Wood and Fiber Science (E-Journal)
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Three-Dimensional Finite-Element Models of Cylindrical Wood Fibers
No full textA finite-element solution is presented for analysis of concentric, multilayered, orthotropic cylinders subjected to loadings that do not vary around the circumference. Model fibers are analyzed, and stress distributions are compared to those obtained, using a closed form solution technique. The influence of boundary-shear restraint on internal stress distribution is studied. Comparing results of the three-dimensional finite-element model to values of axial stiffness and relative twisting angles predicted using simpler, two-dimensional methods indicated that the two-dimensional models can give good estimates of these parameters, at least for the thin-walled models
Effect of Cutting Bill Requirements on Lumber Yield in a Rip-First Rough Mill
Get PDFIn recent years, producers of solid wood dimension parts have emphasized improvements in lumber yield, focusing primarily on lumber grade and cutting technology rather than cutting bill design. Yet, cutting bills have a significant impact on yield. Using rip-first rough mill simulation software, a data bank of red oak lumber samples, and a cutting bill that resembles those used in industry, we determined the effect of changes in part size within an existing cutting bill and the impact of part-quantity requirements on yield. The results indicated that cutting bill requirements have a large influence on yield when the shortest part length in the bill is changed. Medium-length part sizes also affect yield except when the cutting bill requires an unlimited number of small parts; in this case, yield always will be high. When an all-blades-movable arbor is used, length changes in the bill affect yield more than changes in width. This study reveals our current lack of understanding of the complex relationship between cutting bill and lumber yield, and points out the yield gains that are possible when properly designed cutting bills are used
An Enzyme Extract from Douglas-Fir Sapwood and Its Relationship To Brown Staining
Get PDFA chemical or enzymatic brown stain in sapwood of Douglas-fir has caused financial losses to lumber producers, particularly those producing valuable clear grades of export lumber. This work shows that the brown stain may be caused, at least in part, by an enzyme system in the sapwood. Buffered extracts of Douglas-fir sapwood showed enzyme activity when added to solutions containing o-diphenol and polyphenol compounds. No activity for monophenol substrates was detected. The enzymatic extract showed two pH optima for activity, one at pH 5.5 and one at pH 8.0, with the activity at pH 8.0 being somewhat greater. The activity was also temperature-dependent, with the highest activity at 35°. The extract showed highest activities with the compounds (—)-epicatechin, dihydroquercetin, and 4-methylcatechol
An Application of Finite Element Analysis to Wood Drying
Get PDFBecause of the nonhomogeneous and nonlinear properties of wood, exact solutions for heat and mass transfer are difficult to obtain by current methods of analysis. This work presents a numerical solution for the analysis of drying wood using the finite element method. A nonlinear model was established on a two-dimensional finite element grid structure that considers local density variation. Through the finite element method of analysis of unsteady-state heat and moisture transfer in wood, the dynamic profiles of temperature and moisture content were determined at a series of drying times. The resulting numerical solutions match well with experimental results and with published results. The results will help to extend understanding of wood-water and temperature relations. In future studies, these data can be incorporated into drying stress analysis to analyze checking or warping
A Model for the Prediction of Fiber Elasticity
Get PDFA model is presented that enables the elastic properties of wood fibers to be estimated from the properties of its polymeric constituents, cellulose, hemicellulose, and lignin. The influence of the value of the axial stiffness of the cellulose crystal is demonstrated, its proper value being discussed in comparison with experimental data on fibers. The effects on fiber stiffness of the S2 fibril angle, the fibril angles of other layers, the crystallinity, and layer thicknesses are analyzed. The manner in which the effect of a variation in yield can be simulated by a change in shape factor of the reinforcing cellulose crystals is demonstrated, the cell wall thus being considered to be a discontinuous reinforced composite
Erosion Rates of Wood During Natural Weathering. Part I. Effects of Grain Angle and Surface Texture
