2D-4 Characterization of Elastic Parameters of Composite Materials by Electro-Mechanical Impedance Measurement: Application to the Thermal Ageing of Carbon-Epoxy Plates

This study relates to the thermo-oxidative ageing of plates up to 5000 hours (at 160 or 180degC). The electro-mechanical impedance of a commercial transducer (2.25 MHz or higher) coupled to the composite plate is measured. We give here a method to determine the speed and the attenuation of longitudinal waves, propagating along the thickness direction, using an inverse procedure on the impedance of the composite plate. The transducer is modelled and the parameters of this model are identified. The system of the transducer coupled with the composite plate is then studied. We show that the acoustic impedance of the propagation medium can be extracted provided the transducer's parameters are known. This method, applied to composite plates aged thermically, shows modifications of the parameters (velocity and attenuation). These variations are in good agreement with those obtained by other techniques carried out in laboratory which are also reliable but less practice to use "under wings".