Engenharia Mecânica
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/23
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10 resultados
Resultados da Pesquisa
- Surface integrity and residual stresses analysis by strain gages after hard turning process of case hardened steel aisi 8620(2010) Farias A.; Delijaicov S.; De Mello J.D.B.; Filho M.S.; Batalha G.F.This work aims an analysis on the functional surface integrity resulting from turning mechanical components manufactured from case hardened steel AISI 8620 with 1 millimeter average layer depth and hardness of 58-62HRC. A cBN tool with PVD coat and Wiper geometry-edge was used for continuous turning of hardened steel, the cutting conditions (Vc [m/min] and f in [mm/rev]) used were concerned to reflect large running production of mechanical components. © (2010) Trans Tech Publications.
- The sheet metal formability of AA-5083-O sheets processed by friction stir processing(2015) Miori G.F.; Bordinassi E.C.; Delijaicov S.; Batalha G.F.© 2015 G. F. Miori et al.The aim of this study is to determine the sheet metal formability of AA-5083-O sheets processed by the Friction Stir Processing (FSP). The FSP process was studied and a FSP tool was built. Processing quality was verified by the metallography in the processing region, which established the voids presence. Tensile tests were carried out on FSP and non-FSP specimens, and the results showed that FSP specimens have 30% greater resistance than non-FSP ones. The formability of FSP sheets was produced in MSC-MARC and Abaqus and these software products were compared by using the nonlinear FEM code. The Forming Limit Diagram was built with the results from both software products. A device to process FSP sheet metals was developed and the sheets were processed to validate the results from the software. The tools made for the bulge tests were circular and ellipse-shaped. After the bulge tests, the commercial sheets showed close approximation to those obtained from the software. The FSP sheets broke when inferior pressure was applied because of the defects in the FSP process. The results of the FSP presented the same formability of commercial sheets, however, with 30% greater strength.
- Surface integrity analysis in the super duplex stainless steel ASTM-A890 after machining(2008) Bordinassi E.C.; Stipkovic M.F.; Batalha G.F.; Delijaicov S.; De Lima N.B.The purpose of this paper was to study the main effects of the turning in the superficial integrity of the duplex stainless steel ASTM A890-6A. The tests were conducted on a turning centre with carbide tools and the main entrances variables were: tool material class, feed rate, cutting depth, cutting speed and cutting fluid utilisation. The answers were analysed: microstructural analysis by optical microscopy and x-ray diffraction, cutting forces measurements by a piezoelectric dynamometer, surface roughness, residual stress by x-ray diffraction technique and the microhardness measurements. The results do not show any changes in the micro structural of the material, even when the greater cutting parameters were used. The smaller feed rate (0.1 mm/v), smaller cutting speed (110 m/min) and the greater cutting depth (0.5 mm) provided the smaller values for the tensile residual stress, the smaller surface roughness and the greater microhardness. Copyright © 2008 Inderscience Enterprises Ltd.
- Tool wear evaluations in friction stir processing of commercial titanium Ti-6Al-4V(2013) Farias A.; Batalha G.F.; Prados E.F.; Magnabosco R.; Delijaicov S.This research addresses the application of friction stir welding (FWS) of titanium alloy Ti-6Al-4V. Friction stir welding is a recent process, developed in the 1990s for aluminum joining; this joining process is being increasingly applied in many industries from basic materials, such as steel alloys, to high performance alloys, such as titanium. It is a process in great development and has its economic advantages when compared to conventional welding. For high performance alloys such as titanium, a major problem to overcome is the construction of tools that can withstand the extreme process environment. In the literature, the possibilities approached are only few tungsten alloys. Early experiments with tools made of cemented carbide (WC) showed optimistic results consistent with the literature. It was initially thought that WC tools may be an option to the FSW process since it is possible to improve the wear resistance of the tool. The metallographic analysis of the welds did not show primary defects of voids (tunneling) or similar internal defects due to processing, only defects related to tool wear which can cause loss of weld quality. The severe tool wear caused loss of surface quality and inclusions of fragments inside the joining, which should be corrected or mitigated by means of coating techniques on tool, or the replacement of cemented carbide with tungsten alloys, as found in the literature. © 2012 Elsevier B.V..
