Modeling vibrations response of wooden beams with singularities using mechanical models

The diversity and the great variability of wood products, induced either by the manufacture, or by the raw material, makes it necessary to tend to a rigorous grading of each element based on its mechanical performances according to the standards. This study presents the first stage of a work aiming at grading wood products in a production line with the density, the modulus of elasticity and especially the modulus of rupture as a criterion of selection. In order to appraise the modulus of rupture, in addition to the density, and the global modulus of elasticity, it is necessary to characterize mechanically the possible presence of local weaknesses in a beam. For this purpose, we use the finite element method as well as a dynamic analysis technique that could be integrated in a grading process. Classical models related to vibrations of beams can only be applied to homogeneous materials. As a consequence, a new approach is proposed based on the presence of one or several singularities or defects (local weaknesses) in the beam. The vibratory response of a beam to an impulse makes a mechanical characterization possible. The proposed method, based on measurements and the analysis of natural vibrations of manufactured products, is a relatively simple, efficient and cheap answer to the needs of various types of manufactured products. This study clearly shows the pertinence of the vibrations analysis in the acoustic area applied on the non destructive testing of woods and wood composites. (Texte intégral