Recent advances in technology have led to the development of nanostructured materials based on the assembly of carbon nanotubes with applications ranging from micromechanics to electronics and energy storage. An exciting property of carbon nanotubes is its electro-mechanical actuation behavior. The actuation behavior of the carbon nanotube paper (bucky paper) is greatly influenced by its surface resistance. In this work we propose to find out the resistance of the bucky paper, a porous meshwork of carbon nanotubes, automatically in a controlled and reproducible manner. The resistance is measured by using four wire resistance measurement instruments. It has two pairs of identical poles, positive and negative. Opposite polarity poles are short-circuited leading to two probes out of which one is taken as a reference and the other as varying probes. Considering multi walled carbon nanotube (MWNT) paper of 20 mm diameter, the reference probe is kept fixed at a single point and the varying probe is moved in different directions of the bucky paper plane. When performed manually the obtained results are highly nonlinear having many disturbances. In order to avoid these disturbances, an automatic movable probe holder has been designed and tested which provides a reproducible condition for the measurement automated by LabVIEW^® interfacing. A direct measurement of resistance prior and later to the actuation testing is performed. Based on the results, the influence of resistance on actuation performance has been analyzed.

Electrospinning of a SWNT-polyimide composite is accomplished under DC electric field. The resulting composite fibers are characterized to assess the alignment of the SWNTs in the polyimide. Polarized Raman spectroscopy is performed using a Nicolet dispersive Raman spectrometer with a polarizer. The Raman spectrum of SWNT-polyimide fibers is recorded at several angles between the SWNT axis and the incident polarization, in the range of 0° to 180°. The Raman peak in each spectrum corresponds to the tangential mode (1590 cm-1) of the SWNT in the composite. Inspection of the spectra reveals that the maximum intensity is obtained when the polarization of incident radiation is parallel to the SWNT axis, while the smallest intensity is obtained when the polarization of incident radiation is perpendicular to the SWNT axis. Difference in the intensities when the radiation is parallel and perpendicular to the SWNT axis indicates preferential alignment of SWNTs in the polyimide fibers.

We discuss recent improvements of Metal RubberTM materials formed by electrostatic self-assembly (ESA) processing. Free-standing and mechanically robust sheets of Metal RubberTM have been synthesized with electrical conductivities approximately one order of magnitude lower than those of bulk noble metals and with moduli from 1 to 100 MPa.

We consider the possibilities of developing smart nano-structured coverings that allow one dynamically change their color in the reflected light by modify spectral position of their reflection coefficient. The suggested technology is based on the recent progresses in the field of photonics and the fabrication of silicon-compatible photonic band gap (PBG) materials, photonic crystals. It is suggested to compose the PBG structures of porous silicon and infiltrate them with active nano-compounds whose optical features can be changed by the application of the electric field, current or illumination. As a result, the controlled change of color of the composed structure can be achieved.

Nanoscale polymeric films were fabricated on Al coated glass slides using a spin coater. The thicknesses of the films (anti-reflective coatings-ARC) were 350 nm, 240 nm and 195 nm obtained at 1500 rpm, 3000 rpm and 4500 rpm, respectively. Measurement electrodes were fabricated on the ARC films using silver epoxy. Capacitance tests conducted at 1 mV and 15% relative humidity were used to determine the dielectric constant of the films over various temperature and frequency ranges. Based on the test results, it is assumed that this is a very useful technique to accurately and easily measure the capacitance and dielectric constant values of nanothickness polymeric films.

In the present study, nanosized silica particles (~100 nm) were incorporated into epoxy polymers, and then sprayed on molybdenum treated Al coupons (2024-T3) by a nozzle spray unit at different thicknesses. A urethane top coating (1 mil) was also applied on some of the initially coated surfaces. The main purpose of the SiO₂ and urethane was to absorb/block unwanted ions/molecules (i.e., Cl^-, O, OH^-, H₂O, etc.) and increase the coating performance. Several corrosion tests including electrochemical impedance spectroscopy (EIS), salt spray and salt soaking were conducted on the prepared samples using a 0.5 M NaCl solution. The Al coupons coated with such nanocomposites and a urethane top coating showed excellent coating resistances (8x10⁹ ohm-cm²) against corrosion attack. As a result, it is assumed that this novel coating system will allow coating industry to effectively protect the surface of materials.

We develop laser-based technologies for characterization and release of Surface Tension Energy (STE) in nanoparticle structures. Nanoparticle dispersed materials offer a very high potential to store energy in the form of Surface Tension. An important benefit of these systems is the increased safety and control of energy storage compared to existing chemical systems. The release technology is based on excitation of resonant plasmons in metal nanoparticles and their further laser-induced coalescence, whereas the characterization technology is related to the extraordinary sensitivity of nonlinear optical effects in nanoparticles to their surface conditions and properties. The direct relation between STE and nonlinear optical parameters of nanoparticles permits use of optical second-harmonic generation (SHG) to measure STE. The SHG probe can be applied to characterize surface properties of a wide variety of nanoparticle materials, particularly active and smart materials. In terms of surface energy elease, we concentrate on nanoparticle-dispersed materials in the form of arrays of metal nanoparticles. External laser radiation is considered to trigger interparticle coalescence due to excitation of local plasmons that are specific electro-magnetic modes in metal nanoparticles. Local plasmon excitation, in turn, lead to surface energy release in the wake of fusion of excited nanoparticles.

Electro-Active Paper (EAPap) has been investigated as an attractive EAP material for artificial muscles due to its many advantages such as lightweight, availability, low cost, large displacement output, low actuation voltage and low power consumption. The EAPap is based on cellulose material, and is shown to involve primarily transport of ions in response to an external electric field. Depending on the electrode material, EAPap has shown actuation displacement in the range of 2-4mm, at a few volts. Drawbacks of EAPap actuators include a low force output and a dependence on humidity. To address these limitations, a hybrid EAPap actuator is developed by incorporating an electrode fabricated using single-wall carbon nanotubes (SWNT)/Polyaniline (PANI) with different dopants. SWNT is dispersed in 1-Methy-2-pyrrolidone (NMP), and the resulting solution is used as a solvent for PANI and the various dopants. The SWNT/PANI/NMP solution is then deposited on the EAPap by spin coating. The coated EAPap is dried in a vacuum oven. Raman spectroscopy, X-Ray diffractometry and SEM tests are taken to confirm that the SWNT/PANI/dopant electrode material is successfully prepared by in situ polymerization. The actuation output of the SWNT/PANI/EAPap samples is tested in an environmental chamber in terms of free displacement and blocked force. When the SWNT/PANI/Cl- coated hybrid actuator is excited with 7Vp-p, a maximum displacement of 3.1mm and a maximum power output of 0.29mW are obtained. The hybrid actuator shows an improved actuation force as a result of enhanced stiffness of EAPap.

