A comparison of stack load-line (including blocked force and free displacement) as well as dynamic response of two single crystal PMN-32%PT stacks is provided in this study. The first stack is a 7mm diameter by 0.5mm thickness 60 layer single crystal stack while the second stack is a 6mm diameter by 0.3mm thickness 100 layer single crystal stack. Blocked force and free displacement measurements were both performed under DC driving conditions. Free displacement measurements showed that under 500V driving conditions displacements approaching 87&mgr;m (~2500ppm) and 48&mgr;m (~1450ppm) were obtained for the 6mm and 7mm diameter stacks, respectively. Experimental blocked force measurements correlated well with theoretical predictions with experimental values approaching 709N and 685N for the 6mm and 7mm diameter stacks, respectively. The error between the theoretical predictions and experimental values was attributed to the linear load line assumption in the theoretical model whereas the stack stiffness is dependent upon the applied force. Dynamic measurements performed under a pre-stress of 4MPa indicated an increase in the strain at frequencies above 500Hz for driving frequencies up to 1000Hz. This was unexpected as the PMN stack resonance was calculated to be on the order of several kHz.

The time-dependent remanent strain and polarization were measured in initially unpoled PZT-855 under electromechanical loads. Various levels of constant compressive uniaxial stress combined with constant electric field parallel to the stress axis were used to produce the creeping remanent strain and polarization. The remanent quantities were deduced from measurements of total strain and electric displacement by subtracting the linear (reversible) parts of strain and electric displacement, making use of previous measurements of the linear moduli and accounting for their variation with material state. Mechanical compressive stresses alone produce remanent strains that rapidly reach a saturated state. Under combined loading, increasing the compressive stress reduces the observed creep rates caused by an additional electrical loading. The creep behaviour is most significant at loads close to the coercive stress or electric field. At loads well above or below the coercive field levels, the behaviour is nearly rate-independent.

Niobium doped Lead Zirconate Titanate (PZT) with a Zr/Ti ratio of 95/5 (i.e., PZT 95/5-2Nb) is a ferroelectric with a rhombohedral structure at room temperature. A crystal (or a subdomain within a crystal) exhibits a spontaneous polarization in any one of eight crystallographically equivalent directions. Such a material becomes polarized when subjected to a large electric field. When the electric field is removed, a remanent polarization remains and a bound charge is stored. A displacive phase transition from a rhombohedral ferroelectric phase to an orthorhombic anti-ferroelectric phase can be induced with the application of a mechanical load. When this occurs, the material becomes depoled and the bound charge is released. The polycrystalline character of PZT 95/5-2Nb leads to highly non-uniform fields at the grain scale. These local fields lead to very complex material behavior during mechanical depoling that has important implications to device design and performance. This paper presents a microstructurally based numerical model that describes the 3D non-linear behavior of ferroelectric ceramics. The model resolves the structure of polycrystals directly in the topology of the problem domain and uses the extended finite element method (X-FEM) to solve the governing equations of electromechanics. The material response is computed from anisotropic single crystal constants and the volume fractions of the various polarization variants (i.e., three variants for rhombohedral anti-ferroelectric and eight for rhomobohedral ferroelectric ceramic). Evolution of the variant volume fractions is governed by the minimization of internally stored energy and accounts for ferroelectric and ferroelastic domain switching and phase transitions in response to the applied loads. The developed model is used to examine hydrostatic depoling in PZT 95/5-2Nb.

We present a generalized energy based analytical macroscopic model using distribution functions for the polarization and strain response to external electric field in electromechanical materials. Although the distributions are based on classical Boltzmann statistics, we show that they differ only by a factor of 2 in the exponential factor from Fermi-Dirac statistics in the two state system. The electric displacement-field D-E and strain-field S-E curves of antiferroelectric, ferroelectric, relaxor ferroelectric and linear piezoelectrics including hysteresis are described. The polarization model is based on a Weiss molecular field and assumes only net contributions to the polarizations need to be summed. No distinction between 90° and 180° domain contributions or domain dynamics is made. The strain field S-E curves are generated in all cases using the electrostriction relationship S=QD². The model shows utility in modeling phase change between antiferroelectric ⇒ ferroelectric or ferroelectric ⇒ relaxor ferroelectric states. The hysteresis in the strain- field and electric displacement field curves is accounted for using the time derivative of the applied electric field. Although the model was developed for polarizable dielectric materials it is proposed that the same approach can be applied to magnetic, elastic or other ferroic materials.

