RAQUEL DE MORAES LOBO

RAQUEL DE MORAES LOBO

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Correlations of mechanical properties by SPT (Small Punch Test) and conventional tensile test for Al 6061 – T6
2023 - LOBO, RAQUEL de M.; CASTAGNET, MARIANO; MIRANDA, CARLOS A. de J.; FALOPPA, ALTAIR A.; LIMA, JOSE R. de; MATTAR NETO, MIGUEL; PEREIRA, LETICIA dos S.; ANDRADE, ARNALDO H.P. de
The Small Punch Test (SPT) was development by nuclear industries to analyses mechanical properties of irradiated materials principally by small volume of the samples. This technique intend to evaluate the materials behavior during the time life of nuclear reactors, where yours properties changed by irradiation intensity and exposition time. It is considered an almost ¨non-destructive” method [2] due to small sample volume and its applications are spreading for use in situations where conventional methods do not apply. SPT consists of pressing a sphere, with a diameter equal to 2.5 mm, in a miniaturized sample of circular geometry (diameter d = 8 mm and thickness about 0.5 mm)[1], which has fixed edges, tested in conventional mechanical testing machines with the aid of a device developed for their achievement. In this work, mechanical properties of aluminum (Al 6061-T6) were abstained by two different methods: conventional tensile test and the small punch test (SPT). The SPT results depends on graph interpretations and discussions take place at now. Correlations of results guide us in choosing the most appropriated method for interpreting the force x displacement graph from SPT.
The use of miniaturized samples to determine mechanical properties of materials
2022 - LOBO, RAQUEL de M.; CASTAGNET, MARIANO; MIRANDA, CARLOS A. de J.; LIMA, JOSE R. de; FALOPPA, ALTAIR A.; MATTAR NETO, MIGUEL; PEREIRA, LETICIA dos S.; ANDRADE, ARNALDO H.P. de
The caracterization of irradiated materials through the SPT (Small Punch Test) technique uses miniaturized samples, with 8 mm in diameter and 0.5 mm in thickness, which has fixed edges, pressed by a sphere that has a diameter d=2.5 mm[1], tested in convencional mechanical testing machines, with the aid of a device developed for their achivement. This tecnique developed for nuclear industry can be used where conventional methods do not apply because it is considered an almost “non-destructive” method[2]due to the small sample volume. In this work two different devices were developed to perform tests at room and sub-zero temperature. The SPT tests will be carried out on standardized nuclear materials unirradiated (ferritic and stainless steels) for later correlation with conventional mechanical tests. Several mechanical properties will be obtained such as yield stress, tensile strength and fracture properties of the materials such as its toughness.
Small punch tests with a recently developed device in IPEN
2021 - MIRANDA, C.A.J.; ANDRADE, A.H.P. de; CASTAGNET, M.; LOBO, R.M.; FALOPPA, A.A.; MATTAR NETO, M.; LIMA, J.R.; PEREIRA, L.S.
Small punch test devices in development at IPEN aiming to perform tests in RMB hot cells
2021 - MIRANDA, C.A.J.; LIMA, J.R.; FALOPPA, A.A.; ANDRADE, A.H.P. de; MATTAR NETO, M.; CASTAGNET, M.; LOBO, R.M.; PEREIRA, L.S.
Numerical analysis of the small punch test for different theoretical materials
2021 - PEREIRA, L.S.; MATTAR NETO, M.; MIRANDA, C.A.J.; LIMA, J.R.; FALOPPA, A.A.; ANDRADE, A.H.P. de; CASTAGNET, M.; LOBO, R.M.
Slant fracture surface in 7075 aluminum alloy tensile specimens
2017 - LOBO, RAQUEL de M.; MORCELLI, APARECIDO E.; SOUZA, SAUL H.; PADILHA, ANGELO F.; ANDRADE, ARNALDO H.P. de
Rectangular specimen of a 7075 aluminum alloys in three different thermal treatment conditions were tested in a tensile equipment. The samples tested exhibit slant fracture surfaces. Some of the samples presented Portevin-Le Chatelier (PLC) effect. In fact, for aluminum alloys, the PLC phenomenon may occurs even at room temperature. It leads to strain localization and deformation band formation. In this work, the occurrence of slant fracture is studied by scanning electron microscopy and an attempt is done to correlate their presence with the PLC bands.
