Methods for measuring stiffness of young trees

Pinus radiata clones with high modulus of elasticity (MOE). Various ways of measuring MOE are examined: traditional static bending, axial compression of bolts, existing sonic methods, as well as a tool specifically configured for resonance on short bolts. Wood characteristics and microfibril angle are measured on discs taken from each tree. Results show a good correlation between acoustic and static measurements of modulus of elasticity. Moreover, the selected seven radiata clones differ in stiffness by a factor of two, and much of this variation seems to relate to differences in microfibril angle. The results validate the assumption that there is potential to improve wood stiffness of radiata pine genetically. This work does not offer definitive solutions but explores a number of approaches that could be utilised as a selection tool in tree breeding for better product performance of radiata lumber. Here, development of methods based on acoustics is shown to assist in the necessary mass screening of clones for stiffness properties.

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Pinus radiata mit hohen MOE-Werten zu selektieren. Verschiedene Methoden zur MOE-Messung werden untersucht: konventionelle statische Biegetests, axiale Kompression von St?ben, vorhandene (Ultra)-Schallmethoden, sowie ein spezielles Ger?t zum Messen der Resonanz von kurzen St?ben. Holzeigenschaften und Fibrillenwinkel wurden an Scheiben gemessen, die von jedem Baum entnommen wurden. Die Ergebnisse zeigen eine gute Korrelation zwischen akustischen und statischen Messungen des MOE. Die sieben ausgew?hlten Klone unterschieden sich in ihrer Steifigkeit um den Faktor 2, wobei ein Gro?teil dieser Variationen mit Unterschieden im Mikrofibrillenwinkel zusammenh?ngt. Die Ergebnisse best?tigen die Vermutung, da? ein Potential zum Verbessern der Holzfestigkeit durch genetische Methoden bei Pinus radiata vorhanden ist. Diese Arbeit bietet keine definitiven L?sungen. Sie untersucht eine Anzahl von Ans?tzen zur Selektion bei der Züchtung im Hinblick auf bessere Schnittholzprodukte. Die entwicklung von akustischen Methoden erwies sich als hilfreich beim notwendigen Massen-Screening der Festigkeitseigenschaften der Klone.

     

Relationship between non destructive and static modulus of elasticity of commercial wood plastic composites

The relationship between stress wave nondestructive (NDE) modulus of elasticity (MOE) and static MOE determined by four point bending test of commercial wood-plastic composites was evaluated in this study to assess the potential of using the NDE technique as a grading tool for wood plastics as it is currently done for solid lumber. The NDE MOE was evaluated on a Metriguard Model 340 E computer system, and the static MOE of the same boards measured on an Instron Universal Tester model 5587 according to the ASTM standard D 6109. Results showed that the NDE MOE values overestimated the static MOE from 3.5% to 17.6% depending on the boardwalk type. Regression analysis showed no significant correlation between the NDE MOE and the Static MOE. These results suggest that the stress wave NDE technique may not be appropriate to estimate the static MOE of wood plastic lumber. The trend however needs to be confirmed by further testing using a larger sample size and different combination of the raw materials.     

Cell wall structure and wood properties determined by acoustics—a selective review

