at room temperature and under mild normal load at room and elevated temperatures(Universidade Federal do Espírito Santo, 2024-08-26) Xavier, Leonardo Medeiros; Scandian, Cherlio; https://orcid.org/0000-0002-4393-719X; Boher, Christine; Strey, Nathan Fantecelle; Souza, Roberto Martins deThe sliding of the wheel flange against the rail gauge corner is critical in rail transportation, particularly in sharp curves where this sliding prevents derailment of the vehicle. However, this comes at the cost of severe wear due to the elevated stresses and temperatures developed in the contact. Understanding the wear behavior of this tribosystem is crucial in reducing the increased costs associated with the maintenance of the wheels and rails. To provide valuable insights into the wear mechanisms of wheel and rail steels in high stress and high-temperature applications, this work investigated, through two different studies, the evolution of tribologically transformed layers (TTLs) beneath the wear tracks, originated from the sliding of microalloyed wheel steel against high-strength rail steel; as well as the influence of temperature on friction and wear mechanisms. The first study focused on the formation and evolution of TTLs beneath the contact. Ring-on-disc sliding wear tests were carried out in air, at room temperature, and under a very high normal load (8 kN), with AAR Class D wheel steel discs sliding against AREMA TR68 high-strength rail steel rings, over increasing sliding distances and at two sliding speeds. The results showed that the high-load tests produced TTLs with thicknesses comparable to those observed in serviced wheels flanges and rails, with TTLs over 100 µm thick formed even at short sliding distances (6 m). Significant subsurface hardening was observed on discs and rings at different sliding distances, with seizure occurring at 132 m, marked by a sudden increase in temperature and friction. The second study explored the role of temperature in the friction and wear of the aforementioned materials through pin-on-disc sliding wear tests in air, under a normal load of 24.6 N, and at three temperatures: 20 °C, 400 °C and 700 °C. These tests aimed to elucidate the effects of oxidation, thermal softening, and phase transformations on wear mechanisms. The results indicate that the coefficient of friction (COF) and wear rates vary significantly with temperature. At 400 °C, the lowest COFs were observed, as well as the lowest wear rate for the pins (rail), attributed to the formation of an oxide layer that mitigates asperity adhesion. At 700 °C, thermal softening due to decarburization of an upper layer immediately below the surface led to a significant increase in the wear rates on the discs (wheel), suggesting a transition in the wear regime between 400 °C and 700 °C.
- ItemAnálise da influência das tensões residuais na variação do comportamento do ruído magnético de Barkhausen em arames utilizados em dutos flexíveis(Universidade Federal do Espírito Santo, 2024-02-27) Feijó, Gabriel Fracalossi; Co-orientador1; https://orcid.org/; http://lattes.cnpq.br/; Co-orientador2; https://orcid.org/; http://lattes.cnpq.br/; Co-orientador3; https://orcid.org/; http://lattes.cnpq.br/; Co-orientador4; ID do co-orientador4; Lattes do co-orientador4; Orientador1; https://orcid.org/; http://lattes.cnpq.br/; Orientador2; https://orcid.org/; http://lattes.cnpq.br/; https://orcid.org/; http://lattes.cnpq.br/; 1º membro da banca; https://orcid.org/; http://lattes.cnpq.br/; 2º membro da banca; https://orcid.org/; http://lattes.cnpq.br/; 3º membro da banca; https://orcid.org/; http://lattes.cnpq.br/; 4º membro da banca; http://lattes.cnpq.br/; 5º membro da banca; https://orcid.org/; http://lattes.cnpq.br/; 6º membro da banca; https://orcid.org/; http://lattes.cnpq.br/; 7º membro da banca; https://orcid.org/; http://lattes.cnpq.br/Flexible pipelines are used in the oil industry to transport oil and gas, being considered an advantageous option for the challenges encountered in the exploration of deeper areas, such as the pre-salt. These ducts are made up of different layers, including the traction reinforcement, made up of steel wires, which are responsible for resisting traction, compression and radial loads applied to this component. Due to the application of complex stress modules, their failure modes can become unpredictable, therefore, verify their integrity becomes essential. The use of electromagnetic techniques presents itself as a good method for the non-destructive evaluation of these materials. The present work aims to present information that makes it possible to understand the influence of residuals stress on the behavior of Barkhausen magnetic noise. To do this, the residuals stress in the flexible tubes will be tested and correlated with the rotational parameters of the Barkhausen magnetic noise and the envelope behavior of this same method. To this end, in the experimental stage, the residual stress will be proven, using the hole drilling method, in the direction of bending transverse, bending and 45º bending transversal. Next, the Barkhausen magnetic noise rotation test will be carried out at frequencies of 50 Hz and 125 Hz. After the experimental part, the RMS parameters and the Barkhausen magnetic noise envelope will be analyzed and correlated with the variation in residual stress. It is worth mentioning that with plastic deformation there is the development of crystalline anisotropy, which also directly influences the results collected. Note that the rotational RMS presents a more objective characterization of crystalline anisotropy, while the Barkhausen magnetic noise envelope presents a better understanding of the residual stress variation in the tested samples but is a challenge to separating the influence of residuals stress in the envelope of magnetic noise in materials that present crystalline anisotropy