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Inverse identification of early- and latewood hydric properties using full-field measurements

Dang, D., Moutou Pitti, R., Toussaint, E., Grédiac, M.
Wood material science and engineering 2018 v.13 no.1 pp. 50-63
Abies alba, deformation, diffusivity, direct contact, earlywood, engineering, latewood, materials science, mechanical properties, water stress, wood
The study and identification of the water diffusion properties of Abies alba Mill at the growth ring scale are investigated in this paper. A full-field measurement technique, the grid method, is used in the experimental tests in order to observe heterogeneities and to measure strain fields in the annual growth rings. In this case, the mechanical behaviour of latewood (LW) and earlywood (EW) is studied under the effect of water stress. This technique is coupled to an inverse method for parameter identification. It enables us to assess the diffusivity of EW and LW in the tangential diffusion direction (T) and their expansion coefficients in the radial direction (R) from strain maps obtained using the grid method. Thus the water diffusion phenomenon and its effect on the deformation of wood specimens are studied. A suitable experimental device is designed to provide direct contact with water on one side of the specimen, and strain maps are obtained over time on the other side. During the experiments, strain gradients that appear are clearly different between EW and LW, highlighting the different diffusion properties at the ring scale level. The results also show changes in the kinetics of the hydric deformation of the material.