NON DESTRUCTIVE EVALUATION OF WOOD MECHANICAL PROPERTIES THROUGH ULTRASONIC SOUND WAVES - PHYSICAL FOUNDATIONS AND EXPERIMENTAL RESULTS

Abstract

The propagation of ultra-sonic waves in wood can be described through fundamental physical relationships (known as equation of Christoffel), established for a anisotropic solid, among the phase speed, the density and the elastic constants of the wood. However, differently of other solids, the propagation of ultra-sonic waves in wood constitutes a phenomenon of considerable complexity. The propagation constants, the speed (of phase and of group) and the absorption coefficients, are significantly affected, not only by the heterogeneity of the chemical composition, by its microstructure, by the irregularity in the anatomical elements disposition, inherent to the biological nature of the wood, but also by its hygroscopic nature. The sensibility of the group speed or of ultrasonic pulse propagation, along the wood, to factors that determine their mechanical characteristics, indicated that is possible to establish statistical correlations between speed and wood   mechanical properties