- Effect of weld parameters on residual stress, hardness and microstructure of dissimilar AA2024-T3 and AA7475-T761 friction stir welded joints(2018) Delijaicov S.; de Oliveira Silva P.A.; Resende H.B.; Batalha M.H.F.© 2018 Universidade Federal de Sao Carlos. All Rights Reserved.This study presents the effect of the welding parameters variation on the results of forces, temperature, residual stresses and Vickers micro hardness of dissimilar butt joints of AA2024-T3 and AA7475-T761 welded by friction stir welding (FSW). The tool rotational speed, feed rate and tool tilt angle were investigated using the Design of Experiments method. The obtained results of penetration force, temperature in the weld zone compared with the microscopic analysis of the microstructure showed that it is necessary a minimum amount of force and heat input to obtain a defect free weld zone. It was also notable that, friction stir welding has a wide stability range of its most significant parameters - rotational speed and feed rate - which grantee this minimum condition. Micro hardness’ profiles showed the effect of the grain size refinement towards the thermo-mechanically affected zone as well as, the effect of recrystallization inside the nugget. Residual stresses’ profiles showed a tensile stress peak at the shoulder contact area due the pressure with the base material on thermo-mechanically affected zone and the stress relief effect caused by high temperatures in the nugget resulting in a decrease in residual stress value. The most significant variables for residual stress results were rotational speed of the tool and welding feed rate, once their interaction rule the heat input in the weld zone.
- Stress relief by sub-harmonic vibrations: Analysis and parametrization Alívio de tensões por vibrações sub-ressonantes: Análise e parametrização(2018) Martins C.A.P.; Morilla J.C.; Marques P.V.; Delijaicov S.© 2018, Universidade Federal do Rio de Janeiro. All rights reserved.The worldwide industries use the sub-resonant vibration stress relief for over twenty years. In Brazil, this technic has been used for about fifteen years. In the last years, with the searching of new alternatives process aiming energy economy with consequently the Global Heating reduce, the use of this technique can be very interesting. Moreover, the time reduction between vibration and thermal stress relief processes is around 80%, allowing a faster repairing pieces, which is prime factor to make a maintenance stop in a short time. Meanwhile, the scientific literature is rare about the use and the efficacy of this system. This work has the propose of comparing the results of sub-harmonic stress relief process with conventional thermal process and correlate them to the decrease of the resonance peak frequencies, comparing before and after treatments. This work introduces some examples of successful works made at industry and presents an experimental research to measure the residual stress, before and after the treatment, comparing to the conventional heat treatment results. This work shows generally the stress relief by sub-resonant vibrations in the 0.2 mm depth, promotes stress relief on average 10% higher when compared with the results obtained by the conventional heat treatment.
- Characterization of the surface and mechanical properties of the friction stir welding in tri-dissimilar joints with aluminum alloys and titanium alloy(2018) Delijaicov S.; Yakabu D.Y.; De Macedo B.; Resende H.B.; Batalha M.H.F.© 2017, Springer-Verlag London Ltd., part of Springer Nature.The search for lighter and more resistant structures contributed to the development of effective welding methods. Among them, friction stir welding, a recent technique patented in 1991, in which welding is performed by the friction between a rotating tool and the materials to be welded, has widely been studied in the last decades. Among the advantages the technique provides, are the possibility of welding aluminum alloys series 2xxx and 7xxx, and the possibility of welding materials of different chemical compositions. The industry is still cautious about using this technique, yet several studies have been performed to improve knowledge on it. This research investigated the three dissimilar junctions between aluminum alloys 2024-T4 and 7475-T6 with titanium alloy Ti6Al4V. The aluminum alloys were positioned on the top portion of the welding creating a butt weld. The titanium alloy was placed on the bottom portion of the weld creating a lap welding with the aluminum alloy. The parameters of rotation, welding speed, and tilt were varied, following a central composite experimental design. Through the response surface analysis, it was possible to identify the correlation between the input and output parameters. This correlation is used to identify main influence between the parameters and can be used to optimization of the process. The influences of these parameters were evaluated on the welding surface by measuring residual stress and microhardness. The residual stress was analyzed by the hole drilling method on the aluminum side and by X-ray diffraction on the titanium side. The microhardness was analyzed by the Vickers test. On the aluminum side, residual stress and microhardness show a strong relation; high value of residual stress resulted in low value of microhardness. On the titanium side, residual stress shows a relation with temperature; the high value of temperature resulted in low value of stress. The tensile test was used to compare joint efficiency between different welding parameters and the base metal. It was possible to reach parameters in which the welding ultimate tensile stress exceeded the AA2024 value.
