A continuum thermodynamics framework for the diffuse interface or "phase field" approach to domain evolution is presented. The theory distinguishes the fundamental balance laws which are universal (i.e. mechanical equilibrium, Gauss' law, and a new micro-force balance) from the constitutive laws, which describe the behavior of a specific material. A finite element formulation based on a virtual work statement is implemented using mechanical displacements, electrical potential, and polarization components (the vector "order parameter") as nodal degrees of freedom. The finite element code is then applied to simulate the growth of a 180° domain needle through a parent domain.

In the recent years various novel materials have been developed that respond to the application of electrical loading by large strains. An example is the class of so-called electro-active polymers (EAP). Certainly these materials are technologically very interesting, e.g. for the design of actuators in mechatronics or in the area of artificial tissues. This work focuses on the phenomenological modeling of such materials within the setting of continuum-electro-dynamics specialized to the case of electro-hyperelastostatics and the corresponding computational setting. Thereby a highly nonlinear coupled problem for the deformation and the electric potential has to be considered. The finite element method is applied to solve the underlying equations numerically and some exemplary applications are presented.

The behavior of ferroelectric ceramic materials is governed by complex multiscale phenomena. At the macroscale, the constitutive behavior displays time dependent coupling between stress, electric field and temperature. This behavior is dependent on composition, microstructure and dopants. Plasticity based macroscale phenomenological models utilize the concept of internal state variables and their evolution to represent the volume average behavior. These models include many variables that must be determined through a combination of experiment and micromechanical modeling. At the mesoscale, the microstructure plays an important role in the material behavior. Grains form during the sintering process and porosity can occur at grain boundaries. Upon cooling, the material undergoes a phase transformation to a ferroelectric state. Domains form within grains to minimize intergranular stress and electric fields. Within a single domain, the material behavior is governed by the crystal structure and the local fields. Micromechanics approaches connect the mesoscale with the macroscale. Micromechanical models utilize single crystal behavior and a self consistent approach to handling intergranular stress and electric fields to simulate the macroscopic behavior. This approach considers average local fields and utilizes volume fractions of domain types to characterize the state. This work implements measured single crystal behavior in a micromechanics code to predict the macroscopic material behavior. Specimens of the same composition are characterized under combined stress and electric field loading and the results are discussed.

Ferroelectric materials exhibit spontaneous polarization, spontaneous strain and domain structures below the Curie temperature. The phase field approach has been used to simulate the formation of ferroelectric domain structures and the ferroelectric-antiferroelectric phase transformation. The evolution of phases and domain structures was simulated in ferroelectric single crystals by solving the time dependent Ginzburg-Landau (TDGL) equation with polarization as the order parameter. In the TDGL equation the free energy of a ferroelectric crystal is written as a function of polarization and applied fields. Change of temperature as well as application of stress and electric field leads to change of free energy level and therefore evolution of phase and domain states. In this work the temporal evolution of polarization field was computed by solving the TDGL equation with explicit time integration scheme. The finite difference method was implemented for the spatial description of the polarization. Cubic to tetragonal, cubic to rhombohedral and ferroelectric to antiferroelectric (tetragonal or rhombohedral) phase transformations were modeled and the formation of domain structures were simulated. Field induced polarization switching and the macroscopic material responses were simulated.

High-strain piezoelectric materials are often ceramics with a complicated constitution. In particular, PZT is used with compositions near to a so-called morphotropic phase boundary, where not only different variants of the same phase (domains), but different phases may coexist. Micro-mechanical models for ferroelectric ceramics would be much more realistic, if these effects could be incorporated. In this paper, we consider the conditions of mechanical and electrical compatibility of ferroelectric domain structures. We are able to address the question of coexistence of different crystallographic phases within the very same crystallite. In general, the spontaneous strain and spontaneous polarization of different phases are not compatible. The numerical analysis of the derived relationships are susceptible to the crystallographic description of the phases in question. In this presentation, a simple analysis and analytical, composition dependent fit of strain and polarization of PZT at room temperature for available data are used. The outlined approach can be used to model the overall behavior of multi-variant and multi-phase crystallites with certain, simplified geometrical arrangements of the constituents.

In this experimental work, multi-axial, non-proportional polarization rotation tests were performed for a commercial soft PZT material under purely electric field loading. Large pre-poled piezoceramic plates were cut into rectangular blocks of size 15mm × 5mm × 5 mm, with their long axes inclined at a set of angles (from 0° to 180°, in steps of 15°) to the initial poling direction. After cutting, the top and bottom 5mm × 5 mm surfaces were electroded with a thin layer of silver paint and then, a ramp-shaped electric field was applied to cause the polarization to change. In addition to the polarization measurement along the field loading direction, the normal strain responses in all three coordinate directions were monitored simultaneously using strain gauge technique. Based on a series of polarization and strain versus electric field curves, switching (domain reorientation threshold) surfaces were constructed in the bi-axial electric field plane using the conventional offset method. The experimental data can be used to examine the existing switching criteria in phenomenological models for the non-linear constitutive behavior of piezoceramics.

Resonance methods were used to determine the variation of several piezoelectric, elastic and dielectric constants, as well as the corresponding electromechanical coupling factors of soft and hard doped Pb(Zr_xTi_1-x)O₃ (PZT) ceramics, with compositions near the morphotropic phase boundary (MPB), as a function of temperature ranging from −165 °C to 195 °C. The material constants were obtained by analyzing the fundamental resonance of the impedance or admittance spectra as a function of frequency for several sample resonance geometries. The piezoelectric constants d₃₃ and −d₃₁, as well as the dielectric constants ε^T₃₃, generally increased with temperature for both soft and hard PZT samples. However, the elastic constants s^E₁₁ and -s^E₁₂ exhibited abnormal variations seen as broad peaks over parts of the tested temperature range. Furthermore, thermal hystereses were observed in all the studied material constants during the heating and cooling cycles. Finally, it was noted that, overall, the material constants of soft PZT varied significantly more than those of hard PZT under changing temperature conditions.

The dielectric and piezoelectric responses to a constant electric field have been measured on initially unpoled PZT-5H and PLZT 8/65/35. In particular, we are interested in the time dependent remanent strain and polarization due to unipolar electric field because they are associated with the domain switching behaviour. An experimental method has been developed to obtain the remanent strains and polarization by accounting for dielectric and piezoelectric effects. A linear dependence of dielectric and piezoelectric modulus on remanent polarization was found in PZT-5H, but not in PLZT 8/65/35. In PLZT 8/65/35, a transition was observed at a value of remanent polarization of 0.07 Cm^-2 gradually evolving polarization to rapid switching. A change in the dominant mechanism of switching was also observed.

Fatigue crack growth experiments with DCB specimens made of PZT subjected to cyclic electrical and constant mechanical loading are evaluated from the fracture mechanical point of view. Therefore, correlations have been developed from numerical simulations with the Finite Element Method providing the electric displacement intensity factor K_IV which depends on crack length and electromechanical loading conditions. The simulations account for limited permeable crack faces and explain the observation of a dielectric crack closure effect. Fatigue crack growth is then described by a power law. To simulate ferroelectric domain switching, a numerical micromechanical model has been developed. Finite Element calculations shed light on the physical mechanisms of crack growth due to electric cycling.

In this study, multilayered PbZr_xTi_1-xO₃ (PZT) samples were produced by tape-casting and subsequent sintering at temperatures in the range of 1175 °C to 1325 °C. Sintering times were 6 minutes and 24 minutes. Samples were poled and also electrically fatigued by long-term exposure (≈10⁶ cycles) to cyclic electric fields. The parameters of initial and remnant polarization were estimated from hysteresis loops. Changes in the crystallographic microstructure as a function of sintering temperature T_S and sintering time were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD) to gain insight on fatigue mechanisms and their prevention. The microstructural results, such as domain reorientation and amount of secondary phases, explained the results of electrical observations. We found that grain sizes and internal strains were major influence factors on device performance. Domain sizes were about two orders of magnitude smaller than grain sizes. Therefore, domain-grain wall interaction did not influence domain switching. Domain wall movement was facilitated in samples processed at T_S less than 1250 °C, and such samples were more resistant to electrical fatigue. Samples degraded faster at T_S above 1250 °C, but here a higher device performance power was found due to an increased unit cell tetragonality that yielded higher polarization values.