Ionic polymer transducers are a class of active material that exhibit interesting chemoelectromechanical coupling capabilities. Initially recognized for their chemoelectric properties, these materials have begun to receive notice as electromechanical transducers. This electromechanical coupling provides the fundamental mechanism for both actuator and sensor applications. Under relatively low electric stimuli (1-10kV/m) these materials are capable of achieving large bending strains (1-5%). Similarly these transducers provide effective sensing capabilities when subject to an applied external load or deformation. Recent studies indicate that the transducer's performance can be directly related to changes in the polymer's electrical impedance. An analytical model is proposed based upon these findings. The basic tenet of this model is that ion motion is induced as an electric field is applied across the polymer membrane. Transport theory is employed to model this ion motion through an electrostatics approach. This method yields a series of analytical expressions for charge density, electric field and electric potential across the polymer's thickness. The solution of the charge density profile is then used to calculate the isothermal transient ionic current (ITIC). Corresponding to the measured current, this ITIC expression is related to the applied voltage to yield a relationship between the applied voltage and the resultant current.

The application of electroactive polymer devices requires the availability of their properties at various operating conditions. This in turn necessitates a structure-property relationship based on an in-depth understanding of the underlying mechanism responsible for their strain-field response. Cellulose-based Electro-Active Paper (EAPap) has been studied as an attractive EAP material for artificial muscles due to its low cost, availability, lightweight, large displacement output, low actuation voltage and low power consumption. The understanding of the actuation mechanism of this material is important in order to improve the performance and also to better target the application. So far, based on the structure and processing of cellulose-based EAPap, it is believed that two actuation mechanisms are possible: ion transport and dipolar orientation. To physically investigate the actuation mechanism of EAPap, several tests are performed. X-ray diffractogram study exhibits that EAPaps have more amorphous parts than raw cellulose fibers, and there is some possibility of structural change during activation. NMR study shows that the cellulose paper is an ordered structure. TSC current showed a linear relationship with poling electric field, indicating dipolar orientation. . Impedance analysis of EAPap showed an evidence of ionic migration effect. Thus, we conclude that there can be piezoelectric effect and ionic migration effect at the same time associated with dipole moment of cellulose paper ingredients. The amount of these effects may be depending on environmental condition. Quantitative investigation of these two effects on EAPap should be followed with environmental condition.

Reversible electrochemical compound formation has considerable potential to form the basis of a high-strain high-force multifunctional actuator technology. We present preliminary experimental demonstrations of the reversible work capability of solid-state electroplating. Our experimental test case is the volume expansion incurred during the reversible electrochemical formation of thin-film Li metal from a ceramic lithium ion storage medium, LiCoO₂ as part of the standard operation of a state-of-the-art Li-ion battery. Reversible work is accomplished through the plating or stripping of the pure Li film against an external load. With the active portion of the structure as a basis, we observe ~10% strain against loads up to 2 MPa, with the load being limited by battery failure. No change in actuation characteristics is observed up to failure.

A computational micromechanics model applying Monte Carlo methodology has been developed to predict the equilibrium state of a single cluster of an ionomeric polymer with cluster morphology. No assumptions are made regarding the distribution of charge or the shape of the cluster. Assuming a constant solvated state, the model tracks the position of individual ions within a given cluster in response to ion-ion interaction, mechanical stiffness of the pendant chain, cluster surface energy, and external electric field loading. Expressions are developed to directly account for forces imposed on ions due to ion-cluster surface interaction. The model is applied to study the impact of counterion size. Predictions suggest that smaller counterions lead to a system which better facilitates ion transport than larger counterions. Results further suggest that, regardless of ion size, ion pairing is rarely complete; this in turn suggests that the classic assumptions will tend to under-predict electromechanical actuation response in general.

Plants have the ability to develop large mechanical force from chemical energy available with bio-fuels. The energy released by ATP hydrolysis assists the transport of ions and fluids to achieve volumetric expansion and homeostasis. Materials that develop pressure and hence strain similar to bio-materials are classified as nastic materials. Recent calculations for controlled actuation of an active material inspired by biological transport mechanism demonstrated the feasibility of developing such a material with actuation energy densities on the order of 100 kJ/m³. Our initial investigation was based on capsules that generate pressure thus causing strain in the surrounding matrix material. Our present work focuses on our efforts to fabricate a representative actuation structure and describes the chemo-mechanical constitutive equation for such a material. The actuator considered in this work is a laminated arrangement of a hydraulic actuator plate with microscopic barrels and a fluid reservoir kept separated by a semi-permeable membrane dispersed with biological transporters. We present here our initial design and a mathematical model to predict the fluid flux and strain developed in such an actuator.

Reconfigurable and morphing structures can potentially provide a range of new functionalities including system optimization over broad operational conditions and multi-mission capability. Previous efforts in morphing surfaces have generally focused on small deformation of high stiffness structural materials (e.g. aluminum, CFRP) or large deformation of low stiffness non-structural materials (e.g. elastomers). This paper introduces a new approach to achieving large strains in materials with high elastic moduli (5 to 30+ GPa). The work centers on creating variable stiffness composite materials which exhibit a controllable change in elastic modulus (bending or axial) and large reversible strains (5-15%). Several prototype materials were prepared using a commercial shape memory polymer, and measurements on these materials indicate a controllable change in stiffness as a function of temperature along with large reversible strain accommodation. We have fabricated and tested several design variations of laminar morphing materials which exhibit structural stiffness values of 8-12 GPa, changes in modulus of 15-77x, and large reversible bending strain and recovery of 2% area change in specific sample types. Results indicate that significant controllable changes in stiffness are possible.

As the application of fibre reinforced polymer composites (FRP) becomes more widespread there is a desire to add functionality beyond that of simple mechanical properties in order to facilitate the development of 'smart' materials. For example, the functionality being discussed in this paper is the imparting of significant magnetic properties to a FRP. This can take the form of soft magnetic performance for use in electrical machines or hard magnetic performance for novel forms of sensing or power generation. It has been demonstrated that by using hollow glass fibres as a reinforcement, magnetic material can be introduced into these fibres without significant effects on the structural behaviour of the FRP. The current studies have included the assessment of such a magnetic FRP in a variety of applications. The addition of hard magnetic materials, e.g. magnetite and barium ferrite, has been achieved through the use of nanopowders and the resulting FRP has been assessed for morphing structures applications. The magnitude of magnetic performance that can be currently achieved is controlled by the availability of suitable magnetic materials in fine powder form and the volume of magnetic material which can be incorporated within the fibres.

