Poromechanical scale transitions of failure stresses in wood: from the lignin to the spruce level

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, hemicellulose. and hem. and on the shear strength of the latter elementary constituent Relating, through elastic energy-derived higher-order strains in a poromechanical representative volume element. the (quasi-)brittle failure of lignin to overall softwood failure, 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 minimal tensile and compressive strengths. as well as the shear strength of softwood, depend quasi-linearly on the cell water content. but highly nonlinearly on the lumen porosity (C) 2010 WILEY-VCH Verlag GmbH & Co KGaA Weinheim