Comparison of the in-plane shear strength of OSB and plywood using five point bending and EN 789 steel plate test methods

In order to assess the interlaminar shear strength of spruce plywood and oriented strand board (OSB) five point bending tests and shear tests according to EN 789 were performed. Additionally, a linear elastic finite element analysis of both test set-ups was performed to visualise the distribution of shear stresses. While shear stress was homogeneously distributed in EN 789 samples, typical s-shaped stress fields were observed in beam sections of five point bending specimens. Experiments showed a higher shear strength for plywood compared to OSB. In addition, apparent shear strength measured by five point bending was higher than values obtained using EN 789, the difference being significantly more pronounced for plywood (_5-pt/_EN789 = 1.7) than for OSB (_5-pt/_EN789 = 1.3). It is concluded that differences in the structure of OSB and plywood lead to a bias in the measured apparent shear strength of plywood by means of five point bending tests. Since apparent shear strength values determined by five point bending tests are, therefore, not only dependant on span to thickness ratio, but also on composite structure, EN 789 is recommended for interlaminar shear testing of wood composites.     

Comparison of the in-plane shear strength of OSB and plywood using five point bending and EN 789 steel plate test methods

In order to assess the interlaminar shear strength of spruce plywood and oriented strand board (OSB) five point bending tests and shear tests according to EN 789 were performed. Additionally, a linear elastic finite element analysis of both test set-ups was performed to visualise the distribution of shear stresses. While shear stress was homogeneously distributed in EN 789 samples, typical s-shaped stress fields were observed in beam sections of five point bending specimens. Experiments showed a higher shear strength for plywood compared to OSB. In addition, apparent shear strength measured by five point bending was higher than values obtained using EN 789, the difference being significantly more pronounced for plywood (_5-pt/_EN789 = 1.7) than for OSB (_5-pt/_EN789 = 1.3). It is concluded that differences in the structure of OSB and plywood lead to a bias in the measured apparent shear strength of plywood by means of five point bending tests. Since apparent shear strength values determined by five point bending tests are, therefore, not only dependant on span to thickness ratio, but also on composite structure, EN 789 is recommended for interlaminar shear testing of wood composites.

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Vergleichende Untersuchung der Schubfestigkeit von OSB und Sperrholz mittels Fünfpunkt-Biegeprüfung und EN 789

Zusammenfassung Zur Bestimmung der Schubfestigkeit von Fichtensperrholz und OSB wurden Fünfpunkt-Biegeversuche und Tests nach EN 789 durchgeführt. Zusätzlich wurde die Verteilung der Schubspannungen über den Prüfkörper mittels der Methode der finiten Elemente berechnet. Während die Schubspannungen in EN 789 Proben sehr homogen verteilt waren, zeigten sich in Fünfpunkt-Biegeproben typische S-förmige Spannungsfelder zwischen Auflagern und Krafteinleitungspunkten. Experimente ergaben eine höhere Schubfestigkeit für Sperrholz als für OSB. Weiters ergab sich eine höhere Schubfestigkeit mittels Fünfpunkt-Biegung als mit EN 789. Dieser Unterschied war bei Sperrholz (_5-Pkt/_EN789 = 1.7) weitaus stärker ausgeprägt als bei OSB (_5-Pkt/_EN789 = 1.3). Daraus wird geschlossen, dass bei der Fünfpunkt-Biegeprüfung Unterschiede in der Struktur von Sperrholz und OSB zu einem größeren Unterschied der gemessenen Schubfestigkeit als bei EN 789 führen. Da die gemessene Schubfestigkeit bei Fünfpunkt-Biegeprüfung somit nicht nur vom Spannweiten/Dickenverhältnis, sondern auch vom Plattenaufbau abhängt, wird EN 789 für die Prüfung der Schubfestigkeit von Holzwerkstoffen empfohlen.

     

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.

