Using acoustic emission technique for detecting checks on industrial-size beech wood disks during drying

Wood disks are very susceptible to checking during drying. The present study was aimed to determine a suitable transducer mounting configuration to detect the drying checks with acoustic emission (AE) technique. AE generated during drying of 30-mm-thick beech (Fagus orientalis L.) wood disk with a diameter of 300 mm were monitored using piezoelectric AE transducers operating at frequency of 50-200 kHz. The transducers were directly attached on the disks with four combinations depending on the sensor number and grain direction. Total number of AE events and event rate were associated with drying time and checking features. The successive formation of near-bark radial checks was detected due to fluctuations in the AE event rate. Results showed that if the transducers are attached to the disk lateral surfaces, the formation of pith checks cannot be detected in the early stages of the check formation. The V-shaped cracks can be only detected when the transducer is mounted very close to the crack location. Overall, our results showed that more than two transducers are required to detect all types of checks occurred during drying of wood disks of this size. They should be attached parallel to the grain, one near to the pith and the rest at a suitable distance around periphery of the disk