Acoustic emission related to strain energy during drying of Eucalyptus regnans boards |
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| Authors: | J D Booker P E Doe |
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| Institution: | (1) Civil and Mechanical Engineering Department, University of Tasmania, GPO Box 252C, 7001 Hobart, Australia |
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| Abstract: | Summary 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.Symbols E
Young's Modulus (GPa)
- 
instantaneous strain
- m
mechano-sorptive effect
- c
creep strain
- u
unconfined shrinkage
- n
net shrinkage
- o
set (residual) strain
- pl
proportional limit strain
- Win
strain energy (kJ/m3)
- Uu
unrecoverable strain energy (kJ/m3)
- Ur
recoverable strain energy (kJ/m3)
- W
in
*
nondimensional strain energy
- U
u
*
nondimensional unrecoverable strain energy
- U
r
*
nondimensional recoverable strain energy
- 
stress (MPa)
The authors are pleased to acknowledge the assistance of Emeritus Professor A. R. Oliver, University of Tasmania, the Australian Furniture Research and Development Institute and the Tasmanian Timber Promotion Board. |
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