Combining smart materials with other materials to form composites has received attention due to the possibility of obtaining improved performance and functionality. One such composite combines Terfenol-D particulates with a soft epoxy, with the particles magnetically aligned in one direction forming an anisotropic structure. In this paper we consider the fabrication of the particle composites and the implementation of the composites in a hybrid Ferroelectric/ferromagnetic transducer presented previously. The composite was first tested quasistatically for obtaining material property information and identifying suitable bias conditions. The transducer was then tested for dynamic response, both of the individual parts and with the full system powered, for purposes of validating the concept of hybrid actuation and the model. The transducer is modeled through basic mechanical vibration principles, electroacoustics theory, and constitutive relations for electrostrictive and magnetostrictive materials operated in linear regimes. The paper highlights the advantageous properties of the Terfenol-D composite when utilized in this hybrid transducer in regard to the increased resistivity, decreased eddy current losses, and reduced density. The paper also proposes a model based approach for understanding the factors that control the reduced, and hence disadvantageous in some cases, stiffness and electromechanical coupling coefficient of the Terfenol-D composite.

Magnetostrictive Terfenol-D particle actuated epoxy polymer matrix composites were prepared with polyamine and anhydride cured epoxy polymer matrices. The different matrix epoxies exhibited large differences in glass transition and creep behavior. The differences in matrix thermal-mechanical properties resulted in important differences in temperature dependant damage behavior and magneto-elastic strain output in the Terfenol-D particle actuated epoxy polymer matrix composites.

A high sensitive and heat-resistive magnetic sensor using a magnetostrictive/piezoelectric laminate composite is investigated. The sensing principle is based on the magnetostrictive- and piezoelectric effect, whereby a detected yoke displacement is transduced into a voltage on the piezoelectric materials. The sensor is intended to detect the displacement of a ferromagnetic object in a high temperature environment, where conventional magnetic sensors are not useful. Such applications include sensors in engine of automobile and machinery used in material processing. The sensor features combination of a laminate composite of magnetostrictive/piezoelectric materials with high Curie temperatures and an appropriate magnetic circuit to convert mechanical displacement to sensor voltages and suppress temperature fluctuation. This paper describes the sensing principle and shows experimental results using a composite of Terfenol-D and Lithium Niobate to assure high sensitivity of 50V/mm at bias gap of 0.1mm and a temperature operating range over 200 °C.

The primary objective of this study is to estimate the parameters of constitutive models characterizing the rheological properties of ferrous and cobalt nanoparticle-based magnetorheological fluids. Constant shear rate rheometer measurements were carried out using suspensions of nanometer sized particles in hydraulic oil. These measurements yielded shear stress vs. shear rate as a function of applied magnetic field. The MR fluid was characterized using both Bingham-Plastic and Herschel-Bulkley constitutive models. Both these models have two regimes: a rigid pre-yield behavior for shear stress less than a field-dependant yield stress, and viscous behavior for higher shear rates. While the Bingham-Plastic model assumes linear post-yield behavior, the Herschel-Bulkley model uses a power law dependent on the dynamic yield shear stress, a consistency parameter and a flow behavior index. Determination of the model parameters is a complex problem due to the non-linearity of the model and the large amount of scatter in the experimentally observed data. Usual gradient-based numerical methods are not sufficient to determine the characteristic values. In order to estimate the rheological parameters, we have used a genetic algorithm and carried out global optimization. The obtained results provide a good fit to the experimental data.

The addition of Ga to b.c.c. Fe greatly increases the magnetostriction of Fe in the <100> directions (by a factor of 12 in Fe₈₁Ga₁₉). These Fe-based materials are mechanically tough and thus can be used under both compressive and tensile loading. The object of this study is to examine the effects of temperature aging on Fe_81.6Ga_18.4 alloys with built-in uniaxial stress anisotropies. To accomplish this, a transverse anisotropy was built into these positive magnetostrictive Fe-Ga (Galfenol) alloys by heat treatment under high compressive stresses. Annealing temperatures between 600 and 635°C and compressive stresses between 100 and 219 MPa produced uniaxial anisotropies between 2 and 9 kJ/m³. It is now possible to obtain magnetostrictions greater than 250 ppm over a broad range of stresses, extending from far into the compressive stress region through zero stress and into the tensile region. In this paper we examine the effect of aging at elevated temperatures on the built-in uniaxial anisotropy and magnetostriction of these alloys. Aging at 150°C for 697 hours left the magnetostriction unchanged. At 200°C most of the uniaxial anisotropy had disappeared after 525 hours. At 250°C, about two-thirds of the uniaxial stress was lost after 168 hours and very little remained after 336 hours.

Research has demonstrated that a built-in uniaxial stress can be achieved in Galfenol materials such that with no externally applied compressive stress, the material appears to be under compression of up to 48 MPa. This built-in stress creates the opportunity for Galfenol to be used under both tensile and compressive loads with full magnetostrictive capability. In order for this effect to be useful in real-world applications, limitations of the stress-annealing must be identified. Typical applications of magnetostrictive materials result in cyclic stress loads and cyclic magnetic fields being applied to the material along with other loading conditions such as elevated temperatures and shock loads. This research investigated the effect of cyclic stress loading and cyclic magnetic fields on the behavior of stress-annealed Galfenol 18.4 (Fe_81.6Ga_18.4) polycrystal samples with approximately 40 MPa of induced stress in the samples. Testing included cyclic stresses up to 55 MPa for as much as 106 cycles at low frequencies (<10 Hz) and cyclic magnetic fields of amplitudes from 4 kA/m up to 20 kA/m. Because of sample failure issues in the cyclic stress tests, the full 106 cycles were only applied at loads up to 28 MPa. Results of all testing show little or no change in the stress-annealed state of Galfenol 18.4 (Fe_81.6Ga_18.4) polycrystal samples. Future testing will increase levels of cyclic stress tests and combine stress and magnetic cyclic loads.

The surface-energy-induced selective grain growth with a specific surface plane can be governed in polycrystalline (Fe_81.3Ga_18.7) + 0.5at.%B alloys doped with sulfur by controlling the segregation of sulfur through conventional rolling and texture annealing, where boron improves ductility due to suppressing grain boundary fracture during rolling process. The textured sheet, which was annealed at 1200°C for 2h under flowing argon and then quenched in water, exhibits a maximum magnetostriction of about 200 ppm along the rolling direction. During an argon annealing process, a convex profile in magnetostriction as a function of annealing time is formed. As the annealing temperature increases, the observed peak in the convex profiles shifts to less annealing time and also narrows. As-rolled (Fe_81.3Ga_18.7) + 0.5 at.%B + 0.005 at.%S sheets with large amounts of sub-grain which most likely have been deformed by the rolling process have some {100} and {111} grains parallel to the rolling direction. While texture annealing appears to eliminate the majority of the sub-grains present to below 1% of sub-structured or deformed area in the sheet annealed at 1200°C for 2h. From a texture standpoint the some clustered {100} poles were found and ~25° away from the rolling direction. And the {100} poles are centered right on the rolling direction for the highly textured subset.

