http://repositorio.ufc.br/handle/riufc/500 2026-04-06T16:47:29Z http://repositorio.ufc.br/handle/riufc/85303 Título: Thermomechanical modeling and simulation of an electric arc welding process: a computacional analysis of the influence of the element birth and death techinique Autor(es): Costa, Mateus Andrade de Sousa Abstract: Arc welding plays a vital role in modern industry, particularly in the fabrication of complex structures and components. While the process is widely employed and relatively straightforward, it is not without challenges. Welding can introduce residual stresses, distortions, and defects into the material, potentially compromising structural integrity, increasing costs, and necessitating rework. To address these challenges, this study conducts a detailed thermomechanical analysis of the welding process, exploring computational modeling as a viable alternative to traditional experimental methods. The research employs ANSYS® software and the Finite Element Method (FEM) to simulate the thermal and mechanical behavior of materials under specific welding conditions. The study focuses on single-pass butt welding of plates and pipes, incorporating filler metals and utilizing the Element Birth and Death Technique (EBDT) to simulate material addition during welding. By examining different mesh element orders (linear and quadratic), the analysis evaluates temperature distributions, residual stresses, and deformations while also considering computational efficiency. The results revealed that EBDT increased test duration by 16.5%, and a significantly temperature difference (665ºC with EBDT vs. 348ºC without) during heat source passage. Mesh element order notably influenced outcomes: quadratic elements reduced the element count by 85%, balancing accuracy and computational efficiency, while refined linear elements increased execution time by up to 90%. For the heat-affected zone (HAZ), simulations without EBDT may suffice, but weld bead analysis requires further validation, particularly in multi-pass welding, where reheating alters stress distributions. The methodology was validated through comparisons with analytical, numerical, and experimental data available in the literature, confirming its robustness for structural analysis and process optimization. This research contributes to the theoretical understanding of arc welding, offering a computational framework that effectively balances precision and cost. The study lays a strong foundation for future investigations, especially in exploring the complexities of multi-pass welding. Tipo: Dissertação 2025-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/83941 Título: Weldabilty evaluation of corrosion-resistant alloy weld metals for high-temperature service in oil and gas industry using trans-varestraint test Autor(es): Sousa, Ana Beatriz Ferreira Abstract: The flare in the oil and gas industry is responsible for burning harmful gases, ensuring safety. Flares are commonly made of austenitic stainless steels (ASSs), which are highly recommended for application at high temperatures and in reducing/oxidising atmospheres. Despite this, several failure cases of ASS components utilised in oil and gas production and refining have been reported in the literature, mostly related to metallurgical phenomena occurring due to harsh operation conditions. The processes of fabrication and repair per welding may also cause failures once the welding leads to nonequilibrium solidification, microsegregation of alloy elements, and potential rejection of impurities from the solid toward the interdendritic liquid, which are critical factors for the occurrence of solidification cracking. Therefore, this work aimed to assess the weldability through Trans-Varestraint Test (TVT) of consumable electrodes which can be employed in the fabrication and repair of flare components. The welds were made with the shielded metal arc welding (SMAW) using three filler metals: the ASS electrodes AWS E310-15 and AWS E347-17 and the nickel-based alloy electrode AWS ENiCrFe-2. The ASSs AISI 310S and AISI 304H were applied as the base metals. The TVTs was performed with strain levels ranging from 0.5% to 8%. The weldability was evaluated based on the susceptibility of the weld metal to solidification cracking, which was determined through the critical strain, saturated strain, maximum crack length, maximum crack distance, total crack length, and critical strain speed. Additionally, samples of the fusion zones resulting from each welded combination were investigated by light optical microscopy and scanning electron microscopy, with a focus on correlating the microstructural characteristics to the resistance to solidification cracking. Electron backscatter diffraction (EBSD) analysis was used to determine the effects of stress applied during TVT on the microstructures of the weld metals. Considering all the results analysed, the ranking from least to most susceptible to solidification cracking was as follows: (AISI 310S + AWS E347-17) > (AISI 304H + AWS E347-17) > (AISI 304H + AWS E310-15) > (AISI 310S + AWS E310-15) > (AISI 310S + AWS ENiCrFe-2) > (AISI 304H + AWS ENiCrFe- 2). The weld metals most resistant to solidification cracking resulted from the tests with the AWS E347-17 electrode, for which solidification occurred in the primary ferrite/secondary austenite mode. These fusion zones consisted of a combination of austenite and δ-ferrite, and the presence of δ-ferrite is known to be beneficial for preventing solidification cracking. The welds with the AWS E310-15 electrode solidified in the fully austenitic mode, which is favourable for solidification cracking. The fusion zones of tests using the AWS ENiCrFe-2 filler metal were composed of the γ-Ni fcc phase, and evidence of the precipitation of Nb(C,N) was found in the