Modulus Of Wood Research Articles

New four-point bending test protocol for the strength grading of timber: relationship between local and global modulus of elasticity (MOE) of maritime pine

ABSTRACT This study focuses on the characterisation of maritime pine according to standards EN408 and EN384 required for timber grading. A comparison of the EN408 bending test setup is performed with a new four-point bending protocol, reducing as much as possible, the effects of the shear force in the span where the deflection is measured. The study highlights difficulties to estimate accurately, the elasticity modulus of wood by using EN408 bending test setup. This is probably due to inaccuracies in the measurements of small curvatures and due to the local heterogeneities of wood. An original four-point bending test is proposed with 75% of the span of the wood beams in pure bending. This configuration clearly exhibits the convergence of measurements, in comparison to EN408 setup. The deformations generated by this new loading protocol allow a better evaluation of the bending modulus E 0. Moreover, the study reveals that the proposed setup supplies an increase of elasticity modulus close to 20%. In addition, dynamic tests are also performed to characterise the Young’s modulus. The experimental results reveal a better agreement between static test, using the new four-point bending configuration and dynamic method, than considering EN408 as a reference.

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.

Testing of wood shear modulus based on cantilevered square plate torsional vibration method

ABSTRACT The application of the energy method has proposed a dynamic testing method for the shear modulus in two mutually perpendicular directions on the principal surface of wood using a cantilevered square plate torsional vibration method. In the study, this method was applied to measure the shear modulus of larch wood in the LT and TL directions, as well as the longitudinal and transverse shear modulus of Laminated Veneer Lumber (LVL) sheets. The validity of the results was confirmed through experimental verification using the asymmetric four-point bending beam method, the free plate torsional vibration method, and the free square plate torsional mode method. Simulation calculations of the principal shear modulus for six species of trees with width-to-thickness ratios ranging from 10 to 25 were also conducted using this method. The conclusions drawn suggest that a width-to-thickness ratio of 15 for the cantilevered square plate provides sufficient accuracy for testing the principal shear modulus of wood. Furthermore, the difference in shear modulus between two mutually perpendicular directions on the principal surface of wood is dependent on the width-to-thickness ratio of the cantilevered square plate, indicating that this method outperforms other dynamic methods for testing wood shear modulus.

Effect of Wood Specimen Length on Uniaxial Stress–Strain Curve along the Grain Direction

Abstract The axial compression test was carried out on the basis of three different-size specimens of white wax (Fraxinus chinensis), fir (Abies fabri), and Yunnan pine (Pinus yunnanensis) to explore the influence of specimen length on the compression strength parallel to grain, peak strain, and elastic modulus of wood. Weibull’s weakest-link theory, Bazant’s law of size effect, and Carpinteri’s multiple fractal size effect were used for the analysis. The results showed significant size effects on theses parameters of wood along the grain. Using the three theories to predict the compressive strength of 100-mm-length specimens, the predicted value of Bazant’s law of size effect has the smallest error with the measured value, followed by Weibull’s weakest-link theory and Carpinteri’s law of multiple fractal size effect. The size-effect coefficients of the down-grain compressive strength of the three woods obtained using the slope method were 0.06, 0.11, and 0.09, respectively, which were consistent with the values of m in the Weibull fitting function.

Moment-Rotation Calculation Method and Parameter Analysis for Loose Continuous-Tenon Joint in Column-And-Tie Timber Structure

ABSTRACT To quantitatively calculate the moment-rotation relationship of loose continuous-tenon joints in traditional column-and-tie timber frame, the rotational deformation of loose joints is divided into two stages: free sliding and contact compression. Using constitutive, geometric, and equilibrium equations, a theoretical formula for moment-rotation is derived. The calculated values are then compared with experimental results to validate the accuracy of the theoretical calculation method. A sensitivity analysis is conducted on typical parameters, such as beam height, column diameter, joint clearance, and perpendicular compression modulus of wood, to explore their effects on the moment-rotation relationship of tenon joints. The results show that increasing the perpendicular compression modulus of wood leads to greater bending stiffness and load carrying capacity of tenon joints, with the latter increasing more significantly. In the elastic stage, the rotational stiffness of the joint increases with beam height or column diameter, while after entering the elastoplastic stage, the joint stiffness is less influenced by these factors. The initial rotational stiffness and load carrying capacity of the joint both decrease with joint clearance, and the effect of joint clearance on load carrying capacity decreases as the clearance increases when the joint enters the yielding stage.

