Ultrasound grading of round Eucalyptus timber using the Brazilian standard

The structural use of round timber has been considered competitive in terms of both economics and sustainability due to the low energy consumption required for processing it. However, structural uses of wood in round and sawed forms require knowledge of wood properties, which makes the grading of these properties essential. In Brazil, an ultrasound grading standard for wood was proposed based on tests of lumber from tropical species with an average age of approximately 45 years. The objective of the present study was to evaluate whether the grades proposed by this standard could be used, either directly or by applying correction factors, to grade round timber derived from a planted Eucalyptus forest. For this evaluation, round timber with different diameters was tested using ultrasound at saturated moisture content (MC) greater than 30% and at environmental equilibrium (an MC of approximately 12%). Static bending tests were conducted only when the MC was at the environmental equilibrium (approximately 12%). Although it is necessary to validate the conclusions with a larger data set, the results indicate that due to the correlation between the diameter of round timber and its acoustic and mechanical properties, any round timber grading system must consider the diameter of the pieces. The larger the diameter of the round wood is, the greater the difference between the actual velocity in the log and the velocity expected by the grading standard that considers the stiffness.