The porosity formation in castings is very important due to its frequency and its correspondent d... more The porosity formation in castings is very important due to its frequency and its correspondent deleterious effects in the cast parts mechanical properties. In special the presence of porosity has a dramatic effect on the fatigue life in cast aluminum alloys. The objective of this paper is to apply a numerical method based on finite difference to understand dissolved gases and solidification parame-ters roles in the porosity formation in aluminum alloys during the solidification. The model predictions are compared with experimental results unidirectional up-ward solidification of Al 4.5 wt % Cu.
The aim of this study was to provide an experimental investigation on the novel method for recycl... more The aim of this study was to provide an experimental investigation on the novel method for recycling chips of duplex stainless steel, with the addition of vanadium carbide, in order to produce metal/carbide composites from a high-energy mechanical milling process. Powders of duplex stainless steel with the addition of vanadium carbide were prepared by high-energy mechanical ball milling utilizing a planetary ball mill. For this proposal, experiments following a full factorial design with two replicates were planned, performed, and then analyzed. The four factors investigated in this study were rotation speed, milling time, powder to ball weight ratio and carbide percentage. For each factor, the experiments were conducted into two levels so that the internal behavior among them could be statistically estimated: 250 to 350 rpm for rotation speed, 10 to 50 h for milling time, 10:1 to 22:1 for powder to ball weight ratio, and 0 to 3% carbide percentage. In order to measure and character...
The refractory metals and their alloys show excellent mechanical behavior in high temperatures an... more The refractory metals and their alloys show excellent mechanical behavior in high temperatures and high resistance to corrosion and to wear and good thermal conductivity. The metals that constitute this group are, traditionally, tantalum, molybdenum, tungsten and niobium. Niobium (Nb) is a metal with 2468°C melting point, density 8.57 g/cm3 and CCC crystalline structure, is characterized by its excellent ductility and reasonable mechanical resistance in high temperatures. Due to these properties, o Nb is applied in chemical, nuclear and electrical industry and in the superconductor wire production. One of the processes used in niobium plastic deformation is the swage that consists in one direct deformation process, which can be done at hot or cold temperature, used to modify the transversal section area of bars, tubes and wires. The microstructure evolution during a plastic deformation is very important in the relation of deformation mechanism, mechanical property and texture format...
The reuse of waste in civil construction brings environmental and economic benefits. However, for... more The reuse of waste in civil construction brings environmental and economic benefits. However, for these to be used in concrete, it is necessary a previous evaluation of their physical and chemical characteristics. Thus, this study aimed to characterize and analyze the waste foundry exhaust sand (WFES) for use in self-compacting concrete (SCC). Foundry exhaust sand originates from the manufacturing process of sand molds and during demolding of metal parts. It is a fine sand rich in silica in the form of quartz collected by baghouse filter. Characterization of WFES was conducted through laser granulometry, scanning electron microscopy (SEM) in the energy dispersive spectroscopy (EDS) mode, X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and derivative thermogravimetry (DTG) techniques. The waste was classified as non-hazardous and non-inert, with physical and chemical properties suitable for use in SCC compositio...
abstract: The utilization of wastes from demolition in civil construction in self compacting conc... more abstract: The utilization of wastes from demolition in civil construction in self compacting concrete (SCM) has the potential to reduce both the environmental impact and financial cost. In this context, this article aims to verify the behavior of the incorporation of recycled aggregates of civil construction in the mix designs of self-compacting mortar (SCM) in replacing cement, presenting as an interesting alternative to natural raw materials. This study used the EMMA® software to optimize the choice of percentages of fine recycled aggregates when replacing cement. The proportions chosen were 0%, 5%, 15%, and 25%, through the analysis of the granular packing curve of the respective mix designs. The proportion of 0% has in its composition cement, metakaolin, sand, superplasticizer (SP) and water. The parameters obtained, through tests in the fresh state of the mini-slump and mini-funnel V, certified the samples as SCM. The compressive strength and flexural tensile strength tests in ...
