Acoustic Emission Associated with Oak During Drying

Time-domain acoustic emission (AE) parameters were monitored during the drying of 25- and 50-mm-thick California black oak (Quercus kelloggii). Consistent drying conditions (82 C dry bulb temperature/43 C wet bulb temperature) were used throughout the experiment, and an AET 5500 acoustic emission monitoring system was used to monitor AE activity. AE event rates for both thicknesses were similar, with approximately 90% of all activity occurring during the initial 15 to 20 hours of drying, when the average moisture content was still above 50% (oven-dry basis). Active propagation of surface checks was consistently associated with the occurrence of an increasing number of high amplitude events (i.e., those between 60 and 79 dB), although nonvisible micro-failures could have been associated with the large number of lower amplitude events. The high amplitude events typically comprised less than 1% of all events occurring during a given run. Surface-mounted transducers did not detect AE associated with the internal checking that occurred in all test samples