Abstract

The relation between growth stress and stress wave velocity has been investigated on standing trees of Eucalyptus nitens. Longitudinal growth stress and the stress wave velocity were measured at breast height on 155 trees. Large variation in both growth strain and acoustic velocity was observed. The initial investigation with 34 trees showed good correlation (R²=0.68). Measurements on all 155 trees revealed no reliable relationship (R²=0.05). The influence of internal stress on acoustic velocity has also been investigated on radiata pine boards loaded in bending and tension. It was observed that the resonance frequencies were influenced by the position of loaded supports in bending, but were not affected by the bending load. In boards under tensile stresses, there was no change in acoustic velocity measured by the pulse transit time. The two experimental series, one on standing trees with water-filled lumens and the other on air-dried boards, failed to reveal any dependence of the stress wave velocity on growth stress. No valid basis therefore exists for the use of stress wave velocity to determine growth stress levels in either standing trees or in seasoned wood.