共查询到20条相似文献，搜索用时 46 毫秒
1.
Youke Zhao Zhihui Wang Ikuho Iida Rongfeng Huang Jianxiong Lu Jinghui Jiang 《Journal of Wood Science》2016,62(3):226-232
2.
To improve the impregnation of wood, the pre-treatment by compression was systematically studied in terms of effects of compression ratio, compression direction, compression speed and compression-unloading place on the liquid impregnation in poplar and Chinese fir. The results showed: the impregnation increased 0.0065 or 0.0074 g/cm3 for every 1% increase of compression ratio when the compression ratio was lower or equal to 50 and 40% for poplar and Chinese fir, respectively; it continued to increase afterwards while the variation was quite big. There existed a significant difference of the impregnation of wood compressed at different directions in Chinese fir, but not in poplar. There existed a significant difference of the impregnation of wood compressed at different speed in both species. The impregnation of wood is likely to be in favor of radial compression in terms of the amount of impregnation. 5 and 10 mm/min were recommended as a compromise of impregnation and pre-treatment efficiency. The impregnation of wood that the compression unloaded in water was about 18.2 (poplar) and 9.2% (Chinese fir) higher in amount and was much quicker in speed than that the compression unloaded in air, and the difference between them was significant, suggesting that compression unloaded in water is significant to improve the impregnation. 相似文献
3.
Summary The mechanical behaviour of three species of hardwoods, soaked in different liquids, had been investigated at high rates of strain using a Hopkinson pressure bar system. In order to determine the influence of the rate of strain, samples from the same species were subjected to compression-tests at low rates of strain. It was noticed that, at low rates of strain, the saturated samples were always less stiff than the dry ones, which is in agreement with the literature, but differs from the behaviour at high rates of strain. This difference is attributed to the behaviour of the liquid present in the large cavities of the material, which must depend on the rate of strain. It was also noticed that the samples could support higher stresses at high rates of strain. Although permanent sets were measured after the tests, the samples were not always visibly damaged, but some typical failures were detected by means of microscopy. The damaged zones presented similar aspects, whatever the rate of strain. 相似文献
4.
Clemens M. Altaner Elena N. Tokareva Janet C. T. Wong Adrian I. Hapca J. Paul McLean Michael C. Jarvis 《Wood Science and Technology》2009,43(3-4):279-290
As the severity of compression wood influences the mechanical and chemical properties of wood it is desirable to be able to measure compression wood severity. However, so far no satisfactory method has been reported in the literature. Here we describe how scanning FTIR micro-spectroscopy can be employed to achieve CW severity measurements on increment cores of Norway spruce (Picea abies (L. Karst.) and Sitka spruce (Picea sitchensis (Bong.) Carrière). Radial wood strips were converted into sawdust by a process that maintained their spatial orientation. Samples prepared in this way were scanned with an FTIR-microscope in reflective mode and from the spectra obtained a CW-indicator was calculated representing aromatic and carboxyl signals. This FTIR CW-indicator correlated well with alternative CW identification techniques (namely microfibril angle, transmitted light and immunolabelling of beta 1–4 galactan), which have been used to validate the method. Repeatability of the measurements was good and no systematic difference between spruce species was found. The achievable resolution of the measurements was of sub-mm order. The CW indicator described offers the opportunity to correlate CW severity with mechanical wood properties in spruce. 相似文献
5.
T. E. Timell 《Wood Science and Technology》1978,12(2):89-103
Summary Compression wood in the ancient Ginkgo biloba differs from that in most of the younger gymnosperms in the more angular outline of its tracheids, their thinner walls, and their lack of helical cavities. Both normal and compression woods of Ginkgo contain two types of tracheids, one wide, with a thin wall, and another, narrow, with a thicker wall. In all other respects the compression wood tracheids in Ginkgo are ultrastructurally similar to those in other gymnosperms. Helical cavities probably developed relatively late in the evolution of compression wood, since they are missing not only in Ginkgo but also in the Taxales and the Araucariaceae. The occurrence of compression wood in Ginkgo biloba indicates that this tissue probably has existed since the Devonean period. Very likely, the arborescent habit of the gymnosperms has always been dependent on their ability to form compression wood.This investigation was carried out under the McIntire-Stennis Program, Cooperative State Research Service. I am indebted to Mr. A. C. Day of this College and to Mr. A. Rezanowich of the Pulp and Paper Research Institute of Canada for kindly providing the scanning electron micrographs. 相似文献
6.
Summary The mechanical behaviour of three species of hardwoods soaked in different swelling liquids, compressed at high rates of strain, was investigated using a split Hopkinson pressure bar system. Variations in elastic moduli, proportional limit and maximum stress with respect to the treatments were studied. It was found that the saturated specimens could be as stiff as the dry ones. This result was explained by the behaviour of the liquid present in the large cavities of the wood, i.e. the lumens of the cells, which must be different from that observed at low rates of strain. At large rates of strain, this liquid cannot flow out of the pores and must behave like a solid; therefore the structure of the material is reinforced and, as a consequence, the softening effect of the soaking agent can be masked. 相似文献
7.
