Vessels as surface stress raisers during drying of Eucalyptus diversicolor F. Muell

When surface checks form in karri (Eucalyptus diversicolor F.Muell), they almost invariably do so in the bottoms of vessels exposed on the surfaces of the boards. It is postulated that the vessels act as stress raisers, and thus surface checks form at lower values of average surface stress and strain than they would otherwise. Surface checks were seen to form at acoustic emission levels approximately one-third of those corresponding to surface check formation in other eucalypti- Analytical and finite element stress analysis techniques suggested a stress concentration factor at the bottoms of the vessels of approximately three. A trial drying of karri showed a close correlation between predicted surface instantaneous strain using the stress concentration factor found from the stress analysis in a model of drying timber, and measured acoustic emissions.