The Study of Sound Propagation in the Wood-Based Composite Materials
Bekhta P.A. Ukrainian State University of Forestry and Wood Technology 79057 Lviv, Ukraine Niemz P., Kucera L. Swiss Federal Institute of Technology ETH-Zürich, Switzerland
ABSTRACT
For the study of sound propagation in several types of wood-based composite materials (WBCM) two different non-destructive testing techniques were applied. Eigen frequency and sound velocity were determined on boards (particleboards, OSB, MDF) from industrial production. Each type of board was evaluated by measuring the sound velocity both parallel and perpendicular to the direction of production. In addition sound velocity through the thickness of the board was measured. The elastic and mechanical characteristics of properties, as determined by eigen frequency and sound velocity were compared with those determined by static method. The used frequencies were 50, 100 and 200 kHz. With increasing frequency the sound velocity also increases. But it was not possible to demonstrate a clear influence of higher frequency (200 kHz for particleboards, 100 and 200 kHz for OSB) on sound velocity. The results were subject to considerable fluctuations. Between the individual materials types (particleboard, OSB, MDF) and within these clear differences exist in the sound velocity. A clear difference for all types of boards also exists between MOE and MOR in parallel and perpendicular to the direction of production. But the best results are found for measurements perpendicular to the direction of production. The sound velocity through the thickness of MDF also correlated well with MOE and MOR. It was found that a high degree of correlation exists between dynamic and static MOE. Notable is the fact that dynamic methods all give higher values for MOE than DIN testing. Eigen frequency and sound velocity correlated well with MOE and MOR and thus provide an inexpensive NDT method for MOE (MOR) prediction of WBCM. But sound velocity showed the higher correlation coefficients with the MOE and MOR. Thus, for the prediction of MOE and MOR, ultra sound is the easiest way and more effective tool than eigen frequency analysis. Several variables, including relative air humidity (50 to 90%), temperature of board (-35 to +700C), sample width (20 to 200 mm), sample thickness (16 to 96 mm), were introduced to investigate their effects on the sound velocity. By increasing of the values of these variables we found a decreasing of the sound velocity. The measurement of 7 types of particleboard (with different density and thickness) brought different sound velocity for all board types.
Publication Source: Proceedings of the 12th International Symposium on Nondestructive Testing of Wood University of Western Hungary, Sopron, 13-15 September 2000, ISBN 963 7180 88 5 Publisher: University of Western Hungary, H 9400 Sopron, P.O.Box 132, FAX: +36 99 311 103
