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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
281

Evaluation of Balanced Asphalt Surface Mixtures with Conventional and High RAP Contents Using Laboratory and Accelerated Pavement Testing

Tong, Bilin 22 January 2025 (has links)
Balanced Mix Design (BMD) represents an asphalt mixture design methodology that replaces certain traditional volumetric parameters with performance-based testing to address predominant distresses such as rutting and cracking. This approach offers an avenue to properly design and produce engineered asphalt mixtures, including those with high reclaimed asphalt pavement (HRAP) contents, recycling agents (RAs), fibers, and polymer-modified binders. Laboratory performance tests are essential to the BMD process, as they ensure the production of durable, high-performance materials. Beyond laboratory performance evaluation, accelerated pavement testing (APT) plays a crucial role in bridging the gap between laboratory material characterization and field pavement performance. This dissertation aimed to assess the BMD concept for designing durable, long-lasting surface mixtures in Virginia, with particular emphasis on higher RAP content mixtures (HRAP mixtures, i.e., exceeding 30% RAP). The study involved laboratory and APT testing of six surface mixtures featuring a range of RAP contents (both conventional and high), two binder grades (PG 64-22 and PG58-28), one RA, and one warm mix additive. Findings indicated that dense-graded, unmodified surface mixtures with higher RAP contents can be successfully designed using the current Virginia Department of Transportation (VDOT) BMD special provision. These mixtures can be produced in the plant with no significant deviations in aggregate gradation and asphalt binder content from the design specifications. The combined effect of variations in different volumetric properties during production may influence the primary performance of the mixtures, potentially resulting in an imbalance. As a consequence, the produced BMD mixture may fail to meet one or more performance thresholds. Additionally, the results underscored the effectiveness of BMD concept with incorporating RAs and/or a softer binder when designing HRAP surface mixtures. Importantly, the current selected BMD tests characterized the laboratory performance of mixtures, aligning with the performance observed under APT. This research provided a steppingstone towards the examination and validation of the VDOT BMD thresholds, which ensures satisfactory field performance. The study also indicated that while current BMD thresholds provided sufficient margins for satisfactory field cracking performance, rutting resistance may become a concern for overly designed BMD HRAP mixtures. For instance, mixtures with excessively high asphalt binder content may exhibit compromised rutting resistance. Furthermore, to address the challenges uncovered during BMD test analysis—issues like the constraints of traditional pair-wise comparisons, risks of repetitive design processes, and the difficulty in pinpointing critical factors in mixture production—this dissertation proposed innovative solutions to enhance BMD application and streamline the evaluation process. First, a novel Composite Performance Index (CPI), visualized through a 3D plot, captured the "balance" status of various mixtures. Second, a machine learning-enhanced BMD framework was introduced, offering intelligent optimization throughout the design and production phases. The integration of these two tools offers significant potential for simultaneously improving multiple performance indices of asphalt mixtures. Finally, this research demonstrated that the performance of higher RAP content mixtures can exceed that of lower RAP content mixtures through the application of BMD approaches. This dissertation not only advanced the implementation of BMD for surface mixtures but also contributed to the sustainable and performance-driven evolution of asphalt mix design. The insights gained from this study provided practical guidance and strategic recommendations for enhancing asphalt mixture design, production, and performance monitoring. / Doctor of Philosophy / This dissertation evaluated a new way to design asphalt mixtures, called Balanced Mix Design (BMD). Unlike traditional methods that focus mostly on fundamental volumetric properties of materials, BMD uses testing to ensure the pavement will hold up against common issues like cracking and rutting. This approach allows for better use of materials, including high recycled asphalt pavement (HRAP), recycling agents (RAs), fibers, and modified binders. Considering economic and environmental benefits, the study evaluated the application of BMD for designing durable asphalt surfaces for pavements, particularly mixtures with over 30% recycled asphalt pavement (RAP). Tests in the laboratory and with accelerated pavement testing (APT) showed that high RAP mixtures could be designed and produced reliably using current Virginia Department of Transportation (VDOT) guidelines. The addition of recycling agents or softer binders further supported these mixtures in meeting performance standards, ensuring satisfied field performance. To address key challenges, such as the limitations of traditional pair-wise comparisons, risks of repetitive design processes, and the difficulty in finding key factors for production variability, this research introduces two innovative tools to enhance BMD. First, a Composite Performance Index (CPI) with a 3D visual tool offers a way to assess the balance status of mixtures. Second, a machine learning framework was developed to optimize BMD throughout the design and production phases. Together, these tools establish BMD as a valuable approach for designing and producing more sustainable, longer-lasting pavements.
282