Variations of growth and wood traits in standing trees of the third-generation Acacia mangium families in Indonesia

Abstract The breeding of a fast-growing tree species, Acacia mangium Willd. has entered the third-generation cycle in Indonesia. To fulfill timber industry needs, wood traits, as well as growth traits, should be improved by conducting appropriate tree breeding programs for this species. In the present study, growth and wood traits were measured for the 10-year-old third-generation A. mangium from 40 half-sib families originating from four sub-lines from two provenances. The mean values of ten families in each sub-line ranged from 17.7 to 21.8 cm for stem diameter, 14.3 to 16.2 m for tree height, 3.60 to 3.77 km/s for stress-wave velocity, and 19.9 to 20.9 mm for Pilodyn penetration, respectively. The broad-sense heritability values in each sub-line ranged from 0.014 to 0.444 for stem diameter, 0.000 to 0.208 for tree height, 0.261 to 0.715 for stress-wave velocity, and 0.171 to 0.484 for Pilodyn penetration, respectively. These results suggested that families with higher density and Young’s modulus of wood, suitable for solid wood production, can be selected from the third-generation A. mangium. Stem diameter significantly correlated with the other three measured traits, while phenotypic correlation coefficients between stem diameter and stress-wave velocity or Pilodyn penetration were very low. In addition, no significant phenotypic correlations were found between other measured traits. Furthermore, positive- or non-significant genetic correlations were found between growth and wood traits in all sub-lines. Thus, it is concluded that the selection of families with good growth characteristics will not always reduce the wood properties of this species.

Research progress on dynamic testing methods of wood shear modulus: A review

Wood is a non-homogeneous and orthotropic natural polymer material. It is important to test the wood shear modulus and elastic constants accurately and reliably using dynamic methods. Based on the introduction of the advantages of six common methods for dynamic testing of wood shear modulus, such as free plate torsional mode method, free bar torsional vibration method, and Timoshenko beam iterative method, issues associated with the applicability and accuracy of these methods are also pointed out. Recent methods, such as the free square plate torsional mode method and the square plate static torsional strain method, that were developed to dynamically test the shear modulus of wood and wood composite materials, are presented as effective ways to tackle these issues. These new approaches are expected to provide beneficial technical support for using small specimens, overcoming the size effect of specimens, simplifying the testing procedures, improving the test accuracy, and expanding the application range in the dynamic testing of wood shear modulus. These approaches have practical significance in promoting the industrialization and development of structural engineering, furniture and interior decoration, transportation, military, and musical instrument industries.

Evaluation of wood modulus of rupture and modulus of elasticity in the radial and tangential directions in bending and reliability analysis

Evaluation of wood modulus of rupture and modulus of elasticity in the radial and tangential directions in bending and reliability analysis

Study on the Four-Point Bending Beam Method to Improve the Testing Accuracy for the Elastic Modulus, Poisson's Ratio and Shear Modulus of Wood

Study on the Four-Point Bending Beam Method to Improve the Testing Accuracy for the Elastic Modulus, Poisson's Ratio and Shear Modulus of Wood

Mechanical performance of inclined Dougong bracket sets under vertical load: Experimental tests and finite element calculation

