Wood Structural Anisotropy Estimated by Acoustic Invariants

Abstract

Wood anisotropy is induced by the specific deposition of anatomical elements during the life of the tree. The anisotropy becomes evident when acoustical properties are measured in the different main symmetry directions.The first approach for the estimation of wood anisotropy was to calculate the ratios of longitudinal and shear velocities in natural symmetry directions. The modeling of wood structure is required in order to relate the anatomical structure to the acoustical behaviour of wood.The second approach for wood anisotropy interpretation was to compute acoustic invariants and to average them. Considering that those quantities are insensitive to the direction of propagation, they can act as references for anisotropy investigation. Combining the values of invariants in the three main symmetry planes yields a single global value that characterises each species.Values of invariants for 15 species (conifers and broadleaves) are given.