Tensile Strength Of Wood Research Articles

Сравнительная оценка физико-механических свойств древесины различных климатипов сосны обыкновенной

It is important to comprehend the physical and mechanical properties of Scots pine wood from various geographical origins in order to use it effectively and rationally in production. The purpose of the study is to determine the physical and mechanical properties of Scots pine wood from 17 climatic ecotypes and to conduct a comparative analysis of the received indicators for the studied climatypes separately and for subspecies, which were grouped according to the classification of L.F. Pravdin. The physical properties that were chosen for the investigation were wood density in an absolutely dry state and at 12 % moisture content. The mechanical characteristics were the tensile strength of the wood along the fibers and the tensile strength in static bending. The range of geographic origins of the seed harvesting locations was from 47 to 62 °N and 22 to 85 °E. The investigation was conducted using contemporary universal testing equipment, MTS Insight 100. It was found that the density of the wood varied from 370 kg/m3 (Kursk climatype) to 524 kg/m3 (Volgograd climatype) under absolutely dry conditions and from 397 kg/m3 (Kursk climatype) to 550 kg/m3 (Volgograd climatype) at 12 % moisture content. The tensile strength of wood along the fibers ranged from 32 MPa (Kursk climatype) to 54 MPa (Volgograd climatype), while the tensile strength in static bending was from 55 to 92 MPa for the Vologda and Ulyanovsk climatypes, respectively. The maximum wood density at 12 % moisture content was 497±8 kg/m3, which is typical for European subspecies. The minimum value of this indicator was 423±30 kg/m3. The medium values had Lapland subspecies and Steppe subspecies 483±16 kg/m3 and 464±12 kg/m3, respectively. The tensile strength of wood along the fibers in the studied subspecies ranged from 47±1 MPa (European subspecies) to 33±4 MPa (Siberian subspecies). For Lapland subspecies, it was 44±2 MPa and slightly lower for Steppe subspecies, which was 42±2 MPa. The maximum value of the tensile strength in static bending for European subspecies was 78±4 MPa. The minimum value for the Siberian subspecies was 61±14 MPa. This indicator was equal for Steppe subspecies and Lapland subspecies, which was 72±4 MPa. For citation: Rabko S.U., Melnik P.G., Kozel A.V., Paplauskaya L.F., Tupik P.V., Nosnikau V.V. Comparison of Physical and Mechanical Properties of Scots Pine Wood Grown in Different Climatypes. Lesnoy Zhurnal = Russian Forestry Journal, 2023, no. 4, pp. 26–40. (In Russ.). https://doi.org/10.37482/0536-1036-2023-4-26-40

Growth of green wood based on a phase field model

AbstractTree engineering is a young discipline utilizing trees as structural elements, where the determination of limit loads in tree trunks is of great importance. Simple numerical models underestimate the load‐bearing capacity of green wood in contrast to experimental bending tests. A well‐known reason for this is the residual stress state of the living tree lowering compressive stress towards the trunks surface. This results in an overall stress state, which increases the load capacity, since the tensile strength of wood is commonly higher than its compressive strength. By determining the residual growth stress, a more accurate evaluation of the load‐bearing capacity of a living tree is possible. The residual stress state is a non‐linear and time dependent function in thickness direction of the trunk. In order to simulate growth and growth stress, a phase field model is employed.The morphology of a tree is the result of innumerable and often temporary environmental stimuli, which also change and interact with the genetically predisposed growth tropisms. Therefore, we use image processing to capture the individual tree morphology of an existing tree, which is based within the phase field model as predefined growth direction. This is the basis for primary growth in the model. Additionally the model simulates the secondary growth, which corresponds to the thickness of the trunk. Except in tropical areas, this growth is associated with growth rings, which we assign as an attribute to the modelled material. While in the branch structure several tropisms (e.g. gravitropism) are responsible for the off‐centre accumulation of woody material, in the stem region we only follow the stress‐induced growth. This mechanism can respond to either the principal tensile stress or the principal compressive stress in our model, as this difference is observed in hardwoods and softwoods.Since the wood matrix represents an anisotropic material with a distinct fiber direction, we approach it in our model by a transversely isotropic constitutive law, whose principal direction coincides with the growth direction.

The deterioration of the Pueblo Bonito Great House in the Chaco Culture National Historical Park, New Mexico, USA.