Piezoelectric actuators are increasingly used in modern fuel injectors due to their quick response, high efficiency, and excellent repeatability. Current understanding of the thermo-electro-mechanical performance of piezoelectric actuators under dynamic driving fields is very limited. In this paper, the dynamic thermo-electro-mechanical performance of Lead Titanate Zirconate (PZT) stack actuators is experimentally studied over the temperature range of -30 °C to 80 °C, under a driving field of up to 2.4 kV/mm (with an AC drive method) and a constant preload of about 5MPa. Sinusoidal and trapezoidal driving fields with rise times varying from 0.1 ms to 2 ms are applied. It is found that dynamic stroke increases steadily with the temperature. Under driving frequencies lower than the resonance frequency of the testing system ( ≈ 500Hz), the electric field-strain behavior under different temperatures is very similar to the quasi-static results obtained previously. In the case of a trapezoidal pulse, decreasing the rise time is found to be equivalent to increasing the frequency.

Ferroelectroelastic materials exhibit nonlinear behavior when they are subjected to high electromechanical loadings. Using the standard formulation with the scalar potential as electric nodal variable in the nonlinear finite element analysis can lead to a low convergence of the iteration procedures. Therefore the formulation with a vector potential as electric nodal variable is developed, which ensures a positive definite stiffness matrix. Solutions of boundary value problems using the scalar potential formulation lie on a saddle point in the space of the nodal degrees of freedom, whereas solutions for the vector potential formulation are in a minimum. Unfortunately, the latter solutions involving the "curlcurl" operator are non-unique in the three-dimensional case. A Coulomb gauge condition imposed on the electric vector potential improves the convergence behavior of nonlinear problems, and in combination with appropriate boundary conditions, it can enforce unique vector potential solutions. A penalized version of the weak vector potential formulation with the Coulomb gauge is proposed and tested on some numerical examples in ferroelectricity.

A continuum model for ferroelectric materials is presented where the spontaneous polarization is treated as an order parameter. The classic electric enthalpy consisting of elastic, dielectric and ferroelectric terms is extended by a phase separating potential and an interface energy which yields a phase field potential. The coupled material equations and the Ginzburg-Landau type evolution equation are derived from that phase field potential. The evolution equation as well as the mechanical and electro-static balance laws are solved using the Finite Element Method. The model is extended to allow for the simulation of point defects. Numerical examples are given for the defect-free case, and the influence of point defects is investigated.

This paper is concerned with a macroscopic constitutive law for domain switching effects, which occur in piezoelectric ceramics. The thermodynamical framework of the law is based on two scalar valued functions: the electric free Gibbs energy and a switching surface. In common usage, the remanent polarization and the remanent strain are employed as internal variables. The novel aspect of the present work is to introduce an irreversible electric field, which serves besides the irreversible strain as internal variable. The irreversible electric field has only theoretical meaning, but it makes the formulation very suitable for a finite element implementation, where displacements and the electric potential are the nodal degrees of freedom. The constitutive model reproduces the ferroelastic and the ferroelectric hysteresis as well as the butterfly hysteresis and it accounts for the mechanical depolarization effect.

In this study, measurements of the evolving linear elastic, dielectric and piezoelectric moduli of a soft ferroelectric PZT are made during loadings of uniaxial compressive stress combined with an electric field. Using short pulses of electric field and stress, the incremental remanent strain and polarization state of the material and the unloading moduli were determined. The remanent quantities are treated as state variables, with a view to expressing the moduli as functions of the material state. The piezoelectric moduli vary approximately linearly with polarization, whilst the dielectric moduli and elastic compliances show more complex behaviour.

