Determination of local mechanical properties of clear wood in relation to the local fiber deviation

Abstract

Products made with veneers such as Laminated Veneer Lumber can reach higher properties than solid wood because the defects such as knots (but not only) are distributed among the various layers. Visual sorting, even using automatic grading, is only partially efficient for evaluating mechanical properties, which mainly depends on the fiber orientation and the density both at local scale. An experimental protocol has been established to correlate the nondestructive (fiber orientation and density) estimation and the destructive (tensile test) measurement of beech veneer wood. The aim is to understand the impact of the small imperfections on clear wood in fiber orientation on the mechanical properties. In the present study, wood veneer is assumed to be a transverse isotropic material due to the predominant wood fiber direction in the growth direction of the tree. Experimental measurements of modulus of elasticity are based on Digital Image Correlation (DIC) and virtual extensometer. The Young modulus model is based on a composite material model that considers fiber orientation and density. The Young modulus model is used to determine longitudinal, transverse, and shear moduli, for specimens with angles ranging from 0 to 45°. Mechanical properties are obtained by mathematical minimization between experimental and model data. The coefficient of determination obtained was 0.97. The measure of the fiber angle with a resolution of 1 × 1 mm² and the tensile test with the DIC, both local, significantly improve Young modulus measurement compared to previous studies’ assessment accuracy and allow for a better understanding of the wood behavior.