José Saporiti Machado

Investigador Auxiliar

Laboratório Nacional de Engenharia Civil. Núcleo de Estruturas de Madeira. Av. do Brasil, 101, 1700-066 LISBOA

Abstract. Microwave (electromagnetic) energy is currently used in the treatment of biological damage, in the machine grading of timber and its use for timber drying is foreseen. The exposure of structural timber elements to microwaves, such as for other timber treatments (preservation or fire-retardant), implies analyzing its effect on the mechanical properties of the wood. This paper intends to contribute to this discussion, presenting a preliminary study on the effect of microwave exposure (during 5 and 10min) on compression parallel to grain strength of clear Oak wood. The results obtained show a clear loss of strength due to exposure and to an increase in the time of exposure. Considering the results obtained in this study and by other authors, it becomes clear that more thorough research is needed, bearing in mind the establishment of strength correction factors or rules towards the safe use of this technology for assuring the proper mechanical behaviour of timber.

Key words: oak; compression parallel to grain; microwave

Sumário. A energia de microondas (electromagnética) é actualmente utilizada no tratamento de degradação biológica e na classificação mecânica de madeira e perspectiva-se a sua utilização na secagem de madeira. A exposição a microondas de elementos estruturais de madeira implica, tal como para outros processos de preparação da madeira (preservação ou tratamentos ignífugos), analisar o efeito dessa exposição nas propriedades mecânicas da madeira. O presente artigo pretende contribuir para esta discussão, apresentando um estudo preliminar sobre o efeito da exposição a microondas (durante 5 e 10min) na resistência à compressão paralela às fibras de madeira de Carvalho limpa de defeitos. Os resultados obtidos mostram uma clara perda de resistência com a exposição e aumento do tempo de exposição. Considerando os resultados obtidos no presente estudo e por outros autores, torna-se clara a necessidade de estudos mais exaustivos tendo em vista estabelecer possíveis factores de correcção ou regras de utilização segura desta energia de forma a garantir um apropriado comportamento mecânico da madeira.

Palavras-chave: carvalho; compressão paralela às fibras; microondas

Effet du Traitement du Bois de Chêne par des Ultrasons sur la Résistance à la Compression

Résumé. L'énergie des micro-ondes (électromagnétique) est actuellement utilisée dans le traitement de dégradation biologique et dans le classement mécanique du bois et son utilisation dans le séchage de bois de construction est prévue. L'exposition d'éléments structurels en bois à des micro-ondes implique, comme pour d'autres traitements du bois de construction (conservation ou traitements ignifuges), l'analyse de l'effet de cette exposition sur les propriétés mécaniques du bois. Le présent article vise à contribuer à cette discussion, en présentant une étude préliminaire sur l'effet de l'exposition aux micro-ondes (pendant 5 et 10min) sur la contrainte de rupture en compression parallèle au fil du bois de Chêne sans défauts. Les résultats obtenus montrent une claire perte de résistance avec l'exposition et l'augmentation du temps d'exposition. En considérant les résultats obtenus dans la présente étude et par d'autres auteurs, la nécessité d'études plus exhaustives devient évidente en vue d'établir de possibles facteurs de correction pour la résistance ou des règles d'utilisation sûres de cette énergie de manière à garantir un comportement mécanique approprié du bois.

Mots clés: chêne; compression parallèle au fil; micro-ondes

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References

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Entregue para publicação em Junho de 2004

Aceite para publicação em Setembro de 2004