Caracterização microestrutural e de propriedades mecânicas de soldas do aço ASTM A 131 pelos processos FCAW convencional e com adição de arame frio

O trabalho aqui representado retrata de modo comparativo as características mecânicas e microestruturais de metais de solda empregando duas técnicas de soldagem uma já disseminada, FCAW (Soldagem a Arco Voltaico com Arame Tubular) e a outra é inovadora, FCAW-AF (Soldagem a Arco Voltaico com Arame Tubular com Adição de um Arame Frio não energizado) em três níveis de velocidades 6, 8 e 10 m/min. Sendo que este processo variou os diâmetros dos arames frio adicionados, entre 0.8 e 1.0 mm. O metal de base utilizado foi o aço naval ASTM 131 grau A (baixo carbono) em geometria de chapas de 150 mm x 300 mm x 9,5 mm, aplicadas em chanfro em V (Bisel de 22,5º) com ângulo somado de 45º, com leve abertura de raiz de 2,4 mm. A solda usada foi do tipo topo com a aplicação de dois passes, um passe de raiz e o passe de acabamento (ou enchimento). A fim averiguar as condições desses cordões de solda foram realizados 05 tipos de ensaios destrutivos, são eles: dobramento transversal de face, tração, tenacidade ao impacto (tipo Charpy com entalhe em V), microdureza e o ensaio metalográficos. Além das análises não destrutivas como o ensaio visual e o líquido penetrante. De maneira geral, os resultados para o processo FCAW-AF, mostraram-se compatíveis, em relação ao processo FCAW convencional, porém alguns resultados apresentaram valores de propriedades mecânicas menores. Este fato pode, muito provavelmente ter ocorrido pela presença de descontinuidade na junta pelo FCAW-AF. Quanto às caracterizações microestruturais, os resultados da junta FCAW-AF foram semelhantes os da FCAW convencional para todos os níveis estudados.

Efeitos da vibração simultânea nas propriedades mecânicas de juntas de aço ASTM A131 soldadas pelo processo arame tubular (FCAW)

Pós-graduação em Engenharia Mecânica - FEG

Caracterização mecânica e microestrutural do aço MARAGING 300, soldado a plasma e submetidas a reparos

Pós-graduação em Engenharia Mecânica - FEG

Comparison of Physicochemical Surface Conditioning Methods for Adhesion of bis-GMA Resin Cement to Particulate Filler Composite and Surface Characterization

This study compared the effect of physicochemical surface conditioning methods on the adhesion of bis-GMA-based resin cement to particulate filler composite (PFC) used for indirect dental restorations. PFC blocks (N (block)=54, n (block)=9 per group) were polymerized and randomly subjected to one of the following surface conditioning methods: a) No conditioning (Control-C), b) Hydrofluoric acid (HF)etching for 60s (AE60), c) HF for 90s (AE90), d) HF for 120s (AE120), e) HF for 180s (AE180), and f) air-abrasion with 30 mu m silica-coated alumina particles (AB). The conditioned surfaces were silanized with an MPS silane, and an adhesive resin was applied. Resin composite blocks were bonded to PFC using resin cement and photo-polymerized. PFC-cement-resin composite blocks were cut under coolant water to obtain bar specimens (1mmx0.8mm). Microtensile bond strength test (mu TBS)was performed in a universal testing machine (1mm/min). After debonding, failure modes were classified using stereomicroscopy. Surface characterization was performed on a set of separate specimen surfaces using Scanning Electron Microscopy (SEM), X-Ray Dispersive Spectroscopy (XDS), X-Ray Photoelectron Spectroscopy (XPS), and Fourier Transform-Raman Spectroscopy (FT-RS). Mean mu TBS (MPa) of C (35.6 +/- 4.9) was significantly lower than those of other groups (40.2 +/- 5.6-47.4 +/- 6.1) (p<0.05). The highest mu TBS was obtained in Group AB (47.4 +/- 6.1). Prolonged duration of HF etching increased the results (AE180: 41.9 +/- 7), but was not significantly different than that of AB (p>0.05). Failure types were predominantly cohesive in PFC (34 out of 54) followed by cohesive failure in the cement (16 out of 54). Degree of conversion (DC) of the PFC was 63 +/- 10%. SEM analysis showed increased irregularities on PFC surfaces with the increased etching time. Chemical surface analyses with XPS and FT-RS indicated 11-70% silane on the PFC surfaces that contributed to improved bond strength compared to Group C that presented 5% silane, which seemed to be a threshold. Group AB displayed 83% SiO2 and 17% silane on the surfaces.

Effects of laser beam energy on the pulsed Nd:YAG laser welding of thin sheet corrosion resistant materials

The aim of this study was to value the possibility to join, for pulsed Nd:YAG laser welding, thin foils lap joints for sealing components in corrosive environment. Experimental investigations were carried out using a pulsed neodymium: yttrium aluminum garnet laser weld to examine the influence of the pulse energy in the characteristics of the weld fillet. The pulse energy was varied from 1.0 to 2.5 J at increments of 0.25 J with a 4 ms pulse duration. The base materials used for this study were AISI 316L stainless steel and Ni-based alloys foils with 100 mu m thickness. The welds were analyzed by electronic and optical microscopy, tensile shear tests and micro hardness. The results indicate that pulse energy control is of considerable importance to thin foil weld quality because it can generate good mechanical properties and reduce discontinuities in weld joints. The ultimate tensile strength of the welded joints increased at first and then decreased as the pulse energy increased. In all the specimens, fracture occurred in the top foil heat-affected zone next to the fusion line. The microhardness was almost uniform across the parent metal, HAZ and weld metal. A slight increase in the fusion zone and heat-affected zone compared to those measured in the base metal was observed. This is related to the microstructural refinement in the fusion zone, induced by rapid cooling of the laser welding. The process appeared to be very sensitive to the gap between couples.

