Mechanical Properties Of Wood Research Articles

Effect of size on the dynamic and static bending of green wood samples of European beech

In recent years, there has been growing interest in assessing the properties and quality of green hardwood by non-destructive testing (NDT). The frequency resonance technique (FRT) has proven to be an effective NDT method in the assessment of green wood. The properties of green wood with complex structures are often estimated based on the mechanical properties of standard samples. This raises two questions: (1) What effect does size have on the obtained mechanical properties of wood during bending? and (2) Is it possible to describe or predict this effect by using FRT on a different size and structure? In this study we monitored differences in the dynamic modulus of elasticity in bending ( MOED), the flexural modulus of elasticity ( MOE) and the flexural modulus of rupture ( MOR) in samples of different sizes and shapes. Four groups of bending samples with a square cross-section (7 mm×7 mm×100 mm, 20 mm×20 mm×300 mm, 40 mm×40 mm×600 mm and 60 mm×60 mm×900 mm) and two groups of branch samples with near-circular cross-section (±80 mm×880 mm; diameter ±100 mm×1120 mm) of European beech wood were tested. The results show that no relationship between MOED, MOE and MOR and the size of samples was conclusively confirmed. A strong relationship between MOED and MOE or MOR for all square cross-sections was shown by the results.

A Study of Member Displacement According to Seasonal Climate of the Sungnyemun Gate, a Korean Wooden Architectural Heritage Site

This study analyzes the results of a displacement measurement of the Sungnyemun Gate’s structural members, such as column, girder, and hip rafter, carried out by the National Institute of Cultural Heritage for about 10 years from December 2013 to October 2022. Through this, we attempt to examine the behavior of wooden architectural heritage sites according to seasonal changes and infer the factors influencing structural deformation. As a result of the analysis, it was confirmed that the structural members of the Sungnyemun Gate, including the columns, girders, and hip rafters, continued to move and that the displacement of members was accumulated, and the structure was deformed. It was also confirmed that member displacements accumulated in a specific direction. In the case of the Sungnyemun Gate, the column leaning south, the hip rafters’ endpoint sagging, and the girders’ center deflecting were continuously observed. Furthermore, the behavior of wooden architectural heritage sites, where displacement accumulates as it undergoes repeated deformation and recovery according to seasonal changes, was also revealed in detail. The deformation of the Sungnyemun Gate’s members shows a pattern that reflects the mechanical properties of wood, which repeatedly increases and decreases displacement depending on the season. However, seasonal deformation did not appear the same in all the members. Even the same member has an uneven drying speed due to differences in the amount of sunlight it receives depending on its location, which leads to uneven distribution of deformation. The significance of this study is that it examined the behavior of a wooden architectural heritage site in detail based on the quantitative results of long-term measurements and prepared primary data for the future management of wooden architectural heritage sites.

Chemical, Thermal, and Morphological Properties of Sustainable Lignocellulosic Biomaterial

By the present paper, an experimental investigation was proposed to compare the morphological, chemical and mechanical properties of the Petiole Date Palm Wood (PDPW) collected from north and south of Algeria. Both regions have very distinctive climatic conditions – wet conditions in the north (near the Mediterranean Sea) and semi-arid conditions in the south Biskra. To achieve this aim, large quantities of waste from PDPW were collected, cleaned, and cut according to the normalization specific to each type of test. After that, scanning electron micrographs, infrared spectroscopy, dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis were made, and moisture content (MC) and water absorption (WA) were determined, to compare the effect of the different environmental conditions. From the results obtained, petiole date palm wood typical for the southern region had a high fiber content, attributed to its low porosity and excellent mechanical properties, which resulted in low water absorption. In contrast, the northern petiole wood reveals a higher glass transition temperature (Tg) and significant damping coefficient. At comparable relative density values, the specific properties were found to be comparable to those of balsa, foams and metallic honeycombs.

Detecting Early Degradation of Wood Ultrastructure with Nonlinear Optical Imaging and Fluorescence Lifetime Analysis.

