Research on detecting defects of square-edged timber of fir and ribbed birch by infrared thermal imager: A study on nondestructive testing of wood defects by infrared thermal imager

Samples of square-edged timbers of fir and ribbed birch with defects of holes, flaws or knots were tested by thermal infrared imager and infrared lamp. Each sample had only one defect of the three kinds of them. There´re 5 fir samples, two samples with a hole in the middle, one with a hole in either side, and the other two samples with flaws and knots, respectively. Three are 3 samples of ribbed birch, one sample with a hole in the middle of it, the other two samples with flaws and knots, respectively. It could be found out by comparing experiments results that infrared thermal imager could detect holes in the middle, flaws and knots of fir and ribbed birch samples correctly and distinctly, but couldn´t distinguish the kind of defects. It couldn´t detect the holes at the sides of fir samples. Areas of holes and knots had lower temperature and areas of knots had higher temperature. Different testing conditions were necessary in order to detect different defects correctly. Holes in the middle of samples of both fir and ribbed birch could be detected only by double-way detecting model, while flaws could be detected only by one-way detecting model. Knots of fir samples could be detected only by one-way detecting model. Knots of ribbed birch samples could be detected by both one-way and double-way detecting models. The size and position of defects could be determined more accurately with higher moisture content, though the heating time by infrared lamp would be longer.