We have been proposing a magnetic force control method using the inverse magnetostrictive effect of magnetostrictive materials. With a parallel magnetic circuit consisting of iron yokes and permanent magnet, the magnetic force exerting on the yoke can be varied by the mechanical stress applied to the magnetostrictive material. The characteristics of the magnetic force, such as stress-sensitivity and range of the variation, are mostly dependent on the material properties of the magnetostrictive material. So far we have mainly investigated the magnetic force using Terfenol-D (Tb-Dy-Fe alloy) and demonstrated its usefulness in practical applications. Recently, Galfenol, Iron-Gallium is widely noticed for alternative for the Terfenol with several advantages. Even lower magnetostriction, it is superior to the Terfenol with high piezomagnetic constant, low hysteresis loss, high saturation and good machinability. In this paper, we investigate the potential of the Galfenol for the magnetic force control method which can enlarge the variation range of the magnetic force and increase the stress-sensitively. The formulation of the magnetic force and experimental results of fundamental material properties and magnetic force of the Galfenol and Terfenol clarifies the merits of the Galfenol inherited from high saturation and high piezomagnetic constant. The correlation between the piezomagnetic constant and bias field is verified, providing magnetic circuit design strategy to make full use of the material properties of the Galfenol for future applications.

Alloys of iron and non-magnetic gallium (of the form Fe_1-xGa_x), collectively referred to as Galfenol, have been shown to exhibit magnetostrictions in excess of 300 ppm under quasi-static magnetic fields [1]. However, to harness the full potential of this material as an actuator, characterization of Galfenol's magneto-mechanical properties under dynamic operating conditions is required. Broadband frequency domain results include strain per applied magnetic field transfer functions and complex electrical impedance functions. The properties investigated were linear mechanical rod stiffness, magneto-mechanical coupling coefficient, modulus of elasticity, and system structural damping. The samples tested were single-crystal cylindrical Galfenol rods with an atomic percentage of Gallium varying from 18 to 22.5. Some rods were composed of laminated strips of Galfenol to reduce eddy current effects and increase the efficiency of transduction. It was found that lamination did not significantly degrade the stiffness nor increase the structural damping, but did increase the magneto-mechanical coupling coefficient by ~50% over the solid rod for the conditions studied.

In the current study Active Fiber Composites (AFC) utilizing Lead-Zirconate-Titanate (PZT) fibers with Kapton screen printed interdigitated electrodes (IDE) were integrated into orthotropic glass fiber reinforced plastic (GFRP) laminates to investigate integration issues associated with smart structures and host laminate integrity. To aid in this goal surrogate or "Dummy" AFC (DAFC) were designed using a GFRP core and Kapton outer layers to match the longitudinal mechanical and interface properties of the AFC. 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. Two integration techniques, cutout and simple insertion were investigated using DAFC, with little difference seen between the integrity of laminates prepared using these two methods. Using this testing scheme the influence of device placement in relation to position extending away from the laminate symmetric axis was found to have an effect on laminate integrity in tensile loading. As the DAFC were placed far from the laminate symmetry axis, the ultimate tensile strength and strain of the laminates decreased in a linear manner while the Young's modulus of the laminates remained constant. Similar trends were observed with integrated AFC specimens. The performance of integrated AFC was characterized using monotonic cyclic tensile loading with increasing strain levels. A transition region was observed between strains of 0.05%-0.50%, with a dramatic decrease in AFC sensitivity from a maximum to minimum value.

Piezoelectric diaphragms are used as synthetic jets because of their size, rapid time response, and relatively low power consumption. Among the piezoelectric diaphragms used are unimorphs and Bimorphs. In this study, a bimorph diaphragm, a thin Unimorph pre-stressed device and a Radial Field Diaphragm (RFD) are compared. A bimorph consists of two bonded PZT discs, a thin Unimorph pre-stressed device consists of copper, PZT, and stainless steel and a Radial Field Diaphragm consist of a layer of PZT with inter-digitized electrodes encapsulated in Kapton film. The effects of driving waveform on jet velocity are studied for each of these actuators. The actuators are driven at varying frequencies and the differential pressure in the cavity is monitored.

Relaxor ferroelectric PZN-xPT and PMN-xPT single crystals exhibit excellent electromechanical coupling properties that depend on crystallographic orientations. In this study compressive stress and electric field were applied to relaxor single crystals [Pb(Zn_1/3Nb_2/3)O₃]_0.955-[PbTiO₃]_0.045 (PZN-4.5%PT) in a series of crystal orientations between <001> and <111>, and the corresponding strain and electric displacement were measured. It was found that as the angle of the orientation cut is rotated from <001> to <111>, the piezoelectric coefficient d33 drops and hysteresis increases dramatically. A crystal variant based approach was used to model the piezoelectric coefficients and remnant electric displacement. The bipolar electro-mechanical response of these crystals is presented. Observed hysteresis and nonlinear phenomena related to polarization reorientation and phase transitions is discussed. In actuator design and performance control, these results give a guideline regarding appropriate external fields in order to prevent depolarization, heat generation and damage.

TRS is developing new actuators based on single crystal piezoelectric materials such as Pb(Zn_1/3Nb_2/3)_1-xTi_xO₃ (PZN-PT) and Pb(Mg_1/3Nb_2/3)_x-1Ti_xO₃ (PMN-PT) which exhibit very high piezoelectric coefficients (d₃₃ = 1800-2200 pC/N) and electromechanical coupling factors (k₃₃ > 0.9), respectively, for a variety of applications, including active vibration damping, active flow control, high precision positioning, ultrasonic motors, deformable mirrors, and adaptive optics. The d₃₂ cut crystal plate actuators showed d₃₂ ~ -1600 pC/N, inter-digital electroded (IDE) plate actuators showed effective d₃₃ ~ 1100 pC/N. Single crystal stack actuators with stroke of 10 μm-100 μm were developed and tested at both room temperature and cryogenic temperatures. Flextensional single crystal piezoelectric actuators with either stack driver or plate driver were developed with stroke 70 μm - > 250 μm. For large stroke cryogenic actuation (> 1mm), a single crystal piezomotor was developed and tested at temperature of 77 K-300K and stroke of > 10mm and step resolution of 20 nm were achieved. In order to demonstrate the significance of developed single crystal actuators, modeling on single crystal piezoelectric deformable mirrors and helicopter flap control using single crystal actuators were conducted and the modeling results show that more than 20 wavelength wavefront error could be corrected by using the single crystal deformable mirrors and +/- 5.8 ° flap deflection will be obtained for a 36" flap using single crystal stack actuators.

