ACOUSTIC-EMISSION AND SURFACE CHECKING IN EUCALYPTUS-REGNANS BOARDS DURING DRYING

Acoustic emission (AE) was measured in drying 30mm thick Eucalyprus re gnans F. Muell. boards. Incipient surface checks were detected with a hand-held to-times magnifying glass. Surface checks occurred at a very nearly constant AE rate (ring-down counts) in the backsawn and quarte rsawn boards dried at temperatures in the vicinity of 20 degrees C. At higher temperatures, collapse shrinkage beneath the board surface cau sed localised surface checking at significantly lower AE rates. AE is hypothesised to be generated by intermittent slips in the crystalline regions of the cellulose microfibrils comprising fibre cell walls.