Este trabalho apresenta uma analise numerico/experimental da formacao de microporosidades interde... more Este trabalho apresenta uma analise numerico/experimental da formacao de microporosidades interdendriticas durante a solidificacao de ligas. Desenvolveu-se um modelo numerico, baseado no metodo de diferencas finitas, que e aplicado para a simulacao do processo de solidificacao unidirecional. Este modelo permite a determinacao dos principais parâmetros termicos (perfis de temperatura, fracao de solido, coeficiente de transferencia de calor na interface metal/coquilha, gradientes termicos, taxas de solidificacao, posicao das isotermas solidus e liquidus, velocidade de deslocamento das isotermas, tempo local de solidificacao) e parâmetros estruturais tais como espacamentos interdendriticos primarios e secundarios. O modelo permite tambem, a determinacao de parâmetros diretamente relacionados com a previsao da formacao das microporosidades, como exemplo a permeabilidade dos canais interdendriticos e a solubilidade do hidrogenio dentro da zona pastosa. A previsao da formacao de microporosidades leva em consideracao simultaneamente os efeitos da contracao da liga e da evolucao do hidrogenio resultante da diferenca de solubilidade do mesmo, nas fases liquida e solida, durante a solidificacao. Neste trabalho apresenta-se ainda, um estudo comparativo da influencia das variacoes das principais propriedades termofisicas da liga Al-4,5%Cu nos perfis de temperatura, na previsao microestrutural, e na formacao de microporosidades. Objetivando-se a comprovacao e otimizacao do modelo desenvolvido, foram realizados ensaios experimentais empregando-se a liga Al-4,5%Cu, usando um forno especialmente construido, para solidificacao unidirecional juntamente com um sistema de aquisicao de dados computadorizado, e medidas in situ do teor de hidrogenio no metal liquido. Atraves de microscopia otica, obtiveram-se medidas dos espacamentos interdendriticos primario e secundario, incluindo tambem a determinacao das dimensoes, localizacoes e volume percentual das microporosidades. O modelo permite estabelecer o teor de gases e as condicoes termicas ideais para minimizar a formacao das microporosidades Abstract
Este trabalho apresenta o desenvolvimento de um modelo numerico , baseado em diferencas finitas, ... more Este trabalho apresenta o desenvolvimento de um modelo numerico , baseado em diferencas finitas, determinacao dos principais parâmetros termicos e que permite a estruturais processo de solidificacao de ligas metalicas, para casos do de fluxos de esfera). calor unidirecional (placa) e radiais o modelo (cilindro permite e Utilizando tais parâmetros a determinacao da tortuosidade e da permeabilidade os canais interdendriticos que sao importantes para a analise da formacao de microporosidades durante o processo de solidificacao O modelo desenvolvido e aplicado para o estudo da solidificacao de diferentes ligas em diversas condicoes do sistema metal/molde Abstract
Mechanics of Composite and Multi-functional Materials, Volume 5, 2019
In this work, an alternative aluminium matrix composite (AMCs) was designed from the recycled chi... more In this work, an alternative aluminium matrix composite (AMCs) was designed from the recycled chips of the aluminium, Alumix 431 given by Brazilian aeronautic company, through combined method of powder metallurgy followed by Sintering + Forging. We aimed for the application for the connection pieces to transfer motion mainly used in automotive and aeronautical area as an alternative replacement for conventional alloys used in this area. First of all, A typical matrix was developed from recycled aluminium (AA 431) chips by high energy milling in a planetary ball mill with an inert argon atmosphere to prevent oxidation of the powders and this matrix was reinforced basically with TiC (5 wt % and 10 wt %) and molybdenum and copper (Mo 4 wt %, Cu 4 wt %) as a secondary reinforcements respectively. Mechanical and physical properties were evaluated through micro-hardness, static compression and 3 point bending (PB) tests and impact-drop weight tests were carried out. The microstructure analyses have been carried out by Scanning Electron Microscope (SEM).
