Wood and Fiber Science (E-Journal)

    Effects of Early Pruning on Ring Specific Gravity in Young Loblolly Pine Trees

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    Juvenile wood is not well suited for use in many forest products. Understanding factors that affect the formation of juvenile and mature wood is important when managing commercially important conifer species. The purpose of this investigation was to determine the contribution of ring age, relative height in the stem, and crown position (within or not within the green crown) on ring specific gravity of loblolly pine trees pruned at young ages. A designed experiment consisting of five treatments, control; prune at age 3 yr, age 6 yr, or age 9 yr; and at ages 3,6, and 9 yr, was established at two locations in the Piedmont region of Virginia. Wood samples were acquired at three heights along the stem 15 yr after planting. Results showed that differences in ring specific gravity of the treated plots (Half of green crown removed at each scheduled pruning) were significantly higher than that of the control plots. All variables of ring age, relative height and ring position of within or not within the green crown, were statistically significant. The results suggest that cambial age, maturation, and proximity to green crown are important for controlling whole-ring specific gravity in loblolly pine trees. 

    In-Plane Dimensional Stability of Oriented Strand Panel: Effect of Processing Variables

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    Single-layer oriented strand panels were fabricated under a combination of three alignment levels, four densities, and two resin contents. Flake orientation, density gradient across panel thickness, linear expansion (LE), and bending properties were measured. Flake orientation was characterized with the von Mises distribution using mean flake angle and concentration parameter.It was shown that the shape of the LE-moisture content change curve varied with alignment level and test direction. The variation was attributed to whether the LE of a panel was controlled by transverse or longitudinal wood swelling along a particular test direction. Total LE from oven-dry to water-soak condition, modulus of elasticity (MOE), and modulus of rupture (MOR) varied significantly with flake orientation distribution and density. Effects of resin content at the levels used on LE, MOE, and MOR was relatively small and was more diversified. The LE, MOE, and MOR were correlated with the concentration parameter, density, resin content, and moisture content using a power form equation. The experimental data form a database of layer properties for modeling three-layer, cross-laminated oriented strandboards (OSBs) manufactured under hot pressing

    The Influence of Small Grain Angle Variation on Toughness

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    Toughness of solid wood as determined by ASTM D143-52 is known to be sensitive to slope-of-grain in the specimen. Although samples with observed sloping grain are routinely rejected, localized grain deviations in the center of nominally straight-grained specimens may escape detection. The acceptance of this sample is often aided by the difficulty in identifying the grain orientation at a point and by the usual large number of toughness tests that are conducted in any one experiment. In this study 226 standard toughness specimens of redwood were carefully machined to be straight-grained. However, close scrutiny of the center of the specimens (often after they had been failed) showed that only 10 of the 226 samples had truly straight grain and that localized grain deviations ranged from zero to 15°. Regression analysis showed that the slope-of-grain on the specimen face parallel to the impact direction explained a significant amount of variation in toughness. If this slope was accounted for, the coefficients of variation of toughness were reduced from 33 and 30% to 22 and 18% for impact in the radial and tangential direction, respectively. The results of the study showed that toughness was very sensitive to small localized grain deviations and that truly straight-grained toughness samples are rare. A significant amount of the usual high variation in toughness data could be attributed to these small grain deviations

    Notes And Correspondence

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    Fracture zone Characterization—Micro-Mechanical Study

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    The experimental and numerical characterization of the fracture process zone in softwoods is presented. In-situ real-time Scanning Electron Microscopy (SEM) was used as a tool to examine the physical mechanism of fracture in softwoods (spruce) using end-tapered Double Cantilever Beam specimens. Fracture process zone has been characterized in terms of failure mechanisms. It was found that bridging behind the crack tip is the main toughening mechanism, which contributes to nonlinear wood behavior in the presence of stress concentrations

    Vessel Area Studies In White Oak (Quercus Alba L.)

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    White oak wood has a light blond color and a ring-porous character that make it appealing to consumers. Color and texture are two very important wood quality parameters in such woods. This study was done to examine factors that influence variation in the percentage of earlywood, latewood, and total growth ring vessel lumen areas. Attributes studied were age (radial distance from the pith), longitudinal position (stump and 8 1/2 ft height) in the tree, and thinning effects. The percentage of earlywood vessel area was influenced by radial position in the trees, but was not influenced by growth ring width. The percentage of latewood vessel area was significantly and negatively influenced by growth ring width. Thinning had no effect on percentage of earlywood vessel area, but it reduced the percentage of latewood vessel area and total growth ring vessel area. By reducing total growth ring vessel area, thinning had a negative impact on texture in these trees

    On The Lighter Side From The Desk Of "Ole Al"

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    Characterization of Wood Strands From Young, Small-Diameter Douglas-Fir and Western Hemlock Trees

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    Tensile properties of strands processed from small-diameter Douglas-fir and western hemlock trees grown on the Washington coast were analyzed and effects of location within the tree on properties was examined. Reduction factors for strand properties relative to small, clear solid wood specimen properties were determined by correlating strand properties to previously examined small, clear solid wood specimen properties from the same set of trees. These reductions can be assumed to be damage reduction factors that could help in understanding the expected reduction in tensile or flexure property values from testing solid wood specimens to estimate strand tensile properties. The reduction factors ranged between 0.62 and 0.70 for Douglas-fir and 0.79 and 0.82 for western hemlock for the modulus and were approximately 0.46 for both Douglas-fir and western hemlock for strand tensile strength properties. Measured and calculated strand properties, based on transformation equations, will provide needed values for constructing constitutive relationships when modeling strand-based composites. These properties can also be estimated based on solid wood test specimens if necessary

    Oxygen Sensor for Control of Wood Combustion: A Review

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    Zirconia type oxygen sensors, installed in the exhaust manifold of combustion engines, generate a voltage that drastically changes when the carburetor's air/fuel ratio deviates from the stoichiometric optimum. On this basis such sensors automatically regulate the supply of air and fuel in modern automobiles and in large wood-burning boilers. The literature is reviewed for use of the sensors in residential wood-burning furnaces and stoves, whose fires generally receive either too little or too much air. Unfortunately the sensors' temperature should be above 300 C, a temperature that fire effluents of the residential heating implements reach only near the end of the combustion zone, and then rapidly cool off on their further path to the chimney. Therefore, the sensors are far from ideal for residential heating implements, least of all for small stoves operated batchwise. They are more promising for the combustion control of continuously fueled pellet furnaces

    Theoretical Modeling of Bonding Characteristics and Performance of Wood Composites. Part II. Resin Distribution

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    Further to the development of the inter-element contact model reported in Part I of this series (Dai et al 2006), this paper reports the development of a mathematical (analytical) model and a computer simulation (numerical) model of resin distribution. Based on theories of random coverage process and stochastic system, resin distribution is analytically defined by the average and the variance of resin coverage on constituent wood elements. To complement the analytical model, a numerical model using image digitization and Monte Carlo technique is developed on a computer to visualize and simulate the spatial variation of resin coverage. To validate the models, resin distributions on OSB strands are experimentally investigated using an image analysis technique. The analytical and numerical models are validated by close agreements with each other and with experimental results. It is proposed and modeled that resin coverage is classified into area coverage and mass coverage. The former follows an exponential relationship with resin content, while the latter has a linear relationship with resin content. Both area and mass coverage are strongly affected by element/strand thickness and wood density. The resin area coverage is further affected by resin spot thickness, density, and solids content. Resin spot size has no effect on the average but strong effect on the variance of resin coverage. Implications of the model predictions on improving uniformity and efficiency of resin application are also discussed
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