Development of an Acousto-Ultrasonic Scanning System for Nondestructive Evaluation of Wood and Wood Laminates

An acousto-ultrasonic (AU) scanning system was developed and optimized for wood products. It was found that AU probe alignment, coupling pressure, and stabilization time affect the repeatability of AU readings. After optimization of these factors, the error in AU reading (RMS) was negligible. AU transmission through solid wood also showed a relationship of acoustic attenuation to wood anisotropy. A calculated modulus of elasticity in the direction of wave propagation correlated with wave attenuation characteristics in the TR and LR planes. For wave propagation in the TR plane, the greatest attenuation was observed at a growth ring angle (GRA) of about 45°, corresponding to the lowest modulus of elasticity, which is in this plane. The effect of wood anisotropy (GRA) was found to be a major problem for evaluation of laminated wood, since the received signal was strongly affected by wood properties. Consequently, the effect of anisotropy and natural variability of wood will be the major limiting factor of any acoustic NDE technique applied to many wood products