Made available in DSpace on 2014-06-11T19:28:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-08-08Bitstream added on 2014-06-13T19:37:17Z : No. of bitstreams: 1 barbosajr_u_me_guara.pdf: 1865884 bytes, checksum: 83bd72a45ee094f9fe7d582b28f8f175 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No Brasil, as chapas para aplicação em vasos de pressão são produzidas com tratamento térmico de normalização. Devido às exigências de garantias de propriedades mecânicas após tratamento pós-soldagem, há necessidade de se adicionar elementos de liga, que podem segregar-se no centro da chapa. Uma alternativa é produzir chapas de aço pelo processo de resfriamento acelerado (processo termomecânico), mas que requer elevado investimento em equipamentos para as usinas nacionais. O resfriamento rápido logo após a normalização, seguido de revenimento, vem como alternativa para produzir chapas com propriedades mecânicas tão boas quanto às produzidas pelo processo termomecânico, sem a necessidade de adição de elementos de liga e de investimentos em equipamentos. Neste trabalho foram avaliadas as influências do resfriamento rápido nas propriedades mecânicas do aço, onde se verificou redução do tamanho de grão ferrítico, com possível formação de bainita. Obteve-se melhora no limite resistência à tração, limite de escoamento e na tenacidade do aço. Houve, porém, redução no alongamento e aumento da dureza do aço. Foi avaliada também neste trabalho a influência do tratamento térmico póssoldagem, onde se verificaram uma possível esferoidização da cementita e precipitação de cementita nos contornos de grão, reduzindo o limite de resistência à tração, escoamento e a tenacidade do aço, além da redução da dureza do aço. Verificou-se também aumento da tenacidade do aço, possivelmente pelo alívio das tensões residuais internas, ainda existentes após o revenimento. Não foi evidenciada a influência deste tratamento no tamanho de grão ferrítico do aço. / In Brazil, plates for application in pressure vessels are produced by normalization heat treatment. Due to exigencies of guarantees of mechanical properties after postweld heat treatment, it is necessary to add alloy elements that can segregate themselves in the center of the plate. One alternative is to produce steel plates by accelerated cooling process (thermomechanical process), but it requires high investment in equipment for our national mills. Rapid cooling after the normalization, followed by tempering, turns up as alternative to produce plates with so good mechanical properties as those them produced by thermomechanical process, without the necessity of adding alloy elements and without investments in equipment. In this work were evaluated influences of rapid cooling heat treatment in the mechanical properties of the steel, where it was evidenced a reduction of the ferrite grain size with possible bainite formation. It was evidenced improvement in ultimate tensile strength, yield strength and tenacity of the steel. However, it was also evidenced reduction in the elongation and an increase of the hardness of the steel. It was also evaluated in this work the influence of post weld heat treatment, where if it was evidenced the possible occurrence of spheroidization of the cementite and precipitation of cementite in the grain boundary, reducing the ultimate tensile strength, the yield strength and the tenacity of the steel, beyond the reduction of the hardness. It was also evidenced an increase of the tenacity of the steel, probably because the residual internal stress relief, still existing into the steel plate after the tempering heat treatment. It was not evidenced the influence of this treatment in the ferrite grain size of steel.

Orientador: Marcelo dos Santos Pereira. / Banca: Tomaz Manabu Hashimoto. / Banca: José Rubens de Camargo. / Resumo: No Brasil, as chapas para aplicação em vasos de pressão são produzidas com tratamento térmico de normalização. Devido às exigências de garantias de propriedades mecânicas após tratamento pós-soldagem, há necessidade de se adicionar elementos de liga, que podem segregar-se no centro da chapa. Uma alternativa é produzir chapas de aço pelo processo de resfriamento acelerado (processo termomecânico), mas que requer elevado investimento em equipamentos para as usinas nacionais. O resfriamento rápido logo após a normalização, seguido de revenimento, vem como alternativa para produzir chapas com propriedades mecânicas tão boas quanto às produzidas pelo processo termomecânico, sem a necessidade de adição de elementos de liga e de investimentos em equipamentos. Neste trabalho foram avaliadas as influências do resfriamento rápido nas propriedades mecânicas do aço, onde se verificou redução do tamanho de grão ferrítico, com possível formação de bainita. Obteve-se melhora no limite resistência à tração, limite de escoamento e na tenacidade do aço. Houve, porém, redução no alongamento e aumento da dureza do aço. Foi avaliada também neste trabalho a influência do tratamento térmico póssoldagem, onde se verificaram uma possível esferoidização da cementita e precipitação de cementita nos contornos de grão, reduzindo o limite de resistência à tração, escoamento e a tenacidade do aço, além da redução da dureza do aço. Verificou-se também aumento da tenacidade do aço, possivelmente pelo alívio das tensões residuais internas, ainda existentes após o revenimento. Não foi evidenciada a influência deste tratamento no tamanho de grão ferrítico do aço. / Abstract: In Brazil, plates for application in pressure vessels are produced by normalization heat treatment. Due to exigencies of guarantees of mechanical properties after postweld heat treatment, it is necessary to add alloy elements that can segregate themselves in the center of the plate. One alternative is to produce steel plates by accelerated cooling process (thermomechanical process), but it requires high investment in equipment for our national mills. Rapid cooling after the normalization, followed by tempering, turns up as alternative to produce plates with so good mechanical properties as those them produced by thermomechanical process, without the necessity of adding alloy elements and without investments in equipment. In this work were evaluated influences of rapid cooling heat treatment in the mechanical properties of the steel, where it was evidenced a reduction of the ferrite grain size with possible bainite formation. It was evidenced improvement in ultimate tensile strength, yield strength and tenacity of the steel. However, it was also evidenced reduction in the elongation and an increase of the hardness of the steel. It was also evaluated in this work the influence of post weld heat treatment, where if it was evidenced the possible occurrence of spheroidization of the cementite and precipitation of cementite in the grain boundary, reducing the ultimate tensile strength, the yield strength and the tenacity of the steel, beyond the reduction of the hardness. It was also evidenced an increase of the tenacity of the steel, probably because the residual internal stress relief, still existing into the steel plate after the tempering heat treatment. It was not evidenced the influence of this treatment in the ferrite grain size of steel. / Mestre

