Fabrication And Properties Of Piezoelectric Fiber Composites

Compared with conventional piezoelectric materials, piezoelectric fiber composites(PFCs) present the characteristics of thin thickness, light weight, flexibility, high actuation ability, long service life, and the anisotropy. Owing to these merits, PFCs have received wider attention in smart applications, e.g. structural health monitoring, vibration control, energy harvesting and actuation.PFCs were successfully fabricated by the so-called double cutting-filling method developed in this research. The microstructures of PFCs were characterized by optical microscope and scanning electron microscope. The results showed that the fabricated PFCs have unique layered structure which the fibers aligned unidirectional and exhibited well coupling among the fibers, epoxy and interdigitated electrodes. And good alignment between the top and bottom electrodes was clearly found.The piezoelectric properties, free strain properties and mechanical properties of the PFCs were characterized. And the effects of excitation voltage, e.g., the voltage waveform, voltage amplitude, dc bias voltage and frequency on the free strain properties were also characterized. The results indicated that the longitudinal and transverse free strain of the PFCs reached about 1400 ?? and 680 ?? at a 2 kV peak-to-peak alternating voltage, suggesting that the PFCs exhibited good orthotropic property. The d33 piezoelectric coefficient of PFCs enhanced with the increase of the amplitude of voltage, resulting from the fact that larger electric field enhanced the domain switching and effective electric field of piezoceramic fibers so that increased the free strain of the fabricated PFCs. Under high dc bias voltage, the clamping of domain wall motion of piezoceramic fibers decreased of d33 coefficient, which weakened the free strain performance of the fabricated PFCs. Due to the response rate of the domain wall motion of the piezoceramic fibers to the alternative electric field, the free strain decreased gradually with the increase of frequency. The tensile strength reached 49.28 MPa and 36.18 MPa in the longitudinal and transverse direction, respectively, indicating high and comparable tensile strength achieved in both directions.The actuation performance of PFCs was studied and the active vibration control experiment system was designed in order to achieve the desired effect of structural vibration mitigation. The results showed that the vibration response of PFCs was sinusoidal and the vibration frequency was consistent with that of excitation voltage. The received vibration signal amplitude enhanced as the excitation frequency increased. And with the increase of excitation voltage, the higher vibration signal amplitude of PFCs was received. When the excitation voltage was 500 V, frequency was 280 Hz, the acceleration signal response behaviors of PFCs was obvious, the effect of the cantilever beam structural vibration mitigation reached best. It was concluded that the active vibration control could be achieved by optimizing the excitation voltage and frequency of PFCs.The effects of fiber parameters and temperature on the free strain and piezoelectric properties of PFCs were studied. The results showed that the longitudinal free strain of PFCs increased with the increase of fiber width, the fiber width dependence of free strain properties enhanced especially under high electric field. The longitudinal free strain of PFCs increased gradually as the fiber spacing decreased. The fiber thickness has great influence on the strain performance of PFCs, the free strain increased as the fiber thickness decreased. In a certain temperature range, the longitudinal free strain increased with the increase of temperature.The sensing properties of PFCs were studied based on the acoustic emission technique. The results showed that the obtained AE signal amplitudes and voltages of PFCs exhibited dependence on the measuring angles and distances. The AE signal amplitudes were different in the orthogonal direction which indicated that the PFCs exhibited well orthotropic property. The attenuation curves showed that the trend of signal attenuation gradually slowed down as the distance increased. The PFCs received much more acoustic emission signal amplitude on the epoxy test plane than the concrete plane, due to the smooth surface and dense structure of the epoxy plane. The localization of sound source was measured by the PFC sensor, which indicated that the PFCs possessed good sensitivity and good signal responses to achieve the purpose of positioning and had high accuracy in the process of linear and planar localization.