Understanding the deterioration processes in wooden artefacts is essential for accurately assessing their conservation status and developing effective preservation strategies. Advanced imaging techniques are currently being explored to study the impact of chemical changes on the structural and mechanical properties of wood. Nonlinear optical modalities, including second harmonic generation (SHG) and two-photon excited fluorescence (TPEF), combined with fluorescence lifetime imaging microscopy (FLIM), offer a promising non-destructive diagnostic method for evaluating lignocellulose-based materials. In this study, we employed a nonlinear multimodal approach to examine the effects of artificially induced delignification on samples of Norway spruce (Picea abies) and European beech (Fagus sylvatica) subjected to increasing treatment durations. The integration of SHG/TPEF imaging and multi-component fluorescence lifetime analysis enabled the detection of localized variations in nonlinear signals and τ-phase of key biopolymers within wood cell walls. This methodology provides a powerful tool for early detection of wood deterioration, facilitating proactive conservation efforts of wooden artefacts.

Bottom-up engineering strategies for electromagnetic shielding wood-based composites through Ca2+ crosslink and graphene incorporation

ABSTRACT Sustainable electromagnetic interference shielding materials that combine environmental friendliness, robustness, and enhanced performance are critically needed for national development strategies. Wood-based materials, particularly woodchips, are desirable due to their chemical similarity to wood and the potential to eliminate anisotropic properties. In this study, chemically treated woodchips to expose the cellulose within them. The interactions between woodchips, graphene, and calcium ions (Ca²+) was studied to create innovative electromagnetic shielding wood-based materials using a bottom-up approach. Compared to composites formed via hydrogen bonding cross-linking, the introduction of calcium ions significantly increased the degree of cross-linking and improved the mechanical properties of the composites. This resulted in a tensile strength of 9.8 MPa, compressive strength of 43.8 MPa, and flexural strength of 22.3 MPa. By incorporating graphene, an optimal conductive network was established. At a sawdust-to-graphene ratio of 1:1, the material's conductivity and shielding effectiveness were 100 S/cm and 49 dB, respectively, meeting the standards for commercial and residential EMI shielding applications. Moreover, this composite material addresses the anisotropy and inconsistent mechanical properties of natural wood, showing significant potential in the area of green electronics.

Effects of wood density on mechanical properties of mangrove wood from the Amazon coast.

Mangrove forests are essential on the Amazon coast, as local communities widely use their wood. However, it is still necessary to understand the mechanical properties of wood typical of mangroves. Our main objective was to understand the influence of density on mechanical properties. Then, we tested the hypothesis that wood density has a stronger influence on the mechanical properties of R. mangle trees. Five trees of each dominant mangrove species were cut, and the mechanical properties of wood from these species were analyzed according to ASTM D143-14. Rhizophora mangle wood presented the highest average values compared to other mangrove species for mechanical properties (ρ12% = 1031.6 kg m-3; fv0 = 21.8 Mpa; fc0 = 79.6 Mpa; fM = 190.0 Mpa; EM0 = 18.8 Gpa), as well as for resistance and rigidity. Wood from mangrove trees on the Amazon coast has the same trend of mechanical properties as trees from Asian mangroves. Avicennia germinans and Laguncularia racemosa have a moderate rating. Rhizophora mangle stands out for presenting the highest values of these properties, with the species of Rhizophoraceae being considered the most resistant wood among mangrove species worldwide.

Combining boron acid and heat treatment for enhanced durability of Cunninghamia konishii plantation wood

This study evaluated the combined effects of boric acid treatment and heat modification on the durability and mechanical properties of Cunninghamia konishii plantation wood. The results indicated that boric acid treatment significantly improved the termite resistance of C. konishii wood. With a boric acid absorption level of 6.8 kg/m³, the treated wood exhibited a mass loss of only 1.3–2.9 % (meeting the <3 % termite resistance standard), compared to 12.5–21.8 % mass loss in untreated samples. Meanwhile, boron treatment was applied and increased termite mortality to over 99 %. Both boric acid and boron treatments have proven the efficacy in increasing wood durability, in terms of resisting brown-rot fungi and significantly reducing mass loss under specific conditions. This study results demonstrated that heat treatment alone improved wood dimensional stability by reducing wood swelling, with a consequent decrease in the wood air-dried density, from 398 kg/m³ to 373–396 kg/m³. It was also observed that the heat treatment increased the modulus of elasticity (MOE) but decreased the modulus of rupture (MOR). Furthermore, when combined with boric acid treatment, the heat treatment further increased the compressive strength and hardness of wood, but decreased the MOR and shear strength. An optimal treatment, involving a boric acid concentration of 6.8 kg/m³ at 170 °C for 2 hours, was conducted to assess its effectiveness in enhancing both durability and mechanical properties of wood, aiming to seek a balance between these crucial factors for wood applications.

