Electroactive fibers of preferred macro crystalline orientation and ultimately single crystal structure are goals of the research discussed in this paper. Four compositions are under evaluation; lead magnesium niobate- lead titanate solid solution, PMN-31PT, an incongruently melting near-morphotropic phase boundary piezoelectric composition; PMN-10PT, an electrostrictor composition; and two lead free compositions in the sodium bismuth titanate- barium titanate solid solution, NbiT-BaT, family, both congruently melting, one electrostrictor and one piezoelectric. The efficacy of seed crystals in stimulating oriented crystal growth is being evaluated in the lead-based PMN-31PT system. Sub-micron reactive precursor powders of high chemical potential are being evaluated as matrix material. Direct fiber and ribbon extrusion have been shown to orient high chemical potential are being evaluated as matrix material. Direct fiber and ribbon extrusion have been shown to orient high chemical potential are being evaluated as matrix material. Direct fiber and ribbon extrusion have been shown to orient prismatic, needle and platelet shaped seed crystals. Extrusion orifice, seed and initial matrix particle size have not influenced the degree of seed orientation within the tested bounds of our experimental parameters. Non-equilibrium sintering conditions near the melting points of all four compositions noted above will be used to generate exaggerated grain growth under seeded and self-seeding conditions. In the PMN-31PT system, an as yet uncharacterized melt phase appears to stimulate rapid crystal growth, the orientation of which shall be determined by x-ray back reflection Laue methods. Analyses of fiber composition and grain orientation are ongoing. Results to-date will be reported. Analyses of fiber quality and performance, measured using single fiber P-E loop testing, are presented. Loops of sufficient quality to warrant fiber evaluation in active fiber composite packs have been measured. Progress toward program goals is summarized in this paper.

We have developed mK-stabilized cell having a fine temperature stability better than 1 mK which can be used to investigate phase transitions in solids not only by making calorimetric measurements but also, with the heat flux sensor, by making other kinds of measurements at an extremely slow rate of temperature change both on heating and cooling. Precise data with a very fine temperature resolution can be obtained by the measurements. It was applied to the measurements for the cubic-to- tetragonal transition at 408 K in BaTiO₃. A single crystal sample prepared by the top-seeded solution growth method was used and no external field was applied across the sample previously. Dielectric constant and displacement currents were measured as well as calorimetric properties. It was found that BaTiO₃ does not undergo the transition in a single step on cooling but in a multi-step with several thermal anomalies in a temperature range of 0.5 K. The first step corresponds to the process with a large change of dielectric constant but without any displacement currents, while the last step is accompanied by the displacement currents with an appreciably small dielectric change. Flow of the displacement currents implies the loss of the center- of-symmetry. The results obtained may cast light into the elucidation of the transition process.

Phase transitions in CsPbCl₃ have been investigated on a single crystal by X-ray precision method at temperatures ranging from 340 to 90 K. On cooling from room temperature, it was found that abrupt intensity increases of superlattice reflections, X; (0,k,1+1/2)_c and r;)h+1/2,k+1/2,1+1/2)_c in the cubic Brilloun zone, were observed at about 265 K and 200 K, respectively. At 200 K, although accompanied with conspicuous splitting of the hkl Bragg spots along [010]_c^* direction of the cubic reciprocal lattice, weak spots are still observed without splitting. These observations suggest that the crystal undergoes from the room temperature phase to an intermediate low-temperature phase beginning at 265 K and further transforms at 200 K, successively. Coexistence of a tetragonal and a nonoclinic forms is recognized in the lowest temperature phase below 200 K. The results suggest that a new transition series, 320-265-200 K, starting from the multi-step transition at 320 K exists.

Low-density piezoelectric aluminosilicate ceramics were prepared by sol-gel technology. In order to reinforce the fragile aluminosilicate aerogels, the inorganic component was mixed with organic polymers (polyacrylic acid, polyvinyl acetate, polydimethylsiloxane) during the gelling process. The strength of the composite gels increases two- or threefold, the piezoelectricity of the composite gels changes variously depending on the organic polymers. The aerogel containing polyvinyl acetate shows negligible piezoelectricity. The use of polydimethylsiloxane decreases the piezoelectricity by 50%; polyacrylic acid increases it by 100%. The structure and the Al incorporation have strong effects on the piezoelectricity. The chemical structures of the composite gels were investigated by means of ²⁷Al and ²⁹Si MAS NMR. Except for the gel samples with PDMS, the porosity of hybrid gels diminishes.

PZN single crystals are currently under development as actuator materials. They offer high strain and high coupling constants, but the moduli are considerably lower than PZT. Obtaining high energy densities in actuator applications requires that they be driven at high field levels. To accomplish this reliably will involve careful specimen preparation, proper compressive pre-load, and designs that avoid electric field driven fatigue crack growth. This work presents observations of fatigue crack growth under bipolar electric cycling. The crack growth in PZN single crystal is different from that in polycrystalline ceramics.

R-curves were measured for ferroelectric ceramic lead zirconate titanate (PZT) with two different grain sizes using the surface crack in flexure technique. Larger grain size resulted in a higher plateau value of the R-curve. This was consistent with the larger amount of ferroelastic switching observed from the stress/strain curve.