The cell wall of wood tracheids is made up of various layers, distinguished from one other by the alignment of the innumerable, fine crystalline cellulose microfibrils within each layer that helically wind about the cell lumen. Microfibrils themselves are embedded in a more compliant, water-reactive matrix of amorphous lignin and hemicelluloses. The average inclination of microfibrils relative to the axis of the cell affects axial rigidity and dimensional stability of wood which are the two most important properties of wood. High and variable microfibril angles can be found in juvenile and compression wood, thus resulting in variations in product performance of forest products. For instance, seemingly identical trees in a plantation can have moduli of elasticity that differ by a factor of two or more. This is why the future is often seen in engineered wood products, where wood may be chipped, fiberised and blended before being glued together again: the average property values are little changed, but the range—the variability—is greatly reduced. There is the opportunity for better wood allocation and processing of timber, if averaged values for individual log characteristics, such as average microfibril angle, can be identified before the processing. In parallel there is genetic potential to select trees with low average microfibril angles. Unfortunately, determination of the average microfibril angle is a time-consuming, laboratory-based task. Preferably, a non-destructive, simple, field-hardened method should be employed that reflects the average microfibril angle in a given piece of wood. For this reason, acoustic methods have been developed to measure the velocity of sound propagation directly related to the stiffness of wood and in turn is dependent on the ultrastructure of the tracheid cell wall. In the fundamental equation, E_dynamic=V², the acoustic modulus is derived from two components, density, , and velocity of sound, V. The latter relates to the intrinsic wood quality and ultrastructure of the tracheid wall. It is shown that acoustic methods can sort and grade trees and logs according to their suitability for structural lumber and for a range of fiber properties of interest to papermakers. Thus, acoustic methods have applications in tree breeding, harvesting, and wood processing.     

Prediction of the mechanical properties of lumber by stress-wave velocity and Pilodyn penetration of 36-year-old Japanese larch trees

The objective of this study was to obtain basic knowledge for the prediction of the mechanical properties of Japanese larch lumber (Larix kaempferi) on the basis of tree properties, such as the stress-wave velocity (SWV) and Pilodyn penetration value (Py). The values of the correlation coefficient between the SWV of a standing tree and the dynamic Young’s modulus (DMOE) of logs, which were obtained at various heights, gradually decreased with an increase in the log sampling height, indicating that the SWV of a tree is affected by wood properties at the measuring position. A significant correlation between the SWV of trees and the average modulus of elasticity (MOE) of lumber was found (r =0.834). A significant negative correlation between the Py of a tree and the average modulus of rupture (MOR) of lumber was also found (r=-0.859). A high coefficient of determination for an obtained regression curve was found when both the SWV and Py of a tree were used for evaluating the average MOE or MOR of lumber. These results indicate that the average MOE and MOR of lumber can be predicted by using the SWV and Py of the Japanese larch tree.     

Versuche und Berechnungen an allseitig gelagerten 3-schichtigen Brettsperrholzplatten

Within the framework of an extensive research project, cross-laminated solid wood panels, which are used in building industry also as static load bearing elements, were investigated. 3-layered cross-laminated square solid wood panels with side length of 2,5 m and thickness of 70 mm from two producers were statically tested to failure. Three different types of loading and two cross-section compositions were investigated. Ultrasonic measurements of the single layers before bonding served to estimate the modulus of elasticity (MOE) of the single layers. The MOE and the strength of the bonded panels parallel and perpendicular to the grain direction of the outer layers were additionally derived from beam tests. Results and conclusions of the ultrasonic measurements, beam and panel tests are presented. Different beam and plate calculation methods for the cross-laminated wood panels are presented. The results of the tests are compared with the calculations. A calculation proposal for the practice is presented.     

Prediction of non-recoverable collapse in Eucalyptus globulus from near infrared scanning of radial wood samples

Near infrared (NIR) spectroscopy calibrations was used to predict radial profiles of cellulose content, wood density, cellulose microfibril angle (MFA) and modulus of elasticity (MOE) in 20-year-old plantation Eucalyptus globulus to identify non-recoverable collapse zones associated with tension wood. Radial (cambium-to-pith) wood cores were extracted at a height of 1.0 m from trees selected to represent a range of silvicultural treatments. NIR spectra were measured at 1 mm intervals along the radial-longitudinal face of each core after drying to 12 % equilibrium moisture content (EMC) at 40 °C. Tangential shrinkage was measured at eight points along each core, following steam reconditioning and re-drying to 12 % EMC. Additional cores from 20 of the sample trees were collected. Radial profiles of density, MFA and MOE were obtained for wood strips prepared from these cores, using the SilviScan 3 wood assessment system. Trait profiles were matched to radial NIR scans of these cores, enabling the development of NIR calibrations using partial least squares (PLS) regression. These, and an existing NIR calibration for cellulose content, were used to predict the radial profiles of the four wood properties for the first set of cores. Predicted wood properties were then related to actual tangential shrinkage measurements and the occurrence of visible bands of non-recoverable collapse. A regression model was developed to reliably predict regions of non-recoverable collapse from NIR-predicted cellulose content and MOE. Micrography of stained wood sections indicated that the collapse was caused by the presence of tension wood.     