Determination of local mechanical properties of clear wood in relation to the local fiber deviation

Determination of local mechanical properties of clear wood in relation to the local fiber deviation

Mechanical properties of beech wood treated with malic acid-based polyester

Abstract While chemical modification enhances wood’s resistance to deterioration and dimensional stability, it often results in alterations to the mechanical properties, limiting its engineering applications. This study focuses on the in situ esterification of beech wood using malic acid/polyol mixtures and evaluates its impact on mechanical properties. The results of the compression tests yielded limited information, characterized by a notable degree of variability as indicated by the high standard deviation. The four-point bending tests conducted here revealed an increase in the modulus of elasticity (MOE). However, this improvement in MOE was accompanied by a decrease in the modulus of rupture (MOR), indicating a trade-off between stiffness and strength. To better understand the mechanisms affecting the treated wood’s mechanical properties, we compared the experimental and theoretical glass transition (Tg) of the polymers with material stiffness. X-ray computed tomography revealed that treatment increases specimen density and creates a gradient, with higher density near the surface, potentially contributing to increased stiffness. These findings suggest a nuanced impact of the in situ esterification process using malic acid/polyol mixtures on the mechanical properties of beech wood.

Stiffness and hardness of thermally modified timber assessed with explainable machine learning

Thermal modification is an environmentally friendly practice to enhance the durability of wood. Despite the method's effectiveness in improving wood durability and dimensional stability, the mechanical properties of wood could be compromised following the heat treatment process. While most of the literature has focused on studying the impact of wood modification on stiffness or strength, less attention was given to characterization and nondestructive prediction of wood hardness following thermal treatment. Hardness, an important quality indicator of wood, has been a subject of limited research in the context of developing predictive models for assessing the hardness of thermally modified wood. The existing research in this area has either been scarce or unsuccessful, with poor predictive performance being a common issue. This research studies the impact of thermal modification on the longitudinal and transverse hardness of some common North American softwoods (Douglas-fir, Western hemlock, red cedar) and hardwoods (red alder, paper birch). It also aims to develop an explainable machine-learning (TreeNet gradient boosting machine) predictive model for hardness prediction using stress wave data combined with wood density and information about the type of wood species and heat treatment level. The impact of heat treatment on the stress wave velocity, density, and hardness was studied, and the dependency of the variables was assessed using correlation and clustering analysis. Machine learning modeling showed that the longitudinal and transverse hardness could be predicted by having a maximum R2 (test data) of 70.62 and 72.78, respectively, with a relative importance of the predictors in descending order as wood species > density > wave velocity >MOEdyn> heat treatment. Using the top 3 critical parameters yielded an R2 (test data) of ∼69 % for both models. The developed model could predict the hardness of various wood species treated at different temperatures, having only the type of wood species and its density followed by the stress wave velocity, which can be measured at an industrial scale.

Enhancing the bending strength, load-carrying capacity and material efficiency of aspen and black alder plywood through thermo-mechanical densification of face veneers

Many research papers highlight the positive impact of wood densification on mechanical properties of solid wood as well as wood veneers. Previous experimental studies comparing densified to non-densified wood materials of the same thickness consistently demonstrated higher strength properties in bending for densified materials. However, these studies often overlooked an important comparison: the strength and load-carrying capacity of non-densified wood material to its densified state, in which the thickness is reduced and thus the material’s moment of inertia. The current study, aims to address this gap for plywood made from low-quality, underutilized hardwood species, encompassing both non-densified and densified veneers. Additionally, these plywood panels are compared with high-quality birch plywood. Plywood samples made from common aspen (Populus tremula L.) and black alder (Alnus glutinosa L.) species, incorporating densified veneers, are compared to conventional silver birch (Betula pendula Roth.) plywood. The study also considers material utilization efficiency. Results showed that plywood made from non-densified aspen and black alder veneers exhibited comparable strength to standard birch plywood, positioning them as competitive alternatives to high-quality wood species. While densified black alder veneers increased strength in average from 83.6 MPa to 126.3 MPa, a loss in load-carrying capacity was observed from 1930 N to 1637 N due to reduced thickness and moment of inertia.