Sensors and actuators based on piezoelectric ceramics are finding an increasingly large variety of applications under a very wide range of environmental conditions and applied signals. Some actuator applications require the piezoelectric materials to support large mechanical loads and produce high strain output. In order to accomplish this requirement of higher strains, large electric fields must be applied. This results in a significant non-linear behavior and hence affects the performance of the material. It is therefore important to understand the behavior and properties of these materials over a large range of temperature, frequency and applied electric fields and mechanical stresses. We have measured some of the dielectric, elastic and piezoelectric constants of soft (EC-65, EC-76) and hard (EC-64, EC-69) lead zirconate titanate (PZT) piezoelectric ceramics, manufactured by EDO Ceramics, as a function of temperature, frequency, applied field and applied stress. We have also determined the dependence of the piezoelectric constants on an applied DC bias voltage or stress. The time dependence of the piezoelectric response in the piezoelectric ceramics has also been studied. A summary of the results will be presented. Most of these results can be understood on the basis of the extrinsic contributions to the piezoelectric response that arises from the existence of domains in the material.

Piezoelectric single crystals of lead magnesium niobate in solid solution with lead titanate have generated great interest in the Navy sonar community because of the potential they offer for enhanced transducer performance. Two material properties, in particular, make the piezoelectric single crystals unique; their high 33-mode coupling factor and their low short circuit Young's modulus. Measurements of the large signal electromechanical and mechanical properties on single crystal samples are presented in this paper. These measurements elucidate the behavior of piezoelectric single crystals, including the effect of bias field on the Young's modulus. The ramifications of the measured material properties on transducer design are also discussed.

Polarization and longitudinal strain of the commercial soft PZT piezoceramic PIC151 were measured as a function of amplitude and frequency of an AC electric field. The range of frequencies considered was selected in the quasi-static range from 0.01Hz to 1.0 Hz. The electric field was selected as triangular loading. Besides the standard hysteresis loops for polarization (P) and strain (S) versus electric field (E), strain versus polarization curves (S-P curves) were plotted in separate diagrams. It was shown that both polarization and strain were frequency dependent. The coercive field increased with the loading frequency. Furthermore, a significant hysteresis was observed for S-P curves at a loading frequency below 1Hz. At a frequency of 1Hz, however, the S-P plots were nearly close to an idealized parabolic curve without hysteresis. A tentative explanation shall be given for these observations in terms of the rate effects of the domain switching process.

The large signal performance of electrostrictive materials, such as lead magnesium niobate-lead titanate (PMN-PT), is of critical importance to sonar transducer and actuator designers. However, obtaining these large signal parameters properly, particularly under compressive prestress, is an expensive and time-consuming enterprise. The complexity of these measurements, therefore, precludes them as a method for quickly and easily screening materials for their potential as high power materials. Traditionally, resonance measurements, which otherwise are relatively simple to perform, have been used for screening purposes, but they suffer from the drawback that the material parameters obtained are at the incorrect frequency and under no prestress. Furthermore, it was unclear what significance the results of resonance measurements for nonlinear materials such as electrostrictors had. It has recently been suggested that dc biased resonance measurements on electrostrictive ceramics would be an accurate predictor of the coupling factor and optimum bias point. In this paper, dc biased resonance measurements on three different PMN-PT formulations, with varying dielectric maximum temperatures, will be analyzed to determine which composition has the highest predicted coupling factor. This prediction will be compared with large signal quasistatic measurements conducted on NAVSEA Division Newport's SDECS (Stress-dependent Electromechanical Characterization System). The predictive ability of the resonance measurements will also be analyzed as a function of temperature normalized with respect to the dielectric maximum temperature.

A framework to calculate the spontaneous strain and polarization of a polycrystalline ferroelectric is presented, and various applications are discussed.

The effect of crystallographic texture on the electroelastic moduli of piezoelectric polycrystals has been studied using micromechanical modeling that makes use of the uniform field concept. An orientational averaging scheme has been developed for textured piezoelectric polycrystals, which, when combined with the conventional self-consistent approach, provides an estimate of the effective electroelastic moduli in terms of texture. In the special situation where the polycrystal exhibits a fiber texture, a class of uniform fields exist under certain crystal symmetries, so that the effective electroelastic moduli can be determined exactly. This is confirmed by the coincidence of the corresponding upper and lower bounds. Numerical results are presented for both cases and compared to known theoretical predictions where possible.

Single crystal piezoelectrics based on xPb(Zn_1/3Nb_2/3)O₃-(1-x)- PbTiO₃ and xPb(Mg_1/3Nb_2/3)O₃-(1- x)PbTiO₃ show great promise for dramatically improving the performance of medical ultrasound transducers, sonar transducers, active flow control actuators, high strain energy density stack actuators, and microactuators. Improvements in crystal growth and manufacturing are yielding large numbers of crystals for device performance evaluations. Property variations have been minimized by identifying the sources of variations and designing manufacturing processes to eliminate property-degrading defects from the final components. Crystal size increases and cost reductions have resulted from replacing flux grown PZN-PT with PMN-PT crystals produced by the Bridgman method. Finally, low crystal stiffness has been shown to not be a hindrance in maintaining high properties under compressive prestress or in packaged devices such as epoxy bonded stack actuators.

Thin film electro-optic materials have been synthesized by a novel electrostatic self-assembly (ESA) method. This method allows the molecular-level, layer-by-layer formation of multilayer thin and thick films of alternating anionic and cationic molecules and other materials. We have found that during the adsorption of dipolar molecules from solution to form a single molecular layer, the dipoles align themselves. In a multilayered material, this leads to multiple functionalities that require a noncentrosymmetric molecular structure, such as active optical properties and piezoelectric behavior. Such properties are usually achieved in other materials by electric field poling. In this paper, we describe the precursor molecular chemistries that we have developed to make electro-optic thin films by this method, how the films are formed, the resulting molecular orientation within the film, and measured electro- optic coefficients to date.