interdendritic volumes. The formation of secondary phases may have some influence on the cracking propensity, explaining the lower resistance to solidification cracking of these weld metals. The EBSD results showed higher misorientation levels surrounding the cracks and on subgrain boundaries. This may be attributed to the severe deformation level at which the microstructure was subjected to cracking. The regions where dislocations accumulate eventually became subgrain boundaries. Tipo: Dissertação 2024-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/83332 Título: Avanços no desenvolvimento de ligasproduzidas "in-situ" pelo processo soldagem MIG/MAG duplo arame Autor(es): Andrade, Izaac Oliveira Abstract: This study aimed to develop specific alloys by combining the nickel-based alloys Hastelloy C-276 and Inconel 625, applying welding techniques to minimize macrosegregation. Three compositions were produced: 50%H/50%I, 70%H/30%I, and 30%H/70%I. The electrode with the highest deposition rate operated in pulsed mode, while the one with lower contribution operated in short-circuit mode. Pulse parameters were evaluated for all alloys, while in short-circuit mode, the variables Ks, Kd, and Ur were analyzed. The total wire feed speed was kept constant. An exploratory analysis was also conducted regarding electrode arrangement (leading/following) and weaving parameters (speed, frequency, and amplitude), assessing alloy mixing and bead geometry. In the overlay welds, the influence of electrode distance on macrosegregation formation was also investigated. The samples were subjected to chemical, microstructural, and mechanical characterization, including Vickers microhardness, Charpy impact, and tensile tests. The results indicated that it is possible to produce alloys with controlled chemical compositions by properly adjusting the welding parameters according to the intended application. The pulsed and short-circuit modes were optimized to achieve weld beads with good surface finish and without defects. Electrode arrangement did not significantly affect homogenization, but metal transfer mode influenced the bead appearance: when both wires operated in pulsed mode without weaving, distinct color regions were observed (50%H/50%I), while in the mixed mode (pulsed/short-circuit), the weld presented a homogeneous appearance. Increasing weaving frequency, but especially amplitude, improved alloy mixing. Electrode distance showed no significant effect on segregation. Chemical analyses confirmed that the obtained compositions were close to the theoretical ones, and with adequate welding parameters it was possible to avoid macrosegregations. The resulting microstructure exhibited a Ni-FCC matrix, predominantly with columnar and cellular dendritic growth. Regarding mechanical properties, microhardness varied statistically among the alloys, with average values around 260 HV for the alloy with higher Inconel 625 content. Impact toughness showed no significant differences, with average absorbed energy values of about 150 J. In tensile tests, all alloys demonstrated mechanical performance close to commercial Inconel 686, confirming that twin-wire MIG/MAG welding is a viable route for in situ alloy production, eliminating the need for casting or less conventional techniques. Tipo: Dissertação 2025-01-01T00:00:00Z http://repositorio.ufc.br/handle/riufc/82198 Título: Análise das variáveis do processo de fabricação para a obtenção de produtos cerâmicos a partir de argilas do município de Russas - Ce Autor(es): Regis, Rafaella Cavalcante Abstract: The ceramic interlocking pavement, also known as paver, is a product widely used in the international market but not well known in Brazil. It has high added value and the potential to boost the development of the Local Productive Arrangement of Red Ceramics in Russas, located in the State of Ceará. This study aims to evaluate the influence of compaction load and sintering temperature on the production of ceramic pieces from clay masses in the region, with the goal of manufacturing pavers that meet international application standards regarding mechanical, physical, and aesthetic properties. The raw materials used are clays from the municipality of Russas/CE, the central city of the mentioned LPA. The clays were subjected to mineralogical, chemical, and physical characterization using techniques such as energy- dispersive spectroscopy (EDS), scanning electron microscopy (SEM), optical microscopy, x- ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG/DTA), granulometric analysis, and determination of the plasticity index. Test specimens were produced in the laboratory by pressing at 5 kN, 10 kN, and 12.5 kN, and fired at temperatures of 910 °C, 930 °C, 950 °C, and 990 °C. The ceramic samples were characterized for their physical properties, including linear shrinkage, apparent specific mass, porosity, and water absorption, as well as their mechanical properties, such as compressive strength, flexural strength, and abrasion index, and their microstructure, using SEM and XRD. The data were statistically evaluated using ANOVA (analysis of variance) and the Tukey test. The results indicate that, according to Colombian and American standards, the ceramic pieces produced in this study are suitable for light traffic pavements. The analysis of the results shows that the test specimens sintered at 910 °C with a compaction load of 5 kN have physical and mechanical properties comparable to or superior to samples sintered at higher temperatures. These pieces can be classified as type II, for intermediate abrasion areas, and type III, for low abrasion environments. Thus, the results confirm the feasibility of producing ceramic pavers for light traffic roads, with medium and low abrasion resistance. Tipo: Dissertação 2024-01-01T00:00:00Z