两种无损检测方法评估足尺杉木规格材动态弹性模量

利用纵向基频振动和应力波方法测量了不同规格足尺杉木的动态弹性模量,结果表明:不同尺寸的杉木规格材平均动态弹性模量变化不大;杉木规格材纵向基频振动法测得的动态弹性模量Efft在8.18~9.50GPa之间,应力波法测动态弹性模量Esw在9.02~10.38GPa之间,两者的相关性很好,相关系数可达0.9以上;杉木规格材动态弹性模量最大值和最小值差异较大,主要分布在7~11GPa之间。     

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.     

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.

     

Methods for measuring stiffness of young trees

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.     

Variation in selected mechanical properties of Japanese larch (<Emphasis Type="Italic">Larix kaempferi</Emphasis>, [Lamb.] Carr.) progenies/provenances trials in Eastern Canada

12 years old trees from 20 progenies/provenances of Japanese larch (Larix kaempferi, [Lamb.] Carr.), planted in Quebec, were sampled to study the variation in selected mechanical properties. Two standard wood samples and one 10-mm diameter increment core were taken from each tree at breast height. The parallel-to-grain compliance coefficient and ultimate crushing strength were evaluated on the standard samples at air-dry conditions. The dynamic compliance coefficient was measured on increment cores using an ultrasonic wave propagation method. Differences in all mechanical properties among progenies/provenances were significant. Lowest static compliance coefficient and highest ultimate crushing strength were found in progenies/provenances 8934, 7795, 7283, 8962, 8907, 7794, and 8939, being the most interesting for a lumber end-use. Among them, progenies/provenances 7283, 8934, 7794, 7795, 8962, and 8907 also showed lowest dynamic compliance coefficient. The latter coefficient tended to be lowest near the pith and then increased outward towards the bark. There was also a highly significant correlation between static mechanical properties, and a moderate correlation between static and dynamic compliance coefficients. Ultimate crushing strength was moderately correlated to wood density.     

Determining the predictive accuracy of whole tree modulus of elasticity (MOE) of 14-year-old loblolly pine using density and dynamic MOEs estimated by three different acoustic tools

Resonance based acoustic tools for evaluating wood properties have been reported to be more accurate in estimating the expected log MOE than time-of-flight (ToF) ones. However, there is no published study on the variations within different brands on these two major classes of acoustic tools. In this study, models were developed to predict the whole tree static MOE (WMOE_T) and rupture (WMOR_T) using log dynamic MOEs estimated by two resonance tools [Director HM200 (EHM200) and FAKOPP resonance log grader (ERLG)], ToF [FAKOPP Microsecond Timer (EFMT)], and density (green density, air-dry density) for a 14-year-old loblolly pine stand from two sites in the southern USA. The log velocity estimated by ToF was 33 and 30% more as compared to the resonance-based tools (Director HM200 and FAKOPP RLG respectively); translating into whole log static MOE (WMOEL) been 11 and 20% lower than those estimated by the resonance (HM200 and RLG respectively), and 90% lower than that estimated by the ToF tools (EFMT). Although the dynamic MOE estimated by ToF tool (EFMT) was higher, its WMOET predictive performance (R²?=?51%) lies between the 39 and 74% for the resonance based tools (HM200 and RGL respectively). This result supports the theory that ToF tools generate dilatational wave, and hence their velocity will be generally higher than resonance tools. The presence of predictive variation within the resonance suggests the need for within tools calibration. The linear relationship between the WMOE_T vs E_tree was stronger than that of WMOET vs EHM200 suggesting that the ToF acoustic tool measurements are not restricted to the outer wood zone for small diameter logs.     

Bending properties of a novel engineered composite from southern pine lumber

This paper presents the results of a study in which novel engineered composite lumber was developed, manufactured and tested. The engineered composite lumber was made by edge-laminating lower-grade No. 3 solid-sawn southern pine (SP) lumber with higher-grade tension chord material to yield tension chord lumber (TCL). Three groups of TCL (38 mm × 235 mm × 4.9 m) were made with varying combinations of SP lumber including machine stress rated (MSR) 2400Fb-2.0E, MSR 2400Fb-2.0E finger joint, and visually graded No. 1 finger joint material. One group of visually graded No. 3 control lumber (38 mm × 184 mm × 4.9 m) was also tested. All specimens were tested in static four-point bending on a universal testing machine. The modulus of elasticity (MOE) and modulus of rupture (MOR) were determined. The TCL lumber had significantly greater MOE values as compared with the control lumber. The mean MOE values of TCL ranged from 12.4 to 12.6 GPa, as compared with 9.6 GPa for the control group. The mean MOR values of TCL ranged from 39.3 to 47.6 MPa, as compared with 35.9 MPa for the control group. Perhaps most importantly, the 5th percentile values of MOR of the TCL were approximately double those of the control group, 29.1, 27.0, and 27.4 MPa versus 11.8 MPa, respectively.     

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.     

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.     