Many new applications are emerging for piezoelectric ceramics including adaptive structures, active-flow-control devices, and vibration and noise suppression systems. Additionally, there are opportunities to use these devices in the biomedical field for miniature pumps, ultrasonic surgical tools, micro-needle arrays, and nanorobotics. In each of these instances, actuator stability is critical, representing a significant challenge for piezoelectric ceramic materials. In particular, the properties of lead zirconate titanate (PZT) have been found to degrade, often significantly, during continuous operation due to a combination of domain pinning, relaxation of interfacial stress, and, in the worst cases, micro-crack formation. This degradation, referred to as actuator fatigue, can be even more pronounced when high voltages are used to achieve maximum displacement or more complex actuator designs are required. For example, multilayer actuators, such as co-fired stacks, are important for many emerging applications and are now being produced with very small physical dimensions, lowering power requirements. However, multilayer components may be highly susceptible to long-term fatigue due to the large number of interfaces involved in their configuration. In this work, we report a method for rapidly characterizing the reliability of multilayer PZT actuators by monitoring degradation in switching polarization over time. To verify this approach, a series of miniature (3 mm x 3 mm x 2 mm) multilayer actuators were characterized over 1 million cumulative cycles. These actuators were produced commercially from soft PZT materials, and the sintering temperature was varied to tailor the ceramic microstructure and performance characteristics. Evaluation of cyclic polarization degradation was found to be an effective method for illuminating differences among the different actuators tested, as well as serving to predict their long-term resistance to fatigue.

In this paper low voltage single crystal actuators were investigated using thin PMN-PT plates for applications requiring low voltage, large strain, low profile and/or actuation at cryogenic temperatures. Firstly, single crystal thickness effect on piezoelectric properties was studied by investigating the relationship between electromechanical coupling coefficient of PMN-PT crystals and the crystal thickness. It was found that electromechanical coupling coefficient (k_t) of 50 μm, 75 μm and 100 μm PMN-PT single crystal thin plates are 0.5, 0.51, and 0.55, respectively, which are slightly lower than that of bulk single crystal (0.6). A couple of single crystal actuators were then assembled using crystal plates with thickness of 150-200 μm. These actuators were characterized by measuring strain vs. electric field at room temperature and cryogenic temperatures. A 3 mm x 3 mm x 19 mm single crystal stack actuator showed a 21 μm stroke at room temperature under 150 V, and a 10 μm stroke at 60 K under 200 V. A 5 mm x 5 mm x 12 mm single crystal actuator showed 13.5 μm stroke at room temperature under 150 V, and 6 μm stroke at 77 K under 150 V. These low voltage actuators hold promising for space precise positioning and adaptive structures and cryogenic SEM, SPM and STM applications.

Transducers incorporating single crystal piezoelectric Pb(Mg_1/3Nb_2/3)_x-1Ti_xO₃ (PMN-PT) exhibit significant advantages over ceramic piezoelectrics such as PZT, including both high electromechanical coupling (k₃₃ > 90%) and piezoelectric coefficients (d₃₃ > 2000 pC/N). Conventional <001> orientation gives inherently larger bandwidth and output power than PZT ceramics, however, the anisotropy of the crystal also allows for tailoring of the performance by orienting the crystal along different crystallographic axes. This attribute combined with composition refinements can be used to improve thermal or mechanical stability, which is important in high power, high duty cycle sonar applications. By utilizing the "31" resonance mode, the high power performance of PMN-PT can be improved over traditional "33" mode single crystal transducers, due to an improved aspect ratio. Utilizing novel geometries, effective piezoelectric constants of -600 pC/N to -1200 pC/N have been measured. The phase transition point induced by temperature, pre-stress or field is close to that in the "33" mode, and since the prestress is applied perpendicular to the poling direction in "31" mode elements, they exhibit lower loss and can therefore be driven harder. The high power characteristics of tonpilz transducers can also be affected by the composition of the PMN-PT crystal. TRS modified the composition of PMN-PT to improve the thermal stability of the material, while keeping the loss as low as possible. Three dimensional modeling shows that the useable bandwidth of these novel compositions nearly equals that of conventional PMN-PT. A decrease in the source level of up to 6 dB was calculated, which can be compensated for by the higher drive voltages possible.

Galfenol (Fe100-xGax, x = 6, 12.5, 17, 18.4, 19, 22) and Alfenol (Fe81Al19) alloy rods (~50 mm x 6 mm dia.) were annealed under compressive stresses up to 219 MPa at temperatures from 100°C to 700°C for 10 to 100 minutes. Because of the magnetostriction of the alloys, these heat treatments build in a uniaxial magnetic anisotropy that depends upon annealing stress, annealing temperature, and alloy composition. This built-in uniaxial magnetic anisotropy extends the high power capability of these alloys to operate both in tension and in compression. Magnetization and magnetostriction measurements of both unannealed and annealed alloys were taken from −100 MPa to +40 MPa. To fit the magnetization and magnetostriction as a function of magnetic field and stress, an energy expression containing a fourth order anisotropy term (cubic term) plus a second order uniaxial term was utilized. The computed magnetizations and magnetostrictions are found by an energy-weighted average using the Armstrong smoothing constant. Excellent fits to the magnetostriction and moment data were obtained. From the model fits m, d33 and k33 were calculated. Since the built-in stresses can be found simply from the model, it is possible to predict the amount of prestress built into the alloys.

A preliminary theoretical effort has provided a robust three dimensional energy based model of magnetostrictive wave propagation in a general cubic magnetostrictive material. Under high intensity impact we predict that the wave front will split between a higher velocity elastic precursor wave and a lower velocity, strongly dissipative, magnetostrictive shockwave. The wave front solution strongly depends on longitudinal pre-stress level and initial magnetization state. We may expect that a significant portion of the magnetostrictive wave deformation will be reversible under the application of well chosen field paths. In combination these technical characteristics therefore present an opportunity to develop magnetostriction based shock hyper-toughness in safety critical civil and military structures utilizing relatively shock tough magnetostrictive materials such as Terfenol-D particle based composites or homogenous Galfenol rods.

Galfenol (Fe-Ga) is a promising and mechanically robust magnetostrictive actuator material. However, due to its high conductivity, it needs to be in thin sheet form to avoid excessive eddy current losses. Work is underway to develop conventional rolling processes to produce large quantities of thin Galfenol sheet, while retaining a preferred <100> crystallographic texture to optimize magnetostrictive performance. Knowledge of high temperature polycrystalline plasticity is crucial to understanding formability and crystallographic texture evolution during rolling. The deformation behavior of polycrystalline Galfenol at high temperatures was studied. Preliminary results suggest that significant dynamic recovery and/or recrystallization occur during deformation, resulting in a random texture. In-situ neutron diffraction experiments are being developed to obtain qualitative and quantitative information on the high temperature plane strain deformation of Galfenol. These experiments will be used to identify the slip systems that contribute to plastic deformation, and their dependence on temperature. Simultaneously, models of large-scale polycrystal plasticity are being developed to predict internal strains and texture evolution during deformation, which will be validated against the data obtained from the neutron diffraction experiments. Ultimately, the models will be used to develop thermo-mechanical treatments to optimize texture evolution during rolling.

