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Aimene, Y.E.; Nairn, J.A. |
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Simulation of transverse wood compression using a large-deformation, hyperelastic–plastic material model |
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2015 |
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Wood Science and Technology |
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Wood Science and Technology |
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49 |
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1 |
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21-39 |
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Transverse compression of wood is a process that induces large deformations. The process is dominated by elastic and plastic cell wall buckling. This work reports a numerical study of the transverse compression and densification of wood using a large-deformation, elastic–plastic constitutive law. The model is isotropic, formulated within the framework of hyperelasticity, and implemented in explicit material point method (MPM) software. The model was first validated for modeling of cellular materials by compression of an isotropic cellular model specimen. Next, it was used to model compression of wood by first validating use of isotropic, transverse plane properties for tangential compression of hardwood, and then by investigating both tangential and radial compression of softwood. Importantly, the discretization of wood specimens used MPM methods to reproduce accurately the complex morphology of wood anatomy for different species. The simulations have reproduced observations of stress–strain response during wood compression including details of inhomogeneous deformation caused by variations in wood anatomy. © 2014, Springer-Verlag Berlin Heidelberg. |
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Wood Science and Engineering Department, Oregon State University, Corvallis, OR, United States |
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Export Date: 27 August 2015 |
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EcoFoG @ webmaster @ |
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617 |
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Allié, E.; Pélissier, R.; Engel, J.; Petronelli, P.; Freycon, V.; Deblauwe, V.; Soucémarianadin, L.; Weigel, J.; Baraloto, C. |
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Pervasive local-scale tree-soil habitat association in a tropical forest community |
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Journal Article |
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2015 |
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PLoS ONE |
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PLoS ONE |
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10 |
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11 |
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e0141488 |
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We examined tree-soil habitat associations in lowland forest communities at Paracou, French Guiana.We analyzed a large dataset assembling six permanent plots totaling 37.5 ha, in which extensive LIDAR-derived topographical data and soil chemical and physical data have been integrated with precise botanical determinations. Map of relative elevation from the nearest stream summarized both soil fertility and hydromorphic characteristics, with seasonally inundated bottomlands having higher soil phosphate content and base saturation, and plateaus having higher soil carbon, nitrogen and aluminum contents. We employed a statistical test of correlations between tree species density and environmental maps, by generating Monte Carlo simulations of random raster images that preserve autocorrelation of the original maps. Nearly three fourths of the 94 taxa with at least one stem per ha showed a significant correlation between tree density and relative elevation, revealing contrasted species-habitat associations in term of abundance, with seasonally inundated bottomlands (24.5% of species) and well-drained plateaus (48.9% of species). We also observed species preferences for environments with or without steep slopes (13.8% and 10.6%, respectively). We observed that closely-related species were frequently associated with different soil habitats in this region (70% of the 14 genera with congeneric species that have a significant association test) suggesting species-habitat associations have arisen multiple times in this tree community. We also tested if species with similar habitat preferences shared functional strategies. We found that seasonally inundated forest specialists tended to have smaller stature (maximum diameter) than species found on plateaus. Our results underline the importance of tree-soil habitat associations in structuring diverse communities at fine spatial scales and suggest that additional studies are needed to disentangle community assembly mechanisms related to dispersal limitation, biotic interactions and environmental filtering from species-habitat associations. Moreover, they provide a framework to generalize across tropical forest sites. © 2015 Allié et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. |
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International Center for Tropical Botany, Department of Biological Sciences, Florida International University, Miami, FL, United States |
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Export Date: 7 January 2016 |
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EcoFoG @ webmaster @ |
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645 |
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Alméras, T.; Clair, B. |
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Critical review on the mechanisms of maturation stress generation in trees |
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Journal Article |
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2016 |
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Journal of the Royal Society Interface |
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J R Soc Interface |
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13 |
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122 |
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Trees control their posture by generating asymmetric mechanical stress around the periphery of the trunk or branches. This stress is produced in wood during the maturation of the cell wall. When the need for reaction is high, it is accompanied by strong changes in cell organization and composition called reaction wood, namely compression wood in gymnosperms and tension wood in angiosperms. The process by which stress is generated in the cell wall during its formation is not yet known, and various hypothetical mechanisms have been proposed in the literature. Here we aim at discriminating between these models. First, we summarize current knowledge about reaction wood structure, state and behaviour relevant to the understanding of maturation stress generation. Then, the mechanisms proposed in the literature are listed and discussed in order to identify which can be rejected based on their inconsistency with current knowledge at the frontier between plant science and mechanical engineering. |
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EcoFoG @ webmaster @ |
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719 |
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Alméras, T.; Ghislain, B.; Clair, B.; Secerovic, A.; Pilate, G.; Fournier, M. |
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Title |
Quantifying the motor power of trees |
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Journal Article |
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2018 |
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Trees |
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32 |
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3 |
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689-702 |
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Wood maturation strains can be estimated from the change in curvature that occurs when a stem grown staked in tilted position is released from the stake.