Micro-Raman study in the temperature range of 70-575 K was performed to investigate the overlap of the basic phase transitions in barium titanate ceramics and single crystals of low Zr concentration. The possibilities of stress and grain size effects that are crucial for the optimization and reproducibility of the property coefficients were ruled out in these ceramics considering the Raman mode frequencies. The tetragonal to cubic transition temperature is found to decrease by increasing Zr-content. The orthorhombic to tetragonal transition temperature that increases with an initial increase in Zr-content merges with tetragonal-cubic transition for x>=0.15 compositions. The merging of phase transitions in these compositions is supported by the temperature dependent dielectric measurements.

It is well known that many common ferroelectric materials are also ferroelastic, thus the nonlinear behavior of these materials, as governed by domain motion, is highly affected by stress, as well as electric field. The combined influence of stress and electric field on domain motion and the electrostrictive response of ferroelectric single crystals is investigated. Experiments are performed on (001) and (100) oriented single crystals of barium titanate under combined electro-mechanical loading. The crystal is exposed to a constant compressive stress and an oscillating electric field along the [001] direction. Global deformation and polarization are measured as a function of electric field at different values of compressive stress. The use of semi-transparent electrodes and transmitted illumination allow in situ, real-time microscopic observations of domain motion using a long working-distance, polarizing microscope. The combined electro-mechanical loading results in a cycle of stress and electric field induced 90-degree domain switching. The magnitude of the global deformation increases with stress, with maximum steady state actuation strain of 0.57%.

In piezoceramic actuators normally a linear behavior is observed if the excitation is done by a weak electric field. In this paper, however, it is shown that if the system is excited near resonance even for a weak electric field strong nonlinearities may occur. As an example a piezoceramic transformer is investigated. The transformer is simulated using linear constitutive equations. For a very low excitation voltage the simulated results agree well with experimental results. For a moderate excitation voltage the experiments show that linear theory cannot describe all results and nonlinear constitutive equations have to be used.

This paper will present powder metallurgical methods for producing porous NiTi from elemental powders of 50at% Ni and 50at% Ti using a sintering approach in a high pressure environment. Different pore sizes and volume fractions of NiTi SMAs are fabricated and characterized in terms of composition and phase transformation characteristics using calorimetric measurements. Quasi-static and dynamic loading experiments are conducted on samples produced with the presented methodology and their shape recovery and energy absorption characteristics are measured during the forward and reverse phase transformation and detwinning. A micromechanical averaging method for modeling the behavior of porous SMAs is presented. Correlation of experimental results with theoretical predictions of the micromechanical method for the case of quasi-static loading is discussed.

Very large DC field-induced strains ((epsilon) approximately equals 6%) have been reported for Ni-Mn-Ga single-crystal ferromagnetic shape memory alloys (FSMAs) at room temperature. Described here is an AC test system that provides a dynamic bias stress to an FSMA sample. The low- frequency (epsilon) -H curves show a stress dependence consistent with the DC results, i.e. the maximum output strain peaks for a bias stress of order 1.4 Mpa. The AC (epsilon) -H hysteresis at sub-optimal bias stress can be considerably smaller than that for DC actuation. A thermodynamic model of field-induced twin-boundary motion is expanded to include external stress, threshold field and hysteresis in the twin boundary motion. Twin-boundary motion is driven by the Zeeman energy difference across the domain wall, 2M_sH, in the high anisotropy limit and is suppressed by domain magnetization rotation in the weak anisotropy limit. The magnitude of the threshold field and hysteresis can be obtained from features on mechanical stress-versus-strain curves. The field dependence and stress dependence of the AC strain are reasonably well accounted for by the model.

Tb_1-xDy_xZn(01-xDy_x alloys exist in the hexagonal phase, with the c-axis extremely hard, whereas for Tb_1-xDy_xFe₂, a cubic Laves phase alloy, very hard <111> axes can be changed to very hard <100> axes by increasing x from 0 to 1. (In fact, the existence of a near zero magnetic anisotropy by the proper choice of x is the origin of the well-known Terfenol-D alloys, Tb_1-xDy_xFe₂). The Tb$1-x)Dy_xZn system discussed here is particularly attractive because of the simplicity of its crystal structure (CsCl), its relatively high Curie temperatures (for rare earth alloys), and the existence of a large (uv0) phase for T < 50K. A summary of some of the important properties of these three alloy systems is given in Table I. In all these systems, at least one of the magnetostriction constraints is very large.

This paper describes magneto-thermo-mechanical characterization of magnetostrictive composites. The purpose of this study is to evaluate the behavior of magnetostrictive composites under combined magnetic, thermal and mechanical loading, and to determine fundamental properties used for design of actuator and sensor systems that incorporate these materials. Currently the composites are being used in sonar transducers. The magnetostrictive composite contains Terfenol-D (Tb_0.3Dy_0.7Fe₂) particulate embedded into an epoxy binder. Composite form is used due to the relative brittleness and limited operational frequencies of monolithic Terfenol-D. Two different tests were performed both at room temperature and under thermal loading: 1) constant magnetic field with cyclically varying load around a bias load and 2) constant pre-load with varying magnetic field. Testing was performed on five different volume fraction composites, namely, 10%, 20%, 30%, 40% and 50%. Parameters that were evaluated include strain output, magnetic field, magnetization and elastic modulus. Results for the constant magnetic field tests indicate that modulus generally increases with increasing volume fraction and increasing magnetic field. However, for low fields, an initial dip is noticed in modulus (i.e. (Delta) E effect) attributed to domains becoming more mobile at lower magnetic field levels. Results also indicate an increase in modulus with decrease in temperature. Results for the constant load test indicate a strong dependence of strain output on applied pre-stress. Results indicate that max strain peaks at a certain value of the pre-stress and then decreases for increasing pre-stress. Results also indicate that strain output peaks between 0 degree(s)C and +10 degree(s)C and that strain generally increases with increasing volume fraction.

