This PDF file contains the front matter associated with SPIE Proceedings Volume 7289, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing

The homogenized energy model characterizes hysteresis in ferroelectric, ferromagnetic and ferroelastic compounds through a combination of energy analysis at the lattice level and stochastic homogenization techniques to provide macroscopic constitutive relations. Whereas this framework can characterize the frequency, stress and temperature dependent dynamics of these compounds for a variety of operating regimes, the direct implementation of the model is often not sufficiently efficient for applications requiring high speed simulation, model identification, or control implementation. Here we discuss techniques to increase the efficiency of algorithms for forward simulations and parameter identification. This significantly enhances the capability of the model for uncertainty analysis, sensitivity analysis, model calibration, device design, and model-based control implementation.

Piezoelectric actuators used in nano-positioning devices exhibit highly non-linear behavior and strong hysteresis, which limits the efficiency of conventional non-model-based controllers. This paper presents a free energy model based on the theory of thermal activation for single crystal piezoceramics that couples mechanical stress and electric field. It is capable of predicting the hysteretic behavior along with the frequency-dependence present in these materials. The model is then coupled with a spring as a first step toward a 1-D model of a commercial nano-positioning stage and is the basis for future control applications. Quasi-static simulations are conducted to illustrate the effects of spring loading on the actuator behavior. A first step towards adapting the model for polycrystalline material is also presented. Simulations are shown to predict the rate-dependent strain response of a spring loaded polycrystalline stack actuator for various pre-stresses.

Actuators employing ferroelectric or ferromagnetic compounds are solid-state, efficient, and compact making them well-suited for aerospace, aeronautic, industrial and military applications. However, they also exhibit frequency, stress and thermally-dependent hysteresis and constitutive nonlinearities which must be incorporated in models for accurate device characterization and control design. A critical step in the use of these models is the estimation or re-estimation of parameters in a manner that is both efficient and robust. In this presentation, we discuss techniques to estimate densities in the homogenized energy model based on Galerkin expansions using physically motivated basis functions. The yields highly tractable optimization algorithms in which initial parameter estimates can be obtained from measured properties of the data. The efficiency and accuracy of the models and estimation algorithms are validated with experimental data.

The one-dimensional phase transformation model of shape memory alloys [Ikeda et al., Smart Materials and Structures, 13, 916-925 (2004)] is applied to expressing the major and minor hysteresis loops in ferroelectric materials. An analogy between the phase transformation in the shape memory alloys and the switching in the ferroelectric materials is involved. The one-dimensional phase transformation model has the following two features. (i) A specimen is assumed to be comprised of grains with infinitesimal sizes, and the order of the energy required for the transformation of the grains is unchanged independently of the transformation directions. Accordingly, the phase transformation occurs onedimensionally. (ii) The required transformation energy is approximated as a sum of two exponential functions of phase volume fraction. To express the ferroelectric behavior, four phases (variants) are considered, namely, the 0° variant, 90° variant, 180° variant, and initial mixed variant. Electro-mechanical behavior of a ferroelectric material is simulated numerically. The result shows the model can approximately duplicate the electro-mechanical behavior observed in the ferroelectric material.

We studied dielectric and polarization behaviors of piezoelectric cellulose EAPap to understand the detail material behavior. It was shown that the dielectric and the polarization behavior of EAPap were temperature dependent. The largest change of dielectric constant was observed at near 0 °C while the highest dielectric constant was obtained near the boiling point of water molecules, which might be related to dipolar behavior of hydroxyl structure of cellulose and adsorbed or existing internal water molecules in EAPap. The maximum current from polarization behavior of cellulose EAPap was observed near the temperature range of 105-110 °C. Also abnormal polarization of EAPap, observed in electret polymer, under different field strengths was explained.

The microstructure of ferroelectric single crystals is a crucial factor that determines macroscopic properties and poling behaviour. Recent models of domain configuration, (such as that of Li & Liu, Journal of Mechanics and Physics of Solids, 2004) employ multi-rank laminate structures that satisfy compatibility in an average sense. In general, these models result in high-rank structures, corresponding to fine microstructure. However, minimum energy structures may be expected to have low rank and to satisfy compatibility requirements at every domain wall exactly. In this paper, the criteria of exact compatibility and average compatibility are defined and then used to determine energy minimizing microstructure in the tetragonal crystal system. In addition, the lowest rank construction of compatible laminate structure for a given macroscopic state of strain and polarization is found. Based on this, poling paths from unpoled to the fully-poled state in the tetragonal system are found, which allow the structure to stay in the lowest possible rank while maintaining exact compatibility. The application of the theory to a broader class of crystal structures is discussed.

This work presents the design, theory, and measurement of a linearly polarized microstrip patch antenna with a substrate-integrated compensation mechanism to mitigate the detuning effects from a physical deformation (e.g., bending and twisting). In particular, we investigate the ability of an antenna to maintain its impedance bandwidth as it bends sharply through the center (from flat up to 90° pivoted about the ground plane). Compensation for this bending occurs through the displacement of electromagnetically functionalized colloidal dispersions (EFCDs) in a substrate-embedded capillary. By replacing a high permittivity EFCD with a low permittivity EFCD during bending this provides a net length reduction to oppose the length extension (stretching) from the bending action. Stability of the 2:1 VSWR (matched impedance) bandwidth has been examined numerically across the entire range of bending, and examined experimentally using fixed-bend patch antennas on 4 mm thick isiocane foam substrates (one flat patch and one patch bent to 90°) to demonstrate this concept. A deformable patch antenna fabricated on a silicone substrate with conductive elastomers has also been examined and trends between simulated and measured results are in good agreement.

A continuum thermodynamics framework is presented to model the evolution of domain structures in active/smart materials. To investigate the consequences of the theories, fundamental defect interactions are studied. A principle of virtual work is specified for the theory and is implemented to devise a finite element formulation. For ferroelectrics, the theory and numerical methods are used to investigate the interactions of 180° and 90° domain walls with arrays of charged defects and dislocations to determine how strongly domain walls are electromechanically pinned by the arrays of defects. Additionally, the problems of nucleation and growth of domains from crack tips, and the propagation of domain needles are studied. The importance of adaptive mesh refinement and coarsening is discussed in the context of this modeling approach.

