Résumé
Background, Motivation and ObjectiveComposite materials play a key role in a number of fields, including aerospace, automotive and civil engineering. Composite materials are known for their good mechanical properties/density ratio. Composites are generally anisotropic and characterizing their whole mechanical properties is often complex. However, knowledge of these behaviors is essential to ensure the design and reliability of a composite part.Besides standard mechanical testing methods, the elastic constants of composites can be measured using ultrasound waves. The simplest ultrasound method consists in ultrasonic velocity measurement in the principal directions. Nevertheless, it is often necessary to machine several samples along their principal directions. Furthermore, these measurements can only determine the diagonal coefficients of the elasticity matrix. To determine all the elastic constants using ultrasound measurements it is also possible to use a goniometric transmission method based on the measurement of transmission coefficients as a function of incidence angle, with different samples. This last element constitutes the main drawback of such an approach. Modal analysis methods, such as Resonant Ultrasound Spectroscopy, are theoretically able to determine all the elastic coefficients on one sample and are often employed. These methods, which are particularly suitable for estimating shear moduli, lack sensitivity to Poisson's ratios. Thus, the determination of off-diagonal terms of the elasticity matrix is generally impossible.Statement of Contribution/MethodsThe aim of the present communication is to propose an original method. It uses laser interferometry to measure the displacement fields at the samples surface generated by an ultrasonic transducer. The method has been developed on unidirectional glass fiber reinforced epoxy composite with transverse isotropic symmetry. First, an ultrasound transducer is positioned at one of the vertices of the sample. A polar scan of the displacement field in the plane containing the fibers is then used to determine the velocity of the compression waves from 0° to 180° to the fiber direction. The experimental ultrasound velocities are then used to deduce the elastic constants with analytical models of group velocities described by Christoffel's equations.Results/DiscussionFour of the five coefficients of the elasticity matrix in a single angular scan have been successfully determined. The wide angular measurement range guarantees the measurement of ultrasound velocity in the fiber axis and perpendicular to the fibers. This is an advantage over other methods such as goniometry which is limited in terms of the angular sector range. Finally, the method presented here is also applicable to the characterization of thin composite materials.