共查询到20条相似文献,搜索用时 31 毫秒
1.
Julien Ruelle Jacques Beauchêne Hiroyuki Yamamoto Bernard Thibaut 《Wood Science and Technology》2011,45(2):339-357
Growth strains were measured in situ in nine trees of three species from a French Guiana tropical rainforest in a clearly
active verticality restoration process. The aim was to detect tension wood within the samples. Wood specimens were cut in
the vicinity of the growth strain measurements in order to determine the microfibril angle and some mechanical and physical
properties. As suspected, tensile growth strain was much higher in tension wood zones, as shown by the slightly higher longitudinal
modulus of elasticity. Conversely, tension wood showed reduced compression strength. Longitudinal shrinkage was much higher
in tension wood than in opposite wood. Clear relationships between the microfibril angle and longitudinal properties were
noted in comparison (i) with those observed in gymnosperm compression wood and (ii) with expected relationships from the organization
of wood fibres cell wall structure. 相似文献
2.
Julien Ruelle Jacques Beauchene Anne Thibaut Bernard Thibaut 《Annals of Forest Science》2007,64(5):503-510
On 10 trees from 10 species of French Guyana tropical rainforest in a clear active process of restoring verticality growth strains were measured in situ in order to determine the occurrence of tension wood within samples. Wood specimens were cut in the vicinity of the growth strains measurements in order to measure some mechanical and physical properties. As suspected, tensile growth strains was very much higher in tension wood zone, because longitudinal modulus of elasticity was slightly higher. Longitudinal shrinkage was also much higher in tension wood than in opposite wood. 相似文献
3.
Guillaume Pot Catherine Coutand Jean-Benoît Le Cam Evelyne Toussaint 《Wood Science and Technology》2013,47(1):7-25
In this study, longitudinal cyclic tensile tests were performed on green wood samples of Populus cv I4551. Complex mechanical behaviour, such as permanent set in terms of displacement and strain-dependent stiffness, was found. A linear relationship between stiffness and strain enabled each sample to be characterized. A large-scale experimental campaign led to the observation of the evolution of temporal and spatial intra-ring mechanical behaviour of intra-ring sliced specimens during wood maturation and tree gravitropic response. The results showed that tension wood lamellas exhibit strain hardening behaviour whereas normal wood lamellas exhibit strain softening behaviour. Temporal variations in the strain hardening behaviour of tension wood lamellas occurred once cell wall deposition was achieved. Moreover, no correlation was found between infradensity and mechanical behaviour of lamellas. These results show that cells undergo temporal variations in their properties due to a complex maturation process. 相似文献
4.
Ikuho IIDA 《中国林学(英文版)》2012,14(2):107-111
Elastic and strength properties(proportional-limit stress(σ prop ),Young's modulus(E),breaking stress(σ max )in static bending parallel to grain in a longitudinal direction),as well as stress relaxation in air-dried condition and water-saturated conditions at seven different constant temperatures and increasing and decreasing temperatures were investigated for wood from Chinese-fir and poplar plantations.The results show that hygrothermal conditions considerably affect these mechanical properties.The higher the moisture content(MC)or temperature,the lower the strength of wood.Further investigation of the effects of constant temperature on stress relaxation indicates that high temperature specimens have low relaxation moduli and high fluidity.In the case of increasing temperature the range of the modulus of relaxation is larger than in the case of a reduction in temperature,while the residual moduli do not show large differences.This is because the modulus at high temperatures decreases more than that at low temperatures.The fluidity of specimens in a state of water desorption increases slowly at the beginning,increases quickly until the MC reaches an equilibrium moisture content(EMC)and then becomes stable,which is quite different from that in a water-saturated state.Fluidity in a desorption state is much higher than in a water-saturated state.This is probably due to the fact that the former is in an unstable state which can be interpreted as a state with internal strain and has therefore a greater potential to release strain. 相似文献
5.