Terfenol-D particulate composites have been fabricated with and without a preferred crystal orientation of the particles. A 25% volume fraction polymer matrix composite was fabricated in a magnetic field using geometric anisotropy to orient needle shaped particles with long axis [112] orientation along the length of the composite. Results demonstrate that the magnetostriction of a [112] oriented particle composite saturates near 1600 ppm. This is a significant increase when compared to composites without preferential orientation (1200 ppm). The oriented particle composite exhibits the largest reported magnetostriction for a particulate composite material. The magnetization-strain measurements indicate that the strain in the oriented composite is proportional to the (lambda) ₁₁₂ saturation magnetostriction while the non-oriented composite is proportional to the polycrystalline saturation magnetostriction, (lambda) _pc. In addition, the fields necessary for equivalent magnetostriction in the oriented particle composite are reduced when compared to the non-oriented composite, though both require higher fields than commercially available monolithic Terfenol-D.

The present experimental effort characterizes the development of damage in two different forms of experimental magnetostrictive composite material. This effort is intended to identify the various forms of damage mechanisms operating in the two very different materials, and to identify how the development of fine scale damage influences the overall magnetostrictive behavior and performance. Optical examination of as-magneto-strain cycled Terfenol-D particle actuated epoxy matrix composite material strongly suggests the following primary damage processes, particle fracture under cyclic internal stress, severe degradation of the particle to epoxy matrix interfacial bond, and ultimate sample failure by matrix crack coalescence leading to complete granulation.

Magnetically controlled shape memory (MSM) materials are considered now as a potential candidate for a new class of actuators and sensors. Magnetic and mechanical properties of two NiMnGa alloys with different thermally induced martensitic phases have been studied. Five-layered tetragonal martensite (c/a=0.94) in the first alloy is ferromagnetic with easy axis of magnetization. This martensite has low twinning stresses (approximately 2 MPa) and shows a giant magnetic field-induced strain. Non-modulated tetragonal martensite (c/a=1.20) in the second alloy is ferromagnetic with easy plain of magnetization. The absolute value of the magnetic anisotropy constant is approximately twice time higher in the second alloy compare to the first one. After mechanical training of the second alloy, stress at most 15 MPa is enough to produce approximately 19 % strain realized by twin boundary movement. Experimental data and theoretical considerations show, however, that in order to observe a giant magnetic field-induced strain in the second alloy the twinning stresses should be lower.

Present publication gives a detailed report about the experimental results obtained concerning the effect of external constant stress on the magnetic field controlled strain response during the cyclic change of the magnetic field. Simultaneously we represent a brief overview of the most important structural and magneto-mechanical properties of Ni₄₈Mn₃₀Ga₂₂ - family magnetic shape memory alloys. We also discuss the physical mechanism of this effect using our last model developments.

Shape memory alloys (SMAs) offer a unique combination of novel properties, such as shape memory effect, super- elasticity, biocompatibility and high damping capacity, and thin film SMAs have the potential to become a primary actuating mechanism for micro-actuators. In this study, TiNiCu films were successfully prepared by mix sputtering of a Ti₅₅Ni₄₅ target with a separated Cu target. Crystalline structure, residual stress and phase transformation properties of the TiNiCu films were investigated using X-ray diffraction (XRD), differential scanning calorimeter (DSC), and curvature measurement methods. Effects of the processing parameters on the film composition, phase transformation and shape-memory effects were analyzed. Effects of the processing parameters on the film composition, phase transformation and shape-memory effects were analyzed. Results showed that films prepared at high Ar gas pressure exhibited a columnar structure, while films deposited at a low Ar gas pressure showed smooth and featureless structure. Chemical composition of TiNiCu thin films was dependent on the DC power of copper target. DSC, XRD and curvature measurement revealed clearly the martensitic transformation of the deposited TiNiCu films. When the freestanding film was heated and cooled, a two-way shape memory effect can be clearly observed.

This paper presents an experimental investigation into the damping characteristics of piezoelectric ceramic PZT-5H. The material is subjected to cyclic uniaxial compressive stress (up to 200 MPa) at a constant electric field bias (from 0 to 2 MV/m). The experiments are conducted at 25 degree(s)C, 0 degree(s)C, and 50 degree(s)C. Fraction of energy absorbed (a specific damping capacity_ and elastic modulus are evaluated as a function of bias electric field. For investigated stress amplitudes, the specific damping capacity increases with increasing bias field, reaches a maximum (28-33%) at the optimum field level, and then decreases. The optimum electric field values increase as the stress amplitude increases because the positive electric field and the compressive stress counteract each other in terms of domain wall motion. The damping properties are stable in the investigated temperature range. The piezoceramic is found to have superior damping properties compared to common structural methods.

Failure of PZT materials is governed by the crack resistance curve (R-curve). The R-curve was evaluated for a soft PZT: (a) in controlled fracture tests with single-edge-notched bending bars via an improved compliance method combining mechanical compliance and microscopic crack length measurement, (b) by completely stable crack extension tests with a loading device consisting of two pairs of opposite line loads. It was found that the R-curves obtained with different test methods differ strongly. A possible interpretation of the differences is given. A theoretical part deals with the determination of the stress intensity factor solution for bending bars with edge cracks as used in the experiments. Piezoelectric materials exhibit a non-linear stress-strain curve and non-symmetry in tension and compression. Under these conditions the non- linear stress distribution is computed for the bending bar and the stress intensity factor is determined by using the fracture mechanics weight function method. From these computations it results that maximum deviations from the linear-elastic solution of less than 2% occur if a/W>0.3(a=crack length, W=specimen width). In case of the roller loading, it can be shown that maximum errors must be less than 7%.