This paper presents an investigation on the mechanical performance of inclined Dougong bracket sets under the vertical load. Initial inclination angles of Dougongs are determined based on material test results and embedment mechanism theories. Four full-scale Dougongs with different initial inclination angles are tested under the vertical load. The failure patterns, load-displacement curves, load distribution and displacement analyses are disclosed. Moreover, finite element calculation is conducted, model validation, stress and strain analyses are illustrated. Parametric analyses considering initial inclination angles of Dougongs, compressive strength and elastic moduli of wood, and friction coefficients between embedded surfaces are also carried out. The results indicate that inclined Dougongs under the vertical load behave similarly to a timber block under compression in the perpendicular-to-grain direction. Increasing the initial inclination angles can enhance vertical stiffness to some extent, but the bearing capacities of the inclined Dougongs are not promoted. For inclined Dougongs, part of the load transferred in the width direction is gradually carried by other components in the overhanging direction. The inclined Dougong rotates under the vertical load, and as the load increases, the overall rotation becomes more obvious. Parametric studies show that as initial inclination angles increases, plastic stiffness decreases to some extent. With the increment of compressive strength, elastic moduli, and friction coefficients, ultimate displacement decreases but plastic stiffness obviously increases.

Effects of Grain Pattern on the Rolling Shear Properties of Wood in Cross-Laminated Timber

Rolling shear modulus and strength are the key factors affecting the mechanical performance of some wood products such as cross-laminated timber (CLT). As reported, rolling shear property strongly depends on the sawing pattern such as the aspect ratio and grain direction (grain mode). However, the mechanism behind this phenomenon has not yet been clarified. In this work, the rolling shear modulus and strength of spruce-pine-fir (SPF) with different grain modes and aspect ratios were experimentally investigated. In addition, a theoretical investigation was carried out to reveal the mechanism behind this phenomenon. The results exhibited that the rolling shear moduli of 0° and 90° grain-mode wood were the same. This value can be called the pure rolling shear modulus. Rolling shear modulus of wood with angles other than 0° and 90° can be calculated from the pure rolling shear modulus and grain angle. Therefore, this modulus can be called the apparent rolling shear modulus. Thus, using 0° and 90° grain-mode specimens to determine the pure rolling shear modulus and strength of wood is recommended.

Properties of densified poplar wood through partial delignification with alkali and acid pretreatment

Poplar trees can be grown on marginal land to conserve water and recycle nutrients, but the wood has poor mechanical properties for structural applications. This study evaluated the feasibility of densifying poplar wood through delignification to improve mechanical properties. Delignification was conducted using a commercial soda pulping process under various NaOH concentrations of 0–6% with a reduced liquor-to-wood ratio of 3, along with a novel hydrotropic fractionation process using maleic acid. Delignified wood was pressed with or without stop bars at a low pressure of 1 MPa at 150 °C for 15 min or 100 °C for 2 or 10 h. Results indicate that wood density is the key variable dictating wood strength properties rather than extent of delignification. Pressing with stop bars resulted in similar wood densities for samples with different levels of delignification. Wood modulus of rupture (MOR), modulus of elasticity (MOE), and Brinell hardness (HB) all increased linearly with wood density, in agreement with literature results from pure hydrothermal compression. When removing stop bars in pressing, MOR, MOE, and HB were increased to 150 MPa, 20.7 GPa, and 43.2 MPa, respectively, from 88.5 MPa, 6.5 GPa, and 14.8 MPa for undensified poplar when wood density was increased to 0.81 g/cm3 from 0.46 g/cm3. Low-pressure densification with delignification is advantageous to significantly improve wood properties.

Comparison of methods for determining shear modulus of wood

In this study, the relatively new picture frame method applied to wood is compared with three established shear test methods, namely the experimental modal analysis, the square plate twist method and the torsion test. For the investigations, the wood species European beech (Fagus sylvatica L.) and spruce (Picea abies L. Karst.) were used and the shear tests were conducted in LR and RL direction. The results show comparable shear moduli for beech and spruce in the range of 931–1289 Nmm−2 and 495–842 Nmm−2, respectively. In contrast to the theory of linear elastic orthotropic materials, significant differences in the results of the picture frame method between LR and RL direction were observed for spruce.

