Mechanical Properties Of Wood Research Articles

Green bio-derived epoxidized linseed-oil plasticizer improves the toughness, strength, and dimensional stability of furfuryl alcohol-modified wood

Furfuryl alcohol (FA) modification represents a sustainable approach to wood modification; however, it significantly reduces the toughness of the wood, limiting its practical applications. This study introduced epoxidized linseed oil (ELO) as an environmentally friendly and bio-derived plasticizer to enhance the toughness and mechanical properties of FA-modified wood. Microstructural analyses confirmed the integration of FA and ELO into the cellular structure of the wood. The chemical interactions between the epoxy groups of ELO and hydroxyl groups of FA were characterized using Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy, illustrating that a ring-opening reaction occurred that grafted the long flexible aliphatic chains of ELO onto the FA chains, thereby enhancing the chain mobility and flexibility. This interaction significantly decreased the crosslinking density, thereby achieving toughening. FA–ELO modification resulted in significantly enhanced dimensional stability and mechanical properties. Specifically, the anti-swelling efficiency exceeded 80 %, while the modulus of elasticity, modulus of rupture, and along-grain compressive strength increased by up to 35.0 %, 36.8 %, and 45.7 %, respectively. Additionally, significant enhancements in the elongation at break and impact strength were achieved, at 369.1 % and 72.4 %, respectively. The loss factor also increased. The optimal ELO content was 20 wt%. This study effectively demonstrated how ELO mitigates the brittleness of FA-modified wood and supports its application in high-value fields such as construction.

Influence of polyethylene glycol and various carboxylic acids on the physical and mechanical properties of beech wood (Fagus sylvatica) and Scots pine wood (Pinus sylvestris)

ABSTRACT The goal of this study was to investigate the influence on physical and mechanical properties of beech wood (Fagus sylvatica) and Scots pine wood (Pinus sylvestris) modified with polyethylene glycol (PEG) 400 as an alcohol and various carboxylic acids (citric acid, malic acid and 1,2,3,4-butanetetracarboxylic acid). PEG 400, chosen for its large and flexible structure, was expected to minimize the negative effects on mechanical properties. However, contrary to expectations, tensile and impact bending strength decreased – similar to other modifications. Tensile strength decreased (beech: 36.0% to 46.3%), while the modulus of rupture did not show a strong decrease (beech: 2.4% to 15.2%). The modulus of elasticity (beech: 1.6% to 14.7%), compression strength (beech: 11.7% to 40.6%) and hardness (beech: 6.0% to 17.1%) increased. Impact bending strength was reduced (beech: 43.0% to 69.3%). Modifying agents, fixed inside the wood, demonstrated high anti-swelling efficiency during leaching cycles (beech: 27.1% to 45.9%). Equilibrium moisture content was reduced between 20.8% and 39.1% for beech at a relative humidity of 65%.

Effect of slope of grain on mechanical properties of some tropical wood species

ABSTRACT The aim of this work was to study the relationship between the mechanical properties of Cameroonian tropical woods and the slope of grain. The forests of the Cameroonian part of the Congo Basin abound in species that are highly solicited for structural applications. However, little information is available on the influence of the slope of a grain of these wood species. Clear wood specimens of ayous (Triplochiton scleroxylon), azobe (Lophira alata), fraké (Terminalia superbe), okan (Cylicodiscus gabunensis), padouk (Pterocarpus soyauxii), and sapelli (Entandrophragma cylindricum) were prepared. The specimens have a cross section of 20 × 30 mm and a length of 300 mm. These specimens were subjected to a four-point bending test and a double cantilever beam test. Modulus of elasticity (MOE), modulus of rupture (MOR), work at maximum load (WML) and fracture toughness (GIC) were determined. These mechanical properties were calculated for specimens with slopes of grain 0°,15°, 30°,45°,60°, 75° and 90°. The results showed that the slope of grain had significant effects on all the mechanical properties measured on clear wood specimens. MOE, MOR, WML, and GIC decreased with increasing grain slope. On the other hand, azobe and okan absorb much more of the energy that causes microcracking than the other species.