- The influence of turning parameters on surface integrity of nickel alloy 625(2018) Loureiro D.; Diniz A.E.; Farina A.B.; Delijaicov S.© IMechE 2016.Nickel-based alloys are used in industrial sectors where high mechanical strength and corrosion resistance are required at high temperatures. However, these alloys have low machinability as a consequence of inherent properties. Some of these properties such as high cold work hardening rate and low heat conductivity may cause damages to the machined surface. Among the nickel-based alloys, one that has good properties for oil exploration is alloy 625. As the components made of this alloy are frequently used in very rough environments, this study sought to evaluate the influence of tool geometry, cutting conditions (feed and cutting speed) and tool condition (fresh or worn) on the surface integrity of turned alloy 625 parts in order to discover turning practices for this alloy that result in minimal damage to the workpiece surface. A secondary aim was to evaluate how these input variables affected the life of the coated carbide tools used in the turning experiments with this alloy. The main conclusions are that (a) the surfaces produced with a fresh tool with positive geometry had compressive residual stresses, while those produced with negative tool geometry had tensile residual stresses and (b) when a worn tool was used all the surfaces produced had compressive residual stresses.
- Effect of the hardening rules on the creep age forming prediction of 7050 aluminum alloy with experimental verification(2018) Oliveira M.C.; Delijaicov S.; Bortolussi R.© 2018, The Brazilian Society of Mechanical Sciences and Engineering.The creep age forming (CAF) has been used in the aerospace sector due to its attractive characteristics that allows producing a component with low residual stress. The process has been studied from the finite-element simulations which are used mainly to predict the springback. However, to accomplish the simulation, it is necessary to set the CAF constitutive equations in the finite-element software. In addition, it is also necessary to define the hardening rule which is applied to determine the creep strain. This work aims to investigate CAF applying the finite-element analysis with the time-hardening rule and strain-hardening rule and thus predicting creep strain, stress relaxation, and springback. The finite-element simulations were accomplished in dies with single and double curvatures and the blank’s material was the alloy AA7050. Furthermore, the Marin–Pao model was implemented in the MSC.Marc software through a user subroutine. This model was fitted to the creep experimental curves and it generated good agreement with the experimental data. The results of the simulations that used the time-hardening rule were similar to the strain-hardening rule, and therefore, if it had been chosen a hardening rule, it would not have generated a significant impact in the CAF simulation results. At the end, the simulated springback was compared to the experimental springback from the literature and the percentage error ranged from 0.46% to 15.33% that indicate the proximity with the literature data. Moreover, other experimental validation was performed, and when compared to the results of this methodology, the calculated error in springback was 6.3%.
- CAF—a simplified approach to calculate springback in Al 7050 alloys(2017) Brandao F.M.; Delijaicov S.; Bortolussi R.© 2017, Springer-Verlag London.Aeronautical industries have looked for news fabrication processes to reduce the costs and the waste of the material during milling operations. One of these new processes is the creep age forming (CAF). The purpose of this work was based on springback analysis during the forming of single- and double-curved sheets of Al 7050 by the process of CAF. A simplified model based on a Norton power law was used in order to, alongside with a program of finite elements, allow the calculation of springback after the process. The experimental verification was carried out. Beside the springback results, other results were a decrease in the Young’s module of 11.5% in the creep aging temperature, in relation with ambient temperature during the CAF process and the variation of aluminum alloy’s yield stress during the process. The springback effect increased on the basis of aging time and then decreased due to intense aging of the alloy; an ideal time of 8 h is estimated for the Al 7050 alloy to carry out the CAF process. The research is limited to the use of the simplified model and its applicable results to Al 7050 alloys. Al 7050 is aligned with its vast use in the aeronautical industry, and the simplified model’s application may rapidly offer the necessary values of springback for the tooling project.