Surface layer reinforcement modification for wood with high strength and flame retardancy performances

The high-value utilization of low-value wood can effectively address the shortage of wood resource, while also contributing to the global green sustainable development and the implementation of “dual carbon” strategy. The present study employed an innovative technology to achieve controllable surface reinforcement modification of fast-growing poplar wood, resulting in improved strength and exceptional flame retardancy for structural applications. The achievement was realized through a three-step method, involving delignification, impregnation, and surface densification, while minimizing the loss of wood volume. The results demonstrated that surface functional densification can significantly improve the mechanical properties of fast-growing poplar wood, with the modulus of rupture (MOR) and modulus of elasticity (MOE) reaching 140.6 MPa and 11.8 GPa, respectively, representing a 3.4-fold and 2.5-fold increase compared to the control group (CK). The samples were found to possess thin surface-densified layers, while the core layer remained unaltered, thereby exhibiting a sandwich structure with significant disparity in density between the layers, reaching up to a factor of 2. The pores structure of the surface layers underwent significant densification, with a gradual deformation distributed throughout its thickness direction. A process optimized for surface densification involving a 2-hour delignification duration and a pressure of 3 MPa. The sample subjected to surface functional modification exhibited a 90-second delay in the peak of heat release compared with the CK. The heat release rate (HRR) experienced a significant deceleration, accompanied by notable reductions in total heat release (THR) and smoke production rate (SPR). The mechanisms underlying the enhancement of surface functionality were elucidated from the perspectives of physical mechanics, microstructure, and flame retardancy, providing a theoretical foundation for the efficient utilization of fast-growing wood.

Alternative Tree Species for Sustainable Forest Management in the Brazilian Amazon

The scarcity of hardwoods from tropical forests makes the search for alternative species necessary for commercialization. This study aimed to establish groups of timber species from the Amazon Forest with potential for logging purposes through the assessment of their physical-mechanical properties, aiming to identify alternative species that can meet the market demands. We utilized data from the Forest Products Laboratory (LPF) (containing information on basic density and other wood mechanical properties) and the Timberflow platform, as well. We applied a multivariate cluster analysis technique with the aim of grouping species based on the technological characteristics of their wood and evaluating similarity among them to obtain homogeneous groups in terms of economic potential and utilization. The results indicated four homogeneous groups: Cluster 1 (40.72% of species, basic density-db: 690 kg m−3), Cluster 2 (13.92%, db: 260 and 520 kg m−3), Cluster 3 (27.32%, db: 550 and 830 kg m−3), and Cluster 4 (18.04%, db: 830 kg m−3). Most of the 20 listed species are classified as more commercially viable (70%), with high wood density. Species identified as alternatives include Dialium guianense and Zollernia paraensis for Dipteryx odorata, Terminalia argentea for Dinizia excelsa, Terminalia amazonia and Buchenavia grandis for Goupia glabra, and Protium altissimum and Maclura tinctoria for Hymenaea courbaril. The analysis highlighted the overexploitation of a restricted group of species and the need to find alternatives to ensure the sustainability of forest management. This study contributed to identifying species that can serve as alternatives to commercial ones, promoting a more balanced and sustainable forest management.

