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This paper introduces the Dual Electro/Piezo Property (DEPP) gradient technique via Micro-Fabrication through Co-eXtrusion (MFCX) which pairs a high displacement lead zirconate titanate (PZT) piezoceramic with a high permittivity barium titanate (BT) dielectric. By grading with this material combination spatially across an actuator, the electric field is concentrated in the more active region for improved efficiency, higher displacements, and complex motions. To aid in synthesis and analysis of any gradient profile, compositional maps are provided for key material properties (density, stiffness, permittivity, and piezoelectric coefficients). The DEPP technique was validated, independent of the MFCX process, by powder pressing a conventional bimodal gradient beam which demonstrated through experiments high displacement capabilities at lower driving potentials than comparable functionally graded piezoceramic actuators. For more complex gradients, the MFCX process was adapted to the DEPP gradient technique and illustrated by the fabrication of a linearly graded prototype whose monolithic nature and gradual material variation significantly reduces internal stresses, improves reliability, and extends service lifetime. [ABSTRACT FROM AUTHOR]

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 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 modulus ratio, 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, optimal parameter values were identified employing analytical fiber and lamina strain/electric field models and limitations were determined utilizing an analytical embedment stress model. These models assume perfect fibers; as such, practical fabrication of the fibers will have a clear impact on these parameters. To assess this, standard machinery inspection criteria were 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 indicate that there are circumstances under which low aspect ratio (thin walled) fibers will be optimal, but clearly, reliability issues will arise. Unfortunately, little data exist on reliability of either hollow or solid piezoelectric fibers. To identify the primary failure mechanism of both solid and hollow fibers, 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 series of work, it is apparent there will always be design trade-offs present and it is important to consider performance, fabrication, and reliability issues simultaneously in the design of hollow piezoelectric fiber active composites. [Copyright &y& Elsevier]