Este trabalho apresenta resultados de ensaios de fluência não confinada executados pelo modo convencional e acelerado. Foi possível avaliar alguns parâmetros que influenciam o fenômeno da fluência em geotêxteis não tecidos, e ainda comparar o comportamento de dois geotêxteis ensaiados, um de polipropileno e outro de poliéster. Construíram-se as curvas isócronas dos materiais estudados e as análises das mesmas mostram que os geotêxteis de poliéster sofrem menores reduções de rigidez quando submetidos a carregamentos constantes do que os geotêxteis de polipropileno, os resultados dos ensaios acelerados apresentam-se estaticamente compatíveis com os resultados convencionais, denotando a viabilidade do Stepped Isothermal Method (SIM) como ensaio de caracterização fluência não confinada para geotêxteis não tecidos. / This work presents results of conventional and accelerated unconfined creep tests. Some factors that influence the creep behavior of nonwoven geotextiles are evaluated. The performance of polypropylene and polyester geotextiles is also compared. Isochronous curves show that the polyester geotextiles have a smaller rigidity reduction when compared with the polypropylene geotextiles when submitted to constant loads. The results of the accelerated tests are statistically compatible with the results of conventional tests, indicating that the Stepped Isothermal Method is a feasible approach for characterizing the creep behavior of nonwoven geotextiles.

Este trabalho apresenta resultados de ensaios de fluência não confinada executados pelo modo convencional e acelerado. Foi possível avaliar alguns parâmetros que influenciam o fenômeno da fluência em geotêxteis não tecidos, e ainda comparar o comportamento de dois geotêxteis ensaiados, um de polipropileno e outro de poliéster. Construíram-se as curvas isócronas dos materiais estudados e as análises das mesmas mostram que os geotêxteis de poliéster sofrem menores reduções de rigidez quando submetidos a carregamentos constantes do que os geotêxteis de polipropileno, os resultados dos ensaios acelerados apresentam-se estaticamente compatíveis com os resultados convencionais, denotando a viabilidade do Stepped Isothermal Method (SIM) como ensaio de caracterização fluência não confinada para geotêxteis não tecidos. / This work presents results of conventional and accelerated unconfined creep tests. Some factors that influence the creep behavior of nonwoven geotextiles are evaluated. The performance of polypropylene and polyester geotextiles is also compared. Isochronous curves show that the polyester geotextiles have a smaller rigidity reduction when compared with the polypropylene geotextiles when submitted to constant loads. The results of the accelerated tests are statistically compatible with the results of conventional tests, indicating that the Stepped Isothermal Method is a feasible approach for characterizing the creep behavior of nonwoven geotextiles.