Harnessing artificial neural networks and linear regression models for modeling thermal modification processes: Characterization by FTIR and prediction of the mechanical properties of eucalyptus wood

In the present study, an artificial neural network model and multiple linear regression method were constructed to establish a relationship between the parameters of the thermal modification process and the mechanical properties of Eucalyptus camaldulensis wood samples. Three influencing parameters on the mechanical properties during heat treatment were considered input variables, namely water absorption, volumetric mass, and mass loss; the other parameters were kept constant (treatment temperature: 200, 220, 240, and 260 °C, and the duration: 5, 60, and 90 minutes). There were five neurons in the hidden layer that were used, as well as an output layer for the mechanical property. According to the results obtained, the mean square error (MSE) for the training, validation, and testing datasets were determined to be 0.21, 0.25, and 0.22 in the prediction modulus of rupture (MOR) and 0.019, 0.017, and 0.023 in the prediction modulus of elasticity (MOE). Higher coefficients of determination (R2) ranging from 0.93 to 0.98 were obtained for all datasets with the proposed ANN models, while the multiple linear regression models found the MSE to be 1.03 and 1.40 for MOR and MOE, respectively, as well as R2 to be 0.97 and 0.80, respectively. These results show that ANN models can be successfully used to predict the change in mechanical properties of wood during heat treatment.

Manufacture and study the mechanical, thermal and physical properties of plastic wood

Abstract This study focuses on evaluating the mechanical properties and thermal conductivity of unsaturated polyester (UPE) composites reinforced with Pistacia shells (Pi-S). Wood-plastic composites were prepared using UPE reinforced with Pi-S at different weight ratios (50%, 60%, 70%). The main objective of this work is to recycle Pistacia shells in significant proportions and assess the impact of using Pi-S as reinforcing materials in UPE. Mechanical tests, such as Shore D hardness, impact resistance, and compressive strength, were employed to evaluate the mechanical properties of the composites. The results showed that the 50% weight ratio achieved the highest values in all tests compared to other ratios (60%, 70%). Impact resistance increased to 10.15 Kj/m2 at the 50% weight ratio, followed by the 60% weight ratio with the highest impact resistance. The results also indicated a slight decrease in Shore D hardness with an increase in the weight ratio and a decrease in compressive strength. Regarding thermal conductivity, the highest thermal conductivity value was at the 50% weight ratio, with a value of 0.68118762 W/mk. It then decreased at the other weight ratios but remained higher than the thermal conductivity of pure unsaturated polyester. This technique allows for the full utilization of Pistacia shells in the wood-plastic industry, contributing to various applications such as wooden and plastic flooring, surfaces, doors, and more.

Integrated approach for improving mechanical and high-temperature properties of fast-growing poplar wood using lignin-controlled treatment combined with densification

Previous studies on the modification of fast-growing wood have extensively examined the effects of density and lignin content on the strength and high-temperature properties of modified wood. However, a comprehensive quantitative analysis of their effects on high-temperature performance remains insufficient. To address this knowledge gap, we applied alkali treatment and compression densification to fast-growing poplar, resulting in modified specimens with varying densities and lignin levels. The quantitative effects of density and lignin content on high-temperature properties were meticulously evaluated. Chemical changes were analyzed using Fourier transform infrared spectroscopy (FT-IR), while the mechanical and high-temperature properties were comprehensively assessed. Delignification was found to be positively correlated with treatment duration, with hemicellulose degradation also detected via FT-IR analysis. Significant enhancements were recorded in flexural strength, tensile strength, and modulus of elasticity, accompanied by improvements in ductility ratio and compressive strength. The modified poplar wood exhibited increased thermal stability at elevated temperatures. Furthermore, density and lignin content were identified as significant factors affecting high-temperature performance, establishing minimum density thresholds for various lignin contents in modified poplar wood to ensure optimal performance. This study enhances to the understanding of the intricate relationships among wood properties, modification techniques, and high-temperature performance.

CHANGES IN WOOD QUALITY OF BETULA ERMANII LOGS BY HEATING TREATMENT

Logs of Betula ermaniiCham. were heated at a temperature inside the logs of 80°C for different heating durations of 0, 20, 40, and 60 h using a laboratory oven. After heating treatment, several wood qualities were examined, including residual stresses, moisture content, wood color, and physical and mechanical properties. The effects of the heating treatment duration on wood quality were analyzed using linear mixed-effect modeling. The developed models revealed that heating treatment affected residual stresses and wood color but not mechanical properties. The obtained results also suggest that a heating treatment duration of 20 h is sufficient to reduce residual stresses in B. ermaniilogs without reducing the physical and mechanical properties of wood.