TRS is developing new transducers based on single crystal piezoelectric materials such as Pb(Mg_1/3Nb_2/3)_x-1Ti_xO₃ (PMN-PT). Single crystal piezoelectrics such as PMN-PT exhibit very high piezoelectric coefficients (d₃₃ ~ 1800 to >2000 pC/N) and electromechanical coupling factors (k₃₃ > 0.9), respectively, which may be exploited for improving the performance of broad bandwidth and high frequency sonar. Apart from basic performance, much research has been done on reducing the size and increasing the output power of tonpilz transducers for sonar applications. Results are presented from two different studies. "33" mode single crystal tonpilz transducers have reduced stack lengths due to their low elastic stiffness relative to PZTs, however, this produces non-ideal aspect ratios due to large lateral dimensions. Alternative "31" resonance mode tonpilz elements are proposed to improve performance over these "33" designs. d₃₂ values as high as 1600 pC/N have been observed, and since prestress is applied perpendicular to the poling direction, "31" mode Tonpilz elements exhibit lower loss and higher reliability than "33" mode designs. Planar high power tonpilz arrays are the optimum way to obtain the required acoustic pressure and bandwidth for small footprint, high power sensors. An important issue for these sensors is temperature and prestress stability, since fluctuations in tonpilz properties affects power delivery and sensing electronic design. TRS used the approach of modifying the composition of PMN-PT to improve the temperature dependence of properties of the material. Results show up to a 50% decrease in temperature change while losing minimal source level.

Electric-field-induced phase transitions and piezoelectric properties of <001>-oriented Pb(Mg_1/3Nb_2/3)O₃-32%PbTiO₃ (PMN-PT) single crystals have been investigated as a function of temperature. It was found that the phase transitions and piezoelectric properties for PMN-PT crystals are strongly dependent on temperature. The measurements of polarization and longitudinal strain as a function of a unipolar electric field show that the field for the induced monoclinic-tetragonal phase transition decreases linearly with temperature in the range between 23 °C and 75 °C. Raising the temperature can stabilize the tetragonal phase in <001>-oriented PMN-PT crystals. The effective longitudinal piezoelectric constant, d₃₃, in the monoclinic phase increases with temperature. Meanwhile in the field-induced tetragonal phase, d₃₃ is much smaller and has little change with temperature. The electric-field-induced phase transition from a cubic phase to a tetragonal phase was observed at 125 °C.

(1-x)BiScO_3-xPbTiO₃ (BSPT) polycrystalline material with a morphotropic phase boundary (MPB) composition (x=0.64) exhibits a high Curie temperature (T_C) about 450°C and good piezoelectric properties with d₃₃ values around 460pC/N. Manganese (Mn) modified BSPT was utilized in order to increase the electric resistivity and RC time constant. At 450°C, BSPT66-Mn ceramic exhibited a resistivity of 3x10⁷ Ohm.cm and RC value of 0.08s, respectively, significantly higher than the values for undoped BSPT and commercial PZT5 materials. The manganese additive shifts T_C of BSPT materials to lower temperatures, which were found to be 442°C and 462°C for modified BSPT64 and BSPT66, respectively. The piezoelectric behavior for the modified BSPT material was found to deteriorate slightly owing to the hardening effect of manganese, but showed superior temperature stability and enhanced resistivity. The detailed temperature dependent properties were studied in this work and compared to commercial PZT5 materials. The complete set of materials constants, including the elastic s_ij, c_ij, piezoelectric d_ij, e_ij, g_ij, h_ij, dielectric and electromechanical k_ij values were determined using resonance technique and derived from the experimental data.

Piezoceramic materials show nonlinear behavior when they are under high electrical and mechanical field. The nonlinearity is increasing when loading becomes rate or frequency dependent. In addition to understand quasi-static characteristics, dynamic behaviors of piezoelectric materials are also important in some special application. In this paper rate dependent behaviour of tetragonal perovskite type piezoceramic materials is simulated using a three-dimensional micromechanical model. Energy equation is used for the onset of domain switching with taking in to account the probability functions that have been used for the assumption of domain switching under critical electromechanical field. Also, rate dependent properties of piezoceramics are investigated by implementing various frequencies of cyclic loading during the simulations in which nucleation and propagation of domains during polarization switching have been modeled with the help of linear kinetics relations. Different amplitudes of alternating loadings are also applied with changing frequencies in order to understand the macroscopic behavior of piezoelectric and ferroelectric materials such as coercive field and remnant polarization and strain characterization under various loading situations. PIC 151 is chosen as a sample piezoelectric material because of the experimental data that the material has been already observed in some experiments in the literature. The results of simulations have been given in electric displacement versus electric field hysteresis and mechanical strain versus electrical field butterfly curves under different amplitude and frequencies of high electrical field with comparison of experimental ones.

Local fracture properties in poled [Pb(Zn_1/3Nb_2/3)O₃]_(1-x)-[PbTiO₃]_x (x=0.045, PZN-4.5%PT) ferroelectric relaxor single crystals were assessed. The crystals were cut along the [100], [010], and [001] planes. Scanning electron micrographs of Vickers indentations for two different crack orientations were used to determine the crack tip toughness (K_tip) and the local critical energy release rate (G_tip). Cracks oriented along the [010] and [110] crystal planes were found to have practically identical local fracture properties. These properties were determined using Stroh's formalism to account for the large anisotropic material coefficients.

Mode I steady crack growth is analyzed to determine the toughening due to domain switching in poled ferroelectric ceramics. A multi-axial, electromechanically coupled, incremental constitutive theory is applied to model the material behavior of the ferroelectric ceramic. The constitutive law is then implemented within the finite element method to study steady crack growth. The effects of poling direction, either out of plane or in plane, and poling magnitude on the fracture toughness are investigated. Results for the predicted fracture toughness, remanent strain and remanent polarization distributions, and domain switching zone shapes and sizes are presented. Finally, the model predictions are discussed in comparison to experimental observations.

Ferroelasticity and ferroelectricity are the non linear behaviours exhibited by piezoceramics, especially in the case of high electric field or stress. Many studies have focused on the role of ferroelastic and ferroelectric switching in fracture of actuators. However, engineering reliability analyses are carried out with tools like finite element software that do not take into account these non linear phenomena. To overcome such a problem, a simplified phenomenological constitutive law has been developed and describe the hysteresis effect of piezoceramics. It is time-independent and relies on the introduction of remnant polarization and remnant strain as internal variables. Two loading surfaces, similar to the ones used in plasticity, provide the evolution laws for the internal variables. Besides, polarization-induced anisotropy in the piezoelectric tensor is taken into account. That constitutive law has been implemented in the commercial software ABAQUS. It has been necessary to develop a finite element with electrical and mechanical degrees of freedom: it is an eight node hexahedron. The stiffness matrix integrates the constitutive law from the four tangent operators given by the constitutive law. The non linear problem is solved by the Newtons method. This finite element tool is used to study the effects of applied voltage on the electroelastic field concentrations ahead of electrodes in a multilayer piezoelectric actuator. The study lies on the experimental observations made by Shindo et al. [1]. Electroelastic analysis on piezoceramics with surface electrode showed that high values of stress and electric displacement arose in the neighbourhood of the electrode tip. Thus, the strain, stress and electric displacement concentrations were calculated and the numerical results showed that ferroelectric switching arose in the area of the electrode tip, causing a change in remnant polarization and remnant strain.