Mechanical and physical properties of thermally modified Scots pine wood in high pressure reactor under saturated steam at 120, 150 and 180 °C

Scots pine sapwood and heartwood were thermally modified under saturated steam at 120, 150 and 180 °C in a high pressure reactor. Mechanical properties such as dynamic and static modulus of elasticity (MOE), static modulus of rupture (MOR), Brinell hardness and impact toughness were evaluated. The static MOE for sapwood did not decrease substantially (approximately 1 %), not even with a high mass loss of more than 12 %, when the wood was modified at 180 °C. Static MOE of the wood increased approximately 14 %, when modified at 150 °C. Surprisingly, MOR increased by 15 %, when modified at 150 °C with mass loss of 2.3 %. Whereas impact strength and hardness decreased somewhat, when modified at 180 °C. Moreover, high anti-swelling efficiency values were obtained (60 % for sapwood and 52 % for heartwood) when modified at 180 °C.     

Estimating mechanical properties of clear wood from ten‐year‐old Melia azedarach trees using the stress wave method

The objective of this study was to examine the potential of stress wave velocity (SWV) as a rapid and non-destructive method to estimate the mechanical properties of Melia azedarach wood. The SWV, dynamic modulus of elasticity (MOE_d), modulus of elasticity (MOE), modulus of rupture (MOR, bending strength) and density were determined on ninety 20 ? 20 ? 320 mm clear wood specimens, obtained from stems of three ten-year-old M. azedarach trees, and tested at environmental equilibrium in 20°C, 60?% relative humidity (a moisture content of approximately 12?%). There was a statistically significant (0.1?% level) but weak correlation (R²?=?0.23) between the SWV and MOE, but no statistically significant correlation was found between the SWV and MOR. Much better results for prediction of static properties of M. azedarach wood were obtained when SWV and wood density (WD) were used together through calculation of MOE_d in the air-dry condition (MOE: R²?=?0.76, MOR: R²?=?0.47), although in the case of MOR a model based on WD alone is slightly better (R²?=?0.58), and WD is also almost as good as MOE_d for predicting MOE. It is concluded that SWV coupled with WD can be employed as a predicting parameter to evaluate the mechanical properties of M. azedarach wood during the manufacturing process, although WD alone is also effective. The SWV alone would not be useful due to MOE being almost directly proportional to WD at this moisture content.

     

Modelling mechanical properties of spruce and Douglas fir timber by means of X-ray and grain angle measurements for strength grading purpose

This study proposes a model using data from a scanner (X-ray and grain angle measurements) to perform strength grading. The research also includes global measurements of modulus of elasticity (obtained by vibrations and ultrasound methods), static bending stiffness and bending strength of 805 boards of Douglas fir and 437 boards of spruce. This model can be used in an industrial context since it requires low computational time. The results of this study show that the developed model gives better results than the global non-destructive measurements of the elastic modulus commonly used in the industry. It also shows that this improvement is particularly higher in the case of Douglas fir than for spruce. The comparison has been made on both the quality of the mechanical properties assessment and on the improvement of the grading process according to the European standards by using different index.     