Bruno Clair Jérôme Alteyrac Arthur Gronvold Jaime Espejo Bernard Chanson Tancrède Alméras 《Annals of Forest Science》2013,70(8):801-811
Context
Tree orientation is controlled by asymmetric mechanical stresses set during wood maturation. The magnitude of maturation stress differs between longitudinal and tangential directions, and between normal and tension woods.Aims
We aimed at evaluating patterns of maturation stress on eucalypt plantation trees and their relation with growth, with a focus on tangential stress evaluation.Methods
Released maturation strains along longitudinal and tangential directions were measured around the circumference of 29 Eucalyptus nitens trees, including both straight and leaning trees.Results
Most trees produced asymmetric patterns of longitudinal maturation strain, but more than half of the maturation strain variability occurred between trees. Many trees produced high longitudinal tensile stress all around their circumference. High longitudinal tensile stress was not systematically associated with the presence of gelatinous layer. The average magnitude of released longitudinal maturation strain was found negatively correlated to the growth rate. A methodology is proposed to ensure reliable evaluation of released maturation strain in both longitudinal and tangential directions. Tangential strain evaluated with this method was lower than previously reported.Conclusion
The stress was always tensile along the longitudinal direction and compressive along the tangential direction, and their respective magnitude was positively correlated. This correlation does not result from a Poisson effect but may be related to the mechanism of maturation stress generation. 相似文献6.
This study examined how boiling and drying treatments influenced various physical properties of the tension wood with gelatinous
fibers (G-fibers) of a 29-yearold Zelkova branch. By boiling treatment, tension wood with numerous G-fibers contracted considerably in the longitudinal direction and
the longitudinal Young’s modulus decreased in spite of the water-saturated condition. The drying treatment caused green tension
wood and boiled tension wood with numerous G-fibers to shrink longitudinally and increased their longitudinal Young’s moduli.
These specific behaviors in tension wood were highly correlated with the proportion of G-fibers in a specimen and were probably
caused by the microscopic behavior of cellulose microfibril (CMF) in the gelatinous layers (G-layers). The longitudinal shrinkage
of tension wood due to drying suggests the existence of a hygro-sensible, noncrystalline region in the CMF, which is abundant
in the G-layer. Furthermore, the noncrystalline region in the CMF softens during boiling treatment, resulting in the reduction
of the longitudinal Young’s modulus in tension wood. The longitudinal contraction of tension wood with G-fibers by boiling
might be caused by the tensile growth stress remaining in green G-layers. However, no changes were detected in the 004 d-spacing of cellulose crystal in tension wood from the boiling and drying treatments, regardless of the proportion of G-fibers. 相似文献
7.
Summary To advance the discussion on the evolution mechanism of tree growth stresses, the relation between released strain and the chemical components was investigated experimentally. The expansive released strain in the longitudinal direction assumed large values as the lignin content increased in the compression wood, but there was no relation between released strain and lignin content in the normal wood region. The contractive released strain assumed large values as the cellulose content and its crystallinity increased. Their correlation was very high and clear. From these facts, it is considered that the lignin deposition plays an important role in the generation of the growth stresses in compression wood but is not important in normal or tension wood regions. Cellulose microfibrils contract along their longitudinal axis during cell maturation, and the stress included by the contraction creates a longitudinal growth stress in normal and tension woods.The authors thank Prof. R. R. Archer, University of Massachusetts, for his valuable advice. A part of this research was supported by a grant under the Monbusho International Scientific Research Program 相似文献
8.
Joseph Gril Delphine Jullien Sandrine Bardet Hiroyuki Yamamoto 《Journal of Wood Science》2017,63(5):411-432
Tree growth stress, resulted from the combined effects of dead weight increase and cell wall maturation in the growing trees, fulfills biomechanical functions by enhancing the strength of growing stems and by controlling their growth orientation. Its value after new wood formation, named maturation stress, can be determined by measuring the instantaneously released strain at stem periphery. Exceptional levels of longitudinal stress are reached in reaction wood, in the form of compression in gymnosperms or higher-than-usual tension in angiosperms, inspiring theories to explain the generation process of the maturation stress at the level of wood fiber: the synergistic action of compressive stress generated in the amorphous lignin–hemicellulose matrix and tensile stress due to the shortening of the crystalline cellulosic framework is a possible driving force. Besides the elastic component, growth stress bears viscoelastic components that are locked in the matured cell wall. Delayed recovery of locked-in components is triggered by increasing temperature under high moisture content: the rheological analysis of this hygrothermal recovery offers the possibility to gain information on the mechanical conditions during wood formation. After tree felling, the presence of residual stress often causes processing defects during logging and lumbering, thus reducing the final yield of harvested resources. In the near future, we expect to develop plantation forests and utilize more wood as industrial resources; in that case, we need to respond to their large growth stress. Thermal treatment is one of the possible countermeasures: green wood heating involves the hygrothermal recovery of viscoelastic locked-in growth strains and tends to counteract the effect of subsequent drying. Methods such as smoke drying of logs are proposed to increase the processing yield at a reasonable cost. 相似文献
9.
