Wood and Fiber Science (E-Journal)
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Grading lumber with acoustic-based technologies Part 1: modeling acoustic (stress) wave behavior in clear wood and lumber
No full textThis research article summarizes results from Part 1 of a study designed to examine using advanced signal processing techniques with acoustic-based lumber assessment technologies to evaluate the MOE, ultimate tension stress (UTS), and MOR of structural lumber. In Part 1 of this research article, a mathematical model of acoustic wave behavior in an idealized specimen is derived using fundamental mechanics. Published information on the physical and mechanical properties of clear, defect-free wood is input into the model to examine acoustic wave behavior. Wave behavior is then examined experimentally in a series of wood specimens. Observed wave behavior in the clear wood specimens, in both time and frequency domains, closely resembles idealized wave behavior. In Part 2 of this research article, predictions from the model are used to improve estimation of the UTS of wood specimens.
Oriented strand board with improved dimensional stability by extraction of hemicelluloses
Full text linkOriented strand board (OSB) panels are commonly used for wooden building structures such as Walls, floors, ceilings, and furniture. These wood composites are manufactured with small wooden strands held together in specific orientations by adhesives. Other additives such as wax might be added to reduce water absorption. One of the limitations of the panels produced today is their poor performance under high humidity conditions. The goal of the present work was 1) to extract hemicelluloses from pine wood strands before the fabrication of OSB panels and 2) to test the impact of the pretreatment on the dimensional stability of these panels. For that purpose, pressure-assisted hydrothermal processes at three different temperatures (120, 140, and 160oC) were performed for 45 min of extraction time in each case. Hemicelluloses in treated wood strands were quantified using high-performance liquid chromatography. Water absorption, thickness swell, MOE, MOR, and internal bond strength were measured to assess the influence of the pretreatment on OBS properties. According to the results, a hydrothermal pretreatment is beneficial for the performance of OSB panels at high humidity levels. The pretreatment of pine strands at 160oC allowed for the maximum removal of hemicelluloses, without a significant degradation of cellulose or lignin, and the OSB panels pretreated with these pinewood strands displayed the best performance in dimensional stability under wet conditions.
DETERMINING YOUNG’S MODULUS OF WOODEN MEMBERS WITH TENON AND MORTISE JOINT USING LONGITUDINAL VIBRATION
No full textThe aim of this study was to examine the effect of tenon and mortise joints on Young's modulus of wooden members and propose a correcting method of Young's modulus. Young's moduli of the specimens with two additional concentrated masses (CMs) and those of the specimens with tenon and mortise joints were obtained using the longitudinal vibration test. The frequency equation for the longitudinal vibration of a specimen with two additional CMs was experimentally proved. The maximum deviation of 17% in Young's modulus was observed when the specimens with tenon and mortise joints were treated as rectangular bars. The mass ratio (mass of a tenon and a mortise/mass of the main body) and the volume ratio (volume of a tenon and a mortise/volume of the main body) could be used for the aforementioned frequency equation. Using this method, it is possible for one to accurately estimate Young's modulus of a wooden member with a tenon and a mortise on a construction site.
