European Journal of Wood and Wood Products最新文献

Steel hub joints featuring the End-Bearing and the Bolted-Connections in the wood members (EBBC joints) have been widely adopted in wood reticulated domes. Yet, few studies have been conducted on their mechanical behaviour. This paper presents a refined finite model for EBBC joints, which is verified against existing test results and used for further parametric study on the rotational performance of EBBC joints subjected to monotonic bending moment. The flexural stiffness and capacity of joints about the strong and weak axes are investigated, accounting for influences from axial compression and the number of shear bolts. The results indicate that the joints demonstrate typical elastoplastic behaviour. Higher compression force and more shear bolts can enhance rotational stiffness and the ultimate moment of the joint while decreasing the ductility due to the earlier failure of wood within the bearing region of the joint. Conclusions are drawn regarding the feature and failure mechanism of the EBBC joints, which are helpful guidelines for practical design.

As awareness grows regarding the necessity for sustainable technologies across various industries, including wood-based composites, there’s a heightened demand for ecological solutions. One of the proposed solutions is the partial replacement of wood raw materials in composites with forestry and agricultural waste, thus contributing to the circular economy. Suberin, which is a natural polyester present in tree bark, after depolymerization can be converted into suberinic acids, and after this process, post-extraction solid residues (SAR suberinic acid residues) remain, which include suberin monomers, lignin, cellulose and esters. In this study, it was decided to use this waste in the form of a powder with dimensions of 0.250 mesh as a filler for particleboards. Three-layer boards were prepared in four variants of SAR share in all layers (0%, 5%, 10%, 15%). The physical and mechanical properties of the manufactured boards were tested—modulus of rupture, modulus of elasticity, internal bond strength, screw withdrawal resistance, thickness swelling, water absorption, density profile, contact angle. The formaldehyde and total volatile compounds emissions of the boards were also determined. As a result of the research, it was shown that the addition of SAR has a positive effect on the properties of the panels, but only up to the level of 10%, whereas for boards with a SAR content of 15%, a statistically significant decrease in mechanical and physical properties was noted. The values ​obtained, however, were still within the required assumptions of the European Standards. Only the IB value obtained for the SAR 15% variant did not meet the requirements of the EU Standards. As shown, SAR addition significantly minimizes the emissions from boards, however, it decreases also the hydrophobicity. This study shows a great potential in applying post-extraction residues from bark as a filler material for wood-based panels.

The complex structure of timber has traditionally been difficult to model as it is a highly heterogeneous material. The density and material properties for structural species such as Pinus radiata (radiata pine) can vary greatly across the growth rings. Numerical simulation methods are becoming more prevalent as a method of predicting moisture migration, stress and strain distributions, and fungal/rot intrusion in engineered wood products (EWPs). All these applications require a computational mesh that captures the growth ring structure to facilitate an accurate assessment of the performance of EWPs. In this work, a low-cost image-based algorithm is developed for generating a virtual representation of a small cross laminated timber panel sample. Specifically, the proposed method results in a virtual description of an EWP sample comprised of a triangular prismatic mesh where the nodes are aligned on the growth rings of each individual timber component of the EWP, with specific wood material properties allocated to each mesh element. Each small component is treated individually and we assume there is no longitudinal variation in the density, pith location, and pith angle within the mesh structure. The initial step involves analysing an image of the end grain pattern of a single clear wood sample to identify the growth rings using a spectral clustering algorithm. Next, the centre of the tree (pith) is located through an iterative constrained least-squares algorithm to determine the pith angle. Image analysis of an anatomical image combined with the pith location allows for a constant density value to be assigned to each mesh element. The capability of this framework is then demonstrated by simulating the moisture migration and heat transfer throughout a CLT sample under atmospheric and saturating boundary conditions. Furthermore, the virtual representation provides the basis for simulating additional physical and biological phenomena, such as moisture-induced swelling, decay and fungal growth.

