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From lignin to spruce: Poromechanical upscaling of wood strength

Published online by Cambridge University Press:  14 March 2011

Thomas K. Bader ,
K. Hofstetter ,
Ch. Hellmich  and
Josef Eberhardsteiner
Thomas K. Bader
Affiliation:
Institute for Mechanics of Materials and Structures, Vienna University of Technology, A-1040 Vienna, Austria
K. Hofstetter
Affiliation:
Institute for Mechanics of Materials and Structures, Vienna University of Technology, A-1040 Vienna, Austria
Ch. Hellmich
Affiliation:
Institute for Mechanics of Materials and Structures, Vienna University of Technology, A-1040 Vienna, Austria
Josef Eberhardsteiner
Affiliation:
Institute for Mechanics of Materials and Structures, Vienna University of Technology, A-1040 Vienna, Austria
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Abstract

Wood strength is highly anisotropic, due to the inherent structural hierarchy of the material. In the framework of a combined random-periodic multiscale poro-micromechanics model, we here translate compositional information throughout this hierarchy into the resulting anisotropic strength at the softwood level, based on “universal” elastic properties of cellulose, hemicelluloses, and lignin, and on the shear strength of the latter elementary constituent. Therefore, derivation of the elastic energy in a piece (representative volume element – RVE) of softwood, stemming from homogeneous macroscopic strains prescribed in terms of displacements at the boundary of the RVE and from pressure exerted by water filling the nanoporous space between the hemicelluloses-lignin network within the cell walls, with respect to the shear stiffness of lignin, yields higher order strains in the lignin phase, approximating micro-stress peaks leading to local lignin failure. Relating this (quasi-brittle) failure to overall softwood failure (or strictly speaking, elastic limit of softwood) results in a macroscopic microstructure-dependent failure criterion for softwood. The latter satisfactorily predicts the biaxial strength of spruce at various loading angles with respect to the grain direction. The model also predicts the experimentally well-established fact that uniaxial tensile and compressive strengths, as well as the shear strength of wood, depend quasi-linearly on the cell water content, but highly nonlinearly on the lumen porosity.

Keywords

biologicalmicrostructurestrength
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1301: Symposium V/NN/OO/PP – Soft Matter, Biological Materials and Biomedical Materials—Synthesis, Characterization and Applications , 2011 , mrsf10-1301-oo01-06
Copyright
Copyright © Materials Research Society 2011

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References

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