This study is focused on what factor mainly affects the mechanical properties of each wood species in the lateral direction. At first, the influence of the density which is closely related to mechanical properties in the longitudinal direction was also researched in the lateral direction. Thus, the elastic modulus, strength, and failure strain in the lateral tension were measured using thin cross-sectional samples of softwoods and hardwoods, having wide varieties in the density and anatomical features. The results obtained are as follows. The linear relationship between the density and the elastic modulus which has been verified in the longitudinal direction was not observed in the lateral tension for the samples with the annual ring inclination of 90°, which samples were influenced by ray arranged parallel to the tensile direction. However, samples with the annual ring inclination of 45° showed the high correlation between the density and the elastic modulus due to the shearing deformation of the cell shape. On the other hand, the proportional relationship between the elastic modulus and strength which has been verified in the longitudinal direction was not observed in the lateral tension except for the samples with the annual ring inclination of 90°. From the results obtained, it was revealed that the mechanical properties of wood in the lateral direction were significantly affected not only by the density but also by the structural features such as deformation of cell shapes, arrangement of ray or vessels, and the degree of the transition from the earlywood to the latewood. 相似文献
10.
Hiroyuki Yamamoto Julien Ruelle Yoshiharu Arakawa Masato Yoshida Bruno Clair Joseph Gril 《Wood Science and Technology》2010,44(1):149-163
The mechanism responsible for unusual hygro-mechanical properties of tension wood containing the gelatinous layer (G-layer)
was investigated. Tension and normal wood specimens were sampled from the leaning stems of a 75- and a 40-year-old Kunugi
oak (Quercus
acutissima) tree, and the moisture dependencies of the longitudinal Young’s modulus and longitudinal dimensions were measured. The results,
which were analyzed in relation to the anatomical properties of the specimens, revealed that the ratio of increase in the
longitudinal Young’s modulus with drying was higher in the G-layer than in the lignified layer (L-layer); the longitudinal
drying shrinkage displayed a similar pattern. It was found that the lattice distance of the [200] plane in the cellulose crystallite
increased with drying, moreover, the half-width of the [200] diffraction peak increased with drying, which was remarkable
in the tension wood. Those results suggest that in the green state, the polysaccharide matrix in the G-layer behaves like
a water-swollen gel; however, it is transformed into a condensed and hard-packed structure by strong surface tension during
moisture desorption, which is a form of xero-gelation. However, in the L-layer, condensation and subsequent xero-gelation
of the polysaccharide matrix was prevented by the hydrophobic lignin that mechanically reinforces the matrix. 相似文献
11.
Hiroyuki Yamamoto Kentaro Abe Yoshiharu Arakawa Takashi Okuyama Joseph Gril 《Journal of Wood Science》2005,51(3):222-233
The tension wood (TW) properties of a 70-year-old specimen of Acer sieboldianum Miq. were analyzed by using the G-fiber model that was proposed in our previous report. The roles of the G-layer on the origins of (1) a high tensile growth stress, (2) a large longitudinal Young’s modulus, and (3) a high longitudinal drying shrinkage in the TW xylem are discussed on the basis of the simulations using the G-fiber model. The results suggest that the G-layer generates a high tensile stress in the longitudinal direction during xylem maturation; the longitudinal Young’s modulus of the green G-layer becomes significantly higher than that of the lignified layer; furthermore, the G-layer tends to shrink extraordinarily more than that of the lignified layer during moisture desorption.This report follows the previous report “Role of the gelatinous layer on the origin of the physical properties of the tension wood.” J Wood Sci (2004) 50:197–208. Part of this paper was presented at the 49th Annual Meeting of the Japan Wood Research Society, Tokyo, April 1999, and at the 2nd International Conference of the European Society for Wood Mechanics, Stockholm, May 2003This revised version was published online in July 2005. On pages 228–230 the character was replaced by a vertical line. 相似文献
12.
Abel Rodrigues Miguel Casquilho Hélène Oliveira João Bordado 《European Journal of Forest Research》2010,129(2):145-153
An appraisal was made about the impact of pinewood nematode (Bursaphelenchus xylophilus, Nickle) attack symptomatology on the mechanical behaviour of wood from Pinus Pinaster Ait. Two sets of 200 wood specimens were obtained for the study of both mechanical and other physical properties. The specimens,
about half of which presented symptoms of nematode, were obtained from a set of 66 wood planks, cut from an equal number of
trees, originating from the Setúbal Peninsula (Portugal). Logistic analysis using symptomatology as a binary dependent variable
showed adequacy of models containing compression tension to rupture and number of wood rings per unit radial length for the
prediction of nematode attack. Analysis of variance revealed that the presence of the disease symptoms was correlated to static
bending rupture, modulus of elasticity, work to maximum bending load, and axial compression rupture, causing their decrease
at a significance level of 5%. 相似文献
13.