Use of Longitudinal Vibration and Visual Characteristics to Predict Mechanical Properties of No. 2 Southern Pine 2 × 8 and 2 × 10 Lumber
Full text linkThe objective of this study was to evaluate the accuracy of single MOE and MOR and combined mechanical properties with visual characteristics to improve the prediction of 2 x 8 and 2 x 10 No. @ southern pine lumber. This study evaluated the following variables: nondestructive tests, knots (knot diameter ratio [KDR] and knot area ratio), density, and mechanical properties (stiffness [MOE] and strength [MOR]). A total of 486 pieces were used, and linear regression models were constructed using stepwise selects to determine the best variables to estimate the MOE and MOR of southern pine lumber. The best single predictor for MOE and MOR was dynamic MOE (dMOE) followed by density. Among the two knot measurement methods used, the KDR best predicted stiffness and strength. For predicting the MOE, the variables dMOE, density, and KDR. The results showed that the addition of knot measurements to the models is able to improve the prediction of mechanical properties
A Method to Characterize Biological Degradation of Mass Timber Connections
Full text linkBiological durability issues in cross-laminated timber (CLT) have been majorly ignored in North America because of the European origin of the material and careful construction practices in Europe. However, the risks of fungal and insect attacks are increased by the North American climatic conditions and lack of job-site measures to keep the material dry. The methods to evaluate durability in solid timber are inadequate for use in mass timber (MT) for a number of reasons, such as moisture variation and size being critical issues. This study therefore proposes a method, which is suitable to evaluate the strength of MT assemblies that are exposed to fungal degradation. The objective of the study was to explore a controlled method for assessing the effects of wetting and subsequent fungal attack on the behavior of CLT connections. Two different methods were used to create fungal attack on CLT assemblies. Although they were both successful, one was cumbersome, left room for many errors, and was not as efficient as the other. In addition, a standardized method to evaluate and characterize key performance metric for the connections is presented.
A 2D Numerical Model of Ultrasonic Wave Propagation in Wooden Utility Poles Using Embedded Waveguide Excitation Technique
Full text linkEmbedded waveguide technique is often not considered as a method for introducing ultrasonic wave for nondestructive testing (NDT). Because of the unique surface condition of wooden utility poles, the rough and uneven surface between the medium and the sensor introduces variation and signal attenuation, which impedes the use of a contact-based ultrasonic sensor. Many inspection and utility firms have adopted the use of inserting a small nail into the wooden pole for NDT. The mechanisms of excitation and reception of ultrasonic wave, however, are very different from the traditional contact-based mounting technique. Because very little research has been carried out on this methodology, this study focuses on the understanding of embedded waveguide excitation and reception in the time domain for wooden structure assessment in cylindrical symmetry. The resulted time domain waveform response is analyzed, and the associated findings will help infer important structural condition for NDT assessments. The study consists of numerical and empirical results to validate and understand the waveform characteristics and the associated energy modes that exist (Bodig 1982) in the two-dimensional wave propagation in a boundary mediu
COMPARATIVE LIFE-CYCLE ASSESSMENT OF A MASS TIMBER BUILDING AND CONCRETE ALTERNATIVE
Full text linkThe US housing construction market consumes vast amounts of resources, with most structural elements derived from wood, a renewable and sustainable resource. The same cannot be said for all nonresidential or high-rise buildings, which are primarily made of concrete and steel. As part of continuous environmental improvement processes, building life-cycle assessment (LCA) is a useful tool to compare the environmental footprint of building structures. This study is a comparative LCA of an 8360-m2, 12-story mixed-us apartment/office building designed for Portland, OR, and constructed from mainly mass timber. The designed mass timber building had a relatively lightweight structural frame that used 1782 m3 of cross-laminated timber (CLT) and 557 m3 of glue-laminated timber (glulam) and associated materials, which replaced approximately 58% of concrete and 72% of rebar that would have been use in a conventional building. Compared with a similar concrete building, the mass timber building had 18%, 1% and 47% reduction in the impact categories of global warming, ozone depletion, and eutrophication, respectively, for the A1-A5 building LCA. The use of CLT and glulam materials substantially decreased the carbon footprint of the building, although it consumed more primary energy compared with a similar concrete building. The impacts for the mass timber building were affected by large amounts of gypsum board, which accounted for 16% of the total building mass. Both lowering the amount of gypsum and keeping the mass timber production close to the construction site could lower the overall environmental footprint of the mass timber building
Effects of Water Soaking–drying Cycles on Thermally Modified Spruce Wood–plastic Composites.
