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1.
Extractives can affect the vibrational properties tanδ (damping coefficient) and E′/ρ (specific Young’s modulus), but this is highly dependent on species, compounds, and cellular locations. This paper investigates such effects for African Padauk (Pterocarpus soyauxii Taub.), a tropical hardwood with high extractives content and a preferred material for xylophones. Five groups of 26 heartwood specimens with large, yet comparable, ranges in vibrational properties were extracted in different solvents. Changes in vibrational properties were set against yields of extracts and evaluation of their cellular location. Methanol (ME) reached most of the compounds (13%), located about half in lumen and half in cell-wall. Water solubility was extremely low. tanδ and E′/ρ were very strongly related (R 2 ≥ 0.93), but native wood had abnormally low values of tanδ, while extraction shifted this relation towards higher tanδ values. ME extracted heartwood became in agreement with the average of many species, and close to sapwood. Extractions increased tanδ as much as 60%, irrespective of minute moisture changes or initial properties. Apparent E′/ρ was barely changed (+2% to −4%) but, after correcting the mass contribution of extracts, it was in fact slightly reduced (down to −10% for high E′/ρ), and increasingly so for specimens with low initial values of E′/ρ.  相似文献   

2.
The anisotropy of vibrational properties influences the acoustic behaviour of wooden pieces and their dependence on grain angle (GA). As most pieces of wood include some GA, either for technological reasons or due to grain deviations inside trunks, predicting its repercussions would be useful. This paper aims at evaluating the variability in the anisotropy of wood vibrational properties and analysing resulting trends as a function of orientation. GA dependence is described by a model based on transformation formulas applied to complex compliances, and literature data on anisotropic vibrational properties are reviewed. Ranges of variability, as well as representative sets of viscoelastic anisotropic parameters, are defined for mean hardwoods and softwoods and for contrasted wood types. GA-dependence calculations are in close agreement with published experimental results and allow comparing the sensitivity of different woods to GA. Calculated trends in damping coefficient (tanδ) and in specific modulus of elasticity (E′/ρ) allow reconstructing the general tanδ-E′/ρ statistical relationships previously reported. Trends for woods with different mechanical parameters merge into a single curve if anisotropic ratios (both elastic and of damping) are correlated between them, and with axial properties, as is indicated by the collected data. On the other hand, varying damping coefficient independently results in parallel curves, which coincide with observations on chemically modified woods, either “artificially”, or by natural extractives.  相似文献   

3.
The radial trends of vibrational properties, represented by the specific dynamic modulus (E′/ρ) and damping coefficient (tan δ), were investigated for three tropical rainforest hardwood species (Simarouba amara, Carapa procera, and Symphonia globulifera) using free-free flexural vibration tests. The microfibril angle (MFA) was estimated using X-ray diffraction. Consistent patterns of radial variations were observed for all studied properties. E′/ρ was found to decrease from pith to bark, which was strongly related to the increasing pith-bark trend of MFA. The variation of tan δ along the radius could be partly explained by MFA and partly by the gradient of extractives due to heartwood formation. The coupling effect of MFA and extractives could be separated through analysis of the log(tan δ) versus log(E′/ρ) diagram. For the species studied, the extractive content putatively associated with heartwood formation generally tends to decrease the wood damping coefficient. However, this weakening effect of extractives was not observed for the inner part of the heartwood, suggesting that the mechanical action of extractives was reduced during their chemical ageing.  相似文献   

4.
Vibrational properties of wood are affected by several parameters, of which extractives can be one of the most important ones. Wood for European musical instruments has been often studied, but traditional Middle Eastern ones had been left unnoticed. In this study white mulberry (Morus alba L.), the main material for long-necked lutes in Iran, was extracted by five solvents of various polarities (water included). Free-free bar forced vibrations were used to measure longitudinal (L) loss tangent (tanδ), storage (elastic) modulus (E′) and specific modulus (E′/γ) in the acoustic range. Their anisotropy between the 3 axes of orthotropy was determined by dynamic mechanical analysis. Native wood had a quite low E L′/γ but its tanδ was smaller than expected, and the anisotropy of tanδ and E′/γ was very low. Removal of extractives caused tanδ to increase and moduli to decrease. Acetone, the most effective solvent on damping despite a moderate extraction yield, increased tanδ L by at least 20% but did not modify E′/γ as much. When used successively, its effects masked those of solvents used afterwards. Anisotropy of E′/γ was nearly unchanged after extraction in methanol or hot water, while tanδ was much more increased in R than in T direction. Results suggest that in white mulberry, damping is governed more by nature and localization of extractives rather than by their crud abundance.  相似文献   

