MONITORING THE HYDROLYTIC DEGRADATION OF POLYESTER-BASED COMPOSITES BY A PIEZOELECTRIC METHOD (REPRINTED FROM ENERCOMP 95, PROCEEDINGS OF THE INTERNATIONAL-CONFERENCE ON COMPOSITE-MATERIALS AND ENERGY, MAY 8-10, 1995, MONTREAL, CANADA)

Theoretical considerations show that the electric impedance of a piezo electric element depends on the physical and geometrical properties of the element and also on the viscoelastic characteristics of the diffe rent media surrounding it. According to a dynamic model, an original t echnique has been developed by inserting a piezoelectric ceramic in th e composite structure when processed. The electric signal, after signa l processing and numerical treatments, gives access to the viscoelasti c properties of the external medium. This method is an excellent indic ator to display the polymerization kinetics of the resin as well as th e post-curing phase of the composite structure process. Moreover, a fu rther application of this nondestructive method is the monitoring of t he hydrolitic degradation of the composite structure. The evolution of the electric impedance of the piezoelectric sensor is presented here as a function of water exposition time for a polyester-based composite .