A Comparison of the Deformations of Various Piezoceramic Actuators

Presented are the predicted manufactured shapes and actuated shape changes of metal-based THUNDERTM-like actuators and fiber-reinforced-polymer-based LIPCA-C1-and LIPCA-C2-like actuators. As these actuators, which are laminated in nature, are manufactured flat at an elevated temperature and then cooled for use, they deform out of plane as they cool, resulting in residual curvatures. The development of the residual curvatures are predicted with a 23-term Rayleigh-Ritz model based on energy principles. Because of the large out-of-plane deformations due to cooling, geometrically nonlinear effects, in the sense of von Karman, are included. Actuated curvatures due to activation of the piezoceramic material are also predicted. The behaviors of plate and beam-like actuator geometries over a range of sidelength-to-thickness ratios are investigated. Finite element results for selected geometries are presented for comparison with the 23-term model. The results show that geometrically nonlinear effects are quite strong for THUNDER and LIPCA-C2 plate-like actuators, resulting in the potential for more than one cooled shape for THUNDER actuators and of a sudden change in the actuated shape, referred to here as snap-through, for LIPCA-C2 actuators. For the LIPCA-C1 actuators, and the beam-like geometries of the other two actuators, geometrically nonlinear effects are not as strong. Residual stress predictions within the cooled and activated actuators are also presented. Though the actuators considered are specific in design, the results can be interpreted more generally and point to the fact that a wide range of behaviors can be expected from geometrically nonlinear effects interacting with variations in materials (i.e., metals vs. fiber-reinforced materials) and geometry (i.e., platelike vs. beam-like and sidelength-to-thickness ratio).