Aspectos produtivos e análise do desempenho do fibrocimento sem amianto no desenvolvimento de tecnologia para telhas onduladas / Productive aspects and performance of fibrecement without asbestos in the development of technology for undulate roofing tiles

Tonoli, Gustavo Henrique Denzin 03 March 2006 (has links)
Estudos anteriores utilizando matriz cimentícia reforçada exclusivamente com fibras vegetais propiciaram a produção de telhas com desempenho aceitável nas idades iniciais. Porém, com o envelhecimento natural, as telhas apresentaram significativa redução do desempenho mecânico, fato este atribuído principalmente ao ataque alcalino da matriz cimentícia. A presente pesquisa teve como objetivo o aprimoramento de telhas onduladas de fibrocimento sem amianto, a partir de processo automatizado. A primeira etapa do trabalho consistiu na avaliação do efeito da intensidade de refino da polpa Kraft de sisal (Agave sisalana) nas propriedades mecânicas e físicas de placas planas baseadas em matriz de cimento Portland, e o uso conjunto com fibras de poliproprileno (PP). Esta etapa envolveu também a caracterização dos principais atributos das polpas celulósicas refinadas, bem como a caracterização microestrutural (microscopia eletrônica de varredura e porosimetria por intrusão de mercúrio) do material resultante após envelhecimento acelerado e em ambiente natural. Na segunda etapa, séries de telhas onduladas de fibrocimento foram produzidas por técnica de sucção do excesso de água e prensagem, utilizando os melhores parâmetros definidos na etapa anterior. Os efeitos da cura acelerada em autoclave e dos envelhecimentos acelerados (carbonatação acelerada, imersão-secagem e calor-chuva) nas propriedades mecânicas e físicas das telhas foram avaliados. Os resultados obtidos mostraram a grande contribuição do refino da polpa celulósica na melhoria da resistência dos compósitos. Altas intensidades de refino apresentaram os melhores resultados para compósitos reforçados somente com polpa celulósica, mesmo após os envelhecimentos, porém intensidades intermediárias em compósitos híbridos mostraram-se suficientes. A adição das fibras de polipropileno como reforço híbrido teve como ponto forte a manutenção da resistência ao impacto, propriedade esta fortemente afetada pelo envelhecimento acelerado nos compósitos reforçados somente com polpa de sisal. As telhas produzidas mostraram-se mais eficientes no amortecimento térmico do que telhas comerciais de fibrocimento amianto. Melhorias no processo de produção das telhas mostraram efetiva contribuição no desempenho mecânico em relação aos trabalhos anteriores, tanto no curto como no longo prazo. Os resultados também indicaram a utilização da carbonatação acelerada como um procedimento eficiente na mitigação da degradação sofrida pelas fibras celulósicas em meios menos agressivos, no caminho para tornar viáveis os materiais reforçados com fibras vegetais. / Previous studies using exclusively vegetal fibres as the sole reinforcement of cement matrix have propitiated the production of roofing tiles with acceptable performance at the first ages. However, with the natural ageing, the roofing tiles have presented significant reduction in the mechanical performance, attributed to the alkaline attack of the cimentitious matrix mainly. The present research had as objective the improvement of undulate fibrecement roofing tiles without asbestos with automated equipment for production. The study also evaluated the physical, mechanical and microstructural behaviour of the obtained composites. The first stage consisted of evaluating the refinement effect of sisal Kraft pulp on mechanical and physical properties of flat pads based on Ordinay Portland cement and the jointly use of polypropylene fibres (PP). This stage also involved the characterization of the main attributes of refined cellulosic pulps, as well as the microstructural characterization (scanning electron microscopy and mercury intrusion porosimetry) of the resultant material after the accelerated and natural ageing. In the second stage, series of fibrecement roofing tiles were produced by slurry dewatering technique and pressing, using the best parameters of the first stage. Efects of autoclaved curing and accelerated ageing (accelerated carbonation, soak-dry and heat-rain) on mechanical and physical properties of tiles were evaluated. Results showed the great contribution of pulp refinement on mechanical strengh improvement. Higher intensities of refinement provided the best results for composites only reinforced with sisal pulp, despite ageing mechanism. Intermediate refinement revealed to be enough for hybrid composites. Adition of polypropylene fibres as hybrid reinforcement provided toughness maintenance after ageing, which was strongly affected only in sisal reinforced composites. Asbestos free tiles showed to be more efficient on thermal insulating properties than commercial asbestos cement. Improvements on tiles production process showed effective contribution on mechanical performance in relation to the previous works, both at initial ages and after ageing. The results have also indicated the utilization of accelerated carbonation as an effective procedure to mitigate the degradation suffered by the cellulosic fibres in the less aggressive medium, in way of the viability of the cement based materials reinforced by vegetal fibres.
283