Features of the shear analogy method for calculating the bending strength of clt panels

Problem statement. The strength of CLT panels by bending is usually calculated by the γ-method, the Tymoshenko method and the method of shear analogy. The latter is covered in this paper and provides strength analysis by considering the CLT panel as a system of longitudinals connected by a pliable transverse layer of boards. Depending on the configuration of the components of the cross section, the rigidity of the boards is taken into account. Rotation of the cross-sections corresponds to classical Bernoulli theory. The shear analogy method corresponds to the γ-method in the context of symmetric cross sections and is considered as an approximate approach that produces an approximate solution. The purpose of the article is a theoretical analysis of the landslide analogy method used to calculate the strength (PSD) or CLT panels in bending. As the shear modulus of wood and building materials based on it have a significant difference between the shear modulus and elastic modulus, the PCD panel can be considered as a beam consisting of two flexibly connected transverse layers (beam A and B). Thus, the theory of Bernoulli beams is used to determine the bending deformations elements taking into account deformations of each layer of boards. Conclusions. The shear analogy method yields accurate results compared to a symmetrical cross section in two or three parts, and unlike the γ-method, it takes into account arbitrary systems and loads. The determined effect of concentrated loads and internal supports for non-intersecting beams is relatively accurate, and the shift analogy method can be considered as an exclusive approach that can sufficiently determine the existing maximum stresses under bending.

Effects of Radial Growth Rate on Wood and Lumber Properties of 67-Year-Old Japanese Larch (Larix Kaempferi) Trees Planted in Tochigi, Japan

The wood and lumber properties were examined for 67-yr-old Japanese larch (Larix kaempferi) trees with different radial growth rates planted in Tochigi Prefecture, Japan. The trees were categorized into slow-, medium-, and fast-growing groups based on the stem diameter. No significant difference in stresswave velocity of stems, which is closely related with Young’s modulus of wood, was found among three radial growth categories (stem diameter classes). The boundary between juvenile wood (JW) and mature wood (MW) determined by latewood tracheid length (TL) existed about the 20th annual ring from the pith in all sample trees. Significant differences between JW and MW were found in most of examined wood and lumber properties. It was found that trees with fast growth do not always cause lower grade lumberproperties.

Long-Term Creep Behavior Prediction of Sol-Gel Derived SiO2- and TiO2-Wood Composites Using the Stepped Isostress Method.

In this study, methyltrimethoxysilane (MTMOS), methyltriethoxysilane (MTEOS), tetraethoxysilane (TEOS), and titanium(IV) isopropoxide (TTIP) were used as precursor sols to prepare wood-inorganic composites (WICs) by a sol-gel process, and subsequently, the long-term creep behavior of these composites was estimated by application of the stepped isostress method (SSM). The results revealed that the flexural modulus of wood and WICs were in the range of 9.8–10.5 GPa, and there were no significant differences among them. However, the flexural strength of the WICs (93–103 MPa) was stronger than that of wood (86 MPa). Additionally, based on the SSM processes, smooth master curves were obtained from different SSM testing parameters, and they fit well with the experimental data. These results demonstrated that the SSM was a useful approach to evaluate the long-term creep behavior of wood and WICs. According to the Eyring equation, the activation volume of the WICs prepared from MTMOS (0.825 nm3) and TEOS (0.657 nm3) was less than that of the untreated wood (0.832 nm3). Furthermore, the WICs exhibited better performance on the creep resistance than that of wood, except for the WICMTEOS. The reduction of time-dependent modulus for the WIC prepared from MTMOS was 26% at 50 years, which is the least among all WICs tested. These findings clearly indicate that treatment with suitable metal alkoxides could improve the creep resistance of wood.

Effects of heat treatment on the chemical compositions and thermal decomposition kinetics of Japanese cedar and beech wood

This study investigated variations in the chemical compositions and thermal decomposition kinetics of Japanese cedar and beech wood during heat treatment. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectra revealed that various reactions, such as hemicellulose deacetylation, condensation reactions causing lignin cross-linking, and reductions in cellulose amorphous regions, were carried out during the heat treatment process. In addition, combinations of FTIR spectra and principal component analysis (PCA) succeeded in discriminating the major changes in functional groups of wood at various heat treatment temperatures. On the other hand, the decrease in the storage modulus of wood was more rapid in the presence of oxygen than in an oxygen-free atmosphere during heat treatment. Accordingly, the activation energies of thermal decomposition using Arrhenius model for Japanese cedar and beech were 120.6 and 141.3 kJ/mol under air, respectively, while these values were 124.8 and 150.0 kJ/mol under nitrogen, respectively.

