A SIMPLIFIED GEOMETRICALLY NONLINEAR APPROACH TO THE ANALYSIS OF THE MOONIE ACTUATOR

A simplified model for the analysis of ceramic-metal composite actuato rs has been developed, The model consists of two beams symmetrically a rranged about the actuator neutral axis and attached to the actuator a t 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, Th is loading will produce the desired deformation of the beams, Using th e beam-column theory and the appropriate boundary conditions, it is po ssible to derive a set of equations relating the free induced strain ( Lambda) of the actuator to the midspan displacement of the beams. Nonl inear terms which allow for the interaction of the developed in-plane force with the out-of plane displacements have been included in the eq uations. Applying these equations to a particular case, it is found th at 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 sui table augmentation of the moment applied to the beams and an undesirab le diminution of the midspan displacement for a given free induced str ain, From these two positive and negative effects, an optimum value of the offset distance is found. Additionally, it is found that with a t ransverse load applied to the beams, the optimum offset distance is fu rther increased, Furthermore, the nonlinear terms in the governing equ ations are found to have only a small impact on the system in the free induced strain range of typical actuator materials, i.e., Lambda less than or equal to 1500 mu strain. Thus, in conclusion, the effect of t he offset distance of the beams to the actuator is the primary design criteria when maximum displacement of the actuator is required.