Heat stress (HS) is one of the consequential important problems facing the swine industry. The negative effects of HS include reduced growth performance, reproductive efficiency, and carcass quality as well as increased morbidity and mortality. Although, the swine industry has developed several abatement strategies (i.e., fans, cooling pads, sprinklers, etc.), these approaches may be ineffective in the future as global temperatures continue to rise and the frequency of more severe heat waves increases in regions where animal agriculture is prevalent. These extreme heat events put pigs (especially those approaching market weight) at risk for acute hyperthermia that can lead to death unless body temperature is rapidly returned to euthermia and thermoregulatory function is restored.Therefore, evaluating mitigation strategies to promote recovery from acute hyperthermia is of utmost importance for improving pigs’ health and well-being and ensuring profitability and food security. In four experiments, the existence of microclimates in grow-finish barns during late summer was ascertained and a rapid cooling technique using cold water dousing and feed removal to promote recovery from acute hyperthermia in pigs was evaluated. In the first study, it was determined that microclimates exist in grow-finish barns and that pigs raised in pens that were not located directly below air inlets and ventilation fans had greater body temperature and reduced feed efficiency despite similarities in the in-barn ambient temperature and relative humidity. These data exemplifythe importance of adequate ventilation systems in swine barns and the impact of microclimates on pigs’ health and productivity during warm summer months. In the second study, grow-finish pigs that did not have feed access were exposed to acute HS and then rapidly or gradually cooled. Following the acute HS and recovery phase, all pigs were maintained under thermoneutral conditions and then euthanized over three days to determine the temporal effects of the cooling treatment on body temperature and intestinal integrity. The results showed that rapid cooling following acute hyperthermia in pigswas effective in returning body temperature to euthermia more rapidly compared to gradual cooling and rapid cooling prevented further intestinal damage. Based on these results, it was hypothesized that feed removal may have played a role in the effectiveness of rapid cooling. Therefore, a third experiment was conducted in which grow-finish pigs with or without access to feed were exposed to an acute HS challenge and then rapidly cooled. This study concluded that feed access was a determinant factor in the cooling outcome, as the gastrointestinal temperature returned to euthermia during the rapid cooling period more rapidly when feed was removed. Finally, a fourth study was conducted to evaluate the effects of feed removal in the absence of rapid cooling on the systemic inflammatory response and short-term growth performance of grow-finish pigs. However, it was determined that feed removal alone did not reduce the inflammatory response as expected. Overall, these studies demonstrate the risk forgrow-finish pigs during summer heat events and the potential use of rapid cooling in combination with feed removal for promoting recovery from acute hyperthermia in pigs.

MSCAGR (Animal Science) / Department of Animal Science

Hot isostatic pressing (HIP) is a thermal treatment method that is used to consolidate, densify or bondcomponents and materials. Argon gas is commonly used as the pressure medium and is isostaticallyapplied to the material with an excess pressure of 500-2000 bar and a temperature of 500-2200oC. WithHIP treatment being a well-established technology for the last decades, one is now striving to obtain anincreased understanding of local details in the internal gas flow and heat flux inside the HIP apparatus.The main objective of this work is to assess the potential of using computational fluid dynamics (CFD) asa reliable tool for future HIP development. Two simulations are being performed of which the first one isa steady-state analysis of a phase in the HIP-cycle called sustained state. The second simulation is atransient analysis, aiming to describe the cooling phase in the HIP-cycle. The most suitable modelingapproaches are determined through testing and evaluation of methods, models, discretization schemes andother solver parameters. To validate the sustained state simulation, the solution is compared tomeasurements of operating pressure, heat dissipation rate out through the HIP vessel and localtemperature by the vessel wall. However, no validation of the cooling simulations has been conducted. Asensitivity analysis was also performed, from which it could be established that a mesh refinement ofstrong temperature gradients resulted in an increase of wall heat dissipation rate by 1.8%. Both of thesimulation models have shown to yield satisfactory solutions that are consistent with the reality. With theachieved results, CFD has now been introduced into the HIP field and the presented modeling methodsmay serve as guidelines for future simulations.

