A simplified geometrically nonlinear approach to the analysis of the Moonie actuator

A simplified model for the analysis of ceramic-metal composite actuators has been developed. The model consists of two beams symmetrically arranged about the actuator neutral axis and attached to the actuator at the ends with an offset (Moonie shape). When an electrical field is applied such that the actuator will contract, a compressive force and a moment, due to the beams' eccentricity, are applied to the beams. This loading will produce the desired deformation of the beams. Using the beam-column theory and the appropriate boundary conditions, it is possible to derive a set of equations relating the free induced strain (/spl Lambda/) of the actuator to the midspan displacement of the beams. Nonlinear terms which allow for the interaction of the developed in-plane force with the out-of-plane displacements have been included in the equations. Applying these equations to a particular case, it is found that the offset distance of the beams has a large impact on the behavior of the system. An increase in the offset distance produces both a suitable augmentation of the moment applied to the beams and an undesirable diminution of the midspan displacement for a given free induced strain. From these two positive anti negative effects, an optimum value of the offset distance is found. Additionally, it is found that with a transverse load applied to the beams, the optimum offset distance is further increased. Furthermore, the nonlinear terms in the governing equations are found to have only a small impact on the system in the free induced strain range of typical actuator materials, i.e., /spl Lambda//spl les/1500 /spl mu/strain. Thus, in conclusion, the effect of the offset distance of the beams to the actuator is the primary design criteria when maximum displacement of the actuator is required.<
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