POTENTIAL OF PIEZOELECTRIC ELEMENTS IN THE MONITORING OF COMPOSITE MANUFACTURING PROCESS

A piezoelectric wafer is embedded in a glass fibre preform that is pla ced in a mould for resin transfer moulding. The experiment shows that the resonant characteristics of a transfer function, in terms of the r atio between the electric voltage output from the piezoelectric wafer and the input to an electric circuit cascaded with the wafer, depend o n resin injecting and curing process, and indicates the beginning and end of the resin injection as well as the end of the exothermic reacti on in composite manufacturing with the resin transfer moulding. The re lationships of the resonant response to the resin flow and curing can then provide a basis for a prospective in situ monitoring technique of the composite manufacturing. The paper specifically reveals that the mechanical impedance, contributed by surroundings and the resin flow, curing and exothermic induced temperature change, can be correlated wi th or extracted from the transfer function amplitude that is experimen tally obtained at the anti-resonant frequency of the piezoelectric waf er in air. It also provides information about the flow front position and curing state of the resin.