Melt-spun, rapid solidified Galfenol (Fe-Ga) ribbon sample showed large magnetostriction and good ductility as compared with conventional bulk sample because the ribbon has fine columnar grain which was formed during melt-spinning process. The large magnetostriction is caused by the release of considerable large internal stresses in as-spun ribbon as well as the remained [100] oriented strong textures after annealing. In order to obtain larger magnetostrictive force than ribbon sample, in this study, magnetostrictive bulky Fe-Ga alloy was fabricated by combining laminate of rapid-solidified ribbons (80 μm in thickness) and spark plasma sintering/joining (SPSJ). SPSJ is characterized by short time and low temperature heating and sintering process. The laminated sample made by SPSJ maintained the unique metallurgical microstructure of polycrystalline texture of columnar grains as well as almost non-equilibrium metastable phase with little existence of ordered precipitations in as-spun ribbons. The excellent sintered sample having large magnetostoriction was obtained under a condition of the compressive stress of 100 MPa at the temperature of 973 K. The magnetostriction depended on compressive pre-stress level for specimen and reached about 100 ppm which was a half of value obtained for the ribbon sample. Furthermore, by following short annealing for this specimen, the magnetostriction increased to 170-190 ppm comparable to the ribbon's value.

This paper attempts to model the actuation and sensing behavior of polycrystalline magnetostrictive samples by treating them as composed of multiple grains of single-crystals, each with a different orientation to the loading axis. The texture analysis of a typical cross-section of the sample will be used to estimate the fraction of grains that are close to <100>, <110> and <111> orientation. A simple model based on the law of mixtures will be proposed to represent the behavior of the polycrystal in terms of the behavior of <100>, <110> and <111> oriented single crystals. However, the magnetomechanical behavior along each of the crystallographic directions will be simulated using an energy based model as discussed in Ref. 5 and Ref. 9

Iron-Gallium alloys have demonstrated high compressive stress sensitivity (~ 30 T/GPa) along with considerable tensile strength (~ 515 MPa) and Young's modulus (~ 65 GPa) thus making them attractive materials for magnetostrictive sensors. In this work, four-point bending test was performed on single crystal Fe₈₄Ga₁₆ (Galfenol) under magnetic field to characterize its magneto-mechanical response in bending mode. The longitudinal and transverse strains (ε_[100] and ε_[010]) obtained under different mechanical loads (P) and DC magnetic bias fields (H) were used to estimate material properties like average Young's modulus (E_[100]) and Poisson's ratio (ν_[010]). The stress-dependent change in magnetic induction (B) at constant bias fields was obtained for different bending loads. The results of this study helps in understanding the behavior of and challenges related to Galfenol based magnetostrictive sensors which work in bending (flexural) mode.

We investigate the machining properties of Iron-Gallium alloy for microactuator. Iron-Gallium is ductile magnetostrictive material with moderate magnetostriction ranging from 100 to 300ppm. The microactuator of Fe-Ga is expected to have advantages of simple configuration, low voltage driving, high robustness against external force and high temperature environment, compared with that of PZT. Here the rod of Fe-Ga prepared by FSZM technique was machined to distributed pillars of 1mm square by milling process. The comparison of magnetostrictions of machined and non-machined parts by strain gage confirms the strains different in pillars are inherited from the grain distribution and the milling process does not significantly deteriorate the material properties. The measurement of displacements by LASER Doppler vibrometer supports the validity of strain measurement. The success of the fabrication of the distributed pillars of 0.7 and 0.5mm square exhibits the potential of the milling process for Fe-Ga with high aspect ratio suitable for practical micro applications.

A novel configuration of composite of Terfenol-D and stack PZT actuator is proposed for coil-free magnetic force control. This magnetic force control is based on the inverse magnetostrictive effect of magnetostrictive materials whereby the stress resulting magnetic force is controlled by the voltage of the actuator. The advantages, zero power consumption to maintain constant of the magnetic force and small power supply are inherited from characteristics of piezoelectric material. In addition, the configuration of the composite without rigid structure to apply pre-stress is simple and compact compared with our conventional one. In this paper, the measurements of the magnetic force with different size of the magnets and pre-strain clarified the magnetic force is strongly dependent on bias magnetic field and prestress. Linear stepping motor and magnetic levitation taking the advantage of low power consumption to maintain the position of the mover or levitated yoke are also introduced with some experimental results to discuss the potential of the device for practical applications.

Influence of Mn partial substitution for Fe on the magnetic and magnetoimpedance properties of Fe_73.5-xMn_xSi_13.5B₉Nb₃Cu₁ (x = 1, 3, and 5) nanocomposite ribbons were investigated. The results indicated that the Mn addition led to an improved exchange coupling between grains and hence in the magnetic softness. Consequently, the giant magnetoimpedance (GMI) effect was significantly enhanced in these nanocomposites. In the frequency range of 0.1-10 Mhz, the GMI ratio reached the highest values of 83%, 94%, and 130% at the frequency of 2 MHz for x = 1, 3, and 5 compositions, respectively. The corresponding field sensitivity of GMI reached the highest values of 6, 7, and 16 %/Oe, respectively. These indicate that Fe_73.5-xMn_xSi_13.5B₉Nb₃Cu₁ (x = 1, 3, and 5) nanocomposites are potential candidate materials for making GMI sensors.

The aim of the study was to develop an innovative processing method of magnetorheological elastomers (MRE). This method comprises optimization of the MRE structure in the context of their performance in the magnetic field. The influence of the amount of ferromagnetic particles and their arrangement in relation to the external magnetic field was investigated. As matrixes various elastomers, with different stiffness, were used. Their properties were compared with commercially available silicone rubbers. It was found that the structure of the MRE produced depends on the viscosity of the matrix before curing and the magnetic field strength applied. Two different magnetic field strengths were used: 100 and 300 mT. The amount of the carbonyl iron particles was equal to 1.5, 11.5 and 33.0 vol. %. Scanning electron and light microscopy techniques were used for the MRE microstructure observations. The influence of curing conditions on the thermal properties of the MRE was investigated. To evaluate the external magnetic field effect on the magnetorheological properties a deflection under magnetic field was measured. The experiment showed that application of the magnetic field increases stiffness of the material.

A microstructural model of the motion of particle pairs in MR fluids is proposed that accounts for both hydrodynamic and magnetic field forces. A fluid constitutive equation is derived from the model that allows prediction of velocity, particle structure and yield stress. Results for simple shear and elongational flows are presented for cases where particle pairs remain in close contact so they are hydrodynamically equivalent to an ellipsoid of aspect ratio two. In this limiting case, only the magnetic force component normal to the vector connecting the centers of a particle pair affects motion. Shear flow results indicate particle pairs rotate continuously with the flow at low magnetic fields while a steady state is reached at high fields. For elongational flows, when the applied magnetic field is parallel to the elongation direction, particle pairs orient in the field/flow direction. Either orientation is possible when the field is perpendicular to the flow. A second theoretical approach to the prediction of the yield stress is presented. Predictions for various shear rates and magnetic fields are compared with experimental data. The comparison indicates a good agreement between model predictions and experimental data at low to moderate magnetic fields.

Magnetorheological elastomers (MREs) are state-of-the-art elastomagnetic composites comprised of magnetic particles embedded in an elastomer matrix. MREs offer enormous flexibility given that elastomers are easily molded, provide good durability, exhibit hyperelastic behavior, and can be tailored to provide desired mechanical and thermal characteristics. MRE composites combine the capabilities of traditional magnetostrictive materials with the properties of elastomers, creating a novel material capable of both highly responsive sensing and controlled actuation in real-time. This work investigates the response of MRE materials comprised of varying mixtures of 40 and 10 micron iron particles. Samples are tested in compression yielding a compressive modulus and measure of the shear stiffness via Mooney plots. Samples are also tested using a tunable vibration absorber (TVA) designed specifically for this experiment. The TVA loads the samples in oscillatory shear (10-100Hz) under the influence of a magnetic field. In all samples, results show increases in the material's stiffness under the application of a magnetic field as evidenced by the frequency response function of the TVA system. Increases in stiffness of 50% at 0.15T were achieved with samples containing 30%-40 micron particles and 30%-40micron + 2%-10 micron particles. This yields a ratio of over 300%/T. The two-particle MRE appeared not to have reached saturation suggesting further stiffness enhancement was possible beyond the saturated single-particle 40 micron sample. However, this may be a result of the larger iron content. Results also suggest variation in the behavior of two-versus single-particle MRE behavior as evidenced by the shear modulus found in compression, but results are inconclusive. MRE materials made with nanoparticles of hard magnetic barium ferrite show stiffness increases of 70%/T which is comparable to MREs having larger iron particles.