Estudo de matriz cimentícia reforçada com fibra de curauá (Ananas comosus var. erectifolius) e submetida à cura em atmosfera com excesso de dióxido de carbono (CO2) / Study curauá (Ananas comosus var. erectifolius) reinforced cementitious matrix and subjected to curing in an atmosphere with excess carbon dioxide (CO2)

Santana, Patrícia das Neves de Almeida 01 September 2016 (has links)
O uso de fibras lignocelulósicas em compósitos de cimento, aliados a cura em atmosferas com excesso de CO2 para promover processos de carbonatação acelerada são potenciais tecnologias para desenvolvimento de materiais sustentáveis que fixam CO2. O presente estudo avaliou o potencial da fibra de curauá para aplicação em compósitos, bem como comparou fibrocimento com reforço de curauá (FCR) com fibrocimento com reforço de polipropileno (FPP), e estudou os efeitos da cura térmica, da cura em atmosfera com excesso de CO2, e a durabilidade ao longo de 100 ciclos de envelhecimento acelerado nesses compósitos. Para avaliar o potencial da fibra, foi realizada a análise anatômica foliar com intuito de analisar o arranjo, as funções e a morfologia das fibras na folha. Também foram determinadas: influência de comprimentos 20 e 40 mm nas variáveis mecânicas; e propriedades de massa específica; teores químicos e análise térmicas da fibra. Para os fibrocimentos, foram quantificadas propriedades de densidade aparente, porosidade aparente e absorção de água e variáveis mecânica módulo de ruptura, módulo de elasticidade, limite de proporcionalidade e energia específica. Também foram feitas as caracterizações mineralógicas por meio do DRX e microestrutural por MEV. A análise foliar evidenciou três classes de estruturas fibrilares denominadas genericamente como \"fibras\", sendo fibras de reforço primário (FP), fibras de reforço secundário (FS) e fibras associadas aos feixes vasculares (FV). A fibra de 40 mm atingiu melhor comportamento mecânico em relação a 20 mm e os comprimentos influenciam os valores de módulo de Young e módulo de Weibull. A análise química das fibras indicou altos teores de alfacelulose (68%) e extrativos (3,8%) e baixos teores de hemicelulose (10%) e lignina (13%). A análise termogravimétrica demonstrou que as estruturas de hemiceluloses e celuloses iniciam a degradação acima de 200ºC. Os resultados dos fibrocimentos indicaram que a cura em atmosfera com excesso de CO2, proporcionou melhorias nas propriedades mecânicas e físicas em FCR e FPP em relação a cura térmica. O processo de envelhecimento acelerado de 100 ciclos melhorou as propriedades da matriz em FCR e FPP, em ambas as curas. Em FCR a carbonatação acelerada melhorou a durabilidade dos compósitos. A fibra de curauá tem potencial para ser utilizada como reforço de materiais cimentícios, embora apresente limitações por ser instável dimensionalmente, sendo necessários tratamentos adicionais para superar esse problema. A carbonatação acelerada promovida pela cura em atmosfera com excesso de CO2 melhorou a durabilidade e propriedades físicas e mecânicas dos fibrocimentos. / The use of lignocellulosic fibers in cement composites with curing to promote accelerated carbonation is a promising technology for the development of sustainable materials to fix CO2. The aim of this study was to evaluate the potential of curauá fiber for use in composites and to compare fiber cement composite reinforcing with curauá (FCR) and cement reinforcing with polypropylene (FPP). In addition, to study the effects of thermal curing, curing in an atmosphere of excess CO2 and the durability over 100 cycles of accelerated aging in these composites. The potential of the curauá fibers was evaluated by leaf anatomical analysis to characterize their arrangement, function and morphology of the fibers\' leaves. The influence of their length (20 and 40mm) were also determined by the mechanical tests, specific mass properties, chemical contents and thermal analysis of the fibers. In the analysis of the fiber cement the density properties, porosity, water absorption, modulus of rupture (MOR), the modulus of elasticity, the limit of proportionality (LOP) and specific energy were measured. The mineralogical and microstructural characterizations were also carried out by DRX and MEV respectively. Foliar analysis showed three classes of fibrillar structures called generically as \"fibers\", with primary reinforcing fibers (PF), secondary reinforcement fibers (FS) and fibers associated with vascular bundles (FV). The 40 mm fiber showed a better mechanical behavior compared to 20 mm fiber, and the length has influenced Young\'s modulus values and Weibull modulus. The chemical analysis of the fibers has demonstrated high levels of alfacellulose (68%) and extractives (3.8%), and low hemicellulose (10%) and lignin (13%) content. Thermogravimetric analysis showed that the structures of celluloses and hemicelluloses started the degradation above 200°C. The fiber cement curing in an atmosphere with excess of CO2 provided improvements in mechanical and physical properties and for FCR and FPP when compared to thermal curing. The accelerated aging test was performed with 100 soak & dry cycles and showed improved performance of the matrix and for both fibers thru pores refinement. The curauá fiber has potential to be used as reinforcement of cementitious materials, although it has some limitations because it is dimensionally unstable, requiring additional treatments to overcome this problem. Accelerated carbonation promoted by curing in an atmosphere of excess CO2 enhanced the physical durability and the mechanical properties of the fiber cements.
284

Conservação, germinação e efeitos alelopáticos de Lafoensia glyptocarpa Koehne / Accelerated aging and controlled deterioration of Lafoensia glyptocarpa koehne seeds