The effect of silicone on some properties of flakeboard

Waxes are used as water repellent in wood composites, and there are only limited alternative water-repellent systems for wood composites. The aim of this study was to investigate the effectiveness of a silicone compound as a water repellent for flakeboard and to compare the properties of boards made with silicone treated flakes to those made with commercial wax treated flakes. Three levels of silicone and wax application rates were used (0.25, 0.5, and 1%). The hydrophobic nature of silicone-treated flakes was evaluated by measuring the contact angle and the rate of water absorption (WA) on the surface of the wood flake. The internal bonding strength (IB), the modulus of elasticity (MOE) and modulus of rupture (MOR) in bending regime, the WA, and the thickness swelling at edges of boards were evaluated. Results obtained showed that IB, MOE and MOR decreased as the concentration of silicone on the flakes increased from 0.25% to 1%. The IB, MOE and MOR of panels made with 0.25% silicone-treated flakes were comparable to boards made with 1% wax-treated flakes. Thickness swell at edges and WA were significantly reduced as the amount of silicone increased. No significant difference was found for the thickness swelling at edges and the WA between panels made with 1% silicone-treated flakes and 1% wax-treated flakes. The silicone treated flakes had high water repellency.     

The effect of fine strands in core layer on physical and mechanical properties of oriented strand boards (OSB) made of beech (Fagus sylvatica) and poplar (Populus tremula)

This paper discusses the influence of three different content levels of fine strands in the core layers on the physical and mechanical properties of European beech and poplar oriented strand boards (OSB). The results show that increasing the fines content in the core layer from 10 to 50 %, based on total board weight has no significant effect on bending strength and modulus of elasticity (MOE). All panels exceeded the minimum requirement for bending strength and MOE set by EN standards. The highest modulus of rupture (MOR) and modulus of elasticity (MOE) was determined for panels solely made of poplar with different level of fines content. Increasing the amount of fines in the core layer raised the internal bond (IB). Panels made with 30 % fines in the core layer showed highest internal bond strength values. As the fines content increased from 10 to 50 %, thickness swelling decreased. Water absorption after 24 h showed the same declining trend as thickness swelling.     

含水率对落叶松材动态弹性模量的影响

在不同含水率下,利用应力波、纵波共振和横向弯曲振动三种方法对落叶松材试件进行了检测试验,研究了木材含水率对动态弹性模量等的影响,不同含水率下测试参数和动态弹性模量之间关系以及三种测试方法所得动态弹性模量之间的相关性.结果表明,含水率对动态测试结果影响显著;含水率对各测试参数和动态弹性模量之间的相关性影响不大;所得到的三个动态弹性模量之间相关程度相当高.     

Technologische Untersuchungen an Pinus radiata-Importhölzern aus Chile

Technological investigations on small clear, samples of radiata pine timber from Chile have shown lower average densities and moduli of elasticity than conifers from Central Europe. Only bending strength has been higher as compared to spruce and fir; however, the individual values scatter considerably. Piloting investigations on structural timber indicate that the grading criteria according to DIN 4074 are in principle also applicable to radiata pine. Average bending strength and particularly Young's modulus of elasticity of the structural timber investigated were lower than the comparative values of spruce. Swelling and shrinkage caused by changes in moisture are lower as compared to spruce and European redwood.     

Tailor made OSB for special application

The purpose of this study was to develop speciality oriented strand board (OSB) with high stiffness for use in products such as engineered wood flooring (EWF). Three-layer oriented strand boards were manufactured from two feedstocks of strands: a mixture of 90% aspen (Populus tremuloides) and 10% of paper birch (Betula papyrifera), and 100% of small diameter ponderosa pine logs (Pinus ponderosa). The OSB panels were manufactured under a factorial design of three resin contents, two density profiles, and three weight ratios for the face and core layers. Tests to determine density, bending modulus of elasticity (MOE), internal bond (IB) and thickness swelling (TS) were performed according to ASTM standard D 1037-06a. The results showed that the higher values of bending MOE for panels made from aspen/birch mixture and ponderosa pine, 8190 and 9050?MPa, respectively, were obtained for the same combination of factors. Such high bending MOE values are very close to Baltic birch (Betula pendula) plywood, a product known for its high stiffness. The effect of resin content on IB is more pronounced for panels made from ponderosa pine than panels made from the aspen/birch mixture. Thickness swelling of panels made from ponderosa pine strands is higher than thickness swelling of panels made from a mixture of aspen and birch strands. The results indicate the potential to tailor an OSB for a specific application such as EWF.     

