RENE RAMOS DE OLIVEIRA

RENE RAMOS DE OLIVEIRA

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Influência da nitretação por plasma sobre as propriedades de fadiga da liga TI-6AL-4V
2018 - CASTRO, M.C.B. de; COUTO, A.A.; ALMEIDA, G.F.C.; LIMA, N.B.; CASTAGNET, M.; OLIVEIRA, R.R.
As falhas por fadiga na liga Ti-6Al-4V ocorrem pela aplicação de tensões flutuantes, onde as tensões responsáveis pela falhasendo estas são menores do que a tensão de escoamento da liga. , caracterizando essas falhas como catastróficas e sem aviso prévio. A fadiga é responsável por pelo menos 90% das falhas por causas mecânicas, cCom o objetivo de aumentar a resistência a fadiga, foi realizada ao o tratamento termoquímico de nitretação por plasma. A nitretação por plasma é caracterizada pela formaçãoforma de uma camada superficial de nitretos na superficie da liga constituída (pelas fases δ-TiN e Ɛ-Ti2N). A formação dessas fases além de aumentar a sua dureza superficial, cria uma alta tensão superficial de compressão, fazendo com que as tensões trativas necessárias para ocorrer a formação de trincas sejam superiores. Testes de fadiga do tipo flexo rotativas foram realizados nos corpos de prova nitretados e não nitretados, a fim de se comparar a eficiência do tratamento termoquímico. O ensaio de fadiga foi realizado a uma frequência de 50 hz, e razão de carregamento R=-1, variando tensões de 610 a 203 MPa. Foram contados o número de ciclos necessários para as fraturas dos corpos de prova, e os resultados foram plotados em uma curva S-N. Após a fratura dos corpos de prova, suasAs superfícies de fratura foram analisadas em um microscópio eletrônico de varredura (MEV).O comportamento em fadiga das ligas nitretadas foi superior ao das ligas não nitretadas. Conclui-se que quanto após a nitretação por plasma, quanto maior a tensão aplicada ao ensaio, maior é a diferença de resistência entre a liga nitretada e a não nitretada, sendo esta diferença diminuída com a redução da tensão. Para altas tensões a liga nitretada apresentou cerca de 5x mais resistência à fadiga. Palavras chave: Liga Ti-6Al-4V, fadiga, nitretação por plasma.
Efeito da tensão residual na microdeformação da rede cristalina em aço Cr-Si-V jateado por shot peening
2018 - OLIVEIRA, R.R.; LIMA, N.B.; XAVIER, G.L.; CASTRO, M.C.B. de
No presente trabalho foram estudados os efeitos causados pelo shot peening com a avaliação do perfil de tensão residual na região de tensão compressiva. Um efeito anômalo em relação ao perfil característico da distribuição de tensão residual foi notado pela perda de compressão próxima à superfície. Foi observada a região deformada plasticamente permitindo o estudo do mecanismo que infere este efeito. Os resultados fornecem as informações necessárias para comparar os efeitos que a microdeformação influenciam na tensão residual. Esta relação foi comprovada pela sobreposição dos resultados da distribuição da microdeformação com a tensão residual ao longo da espessura na região plasticamente deformada. Os resultados mostraram a existência de anisotropia de tensões entre os planos geradas pela densidade de discordâncias. O método aplicado foi o Williansom-Hall modificado.
Effect of plasma nitriding on fatigue behavior of Ti-6Al-4V alloy
2018 - CASTRO, MICHELE C.B. de; COUTO, ANTONIO A.; ALMEIDA, GISELE F.C.; MASSI, MARCOS; LIMA, NELSON B. de; SILVA SOBRINHO, ARGEMIRO da; CASTAGNET, MARIANO; XAVIER, GLEICY L.; OLIVEIRA, RENE R.