Bamboo possesses inherent plasticity due to its unique fiber structure, especially when subjected to softening treatments that involve moisture and heat. Softening enables bamboo to bend and deform, showcasing its excellent processing adaptability and expanding its range of applications. This study investigates the effects of microwave treatment (at 500W for 30 s with 30% moisture content), boiled-assisted microwace (100 ℃ for 2 h), and alkali-assisted microwave (0.1% NaOH for 2 h) treatments on the mechanical properties, dynamic viscoelasticity, microstructure, chemical composition, and surface wettability of bamboo at four different ages (0.6, 1, 4, and 8 years old). Microwave-assisted softening makes it easier to compress and bend bamboo strips by reducing MOR and MOE. After softening, bamboo exhibits a minimum MOR and MOE of 76.7 MPa and 458.9 MPa, respectively, and a maximum compression of 44.8%. Lignin degradation leads to the formation of new hydrogen bonds, and increased crystallinity is a common factor contributing to enhanced softening properties. The lignin structure undergoes age-related changes, which influence the dynamic viscoelasticity of bamboo. Notably, four-year-old bamboo exhibited increased thermoplasticity when the glass transition temperature decreased by 96.8, 103.5, and 104 °C under various assisted microwave softening conditions. The alkali-assisted method's degradation of hemicellulose and lignin in the Moso bamboo's cell wall was more pronounced compared to boil-assisted methods. This resulted in a loose cell wall structure that is conducive to water infiltration inside the bamboo. However, the alkali-assisted degradation negatively impacted the microstructure, surface wettability, and mechanical properties of bamboo.

Non-contact process monitoring could be a powerful tool to prevent tool misuse, detect wood species, detect tool dullness and reduce electrical energy consumption—all of which could reduce production costs. The aim of this study is to identify recognizable patterns in the sound signals produced during the circular sawing of two different wood species—beech (Fagus moesiaca) and fir (Abies alba)—and to classify them in order to obtain an intelligent machining process capable of recognizing the wood species being machined. These two wood species were selected for this study due to their morphological, physical and mechanical differences. The cutting power was also recorded during the process and measured indirectly via the motor power used. A sound signal can easily be converted into an image (spectrogram), which is suitable as a data basis for the deep learning process. Several neural networks were used to classify the sounds. In order to prepare the raw audio signal for machine learning using image recognition, it was processed in several steps. The relationship between the audio and the recorded cutting power was also investigated and found to be strongly correlated, but only for audio frequencies up to 4500 Hz. Based on the results and further analysis, the classification accuracy for wood species identification varied between 98% for MobileNetV2 and 94% for the InceptionV3 deep learning network.

Bamboo fiber composites (BFCs) possess significant potential for application in the automotive industry. However, the flammability of bamboo fibers and the substantial amount of smoke generated during combustion hinder their application to some extent. Considering the low flame retardancy of a single flame retardant, BFCs were prepared by incorporating ammonium polyphosphate (APP) and nanomagnesium hydroxide (NMH) in this work. The synergistic effect and flame retardant mechanisms were investigated through mechanical properties testing, thermogravimetric analysis, limiting oxygen index testing, cone calorimetry testing, and X-ray photoelectron spectroscopy. When the optimal ratio of APP to NMH was 6:4, the pyrolysis reaction of BFCs was the most difficult to occur, and the oxygen index value reached the noncombustible level. Compared with those of the untreated materials, the peak heat release rate and total smoke production of BFC/6A4N decreased by 45.65% and 59.68%, respectively. APP and NMH exhibited significant synergistic effects during combustion, which enhanced both the flame retardant and smoke suppression properties in the condensed and gas phases, making it a promising synergistic system for BFCs. This work provides possibilities and safety assurances for the preparation of flame retardant and smoke suppression bamboo fiber/phenolic resin composites, promoting the development of materials towards multifunctional and high-performance applications while ensuring cost-effectiveness.

Wood anatomical relationships are essential for several industrial processes because they have straight influence on wood’s natural drying features. The objectives of the present study are to (i) assess and select appropriate hybrids of C. torelliana and C. citriodora clones in comparison to E. urophylla for wood cultivation based on wood drying rates and wood storage time reduction, (ii) to assess differences between C. torelliana x C. citriodora and Eucalyptus clones’ anatomical features and these features’ association with the natural wood drying process. Wood from four hybrids of Corymbia torelliana and Corymbia citriodora clones, and from one Eucalyptus urophylla clone, all of them at the age of 7 years, were assessed. Vessels, fibers and rays’ dimensions, wood basic density, heartwood, sapwood and bark contents, as well as heartwood and sapwood permeability were measured. Wood natural drying curves in logs were plotted by relating moisture content to drying days. The assessed drying parameters were initial moisture; time to rule out the free, bound and total water; water mass and wood basic density to water mass ratio; and rate of time needed to rule out free and bound water. Fibers, heartwood and sapwood dimensions were the features mostly distinguishing the hybrids of C. torelliana and C. citriodora clones from E. urophylla. Among the Corymbia clones, bark content and wood permeability were the variables allowing to separate the four clones into two groups. Both genera showed different anatomical heartwood and sapwood arrangementrs. It was more efficient drying wood from Corymbia clones, mainly due to their higher sapwood content, which enhances free water release and, consequently, makes the drying process faster. The anatomical arrangement of wood from hybrids of C. torelliana and C. citriodora clones favored the drying process; therefore, it can be employed by the forestry industry to select genotypes aimed at reducing wood drying and storage time in the field.