Modern piezoelectric transducers normally have complicated structures and work under severe loading conditions. Application of an external load in excess of a critical level will cause domain switching in the material and therefore lead to a significant nonlinearity and hysteresis in the polarization and strain response. To develop a constitutive model concerning the large-signal nonlinear behavior of ferroelectric piezoceramics, it is desirable to determine a switching criterion in the multiaxial stress and electric field states. In this experimental work, "soft" lead zirconate titanate (PZT) specimens in initially unpoled state were subjected to a proportional electromechanical loading, in which a compressive stress and a parallel, proportional electric field were applied simultaneously. By varying the relative proportions of the stress and E-field between tests, a family of nonlinear polarization and strain responses were obtained. An attempt has been made to explain the experimental findings by simultaneously taking into account the contributions of dielectric response, elastic deformation, piezoeffects, and irreversible domain switching. Based on an offset method, switching (domain reorientation threshold) surfaces were mapped out in the biaxial stress and electric field space. Finally, several switching conditions existing in the literature were summarized and compared with the experimental data obtained in this work.

We investigate the buckling behavior of thin cylindrical shape-memory shells at room temperature, using a modified split Hopkinson bar and an Instron hydraulic testing machine. The quasi-static buckling response is directly observed using a digital camera with a close-up lens and two back mirrors. A high-speed Imacon 200 framing camera is used to record the dynamic buckling modes. The shape-memory shells with an austenite-finish temperature less than the room temperature, buckle gradually and gracefully in quasi-static loading, and fully recover upon unloading, showing a superelastic property, whereas when suitably annealed, the shells do not recover spontaneously upon unloading, but they do so once heated, showing a shape-memory effect. The gradual and graceful buckling of the shape-memory shells is associated with the stress-induced martensite formation and seems to have a profound effect on the unstable deformations of thin structures made from shape-memory alloys.

Future missions to the planets and moons in our Solar System will require new technology. Missions with surface or atmospheric mobility or sample acquisition requirements will need advanced actuation technology to operate in the extreme environments found in the Solar System. Depending on the specific mission this technology may be required to withstand 10's of Kelvin environments or temperatures exceeding that of Venus (460°C). In addition the technology may have to withstand high radiation and corrosive environments and pressures ranging from high vacuum to 100's of MPa. These challenging mission requirements push the limit in performance even under terrestrial conditions. Motors for mobility platforms, deployment devices or actuators for sampling tools are required that can operate reliably and deliver substantial torque and power. These devices must be lightweight, compact and operate effectively under extreme conditions. This paper will focus on a range of actuators based on electromechanical materials used for the applications discussed above and will present some of the challenges of developing these systems for space applications.

Dynamic deformation behavior of TiNi (superelastic grade) and TiNiCu alloy (shape memory grade) were examined using Split Hopkinson Pressure Bar. The stress-strain curves of the TiNi alloy exibits strain rate sensitivity. The flow stress in the plateau region increased with increasing of strain rate logarithmically, and the on-set stress for stress induced martensite also increased slightly. In contrast, the stress-strain curve of the TiNiCu alloy was found to be much less sensitive to strain rate. TEM observations revealed that the microstructure of the dynamically deformed TiNi is similar to that of the sample before dynamic deformation. In contrast, the dynamically deformed TiNiCu has a fine twinned structure than the sample deformed statically. Analytical constitutive equation for the dynamic deformed TiNi alloy was proposed by addition of the terms concerning the strain rate effect and temperature change due to adiabatic deformation and latent heat of martensitic transformation, the revised constitutive equation was in a good agreement with the experimental results.

The microstructure, transformation temperatures, basic tensile properties, shape memory behavior, and work output for two (Ni,Ti)Pt high-temperature shape memory alloys have been characterized. One was a Ni₃₀Pt₂₀Ti₅₀ alloy (referred to as 20Pt) with transformation temperatures above 230 °C and the other was a Ni₂₀Pt₃₀Ti₅₀ alloy (30Pt) with transformation temperatures above 530 °C. Both materials displayed shape memory behavior and were capable of 100% (no-load) strain recovery for strain levels up to their fracture limit (3-4%) when deformed at room temperature. For the 20Pt alloy, the tensile strength, modulus, and ductility dramatically increased when the material was tested just above the austenite finish (Af) temperature. For the 30Pt alloy, a similar change in yield behavior at temperatures above the Af was not observed. In this case the strength of the austenite phase was at best comparable and generally much weaker than the martensite phase. A ductility minimum was also observed just below the As temperature in this alloy. As a result of these differences in tensile behavior, the two alloys performed completely different when thermally cycled under constant load. The 20Pt alloy behaved similar to conventional binary NiTi alloys with work output due to the martensite-to-austenite transformation initially increasing with applied stress. The maximum work output measured in the 20Pt alloy was nearly 9 J/cm³ and was limited by the tensile ductility of the material. In contrast, the martensite-to-austenite transformation in the 30Pt alloy was not capable of performing work against any bias load. The reason for this behavior was traced back to its basic mechanical properties, where the yield strength of the austenite phase was similar to or lower than that of the martensite phase, depending on temperature. Hence, the recovery or transformation strain for the 30Pt alloy under load was essentially zero, resulting in zero work output.

Pt additions substituted for Ni in NiTi alloys are known to increase the transformation temperature of the alloy but only at fairly high Pt levels. However, until now only ternary compositions with a very specific stoichiometry, Ni_50-xPt_xTi₅₀, have been investigated and then only to very limited extent. In order to learn more about this potential high-temperature shape memory alloy system, a series of over twenty alloys along and on either side of a line of constant stoichiometry between NiTi and TiPt were arc melted, homogenized, and characterized in terms of their microstructure, transformation temperatures, and hardness. The resulting microstructures were examined by scanning electron microscopy and the phase compositions quantified by energy dispersive spectroscopy. "Stoichiometric" compositions along a line of constant stoichiometry between NiTi to TiPt were essentially single phase but any deviations from a stoichiometry of (Ni,Pt)₅₀Ti₅₀ resulted in the presence of at least two different intermetallic phases, depending on the overall composition of the alloy. Essentially all alloys, whether single or two-phase, still under went a martensitic transformation. It was found that the transformation temperatures were depressed with initial Pt additions but at levels greater than 10 at.% the transformation temperature increased linearly with Pt content. Also, the transformation temperatures were relatively insensitive to alloy stoichiometry within the range of alloys examined. Finally, the dependence of hardness on Pt content for a series of Ni_50-xPt_xTi₅₀ alloys showed solution softening at low Pt levels, while hardening was observed in ternary alloys containing more than about 10 at.% Pt. On either side of these "stoichiometric" compositions, hardness was also found to increase significantly.

