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1.
The purposes of this study were to accumulate fundamental data on wood properties within large Sugi logs and to take applicable variations in wood properties into consideration for sorting logs and sawing patterns. The characteristics of basic density, moisture content, growth ring width, and microfibril angle (MFA) were measured and the relationship with log and lumber quality was examined. It was considered reasonable to estimate the lumber moisture content based on the moisture content of heartwood rather than that of whole logs, especially when producing large-sized lumber. The MFA reached a constant value before the 15th ring, and within a distance of 10 cm or less from the pith. Since the E fr of lumber correlated with that of the log affected by MFA, it would be possible to produce lumber with a higher E fr from the outer position of the log, based on selecting a log above the E fr . Since the MFA would also affect the lumber warp, a sawing pattern avoiding the area around the pith or enlarging the rough sawn size when a large warp was expected could be effective in improving the lumber quality. To improve the lumber quality, not only one but also multiple wood properties must be applied to the sawing pattern. 相似文献
2.
We measured the longitudinal and tangential shrinking processes in wood specimens from Chamaecyparis obtuse Endl. with different microfibril angles (MFAs). The shape of the shrinking curve was compared with the MFA. Only the longitudinal
shrinking process of specimens with a small MFA clearly showed nonlinearity, and the degree of nonlinearity increased as the
MFA decreased. In contrast, the tangential shrinking process and the longitudinal shrinking process of compression wood with
a large MFA were linear. The nonlinearity is probably caused by the longitudinal shrinkage of the noncrystalline region of
the cellulose microfibril (CMF) in regions of low moisture content during water desorption. When the moisture content is high,
the matrix substance in the cell wall begins to dry; however, the shrinkage in the chain direction is restrained by the rigid
CMF. As the wood dries further, the noncrystalline region of the CMF embedded in the matrix substance begins to shrink. Because
the longitudinal mechanical behavior of wood with a small MFA is greatly affected by a rigid CMF, longitudinal shrinkage increases
suddenly at about 10% moisture content; as a result, the shrinking process shows nonlinearity. 相似文献
3.
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
4.
Bakary Traoré Loïc Brancheriau Patrick Perré Tatjana Stevanovic Papa Diouf 《Annals of Forest Science》2010,67(8):815-815
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• 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
5.
In our previous report, we investigated the effect of the microfibril angle (MFA) in the middle layer of the secondary wall
(S2) on the longitudinal creep behavior of a thin homogeneous earlywood specimen sugi. In the present study, we investigated
the role of moisture on the tensile creep behavior of wood. We discuss the creep behavior of the wood cell wall from the viewpoint
of the composite structure of the cell wall and the properties of the constituent materials. A microtomed thin specimen of
earlywood of sugi (Cryptomeria japonica D.Don) was used for the longitudinal tensile creep test. Creep tests were conducted at three moisture stages (oven-dry, air-dry,
fiber saturation point) over a broad range of MFA. Results showed that the longitudinal tensile creep behavior was highly
dependent on both the moisture content and the MFA. With a small MFA, the variation in the creep function among the three
moisture states was very small. For a large MFA, the variation in the creep function was larger. At low moisture contents,
the magnitude of the creep function was very small, while at high moisture content, it was very large except for the case
of specimens with very small MFA. Those results show that the longitudinal tensile creep behavior was directly affected by
the fine composite structure and the internal properties of the cell wall constituents. 相似文献
6.
Identification of anisotropic vibrational properties of Padauk wood with interlocked grain 总被引:1,自引:0,他引:1
Iris Brémaud Pierre Cabrolier Joseph Gril Bruno Clair Jean Gérard Kazuya Minato Bernard Thibaut 《Wood Science and Technology》2010,44(3):355-367
Grain deviations and high extractives content are common features of many tropical woods. This study aimed at clarifying their
respective impact on vibrational properties, referring to African Padauk (Pterocarpus soyauxii Taub.), a species selected for its interlocked grain, high extractives content and uses in xylophones. Specimens were cut
parallel to the trunk axis (L), and local variations in grain angle (GA), microfibril angle (MFA), specific Young’s modulus
(E′
L
/ρ, where ρ stands for the density) and damping coefficient (tanδL) were measured. GA dependence was analysed by a mechanical model which allowed to identify the specific Young’s modulus (E′3/ρ) and shear modulus (G′/ρ) along the grain (3) as well as their corresponding damping coefficients (tanδ3, tanδG). This analysis was done for native and then for extracted wood. Interlocked grain resulted in 0–25° GA and in variations
of a factor 2 in E′L/ρ and tanδL. Along the grain, Padauk wood was characterized, when compared to typical hardwoods, by a somewhat lower E′3/ρ and elastic anisotropy (E′/G′), due to a wide microfibril angle plus a small weight effect of extracts, and a very low tanδ3 and moderate damping anisotropy (tanδG/tanδ3). Extraction affected mechanical parameters in the order: tanδ3 ≈ tanδG > G′/ρ > > E′3/ρ. That is, extractives’ effects were nearly isotropic on damping but clearly anisotropic on storage moduli. 相似文献
7.