O mercado global de implantes dentários estima o valor de US $ 13,01 bilhões até 2023 contra US $... more O mercado global de implantes dentários estima o valor de US $ 13,01 bilhões até 2023 contra US $ 9,50 bilhões em 2018. O estudo dos materiais para a fabricação dos implantes tem aumentado com o objetivo de estender a vida útil do material evitando sua substituição. Assim, neste estudo investigamos o comportamento eletroquímico de corrosão, molhabilidade e atividade antimicrobiana do titânio e da liga binária Ti-30Ta. O titânio foi cortado em discos de 10 mm de diâmetro. A liga Ti-30Ta foi obtida a partir de titânio e tântalo em forno a arco voltaico, homogeneizada em vácuo a 1000ºC por 24 horas, trabalhada a frio e solubilizada a 950 ºC por 2 horas seguido de resfriamento em água . Em seguida, as barras foram cortadas em discos. Os testes de resistência à corrosão avaliaram o comportamento eletroquímico, a molhabilidade das superfícies do substrato foi investigada usando o método da gota séssil e a formação de biofilme foi investigada por de S epidermidis. Este estudo tem como obje...
Structures with complex maintenance and restrict access need to have as an ally a monitoring proc... more Structures with complex maintenance and restrict access need to have as an ally a monitoring process of structural integrity. The structural health monitoring by means of damage detection studies is present in many engineering applications because they enable that corrective actions be applied to ensure the structural integrity of a given machine or equipment. In this work, we developed a study, using numerical simulations in order to assess damage detection techniques applied to composite materials, because the application of these materials in components and structures have replaced metallic materials due to its low weight and high strength. This research will be based on solving the direct and inverse problem by combining data from a model and the experimental case in order to detect structural damage. It carried out the mechanical modeling of the forward problem by finite element method and heuristic optimization techniques in order to minimize a particular objective function wr...
The electrical resistivity is an important concrete property because it is directly related to th... more The electrical resistivity is an important concrete property because it is directly related to the chloride ions penetration that cause the depassivation of the reinforcement, being a corrosion-causing agent. In Brazil, the bulk electrical resistivity test is described by ABNT NBR 9204/2012 (ABNT, 2012) which defines the specimen dimensions as O 150 x 150mm and the use of liquid mercury electrodes. Several studies of electrical resistivity are found using varying dimensions of specimens. This article aimed to analyze whether the variation in the specimen dimensions has a significant influence on the bulk electrical resistivity results of the same self-compacting concrete mixture. Three specimens were used for each geometry, O 50x100mm, O 100x100mm, O 100x200mm and O 150x150mm. Electrical resistivity was assessed at 28 and 90 days and statistical analysis was performed using the ANOVA program.
Por meio desta pesquisa, objetivou-se analisar as influências da modalidade de home office nas co... more Por meio desta pesquisa, objetivou-se analisar as influências da modalidade de home office nas conversas informais nas organizações, durante a pandemia de COVID-19. Mediante entrevistas on line assíncronas, entrevistaram-se 40 trabalhadores e profissionais que, devido à pandemia, migraram para a modalidade de home office, cujos relatos foram analisados por meio da análise de conteúdo. Os resultados mostram que a maior parte dos participantes passou a se utilizar de tecnologias digitais da informação e da comunicação, como aplicativos de comunicação remota e dispositivos móveis, para manter suas conversas informais. Contudo, para muitos participantes, ocorreu a redução da frequência de conversas informais e, em alguns casos, elas não ocorreram mais. Considerando-se, de um lado, os efeitos positivos da comunicação informal sobre o trabalho e a integração e, de outro, a possível intensificação do isolamento físico e social decorrente do home office em tempos de pandemia, os resultados ...