Smart materials and structures play an important role for sensor and actuator applications. For the simulation of such systems it is essential to predict the material and system behavior as precisely as possible. A reliable simulation may provide an easier, faster and cheaper development of such devices. In a wide range of technical applications piezoelectric sensors and actuators typically have a shell-like structure. This motivates the present contribution to deal with the consistent approximation of a piezoelectric shell formulation. A physical description leads to a system of electromechanical differential equations. Due to the constitutive relations the strains and the electric field are coupled. In case of bending dominated problems incompatible approximation functions of these fields cause incorrect results. This effect occurs in standard finite element formulations, where the mechanical and electrical degrees of freedom are interpolated with lowest order functions. The formulation presented in this paper is based on the classical Reissner-Mindlin shell theory extended by a piezoelectric part. The shell element has four nodes and bilinear interpolation functions. The eight degrees of freedom per node are three displacements, three rotations and the electric potential on top and bottom of the shell. The finite shell element incorporates a 3D-material law and is able to model arbitrary curved shell geometries of piezoelectric devices. In order to overcome the described problem of incompatible approximation spaces a mixed multi-field variational approach is introduced. Six independent fields are employed. These are the displacement, strain, stress, electric potential, dielectric displacement and the electric field. It allows for approximations of the electric field and the strains independent of the bilinear interpolation functions. A quadratic approach for the shear strains and the corresponding electric field is proposed through the shell thickness. This leads to well balanced approximation functions regarding coupling of electrical and mechanical fields. The numerical results are confirmed by analytical considerations and an example illustrates the more precise results of the present formulation in contrast to standard elements.

This paper discusses phase field modeling of tetragonal and rhombohedral ferroelectric domain structures using three dimensional grids. The work is based on the time dependent Ginsberg-Landau (TDGL) equation in which the free energy of the system is minimized subject to constraints on the boundaries of the system. Details are presented regarding the determination of energy functions and the effects of stress and electric field on these functions.

A simple constitutive model for temperature dependent behavior of ferroelectric materials is developed. This model is based on the one-dimensional phase transformation model of shape memory alloys. To model the temperature dependent behavior of the ferroelectric materials, a paraelectric phase is considered in addition to four ferroelectric variants in a ferroelectric phase. These ferroelectric variants are connected in series to each other, whereas the paraelectric phase is connected in parallel to the ferroelectric phase. The internal stress is induced in the material due to this parallel connection, which increases or decreases the driving energy for the switching depending on the switching direction. As the temperature increases up to the Curie temperature, the volume fraction of the paraelectric phase is assumed to increase and the required switching energy is assumed to decrease as observed in experiments. The temperature dependence of the relationships among the electric field, electric displacement, stress, and strain are simulated and compared with published experimental data for a soft PZT. The comparison indicates that the present constitutive model can predict the temperature dependent behavior well. This implies that the proposed model can provide a convenient tool to understand the physical mechanism of the ferroelectric materials and to design smart structures containing the ferroelectric materials.

Neutron diffraction experiments on isothermal pseudoelastic phase transformations in Cu-13.1Al- 4.0Ni (wt.%) single crystal shape memory alloys require a "stop-start" approach at different levels of strain during the austenite (A) to martensite (M) forward transformation and the M to A reverse transformation to collect diffraction data [1]. This stop-start nature of the tests has uncovered creep-like phenomena where there is stress relaxation when the forward transformation is interrupted (at constant strain) and stress recovery when the reverse transformation is interrupted (at constant strain). This material response has been confirmed by independent tests on a table-top thermomechanical tensile test machine. We also report results on strain recovery when the forward transformation is interrupted at constant stress. This type of behavior has been previously reported for Nickel-Titanium(NiTi) tubes [2] and NiTi polycrystalline wires [3]. Certain notable differences between the creep-like behavior and classical creep response of metallic alloys will be highlighted; due to these differences, we refer to the results reported here as "pseudo-creep".

Active structures composed of Shape Memory Alloys (SMAs) are becoming more prominent in applications with high force/low space design constraints, and the capabilities of numerical models intended to aid to the design process must be expanded. New applications have been proposed which require special high temperature SMAs (HTSMAs) where the operating temperatures can exceed one-third the melting temperature. Such imposed thermal conditions induce rate-dependent irreversible phenomena (viscoplasticity). A new 3-D model for SMAs undergoing viscoplastic deformation is discussed for the first time in this work, and new developments in the experimental investigation and numerical analysis pertaining to rate-dependent irrecoverable inelasticity in SMAs are also addressed. The description of simultaneous phase transformation and viscoplastic deformation requires the development of a theoretical framework able to capture the coupling between the rate-independent transformation and the rate-dependent creep. The proposed model is based on continuum thermodynamics, where the evolution equations and the hardening functions are properly chosen. While the transformation processes are rate-independent, the evolution equation for the viscoplastic strain is non-homogeneous in time, and rate-dependency is shown. The viscoplastic strain evolution follows Norton's Law, where the rate of creep is dependent on temperature. Implementation in an Abaqus FEA framework is completed using return mapping algorithms specially derived to consider simultaneous transformation and viscoplastic yielding. The model is experimentally calibrated and a cylindrical compression specimen composed of HTSMA and undergoing simultaneous transformation and viscoplastic yield is modeled in a 3-D environment. This analysis represents the first example of 3-D viscoplastic SMA analysis found in the literature.

The aim of present study is to investigate the local strain band behavior and the influence of it on macroscopic deformation behavior, of NiTi plates under mechanical loading. Firstly, we evaluate the transformation temperature by Differential Scanning Calorimetry (DSC) and investigate the initial phase for two NiTi thin plates with different texture. Next, we investigate the texture by X-ray diffraction method. Then, we measure local strain distribution arising in NiTi thin plates under uniaxial tensile loading, by using in-house measurement system on the basis of digital image correlation. Finally, we discuss about the "Mechanism of angle, nucleation and propagation for local strain band" and "Relationship between macroscopic stress-strain curve and local strain band behavior" on the basis of results in present study.

