The ultrasonic-based methods applied to wood have been quite intensively developed during the last decade. Basically, both the stress wave propagation and the natural frequency vibration methods have been used for timber grading. Tn order to increase the sensitivity of the stress wave method, the acousto-ultrasonics, AUS, have been approached in the way to complete the initial time information. Byjoining time and spectral AUS data, exploratory researches have been supported as NDT of wood. Tests have been made with transducers working in &equency range of 25 kHz. Coupling problems have been partially solved using conical penetrating transducers. An acquisition station was set up, connected to an oscilloscope, amplifiers and software able to compute the AUS spectral characteristics. The maximum voltage picks, the signal energy and the decrement function were selected NDE variables. Applied to a sample of structural timber (solid wood), several AUS variables appear to be correlated to timber strength. Mechanical tests have confirmed the correlations. AUS variables added to the stress wave information give an increase of about 25% of the mechanical NDE of timber strength. This result is very interesting in terms of grading and reliability. The next step is to define a standard industrial acquisition method and to calibrate an applied exploitation model.
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
