Article

Propriedades de resistência e rigidez da madeira juvenil e adulta de Pinus taeda L.

Revista Árvore 01/2003; DOI: 10.1590/S0100-67622003000300014
Source: DOAJ

ABSTRACT O objetivo do presente trabalho foi o estudo da variabilidade das propriedades de resistência e rigidez à flexão estática e à densidade aparente (12%) entre a madeira juvenil e adulta de Pinus taeda L., de 37 anos de idade, procedente do Horto Florestal de Manduri, Estado de São Paulo. Na primeira parte do trabalho foram determinadas a região de madeira juvenil, a região de transição e a região de madeira adulta, por meio de estudos anatômicos (comprimento dos traqueídes axiais), segundo as recomendações das normas ABNT e IAWA. Os resultados mostraram que a região de madeira juvenil dessa espécie ocorre aproximadamente até o 18º anel de crescimento. Na segunda parte do trabalho foram analisados a resistência (módulo de ruptura - MOR) à flexão, o módulo de elasticidade (MOE) nessa mesma solicitação e a densidade aparente (12%) para as madeiras juvenil e adulta. Os resultados mostraram que o MOE e o MOR da madeira juvenil foram menores e mais variáveis que aqueles obtidos para madeira adulta. A densidade apresentou a mesma tendência observada nas propriedades avaliadas no ensaio de flexão estática.

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    [Show abstract] [Hide abstract]
    ABSTRACT: Wood is a natural material and so many factors interfere in estimation of its 10 physical and mechanical properties. Consequently variability in properties should be 11 taken into account to rationalize its application. Longitudinal modulus of elasticity (E) 12 is one of the main mechanical properties of the material, and its value can be obtained 13 via standardized tests. The aim of this study is to evaluate the influence of test 14 conditions compatible with NBR 7190:1997 Code requirements to determine modulus 15 of elasticity in static bending. For each of eight species, eight specimens were tested, all 16 of them four times, with the sample oriented on each of its four faces related to load 17 application. Data analysis was performed independently of species and their respective 18 strength class, using hypothesis testing to evaluate influence of specimens' orientations 19 to determination. It was concluded that specimen orientation is significant in 20 determining modulus of elasticity in static bending according to NBR 7190:1997. This 21 aspect can lead to a future normative review by the National Committee responsible by 22 Maderas-Cienc Tecnol 17(2):2015 Ahead of Print: After Authors Corrections redaction of this Code. To represent natural variability of wood in specimens' volume 23 by only one bending test, values of the modulus of elasticity should be lessened in 8%. 24
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