The focus of the current effort is to characterize the viscoplastic behavior in high temperature shape memory alloys and understand the impact of creep on their actuation characteristics. For this a Ti₅₀Pd₄₀Ni₁₀ alloy was cast and hot rolled. Standard creep tests and isobaric thermal cycling tests were conducted on a custom test setup. The results from the thermomechanical tests indicate large irrecoverable strains due to creep. Varying thermally induced transformation cycling rates did not impact the transformation behavior in the SMA. From these observations, it can be suggested that the rate of thermal cycling can alter the impact of viscoplasticity on the actuators performance. However the creep behavior itself is decoupled from the transformation and does not impact the transformation or the rate independent irrecoverable strain generated.

The recent development of various aerospace applications utilizing Ni-rich NiTi Shape memory Alloys (SMAs) as actuators motivated the need to characterize the cyclic response and the transformation fatigue behavior of such alloys. The fatigue life validation and certification of new designs is required in order to be implemented and used in future applications. For that purpose, a custom built fatigue test frame was designed to perform isobaric thermally induced transformation cycles on small dogbones SMA actuators (test gauge cross-section up to: 1.270 x 0.508 mm²). A parametric study on the cyclic response and transformation fatigue behavior of Ni-rich NiTi SMAs led to the optimization of several material/process and test parameters, namely: the applied stress range, the heat treatment, the heat treatment environment and the specimen thickness. However, fatigue testing was performed in a chilled waterless glycol environment maintained at a temperature of 5°C that showed evidence of corrosion-assisted transformation fatigue failure. Therefore, it was necessary to build a fatigue test frame that would employ a dry and inert cooling methodology to get away from any detrimental interactions between the specimens and the cooling medium (corrosion). The selected cooling method was gaseous nitrogen, sprayed into a thermally insulated chamber, maintaining a temperature of -20°C. The design of the gaseous nitrogen cooling was done in such a way that the actuation frequency is similar to the one obtained using the original design (~ 0.1 Hz). For both cooling methods, Joule resistive heating was used to heat the specimens. In addition and motivated by the difference in surface quality resulting from different material processing such as EDM wire cutting and heat treatments, EDM recast layer and oxide layer were removed. The removal was followed by an ultra-fine polish (0.05 μm) that was performed on a subset of the fatigue specimens. Experimental results are presented for full actuation of the SMA actuators and are given in terms of applied stress, accumulated plastic strain and number of cycles to failure. In addition, the assessment of the influence of the surface quality is supported by fatigue tests results and post-failure microstructure analysis.

This paper reports the simulation results from the dynamic analysis of a Shape Memory Alloy (SMA) actuator. The emphasis is on understanding the dynamic behavior under various loading rates and boundary conditions, resulting in complex scenarios such as thermal and stress gradients. Also, due to the polycrystalline nature of SMA wires, presence of microstructural inhomogeneity is inevitable. Probing the effect of inhomogeneity on the dynamic behavior can facilitate the prediction of life and characteristics of SMA wire actuator under varieties of boundary and loading conditions. To study the effect of these factors, an initial boundary value problem of SMA wire is formulated. This is subsequently solved using finite element method. The dynamic response of the SMA wire actuator is analyzed under mechanical loading and results are reported. Effect of loading rate, micro-structural inhomogeneity and thermal boundary conditions on the dynamic response of SMA wire actuator is investigated and the simulation results are reported.

With interest in improved efficiency and a more complete description of the SMA material, this paper compares finite element (FE) simulations of typical stent geometries using two different constitutive models and two different element types. Typically, continuum elements are used for the simulation of stents, for example the commercial FE software ANSYS offers a continuum element based on Auricchio's SMA model. Almost every stent geometry, however, is made up of long and slender components and can be modeled more efficiently, in the computational sense, with beam elements. Using the ANSYS user programmable material feature, we implement the free energy based SMA model developed by Mueller and Seelecke into the ANSYS beam element 188. Convergence behavior for both, beam and continuum formulations, is studied in terms of element and layer number, respectively. This is systematically illustrated first for the case of a straight cantilever beam under end loading, and subsequently for a section of a z-bend wire, a typical stent sub-geometry. It is shown that the computation times for the beam element are reduced to only one third of those of the continuum element, while both formulations display a comparable force/displacement response.

Shape memory alloys (SMAs) represent a class of smart materials that has been extensively used in many engineering applications due to their unique material properties. To facilitate these new developments, an efficient computational tool like the finite element method has to be used in order to simulate the highly nonlinear, load-history and temperature dependent responses of SMA materials. The particular focus of this paper is on the aspects of modeling and simulation of the inhomogeneous beam bending problem. Based on small deformation Euler-Bernoulli beam theory, the SMA beam is treated as consisting of several layers. Each governed by a 1-D free energy SMA model. The SMA beam is implemented in the finite element software COMSOL using its general PDE form. The ordinary differential equations describing the kinetics of the phase transformations are treated as degenerated PDEs without a flux term and coupled with the mechanical equilibrium equation and the heat transfer equation. In this paper, we study the quasiplastic and superelastic isothermal behavior of an SMA cantilever beam at constant low and high temperature, respectively. Keywords: finite element analysis, shape memory alloy, COMSOL

This paper presents experimental study and numerical simulation of the electro-thermo-mechanical behavior of a commercially available Flexinol shape memory alloy (SMA) wire [1]. Recently, a novel driver device has been presented [2], which simultaneously controls electric power and measures resistance of an SMA wire actuator. This application of a single wire as both actuator and sensor will fully exploit the multifunctional nature of SMA materials and minimize system complexity by avoiding extra sensors. Though the subject is not new [3-6], comprehensive resistance data under controlled conditions for time-resolved and hysteresis-based experiments is not readily available from the literature. A simple experimental setup consisting of a Flexinol wire mounted in series with the tip of a compliant cantilever beam is used to systematically study the SMA behavior. A Labview-based data acquisition system measures actuator displacement and SMA wire stress and resistance and controls the power passed through the SMA actuator wire. The experimental setup is carefully insulated from ambient conditions, as the thermal response of a 50-micron diameter Flexinol wire is extremely sensitive to temperature fluctuation due to convective heat transfer. Actuator performance is reported for a range of actuation frequencies and input power levels. The effect of varying actuator pre-stress is reported as well. All of the experimental data is compared with simulated behavior that is derived from a numerical model for SMA material [7-10].

