MONITORING THE HYDROLYTIC DEGRADATION OF COMPOSITES BY A PIEZOELECTRIC METHOD

The electric impedance of a piezoelectric element depends on the physi cal and geometrical. properties of the element and on the viscoelastic characteristics of the media in which this element is inserted. Accor ding to this model, an original technique has been developed by insert ing a piezoelectric ceramic in the composite structure when processed. The electric signal issued from the sensor, after signal processing a nd comparison with the model, gives access to the evolution of the vis coelastic properties of the surrounding media. An application of this non-destructive method is the monitoring of the hydrolytic degradation in polyester-based composites. The evolutions of the electric impedan ce of the sensor are presented here as a function of water exposition time for the resin and glass reinforced composites. The results are co mpared to degradation kinetics obtained through micromechanical experi ments and classical ultrasonic spectroscopy.