Made available in DSpace on 2014-06-11T19:29:06Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-02Bitstream added on 2014-06-13T19:37:59Z : No. of bitstreams: 1 maianeto_as_me_araiq.pdf: 907997 bytes, checksum: 246ee7468bbd3c17dd5762fc7651b5eb (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho, foi feito um estudo da cinética de precipitação da fase rica em prata, na liga Cu-7%Al-4%Ag, em peso, utilizando-se o modelo cinético isotérmico de Johnson-Mehl-Avrami e os modelos cinéticos nãoisotérmicos de Kissinger e Ozawa. A reação de precipitação da fase rica em prata foi acompanhada por medidas de variação da microdureza da liga com a temperatura de têmpera e o tempo de envelhecimento, e também por medidas de dilatometria. As fases presentes nas diversas temperaturas e tempos considerados, foram identificadas e caracterizadas por microscopia óptica e eletrônica de varredura, análise por dispersão de energias de raios X e por difratometria de raios X. Os resultados obtidos indicaram que a formação dos precipitados ricos em prata corresponde a um processo controlado por difusão da prata nos contornos de grão da matriz, no intervalo de temperaturas de 400 a 600 oC. O cálculo da energia de ativação para a formação dos precipitados, utilizando-se a equação de Johnson-Mehl-Avrami, forneceu um valor bastante próximo daquele encontrado na literatura, confirmando que o processo é controlado pela difusão da prata. O valor da energia de ativação para o crescimento dos precipitados ricos em Ag, calculado a partir de um método que considera o inverso do tempo necessário para o precipitado atingir seu tamanho máximo como proporcional à taxa de crescimento, ficou próximo daquele obtido utilizando-se a equação de Johnson-Mehl-Avrami, indicando que esse método pode ser utilizado para o cálculo da energia de ativação do processo cinético. Os valores da energia de ativação associados ao processo de precipitação de Ag, obtidos por métodos não isotérmicos, ficaram razoavelmente próximos daqueles encontrados na literatura e os valores assim obtidos associados à solubilização de Ag foram maiores do que aqueles encontrados na literatura... / In this work, the Ag-rich phase precipitation kinetics in the Cu-7wt.%Al-4wt.%Ag alloy, was studied using the Johnson-Mehl-Avrami isothermal kinetic model and the Kissinger and Ozawa non-isothermal kinetic models. The Ag-rich phase precipitation reaction was followed by microhardness changes measurements with quenching temperature and with aging time, and also by dilatometric measurements. The identification and characterization of the phases present at the considered temperatures and times were made by optical and scanning electronic microscopy, energy dispersive X-ray analysis and X-ray diffractometry. The results showed that the Ag-rich precipitates formation corresponds to a diffusion controlled process at the matrix grain boundaries, in the temperatures range from 400 to 600 oC. The activation energy value for the precipitates formation, calculated using the Johnson-Mehl-Avrami equation, is close to that found in the literature, thus confirming that the process is diffusion controlled. The activation energy value for the growing of Ag-rich precipitates, obtained considering that the inverse of the time to reach the precipitates maximum size is proportional to the growing rate, is close to that found using the Johnson-Mehl-Avrami equation, indicating that this method is useful to evaluate the activation energy for the kinetic process. The activation energy values obtained by non-isothermal methods and associated to the precipitation process were very close to those found in the literature, and the values associated to Ag dissolution were greater than those reported in the literature. This discrepancy may be associated to the presence of Al, and the Al-Ag interaction may be disturbing the diffusion process.

O método convencional de ensaios para a obtenção das curvas de fluência de geossintéticos pode necessitar de períodos de até 10.000 horas. Entretanto, a utilização de ensaios acelerados têm se mostrado bastante eficiente, especialmente para avaliar rapidamente a qualidade do material. Estudos bem sucedidos realizados por diversos autores, utilizaram o método Stepped Isothermal Method (SIM) para acelerar a fluência nos geotêxteis. Neste trabalho, com base neste método foi estimada a fluência de dois geotêxteis com 300 g/m² do tipo não tecido de poliéster (PET) de fibra curta e contínua. Neste estudo, foi analisada a fluência causada por carregamentos de 5, 10, 20, 40 e 60% da carga que causa a ruptura do material. Com base nos resultados conclui-se que os valores de deformação por fluência obtidos são satisfatórios, pois as previsões de alcance de até 355 anos estão próximos aos valores encontrados na literatura internacional. Ainda, para o tempo de 100 anos ficou evidenciado que para o geotêxtil não tecido do tipo PET, de fibra curta ou contínua, o comportamento mecânico do geotêxtil é mais influenciado pela deformação inicial do que pela fluência. / The conventional method of tests to achieve the geosynthetic creep curves may require times of up to 10,000 hours. However, the use of accelerated tests have shown to be very effective, especially for rapidly assessing the quality of the material. Successful studies by various authors used the Stepped Isothermal Method Method (SIM) to accelerate creep in geotextiles. In this work, based on this method was estimated creep of two non-woven geotextiles of polyester with 300 g/m², short or continuous fiber. In this study, creep caused by loads of 5, 10, 20, 40 and 60% of the rupture load of the material was analyzed. Based on the results, it is concluded that the creep strain values obtained are satisfactory, because up to 355 years range forecasts are close to those found in the literature. Still, for the 100-year time, it became evident that for the nonwoven geotextile type PET with short or continuous fiber, the mechanical behavior of the geotextile is more influenced by the initial deformation than by creep.

