Wood and Fiber Science (E-Journal)
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Specimen Orientation for the Calibration of Direct Scanning X-Ray Wood Densitometers
Get PDFIt was found that specimen orientation has considerable effect on the calibration of direct scanning X-ray wood densitometers. A comparison between various orientations was made and verified by a test. Optimum calibration is accomplished when the specimens are made in such a way that the radiation beam is passed through the wood in the tangential direction and scans it in the radial direction
Dynamic Mechanical Behavior of Black Cherry (Prunus Serotina EHRH.)
Get PDFThe dynamic mechanical properties of black cherry (Prunus serotina Ehrh.) have been investigated as a function of temperature at audio frequencies. Relaxation processes are evident near 200, 360, and 510 K. The process near 200 K was investigated as a function of initial moisture content (based on mass measurements prior to testing). At moisture contents greater than about 20%, the damping peak is centered near 185 K. This relaxation shifts with moisture content, and at moisture contents below 6%, the peak is centered near 225 K. The relaxation in the 360 K region is also associated with initial moisture content. For oven-dry black cherry specimens, the dynamic mechanical properties in the 360 K region are nearly temperature-independent. The relaxation near 510 K is believed to be associated with thermal degradation of wood constituents that are known to degrade in that temperature region
Comparison of Three Equations for Predicting Stress Wave Velocity As A Function of Grain Angle
Get PDFAssessment of a nondestructive test system for detecting defects in the gluelines of edge-glued hardwood panels required development of a mathematical relationship for predicting stress wave velocity as a function of grain angle. This relationship was necessary to understand better how stress waves propagated around gaps or flaws in a glueline. In addition, the relationship was needed to assess the influence of specimen geometry upon the effectiveness of the stress wave technique.Equations were generated by a statistical regression analysis software package and compared to Hankinson's equation. Equations were based upon measured velocity of stress waves traveling at angles between 0 and 90 degrees to the grain at 15 degree intervals in birch, black cherry, red oak, yellow-poplar, and western white pine boards. Regression analyses indicated that the best correlations were found with second order hyperbolic and parabolic equations. The two equations were compared to Hankinson's equation and to each other by using Absolute Average Error (AAE) for each equation for each species and for all species combined at each of the grain angles for which data were collected. Hankinson's equation produces the least AAE of the three equations although the hyperbolic and parabolic equations must also be considered reasonable predictors of stress wave velocity at most angles to the grain
Influence of Pit Aspiration on Earlywood Permeability of Douglas-Fir
No full textSapwood earlywood longitudinal gas permeability is a sensitive barometer of the effect of seasoning conditions on pit aspiration. The proportion of aspirated pit pairs was quantitatively linked with longitudinal gas permeability and can be used to explain the earlywood permeability of a given sample. If comparable levels of pit aspiration are found in two samples differing in permeability, however, it may be necessary to examine other anatomical aspects of the wood being permeated. Permeability is a function of the number of open pits per tracheid, which, coupled with tracheid length, determines the probability of occurrence of a continuous flow path through the wood specimen being permeated. Percentage pit aspiration operates in conjunction with number of pits per tracheid to determine the number of open pits per tracheid. While the proportion of aspirated pits can be measured and related to permeability, it is suggested that tracheid length, total number of pits per tracheid, and number of tracheids per square millimeter also be evaluated in order to assess properly the effect of pit aspiration on permeability
Carbon and Hydrogen Contents of Short-Rotation Biomass of Five Hardwood Species
Get PDFCarbon, hydrogen, and ash contents were determined on three-year-old, short-rotation trees of autumn olive, black alder, black locust, eastern cottonwood, and sycamore. These plantations were established on marginal agricultural land that was not suitable for food production in Midwestern United States. Test results indicated that elemental analysis varied among species, planting site, and spacing. Black locust had the highest hydrogen content, black alder had the highest carbon content, and eastern cottonwood possessed the greatest ash content. The hydrogen content was higher at bottomland than upland, while the carbon content and ash content were both higher on upland as opposed to bottomland sites. The hydrogen content was higher at narrow spacing, while carbon content was higher at wide spacing. Conversely, hydrogen was not significantly affected by the stem portion, while both carbon and ash contents of the wood, bark, and branches mixture portion were higher than those of the wood portion