5.
Despite the exceptional position of yew among the gymnosperms concerning its elastomechanical properties, no reference values for its elastic constants apart from the longitudinal Young’s modulus have been available from literature so far. Hence, this study’s objective was to determine the Young’s moduli E L, E R and E T and the shear moduli G LR, G LT and G RT of yew wood. For that purpose, we measured the ultrasound velocities of longitudinal and transversal waves applied to small cubic specimens and derived the elastic constants from the results. The tests were carried out at varying wood moisture contents and were applied to spruce specimens as well in order to put the results into perspective. Results indicate that E L is in the same order of magnitude for both species, which means that a high-density wood species like yew does not inevitably have to have a high longitudinal Young’s modulus. For the transverse Young’s moduli of yew, however, we obtained 1.5–2 times, for the shear moduli even 3–6 times higher values compared to spruce. The variation of moisture content primarily revealed differences between both species concerning the shear modulus of the RT plane. We concluded that anatomical features such as the microfibril angle, the high ray percentage and presumably the large amount of extractives must fulfil important functions for the extraordinary elastomechanical behaviour of yew wood which still has to be investigated in subsequent micromechanical studies.  相似文献   

6.
–  • Vène wood (Pterocarpus erinaceus Poir.) is currently the favorite wood for manufacture of xylophone in Mali. A dynamic analysis method with free boundary conditions, known as BING, was used to determine the main acoustic properties: specific dynamic modulus (E L /ρ), damping coefficient or internal friction (tan δ), sound radiation coefficient (SRC) and peak response (PR).  相似文献   

7.
 Spruce wood specimens were acetylated with acetic anhydride (AA) solutions of glucose pentaacetate (GPA), and their viscoelastic properties along the radial direction were compared to those of the untreated and the normally acetylated specimens at various relative humidities and temperatures. Higher concentrations of the GPA/AA solution resulted in more swelling of wood when GPA was introducted into the wood cell wall. At room temperature the dynamic Young's modulus (E′) of the acetylated wood was enhanced by 10% with the introduction of GPA, whereas its mechanical loss tangent (tan δ) remained almost unchanged. These changes were interpreted to be an antiplasticizing effect of the bulky GPA molecules in the wood cell wall. On heating in the absence of moisture, the GPA-acetylated wood exhibited a marked drop in E′ and a clear tan δ peak above 150°C, whereas the E′ and tan δ of the untreated wood were relatively stable up to 200°C. The tan δ peak of the GPA-acetylated wood shifted to lower temperatures with increasing GPA content, and there was no tan δ peak due to the melting of GPA itself. Thus the marked thermal softening of the GPA-acetylated wood was attributed to the softening of wood components plasticized with GPA. Received: March 29, 2002 / Accepted: May 21, 2002 Correspondence to:E. Obataya  相似文献   

8.
This study investigated the dynamic modulus of elasticity (DMOE) of wood panels of Fraxinus mandshurica, Pinus koraiensis, and Juglans mandshurica using the natural frequency measurement system of fast Fourier transform (FFT). The results were compared with the static modulus of elasticity (E S) tested by a mechanical test machine. The results show a significant correlation between E S, transverse vibration DMOE (E F), and longitudinal vibration DMOE (E L). For all of these species, the correlation between E S, E F and E L is more significant than the individual species, which indicated that the FFT method is universal. The correlations between E S and sample’s density (ρ) are significant, but the correlation coefficient of E S and ρ is lower than those between E F, E L and E S. The E S of wood is more accurately tested by the analysis based on FFT measurement than by the estimation based on density. __________ Translated from Scientia Silvae Sinicae, 2005, 41(6): 126–131 [译自: 林业科学, 2005, 41(6): 126–131]  相似文献   

