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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.
1

A prototype interactive identification tool to fragmentary wood from eastern central Australia, and its application to Aboriginal Australian ethnographic artefacts

Barker, Jennifer Anne January 2005 (has links)
Wood identification can serve a role wherever wood has been separated from other diagnostic plant structures as a result of cultural or taphonomic processing. In disciplines that study material culture, such as museum anthropology and art history, it may serve to augment and verify existing knowledge, whilst in fields like palaeobotany, zoology and archaeology, wood identification may test existing paradigms of ecology and human behaviour. However, resources to aid wood identification, particularly of non - commercial species, are sorely lacking and, in Australia, there are only a handful of xylotomists, most of whom are attached to Forestry organisations. In addition, wood fragments are commonly the limit of material available for identification. They may be the physical remains of a wider matrix - as may often appear in biological, archaeological, palaeobotanical or forensic contexts - or a splinter removed from an ethnographic artefact or antique. This research involved the development of an updateable, interactive, computer - based identification tool to the wood of 58 arid Australian species. The identification tool comprises a series of keys and sub - keys to reflect the taxonomic hierarchies and the difficulty of separating wood beyond family or genus. The central Sub - key to Arid Australian Hardwood Taxa is comprised of 20 angiosperm taxa which include families and single representatives of genera. The treated taxa in this key are defined by 57 separate characters. They are split into sets of like characters including four sets based upon method of examination : anatomical ( scanning electron microscopy ), anatomical ( light microscopy ), chemical observations and physical properties. These character sets follow a logical progression, in recognition of the variability in available sample size and that noninvasive techniques are often desirable, if not essential. The use of character sets also reflects that this variability in sample size can affect the range of available characters and the available method of identification, and their diagnostic potential tends to increase with the complexity of the identification method. As part of the research, the identification tool is tested against wood fragments removed from several Aboriginal Australian artefacts from central Australia and case studies are provided. / Thesis (Ph.D.)--School of Earth and Environmental Sciences, 2005.
2

Influência de idade da árvore na velocidade de propagação de ondas de ultrassom em peças estruturais de madeira de reflorestamento / Influence of the tree age on the velocity of ultrasonic wave propagation and on the modulus of elasticity

