No abstract

The variation of wood density and mechanical properties with site, tree and within tree (longitudinal and radial) were studied for blackwood (Acacia melanoxylon R. Br.) grown in four sites in Portugal. Twenty trees were randomly selected (40 cm dbh class, 33-51 years of age), sampled at three stem height levels (5%, 35% and 65% of tree height) and three radial positions (10%, 50% and 90% of radius). They were further tested for air-dry density at 12% moisture content, bending strength (MOR), modulus of elasticity (MOE) and compression strength parallel to grain (CS), using ISO standards. The overall mean properties of blackwood were: 654 kg m À3 density, 139 N mm À2 MOR, 141 Â 10 2 N mm À2 MOE and 61 N mm À2 CS. Site was not a significant source of variation for all wood properties. The variation between individual trees was the most important. Within the tree, the radial variation was highly significant for all traits, while the longitudinal variation was only significant for density. The correlation of density with the mechanical properties was moderate. Blackwood showed potential for being an alternative species to supply the industry with valuable hardwood timber. The significant differences found between the trees demonstrate the possibility of selection and improvement for increased wood quality.

Resumen-En numerosos detalles estructurales de construcciones realizadas con madera, el esfuerzo de compresión transversal a las fibras juega un papel muy importante y en muchas ocasiones condiciona su diseño. En este trabajo se analiza el comportamiento a compresión de piezas de madera de pino silvestre de pequeña escuadría sometidas a un esfuerzo de compresión transversal a las fibras y se han obtenido unos valores medios para la tensión de rotura y el módulo de elasticidad de 4,20 MPa y 305,86 MPa, respectivamente.Palabras clave-Madera; construcción; esfuerzo de compresión; deformación.Abstract-In many structural details of buildings made of wood, the transverse compression stress to the fibers plays a very important role and often determines its design. In this work, the compression behavior of small pine wood pieces subjected to a cross -compressive stress to the fibers is analyzed and mean values for the tensile strength and the modulus of elasticity of 4,20 MPa and 305.86 MPa, respectively.

This study evaluated the surface microhardness of four glass ionomer cements and a composite resin (Fuji IX, Ketac Molar, Vidrion R, Vitromolar and Z 250). Ten specimens of each glass ionomer cement with 8.0 mm diameter and 5.0 mm high dimensions were made and Vicker's microhardness measurements were taken at 1 day and 1 week after initial setting reaction. The results were analyzed using Student's T test and Tukey test (p < 0.05) and demonstrated that the values of microhardness increased after 1 week, with the exception of Fuji IX. Resin composite Z250 presented the greatest values for microhardness.