In this work a 1-D constitutive model for high temperature shape memory alloys (HTSMA's) is presented, where the range of operating temperatures allows the appearance of creep mechanisms during transformation. The model aims to capture the coupled phenomenon, where the rate independent transformation and the rate dependent viscoplastic behavior coexist. Based on continuum thermodynamics, the Gibbs free energy and the evolution equations for forward, reverse transformation and creep are properly chosen. The generation of time independent irrecoverable strains during transformation is also taken into account. The calibration and validation of the model in the 1-D case is achieved with the help of experimental tests in Ti₅₀Pd₄₀Ni₁₀, including isobaric tests at selected stress levels with 2 different temperature rates.

Seven epoxy-amine polymers showing shape memory (SM) properties were synthesized. Tunable thermal and mechanical properties with glass transition temperatures ranging from 44 to 93 °C were obtained by varying the molecular structures. The epoxy showed excellent SM properties with shape fixity and shape recovery reaching completeness above about 5% strains. The instantaneous SM behavior was found to be independent of materials structure or properties; however, more stringent experimental conditions were found to be detrimental to SM properties for the networks with lower crosslink density and/or higher molecular flexibility/mobility. Indeed, the impact of the shape memory cycling conditions on the SM behavior was investigated. Specifically, the deformation load, the recovery heating rate, the number of SM cycles, and the holding time in the deformed or temporary shape were varied. The mechanical and SM properties of the materials were characterized using dynamic mechanical analysis in tensile mode.

Shape memory polymer (SMP) is a new class of smart material which attracts great interest in recent years. In this paper, in addition to the synthesizing of three types of epoxy SMPs with various linear epoxy monomer contents, their mechanical properties are focused on. Structure characteristic, dynamic mechanical property and quasi-static tension property and shape memory behavior of the epoxy SMPs are presented. Results indicate that glass transition temperature determined by dynamic mechanical analysis (loss modulus) varies from 69 to 113 °C for the epoxy SMPs. And it should be noted that the linear monomer has no effect on storage modulus in glass state but decrease the storage modulus in rubber state for the polymers. From tensile test, it is found that the content of linear monomer has significant effect on the tensile deformation behavior which varies from a brittle response to elastomeric response at room temperature. And the strength varies from 15 to 62MPa with the corresponding elastic modulus ranging from 2.5 to 1.7GPa for the epoxy system. Characterization of the shape memory effect in epoxy SMP suggests a high (above 99%) shape recovery ratio at 100 °C, besides, the epoxy SMP with higher linear monomer content shows a quicker shape recovery speed. Moreover, effect of linear monomer content on glass transition temperature and thermo-mechanical property is also investigated. Results indicate that, epoxy SMP fabricated in this study possess not only unique shape memory effect but also excellent mechanical properties, which will be the leading candidate for applications in engineering fields.

A new type of fiber reinforced thermoset styrene-based shape-memory polymer composite (SMPC) is developed and analyzed. The main objective is to systematically characterize the shape recovery properties of SMPC, which is a foundation for SMPC used in deployable structures. Firstly, the deployment dynamics of cured SMPC shell is presented. Then, the shape recovery performance is investigated by finite element analysis (FEA). The deployment process of curved SMPC shell (from 0-180 degree) is simulated by the geometrically nonlinear analysis. The deployment moment increases with the increase of the thickness of curved shell, and the strain show somewhat uniform in the central part of the curved shell. Furthermore, a hinge made of SMPC is fabricated, which consists of two curved SMPC shells in opposite directs. The deployment of hinge can be achieved in about100s by applying a 20V voltage. The deployment ratio approaches approximate 100 %. Finally the deployment of a prototype of solar array actuated by the hinge is demonstrated.

This paper is concerned about the influence of radialization dosage on performance of shape memory styrene copolymer. In this paper, the glass transition temperature (T_g) of styrene copolymer was measured by Dynamic Mechanical Analysis (DMA). The shape memory performance of styrene copolymer before and after radiation was also evaluated. Results indicated, the gel content of radiated styrene copolymer decreased by 14.3%, tensile strength reduced by 16.7% and slightly increase in elongation break. The storage modulus decrease sharply and the range of glass transition become narrower; the loss modulus reduces. In radiated styrene copolymer was not new peaks and the just height of the previous peaks varies in the spectra. It indicates, there are no oxidized reaction in the process of radiation. The shape recovery is conducted at different temperature for the SMP and radiated SMP. Below 85°C, the recovery speed of radiated SMP is faster than that of SMP without radiation. Above 85°C, the recovery speed of SMP is faster than that of radiated SMP. It can be explained as: after the radiation, the degradation of the polymer occurs, the chain of the molecule become shorter, the T_g decreases, and the storage modulus reduces consequently.

We report on miscible blends comprised of linear-poly(ε-caprolactone) (l-PCL) and chemically crosslinked network- PCL (n-PCL). The blends demonstrate unique Shape Memory Assisted Self-Healing (SMASH) property, which is the materials ability to close local microscopic cracks and heal those cracks by bonding the crack surfaces. For Shape Memory (SM) characterization, temporary deformation of the networks was achieved at room temperature. Samples were temporarily fixed below their crystalline temperature (T_c) and shape recovery was triggered by a temperature above the blends melting temperature (T_m). Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) were used to study the thermal properties of the blends and Dynamic Mechanical Analysis (DMA) and small-scale tensile testing were used to obtain the mechanical properties and self-healing efficiencies of the blends.

Macro Fiber Composites (MFC) are planar actuators comprised of PZT fibers embedded in an epoxy matrix that is sandwiched between electrodes. Due to their construction, they exhibit significant durability and flexibility in addition to being lightweight and providing broadband inputs. They are presently being considered for a range of applications including positioning and control of membrane mirrors and configurable aerospace structures. However, they also exhibit hysteresis and constitutive nonlinearities that must be incorporated in models to achieve the full potential of the devices. In this paper, we discuss the development of a model that quantifies the hysteresis and constitutive nonlinearities in a manner that promotes subsequent control design. The constitutive model is constructed using the homogenized energy framework for ferroelectric hysteresis and used to develop resulting system models. The performance of the models is validated with experimental data.