The present work examines how the characteristics of the large thermal-compressive response of a 20 vol. % NiTi fiber 6082-T0 composite change with variations in the value of maximum tensile strain imposed during a preceding room temperature tensile process. We observe that the self thermal compression process is shifted to higher temperatures with increasing maximum room temperature tensile strain, and that the maximal thermal compression versus temperature slope becomes larger as the maximum tensile strain is increased from 4 to 6% and then becomes smaller as the maximum tensile strain is further increased to 7%.

Composites containing Shape Memory Alloy (SMA) fiber and polymer (or metal) matrix are expected as smart materials and structural materials. For example, Shape Memory Alloy Composite (SMAC) exhibits creating of compressive residual stress (Creating of internal stress) in matrix and deformation of composite under thermo-loading. In the present study, firstly, the experimental model of SMAC (NiTi/Epoxy) were fabricated, and internal stress, deformation and temperature distribution of SMAC were measured under thermo-loading by using photoelasticity, digital image corelation and infrared radiation thermometry. As a result, some assumptions were obtained to construct analytical model of SMAC. Secondaly, the analytical model considering distribution of stress and strain in SMAC was constructed based on shear lag model. Closed solutions, such as shear stress in matrix and so on, were obtained from this analytical model. Then, some analyses were conducted for predicting internal stress and deformation of SMAC during thermo-mechanical loadings by using present closed solution.

A substantial reduction in the size of control actuation systems employed in today's aerospace vehicles can enhance overall vehicle performance by reducing envelope volume requirements and inert weight. Functional materials such as shape memory alloys (SMA's) offer the opportunity to create compact, solid-state actuation systems by virtue of the material's ability to convert electrical energy to thermal energy to mechanical energy within its microstructure. A hybrid micro-macro-mechanical SMA model is developed for future closed-loop actuator development studies. The constitutive model is a combination of concepts originally presented by Likhatchev for microstructural modeling and Brinson for modeling of transformation kinetics. Global strain of the heterogeneous solid or polycrystal, where the grains are assumed to be randomly oriented, was calculated by averaging the elastic, thermal, stress-induced and autoaccomodation strains of each grain over the total material volume. The introduction of a frequency distribution function in the micromechanical model provided a convenient way to quantify texture. The model was successfully tested under constant temperature conditions and constant load-low frequency cycling conditions.

The method of generating the most practicable shape recovery force in smart composite materials which embedded shape-memory alloy (SMA) fiber under the resin matrix is electric heating. However, because the calorie for the heating of the resin matrix increases in the low temperature environment, it is necessary to control the electric heating corresponding to an ambient temperature to obtaining a steady shape recovery force. In this paper, the main factor which influences the shape recovery force is reviewed first. And, it reports the shape recovery force control system by the electric heating which makes the contribution of composite materials which combine SMA that the phase transformation temperature is different to the stability improvement to the operation environment, and the SMA fiber a strain sensor to be possible.

SMA and superelastic materials (SEM) are mostly used for low force/large displacements applications involving tensile or bending modes of loading. The paper describes experiments on radial compression of SMA and superelastic wires and tubes between flat loading surfaces. Elastic (recoverable) deformations up to 22.5% with high damping under loads in the KN/mm range for solid wires and 10-100 N/mm range for tubes of OD = 0.4-2 mm have been observed. The recoverable deformation as great as 60% has been measured on a thin-walled SEM tube. This phenomenon was named a "Giant Superelasticity Effect" (GSE). The experiments were performed in a broad range of loading rates. Stainless steel specimens were also tested for comparison. A close-form analysis for thin-wall tubes and some realized and potential applications of GSE are described.

Shape-memory alloys can sustain relatively large strains and fully recover without noticeable residual strains. This is referred to as superelasticity. We have been studying quasi-static and dynamic buckling of relatively thin circular cylindrical shells consisting of shape-memory alloys in order to understand the response when used as the core of the sandwich structures. The work consists of experimental characterization of the buckling process, as well as numerical simulation. For comparison, we have also studied both dynamic and quasi-static buckling of aluminum tubes of similar dimensions. This presentation will focus on numerical simulation of dynamic buckling of these tubes and correlation with experimental observations.

This work is concerned with the magnetic field-induced rearrangement of martensitic variants in magnetic shape memory alloys (MSMAs). In addition to the variant reorientation, the rotation of the magnetization and magnetic domain wall motion are considered as the microstructural mechanisms causing the macroscopically observable constitutive response. The considered free energy terms are the elastic strain energy, the Zeeman energy and the magnetocrystalline anisotropy energy. It is shown how thermodynamic constraints on the magnetization rotation lead to only partial reorientation of the martensitic variants under higher stresses. A straightforward methodology has been devised for the calibration of model parameters based on experimental data. The presented model predictions indicate an improvement of the predictability of the nonlinear strain hysteresis and in particular the magnetization hysteresis.

Important advances in multi-scale computer simulation techniques for computational materials science have been made in the last decade as scientists and engineers strive to imbue continuum-based models with more-realistic details at quantum and atomistic scales. One major class of multi-scale models directly couples the atomistic detail to the macro region modeled using continuum concepts and finite element methods. Here, the development of such coupled atomistic/continuum model is presented within a single coherent framework with the aim of providing quantitative description of the constitutive behavior of magnetic shape memory alloys. A formulation of the Helmholtz free energy potential based on one-dimensional Ising model has been derived. The developed thermodynamic potential has been used in the context of the sharp phase front-based continuum model of the first order phase transformations suggested by Stoilov and Bhattacharyya (Acta Mat. 2002).

Single crystal Ni-Mn-Ga ferromagnetic shape memory alloys (FSMAs) are active materials that produce strain when a magnetic field is applied. The large saturation strain (6%) of Ni-Mn-Ga and material energy density comparable to piezoelectric ceramics make tetragonal Ni-Mn-Ga an interesting active material. However, the usefulness of the material is limited by the need for electromagnets to produce a magnetic actuation field. In this paper, an actuation method for shape memory alloys in the martensitic phase is described, in which asymmetric acoustic pulses are used to drive twin boundary motion. Experimental actuators were developed using a combination of Ni-Mn-Ga FSMA single crystals and a piezoelectric stack actuator. In bidirectional actuation without load, strains of over 3% were achieved using repeated pulses (at 100 Hz) over a 30 s interval, while 1% strain was achieved in under 1 s. The maximum strains achieved are comparable to the strains achieved using bidirectional magnetic actuation, although the time required for actuation is longer. No-load actuation also showed a nearly linear relationship between the magnitude of the asymmetric stress pulse and the strain achieved during actuation, and a positive correlation between pulse repetition rate and output strain rate, up to a pulse repetition rate of at least 100 Hz. Acoustic actuation against a spring load showed a maximum output energy density for the actuator of about 1000 J/m³, with a peak-to-peak stress and strain of 100 kPa and 2%, respectively.