Yoshio Kijidani Yoshimitsu Fujii Keita Kimura Yoshitake Fujisawa Yuichiro Hiraoka Ryushi Kitahara 《Journal of Wood Science》2012,58(3):195-202
It was previously believed in Japan that the wood qualities of hinoki (Chamaecyparis obtusa) were superior to sugi (Cryptomeria japonica). However, few studies of wood properties such as MFA (microfibril angle of S2 layer in secondary wall of tracheid) have been completed for hinoki. Some reports have found that hinoki plus tree families have similar mechanical properties to sugi. Here we report the characteristics of MFA and density of hinoki half-sib families in a progeny test stand. There were significant differences in MFA and density between families. The wood properties of two families, Nakatsu 3 and Kanzaki 5, are stable in radial pattern and suitable for structural use. Early selection of hinoki families by MFA and density may be difficult. Effects of MFA and density on E d (dynamic modulus of elasticity) of logs differed between families. The effects of growth rate on MFA and density differed between families and also between juvenile and mature wood. The faster growth rate in Nakatsu 3 appeared to improve wood properties and increase E d of logs, although in many other families, faster growth rate had negative effects on desirable wood properties for structural use. 相似文献
8.
Jun Tanabe Akira Tamura Jyunichi Ohshima Kazuya Iizuka Shinso Yokota 《Scandinavian Journal of Forest Research》2017,32(1):39-44
With emphasis on tree breeding for wood quality in Picea jezoensis, we aimed to evaluate radial and between-family variations in the microfibril angle (MFA) of the S2 layer in the latewood tracheids in 10 open-pollinated families of 43-year-old P. jezoensis trees. In addition, the relationships between MFA/wood density with the modulus of elasticity (MOE) or modulus of rupture (MOR) were investigated. Significant differences in MFA between families were found from the pith toward the bark. MFA showed higher values around the pith area, although some families showed relatively lower values than others around this area. In addition, due to a larger coefficient of variations of MFA near the pith, the potential for juvenile wood MFA improvement may be greater compared with mature wood. MOE was correlated with MFA in juvenile wood and with wood density in mature wood, whereas MOR was mainly correlated with wood density at radial positions in both woods. Therefore, to improve the MOE and MOR of P. jezoensis wood, both MFA and wood density would be factors to consider in both juvenile and mature woods. On the other hand, there are indications that, only wood density would be an important criterion for improving mature wood properties. 相似文献
9.
Daniel Keunecke Walter Sonderegger Karol Pereteanu Thomas Lüthi Peter Niemz 《Wood Science and Technology》2007,41(4):309-327
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
10.
Seppo Andersson Ritva Serimaa Mika Torkkeli Timo Paakkari Pekka Saranpää Erkki Pesonen 《Journal of Wood Science》2000,46(5):343-349
The structure of cellulose, especially the microfibril angles (MFAs), in compression wood of Norway spruce [Picea abies (L.) Karst.] was studied by wide- and small-angle X-ray scattering and polarizing microscopy. On the basis of the X-ray scattering experiments the average MF As of the cell wall layers S2 and S1 of the studied sample are 39 and 89, respectively; and the average diameter and length of the cellulose crystallites are 2.9 and 20.0nm, respectively. The average of the whole MFA distribution is shown to agree with the one obtained by polarizing microscopy of macerated fibers. 相似文献
11.
? ContextThe transition of microfibril angle (MFA) values from juvenile to mature wood marks the change from variable, low-quality wood to stronger and more consistent wood that can produce higher value products.? AimsWe evaluate the utility of different statistical models that predict how much of a log is higher quality mature wood based on MFA.? MethodsMFA was measured from pith to bark at breast height in six lodgepole pine stands in western Canada. Six different forms of two-segment regression models were assessed to determine the point of transition (TP) in MFA from juvenile to mature wood.? ResultsAll six models provided useful and significant TP estimates. In the first segment (juvenile phase), the quadratic form produced the most conservative TPs, the linear form the least conservative, and the exponential form was intermediate. A linear second segment (mature phase) was only a minor improvement over a constant. There were significant differences in MFA TP among some sites. Analyses of the relationships between TP and tree variables, e.g., DBH, height, were inconclusive.? ConclusionsAny of the six two-segment models can be used objectively to estimate MFA transition points; the choice of model will allow mill managers to manage risk in product out-turn. 相似文献12.
