Acoustic emission patterns from the surfaces of red oak wafers under transverse bending stress

Abstract

One of the applications of acoustic emission (AE) technology in the forest products field is likely to be in monitoring and/or controlling the drying of wood. This report describes experiments designed to monitor the acoustic emission patterns from the lower surfaces of small red oak test beams which were undergoing failure in tension perpendicular to the grain. Similar patterns are likely to develop in wood which surface checks during drying. When the wood was green, the emission patterns from beams under test were well defined and could be used to predict the onset of cracking before the surfaces under tension were visibly cracked. These patterns were quite similar to the acoustic response of brittle, glassy polymers under stress. Additional experiments on partially dried test beams showed that the clearly predictable emission patterns disappeared and the general level of acoustic emissions increased. This increase in emissions may correspond to shrinkage, at the cell level, of the partially dried beams.