Delphine Jullien(1), Tancr`ede Alm'eras(1), Kojima Miho(2),
Yamamoto Hiroyuki(2) , Pierre Cabrolier(3)


(1) LMGC, UMR 5508 CNRS - Universit'e Montpellier 2, France
(2) Laboratory of Biomaterial Physics (Wood Biomechanics), Nagoya University
(3) LERFOB, UMR INRA-AgroParisTech 1092, Nancy, France



During tree growth, mechanical stresses accumulate in the stem because of the increasing tree weight and wood maturation. These "growth stresses" fulfill two biomechanical functions: they allow the control of the tree orientation and improve its resistance against bending loads. But they generate technological problems during tree transformation, causing heart checks after cross-cutting, checks and deformations of boards after sawing, etc... These problems cause important economic losses and thus research in this area aims at understanding how these stresses appears during growth, in order to find solutions to reduce them.
Radial profiles of growth stress profiles were measured by measuring the longitudinal strains due to the release of growth stress at different radial positions on diametrical boards. The experimental profiles obtained are consistent with the predictions of biomechanical models, showing a maximal tension at the periphery of the tree, and an increasing compression towards the tree center. Biomechanical models predict that the shape of the profile depends on various parameters of tree growth, such as the eccentricity of the section, the occurrence of juvenile wood, the distribution and intensity of reaction wood, and the gradients in wood stiffness. Experimental profiles were compared to those simulated by the model assuming particular growth scenari. The correspondence between experimental results and simulations provides a validation of the biomechanical model.