Schniewind, Arno P., Professor Emeritus, University of California Forest Products Laboratory 1301 South 46th Street, Richmond, CA 94804, U.S.A.
Johnson, George C., Professor Department of Mechanical Engineering, University of California Berkeley, 6185 Etcheverry Hall, Berkeley, CA,, U.S.A.
ABSTRACT
Nondestructive testing of wood using ultrasound utilizes propagation speed and/or energy loss to indicate the state of a test sample. The propagation velocity of an ultrasonic pulse provides very valuable information because of the well-know connection to elastic moduli, C = rv2. Our recent research has shown that, due to the anisotropic nature of wood, intuitive identification of the elastic modulus being measured in a given experiment is not always correct. Our research also showed that the two quantities needed to determine a velocity, distance travelled and time of flight, may be misidentified due to the nature of wood. We further found that ultrasonic energy incident on wood will almost always be split into three components, at least two of which carry significant amounts of the incident energy. This paper summarizes our results and discusses the potential problems and pitfalls for any ultrasonic evaluation presented by the anisiotropic, inhomogeneous nature of wood. Our findings point out some significant challenges to successful ultrasonic NDT of wood, but also point to new opportunities for overcoming the challenges and for significantly broadening the scope of wood NDT. The paper concludes with suggestions for new approaches to ultrasonic measurements.
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