Effect of laminated structure design on the mechanical properties of bamboo-wood hybrid laminated veneer lumber

The effects of veneer orientation and loading direction on the mechanical properties of bamboo-bundle/poplar veneer laminated veneer lumber (BWLVL) were investigated by a statistical analysis method. Eight types of laminated structure were designed for the BWLVL aiming to explore the feasibility of manufacturing high-performance bamboo-based composites. A specific type of bamboo species named Cizhu bamboo (Neosinocalamus affinis) with a thickness of 6 mm and diameter of 65 mm was used. The wood veneers were from fast-growing poplar tree (Populus ussuriensis Kom.) in China. The bamboo bundles were obtained by a mechanical process. They were then formed into uniform veneers using a one-piece veneer technology. Bamboo bundle and poplar veneer were immersed in water-soluble phenol formaldehyde (PF) resin with low molecular weight for 7 min and dried to MC of 8–12 % under the ambient environment. All specimens were prepared through hand lay-up using compressing molding method. The density and mechanical properties including modulus of elasticity (MOE), modulus of rupture (MOR), and shearing strength (SS) of samples were characterized under loading parallel and perpendicular to the glue line. The results indicated that as the contribution of bamboo bundle increased in laminated structure, especially laminated on the surface layers, the MOE, MOR and SS increased. A lay-up BBPBPBB (B-bamboo, P-poplar) had the highest properties due to the cooperation of bamboo bundle and poplar veneer. A higher value of MOE and MOR was found for the perpendicular loading test than that for the parallel test, while a slightly higher SS was observed parallel to the glue line compared with perpendicular loading. Any lay-up within the homogeneous group can be used to replace others for obtaining the same mechanical properties in applications. These findings suggested that the laminated structure with high stiffness laid-up on the surface layers could improve the performance of natural fiber reinforced composites.     

Die Streuung des Elastizitätsmoduls in Brettlängsrichtung

The modulus of elasticity (MOE) of 100 boards and 640 board sections, 45 cm long, was determined. For the board sections, a regression equation for the MOE, depending on density and knot size was calculated. In more than 80% of the boards the MOE-variability within one board was lower than the residue of the regression equation valid for all board sections.     

Effect of panel properties on the concentrated static load (CSL) performance of oriented strand board (OSB)

The relationship between concentrated static load (CSL) performance of oriented strand board (OSB) and panel thickness, local density, and some mechanical properties (including modulus of elasticity (MOE), modulus of rupture (MOR), and interlaminar shear strength in both major and minor directions) was investigated using both a simple linear regression method and a stepwise multi-linear regression technique. The sample boards were laboratory manufactured OSB panels consisting of eighteen combinations of different strand geometries (length, width, and thickness), strand orientations, and fines contents. Simple linear regression analysis showed that MOE (major direction), MOR (major direction), shear strength (major direction), local thickness, average board density and local density were all significantly and negatively correlated with the CSL deflection; however, in the stepwise multi-linear regression analysis only MOE (major) and local thickness were retained as significant factors possibly due to inter-correlation amongst the variables. Shear strength (major direction), MOR (major direction), average board density, MOE (major direction), MOR (minor direction), local thickness, average board thickness, local density, and shear strength (minor direction) were all found to be significantly and positively correlated with the CSL ultimate load in the simple regression analyses, but only shear strength (major) and local panel thickness were retained in the stepwise multi-linear regression model for the CSL ultimate load.     