     

Some Properties of Composite Panels Manufactured from Eastern Redcedar (Juniperus virginiana L.) Using Modified Starch as a Green Binder

The objective of this study was to evaluate basic properties of particleboard panels manufactured from Eastern redcedar (Juniperus virginiana L.) using modified starch and low percent of urea formaldehyde as binder. Experimental panels in the form of three-layer configuration were made from the raw material at two density levels. Bending characteristics, namely, modulus of elasticity (MOE), modulus of rupture (MOR), and internal bond strength (IB) in addition to dimensional stability and surface roughness of the samples were determined. The highest MOE and MOR values of the samples with 0.80 g/cm³ density level were found as 2344.32 and 12.14 MPa, respectively. Both bending and IB values of the samples were comparable to those of commercially manufactured panels from other species. It appears that dimensional stability of the panels needs to be enhanced. Based on the findings in this work, modified starch could have potential as green binder in particleboard panels manufactured from Eastern redcedar without having substantial adverse influence on their properties.     

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.     

Density and some mechanical properties of densified and heat post-treated Uludağ fir,linden and black poplar woods

The effects of thermo-mechanical densification and heat post-treatment on air-dry density, modulus of elasticity (MOE), bending strength (MOR), and compression strength parallel to the grain (CS) of Uluda? fir (Abies bornmulleriana Mattf.), linden (Tiliagrandifolia Ehrh.), and black poplar (Populus nigra L.) wood samples were investigated. Samples were densified with compression ratios of 25 and 50%, and at 100 and 140?°C. Then, the heat treatment was applied to the samples at 185 and 212?°C for 2 h. According to the results of the study, density of all wood samples increased together with the increase of compression ratio. Regarding compression temperature, the highest density increase was obtained at 100?°C. Mechanical strength (MOE, MOR, and CS) in densified samples increased depending on compression ratio and increase of density. The highest strength increase was in black poplar samples and the lowest was in linden samples. After heat post-treatment, mechanical strength of samples decreased depending on increase in treatment temperature. However, strength values (MOR except) of samples which are 50% compressed and heat-treated were found higher than control samples.     

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.     

Prediction of global bending stiffness of timber beams by local sampling data and visual inspection

The results of visual inspection according to UNI 11119:2004 and bending tests made on 20 old chestnut (Castanea sativa Mill.) beams according to EN 408:2010 were statistically analyzed in order to provide a consistent and feasible procedure to predict their modulus of elasticity (MOE) in bending. Local data obtained from smaller size specimens was used for the prediction of the global mechanical properties of full structural size members and compared with the results of mechanical tests. The prediction models took into account the visual strength classes and the influence of defects on the determination of the MOE. Moreover, random sampling was considered in order to demonstrate the possibility of using smaller representative samples, thus avoiding excessive need of removal of on-site samples and allowing for a smaller number of mechanical tests. The models using random sampling predicted the behavior of full size scale elements accurately, with strong correlations to the experimental results (coefficient of determination r ² ranging from 0.70 to 0.79) and a percentage error lower than 20 %, thus allowing a reliable estimation of mechanical characteristics of existing timber members with a combination of visual inspection and local sampling.     

Comparison of mechanical properties of oriented strand board made from trembling aspen and paper birch

This study compared the performance of oriented strand boards (OSB) made from trembling aspen, a low-density hardwood species, and OSB made from paper birch, a medium-density hardwood species. The birch strands were thinner than the aspen strands to ensure a comparable specific surface. Three levels of adhesive content were used: 3.5%, 5.0%, and 7.0%. Internal bond (IB) and modulus of elasticity (MOE) and modulus of rupture (MOR) for flatwise and edgewise bending were determined. Both species performed equally well in IB (3.5% adhesive content: 0.46 MPa, 5.0%: 0.60 MPa, and 7.0%: 0.65 MPa). The values of MOE in flatwise bending were slightly lower for birch than for aspen panels (11.8 GPa for aspen and 10.6 GPa for birch), and the MOR values were not significantly different (combined 68.3 MPa). Edgewise bending properties were not significantly different for the two species with a MOE of 10.5 GPa and a MOR of 43.2 MPa.     

