Piezoceramic Hollow Fiber Active Composites

While active fiber composites (AFC) based upon solid cross-section piezoelectric fibers are very useful for anisotropic activation of composites, they require high voltages and are constrained to non-conductive matrix materials. AFC’s based upon hollow cross-section piezoelectric fibers have shown promise to lower operating voltages and broaden the choice of possible matrix materials. This paper presents an investigation of the key design parameters for hollow piezoelectric fibers (matrix/fiber Young’s moduli, aspect ratio of the individual fibers, and the overall active composite volume fraction) and their effect on the performance, manufacturing and reliability of active fiber composites. Because the ultimate objective in utilizing active composites centers on their ability to deform, an analysis was conducted on existing fiber and lamina strain/electric field models to identify optimal parameter values and determine limitations via an embedment stress model. Fabrication of the fibers has a clear impact on these factors. To assess this, standard machinery inspection criteria was used to evaluate fibers, manufactured through microfabrication by coextrusion (MFCX), with respect to their geometric (cross-sectional ovality, eccentricity, straightness) and material (density, porosity, piezoelectric properties, Young’s modulus) properties. These studies indicated that there are circumstances under which low aspect ratio (thin walled) fibers will be optimal, but clearly, reliability issues will arise. Unfortunately, little data exists on reliability of either hollow or solid piezoelectric fibers. To identify the primary failure mechanism, ultimate strength, strain-to-failure and interfacial shear strength were examined using three types of experimental tests: 1) tensile strain-to-failure, 2) single fiber fragmentation, and 3) single fiber indentation. From this work, it is clear there will always be design trade-offs present and it is important to consider performance, fabrication, and reliability Copyright  2002 The American Institute of Aeronautics and Astronautics Inc. All rights reserved. issues simultaneously in the design of hollow piezoelectric fiber active composites.