Moraes, Luiza Paiva Silva de 04 May 2010 (has links)
Made available in DSpace on 2016-06-02T19:29:32Z (GMT). No. of bitstreams: 1 3436.pdf: 3258339 bytes, checksum: 7033f00ca9eab7b49ec141759f62e980 (MD5) Previous issue date: 2010-05-04 / Financiadora de Estudos e Projetos / The methodology of the accelerated aging test controlled deterioration to achieve the physiological quality of Lafoensia glyptocarpa Koehne seeds, separated into light and dark seeds, and to correlate if these seeds have their color due to different stages of maturation or whether the color is original phenotypic. The initial quality of the seeds was obtained through the tests of moisture content, conductivity and seedling emergence in greenhouse. The accelerated aging test was conducted at 40ºC during 24, 48, and 72 hours, using the traditional, NaCl saturated solution and controlled deterioration. The research was conducted in a completely randomized design. The saturated salt accelerated aging test and controlled deterioration was efficient for vigor evaluation of Lafoensia glyptocarpa Koehne seeds, and the period of 48hours at 40ºC was considered as the most adequate procedure to evaluate seed vigor levels, leading to the belief that colored seeds come from different stages of maturation. / O presente trabalho teve por objetivo avaliar as diferentes formas de se efetuar o teste de envelhecimento acelerado e deterioração controlada para avaliação do potencial fisiológico de sementes de Lafoensia glyptocarpa Koehne, separadas em sementes claras e sementes escuras, e correlacionar se estas sementes têm sua coloração devido a diferentes estádios de maturação ou se a coloração é de origem fenotípicas. A avaliação inicial dessas sementes consistiu na determinação do grau de umidade, condutividade e emergência de plântulas em casa de vegetação. O envelhecimento artificial foi implementado a 40ºC durante 24, 48, e 72 h, com e sem uso de solução saturada de NaCl, e para o teste de deterioração controlada as sementes foram umedecidas até 20% de umidade e posterior envelhecimento em câmara úmida a 40°C durante 24, 48 e 72h. O experimento foi conduzido em delineamento inteiramente casualizado. Dentre os procedimentos adotados no teste de envelhecimento artificial e o período de exposição de 48 horas a 40ºC com uso de solução saturada de NaCl, e deterioração controlada revelou-se adequado para a avaliação do potencial fisiológico de sementes de Lafoensia glyptocarpa Koehne, levando a crer que a coloração das sementes provem de estádios de maturação diferentes.
285

Estudo de matriz cimentícia reforçada com fibra de curauá (Ananas comosus var. erectifolius) e submetida à cura em atmosfera com excesso de dióxido de carbono (CO2) / Study curauá (Ananas comosus var. erectifolius) reinforced cementitious matrix and subjected to curing in an atmosphere with excess carbon dioxide (CO2)