Study of the relationship between flatwise and edgewise modull of elasticity of sawn timber as a means to improve mechanical strength grading technology

In most of the strength grading machines for sawn timber, the flatwise bending modulus of elasticity (MOE) of timber pieces is measured. Employing regression functions, their edgewise MOE is estimated on the basis of the flatwise MOE and the edgewise bending strength of the weakest part of each piece is calculated to allocate each piece to a standardised strength class. With regard to improvements in the accuracy of timber strength grading machines, it was studied to which extent structural wood characteristics and grading parameters affect the relationship between flatwise and edgewise bending MOE. Edgewise and flatwise MOE have been determined both in knotty and in knot-free sections of boards of Norway spruce. The flatwise MOE was determined in a three-point bending test as it is typically employed in strength graders. The edgewise MOE was determined in a four-point bending test. Additionlly, the MOE and density distributions over the timber cross sections were determined to model the total MOE under consideration of these distribution patterns. Shear deformation accounts for a substantial portion of the difference between flatwise and edgewise MOE. The effect of knots on the MOE could not be defined precisely. Growth ring structure and juvenile wood in the boards lead to 5 to 10% lower flatwise MOE values as compared to the edgewise MOE.     

Prediction of MOE of eucalypt wood from microfibril angle and density

Small clear specimens of 30×30×450 mm were prepared from plantation-grown Eucalyptus globulus, E. nitens and E. regnans that were between 15 and 31 years of age. Their modulus of elasticity (MOE) and modulus of rupture (MOR) were determined using static central-point-loading bending tests. Their microfibril angle (MFA) and density were determined using SilviScan on strip samples removed from the intact portion of the specimens after the bending tests. It was found that MFA alone accounted for 87 percent of the variation in MOE, while density alone accounted for 81 percent. Together, MFA and density (as Density/MFA) accounted for 92 percent of the variation in MOE. The MFA impact diminishing point appears to be 16 degrees for the wood material of three eucalypt species in this study. Density alone accounted for 80 percent of the variation in MOR, whereas MFA had little independent influence on MOR.

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Vorhersage des MOE von Eukalyptusholz aus Fibrillenwinkel und Dichte

Zusammenfassung  Kleine fehlerfreie Proben (30×30×450 mm) wurden aus 15 bis 33 Jahre alten Eucalyptus globulus, E. nitens und E. regnans aus Plantagenanbau geschnitten. Deren MOE und MOR wurden unter statischer zentraler Belastung im Biegetest bestimmt. Außerdem wurden der Mikrofibrillenwinkel (MFA) und die Dichte bestimmt, und zwar mittels SilviScan an Probestreifen, die nach dem Biegetest aus intakten Probeteilen geschnitten wurden. Es zeigte sich, daß allein der Mikrofibrillenwinkel zu 87 Prozent für die Variation des MOE verantwortlich ist, die Dichte für sich allein nur für 81 Prozent. MFA und Dichte zusammen (als Quotient Dichte/MFA) erklären 92 Prozent der Variation des MOE. Die Grenze des negativen Einflusses des Mikrofibrillenwinkels scheint für das vorliegende Probenmaterial bei 16 Grad zu liegen. Im Falle des MOR ist die Dichte allein für 80 Prozent der Variation verantwortlich, wogegen der MFA nur einen geringen unabhängigen Einfluß auf den MOR hat.

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Einfluss von Temperatur und Holzfeuchte auf die dynamischen Eigenschaften von unsortierten Fichtenbrettern

In order to draw conclusions concerning the sound velocity and the dynamic modulus of elasticity of logs and green timber at reference conditions, properties were determined for green timber at temperatures around and below the freezing point. The present investigation includes the analysis of the dependence of sound velocity and dynamic modulus on temperatures between ?20?°C and +20?°C and on moisture contents below and above fibre saturation. Sound velocity and dynamic modulus of elasticity were determined based on natural frequency and density. Both sound velocity and dynamic MOE decreased linearly with increasing moisture content and increasing temperature below fibre saturation. Three temperature areas need to be considered above fiber saturation—below ?5?°C and above 0?°C and the area between ?5?°C and 0?°C. Sound velocity as well as dynamic MOE decrease linearly with increasing temperature. Based on these findings, appropriate adjustment functions for each moisture content and temperature range were found to calculate the dynamic properties at the reference conditions.