Get PDFThis is the first in a series of reports on the erosion rates of wood exposed outdoors near Madison, Wisconsin. The specimens were oriented vertically, facing south; erosion was measured annually for the first several years and biannually for the remainder of the exposure. In the work reported here, the erosion rates of earlywood and latewood were determined for smooth-planed vertical-grained lumber and abrasive-planed and saw-textured flat-grained plywood for an exposure period of 16 years. Lumber species were southern pine, western redcedar, Douglas-fir, and redwood; plywood species were western redcedar, Douglas-fir, and redwood. Erosion rates varied from 34 μm/year for southern pine latewood to 101 μm/year for western redcedar earlywood. Large differences were observed between earlywood and latewood erosion rates during the first 7 years of weathering, but not during subsequent years. A significant change in the erosion rate of just the latewood was observed for redwood, western redcedar, and Douglas-fir after approximately 7 years of exposure, and for southern pine, a significant change occurred after approximately 12 years of exposure. The erosion rates of vertical-grained lumber were higher than those of flat-grained plywood. Only slight differences were observed for saw-textured as compared to smooth plywood
Chemimechanical Pulping of Eucalyptus Grandis
Get PDFEucayptus is currently one of the main fibrous raw materials used in the pulp and paper industry in given parts of the world. The objective of the present paper is to optimize the chemimechanical pulping conditions for Eucalyptus grandis. evaluate the pulp quality obtained, and draw conclusions regarding its potential use. The raw material used was Eucalyptus grandis industrial chips obtained at a Celulosa Argentina mill in Puerto Piray, Misiones, Argentina. For all the experiments, the chemical stage was carried out in a stainless steel digester with a liquor recirculation system. The mechanical stage was carried out in an 8-in. atmospheric disk refiner. Sodium sulfite and sodium hydroxide were added as chemical reactives. The central composite experimental design used involved five levels for the two variables studied (LL factorial design + star + central point). Three repetitions of the central point were carried out to check for errors. The variables studied were: initial amount of sodium sulfite in the wood (0.9 to 3.5% oven-dry wood) and reaction temperature (96 to 124 C). Times until maximum temperature and time at maximum temperature were, respectively, 20 and 90 minutes. A constant level of sodium hydroxide was maintained in all the experiments (1.5% oven-dry wood). Pulp evaluation was carried out using the usual characterization techniques. Chemical and physical evaluations, including optical testing, were, for the most part, done in accordance with TAPPI procedures.The results obtained indicate that the central point of the design used in our research (110 C and 2.5% oven-dry wood sulfite), appears to represent the optimal conditions for the variables studied for the chemimechanical pulping of Eucalyptus grandis. The pulps obtained could be used as furnish in printing and writing paper grades. The positive correlation between sulfonate concentration and water retention value (WRV) suggests that by increasing fiber wall swelling, the number of sites accessible to sulfonation is increased. The tensile index correlates positively with the degree of sulfonation and with the water retention value of the pulps. It decreases according to the fraction retained in a 30-mesh screen (due to the presence of numerous shives) and increases according to the fraction of fines passing through a 270-mesh screen
Effects of Cyclic Loading on Velocities of Ultrasonic Waves Propagating Through Wood
Get PDFThe aim of this study was to determine the acoustoelastic phenomenon of wood under cyclic loading-unloading processes. Compression or tension load was repeatedly applied to wood specimens within an elastic range. Ultrasonic waves used in this study were shear and longitudinal waves, and their propagation directions were normal to, and along, the loading directions. The ultrasonic wave velocities were obtained by the sing-around method, which is a method for measuring transit time of ultrasonics. The experimental results revealed that change in the velocity of ultrasonic waves passing through wood under axial stress was a nearly linear function of applied stress level with similar slope for both loading and unloading cycles. The acoustoelastic effect of wood was found to be a repeatable and reversible phenomenon. The acoustoelastic constant seemed to maintain a fixed value regardless of the number of loading cycles. The acoustoelastic technique could be used in the determination of stress conditions of structural components in timber construction