Patrícia das Neves de Almeida Santana 01 September 2016 (has links)
O uso de fibras lignocelulósicas em compósitos de cimento, aliados a cura em atmosferas com excesso de CO2 para promover processos de carbonatação acelerada são potenciais tecnologias para desenvolvimento de materiais sustentáveis que fixam CO2. O presente estudo avaliou o potencial da fibra de curauá para aplicação em compósitos, bem como comparou fibrocimento com reforço de curauá (FCR) com fibrocimento com reforço de polipropileno (FPP), e estudou os efeitos da cura térmica, da cura em atmosfera com excesso de CO2, e a durabilidade ao longo de 100 ciclos de envelhecimento acelerado nesses compósitos. Para avaliar o potencial da fibra, foi realizada a análise anatômica foliar com intuito de analisar o arranjo, as funções e a morfologia das fibras na folha. Também foram determinadas: influência de comprimentos 20 e 40 mm nas variáveis mecânicas; e propriedades de massa específica; teores químicos e análise térmicas da fibra. Para os fibrocimentos, foram quantificadas propriedades de densidade aparente, porosidade aparente e absorção de água e variáveis mecânica módulo de ruptura, módulo de elasticidade, limite de proporcionalidade e energia específica. Também foram feitas as caracterizações mineralógicas por meio do DRX e microestrutural por MEV. A análise foliar evidenciou três classes de estruturas fibrilares denominadas genericamente como \"fibras\", sendo fibras de reforço primário (FP), fibras de reforço secundário (FS) e fibras associadas aos feixes vasculares (FV). A fibra de 40 mm atingiu melhor comportamento mecânico em relação a 20 mm e os comprimentos influenciam os valores de módulo de Young e módulo de Weibull. A análise química das fibras indicou altos teores de alfacelulose (68%) e extrativos (3,8%) e baixos teores de hemicelulose (10%) e lignina (13%). A análise termogravimétrica demonstrou que as estruturas de hemiceluloses e celuloses iniciam a degradação acima de 200ºC. Os resultados dos fibrocimentos indicaram que a cura em atmosfera com excesso de CO2, proporcionou melhorias nas propriedades mecânicas e físicas em FCR e FPP em relação a cura térmica. O processo de envelhecimento acelerado de 100 ciclos melhorou as propriedades da matriz em FCR e FPP, em ambas as curas. Em FCR a carbonatação acelerada melhorou a durabilidade dos compósitos. A fibra de curauá tem potencial para ser utilizada como reforço de materiais cimentícios, embora apresente limitações por ser instável dimensionalmente, sendo necessários tratamentos adicionais para superar esse problema. A carbonatação acelerada promovida pela cura em atmosfera com excesso de CO2 melhorou a durabilidade e propriedades físicas e mecânicas dos fibrocimentos. / The use of lignocellulosic fibers in cement composites with curing to promote accelerated carbonation is a promising technology for the development of sustainable materials to fix CO2. The aim of this study was to evaluate the potential of curauá fiber for use in composites and to compare fiber cement composite reinforcing with curauá (FCR) and cement reinforcing with polypropylene (FPP). In addition, to study the effects of thermal curing, curing in an atmosphere of excess CO2 and the durability over 100 cycles of accelerated aging in these composites. The potential of the curauá fibers was evaluated by leaf anatomical analysis to characterize their arrangement, function and morphology of the fibers\' leaves. The influence of their length (20 and 40mm) were also determined by the mechanical tests, specific mass properties, chemical contents and thermal analysis of the fibers. In the analysis of the fiber cement the density properties, porosity, water absorption, modulus of rupture (MOR), the modulus of elasticity, the limit of proportionality (LOP) and specific energy were measured. The mineralogical and microstructural characterizations were also carried out by DRX and MEV respectively. Foliar analysis showed three classes of fibrillar structures called generically as \"fibers\", with primary reinforcing fibers (PF), secondary reinforcement fibers (FS) and fibers associated with vascular bundles (FV). The 40 mm fiber showed a better mechanical behavior compared to 20 mm fiber, and the length has influenced Young\'s modulus values and Weibull modulus. The chemical analysis of the fibers has demonstrated high levels of alfacellulose (68%) and extractives (3.8%), and low hemicellulose (10%) and lignin (13%) content. Thermogravimetric analysis showed that the structures of celluloses and hemicelluloses started the degradation above 200°C. The fiber cement curing in an atmosphere with excess of CO2 provided improvements in mechanical and physical properties and for FCR and FPP when compared to thermal curing. The accelerated aging test was performed with 100 soak & dry cycles and showed improved performance of the matrix and for both fibers thru pores refinement. The curauá fiber has potential to be used as reinforcement of cementitious materials, although it has some limitations because it is dimensionally unstable, requiring additional treatments to overcome this problem. Accelerated carbonation promoted by curing in an atmosphere of excess CO2 enhanced the physical durability and the mechanical properties of the fiber cements.
286

Aspectos produtivos e análise do desempenho do fibrocimento sem amianto no desenvolvimento de tecnologia para telhas onduladas / Productive aspects and performance of fibrecement without asbestos in the development of technology for undulate roofing tiles