The porosity formation in castings is very important due to its frequency and its correspondent d... more The porosity formation in castings is very important due to its frequency and its correspondent deleterious effects in the cast parts mechanical properties. In special the presence of porosity has a dramatic effect on the fatigue life in cast aluminum alloys. The objective of this paper is to apply a numerical method based on finite difference to understand dissolved gases and solidification parame-ters roles in the porosity formation in aluminum alloys during the solidification. The model predictions are compared with experimental results unidirectional up-ward solidification of Al 4.5 wt % Cu.
The aim of this study was to provide an experimental investigation on the novel method for recycl... more The aim of this study was to provide an experimental investigation on the novel method for recycling chips of duplex stainless steel, with the addition of vanadium carbide, in order to produce metal/carbide composites from a high-energy mechanical milling process. Powders of duplex stainless steel with the addition of vanadium carbide were prepared by high-energy mechanical ball milling utilizing a planetary ball mill. For this proposal, experiments following a full factorial design with two replicates were planned, performed, and then analyzed. The four factors investigated in this study were rotation speed, milling time, powder to ball weight ratio and carbide percentage. For each factor, the experiments were conducted into two levels so that the internal behavior among them could be statistically estimated: 250 to 350 rpm for rotation speed, 10 to 50 h for milling time, 10:1 to 22:1 for powder to ball weight ratio, and 0 to 3% carbide percentage. In order to measure and character...
The refractory metals and their alloys show excellent mechanical behavior in high temperatures an... more The refractory metals and their alloys show excellent mechanical behavior in high temperatures and high resistance to corrosion and to wear and good thermal conductivity. The metals that constitute this group are, traditionally, tantalum, molybdenum, tungsten and niobium. Niobium (Nb) is a metal with 2468°C melting point, density 8.57 g/cm3 and CCC crystalline structure, is characterized by its excellent ductility and reasonable mechanical resistance in high temperatures. Due to these properties, o Nb is applied in chemical, nuclear and electrical industry and in the superconductor wire production. One of the processes used in niobium plastic deformation is the swage that consists in one direct deformation process, which can be done at hot or cold temperature, used to modify the transversal section area of bars, tubes and wires. The microstructure evolution during a plastic deformation is very important in the relation of deformation mechanism, mechanical property and texture format...
The reuse of waste in civil construction brings environmental and economic benefits. However, for... more The reuse of waste in civil construction brings environmental and economic benefits. However, for these to be used in concrete, it is necessary a previous evaluation of their physical and chemical characteristics. Thus, this study aimed to characterize and analyze the waste foundry exhaust sand (WFES) for use in self-compacting concrete (SCC). Foundry exhaust sand originates from the manufacturing process of sand molds and during demolding of metal parts. It is a fine sand rich in silica in the form of quartz collected by baghouse filter. Characterization of WFES was conducted through laser granulometry, scanning electron microscopy (SEM) in the energy dispersive spectroscopy (EDS) mode, X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared spectroscopy (FTIR), thermogravimetry (TG) and derivative thermogravimetry (DTG) techniques. The waste was classified as non-hazardous and non-inert, with physical and chemical properties suitable for use in SCC compositio...
abstract: The utilization of wastes from demolition in civil construction in self compacting conc... more abstract: The utilization of wastes from demolition in civil construction in self compacting concrete (SCM) has the potential to reduce both the environmental impact and financial cost. In this context, this article aims to verify the behavior of the incorporation of recycled aggregates of civil construction in the mix designs of self-compacting mortar (SCM) in replacing cement, presenting as an interesting alternative to natural raw materials. This study used the EMMA® software to optimize the choice of percentages of fine recycled aggregates when replacing cement. The proportions chosen were 0%, 5%, 15%, and 25%, through the analysis of the granular packing curve of the respective mix designs. The proportion of 0% has in its composition cement, metakaolin, sand, superplasticizer (SP) and water. The parameters obtained, through tests in the fresh state of the mini-slump and mini-funnel V, certified the samples as SCM. The compressive strength and flexural tensile strength tests in ...
