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TECHNICAL PAPERS

Origin of the Biomechanical Properties of Wood Related to the Fine Structure of the Multi-layered Cell Wall

[+] Author and Article Information
H. Yamamoto, Y. Kojima, T. Okuyama, W. P. Abasolo

Dept. of Bio-material Sciences, School of Bio-Agricultural Sciences, Nagoya University, Chikusa, Nagoya 464, Japan

J. Gril

Laboratoire de Mecanique et Genie Civil-Bois, Universite de Montpellier II, CP 81-Place Eugene Batailon, Montpellier, France

J Biomech Eng 124(4), 432-440 (Jul 30, 2002) (9 pages) doi:10.1115/1.1485751 History: Received March 01, 2001; Revised March 01, 2002; Online July 30, 2002
Copyright © 2002 by ASME
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Figures

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Schematic model of the wood. (a) the log level. (b) the cell level. Wood consists of numerous fiber cells. Each fiber cell has a multi-layered structure, CML; compound middle lamella, S1; the outer layer of the secondary wall, S2; the middle layer of the secondary wall, and S3; the innermost layer of the secondary wall. MFA is the microfibril angle in the S2 layer.
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A model of an isolated wood fiber (tracheid)- three layered complex cylinder. CMF; cellulose microfibril.
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Coordinate system used in mechanical description. Direction of x-axis in (b) is parallel to the CMF molecular chains; (a) L, T, R local orthogonal coordinate systems; (b) Flat-board element of the polysaccharides framework bundle.
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A schematic representation to explain the formation and the concentration of polysaccharide framework and lignin in the wood cell wall (based on Terashima and Fukushima 29). CML: compound middle lamella, S1, S2, S3: outer, middle, and inner layers of the secondary wall.
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Relationships between the MFAs and the released strains of growth stresses (εLT) on the surface of the xylem. Shadows are the experimental results of two sugi trees (Crystomerai japonica D. Don). The curves show the calculated results based on Eqs. (13). Solid lines stand for εL, and broaken ones stand for εT. The terminal values (t=T2) of ε1m2m1f, and ε2f are respectively assumed to be a : 0%, 0%, −0.15%, −0.15%, b : 1.0%, 0.5%, −0.15%, −0.15%, c : 1.0%, 0.5%, 0%, 0%.
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Relationships between the MFAs and the oven-dried shrinkages (αLT). Dots are the experimental results of sugi wood (Japanese cedars) 31. Shadowings are the experimental ones from Pinus jeffreyii 42. The curves show the calculated results based on the Eqs. (13). Solid lines stand for εL, and broaken ones stand for εT. The terminal values of ε1m2m1f, and ε2f are respectively assumed to be a : 10%, 10%, 0%, 0%, b : 15%, 15%, 0%, 0%, c : 20%, 20%, 0%, 0%.
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Moisture content dependency of the longitudinal Young’s modulus of the wood (EL). Experimental results are obtained from spruce wood having density 0.48 43. Curves are calculated results by Eq. (16). In this simulation, Ematr increases monotonously from 2GPa at the fiber saturation point to a ; 4, b ; 12, c ; 20, d ; 28 GPa at the oven-dried condition. Elastic modulus of oriented amorphous polysaccharide (Epoly) also increases monotonously from 2GPa to 8GPa during the moisture desorption. MFA in the S2 layer is supposed to be 10 deg.
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Moisture content dependency of the longitudinal Young’s modulus of the wood (EL). Experimental results are obtained from spruce woods having density a ; 0.44, b ; 0.48, c ; 0.52 43. Curves are calculated results by Eq. (16). In this simulation, we supposed that the polysaccharide framework contains unstable cellulose domain which changes from compliant amorphous-like state to rigid crystal-like state in accordance with moisture desorption. Ematr increases monotonously from 2 GPa at the FSP to 4 GPa at the oven-dried state. The weight ratios of the stable crystal to whole substances in each layers of the secondary wall are 40% (S2) and 20% (S1). The weight ratios of the unstable domains to whole substances in each layers of the secondary wall are 12% (S2), and 6% (S1). MFA in the S2 layer is 10 deg.

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