Bending performance of 3-layer beech (Fagus sylvativa L.) and Norway spruce (Picea abies (L.) Karst.) VTC composites bonded with phenol–formaldehyde adhesive and liquefied wood

Low quality beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst.) were densified with viscoelastic thermal compression (VTC) process to two different degrees of densification, and lamellas were used to manufacture different types of 3-layer VTC composites. Bending properties of 3-layer VTC composites bonded with phenol formaldehyde (PF) adhesive and liquefied wood (LW) were determined and compared to 3-layer composites produced with undensified beech or spruce wood lamellas. Morphology of VTC spruce wood of higher density was analysed with fluorescent microscopic technique. All composites produced with densified beech lamellas and bonded with PF adhesive had significantly higher values of modulus of rupture (MOR) and modulus of elasticity (MOE) than composites produced with undensified lamellas. Densified spruce lamellas contributed to better bending performance of 3-layer VTC composites bonded with PF adhesive to some extent. Furthermore, composites bonded with LW had significantly lower MOR and MOE values compared to composites bonded with PF adhesive. Study of VTC spruce wood microstructure showed that densification caused non-uniform deformation of cell wall structure, in which cell wall fractures were observed.     

The mechanical properties of densified VTC wood relevant for structural composites

The mechanical properties of densified wood relevant for structural composites were studied. Low density hybrid poplar (Populus deltoides × Populus trichocarpa) was densified using the viscoelastic thermal compression (VTC) process to three different degrees of densification (63, 98, and 132%). The modulus of rupture (MOR) and the modulus of elasticity (MOE) of the control (undensified) wood and of the VTC wood were determined. The bonding performance of the control and VTC wood, using two phenol-formaldehyde (PF) adhesives, was studied. Four different 3-layer composites were also prepared from undensified and VTC wood, and tested in four-point bending. The results showed that the bending properties of the VTC wood (MOR and MOE) were significantly improved due to the increased density. The bonding performance of VTC wood with PF adhesives was comparable with or better than in the case of the control wood. Increased density of the face layers in the 3-layer VTC composites was advantageous for their mechanical performance.     

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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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.     

Proposal for visual grading criteria of structural timber of sweet chestnut from Spain

Bending strength, modulus of elasticity and density were obtained for 981 specimens of Spanish Sweet Chestnut (Castanea sativa Mill.) sawn timber from five provenances. Four-point bending tests were made with three sizes (40 × 100 × 2,500, 40 × 150 × 3,500 and 70 × 150 × 3,500 mm) according to EN 408 (CEN EN 408:2011). Visual grading criteria were established, resulting in 82 % of the samples being classified as one structural quality, namely MEF. Characteristic values of the density and the mechanical properties were determined according to EN 384 (CEN EN 384:2010a): E _0,mean  = 12.3 kN mm^?2; f _m,k  = 28 N mm^?2 and ρ _k  = 510 kg m^?3. Therefore, a strength class D24 was assigned according to EN 338 (CEN EN 338:2010b). The relationship between the modulus of elasticity and bending strength was lower (R² = 0.26) than for Spanish coniferous species.     

Preliminary study on the variation of the bending properties of poplar rotary-cut veneer

The authors studied the variability of mechanical properties and density within poplar wood veneer. Determinations (EN 310 1993) were done using a tensometer particularly suitable for test pieces of small dimensions, by means of a 100 daN load cell. The bending test method developed seems to be able to provide reliable results, that confirmed the expected strong influence of the ring portions on both density and MOR (latewood being of course heavier and stronger), a difference which seems, however, less noticeable in false heartwood.     

Improvement of termite resistance,dimensional stability and mechanical properties of pine wood by paraffin impregnation

Paraffin has been used as surface protection of wood throughout the ages but its use for impregnation to improve wood resistance to biodegradation is recent. This study determined the main improvements on wood properties with paraffin impregnation. Healthy Pinus pinaster Ait. wood was impregnated with paraffin at different levels using a hot–cold process. Weight gain, equilibrium moisture content and dimensional stability (ASE) at 35 and 65 % relative humidity, termite durability against Reticulitermes grassei (Clément), bending strength, bending stiffness (MOE) and Janka hardness were determined. Density increased from 0.57 to 0.99, ASE ranged between 38–96 % and 16–71 % for 35 and 65 % relative humidity, respectively. Equilibrium moisture content decreased from 9.9 and 12.0 % to 0.8 and 3.6 % for 35 and 65 % relative humidity. Termite durability improved from level 4 to level 3 of attack, and higher termite mortality was found in treated wood (52 % against 17 %). Bending strength (MOR) increased with paraffin weight gain, reaching a 39 % increase. MOE also increased by about 13 % for wood with a weight gain around 80 %. Janka hardness increased significantly reaching about 40 % for wood with 80 % weight gain. Paraffin impregnated wood has improved properties with regard to equilibrium moisture content, dimensional stability and density, bending strength and Janka hardness, and resistance against termites.     