Juvenile wood properties are studied in a ring-porous tropical hardwood – teak (Tectona grandis L. F), to assess the utilisation potential of short rotation timber. Compared to mature wood, it is characterised by wide
rings, short fibres, small diameter, low vessel percentage, high cell wall, wide microfibrillar angle and relatively low or
almost similar mechanical properties. While the average modulus of elasticity and modulus of rupture in juvenile wood are
85% and 82% respectively of the mature wood value, the longitudinal compression strength is similar. With relatively small
fibrillar angle of 15° and the scope for genetic selection of individual trees, teak juvenile wood has potential for desired
dimensional stability. The segmented regression models and visual interpretation of radial patterns of variation in anatomical
properties reveal that juvenility in plantation grown teak extends up to 15, 20–25 years depending on the property, growth
rate and individual tree and plantation site. The fitted regression models, to explain the age-related variations in juvenile
wood properties range from simple, linear to exponential, reciprocal and quadratic equations. Fibre length, microfibrillar
angle, vessel diameter/percentage and ring width appear to be the best anatomical indicators of age demarcation between juvenile
and mature wood, although maturation age often varies among the properties. The projected figures for proportion of juvenile
wood in plantation grown teak at breast height are 80–100% and 25% at ages 20 and 60 years respectively.
Received 3 November 1998 相似文献
14.
Summary Compression wood (CW) of the giant sequoia studied had higher values than normal wood (NW) in crushing strength and ultimate stress in tension parallel to grain, in toughness, in modulus of rupture, and in work to maximum load and total work in static bending. In the green condition CW had higher values than NW in stress at the proportional limit and work to the proportional limit, and about the same modulus of elasticity in static bending. In the dry condition CW was about equivalent to NW in work to the proportional limit, but was slightly weaker in stress at proportional limit and modulus of elasticity in static bending. The compression wood of this giant sequoia, even though formed when the tree was suppressed and having relatively narrow rings, can therefore be said to be essentially equivalent to normal wood so far as the mechanical properties tested in this study are concerned.Given at FPRS meeting in Dallas, Texas, June 1972 相似文献
15.
Futoshi Ishiguri Imam Wahyudi Masae Takeuchi Yuya Takashima Kazuya Iizuka Shinso Yokota Nobuo Yoshizawa 《Journal of Wood Science》2011,57(3):241-246
The relationships between growth characteristics and wood properties were investigated for a threatened species, Pericopsis mooniana, to promote the establishment of plantations of this species in the tropics. Growth characteristics (diameter and height)
and stress-wave velocity (SWV) of trees were measured for 22-year-old P. mooniana trees planted in Indonesia. The trees were categorized into three groups, fast-growing, middle-growing, and slow-growing
trees, to investigate the effect of growth rate on the wood properties. In addition, radial variation of anatomical characteristics
and wood properties were determined. No significant correlation was found between growth characteristics and SWV. The values
for the vessel diameter, cell wall thickness of wood fibers, wood fiber length, basic density, modulus of elasticity, and
modulus of rupture from wood at the bark side were higher than those at the pith side. On the other hand, vessel frequency
gradually decreased from pith to bark. These results suggested that low-quality wood, such as juvenile wood, existed near
the pith area. 相似文献
16.
A hypothetical mechanism for the generation of maturation stress in wood was tested experimentally. The hypothesis was that
the maturation stress could partly originate in a physical mechanism related to daily changes in water pressure and associated
diurnal strains. The matrix of lignin and hemicellulose, deposited in the cell wall during the night, would be put in compression
by the effect of water tension during the next day. The cellulose framework, crystallizing during the day, would be put in
tension by the decrease in tension at night and subsequent cell-wall swelling. This was tested on young saplings of sugi and
beech. Half of the saplings were submitted to continuous lighting, which canceled diurnal strains. Saplings were tilted 40
degrees, and their uprighting movement was measured. The uprighting movement is directly due to the production of reaction
wood and the concomitant development of large longitudinal maturation stress. It occurred in the continuously lighted plants
at least as much as in control plants. We conclude that the generation of longitudinal maturation stress in tension or compression
wood is not directly related to variations in water pressure and diurnal strains. 相似文献
17.