Dr. S. Avramidis Dr. S. G. Hatzikiriakos Dr. J. F. Siau 《Wood Science and Technology》1994,28(5):349-358
Summary A model that predicts heat and moisture transfer through wood in the hygroscopic range and which is based on the principles of irreversible thermodynamics, was evaluated with unsteady-state nonisothermal moisture desorption experimental data. The model predicted the phenomenon of thermal diffusion during the initial stages of desorption and results in a very good simulation of the desorption curve and the center's temperature change with time.Symbols Cp
specific heat of air (= 0.24 cal/g K @ 70 °C)
- CT
specific heat of wood, cal/g K
- D
transverse diffusion coefficient, cm2/s
- Eb
activation energy, cal/mol
- Eo
heat of vaporization, cal/mol
- EL
differential heat of sorption, cal/mol
- G
specific gravity of wood
- H
relative humidity, %
- hT
convective heat transfer coefficient, cal/cm2 s K
- hc
convective mass transfer coefficient based on the concentration of moisture in wood, cm/s
- hv
convective mass transfer coefficient based on the concentration of moisture in the air in equilibrium with the wood surface, cm/s
- KM
coefficient for diffusion due to moisture gradient, g/cm s %
- KT
transverse thermal conductivity coefficient, cal/cm K s
- M
moisture content, %
- Po
saturated vapor pressure, atm
- R
universal gas constant, cal/mol K (= 82.056 cm3 atm/mol K)
- t
time, s
- T
temperature, K
- x
distance, cm
Greek Letters
evaporation or condensation criterion
-
wood density, g/cm3
- W
water density (=1), g/cm3
- a
air density, g/cm3
Department of Wood Science and Forest Products Virginia Polytechnic Institute and State University Blackburg, Virginia 24061-0503 相似文献
13.
Haruna Aiso-Sanada Futoshi Ishiguri Denny Irawati Imam Wahyudi Shinso Yokota 《Journal of Wood Science》2018,64(6):872-879
This study investigated the anatomical and chemical characteristics of the reaction wood of a gymnpsperm species, Gnetum gnemon, and discussed on contributing factor for the type of reaction wood in this species. Cell morphology, microfibril angle (MFA) of the S2 layer and lignin distribution in secondary walls of tracheary elements, and lignin content were examined on three branches. Observations included no G-layer formation, significant decreases in vessel frequency, and altered MFA, and visible-light absorbance after lignin colour reactions in tracheid and fiber tracheid walls on the upper side in almost all samples. These results suggest that reaction wood in G. gnemon was similar to that in ‘tension-wood-like-reaction wood’ in angiosperms. On the other hand, reaction wood showed decrease in the lignin concentration in the fiber tracheid walls compared to the tracheid walls. In addition, the lignin in the tracheid and fiber tracheid walls was originally rich in syringyl units, suggesting that changes in the anatomical and chemical characteristics of secondary xylem due to reaction wood formation might relate to the ratio of the syringyl to guaiacyl units in lignin in the cell walls which function for mechanical support. 相似文献
14.
Single wood cells have complex tensile behavior. To gain insight into this complex functionality, the behavior of single wood
tracheids was studied under controlled cyclic tensile loading. The cyclic tensile stress–strain curves show that beyond the
yield point the tracheid undergoes permanent deformations and its rigidity increases. As in plasticity elastic (or visco-elastic)
unloading takes place and energy is dissipated by permanent deformation. Consequently, single tracheids show a load-history
dependent behavior. To understand the intervening mechanism in the process of elasto-plastic response of a wood tracheid,
a micromechanical based model was developed. This model permits us to describe the influence of non-uniformity of microfibril
angle (MFA) and other defects on the wood cell rigidity and to discuss different scenarios, which may occur during the tensile
test. Successive damage of the hemicelluloses and lignin matrix and reduction of MFA as mainly responsible for elasto-plastic
response of a wood cell were suggested. It should be noted that this paper is part of the research work which has been reported
previously (Navi et al. in Wood Sci Technol 29:411–429, 1995; 36:447–462, 2002; Sedighi-Gilani et al. in Wood Sci Technol 39:419–430, 2005). 相似文献
15.