Estimation of the earlywood and latewood ratio with different particle size of dry and wet milled Japanese cedar wood flour by using hyperspectral imaging

Mechanical properties of wood–plastic composites are influenced by a particle size and surface morphology of wood flour. Generally various sizes of wood flour are produced from single solid wood even if the single process is used. If the different particle size of wood flour is produced from different wood tissue such as earlywood (EW) and latewood (LW), not only particle size but also density and chemical composition of wood flour might influence the mechanical property of final products. This study aims to investigate the relationship between particle size and their origin; EW and LW. EW and LW were separately milled to produce the EW and LW flour by dry and wet milling. Hyperspectral images ranging 400–1000 nm for each wood flour were used as training data. Discriminant model of EW and LW flour developed by PLS-DA showed over 0.77 of accuracy. Then the EW and LW were dry and wet milled together and screened by three different sieve openings to obtain different particle size wood flour. Discriminant model was applied for the hyperspectral images of each size of wood flour to estimate the EW and LW ratio. The result showed that increasing sieve opening resulted in the increasing ratio of LW for dry milled wood flours. The results suggest that the EW was easily pulverized than LW.

Enhancing weatherability and mechanical properties of tung oil wood finishes through natural rubber modification via the Diels-Alder reaction

Tung oil is commonly utilized for coating protection in wooden products, often attracting attention for its appearance, antimicrobial capabilities, and insect-resistant coatings. However, its poor mechanical properties and poor weather resistance stem from excessive self-crosslinking of surplus conjugated double bonds and molecular chains, resulting in poor film wrinkling. Therefore, this study introduces natural rubber via the Diels-Alder reaction to consume the residual double bonds in tung oil, resulting in tung oil/natural rubber composite coatings (NRTO) with excellent mechanical properties and weather resistance. The results indicate that NRTO exhibits excellent mechanical properties, including high elongation (32 %) and strong adhesion (4.55 MPa). Furthermore, NRTO demonstrates outstanding acid resistance and UV aging resistance. Given its many benefits, NRTO film emerges as a promising candidate for substantially protecting wood surfaces in demanding environments.

Response relationships between the color parameters and chemical compositions of heat-treated wood

Abstract The magnitudes of the color changes in heat-treated wood are closely related to the chemical composition of the wood, and changes in the chemical composition are the essential reasons for changes in the mechanical properties of heat-treated wood. The response relationships among the color parameters of heat-treated wood and the chemical composition were constructed to provide a scientific basis for regulating the mechanical properties with the color. The effects and linear correlations of the lightness indicators (L*) for poplar (Populus tomentosa Carr.) and spruce (Picea asperata Mast.) after heat treatment were related to the chemical compositions of the heat-treated woods by constructing relationships between the L* values. The relative content of cellulose in the heat-treated poplar downward trend and was significantly positively correlated with the L* value; however, the correlation with the L* value for the heat-treated spruce was insignificant. The L* value of the heat-treated wood was significantly positively correlated with the relative contents of hemicellulose, and was significantly negatively correlated with lignin. The L* value of the heat-treated wood had a superior response relationship with the crystallite sizes. Therefore, the constructed response relationship provides a theoretical basis for accurate and nondestructive testing of the mechanical properties of heat-treated wood by using the color parameters as rapid detection indicators.

Evaluation of Mechanical Wood Properties of Silver Birch (Betula pendula L. Roth.) of Half-Sib Genetic Families

Silver birch, a widely distributed deciduous tree native to Europe, is valued for its wood applications in construction, furniture making, and paper production. In Lithuania, silver birch ranks as the third most common forest-tree species, comprising 22% of the forested areas, and is an important species for tree breeding due to its potential and adaptability. This study was focused on assessing the mechanical properties of wood (sample and log hardness, wood density, dynamic modulus of elasticity (MOEdyn), static modulus of elasticity (MOE) and bending strength (MOR)) in silver birch (Betula pendula L. Roth.) trees from different half-sibling families. Two experimental plantations of the progenies of Lithuanian populations (half-sib families) of silver birch from different regions were analysed. From these plantations, four genetic families were selected for mechanical properties evaluation. The study findings revealed significant variability in various wood properties among different genetic families, although the static modulus of elasticity did not exhibit significant differences between the chosen genetic families. All measured wood properties decreased from the bottom to the top of the model trees. Wood hardness displayed a moderately negative correlation for wood density and weak correlations for MOE and MOR. Given the weak correlations between wood hardness and other wood mechanical properties, it is suggested that MOEdyn would be a more suitable trait for genetic studies.