J. D. Boyd 《Wood Science and Technology》1978,12(1):25-35
Summary After a -D-1,3-linked glucan had been isolated from compression wood, identified, and named laricinan, other researchers suggested that it occupied the helical cavities in the S2 layer of those tracheids. They postulated that the glucan was responsible for the capacity of compression wood to generate the large forces associated with reorientation of displaced stems and branches, and also caused its severe shrinkage with drying.Analyses herein indicate that it is improbable that such a glucan could be the primary factor responsible for those characteristics of compression wood. An alternative significance is proposed, namely that its presence strengthens the already well-supported deduction that the helical cavities have a schizogenous origin. 相似文献
8.
9.
10.
Compression wood is formed by the living tree to compensate for external loads. It creates wood fibers with properties undesirable in sawn products. Automatic detection of compression wood can lead to production advantages. A wood surface was scanned with a spectrometer, and compression wood was detected by analyzing the spectral composition of light reflected from the wood surface within the visible spectrum. Linear prediction models for compression wood in Norway spruce (Picea abies) were produced using multivariate analysis and regression methods. The resulting prediction coefficients were implemented in a scanning system using the MAPP2200 smart image sensor combined with an imaging spectrograph. This scanning system is capable of making a pixelwise classification of a wood surface in real time. Classification of one spruce plank was compared with analysis by scanning electron microscopy, showing that the automatic classification was correct in 11 of 14 cases. 相似文献
11.
12.
Summary Uniaxial compression creep tests of tubular spruce specimens loaded in uniaxial compression are reported. The relative humidity in the interior of the tube is varied in a controlled manner. The results indicate that creep is greatly increased in magnitude by simultaneous humidity changes of either sign.Thanks are due to Dr. John Zahn of Forest Products Laboratory, Madison, Wisconsin, for various helpful advice, as well as for arranging the manufacture of test specimens in his laboratory. Thanks are also due to Forest Products Laboratory of the U.S. Department of Agriculture, Madison, Wisconsin, for funding a large part of this work under subcontract FP-81-0389. 相似文献
13.
Effect of temperature and compression on the mechanical behavior of steam-treated wood 总被引：2，自引：0，他引：2
The mechanical behavior of steamed spruce wood changes dramatically with compression along the grain, the change being much more moderate perpendicular to the grain. The stiffness decrement due to increased temperature is greatest in the tangential material direction. The stiffness decrement due to compression is greatest along the grain. Compression to 80% compressive strain at 131°C inverts the order of the material directions regarding stiffness, the stiffness being the least along the grain. Plastic strain due to compression is greater at higher temperatures. The compression-induced decrement of stiffness along the grain is greater at higher temperatures, but the off-axis decrement of stiffness is less at higher temperatures. 相似文献
14.
The behaviour of longitudinal shrinkage was investigated in the corewood of a swept, 17-year-old New Zealand radiata pine stem. Wood categories in terms of normal wood, mild compression wood and severe compression wood were identified microscopically using autofluorescence of lignin. Average longitudinal shrinkage was collated according to corewood location and wood category within corewood in the leaning and the vertical parts of the stem, and then maximum radial difference of longitudinal shrinkage within growth ring was examined. The results show that the average longitudinal shrinkage is significant (2.4%) in the corewood of the leaning part of the stem. Among wood categories, severer compression wood displays the highest (2.9%) average longitudinal shrinkage. In the context of this study, growth rings may consist of one of three types of wood: (1) only normal wood; (2) a single compression wood type; and (3) mixed-type wood. Where multiple compression woods co-existed with normal wood, the maximum radial difference of longitudinal shrinkage within the growth ring was found to be 4.0%. A strong correlation (R 2 = 0.90) between average MFA and average longitudinal shrinkage suggests a significant influence of the average MFA on average longitudinal shrinkage across the three growth ring types. 相似文献
15.
Summary A model is introduced which links the mechano-sorptive behaviour of wood subjected to moderate and high compression or bending stresses parallel to grain to the formation of slip planes in the cell wall. Slip plane formation is dependent on the breaking of hydrogen bonds, which process is directly related to the amount of moisture change. The dramatic change of microfibril orientation in slip plane zones cause an increase of the longitudinal shrinkage/swelling and a decrease of the modulus of elasticity. These features of slip plane formation account for both the magnitude and the oscillation of the excessive mechano-sorptive creep associated with compression and bending parallel to grain. A summary is given of the characteristics of the mechano-sorptive effects, and the model is discussed in the light of these effects.The paper is one of the results of a project on the influence of changing moisture content on the mechanical behavior of wood, currently underway in a co-operation between College of Environmental Science and Forestry, State University of New York, and the Technical University of Denmark. Support for this project is provided by the Danish Technical Research Council and by the USDA C--operative Research Program (proj. 85-FSTY-9-0112). The support is gratefully acknowledged 相似文献
16.