In this Paper is introduced a time-discretization scheme for the numerical simulation of SMA structures. A particular feature of this time-discretized problem is that its solution can be expressed as solutions of a variational problem. This variational formulation allows one to study the existence and unicity of solutions. The approach presented is applied to simulate the propagation of a martensitic zone in a circular cylinder under traction.

The volume and weight budgets in missiles and gun-launched munitions have decreased with the military forces' emphasis on soldier-centric systems and rapid deployability. Reduction in the size of control actuation systems employed in today's aerospace vehicles would enhance overall vehicle performance as long as there is no detrimental impact on flight performance. Functional materials such as shape memory alloys (SMA's) offer the opportunity to create compact, solid-state actuation systems for flight applications. A hybrid SMA model was developed for designing micro-actuated flow effectors. It was based on a combination of concepts originally presented by Likhatchev for microstructural modelling and Brinson for modelling of transformation kinetics. The phase diagram for a 0.1mm SMA wire was created by carrying out tensile tests in a Rheometrics RSA-II solids analyser over a range of temperatures from 30°C to 130°C. The characterization parameters were used in the hybrid model to predict the displacement-time trajectories for the wire. Experimental measurements were made for a SMA wire that was subjected to a constant 150g load and short, intense 4.5 to 10V pulses. Actuation frequency was limited by the cooling rate rather than the heating rate. A second set of experiments studied the performance of SMA wires in an antagonistic micro-actuator set-up. A series of 2 or 3V step inputs were alternately injected into each wire to characterize the peak to peak displacement and the motion time constant. A maximum frequency of 0.25Hz was observed. An antagonistic actuator model based on the hybrid SMA model predicted reasonably well the displacement-time results.

Shape memory alloy honeycombs are constitute a novel set of cellular structures developed by the authors using initially centersymmetric honeycomb configurations (hexagonal ones), and pseudo-plastic Nitinol ribbons as core. Chiral honeycomb structures feature a noncentresymmetric unit cell configuration, with rotational symmetry only and in-plane Poisson's ratio equal to -1. Nonlinear unit cell FE models of these chiral honeycombs have been developed using the formulation proposed by Auricchio et al. related to pseudo-elastic and superelastic SMA materials. The numerical results are compared with experimental ones from tensile tests of chiral honeycomb samples subjected to uniaxial tensile loading at full martensite phase, and analytical results from the model proposed by Prall and Lakes on hexachiral configurations. A working prototype of a deployable antenna made out hexachiiral cells with 1-way SMA ribbon is also described.

In this contribution we present a finite deformation material model for SMA which includes the effect of pseudoelasticity. The model is implemented into a FE code by using an innovative implicit time integration scheme. The final aim of the research work is to investigate whether FE simulations of SMA applications, e.g. NiTI-stents or medical foot staples, should be based on large strain formulations as the transformation strain during the phase transition can reach up to 10 %. If such a large strain model was not necessary the computational cost of the numerical investigations could be reduced significantly.

A Ginzburg-Landau free energy model of multivariant phase transformation in shape memory alloy has been developed. This paper is focused on linking the developed microscopic model with the atomistic reordering process which finally give rise to self-accommodating microstructure. It is analyzed how the kinetics influences the computation of stress-temperature induced dynamics of phase transformation in microscopic and larger length-scales without attempting to solve a molecular dynamic problem in a coupled manner. A variational approach is adopted and phase transformation in Ni-Al thin film is simulated. The simulations capture a qualitative picture of the onset of microstructure formation.

Shape memory alloy (SMA) can exhibit interesting features such as the diverse material behaviors according to the induced temperature and stress. SMA changes its material properties progressively under cyclic loading conditions and finally reaches stable path(state) after a certain number of stress/temperature loading-unloading cycles, so called 'training' completion. The presence of permanent deformation, due to plastic strains or irreversible martensite variants during the material training, shifts the material characteristic curves of SMA wire. In this study, SMA wires that have been in a stable state through the training are used. Stress-strain curve of SMA wire at different temperature levels are measured. In addition, we observe other important effects such as the effect of mechanical/thermal training, rate effect according to thermal cycle times or strain rates, etc. Until now, the rate effect is not considered significantly in the SMA research and only extremely slow time rate is considered in most SMA experiments. It is common to use rate independent constitutive relations in the modeling and simulation of SMA behaviors. Therefore to make the actuators using an SMA wire which has the fast response or short-time thermal cycle environment, rate dependency should be properly considered. The result of two-way experiment at each (short or long) cycle time in phenomenological aspect shows that stress-strain-temperature relations and hysteresis characteristics depend upon the cycle time. In short-time cycle, strain-temperature curve moves in counterclockwise and the size of hysteresis envelop is large. As the time rate of the thermal cycle increases, the size of the hysteresis envelop is getting smaller and strain-temperature curve moves along the clockwise direction above a certain thermal cycle time. Above that thermal cycle time, hysteresis trajectory is fixed in the stable state. These new effects of SMA are investigated and the effect would be explained qualitatively. The present work presents the experimental test using 1-D SMA wire after training completion by mechanical/thermal cycling. Through these tests, we measure the characteristics of SMA. With the estimated SMA properties and effects, we compare the experimental results with the simulation results based on the SMA constitutive equation including the training and thermal rate effect.

Potential applications involving high-temperature shape memory alloys have been growing in recent years. Even in those cases where promising new alloys have been identified, the knowledge base for such materials contains gaps crucial to their maturation and implementation in actuator and other applications. We begin to address this issue by characterizing the mechanical behavior of a Ni_19.5Pd₃₀Ti_50.5 high-temperature shape memory alloy in both uniaxial tension and compression at various temperatures. Differences in the isothermal uniaxial deformation behavior were most notable at test temperatures below the martensite finish temperature. The elastic modulus of the material was very dependent on strain level; therefore, dynamic Young's Modulus was determined as a function of temperature by an impulse excitation technique. More importantly, the performance of a thermally activated actuator material is dependent on the work output of the alloy. Consequently, the strain-temperature response of the Ni_19.5Pd₃₀Ti_50.5 alloy under various loads was determined in both tension and compression and the specific work output calculated and compared in both loading conditions. It was found that the transformation strain and thus, the specific work output were similar regardless of the loading condition. Also, in both tension and compression, the strain-temperature loops determined under constant load conditions did not close due to the fact that the transformation strain during cooling was always larger than the transformation strain during heating. This was apparently the result of permanent plastic deformation of the martensite phase with each cycle. Consequently, before this alloy can be used under cyclic actuation conditions, modification of the microstructure or composition would be required to increase the resistance of the alloy to plastic deformation by slip.