Effects of oil heat treatment on poplar wood properties: A pilot scale study

Pilot-scale oil heat treatment was conducted to enhance the quality of poplar wood obtained from a fast-growing plantation. Three target temperatures, namely 180, 190, and 200 ˚C, were chosen for the oil heat treatment process. Clear, small specimens were cut from the lumber, following the prescribed standards for assessing wood quality. Light microscopy revealed the ruptures and deformation of the wood cell wall as the treatment temperature increased. The volumetric swelling of the treated specimen decreased proportionally with the increase in treatment temperature. The impact of oil heat treatment on the mechanical properties of wood varied depending on the specific type of mechanical strength and processing temperature. The modulus of rupture, toughness, and hardness of the treated specimens drastically decreased at 200°C. However, the specimens treated at 200°C exhibited much lower mass loss during the fungal decay test. The results of the analytical test showed an increase in the crystalline cellulose content and thermal stability of the treated wood, due to the thermal degradation of hemicelluloses and amorphous regions of cellulose. Overall, it is concluded that oil heat treatment of poplar wood in the optimal temperature is an efficient approach to upgrade its quality with minimal reduction in mechanical strength.

The influence of road traffic and industrial plant-induced air pollution on the physical, mechanical, chemical and morphological properties of the black pine wood

Road traffic pollution and industrial plant-induced pollution affect negatively the development of forest trees. How forest trees are affected by their growing environment is important for sustainable environment. The study aimed to investigate the physical, mechanical, chemical, and morphological properties of the Pinus nigra (black pine) tree which grows under different conditions. Tree samples were chosen from three different lands where were inside the forest (O), near the roadside (Y), and near the factory (F). It was studied whether there were any significant differences among the “O”, “Y” and “F” in terms of their wood properties such as physical, mechanical, chemical, and morphological. As a result, the “O” samples demonstrated more regular annual ring structure. On the other hand, it was observed that the “Y” samples had longer and wider tracheid cells. In addition, “Y” samples had better mechanical strength than “O” and “F”. Environmental pollution caused the presence of some different elements (chlorine and iron) in “Y” and “F”. As a result, it was determined that the trees growing near the roadside or near industrial plants have significant differences from forest trees which are far away from pollutions. It is possible to say that Pinus nigra (black pine) is resistant to environmental stress. For this reason, it can be recommended to use it as a barrier to reduce air pollution on the roadsides.

Mechanical properties of jabon (Neolamarckia cadamba (Roxb.) Bosser) wood 13 years old and its potential utilization as a structural material

Jabon (Neolamarckia cadamba (Roxb.) Bosser) is a type of fast-growing tree that is expected to meet the national demand for wood because it has fast-growing properties. This study’s objective was to examine the mechanical properties of 13 years old jabon wood based on its position in the stem. The preparation of mechanical properties test samples and their tests refer to the British Standard (BS) 373 Methods of testing small clear specimens of timber and the American Society for Testing and Materials (ASTM) D143 Standard test method for small clear specimens of timber. Based on the results of the study, the stem parts (bottom, middle, and top) had no significant effect on the mechanical properties of wood except for the compressive strength parallel to the grain and hardness. In general, the mechanical properties showed an increase from the bottom to the top of the stem and from the pith toward the bark, although there were some differences. The mechanical properties of jabon wood obtained from this study generally showed higher values than jabon wood used in other studies with younger ages, although in general, it did not change the category of jabon wood from strength class III-IV. However, its use as a structural material would be more profitable than using a younger age of jabon wood, as it is usually harvested so far.

