Acoustic emission related to strain energy during drying of Eucalyptus regnans boards

During timber drying, surface differential shrinkage within a board causes a high surface tensile stress and associated instantaneous strain. Acoustic Emission (AE) is generated when localised irreversible stress release events act to reduce the strain energy imparted to the material. A nonlinear one-dimensional drying model was used to calculate through-thickness moisture, stress and strain profiles during drying. The surface stress and instantaneous strain were used to calculate the strain energy at the surface. AE was measured during drying and the relationship between strain energy and the cumulative count (total ringdown counts) was investigated. The cumulative count is related to the unrecoverable strain energy rather than the elastic or recoverable strain energy. The cumulative count is not a useful measure of the propensity for surface checking. However the peak AE rate values are closely related to the surface instantaneous strain. © 1995 Springer-Verlag.