An accurate measure of a Shape Memory Alloy's (SMA) transition temperatures is necessary for the development of successful SMA actuator designs. Differential Scanning Calorimetry (DSC) is used to obtain SMA transition temperatures associated with changes in alloy formulations, fabrication processes, and forming methods, and to predict an SMA's thermal characteristics when designed into an actuator. However there is little data directly correlating a material's DSC results with its performance in an actuator configuration, particularly for large-scale actuators producing high force and large displacements. In this paper the authors compare the DSC results of several NiTinol samples with the thermal performance of the same material in a rotary actuator. Data are presented for NiTinol torque tubes 14cm (5.5 in) long by 1 cm (0.4 in) in diameter. The tubes were tested over a range of loads exceeding 17 N*m (150 in-lbs) of torque, with angular displacements of more than 60 degrees, and for durations exceeding 3,500 thermal cycles. Data from various NiTinol suppliers, levels of cold work, and a range of aging temperatures is presented. The DSC data is directly compared to the strain vs. temperature hysteresis curves of the same material under various loads; both before and after extended cycling. The value of the DSC measurements as a predictor of a material's thermal characteristics in an actuator configuration is assessed.

The focus of this paper is the study and thermomechanical characterization of High Temperature Shape Memory Alloys (HTSMAs) at different stress levels and temperatures ranging from 300 to 500°C. The stability of the material response under cyclic actuation is also investigated. The observations deduced from the tests are presented in detail. In order to investigate the above issues a Ti₅₀Pd₄₀Ni₁₀ HTSMA was used. The alloy was fabricated by a vacuum arc melting technique, followed by casting and hot rolling. A high temperature experimental setup was developed on a load frame to test the material at high temperatures under constrained actuation conditions. Certain key observations on the material response, in terms of recoverable strains under various applied total strains and actuation stress levels, and cyclic thermomechanical behavior are presented.

Intermediate porosity (25%-40%) NiTi is processed by Spark Plasma Sintering (SPS) method. In order to increase the porosity, the SPS chamber setup is modified. A pair of spacers is added to the chamber punch setup so that the pressure applied on the powder is minimized. As a result, the porosity is increased. TiH₂ powder is added as a pore-forming reagent to the element powder mixture for sintering. The decomposition of TiH₂ increases the porosity efficiently. Two kinds of heat treatments are applied to convert the porous NiTi to superelastic grade. One is homogenization followed by aging treatment, the other is aging treatment only. It is found that homogenization heat treatment reduces the porosity. Compressive testing under both room temperature and temperature above the austenite transformation finish temperature are conducted. Porous NiTi specimens perform ductility and show clear superelestic loop with high flow stress and strain.

This paper presents a model for NiMnGa transducers driven with collinear magnetic fields and stresses. Prior work by the authors demonstrates the existence of reversible strains under the application of collinear magnetic fields and stresses oriented along the [001] crystallographic axis of a cylindrical rod of single-crystal Ni₅₀Mn_28.7Ga_21.3. Internal bias stresses from pinning sites in the material are believed to provide the restoring force which allows for the reversibility of the strain. A constitutive model to describe the motion of twin boundaries in the presence of energetically strong pinning sites is presented. The effective pinning strength is represented by an internal bias stress oriented transversely. Stochastic homogenization is then used to account for variability in the bias stresses throughout the material and inhomogeneity in the interaction field intensity. The internal rod dynamics are modeled through force balancing with boundary conditions dictated by the constructive details of the transducer and mechanical load. The model is formulated in variational form, resulting in a second-order temporal system with magnetic field induced strain as the driving mechanism. Model result for unloaded conditions is compared with experimental measurements.

A major complication in measuring material properties of ferromagnetic materials is the influence of the demagnetization effect. The resulting difference between the internal and applied magnetic field depends on the specimen geometry and the distribution of the magnetization inside the sample. This phenomenon also affects the interpretability of magnetic-field induced strain and magnetization data measured for magnetic shape memory alloys, which in turn makes the formulation of reliable constitutive models for these materials difficult. To solve this problem, the approximation of uniform magnetization is usually adopted, in which case a tabularized demagnetization factor can be used to correct the data. In this paper, the validity of this simplification is tested by explicitly solving the magnetostatic problem for relevant geometries, while taking the nonuniform magnetization of a magnetic shape memory alloy specimen into account. In addition to comparing the relation between the volume averaged internal and applied magnetic field, the local variation of the magnetic field and magnetization is analyzed.

Ferromagnetic Shape Memory Alloy (FSMA) particulate composites are processed using Spark Plasma Sintering (SPS) with various weight fractions of NiTi (51 at% Ni) and Fe powders. Various processing conditions are experimented to obtain the optimum heating rate, holding time and holding temperature in order to maximize relative density, superelasticity and magnetic saturation of the composite. Mechanical strength is evaluated using compression tests.

Ferromagnetic Shape Memory Alloys (FSMAs) in the nickel manganese gallium system have been shown to exhibit large magnetically induced strains of up to 9.5% due to magnetically driven twin variant reorientation. In order for this strain to be reversible, however, an external restoring stress or magnetic field needs to be applied orthogonal to the field and hence the implementation of Ni-Mn-Ga in applications involves the use of electromagnets, which tend to be heavy, bulky and narrowband. In previous work at The Ohio State University a sample of Ni₅₀Mn_28.7Ga_21.3 has been shown to exhibit reversible compressive strains of -4200 microstrain along its [001] direction when a magnetic field is applied along this same direction and no externally applied restoring force is present. This reversible strain is possible because of an internal stress field associated with pinning sites induced during manufacture of the crystal. This paper analyzes the switching between two variant orientations in the presence of magnetic fields (Zeeman energy) and pinning sites (pinning energy) through the formulation of a Gibbs energy functional for the crystal lattice. Minimization of the Gibbs free energy yields a strain kernel which represents the predicted behavior of an idealized 2-dimensional homogeneous single crystal with a single twin boundary and pinning site. While adequate, the kernel has limitations because it does not account for the following: (a) Ni-Mn-Ga consists of a large number of twin variants and boundaries, (b) the strength of the pinning sites may vary, and (c) the local and applied magnetic field will differ due to neighbor-to-neighbor interactions. These limiting factors are addressed in this paper by considering stochastic homogenization. Stochastic distributions are used on the interaction field and on the pinning site strength, yielding a phenomenological model for the bulk strain behavior of Ni₅₀Mn_28.7Ga_21.3. The model quantifies both the hysteresis and saturation of the strain. Constrained optimization is used to determine the necessary parameters and an error analysis is performed to assess the accuracy of the model for various loading conditions.

This paper investigates the nano-macro transition in magnetic shape memory alloy(MSMA) thin films using a recently developed sharp phase front-based three-dimensional (3D) constitutive model outlined by Stoilov (JSMS 2005), and originally proposed in the 1D context by Stoilov and Bhattacharyya (Acta Mat 2002). The key ingredient in the model is the recognition of martensitic variants as separate phases in a MSMA domain. Evolution of the interface between these phases is taken as an indicator of the process of reorientation in progress. A formulation of the Helmholtz free energy potential based on Ising model has been derived. The implications of the external magnetic field on the initiation of phase transformation are studied for various mechanical loading modes.

Due to their large magnetic field induced strains and fast response potential, ferromagnetic shape memory alloys have mainly been studied from the perspective of actuator applications. This paper presents characterization measurements on a commercial Ni-Mn-Ga alloy with a goal to investigate its feasibility as a deformation sensor. Experimental determination of flux density as a function of quasistatic strain loading and unloading at various fixed magnetic fields gives the bias field needed for maximum recoverable flux density change. This bias field is shown to mark the transition from irreversible (quasiplastic) to reversible (pseudoelastic) stress-strain behavior. A reversible flux density change of 145 mT is observed over a range of 5.8 % strain and 4.4 MPa stress at a bias field of 368 kA/m. The alloy investigated therefore shows potential as a high-compliance, high-displacement deformation sensor.

