Piezoceramic Fibers Research Articles

Unit cell models of piezoelectric fiber composites for numerical and analytical calculation ofeffective properties

Numerical unit cell models of 1-3 periodic composites made of piezoceramic unidirectionalcylindrical fibers embedded in a soft non-piezoelectric matrix are developed. The unit cell isused for prediction of the effective coefficients of the periodic transversely isotropicpiezoelectric cylindrical fiber composite. Special emphasis is placed on a formulation of theboundary conditions that allows the simulation of all modes of the overall deformationarising from any arbitrary combination of mechanical and electrical loading. Thenumerical approach is based on the finite element method and it allows extension tocomposites with arbitrary geometrical inclusion configurations, providing a powerfultool for fast calculation of their effective properties. For verification, the effectivecoefficients are evaluated for square and hexagonal arrangements of unidirectionalpiezoelectric cylindrical fiber composites. The results obtained from the numericaltechnique are compared with those obtained by means of the analytical asymptotichomogenization method for different volume fractions. Furthermore, the results arecompared with other analytical and numerical methods reported in the literature.

A Comparison of Dynamic Piezoactuation of Fiber-based Actuators and Conventional PZT Patches

This work aims to extend investigations of the dynamic flexural actuation of a cantilever beam to fiber-based actuators (e.g., active fiber composite (AFC) or macro-fiber composite (MFC)), which consist of a single level of unidirectionally aligned piezoceramic fibers surrounded by a polymer matrix and electrically loaded by interdigitated electrodes. The main advantage of such actuators is their poling in the same direction as the beam length, i.e., they are able to act with the piezoelectric strain constant d33 that is about two times higher than the piezoelectric strain constant d31 used in PZT patches. Modeling using the finite element method is based on the multiplication in both plane directions of a unit cell, which is taken as a fiber unit (with its matrix) within two pairs of half-electrodes of the same polarity. Modeling of the whole system is possible practically only with MFC actuators, whose fibers have a rectangular section, thus reducing the number of required finite elements. In addition to a non-uniform longitudinal free extension of the electrically loaded piezofiber-based actuator, a lateral free shearing has been calculated, which results in a non-planar deformation of the actuator. When two such MFC actuators are bonded on both sides of an aluminum cantilever beam and loaded in the antiphase mode, they conduct into all flexural resonance modes of the actuated beam, as expected. However, a slight interference by the torsion eigenmodes of the actuated beam has also been detected, which was not present in the actuation type using (leadzirconate titanate) PZT patches. The experimental validation of these FEM results first confirms the static values for free strain components of the MFC actuator depending on the loading voltage, then dynamic values regarding the eigenfrequencies, as well as the acceleration amplitudes of the MFC actuated vibrating beam.

Anisotropic Laminar Piezocomposite Actuator Incorporating Machined PMN–PT Single-crystal Fibers

The design, fabrication, and testing of a flexible, laminar, anisotropic piezoelectric composite actuator utilizing machined PMN–32%PT single-crystal fibers is presented. The device consists of a layer of rectangular single-crystal piezoelectric fibers in an epoxy matrix, packaged between interdigitated electrode polyimide films. Quasistatic freestrain measurements of the single-crystal device are compared with measurements from geometrically identical specimens incorporating polycrystalline PZT-5A and PZT-5H piezoceramic fibers. Free-strain actuation of the single-crystal actuator at low bipolar electric fields (±250 V/mm) is ≈400% greater than that of the baseline PZT-5A piezoceramic device, and ≈200% greater than that of the PZT-5H device. Free-strain actuation under high unipolar electric fields (0–4 kV/mm) is 200% of the PZT-5A baseline device, and 150% of the PZT-5H alternate piezoceramic device. Performance increases at low field are qualitatively consistent with predicted increases based on scaling the low-field d33 piezoelectric constants of the respective piezoelectric materials. High-field increases are much less than scaled d33 estimates, but appear consistent with high-field free-strain measurements reported for similar bulk single-crystal and piezoceramic compositions. Measurements of single-crystal actuator capacitance and coupling coefficient are also provided. These properties were poorly predicted using scaled bulk material dielectric and coupling coefficient data. Rule-of-mixture calculations of the effective elastic properties of the single-crystal device and estimated actuation work energy densities are also presented. Results indicate longitudinal stiffnesses significantly lower (50% less) than either piezoceramic device. This suggests that single-crystal piezocomposite actuators will be best suited to low induced-stress, high strain, and deflection applications.