The conventional traction-free models for insulating and conducting cracks in piezoelectrics predict that an electric field induces zero stress intensity factors at the crack tip. This fails to explain the experimentally observed growth of both insulating and conducting cracks under electric field. To remove the discrepancy between theory and experiments, electric field induced crack closure is considered in this study. Conditions for crack closure are derived by using the solutions for traction-free models. Mixed boundary value problems for closed cracks (insulating and conducting) are formulated using the extended Lekhnitskii's formalism for piezoelectric solids. Analytical solutions are derived for both cases of closed cracks. The present solution predicts that electric loading can induce non-zero (positive) mode-I stress intensity factor at an insulating or conducting crack. The intensified tensile stress directly ahead of the tip of a closed crack can give rise to crack growth. This offers a possible explanation for the experimental observations. Additionally, the effect of polarization switching on the crack tip behavior of both insulating and conducting closed cracks is investigated. Numerical studies show that polarization switching may enhance or decrease the intensity of tensile stress ahead of a closed crack.

Experimental results reported by many researchers showed that the coercive electric field for ferroelectric switching depends on mechanical stresses present in the material. Similarly, the coercive stress for ferroelastic switching depends on the electric field. To model these dependences, several domain switching criteria based on different considerations have been proposed in earlier studies. In this paper, these domain switching criteria are briefly reviewed and the predictions based on these domain switching criteria are compared with the available experimental data for 180 degree(s) domain switching in PZT. It is found that the predictions do not match the experimental results. Motivated by this observation, a new domain switching criterion based on internal energy density is proposed. This new criterion is found to yield very good predictions compared with the existing experimental results for 180 degree(s) domain switching in PZT. To verify the new domain switching criterion for 90 degree(s) switching, experiments were conducted using PZT-5H. The new experimental result indicates that the new domain switching criterion gives a much better prediction than other existing criteria.

Loading of piezoelectric materials leads to high electric fields and mechanical stresses in the near-tip-region of cracks or electrodes. The resulting polarization switching processes can contribute to ferroelectric/ferroelastic crack tip shielding or amplification, equivalent to a change of the fracture toughness. In this paper, we present an approximate constitutive law for repolarization of fully poled materials in load situations where the local poling direction is changed but not the degree of poling. Incremental piezoelectric relations are obtained from a micromechanical switching model. The derivation of the evolution laws for the remanent and material properties and of the tangent moduli resembles plasticity theory: A yield surface is postulated, based on an energy criterion for 90 degree(s) switching of randomly oriented crystallites. The switching barrier corresponds to the yield stress in plasticity. The model is tested on literature data for repolarization of homogeneously poled PZT-samples and in a simulation of the ferroelectric process zone at the tip of a conducting crack or electrode.

The degradation of ferroelectric properties (polarization and remnant strain) during cycling of piezoelectric ceramics limits the reliability and applicability of such materials. This ferroelectric fatigue is believed to be caused by domain wall pinning and grain boundary microcracking. In this paper we concentrate on the domain wall pinning effect. The analysis is based on a self-consistent non-linear micro-mechanical model. The particular domain model applies to loading situations according to quasistatic unipolar cycling. Internal fields on the grain level and stored internal energy can be calculated using the solution of the piezoelectric inclusion problem. Nonlinear material response and hysteresis is caused by rearrangement of ferroelectric domain walls which leads to relaxation of internal fields. According to a thermodynamic criterion, domain wall motion takes place if the energy release rate is equal to a critical value. The proposed model assumes that the critical energy release rate is coupled with a microscopic, history dependent internal variable. Thus the evolution of the internal variable determines the fatigue process. Decreasing relaxation of internal fields causes increase of stored energy which could be discussed in relation to the onset of additional fatigue mechanisms like microcracking.

A class of fully coupled, symmetric, multi-axial, ferroelectric constitutive laws is presented. The foundation of the theory is an assumed form for the Helmholtz free energy of the material. Yield surfaces and associated flow rules are postulated in a modified stress and electric field space such that a positive dissipation rate during switching is guaranteed. The resulting tangent moduli relating increments of stress and electric field to increments of strain and electric displacement are symmetric since changes in the linear elastic, dielectric and piezoelectric properties of the material are included in the switching surface and flow law. Symmetry is further investigated with a simple one-dimensional loading situation comparing the thermodynamically consistent framework to a more ad hoc theory.

The scattering of acoustoelectric waves on a continuous cylindrical fiber embedded in a piezoelectric medium of hexagonal (transversely isotropic) symmetry is considered. It is assumed that both the matrix and the fiber has hexagonal symmetry with different material characteristics but with the same axis of symmetry which coincides with the cylinder axis of the fiber. Expressions for scattering amplitudes of the acoustoelectric waves follow from a system of integral equations for the electroelastic fields in the medium containing an inhomogeneity. This system is obtained in terms of Green's function of the coupled dynamic electroelastic problem. Explicit expressions are obtained for the components of the Green's function and scattering amplitudes for the quasiplane dynamic problem in the transversely isotropic piezoelectric medium. General formulae are derived for the total scattering cross-section of acoustoelectric waves propagating in the direction normal to the fiber axis. Finally, explicit expressions are obtained for the scattering amplitudes and scattering cross-sections of three acoustoelectric waves in the long wave limit. The results may be useful for future applications to various acoustoelectric inhomogeneity problems in piezoelectric media with hexagonal symmetry.