Piezoelectric fiber composites (PFCs) are a new group of materials recently developed in order to overcome the fragile nature of monolithic piezoceramics. However, there are some practical limitations associated with these types of materials, namely the generally separate electrode makes them difficult to embed into composites and when imbedded the low tensile properties of the material and the abnormal geometry in comparison with traditional reinforcements lead to stress concentrations reducing the material's strength. To resolve the inadequacies of current PFCs, a novel active structural fiber (ASF) was developed that can be embedded in a composite material to perform sensing and actuation, in addition to providing load bearing functionality. The ASF combines the advantages of the high tensile modulus and strength of the traditional composite reinforcements as well as the sensing and actuation properties of piezoceramic materials. A micromechanics model based on the double inclusion approach and a finite element model were been developed to study the effective piezoelectric coupling coefficient of the ASF as well as the ASF lamina. In order to evaluate the performance of the ASF when embedded in a polymer matrix and validate the model's accuracy, single fiber lamina have been fabricated and characterized through testing with an atomic force microscope. The results of our testing demonstrate the accuracy of the model and show that ASF composites could lead to load bearing composites with electromechanical coupling greater than most pure piezoelectric materials.

Polyimides are presently being investigated for a wide range of aeronautic, aerospace and industrial applications due to the fact that they have good thermal and chemical resistance yet are flexible. Within the realm of aerospace applications, polyimides can be employed for deployment, positioning, and vibration attenuation of large structures including thin-film membrane mirrors and gossamer antennas. The inclusion of single wall carbon nanotubes raises the conductivity levels to permit electric discharge. Additionally, they augment the electromechanical coupling properties of piezoelectric polyimides to provide them with actuator capabilities. We present a temperature-dependent material model based on elasticity theory which characterizes stiffness through the material as a function of varying concentrations of single wall nanotubes (SWNT). We begin by investigating the temperature affects on the polyimide. We then discuss the effects of SWNT volume concentration on the composite storage modulus. The composite model takes into account the alignment, interphase, and geometry of the SWNTs.

Electronic electroactive polymers (EAPs) are an attractive class of smart materials with many advantages such as lightweight, shape conformability, relatively high strain rates and good energy densities. However, there are major obstacles to their transition to applications. Notably they require high actuation voltages, have low blocked stresses and low operating temperatures. These current limitations are linked to inherent polymer properties such as low dielectric constant and low modulus. Our recent efforts in polymer-based nanocomposites provide new avenues to significantly improve their electromechanical response. In this study, we present experimental evidence of the creation of an electrostrictive response in a PVDF nanocomposite system by addition of small quantities of carbon nanotubes. amorphous polymer nanocomposites Further, we have also demonstrated that the piezoelectric response of nanocomposites can be dramatically enhanced through addition of conductive nanoparticles such as carbon nanotubes without additional weight penalties. Most importantly, these improvements were achieved at much lower actuation voltages, and were accompanied by an increase in both mechanical and dielectric properties. The effective dielectric properties of the nanocomposites indicate an increased polarization as the driving force for this enhancement. Possible causes for the enhanced polarization include contributions from SWNTs, polymer dipoles and SWNTpolymer interaction.

In carbon nanotube (CNT) polymer nanocomposites (PNC), the formation of conductive CNT networks results in electrical conductance and piezoresistive behavior. The latter occurs as applied strain affects the electric properties of the nanotubes. Modeling of piezoresistive behavior is investigated in two discrete scales. At the nanoscale, where for the prediction of the CNT piezoresistive behavior the Tight-Binding approximation is employed together with the Miller- Good approximation. At the microscale where percolation is studied using both two- and three- dimensional models and as well as the differences in resultant predictions. Numerical results at both scales are presented.

Base Epon 862 resin was enhanced with two types of fillers, graphitized carbon nanofiber (CNF) and silicon dioxide (SiO₂) particles. The effect of both filler type and filler loading were investigated with respect to the energy absorbing capacity as well as the thermal stability of the hybrid composite material, measured in terms of the coefficient of thermal expansion (CTE). As well the composites with combinations of the fillers were evaluated for both enhanced damping and thermal stability, making it suitable for structural materials that need multiple functions. The composites were evaluated with dynamic mechanical analysis (DMA) to evaluate viscoelastic response, and using strain gauges to measure thermal strain responses. It has been found that the addition of 3wt% SiO₂ along with 3wt% CNF can improve damping loss factors by up to 26% while at the same time improving thermal stability with reductions in CTE of up to 16.5%. Furthermore, these fillers loadings were successfully dispersed as received by mechanical mixing technique, making fabrication more economically suited to engineering applications.

The ductility of high strength nano-TiO₂ reinforced cement-based composites were experimentally studied and compared with that of plain cement-based composite and cement-based composite containing silica fume by stress-strain relationship. The results showed that the ductility of high strength cement-based composite containing nano-TiO₂ were better than that of plain cement-based composite and cement-based composite containing silica fume, which demonstrated that it is an available and effective way to improve ductility of high strength cement-based composite by means of mixing nanophase materials into cement-based composite. The origin of nanoparticles improving ductility of high strengthen cement-based composite was also preliminary interpreted.

Piezoelectric materials offer exceptional sensing and actuation properties however are prone to breakage and difficult to apply to curved surfaces in their monolithic form. One method of alleviating these issues is through the use of 0-3 nanocomposites, which are formed by embedding piezoelectric particles into a polymer matrix. This class of material offers certain advantages over monolithic materials, however has seen little use due to its low coupling. Here we develop a micromechanics and finite element models to study the electroelastic properties of an active nanocomposite as a function of the aspect ratio and alignment of the piezoelectric inclusions. Our results show the aspect ratio is critical to achieving high electromechanical coupling and with an increase from 1 to 10 at 30% volume fraction of piezoelectric filler the coupling can increase by 60 times and achieve a bulk composite coupling as high as 90% of a pure PZT-7A piezoelectric constituent.