Calculation of effective coefficients for piezoelectric fiber composites based on a general numerical homogenization technique

Numerical unit cell models for 1–3 periodic composites made of piezoceramic unidirectional cylindrical fibers embedded in a soft non-piezoelectric matrix are developed. The unit cell is used for prediction of the effective coefficients of the periodic transversely isotropic piezoelectric cylindrical fiber composite. Special emphasis is placed on the formulation of the boundary conditions that allows the simulation of all modes of overall deformation arising from any arbitrary combination of mechanical and electrical loading. The numerical approach is based on the finite element method (FEM) and it allows the extension to composites with arbitrary geometrical inclusion configurations, providing a powerful tool for fast calculation of their effective properties. For verification the effective coefficients are evaluated for square and hexagonal arrangements of unidirectional piezoelectric cylindrical fiber composites. The results obtained from the numerical technique are compared with those obtained by means of the analytical asymptotic homogenization method (AHM) for different fiber volume fractions.

A comprehensive numerical homogenisation technique for calculating effective coefficients of uniaxial piezoelectric fibre composites

This work deals with the modelling of periodic composites made of piezoceramic (lead zirconate-titanat) fibres embedded in a soft non-piezoelectric matrix (polymer). The goal is to predict the effective coefficients of such periodic transversely isotropic piezoelectric fibre composites by use of a representative volume element or unit cell. The solution is based on a numerical approach using finite element method (FEM). The necessary basic equations for the piezoelectric material are introduced and the special concept for definition of generalised periodic boundary conditions for the unit cell is explained. For a composite with square arrangements of cylindrical fibres the algorithm is demonstrated and the extension to other fibre arrangements is shown. For different fibre volume fractions the results are compared with analytical solutions.

Analytical development of single crystal Macro Fiber Composite actuators for active twistrotor blades

A Macro Fiber Composite (MFC) is a piezoelectric fiber composite which has aninterdigitated electrode, rectangular cross-section and unidirectional polycrystallinepiezoceramic (PZT) fibers embedded in the polymer matrix. A MFC actuator has muchhigher actuation performance and flexibility than a monolithic piezoceramic actuator.Moreover, the single crystal piezoelectric material exhibits much higher induced strainlevels, energy density and coupling than those of polycrystalline piezoceramic materials.Thus, the performance of an MFC can be improved by using single crystal piezoelectricfiber instead of polycrystalline piezoceramic fiber. This study investigates theanalytical modeling, material properties and actuation performance of an MFCusing single crystal piezoelectric material (single crystal MFC). For single crystalMFC, the mechanical properties are calculated by the classical lamination theory,and the uniform fields model (UFM) is adopted to predict piezoelectric strainconstants. In addition, the actuation performance of the single crystal MFC withthe active twist rotor blade is studied. The material properties and actuationperformance of single crystal MFC are compared with those of standard MFC.

Hysteresis behavior of ferroelectric fiber composites

The modeling of the nonlinear behavior of multiphase materials with ferroelectric phases isaccomplished via an incremental micromechanical analysis that is based on thehomogenization technique for composites with periodic microstructure. The representationof the monolithic ferroelectric material is based on recently developed nonlinearconstitutive equations. The resulting nonlinear global constitutive relations that govern thehysteresis behavior of ferroelectric composites are implemented to study the response of apolymeric matrix with embedded piezoceramic fibers. The responses of this composite to acomplete cycle of electric field which is acting in the fiber direction, in conjunction withconstant normal tensile and compressive stresses that are applied in the axial andtransverse directions, as well as applied transverse shear and axial shear stresses, areshown.

An analytical and numerical approach for calculating effective material coefficients of piezoelectric fiber composites

The present work deals with the modeling of 1–3 periodic composites made of piezoceramic (PZT) fibers embedded in a soft non-piezoelectric matrix (polymer). We especially focus on predicting the effective coefficients of periodic transversely isotropic piezoelectric fiber composites using representative volume element method (unit cell method). In this paper the focus is on square arrangements of cylindrical fibers in the composite. Two ways for calculating the effective coefficients are presented, an analytical and a numerical approach. The analytical solution is based on the asymptotic homogenization method (AHM) and for the numerical approach the finite element method (FEM) is used. Special attention is given on definition of appropriate boundary conditions for the unit cell to ensure periodicity. With the two introduced methods the effective coefficients were calculated for different fiber volume fractions. Finally the results are compared and discussed.

