Variation in electrical properties of laminates with woven carbon fabric and ferroelectric or piezoelectric particulate epoxy due to tensile loading

Abstract

Measurement of electrical properties of fiber-reinforced plastics (FRPs) is an attractive method for predicting fatigue life and recording strain in FRPs. In this study, we prepared ferroelectric specimens laminated with woven carbon fabric and BaTiO3 particulate epoxy. We measured those specimens' electrical properties during tensile testing. Electrical resistance increased slightly and the electrical capacitance decreased as the tensile stress increased up to 500 MPa. As the tensile stress increased above 500 MPa, the electrical resistance and electrical capacitance increased. The electrical resistance and capacitance may be dependent on the applied tensile stress because of delamination between an epoxy layer and a carbon fabric layer, and fiber breakage in carbon fabric layers. Capacitance degradation from the beginning of tensile testing indicates that the addition of BaTiO3 particles into epoxy layers induced the delamination. Subsequently, piezoelectric specimens laminated with woven carbon fabric and poled lead zirconate titanate (PZT) particulate epoxy were prepared for repeated loading tests. Thereby, we investigated the relationship between loading and piezoelectric signals. Variation in the capacitance of epoxy layers rather than that in the polarization of PZT particles may be the generation mechanism of measured signals in the piezoelectric specimens. The peak interval in the piezoelectric signal waveforms was deeply related to the applied tensile stress. The peak intensity tended to increase with loading cycles. © 2005 The Japan Institute of Metals.