Monitoring the hydrolytic degradation of composites by a piezoelectric method

The electric impedance of a piezoelectric element depends on the physical and geometrical. properties of the element and on the viscoelastic characteristics of the media in which this element is inserted. According to this model, an original technique has been developed by inserting a piezoelectric ceramic in the composite structure when processed. The electric signal issued from the sensor, after signal processing and comparison with the model, gives access to the evolution of the viscoelastic 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 impedance of the sensor are presented here as a function of water exposition time for the resin and glass reinforced composites. The results are compared to degradation kinetics obtained through micromechanical experiments and classical ultrasonic spectroscopy.