9.
This study examined the origin of the moisture dependency of the longitudinal Youngs modulus of wood (E L ) in relation to the microfibril angle (MFA) of the S2 layer of the secondary wall. Microtomed early wood specimen of sugi (Cryptomeria japonica D.Don) were used for the experiment. The following was revealed:
1.  E L tends to decrease as the moisture content increases in the region below the fiber saturation point (FSP).
2.  The percentage reduction of E L from the oven-dried state to the FSP is almost constant regardless of the MFA.
Subsequently, the relationship between E L and the moisture content was simulated theoretically using the simplified wood fiber model proposed in our previous paper (Part 1, 2002). The simulation considered the two hypotheses proposed in Part 1 for the origin of the moisture content dependency of E L . The first is a traditional theory that the reduction of E L is caused mainly by the moisture dependency of the lignin-hemicellulose matrix. The second assumes that an intermediate domain exists between the rigid crystal and the compliant disordered amorphous regions in wood cellulose microfibril (CMF). It is assumed that such a domain fluctuates between the rigid crystal-like and the compliant amorphous-like states at which the elastic modulus is of the same order as the lignin-hemicellulose matrix in accordance with the moisture sorption.When the first hypothesis is adopted for the simulation, the percentage reduction of E L from the oven-dried state to the FSP should increase as MFA increases; this was contradicted by the experimental results (2). On the other hand, when the second hypothesis is applied to the simulation, the experimentally obtained results (1) and (2) are simulated reasonably. This suggests that the moisture dependency of E L is controlled by the second hypothesis.  相似文献   

10.
–  • The vibration damping coefficient (tanδ) of wood is an important property for acoustical uses, including musical instruments. Current difficulties in the availability of some of the preferred species call for diversification, but this comes up against the lack of systematic damping coefficient data.  相似文献   

11.
Several wood-based sandwich panels with low-density fiberboard core were developed for structural insulated walls and floors, with different face material, panel thickness, and core density. The elastic moduli with and without shear effect (E L, E 0) and shear modulus (Gb) were evaluated in four-point bending. Generally, the stiffer face, thicker panel, and higher core density were advantageous in flexural and shear rigidity for structural use, but the weight control was critical for insulation. Therefore, optimum designs of some virtual sandwich structures were analyzed for bending stiffness in relation to weight for fixed core densities, considering the manufactured-panel designs. As a result, the plywood-faced sandwich panel with a panel thickness of 95 mm (PSW-T100), with insulation performance that had been previously confirmed, was most advantageous at a panel density of 430 kg/m3, showing the highest flexural rigidity (E L I = 13 × 10−6 GNm2) among these panels, where E L, E 0, and G b were 3.5, 5.5, and 0.038 GN/m2, respectively. The panel was found to be closest to the optimum design, which meant that its core and face thickness were optimum for stiffness with minimum density. The panel also provided enough internal bond strength and an excellent dimensional stability. The panel was the most feasible for structural insulation use with the weight-saving structure.  相似文献   

12.
Foliar carbon isotope composition (δ 13C), total dry biomass, and long-term water use efficiency (WUEL) of 12 Populus deltoids clones were studied under water stress in a greenhouse. Total dry biomass of clones decreased greatly, while δ 13C increased. Single-element variance analysis in the same water treatment indicated that WUEL difference among clones was significant. Clones J2, J6, J7, J8, and J9 were excellent with high WUEL. Extremely significant δ 13C differences among water treatments and clones were revealed by two-element variance analysis. Water proved to be the primary factor affecting δ 13C under water stress. It showed that there was a good positive correlation between δ 13C and WUEL in the same water treatment, and that a high WUEL always coincided with a high δ 13C. δ 13C might be a reliable indirect index to estimate WUEL among P. deltoids clones. Translated from Scientia Silvae Sinicae, 2005, 41(1) (in Chinese)  相似文献   

13.
The density (), dynamic Young's modulus (E), loss tangent (tanL) in the longitudinal (L) direction, and the dynamic shear modulus (G), loss tangent (tanS) in the LT or LR (T, tangential; R, radial) plane of woods and cane (Arundo donax L.) in air-dried and wet conditions were measured. The acoustic converting efficiency (ACE), expressed by E/3/tanL, and the factors of anisotropy, expressed byE/G and tanS/tanL, of woods were compared with those of the canes. Low-density coniferous woods had higher ACE values and were of a more anisotropic nature than the cane. These woods seemed appropriate for clarinet reed owing to their homogeneous cellular structure. The stability in vibrational properties and the anticreep properties of the woods were enhanced by the acetylation treatment. Professional clarinet players suggested that acetylated Glehn's spruce and sitka spruce were suitable for clarinet reeds.Part of this report was presented at the 48th annual meeting of the Japan Wood Research Society at Shizuoka, April 1998  相似文献   