Gustavo Henrique Denzin Tonoli 03 March 2006 (has links)
Estudos anteriores utilizando matriz cimentícia reforçada exclusivamente com fibras vegetais propiciaram a produção de telhas com desempenho aceitável nas idades iniciais. Porém, com o envelhecimento natural, as telhas apresentaram significativa redução do desempenho mecânico, fato este atribuído principalmente ao ataque alcalino da matriz cimentícia. A presente pesquisa teve como objetivo o aprimoramento de telhas onduladas de fibrocimento sem amianto, a partir de processo automatizado. A primeira etapa do trabalho consistiu na avaliação do efeito da intensidade de refino da polpa Kraft de sisal (Agave sisalana) nas propriedades mecânicas e físicas de placas planas baseadas em matriz de cimento Portland, e o uso conjunto com fibras de poliproprileno (PP). Esta etapa envolveu também a caracterização dos principais atributos das polpas celulósicas refinadas, bem como a caracterização microestrutural (microscopia eletrônica de varredura e porosimetria por intrusão de mercúrio) do material resultante após envelhecimento acelerado e em ambiente natural. Na segunda etapa, séries de telhas onduladas de fibrocimento foram produzidas por técnica de sucção do excesso de água e prensagem, utilizando os melhores parâmetros definidos na etapa anterior. Os efeitos da cura acelerada em autoclave e dos envelhecimentos acelerados (carbonatação acelerada, imersão-secagem e calor-chuva) nas propriedades mecânicas e físicas das telhas foram avaliados. Os resultados obtidos mostraram a grande contribuição do refino da polpa celulósica na melhoria da resistência dos compósitos. Altas intensidades de refino apresentaram os melhores resultados para compósitos reforçados somente com polpa celulósica, mesmo após os envelhecimentos, porém intensidades intermediárias em compósitos híbridos mostraram-se suficientes. A adição das fibras de polipropileno como reforço híbrido teve como ponto forte a manutenção da resistência ao impacto, propriedade esta fortemente afetada pelo envelhecimento acelerado nos compósitos reforçados somente com polpa de sisal. As telhas produzidas mostraram-se mais eficientes no amortecimento térmico do que telhas comerciais de fibrocimento amianto. Melhorias no processo de produção das telhas mostraram efetiva contribuição no desempenho mecânico em relação aos trabalhos anteriores, tanto no curto como no longo prazo. Os resultados também indicaram a utilização da carbonatação acelerada como um procedimento eficiente na mitigação da degradação sofrida pelas fibras celulósicas em meios menos agressivos, no caminho para tornar viáveis os materiais reforçados com fibras vegetais. / Previous studies using exclusively vegetal fibres as the sole reinforcement of cement matrix have propitiated the production of roofing tiles with acceptable performance at the first ages. However, with the natural ageing, the roofing tiles have presented significant reduction in the mechanical performance, attributed to the alkaline attack of the cimentitious matrix mainly. The present research had as objective the improvement of undulate fibrecement roofing tiles without asbestos with automated equipment for production. The study also evaluated the physical, mechanical and microstructural behaviour of the obtained