The Ti-6Al-4V alloy is widely used in the manufacture of components that should have low density, high corrosion resistance, and fatigue strength. The fatigue strength can be improved by surface modification. The aim of this study was to determine the influence of plasma nitriding on the fatigue behavior of Ti-6Al-4V alloy with a lamellar microstructure (Widmanstätten type). Nitriding was executed at 720 °C for 4 hours in an atmosphere with N2, Ar and H2. Samples microstructure characterization was carried out by X-ray diffraction analysis, optical microscopy and scanning electron microscopy. The average roughness of the specimens was determined, and fatigue tests were executed in a bending-rotating machine with reverse tension cycles (R= -1). X-ray diffraction analysis revealed the matrix phases α and β, and the phases Ɛ-Ti2N and δ-TiN in the nitrided alloy. A nitrogen diffusion layer was formed between the substrate and the titanium nitrides. Plasma nitriding resulted in an increase in low cycle fatigue strength, whereas at high cycles, both conditions exhibit similar behavior. The fracture surface of the fatigue tested specimens clearly revealed the lamellar microstructure. The fracture mechanism appears to be due to cracking at the interface of α and β phases of the lamellar microstructure.
Characterization of biodegradable mulch black films incorporated with organics fertilizers and rice husk ash
2017 - HARADA, JULIO; AMORIM, CAMILA A.; BRAGA, PAULA L.; MACHADO, LUCI D.B.; OLIVEIRA, RENE R.; CABRAL NETO, ABNER; MACEDO, JOSE R.N.; SILVA, LEONARDO G.A.; ROSA, DERVAL S.
The effects of organic fertilizer, rice husk ash, both from renewable resources, were evaluated. Both of them were incorporated in biodegradable black mulch films. Morphological, mechanical and thermal properties based on PBAT/PLA composites with 2 % wt. of carbon black were investigated. In addition, the formulations were prepared with 1 % wt. to 2 % wt. rice husk ash and 2 % wt. to 4 % wt. % organic fertilizer The samples were produced by melt extrusion process, using a twin screw extruder machine and blown film extrusion process. As can be seen the properties of biodegradable mulch film samples were investigated by tensile tests, XRD, FTIR, TG, MEV analyses. Correlation between properties were discussed. According to the results it is possible to apply this composite as film for agricultural protection.
Preparation and characterization of PBT/clay nanocomposite
2012 - SARTORI, MARIANA N.; OLIVEIRA, RENE R.; DIAZ, FRANCISCO R.V.; ORTIZ, ANGEL V.; RANGARI, VIJAYA K.; MOURA, ESPERIDIANA A.B.
This work presents the preparation and characterization of a nanocomposite based on Poly(butylene terephthalate) PBT and Brazilian smectitic clay (bentonite chocolate clay). Before being incorporated as clay nanoparticles in PBT resin, the clay was organically modified by the addition of a quaternary salt and sodium carbonate. PBT/Clay nanocomposite (96.3:3.70 wt %) was obtained by using a twin-screw extruder machine. After extrusion process, the nanocomposite was characterized by tensile, flexural and impact tests, SEM, Vicat, HDT, DSC, TGA and XRD tests. The results showed that the properties of the nanocomposite obtained were superior to those of neat PBT. Concerning the temperature of thermal distortion (HDT) an expressive gain of around 45 % was presented to PBT/Clay nanocomposite compared to PBT evidencing the interaction of nanofiller with the polymeric matrix.
Comparison between HDPE/clay and HDPE/piassava fiber/clay treated by electron beam radiation
2013 - ORTIZ, ANGEL; ESCANHOELA, CORDELIA M.F.; GOMES, MICHELLE; OLIVEIRA, RENE R.; DIAZ, FRANCISCO R.V.; MOURA, ESPERIDIANA A.B.
This work evaluates changes in morphological, mechanical and thermo-mechanical properties of electron-beam irradiated HDPE/nanoclay and HDPE/Piassava fiber/nanoclay. Material samples irradiated with 100 and 200 kGy using a 1.5 MeV electron beam accelerator (room temperature, presence of air) were submitted to tensile, flexural, and HDT tests. MFI, SEM and XRD analyses were carried out. Correlation between properties was discussed. Results showed that incorporation of piassava (Attalea funifera Mart) fiber and nanoclay, followed by irradiation represented significant gain in thermo-mechanical properties. Changes in surface morphology and reduction in MFI were observed. In conclusion, it may be claimed that the incorporation of piassava fiber in small size particles and nanoclay in the HDPE followed by electron-beam irradiation effectively improved the polymer properties and led to materials with superior properties suitable for several industrial applications.
Determination of the crystal alignment of SrFe12O19 permanent magnets using the (006) X-ray pole figure
2016 - GUGLIOTTI, C.F.; LIMA, N.B.; OLIVEIRA, R.R.; SILVA, M.R.M.; SILVA, S.C.
