Knots were high in CPerpG MOE and strength but lower for all other properties and had the largest negative impact on tensile strength. Knots were significantly different to clear for all test types and within a range of 48% to 196%. Resin area ratio (RAR) has a moderate correlation with density with an R2 of 0.659 but low to no correlation for mechanical properties. Resin significantly increased density 45% higher than clear, but performed similar with the exception of CPerpG MOE and strength which were significantly different. The results show that in clear wood, the MOE in bending, CParG, CPerpG and shear modulus are 6.9 GPa, 5.78 GPa, 0.27 GPa and 0.59 GPa, respectively, while strengths are 45.8 MPa, 29.4 MPa, 6.7 MPa, 5.7 MPa, respectively. The effect of resin, knots and pith on these properties were also investigated. This study characterised the modulus and strength properties in bending, compression parallel to grain (CParG) and compression perpendicular to grain (CPerpG), shear and tension strength of low-stiffness out-of-grade PEExPCH. hondurensis hybrid (PEExPCH) mean low-stiffness corewood is becoming a larger portion of this out-of-grade population. Increasing trends toward shorter rotation times and fast-grown plantation pines around the world such as Pinus elliottii x P. Out-of-grade pine timber is an abundant material resource that is underutilised because its mechanical properties are not well understood. These results bring into question the standard use of green density to estimate acoustic MOE of live trees and oven dry density is instead recommended. The insignificant slope coupled with better accuracy in MOE supports the hypothesis that the cell wall controls the acoustic velocity while the water in the lumen of the cell wall is insignificant. Also, the static MOE of the green samples was overestimated by 16% by both resonance and ToF tools with oven-dried density, while it was 72% when estimated with density at test. The acoustic velocity decreased by 32.9 and 28.8 m/s for ToF and the resonance acoustic tools respectively for a unit increase in EMC below fiber saturation point (FSP) 5.4 and 6.1 m/s respectively for a unit increase in EMC above FSP although the slope was statistically equivalent to zero. The results indicated the acoustic velocity is sensitive to equilibrium moisture content of loblolly pine, and sensitivity to EMC is similar for both type of tools.
In this study, we explored how the equilibrium moisture content of small clear wood samples (2.5 cm × 2.5 cm × 41 cm) affect the predictive capabilities of two types of acoustic tools namely a microsecond timer (ToF) and a resonance log grader (resonance). This classification is based upon the mode of velocity estimation for wood. There are several types of acoustic tools commercially available for wood characterization, but they are generally classified into resonance and time-of-flight (ToF) tools. A second on-going phase of this study addressing structural size specimens will help to establish more definite conclusions. Therefore, it can be expected that lumber from 25-year-old Paysandú trees will eventually comply with required properties for structural use. Our results on 25-year-old Paysandú small clear specimens showed properties similar to those of previous studies on small clear and structural size pieces. Wood from 15-year-old San José trees showed significantly lower properties than 25-year-old Paysandú trees, and had considerably inferior properties compared with values listed in the Wood Handbook (US Department of Agriculture 1999). The outer wood appears to be denser, stiffer, and stronger than the inner wood in both plantations. Most properties significantly increased radially away from the pith. Specific gravity, bending, compression parallel to grain and perpendicular to grain, and shear tests were conducted. A total of 175 stump bolts from trees from two commercial plantations provided inner and outer small clear specimens for property evaluation. The present study evaluated properties of 15- and 25-year-old loblolly (Pinus taeda L.) and slash (Pinus elliottii Eng.) pine to better understand the current available locally produced wood material. A project was conducted to characterize fast-growing wood, determine engineering properties, and assign visual structural grades of lumber. Trees harvested at this age contain high proportions of juvenile wood that may lead to lumber low in stiffness and strength.
The available wood supply in Uruguay comprises trees that grow so fast in intensively managed plantations that they reach saw timber size in 25 years or fewer.
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