EVALUATION OF DYNAMIC AND STATIC MODULI OF ELASTICITY OF HYBRID EUCALYPTUS WOOD FROM DIFFERENT LOCATIONS IN GHANA

This study explores the mechanical properties of hybrid eucalyptus wood, with a focus on dynamic and static moduli of elasticity (MOE), which is crucial for understanding the stiffness behaviour of wood. The research employs acoustic and static measurements on samples prepared from six trees sourced from Winneba and Amantia in Ghana. The results reveal significant variations in static and dynamic MOE, with higher static MOE observed in both Amantia and Winneba samples. However, Winneba and Amantia samples at the tree level were found to be insignificant statistically. The densities of the samples from the two locations, Winneba and Amantia, were found to be significantly different. Correlation studies revealed strong relationships between wood density and static MOE, as well as static and dynamic MOE, providing valuable insights into the comprehensive characterization of the eucalyptus globulus species grown in Ghana.

Impact of Wood-Boring Larvae of Xylotrechus arvicola (Coleoptera: Cerambycidae) on Mechanical Properties of Vitis vinifera Plants

Xylotrechus arvicola represents a significant insect pest impacting Vitis vinifera within the principal wine-producing territories of the Iberian Peninsula. The larvae of this species bore into grapevine wood, resulting in significant structural and biomechanical deterioration to the plant. Compressive and flexural tests were conducted to assess the mechanical properties of wood affected by X. arvicola. Compressive and flexural strength exhibited a decline with the escalation of the Total Damaged Surface Area (TDSA) of the samples, ranging from 0.31% to 0.73% in trunks and from 0.04 to 0.76% in branches, irrespective of the wood moisture content (fresh and dry). The most significant reduction in resistance occurred in affected dry trunks and branches. Notably, the deflection at break for dry samples was lower compared to fresh samples (65.00 and 97.85 mm, respectively). Moreover, the deflection at break for affected fresh samples (164.37 mm) significantly surpassed that of unaffected fresh samples (72.58 mm) and affected dry samples (37.50 mm). It is noteworthy that a higher percentage of TDSA coincided with diminished wood resistance. The percentage of fungal growth symptoms observed in affected wood samples was 66.66% for dry trunks, 75.00% for fresh branches, and 60.00% for dry branches. The damage inflicted by larvae facilitated the spread of grapevine diseases via emergence of holes created by insects upon exiting the wood and through the larval galleries connected to them. This damage also altered the mechanical properties of grapevine plants, with fresh branches exhibiting the most pronounced effects.

Effect of the Hole Diameter in Mechanical Properties of Wood: Experimental and Numerical Approaches

Introducing openings or holes into wooden structures is a common practice for providing utility services. However, this practice leads to stress concentration, resulting in a reduction in stiffness and load-carrying capacity. Therefore, understanding the effects of holes on beam properties is important for design considerations. This study investigates the mechanical behavior of a wooden beam made from juvenile Pinus elliottii containing open cylindrical holes with three different diameters: 4, 8, and 12 mm. The mechanical properties were evaluated for compression parallel to the fibers, quasi-static bending, and tension perpendicular to the fibers. Numerical simulations were conducted using a finite element (FE) model, considering the orthotropic elastic properties determined from experimental tests and elastic ratios reported in the literature. The experimental results indicated that the influence of hole diameter was not significant on the compressive properties; however, longitudinal crack failures began to form for holes with diameters of 8–12 mm. Regardless of hole size, the compressive and bending characteristics revealed that hole location did not affect the stiffness, strength, or damage mechanisms.

Compressive Strength parallel to grains of Charred Paulownia Wood

Wood is a common flammable in the building fire and the dominant fuel in the wildland fire. In this study, the surface of wood specimens has been pre-heated by various radiative heat fluxes and heating times to achieve varying char layer thicknesses. The compressive strength parallel to grains versus various charring thicknesses has been obtained by an electronic universal testing machine (WDW-20). Experimental results demonstrate that a higher heat flux and longer heating times promote the formation of the char layer, but the compressive strength versus the charring thickness first decreases to its minimum value and subsequently remains stable. For the 7 kW/m2 case, there is a rapid decrease in compressive strength for the 5-7 heating period. For example, the compressive strength is 31.7 MPa after the initial 5-minute period, and 3.69 MPa after the initial 7-minute period. For the radiative heat fluxes from 7 kW/m2 to 10 kW/m2, the reduction rate of compressive strength will increase from 1.32 MPa/min to 3.75 MPa/min for the initial 5-minute period, and increase from 4.95 MPa/min to 5.34 MPa/min for the initial 7-minute heating period. This study helps us understand the influence of charring processes on the mechanical properties of wood and the failure of timber structures.