Piezoelectric sensors and actuators have gained considerable interest by investigators and researchers for their use in intelligent/smart structures and electromechanical systems. Furthermore, demands from industry for sensors and actuators with higher quality and better performance for a variety of applications have lead the researchers to design piezoelectric systems with optimal configurations to enhance the performance of such actuators and sensors. An analytical micromechanics approach is presented to model the effective longitudinal mechanical properties of Metal-Core Piezoelectric Fibers (MPFs) and Macro Fiber Composites (MFCs). The model assumes general orthotropic material properties for both outside and inside materials. Next, using constitutive equations, the exact analytical solutions for the stress distributions are obtained for axially loaded active fibers. To examine the mechanical performance of the MPF and MFC, material properties and geometric dimensions are substituted into the analytical exact solutions and then effective longitudinal mechanical properties as well as the stress distributions within the domain of each constituent material are obtained and then compared. Finally, the results are presented and concluding remarks are addressed and discussed in details.

In the current study Active Fiber Composites (AFC) utilizing Lead-Zirconate-Titanate (PZT) fibers with Kapton^(R) screen printed interdigitated electrodes (IDE) were integrated into carbon fiber reinforced plastic (CFRP) laminates to investigate integration issues associated with smart structures and host laminate integrity. To aid in this goal surrogate or "dummy" AFC (DAFC) using a composite core and Kapton^(R) outer layers (to match the longitudinal mechanical and interface properties of the AFC) were employed. These DAFC were used in place of real AFC to expedite test specimen manufacture and evaluation. This allowed efficient investigation of the impact of an integrated AFC-like inclusion on laminate mechanical integrity. Laminates with integrated AFC were additionally tested with signal monitoring to assess AFC health during the test. Investigation into laminate failure was accomplished via a finite element model of the system which was created in ANSYS to investigate failure in the composite plies. Tsai-Wu failure criterion was calculated to investigate laminate failure characteristics. Integration of AFC into CFRP laminates degraded laminate strength by 13.3% using insertion integration and 7.8% using the interlacing integration technique. The finite element model showed that interlacing integration enabled distribution of critical forces over the entire laminate while insertion integration led to critical forces concentrating over the integration region.

Developed at NASA Langley Research Center during the late 90's, the Macro Fiber Composites (MFC) are manufactured by Smart Material Corp. in a full-scale production, today. Numerous research projects have proven the concept of using the MFC in vibration and noise control applications, as well as for health monitoring, morphing of structures and energy harvesting. Because basic performance parameters of products are considerably improved, like for example energy economy, precision and comfort, a widespread use of active structures is expected in the next future. Different MFC types are commercially available meeting already the requirements of a variety of applications. The migration from research projects to high volume, cost effective commercial applications has generated additional need for new MFC designs, electronics on microcontroller and chip level, and system design tools, as well. In this paper, we give an overview of recent progress in the development of the MFC transducers and MFC systems technology.

In this work, behavior of a unimorph piezoceramic actuator, LIPCA (Lightweight Piezo-Composite Actuator) under compression has been experimentally and numerically investigated. The LIPCA composed of composite laminated tabs, piezoceramic material layer, glass/epoxy composite and carbon fiber composite layers was modeled and analyzed by using a full three-dimensional finite element modeling technique. The geometrically nonlinear analysis was used in the analysis because the LIPCA has the initial curvature due to the curing process, which acts like an initial geometric imperfection. The LIPCA was installed in the simply supported configuration and compressive load was applied in the test jig. By measuring the lateral displacement created by the compressive load, the buckling load of the LIPCA was determined. The measured buckling load agreed well with the computed linear buckling load from the finite element analysis based on the thermal analogy. As various electric fields were applied to the LIPCA under the compressive load, the lateral displacement was measured to examine behavior of the LIPCA under the compressive load and electric field at the same time. From this test, proper combinations of the compressive load and prescribed voltage could be figured out, which can create controlled buckling of the LIPCA under compression by applying the electric field. The measured data showed that the lateral displacement of the LIPCA is significantly increased when a proper electric field is prescribed to the LIPCA in addition to the pre-determined compressive load. The measured data was compared with the computed result from the geometrically nonlinear finite element analysis based on the thermal analogy. The numerical simulation agreed well with the measurement for low compressive load (< 3N) and low electric field (< 150V). The strength of the LIPCA is also calculated to make sure that the actuator can be operated without fracture.

In this paper, we study the no-load behavior of a lightweight piezo-composite curved actuator (LIPCA) subjected to voltage and charge control. First, we examine the effect of hysteresis and creep when the actuator is voltage controlled at a slow scan speed. The experimental results show that creep increases the displacement hysteresis by over 25% when scanning at 1/60 Hz. Afterwards, we discuss the design and implementation of a charge-feedback circuit to control the displacement of the actuator. The hysteresis curves between voltage- and charge-control modes are compared for the scan frequencies of 1 and 5 Hz. The results show that charge control (compared to voltage control) of a LIPCA device exhibits significantly less hysteresis, over 80% less.

In this paper, mechanical properties and piezoelectric effects of cellulose based Electro-Active Paper (EAPap) actuators were investigated. Typical pulling tests of cellulose paper, which is a basic material of EAPap actuator, showed distinct elastic modulus and bifurcation point followed by plastic modulus at ambient conditions. The mechanism of this distinct phenomenon was examined to obtain better understanding of EAPap actuator. After that, in-plane strain of EAPap actuator under constant electric field was experimentally investigated to understand piezoelectricity of EAPap. EAPap samples were made by coating very thin gold electrodes on both sides of cellophane film. When external DC voltages were applied, in-plane contractions were induced due to the converse piezoelectric effect of EAPap. It was observed that the EAPap sample with 45° orientation exhibited the largest in-plane strain compared to other orientation samples.

Vacuum-Assisted Resin Transfer Molding (VARTM) process was used to fabricate the nanocomposites through integrating carbon nanofiber paper into traditional glass fiber reinforced composites. The carbon nanofiber paper had a porous structure with highly entangled carbon nanofibers and short glass fibers. In this study, the carbon nanofiber paper was employed as an inter-layer and surface layer of composite laminates to enhance the damping properties. Experiments conducted using the nanocomposite beam indicated up to 200-700% increase of the damping ratios at higher frequencies. The scanning electron microscopy (SEM) characterization of the carbon nanofiber paper and the nanocomposites was also conducted to investigate the impregnation of carbon nanofiber paper by the resin during the VARTM process and the mechanics of damping augmentation. The study showed a complete penetration of the resin through the carbon nanofiber paper. The connectivities between carbon nanofibers and short glass fibers within the carbon nanofiber paper were responsible for the significant energy dissipation in the nanocomposites during the damping tests.

Transient reflection spectroscopy and degenerate four wave mixing technique were employed to study the light-induced insulator-to-metal phase transition (PT) and ultrafast relaxation dynamics in VO₂. Spectral reflectivity during light- and thermally-induced PT shows close proximity in the relative change. The relaxation dynamics is strongly dependent on the film morphology, laser pump energy and substrate material. After light-induced PT the recovery time demonstrates a near-exponential dependence on the pump power. The recovery owing to cooling is considerably faster for VO₂ films deposited on single-crystal Al₂O₃ or MgO substrates compare to VO₂ on amorphous glass. The noticeable transient nonlinear optical response of metallic VO₂ was observed and interpreted in terms of electronic-polaron and hole-polaron clustering.

The nonequilibrium carrier dynamics in spherical silver nanoparticles embedded in aluminophosphate glass system was explored by femtosecond optical pump-probe technique. Photoluminescence and absorption spectroscopy were used for characterization of linear optical properties and particle size estimation. The two temperature model is employed to study the hot electron subsystem and evolution of electronic and lattice temperatures. The electron scattering dynamics on the 10^-13-10^-12 sec scale and two-photon absorption process are discussed. The laser-induced coherent vibrations of silver nanoparticles were observed in transient transmission experiments for relatively large particles with radii ~35 nm.

The aim of present study is the investigation of the electric reaction arising in bone subjected to mechanical loadings. Firstly, specimen was fabricated from femur of cow, and ultrasonic propagation in bone was measured by ultrasonic technique. Secondary, 4-point bending test was conducted up to fracture, and electric reaction arising in bone was measured during loading. Thirdly, cyclic 4-point bending test was conducted to investigate the effect of applied displacement speed on electric reaction.