Comparison of Modifiers for Durability Improvement of UREA-formaldehyde Resin
No full textSeveral common organic modifiers, having varying degrees of reactivity and functionality, were evaluated at different levels of addition for their improvements to the relative durability of urca-formaldehyde (UF) glue-wood bonds. The recently developed thermal-softening technique was used to determine the thermal sensitivity of cured samples of these modified resins. Urea-formaldehyde resin containing modifiers with aromatic character and high potential reactivity, such as melamine, furfuryl alcohol, and resorcinol, showed significant increases in thermal-softening points compared with unmodified resin. Accelerated-aging tests on Douglas-fir laminates bonded with UF resins modified with either melamine, 2-imidazolidinone, or furfuryl alcohol showed that durability ranking correlated closely to the softening points of these adhesives. One inorganic modifier, aluminum powder, gave an improvement in softening point, but exhibited poor durability with wood bonds in aging tests
Radial and Vertical Variation in Stem Properties of Juvenile Black Locust (Robinia Pseudoacacia)
Get PDFTen 10- to 12-year-old black locust (Robinia pseudoacacia L.) trees from two sites were analyzed to determine the within-tree variation (radially and vertically) and the between-site variation of selected wood properties. Specific gravity, fiber length, and extractive content exhibited significant radial variation for samples taken at breast height. Specific gravity increased radially from 0.57 near the pith to 0.68 near the cambium. Fiber length also increased radially from 0.75 mm (pith) to 1.06 mm (cambium). Radial variation was also exhibited by benzene-EtOH and total extractive content. Sap-wood tissue possessed the lowest benzene-EtOH content (2.70%) and total extractive content (6.81%), while the outer heartwood tissue maintained the highest extractive levels, 4.60% and 8.54%, respectively. Vertical stem analysis of samples obtained at intervals of 20% of the total-tree height showed a positive relationship with height, for ash content and hot-water extractive content, and a negative relationship with height for fiber length and benzene-EtOH extractive content. Stem tissue was composed of 84.7% wood and 15.3% bark. Mean heartwood content was 54.1%. Total stem-wood fiber length, specific gravity, and total extractive content averaged 1.05 mm, 0.68 and 7.32%, respectively. Nonextracted specific gravity was the only property differing significantly between sites averaging 0.69 and 0.66 for the two sites
The Interaction of Electrode Design and Moisture Gradients in Dielectric Measurements on Wood
Get PDFMeasurement of dielectric properties (capacitance and equivalent parallel conductance) of specimens with various moisture gradients, using twenty different electrode designs, showed that no electrode design eliminated the effect of moisture gradients on the measured average dielectric properties. A parallel-plate electrode, with poles on opposite faces of the specimen, was influenced least by moisture gradients, but as applied to dielectric moisture meters, the improvement did not appear to warrant the inconvenience of making contact with both sides of the specimen. There was a weakly defined indication that a dielectric moisture meter using the capacitance principle and operating at about 10 kHz would be least affected by moisture gradients
Creep Buckling of Small, Slender Wood Columns Under Cyclic Environment
Get PDFCreep buckling of small, slender Douglas-fir columns was studied under two types of cyclic environmental conditions. Three load levels were used for an environment with severe changes (Type A), while one load level was used for a less severe one (Type D). Experimental data show in both cases an increase of deflection during the low humidity cycle and recovery during the higher humidity cycle. The reduction of deflection during the wet cycle was more pronounced in Type A than in Type D cycling. Time to buckling failure was nearly one order of magnitude less, at the same load level, in Type A as compared to Type D. Small initial deflections did not appear to have a significant effect on time to failure. The relationship between load level and time to failure under Type A cycling was similar to published data for beams of similarly small size