O grau de alinhamento de ímãs permanentes de ferrita de estrôncio produzidos com diferentes tamanhos médios de partícula foi investigado utilizando análise de figura de pólo. Os ímãs foram produzidos a partir de pós sem moagem e moídos em moinho de bolas com tempos de moagem entre 60 e 360 minutos. O tamanho médio de partícula foi determinado utilizando Fisher Sub-sieve sizer e granulômetro CILAS 1064. A morfologia dos pós foram analisados utilizando imagens de MEV. Os pós foram alinhados a um campo magnético, prensados isostaticamente e sinterizados. Os ímãs foram caracterizados magneticamente utilizando um permeâmetro. O grau de alinhamento dos ímãs sinterizados foi calculado utilizando a reflexão (006) e a morfologia dos grãos do ímã foi analisada utilizando imagens de MEV. Os ímãs permanentes de ferrita de estrôncio produzidos com pós moídos apresentaram maior grau de alinhamento (0,82) quando comparados ao ímã produzido com pós não moídos (0,79).
Comparative study of the effects of cellulose nanowhiskers and microcrystalline cellulose addition as reinforcement in flexible films based on biopolymer blends
2016 - PAIVA, DOUGLAS A.; OLIVEIRA, RENE R.; MAIA, WILSON da S.; AUAD, MARIA L.; RANGARI, VIJAYA K.; MOURA, ESPERIDIANA A.B.
The objective of this study is to compare the effects of the addition of cellulose nanowhiskers and microcrystalline cellulose on properties of flexible films based on biodegradablepolymer blends. Composite films containing 1 wt. % of microcrystalline cellulose and 1-2 wt.% of cellulose nanowhiskers were prepared by melt extrusion, using a twin screw extruder machine and blown extrusion process. The effects of the addition of cellulose nanowhiskers and microcrystalline cellulose on mechanical and thermal properties of biocomposite films were investigated by tensile tests, XRD, TG, DSC and FE-SEM analysis and the correlation between properties was discussed.
Study of flexible films prepared from PBAT/PLA blends reinforced with bio-CaCO3
2016 - CARDOSO, ELIZABETH C.L.; BUENO, NELSON R.; OLIVEIRA, RENE R.; MOURA, ESPERIDIANA A.B.
Plastics global annual production exceeds 250 million tons and more than 40 % of the total plastic production is used as packaging materials. The most widely used materials include polyethylene (PE) and polypropylene (PP), among others. However, petrochemical-based conventional packaging materials are non-biodegradable and cause serious environmental problems. Poly (lactic acid) (PLA), a linear aliphatic polymer is known as a biodegradable thermoplastic polymer with widely potential applications. However, its high brittleness and low toughness limits its application; blending PLA with PBAT (Poly (butylene adipate-co-terepthalate), an aliphatic-aromatic copolyester, was the solution found due to its high toughness and biodegradability. Nevertheless, differences between PLA and PBAT solubility parameter values lead to the formation of immiscible blends as well as reduction in their mechanical performance. CaCO3 from avian eggshells, when added in PLA / PBAT composites imparts optimization of mechanicals properties due to its characteristic as reinforcing filler. This study aims to evaluate the effects of PLA addition in PBAT/PLA blends especially concerned to mechanical and thermal properties of PLA / PBAT / CaCO3 flexible films. Composites were prepared by melt processing, using a twin-screw extruder (L/D - 25). Before blown film processing, the composites were cooled down for a better dimensional stability, pelletized and dried at 60 ± 2 ºC for 24 h. The mechanical and thermal properties of obtained films were investigated by tensile tests, DSC and TG / DTG. In addition, the morphology of blends and composites were also evaluated by XRD and SEM analyses. The results showed important increase in crystallinity and tensile strength at break of flexible films without severe loss in elongation percentage, due to CaCO3 additional in PBAT / PLA blend with higher PLA contents.
Development of bio-based foams prepared from PBAT/PLA reinforced with biio-calcium carbonate compatibilized by electron beam radiation
2016 - CARDOSO, ELIZABETH C.L.; SEIXAS, MARCUS V.S.; WIEBECK, HELIO; OLIVEIRA, RENE R.; MACHADO, GLAUSON A.F.; MOURA, ESPERIDIANA A.B.