Sensitivity of piezoelectric wafers to the curing of thermoset resins and thermoset composites

In-plane vibration of a piezoelectric wafer can be excited by electric voltage across its thickness in the poled direction. Such a characteristic, in turn, builds up a relationship between mechanical and electrical performance of the wafer. The relationship is here especially analysed as the piezoelectric wafer is immersed in a liquid that is modelled by a series of mass-spring-damper systems attached to the wafer. Results demonstrate that mechanical properties such as modulus, mass and damping coefficient of the systems have impact on the capacitance, inductance and resistance of the piezoelectric wafer referred to a component in an electric circuit. Changes in the properties alter the electric resonant response behaviour of the circuit. Two experiments for the curing process of epoxy and a thermoset composite verify the prediction that the variation in amplitude of a transfer function in a resonant region is dominated by the change in viscosity of resins before gelation, while it is mostly affected by the change in temperature after gelation. The paper presents an approach to sense the curing process of thermoset resins and thermoset composites by the electromechanical property of the piezoelectric wafers.