Trees have a motor system to enable upright growth in the field of gravity. This motor function is taken on by reaction wood, a special kind of wood that typically develops in leaning axes and generates mechanical force during its formation, curving up the stem and counteracting the effect of gravity or other mechanical disturbances. Quantifying the mechanical stress induced in wood during maturation is essential to many areas of research ranging from tree architecture to functional genomics. Here, we present a new method for quantifying wood maturation stress. It consists of tilting a tree, tying it to a stake, letting it grow in tilted position, and recording the change in stem curvature that occurs when the stem is released from the stake. A mechanical model is developed to make explicit the link between the change in curvature, maturation strain and morphological traits of the stem section. A parametric study is conducted to analyse how different parameters influence the change in curvature. This method is applied to the estimation of maturation strain in two different datasets. Results show that the method is able to detect genotypic variations in motor power expression. As predicted by the model, we observe that the change in stem curvature is correlated to stem diameter and diameter growth. In contrast, wood maturation strain is independent from these dimensional effects, and is suitable as an intrinsic parameter characterising the magnitude of the plant’s gravitropic reaction. |
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1432-2285 |
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EcoFoG @ webmaster @ Alméras2018 |
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835 |
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Alméras, T.; Gronvold, A.; van der Lee, A.; Clair, B.; Montero, C. |
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Title |
Contribution of cellulose to the moisture-dependent elastic behaviour of wood |
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Journal Article |
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Year |
2017 |
Publication |
Composites Science and Technology |
Abbreviated Journal |
Composites Science and Technology |
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138 |
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151-160 |
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Keywords |
Cellulose; Crystal strain; Micromechanics; Wood; X-ray diffraction |
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Wood has a hierarchical structure involving several levels of organisation. The stiffness of wood relies on its capacity to transfer mechanical stress to its stiffest element at the lowest scale, namely crystalline cellulose. This study aims at quantifying to what extend crystalline cellulose contributes to wood stiffness depending on its moisture content. The crystal strains of cellulose were measured using X-ray diffraction on wet and dry specimens of spruce, based on a previously published methodology. The comparison between crystal strain and macroscopic strain shows that, during elastic loading, cellulose strain is lower than macroscopic strain. The means ratio of crystal/macroscopic strain amounts 0.85 for dry specimens and 0.64 for wet specimens. This strain ratio cannot be explained just by the projection effect due to the difference in orientation between cellulose microfibrils and cell wall, but results from deformation mechanisms in series with cellulose. Analysis shows that this series contribution represents a non-negligible contribution to wood compliance and is strongly moisture-dependent. This contribution amounts 9% for dry specimens and 33% for wet specimens, corresponding to a 4-fold increase in compliance for the series contribution. The origin of these strains is ascribed to mechanisms involving bending or shear strain at different scales, due to the fact that reinforcing element are neither perfectly straight nor infinitely long. © 2016 |
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CNRS, UMR Ecologie des Forêts de Guyane (EcoFoG), AgroParisTech, Cirad, INRA, Université des Antilles, Université de Guyane, Kourou, France |
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Export Date: 26 December 2016 |
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EcoFoG @ webmaster @ |
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701 |
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Author |
Almeras, T. |
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Title |
Mechanical analysis of the strains generated by water tension in plant stems. Part II: strains in wood and bark and apparent compliance |
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Journal Article |
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Year |
2008 |
Publication |
Tree Physiology |
Abbreviated Journal |
Tree Physiol. |
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28 |
Issue |
10 |
Pages |
1513-1523 |
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Keywords |
biomechanics; calibration; diurnal strains; mechanical model; multilayer cylinder; water potential |
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Tree steins shrink in diameter during the day and swell during the night in response to changes in water tension in the xylem. Stein shrinkage can easily be measured in a nondestructive way, to derive continuous information about tree water status. The relationship between the strain and the change in water tension can be evaluated by empirical calibrations, or can be related to the structure of the plant. A mechanical analysis was performed to make this relationship explicit. The stem is modeled as a cylinder made of multiple layers of tissues, including heartwood, sapwood, and inner and outer bark. The effect of changes in water tension on the apparent strain at the surface of a tissue is quantified as a function of parameters defining stem anatomy and the mechanical properties of the tissues. Various possible applications in the context of tree physiology are suggested. |
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INRA UMR Ecofog, Kourou 97379, French Guiana, Email: t_almeras@hotmail.com |