Mechanical anisotropy of ABS specimens 3D printed by FDM
2019 - ANDRADE, ARNALDO H.P. de; LOBO, RAQUEL de M.; BREDA, FRANCISCO J.; CASTAGNET, MARIANO
Additive manufacturing (AM) has been developed as a technique for fast fabrication of component parts through 3D printing, using a process of adding successive layers, one after another. The Fused Deposition Modeling (FDM) technique is a 3D printing process that generally uses a thermoplastic filament as the printing base material. The material is fed by a coil and the head of the extruder performing the process is heated. Printing can be done in several directions, depending on the purpose of the component part. In this work mechanical tests were done on ABS (Acrylonitrile-Butadiene-Styrene) tensile specimens built by FDM, in different orientations, to analyze its properties and to make a correlation between these properties and the influence of the printing direction in the final product. The tensile specimens in dog bone shaped were tested according to the ASTM D638 standards. The experiments were done at room temperature. The horizontal built specimens (H-specimens), fabricated in the z-direction, while the beads were layered along the x and y direction, parallel to the build table, showed the maximum resistance of 30 MPa. The specimens built with their gage length out of x-y plane (V-specimen and D-specimen, vertical and diagonal specimens respectively) presented lower ultimate strength, for instance 14 MPa for the Vspecimen. Additional investigation is on the way to understand the presence of defects (cavities and crazes) in the ABS microstructure since the literature points that the ability to manipulate it is the key to an improved performance of this type of structural material.
Fracture surface analysis of ABS samples printed by the FDM method
2019 - LOBO, RAQUEL de M.; MORCELLI, APARECIDO E.; BREDA, FRANCISCO J.; CASTAGNET, MARIANO; ANDRADE, ARNALDO H.P. de
FDM (Fused Deposition Modeling) is one of the most used technique in additive manufacturing (AM). It can be summarized as printing small components through a heated thermoplastic filament, which is deposited layer by layer through a 3D printer. The print head can be programmed to perform the job in different directions (X, Y and Z) even with predetermined slopes. In this work, flat tensile specimens were prepared in different directions using an ABS (Acrylonitrile-Butadiene-Styrene) filament with a processing temperature between 210-225 ° C. After tensile tests, the fracture surfaces were analyzed to get a better understanding of the deformation and fracture processes. The crosssection view of specimen´s morphology was examined with a scanning electron microscope at a very low accelerating voltage (1 kV). The specimens were coated with gold using a sputtering system. The specimens that showed the smaller ultimate strength (named V-specimen) presented numerous large cavities in its microstructure suggesting that these voids may have a major contribution to the mechanical performance of the material.The fracture surface also shows a possible pull-out between layers indicating a weak point in the microstructure of the built sample that’s requires further investigation.
Advances in the understanding of the mechanisms of iodine-induced SCC cracking in zirconium alloys
2019 - LOBO, RAQUEL de M.; ANDRADE, ARNALDO H.P. de
In pressurized water reactors (PWR) the fuel rod cladding is the first barrier against the spread of fission products. It is therefore essential to guarantee its use in the reactor. Sometimes the production of electricity requires that certain power plants operate in “network monitoring”. The fuel introduced into nuclear power reactors can then undergo so metimes significant power variations. Following a severe reactor power transient, clad failure can occur through a stress corrosion phenomenon (SCC), under the combined action of mechanical stresses and gaseous fission products generated by the fuel pellets. Among those iodine plays a major role, for it may induce SCC in zircaloy. In the early ages of water cooled reactors (PWRs, BWRs or CANDU), series of similar failures took place following sharp startups. Today power increase rates as well as instantaneous local power levels are limited. Indeed, it is well know that cladding failure by iodine induced stress corrosion cracking (I SCC) may occur under pellet cladding interactions (PCI) conditions during power transients in PWRs. In this paper we review the advances in the understanding of these SCC cracking mechanisms of the fuel rod cladding that would then allow better control of the integrity of the clad during the more severe demands related to the operating conditions of th e PWRs.
Monitoring of the ductile to brittle transition temperature of reactor pressure vessel steels by means of small specimens
2019 - ANDRADE, ARNALDO H.P. de; MIRANDA, CARLOS A.J.; LOBO, RAQUEL de M.
Neutron irradiation in nuclear power plants (NPPs) lead to microstructural changes in structural materials which induce a shift of the ductile to brittle transition temperature (DBTT) towards higher temperatures. Monitoring of the DBTT in NPP components receives therefore considerable attention. Small specimen testing techniques are developed for characterizing structural components with a limited amount of materials. One of the most used of these miniature testing is the small punch test (SPT) which is based on disc or square shaped specimens. SPTs may be performed from room to cryogenic temperatures, plotting the absorbed energy until rupture, against the test temperature. A ductile region (high energy) and a brittle region (low energy) with a transition between both zones are usually reported. The transition temperature thus obtained, DBTTSPT, is also related through empirical expressions to the transition temperature obtained in CVN tests, DBTTCVN, or in fracture toughness testing. Linear expressions such as DBTTSPT = α DBTTCVN have been used where α is a material characteristic constant. In all cases, the DBTTSPT temperature is much lower than that obtained in the CVN tests. In this paper, we present a short review of the literature on the determination of the DBTT for nuclear reactors pressure vessels steels by those two techniques analyzing the reason for the difference in their value as mentioned before. In dealing with irradiated materials, is a high priority to limit the exposure of the professional to irradiation. Therefore, the use of miniature specimens receives significant attention in the nuclear community. The high cost of irradiation experiments is a further incentive for using small specimen testing techniques.