Dynamic Elastic-Axis Shifting: An Important Enhancement of Piezoelectric Postbuckled Precompressed Actuators

摘要

A new actuator arrangement that is designed to protect postbuckled precompressed elements is presented. This actuator arrangement uses through-the-thickness dynamic elastic-axis shifting to protect the convex face of postbuckled precompressed bending actuators at high curvatures, which is important, as postbuckled precompressed elements have been shown to possess simultaneous blocked force and deflection-level increases up to four times those of conventional piezoelectric actuators. This innovation allows this new generation of high-performance piezoelectric actuators to be more robust and less sensitive to tensile failure and depoling on the convex face. As the curvature increases, the elastic axis of the element is shifted dynamically from the center of the laminate through the thickness toward or beyond the convex face of the actuator core, thereby relieving the convex face from tensile loads and effectively stiffening the entire laminate. This dynamic elastic-axis shifting is achieved by adding a facing sheet to the laminate that only carries tensile loads at high curvatures. A silicone spacer between the facing sheet and the actuator element increases the moment of inertia of the facing sheet and increases the effectiveness of the facing sheet. This paper presents an investigation into the effects of the facing-sheet/spacer arrangement on the postbuckled precompressed performance. Analytical models are presented that predict the end rotation at which facing-sheet engagement occurs. Experimental tests were done on a variety of spacer and facing-sheet geometries, demonstrating the dynamic elastic-axis shifting principle for each of the configurations. Deflection testing of dynamic elastic-axis-shifting modified postbuckled precompressed beams was carried out through end rotations in excess of 10° on 10-cm-long piezoelectric benders with good correlation between theory and experiment. It is shown that with a weight penalty of only 12% with respect to the baseline actuator element, the robustness of the postbuckled precompressed beam actuator elements can be significantly increased.