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HERON PUBLISHING |
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0829-318X |
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ISI:000260027200009 |
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EcoFoG @ eric.marcon @ |
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129 |
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Almeras, T.; Derycke, M.; Jaouen, G.; Beauchene, J.; Fournier, M. |
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Functional diversity in gravitropic reaction among tropical seedlings in relation to ecological and developmental traits |
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Journal Article |
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2009 |
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Journal of Experimental Botany |
Abbreviated Journal |
J. Exp. Bot. |
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60 |
Issue |
15 |
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4397-4410 |
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Biomechanics; French Guiana; functional diversity; gravitropism; reaction wood; tropical rainforest |
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Gravitropism is necessary for plants to control the orientation of their axes while they grow in height. In woody plants, stem re-orientations are costly because they are achieved through diameter growth. The functional diversity of gravitropism was studied to check if the mechanisms involved and their efficiency may contribute to the differentiation of height growth strategies between forest tree species at the seedling stage. Seedlings of eight tropical species were grown tilted in a greenhouse, and their up-righting movement and diameter growth were measured over three months. Morphological, anatomical, and biomechanical traits were measured at the end of the survey. Curvature analysis was used to analyse the up-righting response along the stems. Variations in stem curvature depend on diameter growth, size effects, the increase in self-weight, and the efficiency of the gravitropic reaction. A biomechanical model was used to separate these contributions. Results showed that (i) gravitropic movements were based on a common mechanism associated to similar dynamic patterns, (ii) clear differences in efficiency (defined as the change in curvature achieved during an elementary diameter increment for a given stem diameter) existed between species, (iii) the equilibrium angle of the stem and the anatomical characters associated with the efficiency of the reaction also differed between species, and (iv) the differences in gravitropic reaction were related to the light requirements: heliophilic species, compared to more shade-tolerant species, had a larger efficiency and an equilibrium angle closer to vertical. This suggests that traits determining the gravitropic reaction are related to the strategy of light interception and may contribute to the differentiation of ecological strategies promoting the maintenance of biodiversity in tropical rainforests. |
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[Almeras, Tancrede; Derycke, Morgane; Jaouen, Gaelle] INRA, UMR Ecol Forets Guyane, F-97310 Kourou, France, Email: t_almeras@hotmail.com |
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OXFORD UNIV PRESS |
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0022-0957 |
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ISI:000271389400017 |
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EcoFoG @ eric.marcon @ |
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96 |
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Author |
Almeras, T.; Fournier, M. |
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Title |
Biomechanical design and long-term stability of trees: Morphological and wood traits involved in the balance between weight increase and the gravitropic reaction |
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Journal Article |
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2009 |
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Journal of Theoretical Biology |
Abbreviated Journal |
J. Theor. Biol. |
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256 |
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3 |
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370-381 |
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Mechanical design; Gravitropism; Bending stresses; Allometry; Reaction wood |
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Studies on tree biomechanical design usually focus on stem stiffness, resistance to breakage or uprooting, and elastic stability. Here we consider another biomechanical constraint related to the interaction between growth and gravity. Because stems are slender structures and are never perfectly symmetric, the increase in tree mass always causes bending movements. Given the current mechanical design of trees, integration of these movements over time would ultimately lead to a weeping habit unless some gravitropic correction occurs. This correction is achieved by asymmetric internal forces induced during the maturation of new wood. The long-term stability of a growing stem therefore depends on how the gravitropic correction that is generated by diameter growth balances the disturbance due to increasing self weight. General mechanical formulations based on beam theory are proposed to model these phenomena. The rates of disturbance and correction associated with a growth increment are deduced and expressed as a function of elementary traits of stem morphology, cross-section anatomy and wood properties. Evaluation of these traits using previously published data shows that the balance between the correction and the disturbance strongly depends on the efficiency of the gravitropic correction, which depends on the asymmetry of wood maturation strain, eccentric growth, and gradients in wood stiffness. By combining disturbance and correction rates, the gravitropic performance indicates the dynamics of stem bending during growth. It depends on stem biomechanical traits and dimensions. By analyzing dimensional effects, we show that the necessity for gravitropic correction might constrain stem allometric growth in the long-term. This constraint is compared to the requirement for elastic stability, showing that gravitropic performance limits the increase in height of tilted stem and branches. The performance of this function may thus limit the slenderness and lean of stems, and therefore the ability of the tree to capture light in a heterogeneous environment. (c) 2008 Elsevier Ltd. All rights reserved. |
