https://repositorio.ufu.br/handle/123456789/19223 2026-09-22T14:01:11Z https://repositorio.ufu.br/handle/123456789/50294 Title: Avaliação da diluição de aço inoxidável ER308LSi depositado em aço carbono SAE1020 via manufatura aditiva por deposição a arco Abstract: Wire arc additive manufacturing (WAAM) has become a viable alternative to produce medium and large-scale metallic components, offering high deposition rates and reduced material waste. When applied to dissimilar material pairs, however, the mixing between filler metal and substrate during weld pool formation changes the first layers’ chemical composition, affecting the microstructure and mechanical properties. This work aims to study the chromium and nickel dilution along the build direction in an ER308LSi austenitic stainless steel preform deposited on carbon steel substrate by WAAM. The preform cross-section was analyzed by macrography, optical microscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy microanalysis and Vickers microhardness testing. The penetration of the first bead into the substrate was 2.8 mm. The compositional profile revealed an abrupt transition at the interface, followed by a plateau of constant composition extending over 3.0 mm, with average contents of 13.22 % chromium and 5.99 % nickel, and by progressive enrichment up to 17.86 % chromium and 7.83 % nickel at the top of the preform. Dilution estimated by mass balance ranged from 32 to 46 % in the first bead, decreasing to between 9 and 30 % at the top. The microhardness profile followed the compositional profile, with a marked increase in the diluted region, attributed to the loss of austenite stability caused by the reduction in nickel content and the consequent formation of martensite, an interpretation supported by the Schaeffler diagram. It was further observed that the microstructural boundary, defined by the hardness drop, lies approximately 0.9 mm above the compositional boundary, a lag consistent with the fact that austenite stability is governed by nickel content. 2026-08-07T00:00:00Z https://repositorio.ufu.br/handle/123456789/50113 Title: Aumento de potência com baixo custo através de indução forçada com turbocompressor centrífugo em motor da década de 90 Abstract: The average age of the Brazilian vehicle fleet has been steadily increasing, which sustains a significant market for modifying vehicles from the 1990s and 2000s for recreational use. Engines from this period, designed as naturally aspirated units, have their power output limited by the intake air mass flow rate, a constraint that can only be overcome by increasing intake air density. This work presents the design, fabrication, installation and calibration of a forced induction system based on a centrifugal turbocharger applied to a BMW M50B25TU engine, converted to hydrous ethanol and managed by a Speeduino open-source programmable engine control unit, aiming to double the original power output and sized for an intake gauge pressure of up to 100 kPa. The use of components available on the Brazilian used- parts market was adopted as a cross-cutting design constraint, in order to ensure low cost and replicability. The sizing procedure covered the fuel system, the compressor, the turbine housing, the wastegate valve, the exhaust manifold, the pressurised piping and the intercooler, with analytical verification of each component. Tests were carried out on an inertial roller dynamometer developed during the project, across four successive configurations: baseline, ethanol and programmable engine management conversion, boosted operation at 25 kPa, and boosted operation under electronic boost control. A progressive performance improvement was observed, rising from 201.3 hp and 261.2 N·m in the baseline configuration to 409.2 hp and 489.7 N·m in the final configuration. Ignition timing was maintained at maximum brake torque under all wide-open-throttle conditions, with no knock limitation, confirming the margin provided by hydrous ethanol in an engine with a 10:1 compression ratio. The first failure observed was clutch slippage, a non-destructive failure mode anticipated during the design phase. The metrological limitations of the dynamometer are discussed, whose evidence of overestimation restricts the validity of the results to relative comparison between configurations. 2026-08-13T00:00:00Z https://repositorio.ufu.br/handle/123456789/50104 Title: Usinagem de materiais fabricados por manufatura aditiva por deposição de arco (MADA) com e sem alívio de tensão Abstract: Additive manufacturing has established itself as one of the main technologies of Industry 4.0, enabling the production of metal parts through controlled layer-by-layer material deposition. Among the different processes, the use of arc welding techniques, such as MIG/MAG, stands out, enabling the manufacture of medium and large components with a high deposition rate. However, due to the intrinsic characteristics of the process, in which the resulting irregular surface, wide tolerances and poor finishing, subsequent machining operations are necessary to ensure better accuracy and finishing or workpieces. This work aimed to evaluate the machinability of two tubes manufactured by additive manufacturing using the MIG/MAG process with A5.28 ER90S-B3 wire with a 90 mm diameter x 120 mm length x 9 mm thickness. One of the workpieces was subjected to a residual stress relief test using the post-deposition vibration method. The same machining parameters were used for both parts. Two cutting speeds (vc) were varied (56 m/min and 140 m/min). Feed and depth of cut were kept constant in all tests (f = 0.05 mm/rev. and ap = 0.5 mm). Test were carried out with coolant. To evaluate the surface integrity of workpieces, the roughness (Ra and Rt), microhardness and microstructure below the machined surface were analyzed. Tool wear was also monitored. The results showed that the part subjected to post-treatment by vibration presented lower surface roughness values. For a cutting speed of 56 mm/min, there was a 27% reduction in the Ra parameter, while for 140 mm/min the reduction was 47%. As for microhardness, post-stress relief treatment contributes to a decrease in the average hardness of the deposited and stress-relieved sample, dropping from 306 HV (conventional deposition) to 271 HV (vibration stress relief). However, after the turning processes, the average hardness of the conventionally deposited sample increased regardless of the cutting speed. A lower tool wear rate was observed after machining the part subjected to stress relief treatment, reinforcing the potential of the technique as a viable alternative for improving machinability of the material made by MA tested in this work. 2025-12-18T00:00:00Z https://repositorio.ufu.br/handle/123456789/50067 Title: Avaliação da eficiência térmica de caldeiras em regime de carga parcial e plena por métodos direto e indireto via modelagem computacional Abstract: This work aims to analyze, through computational modeling, the influence of boiler operating load on the thermal efficiency of a biomass-fired boiler, evaluating this behavior using both the direct and indirect methods of efficiency determination. To this end, a model was developed in EES (Engineering Equation Solver) software, based on energy balances, a stoichiometric combustion balance derived from the fuel's elemental analysis, and the formulations established in the literature for the direct and indirect methods of boiler efficiency calculation. Four load levels were simulated (100%, 60%, 30%, and 10% of nominal capacity), with operating parameters, excess air, flue gas temperature, and CO contente, obtained from published experimental data for a biomass grate boiler, ensuring greater adherence of the model to real operating conditions. The results showed that thermal efficiency undergoes significant degradation under low-load conditions, particularly below 30% of nominal capacity, and that this relationship is not strictly monotonic, exhibiting non-linear behavior at intermediate loads due to the interaction between increasing excess air and varying flue gas temperature. The comparison between methods showed good numerical agreement between them, while also reinforcing that the indirect method is more suitable for solid fuels such as biomass, since it does not require direct measurement of fuel flow rate and allows individual identification of which loss mechanism is responsible for efficiency degradation under each load condition, with radiation and convection losses identified as the mechanism most sensitive to load reduction. Finally, a gap was identified in the literature regarding the quantitative variation of operational combustion parameters as a function of load for biomass boilers, suggesting as a proposal for future work the conduction of an experimental measurement campaign on a real boiler, in order to validate and refine the relationships adopted in this study. 2026-08-06T00:00:00Z