Wood NDT-2000 Session VI.: Microwave and Miscellaneous
Kaiser Effect Experiments in Wood by Acoustic Emission Testing
Antal Kánnár University of West Hungary Institute for Applied Mechanics and Structures H-9400 Sopron Ady E. ut.5.; e-mail anti@efe.hu
ABSTRACT
It is a well known phenomenon that the damage process of wood is accompanied by creaking sounds. However sounds may exist under the break stress in the ultrasonic area too. The acoustic emission measuring method is capable to examine these signs and evaluating of data gives valuable information about the tested material. It is well known in the field of metal research that if the metal is loaded with a certain force then the load is taken away, in the next loading period the material does not show acoustic activity, while the stress reaches the maximum of the last load. This is called Kaiser effect. The question is whether the wood shows this effect or not? The examination consisted of short term experiments - also with changed moisture content and temperature - and longer term experiments. The second loading period followed the previous one directly in short term experiments and in l, 2 or 5 months in the case of longer term tests. The tested species was Scots pine. The investigation proved that Scots pine shows the Kaiser effect during short term experiments. However the more time elapses till the second loading period the less the effect can be observed . Also the significant change in moisture content and temperature results in disappearing of the Kaiser effect. The results help us to understand the special behavior of wood, namely, it gives a possible answer why the wood does not show the Kaiser effect in the first loading period while living trees endure loads of wind and snow up to the 60-70% of its ultimate strange.
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