Este trabalho apresenta uma analise numerico/experimental da formacao de microporosidades interde... more Este trabalho apresenta uma analise numerico/experimental da formacao de microporosidades interdendriticas durante a solidificacao de ligas. Desenvolveu-se um modelo numerico, baseado no metodo de diferencas finitas, que e aplicado para a simulacao do processo de solidificacao unidirecional. Este modelo permite a determinacao dos principais parâmetros termicos (perfis de temperatura, fracao de solido, coeficiente de transferencia de calor na interface metal/coquilha, gradientes termicos, taxas de solidificacao, posicao das isotermas solidus e liquidus, velocidade de deslocamento das isotermas, tempo local de solidificacao) e parâmetros estruturais tais como espacamentos interdendriticos primarios e secundarios. O modelo permite tambem, a determinacao de parâmetros diretamente relacionados com a previsao da formacao das microporosidades, como exemplo a permeabilidade dos canais interdendriticos e a solubilidade do hidrogenio dentro da zona pastosa. A previsao da formacao de microporosidades leva em consideracao simultaneamente os efeitos da contracao da liga e da evolucao do hidrogenio resultante da diferenca de solubilidade do mesmo, nas fases liquida e solida, durante a solidificacao. Neste trabalho apresenta-se ainda, um estudo comparativo da influencia das variacoes das principais propriedades termofisicas da liga Al-4,5%Cu nos perfis de temperatura, na previsao microestrutural, e na formacao de microporosidades. Objetivando-se a comprovacao e otimizacao do modelo desenvolvido, foram realizados ensaios experimentais empregando-se a liga Al-4,5%Cu, usando um forno especialmente construido, para solidificacao unidirecional juntamente com um sistema de aquisicao de dados computadorizado, e medidas in situ do teor de hidrogenio no metal liquido. Atraves de microscopia otica, obtiveram-se medidas dos espacamentos interdendriticos primario e secundario, incluindo tambem a determinacao das dimensoes, localizacoes e volume percentual das microporosidades. O modelo permite estabelecer o teor de gases e as condicoes termicas ideais para minimizar a formacao das microporosidades Abstract
Este trabalho apresenta o desenvolvimento de um modelo numerico , baseado em diferencas finitas, ... more Este trabalho apresenta o desenvolvimento de um modelo numerico , baseado em diferencas finitas, determinacao dos principais parâmetros termicos e que permite a estruturais processo de solidificacao de ligas metalicas, para casos do de fluxos de esfera). calor unidirecional (placa) e radiais o modelo (cilindro permite e Utilizando tais parâmetros a determinacao da tortuosidade e da permeabilidade os canais interdendriticos que sao importantes para a analise da formacao de microporosidades durante o processo de solidificacao O modelo desenvolvido e aplicado para o estudo da solidificacao de diferentes ligas em diversas condicoes do sistema metal/molde Abstract
Mechanics of Composite and Multi-functional Materials, Volume 5, 2019
In this work, an alternative aluminium matrix composite (AMCs) was designed from the recycled chi... more In this work, an alternative aluminium matrix composite (AMCs) was designed from the recycled chips of the aluminium, Alumix 431 given by Brazilian aeronautic company, through combined method of powder metallurgy followed by Sintering + Forging. We aimed for the application for the connection pieces to transfer motion mainly used in automotive and aeronautical area as an alternative replacement for conventional alloys used in this area. First of all, A typical matrix was developed from recycled aluminium (AA 431) chips by high energy milling in a planetary ball mill with an inert argon atmosphere to prevent oxidation of the powders and this matrix was reinforced basically with TiC (5 wt % and 10 wt %) and molybdenum and copper (Mo 4 wt %, Cu 4 wt %) as a secondary reinforcements respectively. Mechanical and physical properties were evaluated through micro-hardness, static compression and 3 point bending (PB) tests and impact-drop weight tests were carried out. The microstructure analyses have been carried out by Scanning Electron Microscope (SEM).