In our previous studies, we first introduced the phase interaction energy function as a dissipation potential for the phase transformation of pseudoelasticity between austenite and martensite of shape memory alloy wires. Next, to treat both shape memory effect between twinned and detwinned martensites and the pseudoelasticity in a unified manner, we developed the phase interaction energy function and performed a thermomechanical analysis of the wire based on the developed phase interaction energy function. In the present study, the phase interaction energy function is further extended to include the effect of phase rearrangement and transformations associated with twinned and detwinned rhombohedral phases.

Tension and torsion as well as combined tension-torsion tests on NiTi Tubes are presented in this article. Two different specimens are used in the experiments: one is austenitic and the other is martensitic at room temperature. The experiments are performed at nearly isothermal conditions. However, non-isothermal effects occur as well because of the self-heating of the material during the phase transitions and the detwinning of the martensite. These effects can be excluded applying very small deformation rates. In contrast to this, the influence of the self- heating on the material behavior is investigated in other experiments, where temperature fields are measured by means of infrared thermography. This allows detailed observations of the temperature field on the surface of the specimen and leads to additional insight into the thermomechanical behavior of shape memory alloys. In simple tension and pure torsion experiments the various effects of the material behavior can be decoupled. In particular, relaxation and creep processes are observed as a result of self-heating, but also as a consequence of the viscosity of the material. The combined tension-torsion experiments make it possible to analyze coupling effects of the biaxial behavior. In this context, a proportional and non-proportional deformation path is carried out.

This study aims to fabricate Pb(Zr,Ti)O₃ (PZT) piezoelectric ceramic fibers by extrusion with mixture of PZT powder and PZT sol. The added PZT sol in this study played a role as a binder; the sol changed into PZT crystalline during sintering, and removal process of additives before sintering was not required. To obtain PZT fibers, the condition of sol viscosity adjustment, the mixture ratio of powder and sol for fiber extrusion, and the sintering condition for obtaining polycrystalline fibers were investigated. PZT precursor solution was synthesized from lead acetate trihydrate, zirconium n-propoxide and titanium isopropoxide by reflux at 120 degree(s)C for 3 hours with 2-methoxyethanol. The appropriate adjustment of spinnable sol was achieved by the addition of acetic acid for suppressing the hydrolysis reaction and the curing sol at 80 degree(s)C for promoting the condensation of sol. Green fibers with diameter of about 300micrometers were successfully extruded from the mixture of PZT powder and sol. The extruded fibers sintered at 1200 degree(s)C had the microstructure with 2-6micrometers grains and had no pores or cracks. From the result of displacement behavior measurement, PZT fibers fabricated by firing at 1200 degree(s)C in this study were considered to have desired piezoelectric properties.

Aeroelastic control of wings by means of a distributed, trailing-edge control surface is of interest with regards to maneuvers, gust alleviation, and flutter suppression. The use of high energy density, piezoelectric materials as motors provides an appealing solution to this problem. A comparative analysis of the state of the art actuators is currently being conducted. A new piezoelectric actuator design is presented. This actuator meets the requirements for trailing edge flap actuation in both stroke and force. It is compact, simple, sturdy, and leverages stroke geometrically with minimum force penalties while displaying linearity over a wide range of stroke. The V-Stack Piezoelectric Actuator, consists of a base, a lever, two piezoelectric stacks, and a pre-tensioning element. The work is performed alternately by the two stacks, placed on both sides of the lever. Pre-tensioning can be readily applied using a torque wrench, obviating the need for elastic elements and this is for the benefit of the stiffness of the actuator. The characteristics of the actuator are easily modified by changing the base or the stacks. A prototype was constructed and tested experimentally to validate the theoretical model.

A numerical method for the performance evaluation of LIPCA actuators is proposed using a finite element method. Fully-coupled formulations for piezo-electric materials are introduced and eight-node incompatible elements used. After verifying the developed code, the behavior of LIPCA actuators is investigated.

Results from an effort to fabrication shape memory alloy hybrid composite (SMAHC) test specimens and characterize the material system are presented in this study. The SMAHC specimens are conventional composite structures with an embedded SMA constituent. The fabrication and characterization work was undertaken to better understand the mechanics of the material system, address fabrication issues cited in the literature, and provide specimens for experimental validation of a recently developed thermomechanical model for SMAHC structures. Processes and hardware developed for fabrication of the SMAHC specimens are described. Fabrication of a SMAHC laminate with quasi-isotropic lamination and ribbon-type Nitinol actuators embedded in the 0°layers is presented. Beam specimens are machined from the laminate and are the focus of recent work, but the processes and hardware are readily extensible to more practical structures. Results of thermomechanical property testing on the composite matrix and Nitinol ribbon are presented. Test results from the Nitinol include stress-strain behavior, modulus versus temperature, and constrained recovery stress versus temperature and thermal cycle. Complex thermomechanical behaviors of the Nitinol and composite matrix are demonstrated, which have significant implications for modeling of SMAHC structures.