14.
 The mechanical performance of pine sapwood (pinus sylvestris), impregnated with linseed oil to different take-up levels, is evaluated using several test methods. SEM is used to study morphological changes following the impregnation procedure. The reduction of mechanical properties is attributed to a) localized cell wall damage in the ray region that facilitates longitudinal inter-cell split in L-R plane (macrocrack) initiation and propagation; b) submicroscopical cracking in the S1 sublayer that reduces the resistance to Mode I and Mode II inter-cell splitting at any location where the oil front has passed. Mechanical testing shows the following effect of the impregnation on failure a) the Mode I fracture toughness G Ic in L-T and L-R planes, determined in DCB test, is significantly lowered with no significant difference in fracture resistance reduction in between planes; b) 3-point flexural test for specimen geometry leading to cracking in R-L and T-L planes show that the flexural strength as well as flexural modulus are reduced due to impregnation; c) 3-point flexural tests on longitudinal specimens used to determine the impregnation effect on longitudinal modulus E L and shear moduli G LT and G LR , reveal only minor changes. Fracture surfaces in mechanical tests are analyzed using SEM, and differences are explained by described microdamage mechanisms. Received 10 August 1999  相似文献   

15.
The dynamic and static modulus of elasticity （MOE） between bluestained and non-bluestained lumber of Lodgepole pine were tested and analyzed by using three methods of Non-destructive testing （NDT）, Portable Ultrasonic Non-destructive Digital Indicating Testing （Pundit）, Metriguard and Fast Fourier Transform （FFT） and the normal bending method. Results showed that the dynamic and static MOE of bluestained wood were higher than those of non-bluestained wood. The significant differences in dynamic MOE and static MOE were found between bulestained and non-bluestained wood, of which, the difference in each of three dynamic MOE （Ep. the ultrasonic wave modulus of elasticity, Ems, the stress wave modulus of elasticity and El, the longitudinal wave modulus of elasticity） between bulestained and non-bluestained wood arrived at the 0.01 significance level, whereas that in the static MOE at the 0.05 significance level. The differences in MOE between bulestained and non-bluestained wood were induced by the variation between sapwood and heartwood and the different densities of bulestained and non-bluestained wood. The correlation between dynamic MOE and static MOE was statistically significant at the 0.01 significance level. Although the dynamic MOE values of Ep, Em, Er were significantly different, there exists a close relationship between them （arriving at the 0.01 correlation level）. Comparative analysis among the three techniques indicated that the accurateness of FFT was higher than that of Pundit and Metriguard. Effect of tree knots on MOE was also investigated. Result showed that the dynamic and static MOE gradually decreased with the increase of knot number, indicating that knot number had significant effect on MOE value.  相似文献   

16.
The colour parameters (CIE L*a*b*) of black locust (Robinia pseudoacacia L.) wood meals extracted with seven solvents and heated under saturate vapour at 120°C are measured and the UV–vis spectrum analysis of dioxane extractives is performed to investigate the influence of extraction and thermal treatment on wood discolouration. The results show that extractions with polar solvents such as water, ethanol and dioxane can cause substantial decrease of b* but have little effect on a* and that extractions with less or non-polar solvents such as chloroform, ether and hexane can hardly influence both a* and b*. Extractions with ethanol and dioxane can also increase the optical reflection (L*) and arise a higher ΔE change than that with less or non-polar solvents. Heat treatment has much more influence on colour parameters than extractions do. After heat treatment, the lightness index of all the samples declines but a* value increases. The discolouration during thermal treatment is mainly due to the existence of polar extractives. Tannins, flavonoids and hydroxyanthraquinones are found in the dioxane extractives. The heated dioxane extractives have an obvious absorption between 400 and 600 nm. The condensation of the tannin molecules and the oxidation of the hydroxyl groups in flavonol molecules make up the potential reason of the formation of new colour substances during heat treatment. The elimination of the dioxane extractives can effectively reduce the extent of thermally induced discolouration.  相似文献   

