Transverse vibration tests for prediction of stiffness and strength properties of full size Eucalyptus grandis

The current method for determining the modulus of elasticity (MOE) of South African timber is contained in the South African standard SABS 1122-1994 (13). The European standard method for determining MOE is stipulated in EN 408 (5) and the American standard is in ASTM D4761 (1). Both the South African and European standards specify specimens with a span-to-depth ratio of 18, whereas the ASTM method specifies a span-to-depth ratio of between 17 and 21. These methods give varying and inconsistent results when evaluating MOE. This has led to a difference in interpreting the results and in the experimental procedures regarding the placement of deflection yokes and linear-variable deflection transducers ( 6). This paper discusses, in our opinion, a more consistent and reliable method of transverse vibration for evaluating MOE and bases the arguments on experimental results from tests performed on Eucalyptus grandis. The results were evaluated and checked for consistency and the relationship to other stiffness and strength characteristics was determined. The suggested method can be used to evaluate the bending MOE of Eucalyptus grandis because it correlates well with MOE determined in the more traditional way. The correlation between the vibration MOE and the bending strength is found to be not particularly good, but the vibration MOE could still serve as a rough estimate of the bending strength. Flatwise and edgewise MOE are evaluated and correlated to modulus of rupture and density. With these results, the conclusion is drawn that the vibration method of determining MOE can be used as a general predictor of strength and stiffness characteristics of timber.

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