Pueblo Bonito is the iconic pre- Columbian structure in Chaco Culture National Historical Park, a World Heritage Site in northwestern New Mexico, USA. The structure, dating to about 850–1150 Current Era, and built of quarried sandstones, wooden timbers and a mud mortar, has been the subject of archaeological investigations for over a century. The present study is based on the examination of historical photographs of Pueblo Bonito dating from 1887 to the 1920s. It is a retrospective assessment to determine if structural damages, depicted on the photographs, could be attributed to identifiable agents that might have been present at the time of Pueblo Bonito occupancy. A likely causal agent of deterioration at Pueblo Bonito was the inability of Ancestral Puebloan engineers to manage the impacts from the annual precipitation, presently measured at about 220 mm. A resulting time-dependent event was rot to wetted roof and ceiling timbers, lintels, and wall support beams which required decades of incubation by wood decay fungi to reduce wood tensile strength to levels leading to roof and wall collapse. Important time- independent events that could occur any time after construction include water action on the mud mortar which resulted in unstable gravity load paths in stone walls, ponding of water in walls which when frozen would lead to the blowout of wall segments, and the occasional flood that disrupted foundations. Pueblo Bonito may have been an occupation site for centuries but the lifetime of individually constructed rooms may have only been decades, resulting in several build- repair- or abandon cycles being part of the history of that Great House.

Tensile strength of wood in high temperatures before charring

SummaryThe main focus of this paper is on the tensile strength of wood at high temperatures. On analysing previous literature, it was observed that results by different researchers are different, even though a vast reduction of the tensile strength at elevated temperatures was clear in all of them. Thus, a need for further investigation into the matter became apparent. As a key part of this paper, steady‐state tensile strength experiments below charring temperatures were carried out, and their results were analysed. The results were then used in analysing the tensile strength of a wooden beam subjected to a fire using the Fire Dynamics Simulator.

Rotational Behavior of Bolted Glulam Beam-to-Column Connections Reinforced with Section Steel

Bolted connections with slotted-in steel plates are commonly used to connect beams and columns in heavy timber structures. While due to the low tensile strength of wood in the perpendicular-to-grain direction, these connections are usually not able to present satisfying rotational performance. In order to solve this problem, a relatively new type of bolted connection, reinforced with section steel, was designed and tested in this paper. Two groups of total six specimens were tested under monotonic loading to investigate their rotational behavior. Tests showed that the brittle failure mode of wood splitting in the perpendicular-to-grain direction was fully restrained. Only slight cracks were observed in most specimens, except one that underwent bending failure in the beam member. Test results indicated an average increase of 78.7% in moment resistance and a 54.8% increase in ductility ratio for middle-storey connections, compared with conventional connections simply using slotted-in steel plates. Top-storey connections, without previous test results as comparison, also presented high moment-bearing capacity and reliable deformability. As a result, such connection may receive a broad application, especially in multi-storey heavy timber structures.

Tensile Strength, Elasticity and Cracking Character of Softwood Tissues

Wood tensile strength in longitudinal direction depends on wood density and structure. Growth rings in wood consist of earlywood and latewood which differ greatly in their properties. Latewood is denser, less porous and more resistant to tension along the fiber compared earlywod. The ratio of latewood and earlywood is different for each type of wood species and also depends on growing conditions, climate and etc. The study is aimed to evaluate the tensile strength, elasticity and cracking character of Lithuanian-grown softwood tissues, depending on the wood species, tissue width and latewood ratio in the sample. For the study three species of wood (spruce, pine and larch) were chosen. Samples were cut with the microtome, tissues cross-sectional area of about 0.15-0.50 mm2. The ratio of latewood and earlywood was evaluated using microscope. Wood tissue tensile strength was tested in the tensile machine with a feed rate of 0.2 mm/min. Research results showed that the highest tensile strength was obtained for larch wood samples, while the spruce wood most tended to deformation. Ir was determined that the tensile strength and elasticity of wood are highly influenced by wood microstructure and earlywood and latewood ratio in the sample. Also the wood microstructure and failure mechanism of the samples were evaluated. DOI: http://dx.doi.org/10.5755/j01.ms.21.2.6881

Variation in Mechanical Properties within Individual Annual Rings in the Resonance Spruce Wood (Picea abies (L.) Karst.)

This paper shows results of specifi c modulus of elasticity and specifi c tensile strength in the resonance spruce wood [Picea abies (L.) Karst.] in relation to its heterogeneity within individual annual rings. It also presents changes in the average values of microfi bril angle in S2 layer measured in tangential walls of tracheids (MFA) within individual annual rings. On the grounds of the results, it can be concluded that specifi c modulus of elasticity and specifi c tensile strength of wood are strongly infl uenced by the position of the sample in annual rings. Generally, the values of these parameters increase along the width of annual rings. It is also noted that the specifi c modulus of elasticity and specifi c tensile strength depend on MFA. As MFA decreases, the values of these parameters increase.