Prediction of Physical and Mechanical Properties of Heat-Treated Wood Based on the Improved Beluga Whale Optimisation Back Propagation (IBWO-BP) Neural Network

The physical and mechanical properties of heat-treated wood are essential factors in assessing its appropriateness for different applications. While back-propagation (BP) neural networks are widely used for predicting wood properties, their accuracy often falls short of expectations. This paper introduces an improved Beluga Whale Optimisation (IBWO)-BP model as a solution to this challenge. We improved the standard Beluga Whale Optimisation (BWO) algorithm in three ways: (1) use Bernoulli chaos mapping to explore the entire search space during population initialization; (2) incorporate the position update formula of the Firefly Algorithm (FA) to improve the position update strategy and convergence speed; (3) apply the opposition-based learning based on the lens imaging (lensOBL) mechanism to the optimal individual, which prevents the algorithm from getting stuck in local optima during each iteration. Subsequently, we adjusted the weights and thresholds of the BP model, deploying the IBWO approach. Ultimately, we employ the IBWO-BP model to predict the swelling and shrinkage ratio of air-dry volume, as well as the modulus of elasticity (MOE) and bending strength (MOR) of heat-treated wood. The benefit of IBWO is demonstrated through comparison with other meta-heuristic algorithms (MHAs). When compared to earlier prediction models, the results revealed that the mean square error (MSE) decreased by 39.7%, the root mean square error (RMSE) by 22.4%, the mean absolute percentage error (MAPE) by 9.8%, the mean absolute error (MAE) by 31.5%, and the standard deviation (STD) by 18.9%. Therefore, this model has excellent generalisation ability and relatively good prediction accuracy.

Effect of partial delignification and densification on chemical, morphological, and mechanical properties‏ of wood: Structural property evolution

Efforts have been dedicated to developing sustainable alternatives for conventional construction materials, resulting in the development of densified wood as an innovative, environmentally friendly, and high-performance material. This study focuses on investigating the effects of treatment parameters (e.g., partial delignification boiling time, chemical concentrations, and hot-pressing pressures) on the chemical, morphological, and mechanical properties of the densified wood. Results revealed that the partial delignification process of low-density Balsa wood reduced lignin content by 50–80%, which enhanced the crystallinity of the wood by 21–54%. However, prolonged periods of partial delignification caused a degradation in the crystalline regions in wood. The modulus of rupture (MOR) and modulus of elasticity (MOE) of the densified wood samples increased by 90–680% and 10–810% compared with those of the raw wood samples, respectively. The MOR of the densified wood also showed a dependency on lignin content and porosity. An optimal lignin content of approximately 10% was associated with the highest MOR in densified wood. Moreover, the relationship between the MOR and porosity suggested that the MOR improvement occurred in two stages. The first stage of MOR improvement is controlled by the reduction in the porosity and the second stage is controlled by the improved hydrogen bonding among cellulose nanofibrils.

Experimental study and numerical simulation of adhesively bonded timber-concrete composite panels: bending behavior, adhesive shear and peel stress distributions

This study investigated the structural response of timber-plain concrete panels bonded with epoxy and PUR adhesives under a four-point bending load, both experimentally and numerically. Tests evaluating epoxy- and PUR-bonded glulam-plain concrete panels measured ultimate load (Fult), effective bending stiffness (EIeff), and mid-span deflection (∆ult). Shear stress within the adhesives was monitored using fiber optic sensors. Numerical simulations estimated Fult and EIeff with errors of 5% and 14%, respectively. These discrepancies may stem from assuming defect-free wood (e.g., no knots), idealized boundary conditions, uniform adhesive thickness assumptions, and unmeasured mechanical and damage properties of wood and concrete (Detailed error source analysis is available in Section 4). Qualitative validation involved comparing sensor-recorded shear stress with simulation results. A parametric study evaluated the effects of adhesive thickness (0.5, 1, and 3 mm), concrete-wood depth ratio (50/85, 85/85, and 150/85 mm/mm), wood type (spruce (Picea), beech (Fagus), and Azobe (Lophira)), concrete strength class (C12/15 and C30/37), and span length (2, 4, and 8 m) on the bending behavior of the panel, and the shear and peel stress distribution within the adhesive bond line. Shear stress prevailed over peel stress in the adhesives, with peel stress approaching shear stress as span length increased (max. τa / max. σa ∼ 3.5–7). The ultimate load typically resulted in concrete compression damage and wood fiber damage, influenced by the concrete strength class and wood type. Higher depth ratios led to tension damage in concrete, while adhesive thickness had a minimal impact on stress distribution and failure modes.

