Composite Materials Research Progress

272 Yasuhide Shindo and Fumio Narita
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Figure 16. Tip deflection versus voltage for disk composite bending actuator.
Fig. 15 shows the similar results for the shear stress distribution σzr. A singularity in the
interface shear stress also develops at the circular electrode tip. Note that for the C-91 + /C-
91 + disk bending actuator, since the problem is unsymmetrical to the r-axis, the shear stress
does not become zero along the whole r-axis. Fig.16 gives a plot of the tip deflection uz at
r =10mm and z =0mm with applied voltage V0, based on work, for C-91 + /C-91 + disk
bending actuator with b =8and 10 mm. The curve rises steeply at first when the voltage is
increased from zero. The tip deflection then gradually levels off when the voltage reaches
about 220 V, because of switching in the lower layer (see Fig. 13). A similar phenomenon
can be observed for negative voltage. The bending actuator for b =10mm exhibits higher
deflection.
5. Conclusions
The electromechanical field distributionsin the neighborhood of the electrodes in piezoelectric
composites were investigated. Two criteria for polarization switching in piezoelectric
materials were incorporated into a finite element procedure. The results indicated that high
values of electromechanical fields cause the localized polarization switching near the electrode
tip, and the strain vs electric field curves show the non-linear behavior. Also, the
size of the switching zone in the piezoelectric composites increased with increasing electric
fields. As a remark, we note that this study may be useful in designing advanced piezoelectric
composite actuators.