NDT.net - November 1999, Vol. 4 No. 11

Acoustoelastic Phenomena of Wood

Yasutoshi Sasaki and Kosei Ando
Faculty of Agricultural Sciences, Nagoya University
Nagoya 464-8601, Japan

5th World Conference on Timber Engineering
1998 August 17-20, Montreaux, Switzerland.
Reproduced with the publisher's autorization.
©1998, Presses polytechniques et universitaires romandes, Lausanne, Suisse.






    The effect of stresses on ultrasonic velocity propagating transverse to the direction of applied stress in wood was investigated experimentally. The experimental results indicated the existence of an acoustoelastic phenomenon in this experimental mode. The changes in the velocities of propagation of ultrasonic waves were given as functions of the applied stress. The relationships between the velocity and stress at the initial level, and those between the velocity and strain at the range of large deformation were straight lines. The acoustoelastic constants were obtained from the relationships between the changes in the velocities and the applied stresses at a low stress level. The absolute values of the constants of wood were larger than those of metallic materials.

    The patterns of the changes in the ultrasonic velocities depended on species of wood and ultrasonic modes. The acoustoelastic phenomena by using shear waves showed a difference in character under compressive and tensile stresses. On the contrary, the phenomena by using longitudinal waves for white spruce showed the same character under both stresses. This point should be considered when applying the acoustoelastic technique by using longitudinal waves for stress determination of wood.

    The bending stress values from the acoustoelastic stress measurements seem to have been adequately estimated and agree well with those obtained by the strain gauge method and mechanical calculation.

    The above results indicate that ultrasonic velocity propagating through wood changes with great sensitivity to the applied stress, and suggest the possible application of acoustoelastic technique for the determination of the stress conditions of wood. The origins or the mechanism of the changes in the ultrasonic velocities are, however, not explained for wood. The results of the present and previous studies [7-9], suggest the existence of a relationship between the acoustoelastic phenomena and the anatomical structure of wood. This may also explain the difference in the mechanism of acoustoelastic phenomena of wood and metallic materials.

    Further experimental and theoretical investigations should be made to find explanation for the mechanism and the application of the technique.


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