In lead zirconate titanate piezoceramics, external stresses can cause substantial changes in the piezoelectric coefficients, dielectric constant, and elastic compliance due to nonlinear effects and stress depoling effects. In both soft and hard PZT piezoceramics, the aging can produce a memory effect that will facilitate the recovery of the poled state in the ceramics from momentary electric or stress depoling. In hard PZT ceramics, the local defect fields built up during the aging process can stabilize the ceramic against external stress depoling that results in a marked increase in the piezoelectric coefficient and electromechanical coupling factor in the ceramic under the stress. Although soft PZT ceramics can be easily stress depoled (losing piezoelectricity), a DC bias electric field, parallel to the original poling direction, can be employed to maintain the ceramic poling state so that the ceramic can be used at high stresses without depoling.
The properties of several piezoceramics such as soft PZT and hard PZT and relaxor ferroelectric 0.9PMN-O.1PT under uniaxial stress were characterized. It was observed that uniaxial compressive stresses have marked effect on the soft PZT, including reducing the piezoelectric coefficient and depoling the sample at relatively low stress level. On the other hand, the uniaxial compressive stress increases the piezoelectric coefficients in hard PZT. The different response to the stress between the hard and soft PZT was elucidated here. The influence of the uniaxial stress on 0.9PMN-O.1PT depends on the DC electric field applied to it. The change of the elastic compliance with uniaxial stress was also dealt with in this paper.I.
The static equilibrium conditions have been derived for piezoelectric-ceramic-polymer composite structures. Rigorous solutions are obtained for a 2-2 composite of lamellar configuration. Under a uniaxial stress or an electric field the strain profile becomes inhomogeneous due to different elastic stiffness of the two components (hard piezoelectric ceramics and soft polymer). The stress transfer between the two components is identified as due to an additional shear stress produced at the ceramic-polymer interface, and the amplification factor is defined for the enhancement of the response of the active piezoelectric ceramic resulting from this stress transfer. It is shown that this enhancement effect not only depends on the volume percentage of the active component but also on the aspect ratio of the two components.
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