NiMnGa-based magnetic shape memory (MSM) alloys have attained magnetic-field-induced strains up to approximately 10%, making them very attractive for a variety of applications. However, for applications that require the use of an alternating magnetic field, eddy current losses can be significant. Also, NiMnGa-based MSM alloys' fracture toughness is relatively low. Using these materials in the form of particles embedded in a polymer matrix composite could mitigate these limitations. Since the MSM effect is anisotropic, the crystallographic texture of the particles in the composites is of great interest. In this work, a procedure for fabricating NiMnGa-based MSMA/elastomer composites is described. Processing routes for optimizing the crystallographic texture in the composites are considered.

Our previous work on ferromagnetic shape memory Ni₅₀Mn_28.7Ga_21.3 demonstrates reversible compressive strains of -4100 microstrain along the [001] direction under the application of a magnetic field also along the [001] direction with no external orthogonal restoring force. The reversibility of the strains is due to internal bias stresses oriented orthogonal to the field. These results show promise for the use of Ni-Mn-Ga as the core material in solenoid transducers. In this paper, the reversible strains are explained by considering pinning sites as the source of the internal bias stresses in the material. Following prior work by Kiefer and Lagoudas, a phenomenological model is constructed for the motion of twin variants in the presence of an orthogonal pair formed by a magnetic field and an internal bias stress. The model is formulated by considering the Zeeman, elastic, and pinning energies, from which an appropriate Gibbs energy function is constructed. Minimization of the Gibbs function then yields a constitutive model for the strain. The accuracy of this model is studied and its implementation as a hysteresis kernel in homogenization theories is discussed.

Single crystal specimens of having compositions close to Ni₂MnGa and exhibiting magnetic shape memory effect (MSME) were tested in a rotating magnetic field at a frequency of 5.7 Hz. The applied magnetic field, about 0.7 T was strong enough to induce the MSME. Test of one specimen was discontinued because of the structural failure of the specimens after 0.5 million cycles. Second specimen was tested up to 37 millions cycles. The evolution of the martensitic morphology and crack propagation were observed by optical microscopy. To characterize the magnetic shape memory behavior the simultaneous measurements of the field-induced strain and magnetization as a function of the magnetic field and external load was used. The full MSM effect, about 6% obtained prior the test, decreased to about 3% during the first million cycles. This value stayed then approximately constant up to 37 millions cycles of rotating magnetic field. The magnetic field needed to initiate the MSME increased. The observed behavior is discussed within the framework of observed martensitic band structure in the specimens and the existence of initial cracks and other obstacles for martensitic twin boundary motion.

The field-induced domain evolution is investigated in a single-domain ferroelectric solid undergoing spontaneous polarization and polarization reorientation. Domain wall velocities have been correlated with the driving force acting on the domain interface. This boundary driving force, which depends on the local electromechanical fields and local changes of the material properties due to reorientation of the crystal structure, has been associated with Eshelby's energy momentum tensor. Finite element analysis that implements an efficient computation method for Eshelby's energy momentum tensor is developed. The domain boundary's geometry is elastically updated during the finite element computation to capture the characteristic of the domain evolution. An analytical solution for the domain interface driving force will be given by implementing Eshelby's solution for piezoelectric inclusion. The numerical results are compared to the analytical solutions to conclude the validity of this approach. Finally, the finite element computation program is used in two domain switch simulations.

The scientific community has put significant efforts into the manufacturing and optimization of sensors and actuators made of piezoelectric fibres with interdigitated electrodes, well known as Active Fibre Composites (AFC). A great advantage of such AFC is their flexibility and the possibility to integrate them into composite structures. In the current study an approach of optimizing the manufacturing process as well as the polarization of AFCs utilizing piezoelectric Lead-Zirconate-Titanate (PZT) fibres embedded in an epoxy matrix between interdigital Electrodes (IDE) screenprinted on Kapton will be discussed. During the poling process, an electric field is applied over the interdigitated electrodes of the AFC to its piezoelectric fibres along the fibre axis. One of the most important parameters of this polarization is, beside temperature and time, the applied voltage. An increase of the electric field results in an increase of the AFCs performance as shown by free-strain measurements. The manufacturing process developed and used at Empa consists of laminating the piezoelectric fibres in an epoxy matrix between the electrodes. An essential goal of this lamination, carried out in a hot press, is to get a proper contact between piezo fibres and the electrode. By adding soft layers between the Kapton foil and the mould, the interdigitated electrodes are deformed by each single fibre and therefore build up a contact area which in its cross section can be described by a contact angle. This optimization of the manufacturing process is also shown by free strain measurements of the AFC.

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. The magnetic properties of these composite specimens were experimentally evaluated using Vibration Sample Magnetometry (VSM). A model for calculating the effective magnetic properties has been presented in this work where Eshelby's inhomogeneous inclusion method considering Mori-Tanaka's mean field theory for larger concentrations of Fe has been used to predict the effective magnetic properties. The analytical results thus obtained are compared with experimental data resulting in a reasonably good agreement.

A smart bridge model was proposed for active control on strength and vibration by changing material properties of shape memory alloy embedded in the bridge structure using TiNi/acrylic composite. A systemic experimental study was carried out to investigate the self-strengthening effect by shape recovery of pre-strained TiNi wires as well as vibration control by stiffness changing with direct electric heating method. The deflection and vibration responses are measured by electric strain gages affixed on the bridge floor on which the model train goes through. From these results, we know the smart bridge model of composite material beam has not only been able to reduce the vibration response, but also change the frequency of the structure. The damping and vibration control for the bridge model is confirmed by the measurement.

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 the prediction of velocity and particle structure fields. The analysis is similar to that of bead-spring models of polymeric liquids with replacement of the elastic connector force by a magnetic force. Results for simple shear flow are presented for the case when the two particles remain in close contact so they are hydrodynamically equivalent to an ellipsoid with an aspect ratio of two and only the component of the magnetic force normal to the connecting vector between the centers of the two particles affects motion. The model predicts oscillatory motion of the particle pairs at low magnetic fields. The fluid reaches a steady state at high magnetic fields. The time required to reach the steady state for a given shear rate reduces significantly as the field increases.

The usage of shape memory materials has extended rapidly to many fields, including medical devices, actuators, composites, structures and MEMS devices. For these various applications, shape memory alloys (SMAs) are available in various forms: bulk, wire, ribbon, thin film, and porous. In this work, the focus is on SMA hybrid composites with adaptive-stiffening or morphing functions. These composites are created by using SMA ribbons or wires embedded in a polymeric based composite panel/beam. Adaptive stiffening or morphing is activated via selective resistance heating or uniform thermal loads. To simulate the thermomechanical behavior of these composites, a SMA model was implemented using ABAQUS' user element interface and finite element simulations of the systems were studied. Several examples are presented which show that the implemented model can be a very useful design and simulation tool for SMA hybrid composites.