Application of pulsed Nd:YAG laser in thin foil microwelding

Experimental investigations were carried out using a Nd:YAG laser operating in pulsed mode for welding a lap joint between thin foil and thick sheet. The pulse energy was varied from 1.5 to 3.0 J at increments of 0.25 J with a 4 ms pulse duration. The base material used for this study was AISI 316L foils with 100 mu m thickness and sheet with 3.0 mm thickness. The welds were analysed by optical and electronic microscopy, tensile shear tests and micro hardness. The results indicate that pulse energy control is of considerable importance to join thin foil and thick sheet with good quality. The ultimate tensile strength of the welded joints increased at first and then decreased as the pulse energy increased. The process appeared to be very sensitive to the gap between couples. Large voids delimited by the molten zone boundary were observed in joints welded with high pulse energy.

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.

Influência da potência de laser Nd: YAG na soldagem do aço inoxidável duplex UNS S32205

Pós-graduação em Engenharia Mecânica - FEIS

Avaliação do tipo de carregamento, pela análise de elementos finitos, sobre a resistência de união ao cisalhamento da interface metal/porcelana (Ni-Cr/vita omega 900)

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Discrepâncias de assentamento ocorrido em coroas totais metálicas, com e sem alívio interno, variando-se os términos cervicais e os agentes cimentantes

Pós-graduação em Odontologia Restauradora - ICT

Cardiovascular Responses Induced by Catalase Inhibitior into the Fourth Cerebral Ventricle is Changed in Wistar Rats Exposed to Sidestream Cigarette Smoke

Objectives: This experimental study aimed to evaluate the effects of central catalase inhibition on cardiovascular responses in rats exposed to sidestream cigarette smoke (SSCS) for 3 weeks. Methodology: A total of 20 males Wistar rats (320–370g) were implanted with a stainless steel guide cannula into the fourth cerebral ventricle (4thV). Femoral artery and vein were cannulated for mean arterial pressure (MAP) and heart rate (HR) measurement and drug infusion, respectively. Rats were exposed to SSCS for three weeks, 180 minutes per day, 5 days/week [carbon monoxide (CO): 100–300 ppm)]. Baroreflex was tested with one pressor dose of phenylephrine (PHE, 8 μg/kg, bolus) and one depressor dose of sodium nitroprusside (SNP, 50 μg/kg, bolus). Cardiovascular responses were evaluated before and 15 minutes after 3-amino-1, 2, 4-triazole (ATZ, catalase inhibitor, 0.001g/100μL) injection into the 4th V. Results: Vehicle treatment into the 4th V did not change cardiovascular responses. Central catalase inhibition increased tachycardic peak, attenuated bradycardic peak and reduced HR range at 15 minutes, increased MAP at 5, 15 and 30 min and increased HR at 5 and 15 min. In rats exposed to SSCS, central ATZ increased basal MAP after 5 min and increased HR at 5, 15 and 30 minutes, respectively, and attenuated bradycardic peak at 15 minutes. Conclusion: This study suggests that brain oxidative stress caused by SSCS influences autonomic regulation of the cardiovascular system.

MTA e hidróxido de cálcio como materiais obturadores de canal radicular em reimplante tardio de dente de macaco

O tratamento endodôntico é uma etapa importante do protocolo de atendimento do reimplante dentário e tem uma relação direta com o aparecimento das reabsorções radiculares, maior causa de perda dos dentes reimplantados. O objetivo do trabalho foi analisar o processo de reparo no reimplante tardio de dente de macaco, utilizando o hidróxido de cálcio (Ca(OH)2) e o MTA como materiais obturadores de canal. Cinco macacos Cebus apella adultos tiveram seus incisivos laterais superiores e inferiores, direito e esquerdo, extraídos e deixados em meio ambiente por 60 minutos. Decorrido esse período, foi realizado o preparo biomecânico dos canais e os dentes foram divididos em dois grupos experimentais: grupo I - canal preenchido com pasta de Ca(OH)2 e grupo II - canal preenchido com MTA (Angelus®). Após o selamento da abertura coronária com ionômero de vidro, o ligamento periodontal foi removido e os dentes imersos em solução de fluoreto de sódio 2%, pH 5,5, por 10 minutos. Em seguida, os alvéolos foram irrigados com soro fisiológico e os dentes reimplantados e contidos por 30 dias com fio de aço e resina composta. A eutanásia dos animais foi realizada 60 dias após o reimplante. Os espécimes de ambos os grupos apresentaram reabsorção por substituição e pontos de anquilose ao longo dos três terços radiculares e ausência de reabsorção inflamatória. Não houve diferença significante entre os dois grupos com relação à reabsorção por substituição, porém a quantidade de anquilose foi significativamente maior no grupo do Ca(OH)2. Baseado nesses resultados conclui-se que o MTA pode ser uma opção clínica viável para a obturação de dentes tardiamente reimplantados que necessitam de um longo período de curativo com hidróxido de cálcio.

