An Analysis of Composite Piezoelectric Actuators Incorporating Nonlinear Material Behavior

Piezoelectric actuators of various composite designs have been proposed during the last few years including extension and shear bimorphs, tubular composites and multilayered actuators. These designs exploit the ability to define the actuation direction by varying the alignment between poling direction and applied electric field. Considerable research effort has been put to accurately model these actuators in order to attain predictive capability. The common factor in almost all of these studies is the assumption that the poled material behaves linearly under applied electric field. However, this assumption may only be accurate for the limited case of a homogenous actuator under relatively unconstrained environment, such as that of simply supported boundary conditions. In the case of composite structures, the actuation can potentially be restricted by non-actuating constituents resulting in multi-dimensional loading states, which may cause domain switching. The same argument can be made for most boundary conditions that are imposed in practical applications, such as when the actuator is clamped or fixed. Another point of concern is the presence of discontinuities and minor defects in the actuator. Both of these would promote non-uniform electric field causing domain switching, and hence, unexpected actuator output. Unless proven otherwise, these concerns directly affect the credibility of life cycle estimates based upon linear models. In this paper linear and nonlinear material models will be used to determine actuator performance using an established constitutive model in a commercial finite element code. Actuator performance for both material cases will be calculated and compared with existing analytical predictions under the same set of boundary conditions.