Properties evaluation and defects detection in timbers by ultrasonic non-destructive technique

Abstract

Three commercial timber species viz. Acacia mangium, Grevillea robusta and Mangifera indica were selected to study the occurrence of natural and biological defects using ultrasonic non-destructive technique. Different tests were conducted on defective as well as sound (defect free) wood specimens to investigate the effect of defects (grain orientation and hole/defect size) on the ultrasonic velocity. Effect of specific gravity and moisture content on the ultrasonic velocity was studied. Mechanical tests were carried out to evaluate the modulus of elasticity by conventional procedure using universal testing machine. The ultrasonic velocity in wood was found to be dependent on several factors such as moisture content, specific gravity, grain orientation, presence of natural or artificial defects/inclusions inside the wood. The ultrasonic velocities in wood and strength properties were correlated and decrease in velocity in timbers due to various defects was also worked out. Detection of defects was carried by observing the change in ultrasonic velocity compared to sound wood pieces. The outcome of present study will help timber users to detect the defect/decay by rapid examination of timber components/log and to determine the extent of degradation so that degraded wood could be replaced at an early stage.