Massak, Marcus Vinicius 07 August 2010 (has links)
Orientador: Raquel Gonçalves / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Agrícola / Made available in DSpace on 2018-08-16T20:25:21Z (GMT). No. of bitstreams: 1 Massak_MarcusVinicius_M.pdf: 5087729 bytes, checksum: 1151f8522e1d2d75694f1f4d3479eca3 (MD5) Previous issue date: 2010 / Resumo: Em 2007 foi aprovada, pela Associação Brasileira de Normas Técnicas (ABNT), norma para classificação de madeira de dicotiledônea (NBR 15521, 2007). Essa norma, elaborada com base em ensaios de espécies tropicais com idade média de 45 anos, propõe a classificação de peças estruturais por meio de faixas de velocidade de propagação de ondas de ultrassom, associadas à faixas de rigidez. Em 2008 iniciou-se a elaboração de norma equivalente para as coníferas. No entanto, de forma geral, as madeiras de reflorestamento vêm sendo comercializadas com bem menos idade do que as espécies nativas indicando a necessidade de, tanto para a norma já aprovada quanto para a norma em estudo, serem obtidas informações a respeito da influência da idade na velocidade de propagação das ondas de ultrassom. Esse estudo é importante uma vez que, caso as variações de velocidade com a idade não forem acompanhadas por variações de propriedades mecânicas a classificação poderia ser afetada. Considerando-se o exposto, o objetivo principal dessa pesquisa foi avaliar a variação da velocidade de propagação de ondas de ultrassom e a variação das propriedades de resistência e de rigidez de peças estruturais (vigas) de Pinus elliottii e de Eucalyptus grandis em função da idade. As variações de idade foram estudadas de duas diferentes maneiras. Para o Pinus elliottii as peças foram retiradas de 12 árvores com 6 diferentes idades e para o Eucalyptus grandis de 5 árvores, todas de 34 anos, considerando a variação da idade em função do posicionamento de retirada das toras em relação a altura do tronco. Os ensaios de ultrassom nas vigas foram realizados utilizando-se a NBR 15521 (2007) e os ensaios de flexão estática utilizando-se a ASTM D198 (2008). Os resultados demonstraram que, para o Pinus elliottii, os parâmetros obtidos por ultrassom (velocidade de propagação das ondas - VLL e coeficiente da matriz de rigidez - CLL) e o módulo de elasticidade (EM) obtido na flexão estática tiveram o mesmo comportamento de variação com a idade. Para o Eucalyptus grandis não foi possível associar a posição de retirada no tronco com a idade, mas VLL, CLL e EM tiveram o mesmo comportamento de variação com a posição de retirada. O módulo de ruptura obtido na flexão estática (fm) não variou com a idade nem com a posição de retirada. As correlações entre os ensaios não destrutivos e destrutivos foram todas estatisticamente significativas, com coeficientes de correlação superiores para o parâmetro de rigidez (EM). Para o Eucalyptus grandis o enquadramento dos resultados de VLL e EM nas faixas de classificação da NBR 15521 (2007) foi realizado aplicando-se coeficiente de redução de 12% (fator de calibração) aos valores de velocidade obtidos na condição saturada / Abstract: In 2007 was approved, by the Brazilian Standard Association (ABNT), standard for hardwood grading (NBR 15521, 2007). This standard, based on tests in tropical species with average age 45 years old, proposes grading the hardwood structural sizes lumber based on the ultrasonic velocity ranges associated to the stiffness ranges. In 2008 it was beginning the studies for developing an equivalent standard for softwoods. However, reforestation wood is, in general, put on the market younger than native wood, so it was important, for the cited standard and for the new one, evaluates the influence of the age on the velocity of wave propagation. This study is important because if the variation of the velocity is not follow by the rigidity variation, the grading will be affected. The aim of this research was to obtain technical information about the influence of the tree age on the velocity of ultrasonic wave propagation and on the stiffness and strength of the Pinus elliottii and Eucalyptus grandis structural beams. The age variation was studied using two ways. For Pinus elliottii the beams was cutting from 12 trees with 6 different ages and for Eucalyptus grandis the beam was obtained from 5 trees, all with 34 years old, considering the different ages as a function of the beam position in the trunk. The ultrasonic tests were performed using the NBR 15521 (2007) and the static bending test using the ASTM D198 (2008). The results showed that, for Pinus elliottii, the parameters obtained by the ultrasonic test (velocity of wave propagation - VLL and rigidity coefficient - CLL) and the modulus of elasticity (EM) obtained in bending test had the same pattern of variation with age. For Eucalyptus grandis it was not possible to associate the position of the beam along the trunk with the age, but VLL, CLL and EM had the same pattern of variation with this position. The modulus of rupture obtained in bending (fm) did not present variation with age or with the extraction position. The correlations between nondestructive tests and destructive tests were all statistically significant, with higher correlation coefficients for the stiffness (EM) than for the strength (fm). To use the grade ranges of the NBR 15521 (2007) to the Eucalyptus grandis was necessary to apply 12% as reduction factor (calibrating) in the velocity values obtained in the saturated condition / Mestrado / Construções Rurais e Ambiencia / Mestre em Engenharia Agrícola
3

Variación en la clasificación visual de madera aserrada y su impacto en la fabricación, comportamiento mecánico y estabilidad lateral en MLE de Campnosperma panamense Standl. y Acacia mangium Willd. / Variation of visual grade classification of sawn timber and its impact on the industry, mechanical behavior and lateral stability of Campnosperma panamense Standl. and Acacia mangium Willd. GLULAM