composites. The first stage consisted of evaluating the refinement effect of sisal Kraft pulp on mechanical and physical properties of flat pads based on Ordinay Portland cement and the jointly use of polypropylene fibres (PP). This stage also involved the characterization of the main attributes of refined cellulosic pulps, as well as the microstructural characterization (scanning electron microscopy and mercury intrusion porosimetry) of the resultant material after the accelerated and natural ageing. In the second stage, series of fibrecement roofing tiles were produced by slurry dewatering technique and pressing, using the best parameters of the first stage. Efects of autoclaved curing and accelerated ageing (accelerated carbonation, soak-dry and heat-rain) on mechanical and physical properties of tiles were evaluated. Results showed the great contribution of pulp refinement on mechanical strengh improvement. Higher intensities of refinement provided the best results for composites only reinforced with sisal pulp, despite ageing mechanism. Intermediate refinement revealed to be enough for hybrid composites. Adition of polypropylene fibres as hybrid reinforcement provided toughness maintenance after ageing, which was strongly affected only in sisal reinforced composites. Asbestos free tiles showed to be more efficient on thermal insulating properties than commercial asbestos cement. Improvements on tiles production process showed effective contribution on mechanical performance in relation to the previous works, both at initial ages and after ageing. The results have also indicated the utilization of accelerated carbonation as an effective procedure to mitigate the degradation suffered by the cellulosic fibres in the less aggressive medium, in way of the viability of the cement based materials reinforced by vegetal fibres.
287

Simulační modelování elektrických pohonů pro vybrané kritické aplikace / Simulation modeling of electric actuators for selected critical application

Toman, Jiří Unknown Date (has links)
The dissertation thesis with the topic „Simulation Modelling of Electrical Drives for Selected Critical Applications“ focuses on the area of given applications in civil aviation. The selected application that the thesis deals with is an electrically driven and electronically controlled fuel pump supplying fuel to an aviation motor of the APU type. The thesis gives a comprehensive description of the design cycle of the unit and demonstrates implementing all the required critical functions. In the course of the design of the unit modern techniques in mathematical modelling, simulation, verification, monitoring and prediction of the operation status of airborne equipment were uses to the utmost extent. The purpose of these was to show the suitability of their application with regard to decreasing design time and cost, increasing lifetime and servicing intervals, as well as increasing user comfort and decreasing price. At the same time the required reliability was to be kept. The thesis also aims to prove and verify the suitability of using electronically commutated dc motors in critical applications in civil aviation. To reach this goal, it is necessary to design a robust drive control which would meet the given reliability requirements.
288