Micro‐Macro Modelling of Piezoelectric Fiber Composites

AbstractThe present work deals with the numerical modeling of 1‐3 periodic composites made of piezoceramic (PZT) fibers embedded in a soft non‐piezoelectric matrix. We especially focus on predicting the effective co‐efficients of the periodic transversely isotropic piezoelectric fiber composites using representative volume element method (unit cell method). The results which are obtained from the FEM technique are compared with analytical homogenization method for different volume fractions. The effective co‐efficients are obtained for rectangular and hexagonal arrangement of unidirectional piezoelectric fiber composites. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Manufacturing and Cure Kinetics Modeling for Macro Fiber Composite Actuators

The use of piezoelectric ceramic materials for structural actuation is a fairly welldeveloped practice that has found use in a wide variety of applications. However, just as advanced composites offer many benefits over traditional engineering materials for structural design, actuators that utilize the active properties of piezoelectric fibers can improve upon many of the limitations encountered with monolithic piezoceramic devices used to control structural dynamics. This paper discusses the Macro Fiber Composite (MFC) actuator, which utilizes piezoceramic fibers, for example, lead zirconate titanate (PZT), embedded in an epoxy matrix for structural actuation. An overview of the MFC assembly process is presented, followed by a cure kinetics model that describes the behavior of the thermosetting epoxy matrix. This empirical model is seen to agree closely with the experimental data.

Durability Characterization of Active Fiber Composite Actuators for Helicopter Rotor Blade Applications

Theprimary objective of this work was to characterize the long-term durability performance of the Active Fiber Composite (AFC) actuator material system for the Boeing Active Material Rotor (AMR) blade application. The AFCs were a new structural actuator system consisting of piezoceramic fibers embedded in an epoxy matrix and sandwiched between interdigitated electrodes. These actuators were integrated directly into the blade spar as active plies within the composite structure to perform structural actuation for helicopter vibration control. Therefore, it was necessary to conduct extensive electromechanical material characterization to evaluate AFCs both as actuators and as structural components of the blade. The long-term durability characterization tests designed to extract important electromechanical properties were electrical fatigue tests and mechanical fatigue tests. This paper presents the test results as well as the comprehensive testing process developed to evaluate the relevant AFC durability properties. The durability tests conducted under simulated electromechanical loading conditions expected on AFCs during the blade operation provided an invaluable insight into the behavior of the AFCs under dynamic loading environment. The results from this comprehensive durability characterization of the AFC material system supported the design and operation of the Boeing AMR blade scheduled for wind tunnel tests.

Lamb Wave Detection Using PZT and Fiber Optic Sensor

The surface mounted piezoceramic transducers and fiber optic sensor can detect signals in both symmetric and antisymmetric Lamb wave modes. Hanning windowed sine torn bursts were used for the piezoceramic transducer excitation signals. In order to overcome the difficulties in the signal processing of the simultaneous modes, the symmetric and antisymmetric modes were separated by using the two sensors bonded on the opposite surfaces at the same planer location. Spectral analyses of the separated symmetric and antisymmetric Lamb waves showed that each mode propagated with different frequency characteristics in the exciting frequency band range. In case of a fiber optic sensor, its geometric characteristics induce sensing directivity of Lamb wave. In this paper, the directivity of a fiber optic sensor was investigated using EFPI (extrinsic Fabry-Perot interferometer) sensor.

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 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.

Faraday plasma current sensor with compensation for reciprocal birefringence induced by mechanical perturbations

A Faraday fiber-optic current sensor was employed to measure the tokamak plasma current. In order to decrease the influence of mechanical perturbations on the sensor sensitivity, a two-pass optical scheme with a variable Faraday mirror at the fiber end is proposed. A decrease, by two orders of magnitude, in the influence of the linear birefringence produced by an external piezoceramic fiber modulator was experimentally observed.

