Composite Materials Research Progress

MV/m.
Eletromechanical Field Concentrations and Polarization Switching... 269
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Figure 11. Displacement versus voltage for disk composite tension actuator.
the circular electrode tip, the normal stress at the interface is singular, and the stress ahead of
the circular electrode tip is tensile, while the stress behind the electrode tip is compressive.
The normal stress, apart from the interface, near the electrode tip has smaller value than the
interface stress. Fig. 10 gives the distribution of the shear stress σzr as a function of r at
z =0.01 and 0.2 mm for the same disk tension actuator. The magnitudes of the shear stress
increase toward the circular electrode tip as is expected. Fig. 11 shows the predictions of
displacement uz at r =0mm and z =1mm as a function of applied voltage V0, based
on work, for b =8and 10 mm. There is a small influence of the electrode radius on the
displacement versus voltage curves.
Fig. 12 shows the computed strain εrr of C-91 + /C-91 + disk bending actuator corresponding
to Fig. 8. The negative electric field increases the compressive strain, similar to
C-91 + /C-91 − disk tension actuator. After the electric field reaches about −0.25 MV/m,
polarization switching leads to a decrease in the compressive strain. As the electric field
E0 continues to be reduced, the strain becomes tensile. On the other hand, as the positive
electric field is increased, the strain near the electrode tip increases gradually due to the
piezoelectric effect and then sharply increases as switching occurs due to electromechanical
field concentrations. Little difference is observed between two criteria. Fig. 13 shows
the predicted switching zones, based on work, near the circular electrode tip. As the electric
fields increase, the area of the switched region grows. Fig. 14 shows the normal stress
distribution σzz as a function of r at z =0and 0.2 mm for C-91 + /C-91 + disk bending
actuator with b =8mm. The interface normal stress of the disk bending actuator is singular
at the circular electrode tip, similar to the disk tension actuator. The stress ahead of
the circular electrode tip is tensile, while the stress behind the circular electrode tip changes
from tensile to compressive in the neighborhood of the electrode tip.
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