Surface wave propagation in wood: prospective method for the determination of wood off-diagonal terms of stiffness matrix

Abstract

Overall elastic properties of wood can be studied by ultrasonic methods. Orthotropic symmetry is assumed (nine constants). This article describes two methods developed for the determination of three off-diagonal terms of the stiffness matrix. The first method deals with bulk waves (BAW), and the second with surface wave (SAW) measurements. The BAW method requires repeated off-axis measurements and an optimization criterion for selecting the C ij -terms. The SAW method gives the value of the C ij -term corresponding to a specific plane of symmetry, from only one on-axis measurement. The six diagonal terms of the stiffness matrix can be obtained easily from on-axis bulk wave measurements. From the nine terms of the matrix, the compliance terms ( S ij ) and corresponding technical terms are calculated. Technical constants determined from ultrasonic measurements are in agreement with those obtained by classical statistical methods. The experiments were performed on beech and spruce. The SAW technique is expected to be of more interest for further investigations of wood mechanical properties.