Polanco Tapia, Cesar Augusto 17 December 2018 (has links)
La madera laminada encolada (MLE) representa una alternativa para masificar el uso de materias primas madereras en los países en vía de desarrollo. A pesar que en la actualidad tienen auge productos como el CLT y similares, nuestros países deben todavía hacer un esfuerzo mayúsculo para disponer masivamente de estos productos en las obras civiles, pues deben esperar cambios en la legislación, así como en la normatividad técnica especializada, además de generar capacidades comerciales para la oferta mercantil. Más cerca parece estar la incursión de productos con factibilidad de fabricación local en el mediano y corto plazo, como la MLE. Una buena cuota inicial la constituyen algunas experiencias locales con MLE, donde han trabajado de manera conjunta clientes, diseñadores instaladores, fabricantes y proveedores de materias primas e insumos. Otra, es el mercado que en la actualidad tiene mayor conciencia sobre las ventajas en el uso de la madera y su contribución ambiental. No obstante, hace falta una mayor participación en el mercado detallado, que permita mayor contacto con el cliente, y eso se lograría sin duda alguna con la elaboración de productos en serie que puedan ser colocados fácilmente en los puntos de venta minoristas y posiblemente con algún grado de customization. Aportando en ese camino, el presente estudio aborda detalles en la construcción de vigas laminadas (VLC) a escala real y su caracterización mecánica estructural enfatizando en el concepto de estabilidad, pandeo o vuelco lateral. Para ello se han consultado los estándares nacionales e internacionales (Brasil, Chile, EUA, Europa, Canadá, Reino Unido, India), que han permitido la consolidación de toda la investigación. Como hilo conductor se propone en todos los casos dos situaciones comparables. La primera, es el uso de dos especies con futuro potencial en Colombia como el Sajo (Campnosperma panamense Standl.) y la Acacia (Acacia mangium Willd.). El Sajo hace parte de una gran extensión de los bosques naturales del pacífico colombiano susceptible de Manejo Forestal Sostenible (MFS) y la Acacia ha tenido alta aceptación entre los reforestadores del país por su rápido crecimiento, corta rotación y alta expectativa financiera. La segunda, una modificación en la normatividad colombiana referente a la clasificación visual de la madera, la cual lleva más de 35 años en el país, y a criterio del autor, más que un promotor para el uso en la construcción ha sido un gran obstáculo, ya que su rigurosidad propicia el rechazo de grandes volúmenes para uso estructural, ignorando que la madera por ser un material de origen natural, debe ser gerenciada, más allá de rechazada; y eso trae consigo una mayor responsabilidad en su conocimiento para asignar su mejor uso. En el mundo moderno, aunque persiste, la discriminación tiende a desaparecer, entonces ¿por qué no darle una oportunidad a la madera y convivir con sus \"desventajas\"?. De otra parte, la filosofía de controlar lateralmente la estabilidad de las VLC surge de la premisa de aumentar los momentos de inercia hasta su máximo límite, haciendo que la madera exhiba todo su potencial como viga, logrando los mayores valores de carga vertical, convirtiéndola de paso en un producto más atractivo para la construcción civil. / GLULAM represents an alternative to expand the use of wood raw materials in developing countries. Although currently have booming products such as CLT and the like, our countries must still make a major effort to provide massive scale of these products in the civil construction, they must expect changes in legislation, as well as technical regulations specialized, and generate business capabilities for commercial offer. Closer seems to be the raid of products with local manufacturing feasibility in the medium and short term as the glued laminated timber. For begin good, we have some local experiences with GLULAM, which have worked together customers, installers, designers, manufacturers and suppliers of raw materials and supplies. Another advantage is the market that currently has greater awareness of the advantages in the use of wood and its environmental contribution. However, it takes a greater share of the detailed market, would be allowing more contact with the customer, and that would be achieved without any doubt with the development of serial products that can be easily placed in retail outlets and possibly with some degree of customization. Contributing in this way, this study addresses details on the construction of laminated beams (VLC) to real scale and the mechanical structural characterization, emphasizing the concept of lateral stability, buckling or tipping. For this, has been consulted national and international standards (Brazil, Chile, USA, Europe, Canada, UK, India), enabling the consolidation of all research. The work propose in all cases, two comparable situations. The first is the use of two species with future potential in Colombia as the Sajo (Campnosperma panamense Standl.) and Acacia (Acacia mangium Willd.). The Sajo is part of a large expanse of natural forests Colombian Pacific with Sustainable Forest Management (SFM) potential, and Acacia has high acceptance among reforestation companies of the country for its rapid growth, short rotation and high financial expectation. The second, a change in relation to the law visual classification of wood, which has more than 35 years in the country, and at the discretion of the author, rather than a promoter for use in building has been a major obstacle, as its stringency favors rejection of large volumes for structural use, ignoring which the wood is a natural material, and must be administered rather than rejected. This brings with it a greater responsibility on their knowledge to assign their best use. In the modern world, although persists, discrimination tends to disappear, then why not give it a chance to the wood and coexist with their \"disadvantages\" ?. Moreover, the philosophy of controlling lateral stability of the VLC arises from the premise of increasing the moment of inertia to its maximum limit, with achieving values highest in the vertical load, making the VLC a more attractive and competitive product for civil construction.

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