In order to appraise the modulus of rupture, in addition to the density, the global modulus of elasticity, it is necessary to characterize mechanically the possible presence of local weaknesses in a beam. With this aim, we use the finite elements method as well as a dynamic analysis technique that could be integrated in a grading process. Classic models in vibrations of beams must be applied only for homogeneous materials. In 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 allows then its mechanical characterization.

The proposed method, based on the measurement and the analysis of natural vibrations of manufactured products, is a relatively simple answer, efficient and cheap to the needs of various types of manufactured products. This study puts in obviousness the pertinence of the utilization of the vibrations analysis in the acoustic area applied on the non destructive testing of woods and wood composites.