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[Almeras, T.; Fournier, M.] INRA, UMR Ecol Forets Guyane, F-97310 Kourou, France, Email: t_almeras@hotmail.com |
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ACADEMIC PRESS LTD ELSEVIER SCIENCE LTD |
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0022-5193 |
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ISI:000263077100008 |
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EcoFoG @ eric.marcon @ |
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123 |
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Almeras, T.; Gril, J. |
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Mechanical analysis of the strains generated by water tension in plant stems. Part 1: stress transmission from the water to the cell walls |
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Journal Article |
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2007 |
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Tree Physiology |
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Tree Physiol. |
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27 |
Issue |
11 |
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1505-1516 |
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biomechanics; cell mechanics; diurnal strains; mechanical model; multilayer cylinder; stress transtnissionjactor |
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Plant tissues shrink and swell in response to changes in water pressure. These strains can be easily measured, e.g., at the surface of tree stems, to obtain indirect information about plant water status and other physiological parameters. We developed a mechanical model to clarify how water pressure is transmitted to cell walls and causes shrinkage of plant tissues, particularly in the case of thick-walled cells such as wood fibers. Our analysis shows that the stress inside the fiber cell walls is lower than the water tension. The difference is accounted for by a stress transmission factor that depends on two main effects. The first effect is the dilution of the stress through the cell wall, because water acts at the lumen border and is transmitted to the cuter border of the cell, which has a larger circumference. The second effect is the partial conversion of radial stress into tangential stress. Both effects are quantified as functions of parameters of the cell wall structure and its mechanical properties. |
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INRA, UMR Ecofog, F-97379 Kourou, French Guiana, France, Email: t_almeras@hotmail.com |
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HERON PUBLISHING |
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0829-318X |
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ISI:000250847000001 |
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EcoFoG @ eric.marcon @ |
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152 |
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Almeras, T.; Gril, J.; Yamamoto, H. |
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Modelling anisotropic maturation strains in wood in relation to fibre boundary conditions, microstructure and maturation kinetics |
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Journal Article |
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2005 |
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Holzforschung |
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Holzforschung |
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59 |
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3 |
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347-353 |
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anisotropy; boundary conditions; cell-wall maturation; growth strain; multilayer model; residual stress; wood fibre |
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A generalisation of existing mechanical models is proposed to account for the relation between wood macroscopic properties and fibre microstructure and chemical composition. It is applied to understanding of the origin of anisotropic maturation strains measured at the outermost surface of the xylem. Various assumptions are considered for boundary conditions of the fibre during the progressive maturation process and are applied to experimental data from the literature. Assumptions that the fibre is fully restrained in displacement, or fully unrestrained or unrestrained in the transverse direction only are all incompatible with observations. Indeed, within the tree, the fibre is restrained in the longitudinal and tangential directions, but unrestrained in the radial direction towards the bark. Mixed boundary conditions must be introduced to correctly simulate both longitudinal and tangential maturation strains. In the context of an analytical axisymmetric model, this is estimated by considering a parameter of partial release of tangential stress during maturation. Consistence with data and with finite element computation in the case of a square fibre confirmed that, because of the unrestrained radial condition, a large part of the tangential maturation stress is released in situ. |
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Nagoya Univ, Grad Sch Bioagr Sci, Lab Biomat Phys, Chikusa Ku, Nagoya, Aichi 4648601, Japan, Email: tancrede@nuagr1.agr.nagoya-u.ac.jp |
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WALTER DE GRUYTER & CO |
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0018-3830 |
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ISI:000228828800016 |
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EcoFoG @ eric.marcon @ |
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256 |
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