RAQUEL DE MORAES LOBO

RAQUEL DE MORAES LOBO

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Correlations of mechanical properties by SPT and conventional tensile test for stainless steel 316L
2024 - LOBO, RAQUEL de M.; MIRANDA, CARLOS A. de J.; FALOPPA, ALTAIR A.; LIMA, JOSE R. de; MATTAR NETO, MIGUEL; CAJA, FERNANDO
The Small Punch Test (SPT) method is an “almost non-destructive”[1] method by uses miniaturized samples to obtain mechanical properties of materials. It was development by nuclear industry to analyses mechanical behavior of irradiated materials principally by small volume of the samples, which facilitates their storage and handling. Its applications are spreading across several areas of materials engineering, 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)[2], 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 stainless steel (316 L) were abstained by two different methods: conventional tensile test and the small punch test (SPT), for comparing the results and allow the evaluation of the method. 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.
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.
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.
Fractography and failure mechanisms in cfrp tubes submitted to burst testing
2016 - LOBO, RAQUEL de M.; DIAS, ALDISON D.F.; MARINUCCI, GERSON; ANDRADE, ARNALDO H.P. de
The characterization of the failure mechanisms of CFRP components has been expanded as its demand for structural members in several applications increases.Composite tubular elements are used as biaxial structural components in applications where high mechanical performance per unit weight is a vital design requirement.In composite materials it is well known that the interface between fiber and matrix or interphases in those regions influences the overall composite properties.Crack propagation between plies (delamination) is the most commonly observed damage in CFRP since the fracture energy for cracking through the resin layer is lower than that for cracking through the fibers.Composite materials are known to display complex failure modes, typically involving multiple interacting damage processes, occurring over various length-scales. Fiber breaks occur in the micrometer range, whereas delaminations may occur over millimeter to meter scales, depending on the structure´s size and geometry.In recent years, quantitative fractography has become a method by which one can analyze the evolution of the interaction between crack and microstructure.Fracture morphology reveals that the dominant failure surface features were found to be fiber breakage, pull-out, and matrix cleavage and hackle formation resulting from interfacial tensile or shear failure.In the present work, specimens extracted from filament wound tubes subjected to burst test at room temperature were examined by optical and scanning electron microscopies in order to understand the failure mechanisms of such tubes.
Tensile properties characterization of an stainless steel tube for LBB evaluation
2015 - PAES de ANDRADE, ARNALDO H.; CUNTO, GABRIEL G. de; LOBO, RAQUEL de M.; MONTEIRO, WALDEMAR A.
In-situ SEM observations of Co-Cr alloys under deformation
2015 - LOBO, RAQUEL de M.; MORCELLI, APARECIDO E.; SOUZA NETO, DIOGENS C.; MONTEIRO, WALDEMAR A.; PAES de ANDRADE, ARNALDO H.
Obtaining pure praseodymium acetate to use in researches and development
2010 - QUEIROZ, CARLOS A. da S.; ROCHA, SORAYA M.R. da; PEDREIRA, WALTER R.; SENEDA, JOSE A.; LOBO, RAQUEL M.; S. FILHO, WALTER
This paper presents a simple and economical procedure to obtain high purity praseodymium acetate. The raw material in the form of mixed rare earths carbonate comes from a industrial separation of rare earths, thorium and uranium in the brasilian monazite. It is used the tecnique of strong cation exchange resin, proper to water treatment, to the praseodymium's fractionation and it is achieved a purity of 99.9% in Pr6O11 and yield greater than or equal 60%, with the elution of rare earths by EDTA solution in pH controlled. The complex of EDTA-praseodymium is transformed in praseodymium oxide, subsequently the oxide is dissolved in acetic acid to obtain the praseodymium acetate. The molecular absorption spectrophotometry tecnique is used to monitoring the praseodymium content during the process and mass spectrometry to certification the purity of the praseodymium acetate. The typical praseodymium acetate obtained presents the followings contaminants in micrograms per gram: Sc(18.20±0.22); Y (20.20 ± 0.20); La (6.75 ± 0.81); Ce (26.10 ± 0.70); Nd (3.31 ± 0.63); Sm (18.30 ± 0.80); Eu (17.00 ± 0.90); Gd (19.40 ± 0.40); Tb (16.30 ± 0.50); Dy (16.90 ± 0.50), Ho(17.90 ± 0.10); Er (18.40 ± 0.70); Tm (16.90 ± 0.10); Yb (17.60 ± 0.60); Lu (17.70 ± 0.50). The high purity praseodymium acetate comes being applied, replacing the imported product, in research and development area on rare earth catalysts.