A study of dimensional effects on the stress characteristics of Yunnan pine shafts considering seismic strain rates

Abstract The mechanical properties of wood are affected by member size and loading rate. Axial compression tests with different seismic strain rates and sizes of specimens were carried out to investigate the static and dynamic dimensional effects of Yunnan pine timber. And obtained load-displacement curves, compressive strength, modulus of elasticity, peak strain and Poisson’s ratio. Weibull’s weakest chain theory, Bazant’s law of dimensional effects and Carpinteri’s law of multiple fractal dimensional effects were used to analyze the dimensional effects on the compressive strength of wood, and to establish a wood strength model that takes strain rate effects and dimensional effects into account. The results showed that the compressive strength, elastic modulus, and Poisson’s ratio of Yunnan pine wood exhibit both size and strain rate effects. Under the coupling effect of strain rate effect and size effect, the size effect of Yunnan pine wood strength decreases with increasing strain rate, while the strain rate effect increases with increasing size. A size effect model for compressive strength of wood considering strain rate effect based on three theories and experimental data can well describe the dynamic size effect of Yunnan pine wood strength.

Chemical Composition and Mechanical Properties of Wood after Thermal Modification in Closed Process under Pressure in Nitrogen.

In this study, silver birch (Betula pendula) and Scots pine (Pinus sylvestris) wood planks (1000 × 100 × 25 mm) were thermally modified in pilot-scale equipment. Research extended our knowledge of the thermal modification (TM) process in a closed system under nitrogen pressure, as well as how process parameters affect the chemical composition and mechanical strength of wood. Various TM regimes were selected-maximum temperature (150-180 °C), modification time (30-180 min), and initial nitrogen pressure (3-6 bar). Chemical analyses were performed to assess the amount of extractives, lignin, polysaccharides and acetyl group content following the TM process. The mechanical properties of TM wood were characterized using the modulus of rupture (MOR), modulus of elasticity (MOE), and Brinell hardness. The MOR of both studied wood species following TM in nitrogen was reduced, but MOE changes were insignificant. The Brinell hardness of TM birch wood's tangential surface was much higher than that of the radial surface, although Scots pine wood showed the opposite pattern. TM birch and pine wood specimens with the highest mass loss, acetone soluble extractive amount, and the lowest xylan and acetyl group content had the lowest MOR and Brinell hardness.

Removal of Plastics from Micron Size to Nanoscale Using Wood Filter.

Plastic pollution, particularly microplastic (MP) and nanoplastic (NP) pollution, has become a significant concern. This study explores the use of porous wood for filtration to remove MPs and NPs and investigates their removal mechanisms. Undecorated fir wood with a thickness of 4 mm achieves a 91% removal rate for model polystyrene (PS) MPs (2.6 μm) at a water flux of 198 L/m2h. However, its separation performance for NPs (255.8 and 50.9 nm) is poor. It also shows that fir wood (coniferous wood) has a higher PS removal rate than poplar wood (hard wood). With poly dimethyl diallyl ammonium chloride (PDDA) modification, both MPs and NPs are effectively removed, with NPs' removal rate increasing from <10% to 90% for PDDA/wood. Characterization results reveal that size-exclusive interception dominates for micron-sized particles, and electrostatic interaction is crucial for nanosized particles. Additionally, intercepted NPs have been used as a strong binder for hot-pressed wood to remarkably enhance the mechanical properties of wood, suggesting a novel recycle utilization of discarded wood filters. Overall, this renewable wood material offers a simple solution for tackling MP/NP pollution.