In this study, we compare the characteristics of ferrogels prepared using γ-Fe₂O₃ and Fe₃O₄ nanoparticles. The magnetic nanoparticles with ~ 20 nm diameter were distributed in N-isopropylacrylamide (NIPAM) gel prepared using N,N'-methylenebisacrylamide (BIS), ammonium persulfate (APS) and N,N,N',N'-tetramethylethylenediamine (TEMED). Particle distribution and agglomeration characteristics of the prepared ferrogels were investigated using ultra small angle x-ray scattering (USAXS) and transmission electron microscopy (TEM). The ferrogel samples prepared using Fe₃O₄ and γ-Fe₂O₃ particles have similar particle distribution. The ferrogels, prepared with γ-Fe₂O₃ nanoparticles, however, demonstrate significantly different agglomeration characteristics compared to the ferrogels prepared using Fe₃O₄. In both systems, the agglomerated particles appear to be spherical, with few of those indicating chain like structures. Based on the particle concentration and sizes, the DC SQUID magnetometry data of these samples showed the magnetic moments range between 0.9 to 2.5 emu/g. Details of our results and analysis are presented.

Studies have shown that electrical parameters such as voltage drop and surface resistance are in correlation with curvature of IPMC. The electrical current in the surface of an IPMC could be calculated from the movement of the counter ions inside the polymer backbone of the IPMC. By using FEM we can calculate voltage drop in the platinum electrodes along the IPMC sheet. To get the relation between the voltage drop and current density, we use Ramo-Shockley theorem. The calculated voltage could again be applied as an input to the base model to calculate the curvature. This results in the Finite Element Model of an IPMC, which could be used for simulating basic actuation of an IPMC and furthermore, dynamic voltage changes on the electrodes. The current paper proposes a dynamical model of an IPMC with surface resistance taken into account. Also the voltage drop along the surface and overall currents are studied.

In this work a model of ion transport in ionic liquid-based ionic polymer-metal composites (IPMC's) is formulated using Nernst-Planck/Poisson (NPP) theory and numerical simulations are performed using the finite element method. IPMC's are smart materials which act as both sensors and actuators, and the use of an ionic liquid has been shown to dramatically increase transducer lifetime in free-air use while also allowing for higher applied voltages without chemical decomposition. We consider both the cation and anion of the ionic liquid to be mobile in addition to the mobile countercation of the transducer. The results show a nonlinear dynamic response which gives insight into transduction mechanisms which are unique to ionic liquid IPMC's as compared to their water-based counterparts.

Conventionally, energy harvesting from IPMC is studied in the bender configuration. However, for energy harvesting from uncontrolled or multi-directional vibration, there is a need to produce 2-D and/or 3-D energy harvester. This paper discusses the use of IPMC for energy harvesting using disc-shaped IPMCs. Making disc imparts more flexibility to the sample and enables energy harvesting from all around the perimeter of the disc without increase in size. Disc-shaped IPMCs were prepared from Nafion granules using a hot press method. The manufactured discs are flexible and suitable for bending not only along the diameter but also side ways. The sample was vibrated along the diameter at 1Hz, 0.25 inch displacement using a TIRA shaker for the testing.

Dielectric Electro-Active Polymers (EAP's) can achieve substantial deformation (>300% strain) while, compared to their ionic counterparts, sustaining large forces. This makes them attractive for various actuation and sensing applications such as light weight and energy efficient valve and pumping systems.. This paper provides a systematic experimental investigation of the quasi-static and dynamic electro-mechanical properties of a commercially available dielectric EAP actuator in the frequency range up to 20Hz. In order to completely characterize the fully coupled behavior force vs. displacement measurements at various constant voltages and force vs. voltage measurements at various fixed displacements are conducted. The experiments are conducted with a particular focus on the hysteretic and ratedependent material behavior.

Understanding of creep effects on actuating mechanisms is important to precisely figure out the behavior of material. Creep behaviors of cellulose based Electro-Active Paper (EAPap) were studied under different constant loading conditions. We found the structural modification of microfibrils in EAPap after creep test. Structural differences of as-prepared and after creep tested samples were compared by SEM measurements. From the measured creep behaviors by different loading conditions, two different regions of induced strain and current were clearly observed as the measurement time increased. It is consider that local defects may occur and becomes micro-dimple or micro-crack formations in lower load cases as localized deformation proceeds, while the shrinkage of diameter of elongated fibers was observed only at the high level of loading. Therefore, cellulose nanofibers may play a role to be against the creep load and prevent the localized structural deformations. The results provide useful creep behavior and mechanism to understand the mechanical behavior of thin visco-elastic EAPap actuator.

A cellulose solution was prepared by dissolving cotton pulp in LiCl/DMAc solution. Functionalized multi-walled carbon nanotubes (MWNTs) were reacted with N, N-Carbonyldiimidazoles to obtain MWNTs-imidazolides. By acylation of cellulose with MWNTs-imidazolides, MWNTs were covalently bonded with cellulose. Using the product, MWNTs- Cellulose (M/C) composite were fabricated and its characteristics were investigated by FT-IR and Raman spectroscopy, scanning electron microscopy and Young's modulus. The presence of covalent bonds remarkably enhanced mechanical property of M/C composite, which improved its actuator performance. The actuator performance of M/C EAPap is investigated in terms of bending displacement and resonance frequency depending on humidity level.

Liquid crystal elastomers combine both liquid crystals and polymers, which gives rise to many fascinating properties, such as unparalleled elastic anisotropy, photo-mechanics and flexoelectric behavior. The potential applications for these materials widely range from wings for micro-air vehicles to reversible adhesion skins for mobile climbing robots. However, significant challenges remain to understand the rich range of microstructure evolution exibited by these materials. This paper presents a model for domain structure evolution within the Ginzburg-Landau framework. The free energy consists of two parts: the distortion energy introduced by Ericksen [1] and a Landau energy. The finite element method has been implemented to solve the governing equations developed. Numerical examples are given to demonstrate the microstructure evolution.