Probabilistic sensitivity analysis to understand the influence of micromechanical properties of wood on its macroscopic response

This paper investigates the influence of the uncertainty in different micromechanical properties on the variability of the macroscopic response of cross-laminated timber plates, by means of a probabilistic sensitivity analysis. Cross-laminated timber plates can be modelled using a multiscale finite element approach which although suitable, suffers from high computational cost. Investigating parametric importance can incur considerable time penalty since conventional sensitivity analysis relies on a large number of code evaluations to produce accurate results. In order to address this issue, we build a statistical approximation to the code output and use it to perform sensitivity analysis. We investigate the effect of a collection of parameters on the density and Young’s moduli of wood. Additionally, the influence on the response of cross-laminated timber plates subject to bending, in-plane shear and compression loads is investigated due to its relevance within the engineering community. The presented results provide a practical insight into the importance of each micromechanical parameter, which allows research effort to be focused on important wood properties.

Modeling of orthotropic plates out of cross laminated timber in the mid and high frequency range

Within the context of efficient and sustainable design of buildings a trend towards lightweight structures, e.g. timber structures, is recognizable. This trend implies the necessity of being able to predict serviceability and comfort as well as sound transmission in order to fulfill vibroacoustic requirements. To generate reliable prediction methods, the transfer of energy between building components has to be investigated. Therefore, a detailed understanding of the modeling of the building components, e.g. walls or ceilings, is compulsory. In the low frequency range the Finite Element Method (FEM) is a convenient tool to predict the vibroacoustic behavior. However, without appropriate post-processing it is limited due to the sensitivity of the results at higher frequencies. In the mid-frequency range a sufficient number of modes per band enables the use of statistical methods like the Statistical Energy Analysis (SEA). It delivers averaged results and thus copes with the sensitivity. As both techniques have a restricted validity regarding the frequency range, averaging techniques of the SEA are applied in the post-processing of the FEM to obtain an adapted hybrid approach, the Energy Flow Analysis. This contribution will focus on the Finite Element Model of the building components out of cross laminated timber modeled as orthotropic plates. The Young’s modulus of wood is perpendicular to the fiber comparatively low, which leads to low velocities of longitudinal and shear waves. Hence, at high frequencies thickness-stretch and thickness-shear modes play an important role. These can be activated already at low frequencies within the stiffness controlled region of their amplification function. Hence, their non-resonant contribution can be identified evaluating the potential energy compared to the kinetic one. This phenomenon is verified with the help of solid elements - in comparison with shell elements - by varying the points of excitation across the thickness. Moreover, the dimensions will be modified as well as the junction by inserting an elastic layer. Whereas the SEA is typically not able to represent through-thickness effects of plate-like structures, the energy flow between a wall and a ceiling will be investigated using the hybrid approach.

Dynamic Modulus of Wood Containing Water-Resistant Glue Finger Joint after Severe Steaming

The effect of steaming treatment on the dynamic modulus of oak wood (Quercus castaneifolia, C. A. Mey.; Fagaceae) containing a water resistant glue-finger joint was investigated. Sample joints were made with two different types of waterproof adhesives, polyurethane (PU) and epoxy, and the samples were tested by a free flexural vibration method according to flexural and longitudinal free vibration modes. Compared with the epoxy joints, the PU finger-joints retained elastic moduli closer to their initial values. In all three vibration tests, finger-jointed oak wood specimens with either glue retained their moduli of elasticity, after the steaming treatments. In the case of longitudinal-tangential (LT) vibration, some increases were observed for the evaluated elastic moduli. After steaming, the obtained dynamic values decreased. For epoxy-bonded specimens, the correlation coefficient in terms of the elastic modulus before and after steaming were weak. There were some acceptable PU-bonded specimens, but there was a considerable decrease after steaming.