Equipment for Accelerated Vibration Testing / Utrustning för Accelererad Vibrationstestning

Hideblad, Daniel January 2017 (has links)
The increasing complexity with the decrease in size of EEE – components (Electronic, electric and electromagnetic) raises the question on how higher energy frequencies will affect the components and their continuous development. The most common vibration testing equipment currently in use within the automotive industry and SCANIA CV AB are the electrodynamic shaker (ED system). This thesis covers the characteristics of different vibration testing equipment while analysing their strengths and weaknesses, not only for the automotive industry but also including equipment more commonly handled within the aero and space industry. The project aims to find a complement for the ED system and study the possibility for its replacement in the automotive industry.In particular, experiments are carried out and documented on a so-called “Repeatable shaker system” (RS system) for the purpose to get a better understanding on the functions of the equipment and its overall differences compared to the electrodynamic system when it comes to random vibration testing.It became clear that complementing or replacing the ED system is difficult and that the RS system work fundamentally different in comparison. Accordingly, the RS system is not a potential replacement for our purpose and it cannot perform at the same level of precision but instead is able to achieve higher energy frequencies overall, making it still ideal for its intended purposes, but not as a replacement of the ED system.
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Sketch-based intuitive 3D model deformations

Bao, Xin January 2014 (has links)
In 3D modelling software, deformations are used to add, to remove, or to modify geometric features of existing 3D models to create new models with similar but slightly different details. Traditional techniques for deforming virtual 3D models require users to explicitly define control points and regions of interest (ROIs), and to define precisely how to deform ROIs using control points. The awkwardness of defining these factors in traditional 3D modelling software makes it difficult for people with limited experience of 3D modelling to deform existing 3D models as they expect. As applications which require virtual 3D model processing become more and more widespread, it becomes increasingly desirable to lower the "difficulty of use" threshold of 3D model deformations for users. This thesis argues that the user experience, in terms of intuitiveness and ease of use, of a user interface for deforming virtual 3D models, can be greatly enhanced by employing sketch-based 3D model deformation techniques, which require the minimal quantities of interactions, while keeping the plausibility of the results of deformations as well as the responsiveness of the algorithms, based on modern home grade computing devices. A prototype system for sketch-based 3D model deformations is developed and implemented to support this hypothesis, which allows the user to perform a deformation using a single deforming stroke, eliminating the need to explicitly select control points, the ROI and the deforming operation. GPU based accelerations have been employed to optimise the runtime performance of the system, so that the system is responsive enough for real-time interactions. The studies of the runtime performance and the usability of the prototype system are conducted to provide evidence to support the hypothesis.
290

Simulační modelování elektrických pohonů pro vybrané kritické aplikace / Simulation Modeling of Electric Actuators for Selected Critical Application

Toman, Jiří January 2017 (has links)
The dissertation thesis with the topic „Simulation Modelling of Electrical Drives for Selected Critical Applications“ focuses on the area of given applications in civil aviation. The selected application that the thesis deals with is an electrically driven and electronically controlled fuel pump supplying fuel to an aviation motor of the APU type. The thesis gives a comprehensive description of the design cycle of the unit and demonstrates implementing all the required critical functions. In the course of the design of the unit modern techniques in mathematical modelling, simulation, verification, monitoring and prediction of the operation status of airborne equipment were uses to the utmost extent. The purpose of these was to show the suitability of their application with regard to decreasing design time and cost, increasing lifetime and servicing intervals, as well as increasing user comfort and decreasing price. At the same time the required reliability was to be kept. The thesis also aims to prove and verify the suitability of using electronically commutated dc motors in critical applications in civil aviation. To reach this goal, it is necessary to design a robust drive control which would meet the given reliability requirements.

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