Master thesis deals with the influence of polyvinylacetate, polycaprolactone, poly(butylene-adipate-co-terephtalate) and talc, ethylenevinylacetate, polyethylene glycol and monosodium citrate on the flow properties, mechanical properties and crystallization ability of PLA. The flow properties were studied using the melt flow index and mechanical properties were studied using a tensile test. The crystallinity was studied by differential scanning calorimetry and on a polarization optical microscope equipped with hot stage. Isothermal crystallization was performed at 95 and 105 °C for 3 h and non-isothermal crystallization was performed with a calorimeter at two cooling rates (1 and 10 °C/min). Upon the isothermal crystallization at 95 °C, the formation of denser crystalline structure was observed and the content of crystalline phase increased in most of the samples. The formation of spherulitic structure was observed at 105 °C in samples with 30 % PVAc, 30 % EVA and PEG. Reducing the cooling rate to 1 °C/min at non-isothermal crystallization had nearly no effect on the crystallization process of the most samples; the content of crystalline phase increased in the samples containing PBAT and PEG, which revealed double melting peak during subsequent heating. The crystalline fraction was the most significantly affected by the addition of PEG. All added polymers except PVAc affected the mechanical properties; PBAT, PCL, EVA and PEG increased the strain and decreased the strength and modulus of elasticity. The samples containing monosodium citrate showed unsatisfactory mechanical properties and could not be measured. The samples containing higher concentration of EVA copolymer showed the phase separation.

The efficient and enhanced mixing of heat and incoming reactants is achieved in modern gas turbine systems by employing swirling flows. This is realized by a low velocity region (internal recirculation zone -IRZ) zone resulting from vortex breakdown phenomenon. Besides, IRZ acts as effective flame holder/stabilization mode. Double concentric swirling jet is employed in plethora of industrial applications such as heat exchange, spray drying and combustion. As such, understanding essential features of vortex breakdown induced IRZ and its acoustic response in swirling flow/flame is important in thermo-acoustic instability studies. The key results of the present experimental investigation are discussed in four parts. In the first part, primary transition (sub-critical states) from a pre-vortex breakdown (Pre-VB) flow reversal to a fully-developed central toroidal recirculation zone (CTRZ) in a non-reacting, double-concentric swirling jet configuration is discussed when the swirl number is varied in the range 0.592 S 0.801. This transition proceeds with the formation of two intermediate, critical flow regimes. First, a partially-penetrated vortex breakdown bubble (VBB) is formed that indicates the first occurrence of an enclosed structure resulting in an opposed flow stagnation region. Second, a metastable transition structure is formed that marks the collapse of inner mixing vortices. In this study, the time-averaged topological changes in the coherent recirculation structures are discussed based on the non-dimensional modified Rossby number (Rom) which appears to describe the spreading of the zone of swirl influence in different flow regimes. The second part describes a secondary transition from an open-bubble type axisymmetric vortex breakdown (sub-critical states) to partially-open bubble mode (super-critical states) through an intermediate, critical regime of conical sheet formation for flow modes Rom ≤ 1 is discussed when the swirl number (S) is increased beyond 0.801. In the third part, amplitude dependent acoustic response of above mentioned sub and supercritical flow states is discussed. It was observed that the global acoustic response of the sub-critical VB states was fundamentally different from their corresponding super-critical modes. In particular, with a stepwise increase in excitation amplitude till a critical value, the sub-critical VB topology moved downstream and radially outward. Beyond a critical magnitude, the VB bubble transited back upstream and finally underwent radial shrinkage at the threshold excitation amplitude. On the other hand, the topology of the super-critical VB state continuously moved downstream and radially outwards and finally widened/fanned-out at threshold amplitude. In the final part, transition in time-averaged flame global flame structure is reported as a function of geometric swirl number. In particular, with a stepwise increase in swirl intensity, primary transition is depicted as a transformation from zero-swirl straight jet flame to lifted flame with blue base and finally to swirling seated flame. Further, a secondary transition is reported which consists of transformation from swirling seated flame to swirling flame with a conical tailpiece and finally to highly-swirled near blowout ultra-lean flame. For this purpose, CH* chemiluminescence imaging and 2D PIV in meridional planes were employed. Three baseline fuel flow rates through the central fuel injection pipe were considered. For each of the fuel flow cases (Ref), six different co-airflow rate settings (Rea) were employed. The geometric swirl number (SG) was increased in steps from zero till blowout for a particular fuel and co-airflow setting. A regime map (SG vs Rea) depicting different regions of flame stabilization were then drawn for each fuel flow case. The secondary transformation is explained on the basis of physical significance of Rom.