Efeitos dentoesqueléticos do tratamento da classe II utilizando o aparelho de Herbst associados à mecânica Straight-wire

This study compared the effect of the treatment protocol for correcting Class Il malocclusion using the Herbst appliance followed by full fixed Straigh-wire mechanics, in two populations, one Brazilian and one of North American origin As a untreated control sample the data from the University of Michigan Elementary and Secondary School Growth Study (UMGS) was used. Our sample was composed of 12 males and 12 females, with initial mean age of 12 years 7 months and final mean ages of 15 years and 3 months. The Michigan patients comprised 21 females and 7 males, with an initial mean age of 11 years and 9 months and final mean age of 14 years and 4 months. The control sample was paired in number, sex and age to the treated Michigan sample. ln both treated groups, lateral cephalometric radiographs were obtained before the Herbst appliance was cemented and at the end of the fixed appliance phase, The first comparison involved the Brazil group and the untreated controls, which demonstrated that the association of the Herbst appliance followed by fixed Straight-wire appliances provoked positive effects on the dentofacial complex, improving pre-existing maxillo-mandibular relationships, besides increasing dentoalveolar compensations which contributed to correct the malocclusion. The second comparison, involved the Brazl1ian and North-American patients treated with the same protocol. Although the pre-treatment comparison showed that the two groups were not similar in all aspects, they presented almost identical therapeutic modifications, which indicate that the effect of' treatment was very similar. These results point out that, in Class ll treatment, the combination of Herbst/Straight-wire mechanics produce consistent and systematic effects, correcting or minimizing possible skeletal imbalances

Heat Treatment and Yb-Fiber Laser Welding of a Maraging Steel

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Avaliação da influência dos parâmetros de processo de soldagem MIG no surgimento de poros em tubos de alumínio

The process of electric arc welding with shielding gas (GMAW) is being increasingly used in various industrial applications. This process occurs by which an electric arc is established between the work piece and a consumable in the form of wire, the arc melts the wire continuously as it is fed to the weld pool. The weld metal is protected from the atmosphere by flowing a gas (or gas mixture) inert or active. This paper presents a study of the welding process GMAW - MIG on aluminum tubes, alloy 6101 - T6, used in the manufacture of armored busbar, intended for driving electric power plants. 5(five) were welded specimens, changing certain welding parameters at each time was monitored welding joint as well as the interpass temperature. Tests were performed bending, tensile and macrographical analysis of body-of-evidence and through its results was possible to reach a better welding condition, which minimizes the appearance of pores, since the porosity has great influence on the mechanical strength and electrical conductivity of welded pipes

Comparação de junta soldada aço carbono/ aço inox utilizando como metal de adição aço carbono e aço inox

In contemporary industrial, welding processes are widely used, this is the most important process of joining metals used industrially. The welding can be used to build simple structures, like doors and gates for instance, in the same way can be used in situations of high responsibility, such as the nuclear industry and oil industry. Dissimilar welding is a case of welded joints, is characterized by the junction between different materials, for this case, stainless steel and carbon steel that are widely used in steam lines, power plants, nuclear reactors, petrochemical plants. Because their different mechanical and corrosive properties, the join, stainless steel with carbon steel, not only meets environmental requirements and also reduces cost. By using penetrating liquid tests, macrograph, hardness and tensile test was compared the possibility of replacing the current use of 309 rods as filler metal in dissimilar welding between carbon steel and stainless steel by add-on material carbon steel essentially, in this case E7018 coated electrode was used, but without the coating. After analysis of the results and for comparison, was proposed with some certainty that it is possible to replace the addition of materials, thus leading economy in this process widely used in the modern industry

Recuperação de turbinas hidráulicas danificadas por erosão cavitacional por soldagem com aço inoxidável/cobalto

Pós-graduação em Engenharia Mecânica - FEIS

Disposição construtiva aplicada em contenção ortodôntica

Disposição construtiva aplicada em contenção ortodôntica. Patente de modelo de utilidade para uma disposição construtiva aplicada em contenção ortodôntica, compreendida por ser do tipo 3x3, com encaixe do tipo "macho-fêmea", sendo que na base da "fêmea" (1) são procedidas retenções (2) mecânicas para fixação por meio de colagem na face lingual dos caninos (3) inferiores, com resina composta, de modo que no interior da "fêmea" (1) é provido um orifício (4) para o encaixe do "macho" (5) e, no centro da cavidade é provido um anel (6) elástico que se encaixa precisamente numa canaleta feita no pino (7) de encaixe do "macho" (5), sendo que, na extremidade dos "machos" (5) podem existir prolongamentos (8) metálicos para retenção de acrílico (9) ou então meios de encaixe para soldagem de um fio metálico (10) espesso, que contorna a face lingual dos dentes (11); inferiores anteriores, de modo que, quando se optar pela retenção em acrilico (9), um fio metálico (10) mais delgado é soldado no terminal de encaixe do "macho" (5) e logo após, o fio (10) e o terminal são recobertos por acrilico (9), sendo que os "machos" (5) poderão ter angulações nos braços (12) de encaixes.

Sugarcane Bagasse Ash as a Reinforcing Filler in Thermoplastic Elastomers: Structural and Mechanical Characterizations

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Sugarcane bagasse ash: new filler to natural rubber composite

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

The fitness of copings constructed over UCLA abutments and the implant, constructed by different techniques: casting and casting with laser welding

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Ultrasonic sensor signals and optimum path forest classifier for the microstructural characterization of thermally-aged inconel 625 alloy

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)