The wood of thuja burr plays an important economic and social role for the Moroccan artisanal sector. In last decades, as demand increased, thuja burr was overexploited resulting in an important degradation of Moroccan thuja forests. One possible solution, in the short term, consists in limiting waste machining. This approach requires the characterization of the material, especially of its materiel symmetries. This work aims thus at characterizing the wood of thuja burr (Tetraclinis articulata (Vahl) Masters), that was little studied up to now. First, a multi-scale characterization is proposed. At the global scale, the internal structure of an entire thuja is observed using X ray tomography, especially the distribution of dark growth elements typical of thuja burr. This macroscopic characterization is completed, at the microscopic scale, by a comparative analysis of anatomical microsections of thuja wood and thuja burr. At the material scale, the dispersion of the thuja burr stiffness is observed using a direct contact ultrasonic method. In order to progress further in the study of the mechanical anisotropy, a direct contact ultrasonic method for spherical samples is developed allowing to identify material symmetries. By applying this method to the thuja burr wood, a transverse isotropic behaviour is observed. Hence thuja burr wood does not exhibit the same natural symmetries as what is found in the trunk of the same tree. However, this method does not yield the complete stiffness matrix. In the case of an orthotropic material, it gives the access to 3 diagonal terms of the matrix and 3 linear combinations of the six other terms. The use of Resonance Ultrasound Spectroscopy (RUS) is proposed to identify the stiffness matrix completely: the coupling of the direct contact ultrasonic method developed and RUS method allows to determine the symmetries and stiffness matrix on the same sample. Finally, scanned images obtained by X-ray tomography can be superimposed on stiffness graphs to analyze the relationship between the internal structure and the elastic behavior of thuja burr.
Caractérisation mécanique de la loupe de thuya (Tetraclinis Articulata (Vahl) Masters) en vue de sa valorisation