In this study we determined soil moisture storage, evapotranspiration (ET) and light interception in an agroforestry trial consisting of pine trees grown over (1) control (bare ground), (2) ryegrass/clovers (Lolium perene/Trifolium spp.), (3) lucerne (Medicago sativa), and (4) ryegrass only during the third growing season between 1992 and 1993. The results show that:
16.
杨树微纤丝角的变异及其与木材性质的相关关系 总被引:6,自引:0,他引:6
微纤丝角为细胞次生壁S2层微纤丝排列方向与细胞主轴所形成的夹角,与木材的物理性质、力学性质和化学性质都有着直接的关系。应用x射线衍射法测定了7个杨树无性系(14株样木)胸径处各年轮的微纤丝角,并对应分析和测定了各年轮的木材基本密度、纤维长度、纤维宽度和纤维素含量。研究结果表明,杨树微纤丝角在年轮间存在显著差异,其径向变异规律为从髓心向外以微纤丝角逐渐降低,年轮间的平均微纤丝角在7.8旱?8褐洌荒静幕久芏取⑾宋ざ取⑾宋矶群拖宋睾吭谀曷旨湟泊嬖谙灾钜臁O喙胤治霰砻鳎⑾怂拷怯肽静幕久芏取⑾宋ざ取⑾宋矶群拖宋睾看嬖谙灾母合喙毓叵??0.01),相关系数分别为-0.450、-0.586、-0.516和-0.660。回归分析结果表明,多项式方程可较好地描述杨树微纤丝角与所测定的木材性质的关系,相关系数均在-0.45以上(n=125)。本文的研究结果认为,在今后针对杨树材性改良的育种计划中,微纤丝角是一个重要的选育和改良指标。图3表3参34。 相似文献
17.
Summary Various chemicals are used for protecting wood samples against fungi, and some of them are released in water, leading to pollution of the water. The kinetics of pentachlorophenol release in water has here been studied by considering the diffusion through the wood along the three principal axes of diffusion. The experiments and the modelling of the process is successfully coupled. The numerical model takes into account the three principal diffusivities, the partition factor, the volumes of wood and water. The effect of wood sample length along the longitudinal axis of diffusion is studied especially, as longitudinal diffusivity is much higher than the other two principal diffusivities. The effects of the relative volumes of wood and water are also of considerable interest not only for the concentration of the chemical in water but also for the rate of release.Symbols
C
concentration of liquid (g/cm3)_
-
C
c
,C
eq
concentration of liquid on the surface, at equilibrium with the surrounding, respectively
-
C
i,j,k
concentration of liquid in the wood at positioni, j, k
-
D
diffusivity (cm2/s)
-
h
coefficient of mass transfer on the surface (cm/s)
-
K
partition factor
-
i, j, k
integers characterizing the position in the wood
-
M
L
,M
R
,M
T
dimensionless numbers
-
M
t
,M
amount of chemical released after time t, after infinite time, respectively
-
t
increment of time
-
L, R, T
thickness of the slices taken in the wood for calculation
-
N
L
,N
R
,N
T
number of slices taken in the wood
-
x, y, z
coordinates
-
V
water
volume of the surrounding water 相似文献
18.
Tian Zhang Shu-Lin Bai Sandrine Bardet Tancrède Alméras Bernard Thibaut Jacques Beauchêne 《Journal of Wood Science》2011,57(5):377-386
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
19.
Changes of crystallinity in wood cellulose by heat treatment under dried and moist conditions 总被引:8,自引:0,他引:8
The different effects of heat treatment on wood, especially on the cellulose crystallites of wood under ovendried and highly moist conditions, were investigated by X-ray diffractometer. Heat was found to increase significantly the crystallinity of wood cellulose; moreover, almost twice as much crystallization was observed after heat treatment of spruce and buna under a highly moist condition than under the oven-dried condition. In pure cellulose almost the same crystallization was observed under both the conditions, whereas more crystallization occurred in wood cellulose than in pure cellulose. Absolute crystallization was observed for the wood species and pure cellulose under both conditions, considering the thermal decomposition of the amorphous region in addition to crystallization. Our results suggested that other components accomparying wood cellulose were involved in the increase of crystallinity by heat treatment, and that wood cellulose contained more quasicrystalline regions than pure cellulose. Moreover, calculated apparent activation energies revealed that crystallization and decrystallization in pure and wood cellulose under heat treatment of highly moist condition were some-what easier than those under the oven-dried condition. The behavior of the piezoelectric modulusd
25 almost paralleled that of crystallinity. 相似文献
20.
David M. Drew Geoffrey M. Downes Anthony P. O’Grady Jennifer Read Dale Worledge 《Annals of Forest Science》2009,66(4):406-406
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