THERMOGRAPHIC DETECTION OF STARVED JOINTS OF WOOD

To examine the feasibility of thermographic nondestructive testing of wood adhesive joints, several samples with starved joints, 10-50 mm square, were prepared using wood plates 1.3-3 mm thick of white seraya and urea-formaldehyde resin. Their thermal images were obtained with a thermographic device during heating by tungsten lamps and natural cooling. Surface temperatures were always more in an area of a starved joint than in other parts, and the poor joints were clearly visible in the thermal images. The thinner a wood plate and the greater the adhesive spread, the easier the defects were detected. The detectability was greatest for samples just after pressing, probably due to the insufficient diffusion of water. For the sample plates, 3 mm thick, starved joints were detected easier during cooling rather than during heating, and even defects 10-20 mm square were visible in the thermal images.