WOOD

Wood is widely used in structural applications and offers many advantages such as high strength, electrical resistance, fire resistance and immunity from oxidation processes. It suffers one major defect in being susceptible to biological attack.

A new NDT technique, Acoustic Scan Testing (AST), has been developed to detect the presence of structural defects caused by fungal or insect attack in wood members such as poles, piles, beams and girders. The technique relies on the propagation of acoustic waves along the wood, detection of these waves and subsequent digital processing. The technique has been successfully applied to the testing of wood bridge piles and girders.

The Laboratory is currently involved in a large scale project funded by the Electricity Association of NSW to examine the effectiveness of various NDT methods to predict the strength of erected utility poles. The techniques being assessed include tomography by x-rays and other ionising radiation, acoustic transmission from the sonic to the ultrasonic, acoustic emission, bending deflection, moisture content and others.

Three hundred and sixty poles were erected at a site at Schofields, NSW in January 1998. They have been tested by some twenty different organisations and groups involved in non-destructive testing and have been pulled for breaking on a test rig at the site for determination of their breaking strengths. Assessment of the trial is now underway.

Acoustic Properties of Wood

Wood has traditionally been the choice of material for the making of musical instruments, particularly the string instruments. The choice of wood species and its acoustic properties are critical to the qualities of the instrument produced. Research is continuing to further our understanding of these phenomena and to produce data on the unique range of species indigenous to local and South East Asian forests.

Measurements have been made on these woods of the dynamic moduli and damping constants at frequencies in the range 50 Hz to 5 kHz using a cantilever technique. Ultrasonic pulse techniques are used to determine properties at higher frequencies. A wide range of Australian and Indonesian woods have been studied and reported on..

References:

J.I. Dunlop, (1978), Damping Loss in Wood at Mid-kilohertz Frequencies, Wood Sci. & Tech., 12, 49-62.
J.I. Dunlop, 1980, Testing of Particle Board by Acoustic Techniques, Wood Sci. and Tech., 14, 69-78.
J.I. Dunlop, (1981), Testing of Poles by Acoustic Pulse Techniques, Wood Sci. and Tech., 15, 301-307.
J.I. Dunlop, (1983), Testing of Poles by Acoustic Resonance, Wood Science \& Tech., 17, 31-38.
N. Garben and J.I. Dunlop, (1990), Acoustic Pole Testing, Electrical Engineer, 49, 70-74.
J.I. Dunlop and M. Shaw, (1991), Acoustical Properties of Some Australian Woods, J. Catgut Acoust. Soc., 44, 79-83.
J.I. Dunlop, (1989), The Acoustical Properties of Wood in Relation to Musical Instruments, Acoustics Australia, 17, 37-40.
R.D.Harjono and J.I. Dunlop, (1998), Acoustical Properties of Some Australian and Indonesian Woods, Catgut Acoust. Soc. J. 3 No. 5 Series 2 10-13.