OS09W0212 Health monitoring in composite structures using piezoceramic sensors and fiber optic sensors

OS09W0212 Health monitoring in composite structures using piezoceramic sensors and fiber optic sensors

A 3-D Connectivity Model for Effective Piezoelectric Properties of Yarn Composites

The purpose of this paper is to develop a 3-D connectivity model that enables better understanding, at the micro-structural level, the effect of fiber orientation, matrix properties, and inter-fiber contact on the effective piezoelectric properties of a composite consisting of a unidirectional piezoceramic fiber yarn in a polymeric matrix. It is assumed in the 3-D connectivity model that the piezoceramic fiber and matrix are connected in parallel in the fiber direction and in series transverse to the fiber direction. The poling direction is at an arbitrary angle from the fiber axis. Using these assumptions and coordinate transformation, the effective piezoelectric properties of yarn composites can be determined. It is concluded that the effective piezoelectric constants are very sensitive to the fiber orientation. There is a significant effect of the dielectric permittivity of the matrix material on the effective piezoelectric constants, and the effective piezoelectric constants obtained from the 3-D connectivity model can change dramatically depending on the non-contact and contact assumptions of the fibers.

Adaptronics as a Key Technology for Intelligent Lightweight Structures

Adaptronics is a new and highly innovative technology in mechanical engineering. The main objectives are active noise and vibration control, active form and positioning control, and health monitoring. This concept starts from the development of adaptive systems which, due to their self-regulating mechanisms, are able to self-adapt to different external conditions. This requires a system-optimized linking of sensors and actuators on the basis of new functional materials, such as piezoceramic fibers and patches with adaptive controllers. Adaptronic structures fulfill both load-bearing and actuator/sensor functions and, hence, are multifunctional. Therefore, adaptronics will become an essential prerequisite for further development of ultralight structures.

Adaptronics as a Key Technology for Intelligent Lightweight Structures

Adaptronics is a new and highly innovative technology in mechanical engineering. The main objectives are active noise and vibration control, active form and positioning control, and health monitoring. This concept starts from the development of adaptive systems which, due to their self-regulating mechanisms, are able to self-adapt to different external conditions. This requires a system-optimized linking of sensors and actuators on the basis of new functional materials, such as piezoceramic fibers and patches with adaptive controllers. Adaptronic structures fulfill both load-bearing and actuator/sensor functions and, hence, are multifunctional. Therefore, adaptronics will become an essential prerequisite for further development of ultralight structures.

A Continuous Sensor to Measure Acoustic Waves in Plates

An active fiber composite tape with segmented electrodes was modeled for use as a continuous sensor for structural health monitoring of plate structures. The material has unidirectional piezoceramic fibers with interdigital electrodes on the top and bottom surfaces and is poled in the fiber direction. The elastic response of a plate with the modeled sensor was computed in closed form at small time steps, and the coupled piezoceramic constitutive equations were solved. Wave propagation responses and the corresponding sensor voltages were computed in the simulations. The simulations indicate that the continuous sensor can detect damage to the plate based upon high frequency wave propagation characteristics. A continuous sensor comprised of monolithic piezoceramic patches was built and tested to measure simulated acoustic emissions on panel structures. The monolithic patches were used to simplify fabrication of the sensor. The sensor detected simulated acoustic emissions in a fiberglass panel using only one channel of data acquisition. The continuous sensor can potentially reduce the cost, complexity, number of channels of data acquisition, and the weight of monitoring instrumentation to a level where it becomes practical to perform health monitoring on large structures.

Processing and properties of 15–70 MHz 1–3 PZT fiber/polymer composites

This paper reports on the fabrication and characterization of fine scale piezoelectric composites with 1–3 connectivity using fibers derived from a metal alkoxide sol-gel process. Using this technique, pure thickness mode resonance for this type of composite has been increased from 15 MHz up to 70 MHz by maintaining pillar aspect ratio requirements. Piezoceramic fibers of Nb or La modified lead zirconate titanate (PZT) were produced with final diameters ranging from 15 to 50 μm.Composites having 1–3 connectivity were produced using the fibers as pillars. Composites could be fabricated with volume fractions from 10 to 45% allowing tailoring of both the dielectric constant and acoustic impedance without degrading coupling. Dielectric constant, polarization and coercive field values varied slightly from bulk values due to clamping by the polymer matrix, increasing as the fiber diameter decreased. Composites with resonance frequencies ranging from 15 to 70 MHz were studied. The thickness dependence of the properties gave indications to radial mode/thickness mode interactions at pillar aspect ratios near 1.7 to 1 thickness to diameter. Coupling coefficients (kt) from 58% to 73% with mechanical quality factors <15 were detected.