Plants have the ability to develop large mechanical force from chemical energy available with bio-fuels. The energy released by the cleavage of a terminal phosphate ion during the hydrolysis of a bio-fuel assists the transport of ions and fluids in cellular homeostasis. Materials that develop pressure and hence strain similar to the response of plants to an external stimuli are classified as nastic materials. This new class of actuators use protein transporters as functional units to move species and result in deformation [Leo et al 2005 (Proceedings of IMECE - 06)]. The ion transporters are hydrocarbons which are formed across the cellular membranes. The membranes that house the ion transporters are aggregates of phospholipids rigidized by cytoskeleton. Reconstituting these nano-machines on a harder matrix is quintessential to build a functional device. Artificial phospholipid membranes or Biliayer lipid membranes (BLM) have poor structural integrity and do not adhere to most surfaces. Patterned arrays of pores made on Poly-propylene glycol-diacrylate (PPG-DA) substrate, a photo curable polymer was made available to us for initial design iterations for an actuator. Hydrophobicity of PPG-DA posed initial problems to support a BLM. We modified the surface of micropatterned PPG-DA membrane by gold plating it. The surface of the porous PPG-DA membranes was plated with gold (Au). A 10nm seeding layer of Au was sputtered on the surface of the membrane. Further gold was reduced onto the sputtered gold surface [Supriya et al(Langmuir 2004, 20, 8870-8876)] by suspending the samples in a solution of hydroxylamine and Hydrogen tetrachloroaurate(III) trihydrate [HAuCl4.3H2O]. This reduction process increased the thickness of the gold, enhanced its adhesion to the PPG-DA substrate and improved the shapes of the pores. This surface modification of PPG-DA helped us form stable BLM with 1-Palmitoyl-2-Oleoyl-sn-Glycero-3- [Phospho-L-Serine] (Sodium Salt) (POPS), 1-Palmitoyl-2-Oleoyl-sn-Glycero- 3-Phosphoethanolamine (POPE) lipids. The observed ionic resistance of the BLM remained stable and sustained 4 mm water column for the the four hours observation period. This article describes the procedure we adopted to modify the PPG-DA substrate, form a BLM and the procedure to quantify the stability of the BLM formed with -amine and -thiol head groups in the lipids.

Nastic materials are high energy density active materials that mimic processes used in the plant kingdom to produce large deformations through the conversion of chemical energy. These materials utilize the controlled transport of charge and fluid across a selectively-permeable membrane to achieve bulk deformation in a process referred to in the plant kingdom as nastic movements. The nastic material being developed consists of synthetic membranes containing biological ion pumps, ion channels, and ion exchangers surrounding fluid-filled cavities embedded within a polymer matrix. In this paper the formulation of a biological transport model and its coupling with a hyperelastic finite element model of the polymer matrix is discussed. The transport model includes contributions from ion pumps, ion exchangers, and solvent flux. This work will form the basis for a feedback loop in material synthesis efforts. The goal of these studies is to determine the relative importance of the various parameters associated with both the polymer matrix and the biological transport components.

The motion and growth of plants is the inspiration for a new biomimetic actuator that uses fluid transport across a bilayer lipid membrane (BLM) to create internal pressure and cause displacement in the actuator. In order for the actuator to be viable the BLM must be able to withstand this internal pressure without failing. In this study BLMs are formed over a porous polycarbonate substrate and a hydrostatic pressure is applied to the BLM and gradually increased until it fails. This test is performed over different pore sizes to measure the failure pressure of the BLM as a function of pore radius. A similar test is used for polymer films to compare the failure pressure trends of a BLM to conventional engineering materials. The polymer films and BLMs are modeled as a simply supported circular plate under uniform load, first with the assumption of small deflections and then with the assumption of large deflections. It was found that the large deflection model better represents the trend of failure pressure versus pore radius than the small deflection model.

Electro-Active Paper (EAPap) materials based on cellulose are attractive for many applications because of their low voltage operation, lightweight, dryness and low power consumption. In addition, EAPap materials are bio-degradable that is important property for artificial muscle actuators as bio-mimetic actuators with controlled properties and shapes. EAPap actuators have been made using cellulose papers coated with thin electrode layers. This actuator showed a reversible and reproducible bending movement. In order to improve both displacement and force of this, complementary conjugated novel material, composed of conductive polymer and carbon nanotubes, is coated on both sides of EAPap. This composite coated EAPap is termed as hybrid EAPap. Used composite consist of multi-walled carbon nanotubes (MWNT) and polyaniline (PANi). It is expected that the use of MWNT can enhance the stiffness of the tri-layered actuator as well as improving the force output. Furthermore, the presence of the MWNT/PANi electrodes may increase the actuation performance of the EAPap material. MWNTs are dispersed in NMP (1-Methyl-2-pyrrolidine), and the resulting suspension is mixed and sonicated with anion doped PANi. Obtained MWNT/PANi/NMP solution is cast on the EAPap by spin coating, and it is dried in a vacuum oven. The effect of processing parameters on the final performance of the composite electrodes is assessed and quantified in terms of the electrical conductivity under dc and ac measurement conditions. The actuation output of the MWNT/PANi/EAPap samples is tested in an environmental chamber in terms of free displacement and blocking force. The performance of the hybrid actuators is also investigated in terms of frequency, voltage and humidity to help shed light on the mechanism responsible for actuation. Comparison of these results in that of the EAPap with PANi and EAPap are also accomplished.

Electro-Active Paper (EAPap) has been interested in due to its merits in terms of lightweight, dry condition, large displacement output, low actuation voltage, low power consumption and biodegradability. EAPap actuator has been made with cellulose material. Cellulose fibers are dissolved into a solution and extruded in a sheet form, and thin gold electrodes are made on it. This out-of-plane bending deformation is useful for achieving flapping wings, micro-insect robots, and smart wall papers. On the other hand, in-plane strains, such as extension and contraction of EAPap materials are also promising for artificial muscle applications since the Young's modulus of EAPap materials is large. Therefore, we intended to investigate the in-plane strain of EAPap materials in the presence of electric fields. The EAPap samples preparation and the in-plane strain measurement are explained. The test results are shown in terms of electric field, frequency and the orientation of the samples. The power consumption and the strain energy of EAPap samples are discussed. Although there are still unknown facts in EAPap materials, this in-plane strain may be useful for artificial muscle applications.

Electrorheological properties of PDMS gel and PPV/PDMS blend were investigated experimentally under an oscillatory shear mode at the temperature of 27 °C to determine the effects of crosslink ratio, electric field strength and doping level. For the pure PDMS gels, the storage modulus, G', increases with increasing crosslinking ratio and electric field at all frequencies between 0.1-100 rad/s. As an electric field is applied, the polymer molecules become polarized resulting in the interaction through the electrostatic force between the polarized PDMS molecules. The PDMS gel system with the crosslinking ratio of 0.01 possesses the highest G sensitivity to electric field. For the PPV/PDMS blends (PPV/PDMS_10), the dynamic moduli, G' and G", are higher than those of pure PDMS in the absence of electric field because PPV particles act as a filler in PDMS matrix. The G' sensitivity of PDMS increases up to 35 % at the electric filed strength of 2 kV/mm. Moreover, the doped PPV/PDMS blend (doped PPV (1:10)/PDMS_10) shows the highest G' sensitivity (170 %) due to interacting electrostatic forces between electric field induced dipole moments of the conductive molecules.