Evolution of internal stress during drying, cooling and conditioning of rubberwood lumber

In an attempt to develop a real-time measurement technique for an internal stress perpendicular to grain in the radial direction of rubberwood lumber during drying and conditioning, a novel design of a force measuring device, consisting of a restrained half-sawn specimen and a restrained free shrinkage specimen, was constructed. The measured force was verified with a differential released strain obtained from the conventional McMillen slice technique. The device was then employed to investigate the internal stress evolution during drying and conditioning of rubberwood lumber. It was shown that the force measured using the device strongly correlates with the differential released strain. The extents of the internal stress characteristics such as the maximum tensile and compressive forces and the reciprocal of time at stress reversal obey the Arrhenius equation and the adapted equation of sorption for the temperature and humidity dependences, respectively. The results also indicate that cooling under relatively high humidity after drying improves the internal stress relaxation process during conditioning. Possible application of the technique in kiln drying of rubberwood has been demonstrated. The measured force could be used as controlling parameter for an adaptive wood drying control system taking into account real-time material response of wood during drying and conditioning.     

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.     

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 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.     

酚醛树脂桉木单板层积材生产工艺研究

探讨利用酚醛树脂胶黏剂压制桉木单板层积材的工艺,分析了热压温度、热压时间和面粉添加量对桉木单板层积材力学性能的影响。研究表明：面粉添加量对桉木单板层积材的静曲强度和弹性模量有显著影响,而热压温度和热压时间的影响则不显著。就产品力学强度而言,较佳的工艺条件为：热压温度135℃,热压时间1.2 min/mm,面粉添加量0。验证试验证明,在实际生产中,综合生产成本及产品性能等多方面考虑,添加15%的面粉是可行的。     

Effects of ACQ preservative treatment on the mechanical properties of hardwood glulam

The purpose of this study is to examine the mechanical properties of ACQ-treated glulam made from three hardwood lumbers. Two nondestructive methods, ultrasonic wave and tap tone method, were also used in this study. The results showed that the dynamic MOE and static MOE of lumbers decreased with increased ACQ preservative retention. ANOVA showed no significant difference in the MOE values of glulam between untreated and ACQ-treated group. However, it was also found that glulam made from red oak lumbers had the highest bending strength retention ratio. The shear strength of the glulam also showed similar results. Finally, no delaminating was found in all glulams after the specimens under soaked and boiled delamination tests.     

Swelling restraint of thermally modified ash wood perpendicular to the grain

The paper reports on creep of ash wood (Fraxinus excelsior L.) thermally modified at 180 and 200 °C, and subsequently subjected to compression in tangential and radial directions and simultaneously wetted, from the moisture content (MC) of 6% to above the fibre saturation point (FSP). The compressing load made 0.00, 0.25, 0.50 and 0.75 of impact stress at the proportional limit (R_c). The compression stress needed to restrain the swelling of wood, the so-called swelling pressure, was indirectly determined from isochrones of mechano-sorptive creep. The most important finding was that thermal modification reduces the strain of ash wood subjected to compression perpendicular to the grain to a degree proportional to the mass loss. The compression stress needed to restrain the swelling of thermally modified wood is ca. 10 and 20% smaller in the tangential and radial directions, respectively. This effect leads to a reduction in the anisotropy of swelling pressure of thermally modified wood perpendicular to the grain. Moreover, although upon thermal modification the mass loss of wood takes place, at the MC of 6% it shows practically the same modulus of elasticity (MOE) and Rc as the unmodified wood. After wetting to MC higher than the FSP, the thermally modified wood at 200 °C shows significantly higher MOE and Rc than the wood modified at 180 °C and untreated wood. Reduction of wood hygroscopicity, an inevitable effect of thermal modification, also reduces the range of changes in mechanical properties of wood caused by the increase in its MC to the FSP.     

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.

     

单板含水率与桉木单板层积材性能关系初探

对不同含水率桉木单板压制的单板层积材的静曲强度、弹性模量和水平剪切强度进行检测并对比分析,结果表明,结构用单板层积材所用单板的含水率应控制在8%～12%之间。     

Within-tree variability of internal stress generated during drying of rubberwood lumber

The generation of drying stress within the lumber from the trunk of a rubber tree prepared from different locations (radial distance up to 110 mm and height up to 4 m) has been investigated in real-time by using a restoring force measurement on half-split specimens. Drying was performed at constant dry-bulb and wet-bulb temperatures of 90 and 60?°C, respectively. The entire restoring force profiles do not vary significantly with height. In addition, before and after the reversal of stress, the force profiles are largely similar and the maximum negative and positive forces are approximately equal regardless of wood locations within the tree trunk. However in the radial direction, the process of stress reversal consisting of two negative force maxima appears to proceed slower in the inner juvenile wood than in the outer mature wood. Upon water immersion of the specimens for 4 months, the second negative force maximum gradually disappears and the force profiles with a shorter stress reversal period become less sensitive to the wood locations. An examination of the drying curves in the second stage of drying during stress reversal also indicates a slower migration of bound water out of the lumber in the juvenile wood compared to that in the mature wood. The drying is also faster in the water-immersed specimens. It is concluded that variability of the internal stress within the trunk of a rubber tree originated from the role of cell wall amorphous constituents and cell wall extractives on creep property and the movement of bound water within the wood cell wall during drying.     

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.