No description available.

Submitted by Alison Vanceto (alison-vanceto@hotmail.com) on 2017-08-30T12:06:28Z No. of bitstreams: 1 DissMRS.pdf: 7292710 bytes, checksum: b518987951bcfa31933df3cece2f16cf (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-09-06T18:24:26Z (GMT) No. of bitstreams: 1 DissMRS.pdf: 7292710 bytes, checksum: b518987951bcfa31933df3cece2f16cf (MD5) / Approved for entry into archive by Ronildo Prado (ronisp@ufscar.br) on 2017-09-06T18:33:14Z (GMT) No. of bitstreams: 1 DissMRS.pdf: 7292710 bytes, checksum: b518987951bcfa31933df3cece2f16cf (MD5) / Made available in DSpace on 2017-09-06T18:34:27Z (GMT). No. of bitstreams: 1 DissMRS.pdf: 7292710 bytes, checksum: b518987951bcfa31933df3cece2f16cf (MD5) Previous issue date: 2017-02-10 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Shape memory alloys (SMA) are alloys that undergo martensitic transformation due to an external solicitation (temperature, stress, strain or magnetic field) and are capable of recovering permanent deformation when heated above a critical temperature. The most used shape memory alloys are Ti-Ni- and Cu-based. Cu-based SMA have some advantages due to better thermal and electrical conductivity, lower production cost and are easier to process. The main disadvantage of Cu-based SMA is its low ductility. This property is improved by decreasing the grain size and by a reduction of microstructural heterogeneities. This can be achieved at the surface of structural components after LASER remelting, through which the surface of the material is remelted by a LASER beam and solidifies under extremely high cooling rates. In this context, the aim of the present work is to investigate the influence of LASER surface remelting in the microstructure, thermal stability and mechanical properties of Cu-11.8Al-3.2Ni-3Mn (wt. %) SMA plates obtained by suction casting. The samples were characterized by optical and scanning electron microscopy, energy dispersive X-ray spectroscopy, electron backscatter diffraction, X-ray computed tomography, X-ray diffraction, differential scanning calorimetry as well as by tensile and microhardness tests. The results show that small shifts in the transformation temperatures occur due to the LASER treatment. It was observed that only the monoclinic β’1 martensitic phase formed in the as cast and LASER treated samples. The LASER treatment provided an improvement in mechanical properties with an increase of up to 162 MPa in fracture stress, up to 2.2% in fracture strain and up to 21 HV in microhardness when compared with the as-cast sample. This makes the surface remelting treatment a promising method for improving the mechanical properties of Cu-based SMA. / Ligas com memória de forma (LMF) sofrem transformação martensítica devido a uma solicitação externa (temperatura, tensão, deformação ou campo magnético) e são capazes de recuperar deformações permanentes quando aquecidas acima de uma temperatura crítica. Dentre as LMF mais utilizadas se destacam aquelas à base de Ti e Ni e aquelas à base de Cu. As à base de Cu apresentam vantagens devido a melhor condutividade térmica e elétrica, menor custo de produção e maior facilidade de processamento. A principal desvantagem das LMF à base de cobre é a baixa ductilidade. Uma forma de melhorar essa propriedade é promovendo uma diminuição no tamanho de grão e uma redução das heterogeneidades microestruturais. Isso pode ser obtido no tratamento de refusão superficial a LASER, no qual a superfície do material é refundida por um feixe de LASER e solidificada sob altas taxas de resfriamento. Nesse contexto, o objetivo da presente dissertação de mestrado é analisar a influência do tratamento de refusão superficial a LASER na microestrutura, na estabilidade térmica e nas propriedades mecânicas de placas da LMF Cu-11,8Al-3,2Ni-3Mn (% peso) obtidas através de fundição por sucção. As amostras foram caracterizadas por microscopia óptica e eletrônica de varredura, espectometria de energia dispersiva de raios X, difração de elétrons retroespalhados, tomografia computacional por raios X, calorimetria diferencial de varredura, difração de raios X, ensaio de tração e microdureza. A análise dos resultados mostrou que as temperaturas de transformação sofreram pequenas variações e nenhuma nova fase foi observada após o tratamento de refusão a LASER, sendo observada apenas a presença da fase monoclínica martensítica β’1. O tratamento propiciou uma melhoria nas propriedades mecânicas das placas obtidas por fundição por sucção, com um aumento em até 162 MPa na tensão de fratura, em até 2,2 % na deformação de fratua e em até 21 HV na microdureza, fazendo deste tratamento um método promissor para melhorar as propriedades mecânicas das LMF à base de Cu. / CNPq: 132132/2015-0 / FAPESP: 2015/04134-7