Anisotropy and Dissipative Properties of Wood

Abstract

Mathematical models describing energy dissipation during oscillations of structures made of isotropic materials are approximate and empirical. The issue of accurately describing the energy dissipation of oscillations becomes even more acute when the oscillations occur in an anisotropic body containing inhomogeneities. This paper is devoted to a computational and experimental study of the dissipative properties of wood. In the majority of cases, these wood properties are determined by a single parameter: the decrement of mechanical oscillations. This is insufficient for accurately modeling the dynamic behavior of wood structures. It is known that the decrement of mechanical oscillations is not constant across the frequency range and depends on the orientation of the wood fibers relative to the direction of the driving force. These features have to be taken into account when developing appropriate mathematical models of wood structures. Therefore, development of new methods and determination of the energy dissipation fundamental patterns (both throughout the object volume and across various areas of the frequency range) appear to be of current relevance. This paper applies an original experimental method for assessing the elastic and dissipative properties of spruce and birch wood samples. Elastic moduli and mechanical oscillation decrements are determined for these samples. We studied the influence of anisotropy and the scale factor on these. A correlation has been found between the elastic and dissipative properties of wood. As the modulus of elasticity in the longitudinal direction of the sample increases, its dissipative properties decrease: the logarithmic decrement of the oscillations decreases. A hypothesis has been proposed concerning the relationship between the elastic and dissipative properties of wood. This means that an accurate description of the energy dissipation properties of a given type of wood should include not one damping constant, but nine (number of elastic constants for an orthotropic body). The validity of the results obtained was tested using a finite-element model of a wood sample. The computed ratios for wood are derived based on the orthotropic body model. Shear deformations are treated according to S.P. Timoshenko’s hypothesis. The results of the numerical studies are confirmed by their high correspondence with the data from field experiments.