Deflections in sawn timber beams with stochastic properties

A stochastic model is proposed to study the behavior of structural sawn beams of Argentinean Eucalyptus grandis with the aim of improving the predictability of the elastic deformations. The enhancement of the mid-span deflection calculation is based on a probabilistic model of the Modulus of Elasticity (MOE) and the representation of its lengthwise variability through a random field. The standard model that uses a MOE variable assumed random from piece to piece but deterministic (constant) within each piece is obtained as a particular case. In order to obtain a statistical representation of the MOE, the Principle of Maximum Entropy (PME) is employed. Experimental data obtained from bending tests are employed to find the parameters of the derived Probability Density Function (PDF). The PDF of the mid-span deformations is numerically obtained through the Stochastic Finite Element Method (SFEM) and Monte Carlo Simulations (MCS). Numerical results are validated with experimental values. Deflections of structural sized beams under usual loads are obtained. Finally, the stochastic model is used to compare with the serviceability requirements established in the Argentinean design code. It is shown that the structural performance of timber beams is found through a more realistic material approach.     

Quality assessment of heat-treated wood by NIR spectroscopy

NIR spectroscopy was tested for predicting the properties of heat treated wood using pine (Pinus pinaster) and eucalypt (Eucalyptus globulus) woods with two types of treatment: in oven and in a steam autoclave. Mass loss, equilibrium moisture content, dimensional stability, MOE, bending strength, colour CIELAB parameters and extractives content were determined. NIR spectra were obtained using a fibre probe on the radial surface of the samples. NIR models for mass loss showed very high coefficients of determination (R²) for cross validation ranging from 96–98%. The models obtained for wood properties were in general good with coefficients of determination ranging from 78–95% for equilibrium moisture content, 53–78% for dimensional stability, 47–89% for MOE, 75–77% for bending strength and 84–99%, 52–96% and 66–98% for colour parameters L, a^* and b^*, respectively. R² of the models for extractive content varied between 41.9–79.8% for pine and between 35.3–82.2% for eucalypt wood. NIR spectroscopy showed a good potential for quality control and characterization of heat treated woods.     

The influence of compression failure on the bending, impact bending and tensile strength of spruce wood and the evaluation of non-destructive methods for early detection

Bending strength (MOR) and bending Young’s modulus (MOE) according to DIN 52186 and MOE calculated on the basis of eigenfrequency and sound velocity were tested on small clear wood specimens of Norway spruce wood with and without compression failure. One group of specimens was climatised in a normal climate of 20°C and 65% relative humidity, while the other group was stored for one month under water before testing. The MOR of specimens with compression failure decreased about 20% on average (normal climate and wet) compared with the specimens without compression failure. The MOE of the specimens with compression failure was reduced only minimally compared with the specimens without compression failure stored in a normal climate, but very distinct differences (more then 30%) were found under wet conditions. The MOE of the specimens with compression failure calculated on the basis of eigenfrequency and sound velocity were not reduced or only minimally compared with the specimens without compression failure. It is therefore not possible to detect compression failure and to determine reduction in MOR using eigenfrequency or sound velocity. In addition, impact bending (DIN 52189), tensile strength and tensile MOE (DIN 52188) were tested on small clear wood specimens of Norway spruce wood with and without compression failure. The specimens with compression failure revealed an average reduction in impact strength of about 40% and an average reduction in tensile strength of about 20% compared with the specimens without compression failure, whereas tensile MOE of the specimens with compression failure was not reduced compared with the specimens without compression failure. The detection of compression failure by computer tomography (CT) was tested on Norway spruce wood boards 10 cm in thickness, and detection by optical scanner was tested on planed Norway spruce wood boards. CT recognised large compression failures easily, whereas the scanner was not able to detect them.     

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.