The present work develops a quantitative theory of the self thermal-plastic response of NiTi shape memory alloy actuated metal matrix composite materials. Model calculations are compared with existing experimental data obtained from a testing procedure consisting of an initial room temperature, 5% tensile elongation process, and a subsequent room temperature to 120 degree(s)C unconstrained (external stress free) heating process. During the unconstrained heating process the composite fiber actuators attempt to recover pseudo-plastic strain imparted during the room temperature tensile prestrain process. As the temperature increases, the fiber stress-temperature state enters increasing phase transformation intensity, resulting in strong increases in fiber longitudinal tensile stress, matrix longitudinal compressive stress and composite compressive longitudinal external strain. Sufficient temperature brings the matrix stress state to the point of plastic yield. The composite then exhibits a very unusual, self thermal-plastic compression response, recovering approximately 2.2% strain.

Adaptable hybrid composites are materials into which actuators are embedded in polymer matrix composites. Shape memory alloys (SMA) are amongst the potential candidates for actuators embedded in such composite smart structures. In order to test the influence of the processing conditions on the actuation properties of adaptive hybrid composites, a model system based on a glass epoxy asymmetric laminate composite with prestrained shape memory nitinol-copper wires, was used. When the SMA wires were electrically heated and cooled, undergoing a reversible martensite to austenite transformation, reversible bending of the host composite was observed. The most important deflection of the host composite was obtained for the material, processed with embedded wires in TWSME conditions. Nevertheless, for samples just prestrained for the OWSME, a self-training effect occurred in relation to the reverse polarized austenite to martensite transformation, during cooling after actuation. The experimental results obtained in the conditions of the sample processed with embedded wires in TWSME conditions can be modeled in the frame of recent phenomenological modeling. In spite of some drastic simplifications, the quasi-linear variation of the bending effect with temperature is correctly described using the metallurgical parameters defined from the Clausius-Clapeyron diagrams of this alloy previously determined.

Adaptive composites have been produced by embedding prestrained shape memory alloy (SMA) wires into an epoxy matrix, reinforced with aramid fibers. These materials demonstrate attractive effects such as shape change or a shift in the vibration frequency upon activation. When heated above their transformation temperature, the wires' strain recovery is confined, and recovery stresses are generated. As a result, if the wires are placed along the neutral axis of a composite beam, a shift in resonance vibration frequency can be observed. To optimize the design of such composites, the matrix - SMA wire interfacial shear strength has been analyzed with the pull out testing technique. It is shown that the nature of the wire surface influences the interfacial shear strength, and that satisfactory results are obtained for SMA wires with a thin oxide layer. Composite samples consisting of two different types of pre- strained NiTiCu wires embedded in either pure epoxy matrix or Kevlar-epoxy matrix were produced. The recovery force and vibration response of composites were measured in a clamped-clamped configuration, to assess the effect of wire type and volume fraction. The results are highly reproducible in all cases with a narrow hysteresis loop, which makes NiTiCu wires good candidates for adaptive composites. The recovery forces increase with the volume fraction of the embedded wires, are higher when the wires are embedded in a low CTE matrix and, at a given temperature, are higher when the wire transformation temperature is lower.

Some recent studies have suggested possible applications of Shape Memory Alloy (SMA) for a smart health monitoring and suppression of damage growth. The authors have been conducting research and development studies on applications of embedded SMA foil actuators in CFRP laminates as the basic research for next generation aircrafts. First the effective surface treatment for improvement of bonding properties between SMA and CFRP was studied. It was certified that the anodic oxide treatment by 10% NaOH solution was the most effective treatment from the results of peel resistance test and shear strength test. Then, CFRP laminates with embedded SMA foils were successfully fabricated using this effective surface treatment. The damage behavior of quasi-isotropic CFRP laminates with embedded SMA foils was characterized in both quasi-static load-unload and fatigue tests. The relationship between crack density and applied strain was obtained. The recovery stress generated by embedded SMA foils could increase the onset strain of transverse cracking by 0.2%. The onset strain of delmination in CFRP laminates was also increased accordingly. The shear-lag analysis was also conducted to predict the damage evolution in CFRP laminates with embedded SMA foils. The adhesive layers on both sides of SMA foils were treated as shear elements. The theoretical analysis successfully predicted the experimental results.

THUNDER (THin Unimorph DrivER) actuators are pre-stressed piezoelectric devices developed at NASA LaRC that exhibit enhanced strain capabilities. As a result, they are of interest in a variety of aerospace applications. Characterization of their performance as a function of electric field, temperature and frequency is needed in order to optimize their operation. Towards that end, a number of THUNDER devices were obtained from FACE International Co. with a stainless steel substrate varying in thickness form 1 mil to 20 mils. The various devices were evaluated to determine low-field and high-field displacement as well as the polarization hysteresis loops. The thermal stability of these drivers was evaluated by two different methods. First, the samples were thermally cycled under electric field by systematically increasing the maximum temperature from 25 degree(s)C to 200 degree(s)C while the displacement was being measured. Second, the samples were isothermally ages at 0 degree(s)C, 50 degree(s)C, 100 degree(s)C, and 150 degree(s)C in air, and the isothermal decay of the displacement was measured at room temperature as a function of time.

Stress-biased actuators, such as Rainbow and Thunder^TM devices, offer enhanced displacement performance compared to unimorph and bimorph actuators. Quantifying the relative contributions of mechanics (layer thickness ratio) versus stress effects on actuator performance has proven difficult. In this paper, the importance of domain switching and altered domain configuration on actuator performance is considered. X-ray diffraction has been used to characterize the initial domain configuration in the surface region of the actuators, as well as the domain switching characteristics of the devices under moderate electric fields. Samples with different reduced layer thicknesses were fabricated to alter device stress state, and consequently, domain configuration and switching characteristics. Compared to poled polycrystalline ceramics of the same composition, Rainbow actuators display a slightly higher a-domain population in the surface region of the devices. Interestingly, despite the presence of comparatively large lateral tensile stresses in this region of the device, x-ray diffraction indicates these devices also display greater 90 degree(s) (a- to c-domain) switching, which contributes to the large displacement responses that are observed. The contribution of stress to the enhanced performance of Rainbow and Thunder^TM devices is, thus, more accurately described as arising from a change in the initial domain configuration together with minimal suppression in the switching response under high lateral tensile stresses, rather than simply a stress-enhancement of domain switching. The effects of stress on the initial domain configuration and switching response were quantified to define the specific role of stress on the electromechanical response of the devices.