Full text linkThe overall aim of this work was to gain more insight on the potential of modified wood (TMW) components for use in wood–thermoplastic composites (WPCs). Laboratory-scale TMWPCs were produced, and the effects of severe water soaking–drying cycles on the samples were studied. Water sorption behavior and resulting dimensional and micromorphological changes were also studied, and the results were compared with those of unmodified wood–plastic composites (UWPCs) used as control. The TMW was prepared by cutting a spruce board into half and subjecting one-half to an atmosphere of superheated steam at atmospheric pressure with a peak temperature of 210°C, with the other unmodified wood (UW) half as a control. The TMW and UW components were then prepared by a Wiley mill and thereafter sifted into smaller (mesh 0.20-0.40 mm) and larger (mesh 0.40-0.63 mm) size fractions. A portion of the wood components were also subjected to thermal extraction (HE). Composite samples with these different wood components, polypropylene (PP) matrix, and maleated PP (MAPP) as coupling agent (50/48/2 wood/PP/MAPP ratio by weight) were then prepared by using a Brabender mixer followed by hot pressing. The matching micromorphology of the composites before and after the soaking–drying cycles was analyzed using a surface preparation technique based on ultraviolet-laser ablation combined with scanning electron microscopy. The results of the water absorption tests showed, as hypothesized, a significantly reduced water absorption and resulting thickness swelling at the end of a soaking cycle for the TMWPCs compared with the controls (UWPCs). The water absorption was reduced with about 50-70% for TMWPC and 60-75% for HE-TMWPC. The thickness swelling for TMWPCs was reduced with about 40-70% compared with the controls. Similarly, the WPCs with HE-UW components absorbed about 20-45% less moisture and showed a reduced thickness swelling of about 25-40% compared with the controls. These observations also were in agreement with the micromorphology analysis of the composites before and after the moisture cycling which showed a more pronounced wood–plastic interfacial cracking (de-bonding) as well as other microstructure changes in the controls compared with those prepared with TMW and HE-UW components. Based on these observations, it is suggested that these potential bio-based building materials show increased potential durability for applications in harsh outdoor environments, in particular TMWPCs with a well-defined and comparably small size fractions of TMW components.
Influence of cotton fiber properties on the microstructural characteristics of mercerized fibers by regression analysis
Full text linkThis study is conducted on a raw material imported from several countries for the purpose of promoting the development of the world’s cotton spinning industry. If the time for selecting the raw material as well as the quality of the cotton spinning is improved, then time and money will be saved and the spinning industry will be improved. For this study, different cotton fibers were selected from different ecological regions. The cotton fibers were processed using the mercerization process, and then they were examined using X-ray diffraction (XRD), Fourier transform IR (FTIR) and scanning electronic microscope (SEM). High-volume instrument study was conducted to evaluate the physical properties of cotton fibers, including short fiber content, tensile strength, elongation at break, Micronaire value, and upper half mean length. In addition a change in fiber strength, the degree of crystallinity, and degree of orientation of cotton fibers before and after mercerization was also examined. SEM results show that the surface of cotton fibers became smooth and shiny after the treatment. FTIR and XRD revealed that the chemical composition did not change, but the degree of crystallinity decreased and the degree of orientation of alkalized cotton fibers increased after mercerization. In the second phase of this study, a correlation analysis was made between the physical properties of cotton fibers and the microstructural properties of alkalized cotton samples. This analysis revealed that the breaking strength of cotton fibers is strongly negatively correlated with the crystallinity of cotton fibers. The higher the tensile strength, the lower the crystallinity of cotton fibers, which leads to better mechanical properties of the end product. The degree of the orientation of cotton fibers is highly correlated with a tensile strength of cotton fibers. Xinjiang-Cn, BG-Au, and BG-Tu samples exhibited relatively better physical properties. BG-Au, BG-Tu, and Pakistan samples have higher values of tensile strength and lower values of yellowness; moreover, the raw material from these samples can be preferred according to correlation analysis. Correlation analysis between physical properties reveals that the tensile strength of cotton fibers is positively correlated with the Micronaire value; however, the correlation is not strong because of the lower value of the correlation coefficient as 0.4809