Genotype- and age-dependent patterns of lignin and cellulose in regenerants derived from 80-year-old trees of black mulberry (Morus nigra L.)

Proliferating shoot cultures of black mulberry (Morus nigra), derived from axillary buds of two donor trees designated as Mn1 and Mn2, more than 80 years of age, were established in vitro. Subsequently, shoot-tips were used to induce both axillary and adventitious shoot regeneration following incubation on Murashige and Skoog medium containing 14 different treatments of various concentrations of plant growth regulators, including 6-benzyladenine (BA), thidiazuron (TDZ), and combinations of BA with indole-3-butyric acid (IBA) and TDZ with BA. The highest shoot proliferation of 5.3 shoots per explant for the Mn1 tree and 6.9 shoots per explant for the Mn2 tree were obtained when explants were incubated on a medium containing 0.5 mg l−1 BA and 0.1 mg l−1 IBA. The maximum frequency of adventitious rooting was similar for both genotypes. Changes in lignin and cellulose content, macromolecular properties of dioxane and Klason lignins, lignin monomer composition, and macromolecular properties of cellulose were determined in 1-year-old and 3 year-old micropropagated plants, as well as in the donor trees. Lignin and cellulose properties were significantly dependent on the genotype, the age and the mutual interaction of both these factors. The syringyl to guaiacyl weight ratio in lignin rose with the age of the micropropagated plants. Moreover, the tensile strength of wood in 1-year-old plants was supported by a high cellulose degree of polymerization. The highest polydispersity index of cellulose was detected in 3-year-old plants.

A 3D multilevel model of damage and strength of wood: Analysis of microstructural effects

A 3D hierarchical computational model of damage and strength of wood is developed. The model takes into account the four scale microstructures of wood, including the microfibril reinforced structure at nanoscale, multilayered cell walls at microscale, hexagon-shape-tube cellular structure at mesoscale and annual rings at the macroscale. With the use of the developed hierarchical model, the influence of the microstructure, including microfibril angle (MFA), the cell shape and the wood density (annual ring structure), differences between earlywood and latewood as well as microstructural arrangements and cellulose strength distributions on the tensile strength of wood is studied numerically. Good agreement of the theoretical results with experimental data has been obtained.

Effect of treatments with 1,3-dimethylol-4,5-dihydroxy-ethyleneurea (DMDHEU) on the tensile properties of wood

Abstract The thin-veneer strip technique was applied to investigate the modifying effects of 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) on the tensile strength of wood. Pinewood veneers treated with solutions of DMDHEU alone and in combination with magnesium chloride (MgCl2) as a catalyst showed considerable strength losses of up to 50% in zero-span and up to 70% in finite-span testing modes. The higher strength losses in the latter case are due to hemicellulose degradation, which cannot be assessed in zero-span testing. Strength loss observed after treatment with DMDHEU and MgCl2 was approximately as high as the sum of the strength losses determined after individual treatments with MgCl2 or DMDHEU. Micrographs of veneers after finite-span testing revealed that catalysed DMDHEU treatment changed the predominant failure mode from interfibre fracture (in controls) to intrafibre fracture. The mechanism of strength loss resulting from treatment with DMDHEU is discussed.

Near-Infrared Spectroscopic Study of the Physical and Mechanical Properties of Wood with Meso- and Micro-Scale Anatomical Observation

Estimation of the density along with the tensile strength of wood within both the elastic and plastic deformation ranges, represented as modulus of elasticity (MOE) and ultimate tensile stress (UTS), respectively, were performed using near-infrared (NIR) spectroscopy. A partial least squares (PLS) analysis was applied to the measurements of density, MOE, and UTS, and resulted in a high accuracy of prediction, independent of wood species. The correlation coefficient between the NIR spectra and criterion variables, and the regression vector resulting from the PLS analysis, suggested that the characteristic absorption bands were strongly related to the predictability of each property. In the case of softwood, absorption bands due to intra-molecular hydrogen-bonded OH groups in the crystalline regions of cellulose, which are oriented preferentially in a direction parallel to the cellulose chain, might strongly affect the tensile strength of softwood. Hardwoods have much more complex and variable structures than softwoods; therefore, it was supposed that the key factor governing the tensile strength in hardwood would be the interaction between the three principal constituents (i. e., cellulose, hemicellulose, and lignin) of wood.

木材の引張強度に及ぼす節の影響に關する研究

木材の引張強度に及ぼす節の影響に關する研究