Avaliação in vitro da adaptação cervical de coroas totais metálicas, variando os preparos dos términos cervicais, aliviando ou não as superfícies internas das coroas e empregando diferentes cimentos definitivos

Este trabalho avaliou a qualidade das adaptações cervicais de coroas totais metálicas, tendo como fonte de variação: a) o término do ombro cervical do preparo - biselado, inclinado em 1350; reto em 900, chanfro e gume de faca; b) o alívio ou não das superfícies internas das coroas; e, c) os tipos de agente de cimentação permanente, cimentos - fosfato de zinco Harvard; ionômero de vidro Ketac-Cem, policarboxilato de zinco Durelon e resinoso Panavia Ex. Inicialmente, foram confeccionados corpos-de-prova em modelos-padrão de aço inoxidável usinado, de acordo com o tipo de preparo dos términos cervicais experimentais. As cápsulas metálicas de aço inoxidável preparadas, tendo ou não alívio da superfície interna de 30 micrometros até a distância de 0,5 mm do limite do término cervical, justapunham-se precisamente e formavam um conjunto com adaptação e assentamento exatos. Estas foram cimentadas nos corpos-de-prova com os diferentes agentes cimentantes, os quais foram manipulados de acordo com as instruções dos fabricantes. Desenvolveram-se metodologias de reaproveitamento dos corpos-de-prova, estabilidade das cápsulas impedindo seu deslocamento durante a tomada das medidas e mensuração precisa. Concluiu-se que: a) as melhores médias de adaptações cervicais, semelhantes entre si, foram obtidas em modelos-padrão com ombros: lâmina de faca, ombro inclinado em 1350 e chanfro; b) as piores médias de adaptações cervicais, semelhantes entre si, foram obtidas em modelos-padrão com ombros reto em 900 e degrau em 900 com bisel de 450; c) houve melhora significativa na adaptação quando cápsulas metálicas foram cimentadas com alívio de sua superfície interna; d) os cimentos...(Resumo completo, clicar acesso eletrônico abaixo)

Comparison of cyclic fatigue and torsional resistance in reciprocating single-file systems and continuous rotary instrumentation systems

As compared with continuous rotary systems, reciprocating motion is believed to increase the fatigue resistance of NiTi instruments. We compared the cyclic fatigue and torsional resistance of reciprocating single-file systems and continuous rotary instrumentation systems in simulated root canals. Eighty instruments from the ProTaper Universal, WaveOne, MTwo, and Reciproc systems (n = 20) were submitted to dynamic bending testing in stainless-steel simulated curved canals. Axial displacement of the simulated canals was performed with half of the instruments (n = 10), with back-and-forth movements in a range of 1.5 mm. Time until fracture was recorded, and the number of cycles until instrument fracture was calculated. Cyclic fatigue resistance was greater for reciprocating systems than for rotary systems (P < 0.05). Instruments from the Reciproc and WaveOne systems significantly differed only when axial displacement occurred (P < 0.05). Instruments of the ProTaper Universal and MTwo systems did not significantly differ (P > 0.05). Cyclic fatigue and torsional resistance were greater for reciprocating systems than for continuous rotary systems, irrespective of axial displacement.

Estudo da fluência dos aços inoxidáveis ferríticos estabilizados ao titânio e nióbio e simulação numérica do processo no abaqus

The purpose of this research was tested a finite element model (FEM) that represented the creep of a slab during the reheating process of hot rolling. The aim is to prevent creep phenomenon changing the reheating profile with hot tensile test in Gleeble 3500, and, also, understand the former defect crisis. The goal of this work is to have a predictive tool to optimize the reheating process changing parameters (length and thickness). Then, use input parameters obtained from the tests to approximate the solution of the problem aided by Abaqus CAE. The results have showed that the ferritic stainless steel AISI 409 has a lower sensitivity to creep comparing to the stainless steel AISI 409, AISI 430Ti, AISI 441 and AISI 444

Fadiga axial do aço inoxidável 15-5 PH tratado pela implantação iônica por imersão em plasma

When materials for application in aircraft structural components are studied, it must be considered that they will be submitted to cyclic loading, and this is an important parameter to design the study in fatigue life of the materials. Whereas, for example, a landing gear operation, the study of fatigue life and corrosion in the materials used in it is essential, especially when you want to use new techniques for surface treatments. The objective is to study the influence of surface treatment of immersion ion implantation nitrogen plasma, in axial fatigue of Stainless steel 15-5 PH in 39-42 HRC condition. Stainless steel 15-5 PH was tested in axial fatigue and corrosion in salt spray. It was also performed microindentation tests, optical microscopy for microstructural analysis and scanning electron microscopy for fractographic analysis. It was observed that the 3IP had no effect on the thickness of the material and not the hardness of it, and still provided a significant increase in fatigue life of the material

Analise de desgaste em materiais aplicados em discos de freio

Baja SAE competitions challenge engineering students to design and build offroad vehicles, preparing them for the competitive job market. This monograph aims to study a part of the braking of a Baja SAE vehicle system, the brake disc. Giving attention to the wear suffered by discs of two different materials, steel 1045 and stainless steel 304, helping the team Piratas do Vale Bardahl in the best selection between them. Braking tests were performed on a test bench. Both discs have suffered the same braking conditions. Brake pads material, brake line pressure, braking time, number of braking, were parameters which were repeated in the testing of different types of disk, in order to ensure a high power comparison between the obtained data. Before and after the disk tests were weighed and measured, to make a comparison. After the brake tests, the disks were subjected to hardness and surface roughness testing. With the data collected and observations made in the worn parts, the comparison between these two materials was made, obtaining a selection of the best material for the team. The tests showed that steel 1045 has more advantages, compared to stainless steel 304, when applied to brake discs, on the tested conditions

Incorporação da apatita na superfície da liga Ti30ta empregando tratamento alcalino associado à eletrofiação de fibras de PCL

Pós-graduação em Engenharia Mecânica - FEG

Efeito de protocolos de cimentação na carga de fratura para uma cerâmica de dissilicato de lítio

Pós-graduação em Odontologia Restauradora - ICT

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