Functionally gradient piezoelectric bimorph type actuator

A new type of piezoelectric actuator has been developed by combining two piezoelectric Functionally Gradient Material (FGM) composite laminates into a bimorph to produce an actuator with large out of plane displacements while having reduced mid-plane stresses. This combination of high displacement with reduced stress keeps the benefit of the bimorph while reducing one of its drawbacks. These properties are varied symmetrically about the mid-plane of the actuator with the entire actuator being poled in one direction through the thickness of the device. These devices are produced by stacking individual layers of piezoelectric fibers in a modified epoxy matrix with varying fiber volume fraction from layer to layer thereby leading to varying material properties through the thickness of the composite. The focus of this work has been to use the finite element method to first predict the material properties for individual piezoelectric fiber based layers using a symmetrical unit cell model, which allowed the inter-layer (thickness) and intra-layer (width) volume fractions to be varied independently reflecting the rectangular packing of fibers present in the actual devices. And, then to predict the behavior of the actual composite devices using these predicted properties.