Piezoelectric actuation mechanisms for intelligent sandwich structures

Surface-mounted piezoelectric materials poled in the same direction as the applied electric field are known to induce membrane strains only. This could be seen as their conventional extension actuation mechanism. However, when piezoelectric materials are constrained and poled perpendicularly to the applied electric field, they act through their shear modes. This is the newly defined shear actuation mechanism. The present paper compares both mechanisms with the help of an adaptive sandwich beam finite element, with either active surface layers (for the extension mechanism) or active core (for the shear mechanism). Segmented configurations are studied for cantilever beams. Deflection, stress and vibration characteristics are compared for various parameters (structure/actuator stiffness and thickness ratios, actuator position and length). The shear actuation mechanism is found to present several promising features for brittle piezoceramics' use. In particular, it was found that the shear actuation mechanism is more efficient than the extension mechanism for stiff structures and thick piezoelectric actuators.