Magnetic shape memory alloys (MSMAs) are new materials that emerged in the late 1990s. The magnetic shape memory effect is a result of the rearrangement of martensitic variants under the influence of magnetic fields. Due to their newness there is limited understanding of the mechanical behavior of MSMAs. However, it is know that MSMAs are able to produce relatively large strains as compared to piezoelectric materials or conventional shape memory alloys (SMAs). In addition, MSMAs have a lower time constant than conventional SMAs, since their actuation frequency is not limited by heat transfer. These features make MSMAs attractive for a number of applications, but they must be thoroughly understood before they can be used. This work includes an experimental investigation on MSMAs where the material is loaded and unloaded in uniaxial compression in the presence of a perpendicular constant magnetic field. The modeling of the magneto-mechanical behavior of MSMAs under such loading is also presented. The experiments are performed on prismatic specimens with square and rectangular base. The experimental data is simulated using the Kiefer and Lagoudas model and a polynomial hardening rule calibrated on data from Couch et al.

Magnetic Shape Memory Alloys (MSMAs) are promising high-frequency active materials for actuation, sensing, shape control, vibration suppression and energy harvesting applications. The macroscopic functionality of MSMAs originates from the coupled evolution of highly heterogeneous magnetic and elastic domain microstructures. Microstructure dependence of phase transformations in MSMAs introduces internal variables into the model to account for strong effects of domain microstructure processes on MSMA properties and varying elastic and magnetic coupling. Selection of internal variables and their incorporation into constitutive modeling has been done for the problem of field-induced martensite reorientation. Introducing a new internal variable, the austenitic volume fraction, the study of field induced phase transformation between the parent and martensitic phases is performed.

We report electric field control of nanoscale magnetic domain pattern transformation processes due to the converse magnetoelectric effect in a magnetoelectric device. The magnetoelectric device is a Ni-microdot/PZT-film bi-layer heterostructure. Due to the converse magnetoelectric effect, nanoscale magnetic domain (i.e. dot-domain/pseudo-single-domain/ short-stripe-domain/vortex-core) in the central region of a Ni microdot is controlled under an electric field (1.6 MV/m). The electric field induced domain-pattern transformation process (i.e. deformation and rotation of the nanoscale domain in the central region of the Ni microdot) is observed with the magnetic force microscopy. Upon removal of the electric field, the deformed/rotated nanoscale magnetic domain-pattern/vortex-core returns to its original state, i.e. reversible domain-pattern-transformation/vortex-core-motion.

Ferrogels are compliant composite materials formed of a soft polymer matrix with a filler of magnetic powder. The interaction of the magnetic filler with an applied magnetic field causes the deformation of the ferrogel. Strains of up to 40% have been measured with load capabilities of up to four times the sample's weight. As these materials move toward application it is important to capture the actuator behavior in mathematical models so that materials can be designed and the behavior predicted. In this work experimental testing captures the strain and strain rate behavior of these materials at fields up to 0.5 T. A lumped parameter model is then developed that is much less computationally intensive than existing modeling approaches. The ability of this model to capture the behavior of interest will be assessed.

A new method for the preparation of magnetorheological elastomers or solid composites with intriguing properties is presented. The method makes use of magnetorheological fluids formed by micron-sized magnetic particles dispersed in ionic liquids. These dispersions are combined with suitable polymers to obtain novel magnetoresponsive solid materials which may find interesting applications, for instance, as actuators, in diverse fields of science and engineering.

This work presents the nonlinear bending response of magnetostrictive/piezoelectric laminated actuators under magnetic fields both numerically and experimentally. The actuators are fabricated using thin Terfenol-D and PZT layers, and the magnetostriction of the actuators is measured. A nonlinear finite element analysis is also performed to evaluate the contribution of magnetic domain switching to the second-order magnetoelastic constants in Terfenol-D layer, and the effect of magnetic field on the deflection, internal stresses and induced voltage for the magnetostrictive/piezoelectric laminated actuators are discussed in detail.

Magnetorheological (MR) fluids have rheological properties, such as the viscosity and yield stress that can be altered by an external magnetic field. The design of novel devices utilizing the MR fluid behavior in multi-degree of freedom applications require three dimensional models characterizing the coupling of magnetic behavior to mechanical behavior in MR fluids. A 3-D MR fluid model based on multiscale kinetic theory is presented. The kinetic theory-based model relates macroscale MR fluid behavior to a first-principle description of magnetomechanical coupling at the microscale. A constitutive relation is also proposed that accounts for the various forces transmitted through the fluid. This model accounts for the viscous drag on the spherical particles as well as Brownian forces. Interparticle forces due to magnetization and external magnetic forces applied to ferrous particles are considered. The tunable rheological properties of the MR fluids are studied using a MR rheological instrument. High and low viscosity carrier fluids along with small and large carbonyl iron particles are used to make and study the behavior of four different MR fluids. Experiments measuring steady, and dynamic oscillatory shear response under a range of magnetic field strengths are performed. The rheological properties of the MR fluid samples are investigated and compared to the proposed kinetic theory-based model. The storage (G') and loss (G") moduli of the MR fluids are studied as well.

Measurements are performed to characterize the nonlinear and hysteretic magnetomechanical coupling of iron-gallium (Galfenol) alloys. Magnetization of production and research grade Galfenol is measured under applied stress at constant field, applied field at constant stress, and alternately applied field and stress. A high degree of reversibility in the magnetomechanical coupling is observed by comparing a series of applied field at constant stress experiments with a single applied stress at constant field experiment. Accommodation is not evident and magnetic hysteresis for both applied field and stress is shown to be coupled. A stress, field, and orientation dependent hysteron is developed from continuum thermodynamics which employs a unified hysteresis mechanism for both applied stress and field. The hysteron has an instantaneous loss mechanism similar to Coulomb-friction or Preisach-type models and is shown to satisfy the second law of thermodynamics. Stochastic homogenization is employed to account for the smoothing effect that material inhomogeneities have on the magnetization.