An eco-friendly strategy of cell wall stapling: In situ crosslinking of acrylic acid emulsion impregnated in thermally treated poplar wood

Traditional wood modification methods often result in the release of harmful substances and energy wastage. This study proposes an efficient and environmentally friendly modification strategy for fast-growing poplar wood. The approach involves polymerizing organic linear molecules within the cell wall to form stitches, thereby enhancing the dimensional stability and mechanical properties of wood and increasing its ability to withstand various environments. Poplar wood specimens were treated via a method that combines heat treatment with acrylic emulsion impregnation. The research findings indicated an improvement in the mechanical properties of poplar wood following the combined treatment. Moreover, poplar wood subjected to this treatment approach exhibited a 35.24 % lower water absorption rate after a 7-day water immersion test, and tangential and radial swelling rates of the wood were reduced by 29.66 % and 45.68 %, respectively. Scanning electron microscopy revealed excellent penetration of acrylic emulsion into wood cells; the emulsion infiltrated the wood and adhered to the cell walls, forming a crosslinked network structure. Analysis of the modification mechanism through X-ray diffraction, Fourier-transform infrared spectroscopy, and X-ray photoelectron spectroscopy showed that the successful infusion of acrylic emulsion compensated for the lower mechanical properties of thermally treated wood, thus improving the utilization value of poplar. The acrylic emulsion is an environmentally friendly and harmless modifier, making the modified wood suitable for various applications, including indoor furniture, logistics, and outdoor facilities. This modification strategy enables efficient resource utilization and provides valuable insights for the sustainable development of the timber industry.

Acetylation of Aspen and Alder Wood - Preliminary Tests

An experimental study of the physical and mechanical properties of untreated and acetylated wood was conducted. The effect of acetylation on wood density was investigated. It was established that the density of the samples generally decreases after acetylation. As the level of acetylation increases, the fiber saturation point decreases in both conifers and hardwoods. Acetylation of wood helps to reduce the sorption properties of wood. The amount of swelling was analyzed. For untreated wood (aspen and alder), the volume swelling index is at the level of 7.5 %. Acetylation contributes to the stability of the geometric dimensions of structures, as the volume swelling index for aspen decreased by 4 times, for alder – by 2 times. An increase in the amount of swelling along the fibers is observed in all samples. Regarding the nature of the destruction of the samples during compression, the aspen (both untreated and acetylated) only crumples without visible signs of destruction. In some samples of alder, partial exfoliation is visible. It was found that acetylation has an ambiguous effect on the mechanical properties of wood of both species.

WD-1D-VGG19-FEA: An Efficient Wood Defect Elastic Modulus Predictive Model.

As a mature non-destructive testing technology, near-infrared (NIR) spectroscopy can effectively identify and distinguish the structural characteristics of wood. The Wood Defect One-Dimensional Visual Geometry Group 19-Finite Element Analysis (WD-1D-VGG19-FEA) algorithm is used in this study. 1D-VGG19 classifies the near-infrared spectroscopy data to determine the knot area, fiber deviation area, transition area, and net wood area of the solid wood board surface and generates a two-dimensional image of the board surface through inversion. Then, the nonlinear three-dimensional model of wood with defects was established by using the inverse image, and the finite element analysis was carried out to predict the elastic modulus of wood. In the experiment, 270 points were selected from each of the four regions of the wood, totaling 1080 sets of near-infrared data, and the 1D-VGG19 model was used for classification. The results showed that the identification accuracy of the knot area was 95.1%, the fiber deviation area was 92.7%, the transition area was 90.2%, the net wood area was 100%, and the average accuracy was 94.5%. The error range of the elastic modulus prediction of the three-dimensional model established by the VGG19 classification model in the finite element analysis is between 2% and 10%, the root mean square error (RMSE) is about 598. 2, and the coefficient of determination (R2) is 0. 91. This study shows that the combination of the VGG19 algorithm and finite element analysis can accurately describe the nonlinear defect morphology of wood, thus establishing a more accurate prediction model of wood mechanical properties to maximize the use of wood mechanical properties.