O mercado global de implantes dentários estima o valor de US $ 13,01 bilhões até 2023 contra US $... more O mercado global de implantes dentários estima o valor de US $ 13,01 bilhões até 2023 contra US $ 9,50 bilhões em 2018. O estudo dos materiais para a fabricação dos implantes tem aumentado com o objetivo de estender a vida útil do material evitando sua substituição. Assim, neste estudo investigamos o comportamento eletroquímico de corrosão, molhabilidade e atividade antimicrobiana do titânio e da liga binária Ti-30Ta. O titânio foi cortado em discos de 10 mm de diâmetro. A liga Ti-30Ta foi obtida a partir de titânio e tântalo em forno a arco voltaico, homogeneizada em vácuo a 1000ºC por 24 horas, trabalhada a frio e solubilizada a 950 ºC por 2 horas seguido de resfriamento em água . Em seguida, as barras foram cortadas em discos. Os testes de resistência à corrosão avaliaram o comportamento eletroquímico, a molhabilidade das superfícies do substrato foi investigada usando o método da gota séssil e a formação de biofilme foi investigada por de S epidermidis. Este estudo tem como obje...
Structures with complex maintenance and restrict access need to have as an ally a monitoring proc... more Structures with complex maintenance and restrict access need to have as an ally a monitoring process of structural integrity. The structural health monitoring by means of damage detection studies is present in many engineering applications because they enable that corrective actions be applied to ensure the structural integrity of a given machine or equipment. In this work, we developed a study, using numerical simulations in order to assess damage detection techniques applied to composite materials, because the application of these materials in components and structures have replaced metallic materials due to its low weight and high strength. This research will be based on solving the direct and inverse problem by combining data from a model and the experimental case in order to detect structural damage. It carried out the mechanical modeling of the forward problem by finite element method and heuristic optimization techniques in order to minimize a particular objective function wr...
The electrical resistivity is an important concrete property because it is directly related to th... more The electrical resistivity is an important concrete property because it is directly related to the chloride ions penetration that cause the depassivation of the reinforcement, being a corrosion-causing agent. In Brazil, the bulk electrical resistivity test is described by ABNT NBR 9204/2012 (ABNT, 2012) which defines the specimen dimensions as O 150 x 150mm and the use of liquid mercury electrodes. Several studies of electrical resistivity are found using varying dimensions of specimens. This article aimed to analyze whether the variation in the specimen dimensions has a significant influence on the bulk electrical resistivity results of the same self-compacting concrete mixture. Three specimens were used for each geometry, O 50x100mm, O 100x100mm, O 100x200mm and O 150x150mm. Electrical resistivity was assessed at 28 and 90 days and statistical analysis was performed using the ANOVA program.
Por meio desta pesquisa, objetivou-se analisar as influências da modalidade de home office nas co... more Por meio desta pesquisa, objetivou-se analisar as influências da modalidade de home office nas conversas informais nas organizações, durante a pandemia de COVID-19. Mediante entrevistas on line assíncronas, entrevistaram-se 40 trabalhadores e profissionais que, devido à pandemia, migraram para a modalidade de home office, cujos relatos foram analisados por meio da análise de conteúdo. Os resultados mostram que a maior parte dos participantes passou a se utilizar de tecnologias digitais da informação e da comunicação, como aplicativos de comunicação remota e dispositivos móveis, para manter suas conversas informais. Contudo, para muitos participantes, ocorreu a redução da frequência de conversas informais e, em alguns casos, elas não ocorreram mais. Considerando-se, de um lado, os efeitos positivos da comunicação informal sobre o trabalho e a integração e, de outro, a possível intensificação do isolamento físico e social decorrente do home office em tempos de pandemia, os resultados ...
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