This paper presents the results of numerical and experimental investigations into the elastic properties of iron-gallium alloys known as Galfenol, one of only a few metal alloys known to exhibit large auxetic or negative Poisson's ratio behavior. This research was undertaken to develop an understanding of the molecular mechanisms that lead to the unusual macro-scale trends in Galfenol elastic properties, as well as to create an experimentally determined database of these composition-dependent properties. To accomplish this, we have developed quantum theory-based models of the composition-dependent electronic structure of Galfenol alloys. We first present a modeling approach in which systematic density functional calculations and relationships between strains and total energies are employed to predict elastic stiffness constants C₁₁,C₁₂ and C₄₄, from which Poisson's ratio and Young's modulus are calculated. This modeling approach is also used to simulate elastic constants for the iron-aluminum alloy known as Alfenol, which is shown to exhibit similar behavior. We also use these models to simulate the relationship between strains along orthogonal crystallographic directions as an alternate approach for predicting Poisson's ratio values. The second portion of this paper addresses the experimental aspects of this study. Tensile tests of single-crystal Galfenol specimens with compositions of 12 to 25 atomic percent gallium were conducted to determine the composition dependent values of Young's modulus and Poisson's ratio. These experimental results are used to validate model predictions and to provide experimental data to further aid in visualizing trends in elastic properties. This project will enable future researchers to refer to the elastic properties of the alloy obtained using two different techniques, as well as enable them to select the alloy with optimum elastic properties for their applications.

In the past ten years, there have been several investigations on the effects of particle size on magnetostrictive properties of polymer-bonded Terfenol-D composites, but they didn't get an agreement. To solve the conflict among them, Terfenol-D/unsaturated polyester resin composite samples were prepared from Tb_0.3Dy_0.7Fe₂ powder with 20% volume fraction in six particle-size ranges (30-53, 53-150, 150-300, 300-450, 450-500 and 30-500μm). Then their magnetostrictive properties were tested. The results indicate the 53-150μm distribution presents the largest static and dynamic magnetostriction among the five monodispersed distribution samples. But the 30-500μm (polydispersed) distribution shows even larger response than 53-150μm distribution. It indicates the particle size level plays a doubleedged sword on magnetostrictive properties of magnetostrictive composites. The existence of the optimal particle size to prepare polymer-bonded Terfenol-D, whose composition is Tb_0.3Dy_0.7Fe₂, is resulted from the competition between the positive effects and negative effects of increasing particle size. At small particle size level, the voids and the demagnetization effect decrease significantly with increasing particle size and leads to the increase of magnetostriction; while at lager particle size level, the percentage of single-crystal particles and packing density becomes increasingly smaller with increasing particle size and results in the decrease of magnetostriction. The reason for the other scholars got different results is analyzed.

A novel PEM based on sulfonated poly(ether ether ketone) (S-PEEK) was synthesized by the nucleophilic aromatic substitution polycondensation between bisphonol-S and 4,4'-difluorobenzophenone (system A), bisphenol S and 4,4'- dichlorobenzophenone (system B), whose properties are compared with commercial PEEK 150XF (system C) from Victrex. The main difference between the systems A and B is the cost of 4,4'-difluorobenzophenone which is 4 times more expensive than 4,4'-dichlorobenzophenone. Bisphenol-S increase the thermal stability due to its high melting point (245°C). The post-sulfonation reaction was carried out using a concentrated sulfuric acid. Sulfonated poly(ether ether ketone) (S-PEEK) samples were characterized by FTIR and ¹H-NMR to confirm the chemical structure of the S-PEEK, by TGA to investigate the thermal property, and by a LCR meter to determine the dependences of the dielectric permittivity on frequency. Both FTIR and ¹H-NMR data show the characteristic peaks of sulfonic acid group confirming the successful sulfonation. The PEEK thermal data show 2-steps degradation temperatures. The first degradation represents the splitting of the sulfonic group, and the second is due to polymer backbone degradation. The IEC, DS, and water uptake (%) increase with increasing sulfonation time. Most of all S-PEEK systems showed the dielectric permittivities (ε') were independent with the frequencies.

In the present study, a digital image correlation method has been applied to measure the elastic modulus of a beetle wing membrane. Specimens were prepared by cutting beetle wing carefully with a size of 3.0 mm in width and 5.0 mm in length. We used a scanning electron microscope for exactly measuring the membrane thickness of a beetle wing membrane. The specimen was attached to a designed fixture to induce a uniform displacement using a micromanipulator. We measured the applied load and the corresponding displacement by a load cell with a maximum capacity of 5 N and by an ARAMIS system based on the digital image correlation method respectively. The measured thickness of a beetle wing varied from point to point of the wing part and the elastic modulus was different according to the loading direction. In conclusion, we successfully measured the elastic modulus of a beetle wing with an ARAMIS system based on the digital image correlation method.

This paper presents the temperature-pressure characteristics of a newly developed SMH actuator using hydrogen-absorbing alloys. The new special metal hydride(SMH) actuator is characterized by its small size, low weight, noiseless operation, and compliance similar to that of human bodies. The simple SMH actuator, consisting of plated hydrogen-absorbing alloys as a power source, Peltier modules as a thermal source, and a cylinder with metal bellows as a mechanical functioning part, has been developed. An assembly of copper pipes has been constructed to improve the thermal conductivity of the hydrogen-absorbing alloys. It is well known that hydrogen-absorbing alloys can reversibly absorb and desorb a large amount of hydrogen, more than about one thousand times of their own volume. By heating the hydrogen-absorbing alloys, the hydrogen equilibrium pressure increases due to desorption of hydrogen, whereas, by cooling the alloys, the hydrogen equilibrium pressure drops due to absorption of hydrogen by the alloys. The new SMH actuator utilizes the reversible reaction between the thermal energy and mechanical energy of the hydrogen absorbing alloys. To be able to use the SMH actuator in medical and rehabilitation applications, the desirable characteristics of the actuator have been studied. For this purpose, the detailed characteristics of the new SMH actuator for different temperature, pressure, and external loads were explored.

Based on the nonlinear constructive model for magnetostrictive materials proposed by [1], a dynamic model is established to depict the natural characteristics of electro-magneto-mechanical coupling for magnetostrictive actuators. In this model, the change of Young's modulus of magnetostrictive materials with the magnetic field and the stress level in the operating actuators is considered. Due to this feature, the property of nonlinear parametric vibration with time-variant stiffness is presented in the dynamic characteristic of magnetostrictive actuators. By virtue of the numerical solution of the equation, the parametric frequency response characteristics of magnetostrictive actuators are obtained. Simultaneously, the effect of the amplitude of drive current and load mass on the dynamic characteristics of magnetostrictive actuators are investigated. The results are also compared with relative experimental investigations.