A obtenção de resultados de fluência em geossintéticos (isócronas e curva de ruptura por fluência) requer longo tempo de observação e rigoroso controle laboratorial. Dessa forma, muitos produtos disponíveis no mercado brasileiro não foram ensaiados quanto a este fenômeno dificultando sobremaneira a elaboração de projetos mais seguros e econômicos. Há, portanto, a necessidade de estudos não só do fenômeno da fluência em si, mas também de métodos de ensaio que facilitem e acelerem a obtenção das curvas de fluência. Este trabalho apresenta um estudo da fluência de dois geotêxteis não tecidos, um de polipropileno e outro de poliéster, através de ensaios acelerados, utilizando-se o processo denominado Stepped Isothermal Method (SIM). Os valores obtidos pelo método SIM foram comparados aos valores obtidos nos ensaios convencionais, realizados segundo a norma ISO 13431. Os resultados experimentais indicam que os ensaios acelerados, utilizando o método SIM, foram capazes de simular o fenômeno da fluência com boa precisão e, portanto, podem trazer uma grande economia de tempo, além de facilitar e agilizar a caracterização da fluência de geossintéticos. / Creep tests are time consuming and require rigorous laboratory testing control. Because of that many products commercially available in Brazil were not tested regarding this phenomenon. The absence of creep data is an obstacle to the design soil reinforced structures. It is therefore required continuous research effort not only to elucidate creep phenomenon but also to help in the development of test methods that ease and speed up the obtaining of creep curves. This paper presents a creep study carried out on two non-woven geotextiles (PP and PET) using temperature accelerated creep test, namely the Stepped Isothermal Method (SIM). The values obtained using the SIM method were compared to the ones obtained using conventional creep tests following the ISO 13431. The experimental results indicate that the accelerated creep tests, using the SIM method, were capable of simulating the creep phenomenon with good accuracy and, hence, they can bring a great deal of time saving to the characterization of creep in geosynthetics.

A obtenção de resultados de fluência em geossintéticos (isócronas e curva de ruptura por fluência) requer longo tempo de observação e rigoroso controle laboratorial. Dessa forma, muitos produtos disponíveis no mercado brasileiro não foram ensaiados quanto a este fenômeno dificultando sobremaneira a elaboração de projetos mais seguros e econômicos. Há, portanto, a necessidade de estudos não só do fenômeno da fluência em si, mas também de métodos de ensaio que facilitem e acelerem a obtenção das curvas de fluência. Este trabalho apresenta um estudo da fluência de dois geotêxteis não tecidos, um de polipropileno e outro de poliéster, através de ensaios acelerados, utilizando-se o processo denominado Stepped Isothermal Method (SIM). Os valores obtidos pelo método SIM foram comparados aos valores obtidos nos ensaios convencionais, realizados segundo a norma ISO 13431. Os resultados experimentais indicam que os ensaios acelerados, utilizando o método SIM, foram capazes de simular o fenômeno da fluência com boa precisão e, portanto, podem trazer uma grande economia de tempo, além de facilitar e agilizar a caracterização da fluência de geossintéticos. / Creep tests are time consuming and require rigorous laboratory testing control. Because of that many products commercially available in Brazil were not tested regarding this phenomenon. The absence of creep data is an obstacle to the design soil reinforced structures. It is therefore required continuous research effort not only to elucidate creep phenomenon but also to help in the development of test methods that ease and speed up the obtaining of creep curves. This paper presents a creep study carried out on two non-woven geotextiles (PP and PET) using temperature accelerated creep test, namely the Stepped Isothermal Method (SIM). The values obtained using the SIM method were compared to the ones obtained using conventional creep tests following the ISO 13431. The experimental results indicate that the accelerated creep tests, using the SIM method, were capable of simulating the creep phenomenon with good accuracy and, hence, they can bring a great deal of time saving to the characterization of creep in geosynthetics.