17.
Dynamic elastic modulus (EL) and wave velocity (V) were determined using resonance vibrations from initially green, 100 × 50 mm sample boards of Eucalyptus regnans F. Muell., and after several stages of drying to oven dry. EL and V were determined from impact induced vibrations and spectral analysis. EL and V from green wood were positively related to basic density and normal shrinkage, only V was negatively related to green density, and both EL and V were negatively related to green moisture content and the number of internal checks after drying. The latter relationship has the potential to provide a simple method of segregating highly check prone material. No significant relationships were obtained with collapse. Outside the hygroscopic range, in low shrinkage material, EL increased little or gradually, while in high shrinkage, collapse prone material, it increased more rapidly, but no clear breakpoint was evident. In the hygroscopic range, EL increased rapidly in all samples. V increased curvilinearly throughout the entire moisture range, but no difference between collapse prone and non-collapse prone material was observed. Received 16 February 1998  相似文献   

18.
Influence of heating and drying history on micropores in dry wood   总被引：1，自引：1，他引：0  
To investigate the influence of heating and drying history on the microstructure of dry wood, in addition to the dynamic viscoelastic properties, CO2 adsorption onto dry wood at ice.water temperature (273 K) was measured, and the micropore size distribution was obtained using the Horvath-Kawazoe (HK) method. Micropores smaller than 0.6 nm exist in the microstructures of dry wood, and they decreased with elevating out-gassing temperature and increased again after rewetting and drying. Dry wood subjected to higher temperatures showed larger dynamic elastic modulus (E′) and smaller loss modulus (E″). This is interpreted as the result of the modification at higher temperature of the instability caused by drying. Drying history influenced the number of micropores smaller than 0.6 nm in dry wood not subjected to high temperature, although the difference in the number of micropores resulting from the drying history decreased with increasing out-gassing temperature. A larger number of micropores smaller than 0.6 nm exist in the microstructure of dry wood in more unstable states, corresponding to smaller E′ and larger E″ than in the stable state. Consequently, unstable states are considered to result from the existence of temporary micropores in the microstructures of dry wood, probably in lignin. Part of this report was presented at the 55th Annual Meeting of the Japan Wood Research Society, Kyoto, March 2005, and at the 56th Annual Meeting of the Japan Wood Research Society, Akita, August 2006  相似文献   

19.
The influence of moisture content (MC) on the dynamic modulus of elasticity of structural lumber was investigated using transverse vibration testing methods. The flexural rigidity (EI) of a transversely vibrating beam was calculated as the modulus of elasticity (E) multiplied by the moment of inertia (I). The increase in E of lumber due to reduction in moisture content was computed by assuming that the flexural rigidity remains constant with changes in moisture content. Reductions in I due to shrinkage were compensated by the increases in E which led to a proposal for a species-dependent MC adjustment model for modulus of elasticity. The model was validated using 38 mm × 89 mm × 4,290 mm western Canadian Spruce–Pine–Fir dimension lumber evaluated in the “as-received” and “dry” conditions. Results obtained from the species-dependent model agreed closely with those from the E adjustment equation for dimension lumber given in ASTM D 1990. The results show that the ASTM moisture adjustment procedures can be used to adjust dynamic E values for changes in moisture content also.  相似文献   

20.
The use of calibrated near-infrared (NIR) spectroscopy for predicting of a range of solid wood properties is described. The methods developed are applicable to large-scale nondestructive forest resource assessment and to tree breeding and silviculture programs. A series ofPinus radiata D. Don (radiata pine) samples were characterized in terms of density, longitudinal modulus of elasticity (E L), and microfibril angle (MFA). NIR spectra were obtained from the radial/longitudinal face of each sample and used to generate calibrations for the measured physical properties. The relations between laboratory-determined data and NIR fitted data were good in all cases, with coefficients of determination (R 2) ranging from 0.68 for 100/MFA to 0.94 for densitystrip. A good relation (R 2 = 0.83) was also obtained forE L estimated using data collected by SilviScan-2. The finding suggests that an NIR instrument could be calibrated to estimate theE L of increment cores based on SilviScan data. In view of the rapidly expanding range of applications for this technique, it is concluded that appropriately calibrated NIR spectroscopy could form the basis of a testing instrument capable of predicting a range of properties from a single spectrum obtained from the product or from the raw material.  相似文献   

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