Ionic polymer transducers are a class of electroactive polymers that are able to generate large strains (1-5%) in response to low voltage inputs (1-5 V). Additionally, these materials generate electrical charge in response to mechanical strain and are therefore able to operate as soft, distributed sensors. Traditionally, ionic polymer transducers have been limited in their application by their hydration dependence. This work seeks to overcome this limitation by replacing the water with an ionic liquid. Ionic liquids are molten salts that exhibit very high thermal and electrochemical stability while also possessing high ionic conductivity. Results have shown that an ionic liquid-swollen ionic polymer transducer can operate for more than 250,000 cycles in air as compared to about 2,000 cycles for a water-swollen transducer. The current work examines the mechanisms of transduction in ionic liquid-swollen transducers based on Nafion polymer membranes. Specifically, the morphology and relevant ion associations within these membranes are investigated by the use of small-angle X-ray scattering (SAXS), Fourier transform infrared spectroscopy (FTIR), and nuclear magnetic resonance spectroscopy (NMR). These results reveal that the ionic liquid interacts with the membrane in much the same way that water does, and that the counterions of the Nafion polymer are the primary charge carriers. The results of these analyses are compared to the macroscopic transduction behavior in order to develop a model of the charge transport mechanism responsible for electromechanical coupling in these membranes.

Structures that can physically adapt to fulfill many roles can enable a new generation of high-performance military systems. The key to achieving substantial benefit from shape-changing operations is large changes in structural geometry and stiffness. In this study, we demonstrate variable stiffness cellular materials capable of large global changes in area through local buckling modes. Furthermore, stiffness properties and Poisson ratios may be tailored to provide desirable structural reconfiguration properties such as negative Poisson ratio and highly anisotropic stiffness. However, stiffness properties of cellular materials are two to three orders of magnitude below their constitutive materials properties. Their elastic properties can vary considerably as a function of the applied strain level due to the redistribution of structural material within the cells. Another complication is the difficulty in controlling the local buckling mode due to sensitivity to boundary conditions and loading conditions.

We examine the mechanical response of a heterogeneous dielectric media to electorstatic excitation. The governing equations for the coupled electromechanical problem are determined together with the required statements of the boundary and the interface continuity conditions. Results for the class of sequentially laminated composites are calculated and compared with corresponding finite element simulations and analytical estimates. These calculations demonstrate that the electromechanical coupling can be improved by considering non-homogeneous electromechanical actuators. These findings are in agreement with recent experimental works showing that the limitations of EAP actuators can be overcome by making composites of flexible and high dielectric modulus materials.

This paper examines the dynamic electroelastic response of Rosen-type piezoelectric transformers in a combined experimental and numerical investigation. Experiments were performed to measure the electrical impedance and voltage gain at various frequencies. The finite element method was also used to solve the coupled electro-elastic boundary value problem. The electrical impedance and voltage gain were calculated and a comparison was made between experiment and simulation. The effects of load resistance and capacitance on the voltage gain and electroelastic field concentrations were also discussed.

In this study, we derive an analytical solution for the simply supported and multilayered unimorph piezoelectric composite actuator as a beam model under applied voltage and external mechanical loads. The obtained solutions based on Rayleigh-Ritz technique including thermal effect and piezo-mechanical coupling effect show their convenience in various problems with different loading and boundary conditions. The von-Karman nonlinear terms in strain-displacement relations is also taken into account in the model. As a numerical illustration, model of LIPCA-C3 (LIghtweight Piezo-Composite Actuator) is analyzed. The results are compared with finite element analysis and experiment ones. Discussion on the approach and suggestions for future research activities are also presented.

TiNi shape memory alloy has been used in many application fields due to its excellent shape memory effect (SME) and superelasticity (SE). However, it is difficult and costly to machine TiNi alloy into complex shapes due to its low ductility. To address this problem, one approach is near-net shape processing by vacuum plasma spraying (VPS). In this study, the transformation behavior, mechanical properties and microstructure of TiNi alloy processed by VPS method are studied. The as-sprayed and homogenized TiNi alloy exhibited compositional variations in the sample, though both samples exhibited a single TiNi phase with low transformation temperatures, below 170 K Aging the homogenized sample at 773 K for 18 ks led to an increase in the transformation temperature, resulting in good transformation behavior. Specifically, DSC measurement revealed clear transformation peaks due to Martensite, austenite and R-phase transitions. Compression testing of a sample aged at 773 K for 18 ks exhibited a good SME below M_f and superelasticity (SE) above A_f. The recoverable strain due to SME and SE were more than 2.4 % and 5.0 %, respectively. TEM studies confirmed that aTi₃Ni₄ precipitate was formed by aging at 773 K for 18 ks.

Effect of terbium addition on the structure, phase constitution and hardness of the Ni₄₉Mn₂₉Ga₂₂ alloy was studied. The Tb content varied in the range of 0-2 at.%. It was found that the Tb addition substantially refines the grain size, which dropped from 200-400 μm, for the Tb-free alloy, down to 30-50 μm for the 2 at.% Tb material. The terbium exhibited negligible solubility in the matrix phase and formed grain boundary layer. The mean composition of the boundary layer was: Tb - 16, Ni - 55, Mn - 7 and Ga - 22 at.%. The phase analysis revealed the presence of the following major phases in the alloys: Ni₂MnGa, Ni₃Ga. All the alloys studied exhibited martensitic structure at room temperature. The Tb addition did not affect the Curie temperature, which is consistent with the finding that Tb does not dissolve in the Ni₂MnGa phase. However, it was found that Tb addition changed the phase transformations temperatures. The A_s temperature (martensite-to-austenite transformation starting temperature) and M_s temperature (martensite-to-austenite starting temperature) grow slightly for low Tb concentrations and subsequently decrease for higher the Tb contents. The Tb containing alloys exhibited increased hardness, by about 40%, which was apparently caused by the grain refinement. No significant effect of the Tb addition on the magnetic shape memory effect was observed.

This paper describes a novel approach for the actuation of a Ni-Mn-Ga single crystal in the martensite phase using transverse acoustic waves. The acoustic waves, generated by piezoelectric stacks, produce shear stress levels high enough to induce twin boundary motion in the Ni-Mn-Ga crystal. By using repeated asymmetric pulses, the crystal can be made to transform reversibly from one of two variants to the other. The resulting engineering shear strain as the crystal transforms is theoretically as high as 12%. Two experimental apparatuses were developed that are able to produce actuation through this acoustic mechanism. In the first, two 33-mode piezoelectric stacks are mounted at a 45 deg angle to the base of a single Ni-Mn-Ga crystal. This geometry allows the longitudinal motion of each stack to be converted into transverse motion of the Ni-Mn-Ga crystal. In experiments using this apparatus, we were able to obtain 7.7% engineering shear strain over the length of the Ni-Mn-Ga crystal, and about 10.6% engineering shear strain over that portion of the crystal that exhibited twin boundary motion, close to the theoretical maximum. Some portions of the crystal appeared to be inactive, due to locking of incompatible twin systems. In the second apparatus, a single 15-mode piezoelectric stack was used to generate shear waves directly. In preliminary testing, we were able to achieve only about 1.9% engineering shear strain, probably due to incomplete conditioning of the Ni-Mn-Ga crystal to improve twin boundary motion.

This paper deals with the synthesis, characterization, and some applications of Mn-Zn ferrite nanoparticles. The Mn-Zn ferrite was prepared from metallic nitrates, iron citrate and citric acid with the co-precipitation method with different pH values and it was further used to synthesis Mn-Zn ferrite with polariser i.e. H₂O₂ (Hydrogen peroxide). The X-ray diffraction pattern shows the single phase spinel structure of the ferrites. The effect of pH and the oxidizing agent on the electrical properties of Mn-Zn ferrite was studied. The d.c. resistivity is improved with the pH value and further improved by the addition of H₂O₂ (Hydrogen peroxide), which acts as a strong oxidizing agent. The dielectric constant decreases with increasing pH value; at the same time the dielectric loss also decreases. Further the decrease in dielectric properties by addition of oxidizing agent are justified by inverse proportionality between resistivity and dielectric constant.