This research presents a unique perspective on noise reduction in buildings, focusing on the use of bamboo, a rapidly renewable building resource, for sound absorption. The study investigates the acoustic properties of bamboo with saw-cutting holes, aiming to explore their potential as resonating multi-frequency sound absorbers in a low-frequency range. Bamboo inherently features hollow spaces between nodes, with consistent distances between them, although this gap may vary depending on the bamboo type and its dimensions, including length and width. The study examined saw-cut holes of varying sizes (3 mm, 5 mm, and 6 mm) for their sound absorption coefficients using two microphone impedance tube methods. Surprisingly, samples with different hole sizes exhibited nearly identical sound absorption coefficients (α = 0.90), but their maximum absorption frequencies shifted based on the hole size. Statistical t-test results also revealed significant differences in sound absorption performance across low-frequency bands. Additionally, numerical analysis of resonance frequency aligns with the estimated resonance frequency of samples. These findings could inform on the design of green walls for multi-frequency sound absorption in houses.

This study investigates the macromechanical and micromechanical behavior of oil palm wood by testing the elastomechanical properties in bending, compression parallel and perpendicular and tension parallel and perpendicular to the vascular bundles of small-size test specimen depending on the position within the trunk, the density and the number of vascular bundles per unit area as well as the plantation site. All properties tested show a much higher exponential increase with the density, following power law relationships with exponents > 1, than common wood species and a significant gradient over both trunk height and cross section. Oil palm wood can be seen as a unidirectional long-fiber-reinforced bio-composite, if vascular bundles are considered as reinforcements (fibers) and parenchymatous ground tissue as matrix. The adapted rule-of-mixture based on the number of vascular bundles per unit area can be confirmed for the density, but not for the tensile properties, because the number of vascular bundles per unit area and share of fibers within the bundles is greater in the periphery than in the trunk central tissue. Furthermore, cell wall thickening over time is more pronounced in the peripheral than in the central tissue and more at the bottom than near the top. Different from small test specimens from common wood species, the compression strength exceeds the tensile strength: f_c,0 : f_m : f_t,0 is 1.4 : 2.2–1.2 : 1. The performance indices for minimum weight design by Ashby and coworkers are comparable to that for coconut and date palm wood.

Bamboo is comprised of parenchyma and vascular bundles, which contain vessels, sieve tubes, and fiber cells exhibiting numerous cavities or loose structures. Bamboo bundles undergo a series of mechanical rolling and disintegration processes to transform them into longitudinally continuous and transversely separated bamboo bundles and there is still a significant amount of vascular bundles and parenchyma that remain undissociated. Partial vessels, sieve tubes, and a majority of the parenchyma cell cavities are still discernible in the bamboo scrimber through the process of hot pressing, which significantly diminishes properties of bamboo scrimber, such as the strength, rigidity, and the water resistance. Therefore, this paper presented a new type of bamboo scrimber made from refined bamboo bundles, which is called high-density bamboo scrimber. That is, based on conventional bamboo bundles, a small amount of NaOH was employed to selectively eliminate a portion of the hemicellulose and soften bamboo bundles. Subsequently, a mechanical hammering technique was employed to disintegrate the bamboo bundles into single vascular bundles and surrounding parenchyma. This process increased the resin infiltration pathways and a multi-scale bonding interface structure was formed, and the densification and physical properties of the bamboo scrimber were improved. In high-density bamboo scrimber, the fiber cells maintained their original structural morphology, while the vessel cells and parenchyma cells were completely compacted, resulting in indistinguishable cell contours, and there was no discernible demarcation between the vascular bundles and parenchyma. Compared to ordinary bamboo scrimber, the bending strength, bending modulus, and maximum displacement of high-density bamboo scrimber exhibited a significant increase of 40.1%, 37.3%, and 18.2% respectively. The water resistance, surface roughness after sanding, and mildew resistance of this particular bamboo scrimber were better than those of ordinary bamboo scrimber. High-density bamboo scrimber exhibited a broader spectrum of applications within architectural structures.