Laminated products, such as laminated veneer lumber (LVL) or plywood (PW), have become important recently. The objective of
this study was to determine and compare properties of panels fabricated with veneers of Gmelina arborea trees in a fast-growth plantation and glued with phenol formaldehyde resin. The results showed that LVL and PW physical and
mechanical properties are comparable to those of solid wood with a specify gravity of 0.60. Moreover, these panels can be
cataloged into group 2 of PS 1–95 of the Voluntary Products Standard of the United States. The difference in physical properties
was not statistically significant between LVL and PW panels, except for water absorption. Some mechanical properties, such
as hardness and glue-line shear, modulus of rupture in perpendicular flexure, nail and screw withdrawal parallel, and perpendicular
strength, were statistically different between LVL and PW. However, no differences were established for the modulus of elasticity,
tensile strength parallel to the surface, or tensile strength perpendicular to the surface. The differences were attributed
to the venners’ orientation in the panels studied. 相似文献
18.
The wood quality from 50- to 70-year-old Tectona grandis trees from an unmanaged forest in East Timor was assessed. The aim was to evaluate teak in mature stands that had undergone
uncontrolled disturbances, e.g., fire and local community usage. Heartwood represented 91% of the tree radius at a height
of 1.7 m, and sapwood contained on average nine rings. The mean ring width showed within-tree and between-tree variability.
The chemical compositions of heartwood and sapwood were similar. Within-tree chemical variation occurred only in terms of
extractives, which increased from the pith (8.3%) to the heartwood-sapwood transition (12.7%) and decreased in the sapwood
(9.2%). Overall, the wood properties of teak from a unmanaged forest in East Timor were comparable to those reported for plantation
teaks of other origin: 607 kg/m3 basic density, 3.5% and 5.2% radial and tangential shrinkage, 141 N/mm2 modulus of rupture, 10684 N/mm2 modulus of elasticity, and 50 N/mm2 maximum crushing strength in compression parallel to the grain. Disturbances on individual tree growth arising from the unmanaged
status of the stand were evidenced by higher within-tree variability of ring width. However, the longitudinal and radial variations
of wood density and mechanical properties were of low magnitude and in a degree that did not negatively impact on timber quality. 相似文献
19.
Patrick Perre Anh Tuan Dinh Carole Assor Xavier Frank Gilles Pilate 《Wood Science and Technology》2013,47(3):481-498
Mechanical tests on micro-samples were performed in the three material directions in normal, opposite, and tension wood collected from a poplar tree. Two custom micro-devices were designed and built in the laboratory to test samples under pure tension in the transverse direction and under 4-point bending conditions in the longitudinal direction. Both devices were designed to handle samples with a small transverse section (a few square mm), which allowed to select zones with homogenous anatomical features. The results indicate a very high longitudinal stiffness in tension wood (up to 35 GPa compared to an average of 18 GPa for normal wood). Considering wood density, the value represents a specific modulus that is nearly 70 % crystalline cellulose. However, tension wood is slightly less stiff in the tangential and radial directions (1,150 vs. 1,500 MPa for normal wood in the radial direction and 430 vs. 530 MPa in the tangential direction). 相似文献
20.
Most tree biomechanics models assume uniformity of mechanical properties within a tree, and only a few studies have focused on differences in mechanical status among branches. We examined mechanical properties of 49 branches of two 10-year-old trees of Acer rufinerve Sieb. et Zucc. For each branch, bending moment due to its own fresh mass, elastic modulus, section modulus and flexural stiffness were obtained. Elastic modulus of the branch was correlated with the density and thickness of the fiber cell wall and decreased with crown depth, indicating that branches at lower positions were more elastic than branches at upper positions. Compared to lower branches, upper branches were less inclined, possessed thicker growth rings, more long shoots and were subject to smaller stresses. The leaf arrangement in the upper branches might be effective in transmitting more light to the lower branches. In contrast, the lower branches were more inclined toward the horizontal and subject to greater stresses than the upper branches. Lower branch inclinations were attributed to smaller dry matter investment in diameter growth. Upper and lower branch inclinations were slightly greater and smaller, respectively, than those predicted by beam theory. The alleviation in inclination of the lower branches is probably caused by negative gravitropic responses such as tension wood formation or upward shoot elongation, or both. The horizontal display of leaves in the lower branches would be effective in light interception. The reduction in cost of the lower branches can be adaptive because they have a shorter life expectancy than the upper branches. The results showed that an adaptive tree form is realized by a vertical gradient in branch mechanical properties. 相似文献