Orientador: Antonio Tallarico Vicente Adorno / Resumo: Neste trabalho, foi feito um estudo da cinética de precipitação da fase rica em prata, na liga Cu-7%Al-4%Ag, em peso, utilizando-se o modelo cinético isotérmico de Johnson-Mehl-Avrami e os modelos cinéticos nãoisotérmicos de Kissinger e Ozawa. A reação de precipitação da fase rica em prata foi acompanhada por medidas de variação da microdureza da liga com a temperatura de têmpera e o tempo de envelhecimento, e também por medidas de dilatometria. As fases presentes nas diversas temperaturas e tempos considerados, foram identificadas e caracterizadas por microscopia óptica e eletrônica de varredura, análise por dispersão de energias de raios X e por difratometria de raios X. Os resultados obtidos indicaram que a formação dos precipitados ricos em prata corresponde a um processo controlado por difusão da prata nos contornos de grão da matriz, no intervalo de temperaturas de 400 a 600 oC. O cálculo da energia de ativação para a formação dos precipitados, utilizando-se a equação de Johnson-Mehl-Avrami, forneceu um valor bastante próximo daquele encontrado na literatura, confirmando que o processo é controlado pela difusão da prata. O valor da energia de ativação para o crescimento dos precipitados ricos em Ag, calculado a partir de um método que considera o inverso do tempo necessário para o precipitado atingir seu tamanho máximo como proporcional à taxa de crescimento, ficou próximo daquele obtido utilizando-se a equação de Johnson-Mehl-Avrami, indicando que esse método pode ser utilizado para o cálculo da energia de ativação do processo cinético. Os valores da energia de ativação associados ao processo de precipitação de Ag, obtidos por métodos não isotérmicos, ficaram razoavelmente próximos daqueles encontrados na literatura e os valores assim obtidos associados à solubilização de Ag foram maiores do que aqueles encontrados na literatura...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this work, the Ag-rich phase precipitation kinetics in the Cu-7wt.%Al-4wt.%Ag alloy, was studied using the Johnson-Mehl-Avrami isothermal kinetic model and the Kissinger and Ozawa non-isothermal kinetic models. The Ag-rich phase precipitation reaction was followed by microhardness changes measurements with quenching temperature and with aging time, and also by dilatometric measurements. The identification and characterization of the phases present at the considered temperatures and times were made by optical and scanning electronic microscopy, energy dispersive X-ray analysis and X-ray diffractometry. The results showed that the Ag-rich precipitates formation corresponds to a diffusion controlled process at the matrix grain boundaries, in the temperatures range from 400 to 600 oC. The activation energy value for the precipitates formation, calculated using the Johnson-Mehl-Avrami equation, is close to that found in the literature, thus confirming that the process is diffusion controlled. The activation energy value for the growing of Ag-rich precipitates, obtained considering that the inverse of the time to reach the precipitates maximum size is proportional to the growing rate, is close to that found using the Johnson-Mehl-Avrami equation, indicating that this method is useful to evaluate the activation energy for the kinetic process. The activation energy values obtained by non-isothermal methods and associated to the precipitation process were very close to those found in the literature, and the values associated to Ag dissolution were greater than those reported in the literature. This discrepancy may be associated to the presence of Al, and the Al-Ag interaction may be disturbing the diffusion process. / Mestre

This diploma thesis deals with study of crystalline structure of polyhydroxybutyrate (PHB), which contains different types of additives for studying of their nucleation activity and which were prepared by mixing. It is about boronitrid (BN), sacharin, hydroxapatit, plasticizer Tegmer a tree types of talc. Crystal structure was analysed by differential scanning calorimetry and x-ray diffraction, supramolecular structure was observed by optical microscopy (polarized and confocal laser scanning). Nucleating activity was evaluated by isothermal and non-isothermal crystallization made on calorimeter and heated table of optical microscope. There is not influence of additives on crystallographic structure, but additives affects number and size of spherulites including crystal domains defects, which can have impact on final mechanical properties. BN and talcs react as nucleating agents, other additives during low and high cooling speeds (vc) inhibit nucleation and in middle cooling speeds are without effect. Nucleating activity is not evaluated by numerically, because decrease of crystallization temperature together with vc is not linear. Results of direct methods are based on picture analysis, which is great benefit for understanding of crystal behaviour of PHB.