LIPCA (LIghtweight Piezo-composite Curved Actuator) is an actuator device which is lighter than other conventional piezoelectric ceramic type actuator. LIPCA is composed of a piezoelectric ceramic layer and fiber reinforced light composite layers, typically a PZT ceramic layer is sandwiched by a top fiber layer with low CTE (Coefficient of thermal expansion) and base layers with high CTE. LIPCA has curved shape like a typical THUNDER (Thin-layer composite unimorph ferroelectric driver and sensor), but it is lighter than THUNDER. Since the curved shape of LIPCA is from the thermal deformation during the manufacturing process of unsymmetrically laminated lay-up structure, and analysis for the thermal deformation and residual stresses induced during the manufacturing process is very important for an optimal design to increase the performance of LIPCA. To investigate the thermal deformation behavior and the induced residual stresses of LIPCA at room temperature, the curvatures of LIPCA were measured and compared with those predicted from the analysis using the classical lamination theory. A methodology is being studied to find an optimal stacking sequence and geometry of LIPCA to have larger specific actuating displacement and higher force. The residual stresses induced during the cooling process of the piezo- composite actuators have been calculated. A lay-up geometry for the PZT ceramic layer to have compression stress in the geometrical principal direction has been designed.

A new process parameter viz.; target temperature, has been introduced to decrease the composition variables between the target and substrate. A DC magnetron sputtering system has been used for the deposition of NiTi film from equiatomic NiTi target on silicon substrate. The target transitions from a low temperature value to a high temperature value (>700 degree(s)C) during sputtering. The sputtered films were crystallized by heating to 500 degree(s)C for 10 minutes in situ prior to removal from the sputtering system. X-ray diffractogram shows that the film peaks correspond to martensite as well as austenite phases. The film developed under this process displays the two-way shape memory effect without post annealing. Electrical resistivity measurement reveals that there are three different phases present viz.; austenite, rhombohedral and martensite, which exists at different temperature ranges. The characteristic transformation temperatures determined by the electrical resistivity method are compared with those obtained with DSC thermograms.

The effects of aging and thermo-mechanical training on the two-way shape memory effect (TWSME) of a NiAl-Fe alloy have been investigated. It was found that the two-way shape memory property of NiAl-Fe alloy was increased obviously after training. The two-way shape recovery of NiAl-Fe specimens aged at 400 degree(s)C for 1 hour was higher than that of specimens without aging, and kept unchanged up to 1x10³ heating-cooling cycles. The fatigue life of NiAl- Fe specimens aged at 400 degree(s)C for 1 hour showing TWSME was more than 1x10³ cycles. The mechanisms for the effects of thermo-mechanical training, as well as aging precipitates on the TWSME have also been discussed.

Samples of fine grain piezoelectric ceramics (less than or equal to 1 micrometers ) exhibit increased mechanical strength and improved machinability over conventional materials, which should result in actuators which have increased reliability with fewer rejected parts. The focus of the work presented here is to compare the properties of several fine grain and conventional actuators provided by TRS Ceramics. Specimens are constructed of TRS200 (a PZT-5A or DOD Type II equivalent material) and TRS600 (a PZT-5H or DOD Type VI equivalent material). All of the actuators consist of ceramic wafers bonded together with electrodes between them to form a stack. Several actuator overall dimensions and two wafer thicknesses (250 micrometers and 500 micrometers ) are investigated as well as material which has been subjected to hot isopress. The two main figures of merit in the stack actuator comparisons are free strain and blocked stress. Strain and stress loops are measured under a variety of field levels, including negative fields up to the coercive limit (full butterfly loops were not performed). Also compared are values of energy density and hysteresis in the strain, stress and electric displacement vs. field loops. Stack longevity is addressed through duration tests in which stacks are used to drive representative mechanical impedance for an extended period. Results show that fine grain stacks completed 10⁹ continuous actuation cycles with no sign of performance degradation.

In off stoichiometric Ti_50+xPd₃₀Ni_20+x alloys, it has been confirmed that B2-B19 phase transformations take place as temperature changes, and found that the phase transformation temperatures decrease with the increase of Ti content deviation from 50 at. %. Shape memory effect (SME) was determined at room temperature and at temperature higher than the austenite finish temperature, respectively. The room temperature SME is evaluated as a total strain of 7.2% with a recovery rate of 100%, and weakens with the increase of tensile strain. SME at high temperature indicates that stress-induced martensite remains in the alloys after unloading. Complete linear superelasticity has been observed by training the specimen under loading-unloading cycling. The shapes of superelastic cycles for specimens of different phases are different, and superelastic strain can be changed according to the load level of training. The yield stress for specimen in austenitic state is much higher than that in martensitic state, and the two kinds of specimens show different strain-hardening ability. The fracture surface shows overall characteristics of brittle failure for specimens both in austenitic and martensitic state. The microstructures of the specimens were also investigated. It is revealed that thermomechanical treatment and training process are necessary steps for preparation the superelastic alloy.