The identification of fracture in dried wood based on theoretical modelling and acoustic emission

Physical interpretation of the three characteristic groups of acoustic signals emitted during convective drying of wood is the main subject of this paper. The acoustic emission (AE) was to evidence the fracture intensity during drying of a birch wood sample of cylindrical shape. To explain the three characteristic groups of acoustic signals, and particularly the last one, a mechanistic model of drying was applied to analyse the drying induced stresses in the tested sample. One can conclude from this analysis that the third group of acoustic signals arises when the surface stop to shrink and the wet core (initially in compression) begins to dry. The shrinkage of the core causes compression of the boundary layer and tension of the core. Thus, the reverse of the stress signs in the cylinder cross-section takes place and this possibly involves the destruction of wood structure in the tensed core.