Needle penetration resistance (NPR) and screw withdrawal resistance (SWR) are widely used techniques for density estimation of woods integrated in timber structures. The moisture content (MC) influences these measurements and correction coefficients are needed to ensure the accuracy of results. The goal of the present paper was to scrutinize the relation between NPR and SWR measurements and MC in case of radiata pine, Scots pine, Salzmann pine, and maritime pine usually used in wood constructions, from which 25 specimens from each species were probed. The specimen’s MC ranged from 65.1 to 8.3%. Results show that NPR depth has a positive linear relationship with MC while the SWR force a negative one below the fiber saturation point (FSP). Above the FSP, the MC influence is less pronounced and less regular. MC correction factors of measurements below the FSP are proposed for the species studied.
RESUMENSe han realizado mediciones detalladas de las fendas de secado en 28 piezas de madera de pino silvestre de gran escuadría. Se han propuesto diferentes parámetros para medir su magnitud en longitud, profundidad, grosor e inclinación, así como un índice de áreas en el plano medio de rasante (superficie eficaz respecto a superficie total). Se han relacionado los parámetros de fendas con resistencia a flexión, resistencia a cortante, módulo de elasticidad y energía de rotura obtenidos mediante ensayos mecánicos, teniendo en cuenta si la rotura se produce por flexión o por cortante. Todas las fendas observadas permiten clasificar las piezas como MEG según la norma UNE 56544. Se propone cuantificar las fendas mediante el índice de áreas y las propiedades mecánicas mediante la energía de rotura. El análisis realizado no muestra una relación significativa entre las fendas analizadas, los modos de rotura o las propiedades mecánicas.Palabras clave: madera, propiedades mecánicas, caracterización, fendas de secado.
INTRODUCCIÓNLa calidad de la madera para uso estructural se evalúa en función de la cantidad y tamaño de los defectos (nudos, fendas, desviación de la fibra, gemas, etc.) de SUMMARY Detailed measurements of drying fissures were carried out on 28 pieces of gross cross-section structural Scots pine timber. Different parameters have been proposed to measure their magnitude: length, depth, thickness and slope of grain, as well as an index of area in the neutral axis plane (ratio of effective to total surface). The parameters of fissures have been related to bending strength, shear strength, modulus of elasticity and rupture energy obtained from mechanical tests, considering whether rupture is due to bending or shear. All of the fissures observed allows to classify the pieces as MEG according to the UNE 56544 standard. To quantify the magnitude of fissures the index of areas is proposed, while mechanical properties can be quantified by rupture energy. Analysis of the results does not show any relation between the fissures analyzed and the mode of failure, their magnitude and mechanical properties.
Density estimation by non-destructive or semi-destructive methods is applied mainly on softwood species. The instruments are expensive, the methods are complicated and the determination coefficients are low. In the present study, the simple core hollow drilling approach is revisited. Data of 600 cores or cylindrical specimens from 300 pieces of 10 different softwood and hardwood species were evaluated in the density range from 350 to 975 kg m−3. The data were obtained from complete pieces and from the cores from core drilling, while the difference between the two data sets is 1.7%. At higher densities, the differences are greater. A model was proposed concerning the piece density estimation with a determination coefficient of 0.98. It is concluded that core drill is a cheap and reliable method for density estimation and the data are equally reliable for radial (R) or tangential (T) probing. The cylindrical cores obtained are suitable for moisture content (MC) and species determination.
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