During refining of mechanical pulp, a process occurring at high speed at temperatures of 140–160°C, the flexibility and bonding
ability of wood fibres are increased. To understand the mechanical behaviour of the fibres in this operation, deformations
at low speed of wet wood specimens at 50°C were studied under two different combinations of shear and compression loadings.
The results were compared with the behaviour of wet wood in pure compression. Some features of the deformation that occurred
in earlywood were analysed using an image analysis procedure. During pure compression the cell walls bend independently of
the shape of the fibre cells and their cell wall thickness. Under combined shear and compression, however, mainly the corners
of the fibre cells get deformed. In a second deformation performed in compression, the fibre cells follow the same deformation
pattern as given by the first deformation type whether in compression or in combined shear and compression. The interpretation
was that permanent defects in the cells themselves were introduced already in the first load cycle of the wood samples. The
load combination with lower shear gave the same permanent strain as the case of pure compression but using less energy. 相似文献
17.
We measured Young's modulus, proportional limit stress, and bending strength by the compression bending test and examined the applicability of the testing method by comparing it with conventional bending test methods. Long columns of todomatsu (Japanese fir,Abies sachalinensis Fr. Schmidt) with various length/thickness ratios were the specimens. A compressive load was axially applied to the specimen supported with pin ends. Young's modulus, the proportional limit stress, and the bending strength were obtained from the load-loading point displacement and load-strains at the outer surfaces until the occurrence of bending failure. Four-point bending tests were also conducted, and the bending properties obtained were compared with the corresponding properties obtained by the compression bending tests. Based on the experimental results, we believe that when the stress-strain relation is measured by the load-loading point displacement relation using specimens whose length/thickness ratio is large enough, the bending properties can be obtained properly using the compression bending test. 相似文献
18.
Marjan Sedighi-Gilani Homeira Sunderland Parviz Navi 《Wood Science and Technology》2005,39(6):419-430
The pattern and extent of variation of microfibril angle (MFA) in normal and compression tracheids of softwood were investigated
by using confocal laser scanning microscopy technique. All measurements support the idea that the orientation of microfibrils
in single wood tracheids is not uniform. MFA of the radial wall of earlywood tracheids was highly non-uniform and had an approximately
circular form of arrangement around the bordered pits (inside the border). Between the bordered pits the measured MFAs were
less than the other parts of the tracheid. In the latewood tracheids MFA was less variable. The average orientation of simple
pits in the crossfield region was consistent with the mean MFA of the tracheids; however some of the measurements showed a
highly variable arrangement in the areas between the simple pits. In many cases the local measured MFAs of compression wood
tracheids agreed with the orientation of natural helical cavities of compression wood. Comparing the measured results in different
growth rings showed that MFAs in juvenile wood are generally larger than in perfect wood. 相似文献
19.
T. E. Timell 《Wood Science and Technology》1982,16(2):83-122
Summary A review of the chemistry and topochemistry of compression wood with 200 references. Compression wood contains on the average 30% cellulose, 35–40% lignin, 10% galactan, 9% galactoglucomannan, 8% xylan, and 2% of a 1,3-glucan (laricinan). The cellulose is less crystalline, and the xylan has fewer arabinose side chains than in normal wood. The lignin is composed of guaiacylpropane and p-hydroxyphenylpropane units. It is more condensed, has a higher proportion of carbon-carbon bonds, and contains fewer arylglycerol--aryl ether structures than a normal conifer lignin. The ray cells and the primary wall of the tracheids have the same chemical composition in normal and compression woods. The galactan is largely located in the outer region of the secondary wall. Only 5–10% of the lignin in compression wood tracheids is extracellular. The middle lamella is less lignified than in normal wood, while the S1 and inner S2 layers have a lignin concentration of 30–40% which is twice as high as in normal wood. The lignin content of the S2 (L) layer is equal to or higher than that of the intercellular region along the wall. The review is concluded with a brief reference to areas where present information is incomplete or lacking.A portion of an Academy Lecture of the International Academy of Wood Science, presented at the International Symposium on Wood and Pulping Chemistry (Ekmandagarna 1981), held in Stockholm, Sweden, June 9–12, 1981. Reprints of the unabridged review, published under the title Recent Progress in the Chemistry, Ultrastructure, and Formation of Compression Wood in the preprints of the symposium (SPCI Report 38, Vol. 1, p. 99–147) are available from the author. I wish to express my gratitude to my colleague Professor Robert A. Zabel for generous travel assistance 相似文献