Two measurement methods are presented to determine precisely and reliable the electrical and electromechanical response of piezoelectric thin film structures. A double beam laser interferometer (DBLI) was used to measure large signal polarization, displacement, dielectric constant and the effective longitudinal piezoelectric coefficient d_33,f in out of plane direction of the film. Secondly, a unique and newly developed measurement setup based on a 4-point bending sample holder for cantilever devices was used to determine the transverse effective piezoelectric coefficient e_31,f. This setup allows the application of precisely defined and homogeneous in plain mechanical strains to the piezoelectric film. The homogeneous stress and strain distributions were proved by Finite Element Simulations. Additional measurements have been performed to investigate the influence of in plane mechanical preloads on the transverse coefficient. Measurements are shown on Pb(Zr₅₃,Ti₄₇)O₃ (PZT) thin film samples deposited by a sol-gel based chemical solution deposition process which was optimized to maximize the e_31,f coefficient. Exceptional high e_31,f coefficients demonstrate the quality of the processed films.

The governing equations of piezo-thermoelastic materials show full coupling between mechanical, electric, and temperature fields. It is often assumed in the literature that in high-frequency oscillations, the coupling between the temperature and mechanical displacement and electric field is small and, therefore, can be neglected. A solution for the temperature field is then determined from an uncoupled equation. A finite element (FE) model that accounts for full coupling between the mechanical, electric, and thermal fields, nonlinear constitutive behavior and heat generation resulting from dielectric losses under alternating driving fields is under development. This paper presents a linear fully coupled model as an early development of the fully coupled nonlinear FE model. In the linear model, a solution for all field variables is obtained simultaneously and compared with the uncoupled solution. The finite element model is based on the weighted-residual principle and uses 2-D four-node isoparametric finite elements with four degrees of freedom per node. A thin piezoelectric square disk is modeled to obtain some preliminary understanding of the coupled fields in a piezoelectric stack actuator.

In this paper, rate-dependent switching effects of ferroelastic materials are studied by means of a micromechanically motivated approach. The onset of domain switching is thereby initiated as soon as a related reduction in energy per unit volume exceeds a critical value. Subsequent nucleation and propagation of domain walls during switching process are incorporated via a linear kinetics theory. Along with this micromechanical model, intergranular effects are accounted for by making use of a probabilistic ansatz; to be specific, a phenomenologically motivated Weibull distribution function is adopted. In view of finite-element-based simulations, each domain is represented by a single finite element and initial dipole directions are randomly oriented so that the virgin state of the particular bulk ceramics of interest reflects an un-poled material. Based on a staggered iteration technique and straightforward volume averaging, representative stress versus strain hysteresis loops are computed for various loading amplitudes and frequencies. Simulation results for the rate-independent case are in good agreement with experimentally measure data reported in the literature and, moreover, are extended to rate-dependent computations.

This paper reports a study about the possibilities for direct integration of piezo-fibers in sheet metal. In the Transregional Collaborative Research Centre 39 PT-PIESA "Production Technologies for light metal and fiber reinforced composite based components with integrated PIEzoceramic Sensorand and Actuators", set up with the promotion of the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG), effective technologies for the production of adaptronic components are investigated. One idea is the direct integration of piezo-fibers in sheet metal like for instance aluminum sheets. A detailed finite-element-model was developed to design a functional part in the sheet metal by means of directly integrated fibers or micro-structured composite elements. Several versions of design were investigated. So the geometry of the microstructure, the material parameter and the geometry of the isolation layer, the piezo-elements and the piezo-mode (d₃₁- or d₃₃-effect) and also the field direction was varied. Two different designs are promising. The first design is characterized by the usage of the d₃₃-effect across the fiber. The second promising design is characterized by the use of slotted piezo-fiber-composites.

Energy harvesting is a process in which energy which would otherwise be wasted is captured, stored and then used to power a system. Devices having such capabilities enjoy an extended life particularly advantageous in systems with limited accessibility, such as biomedical implants and structure embedded micro and wireless sensors. A viable family of materials for this purpose is piezoelectric materials because of their inherent ability to convert vibrations into electrical energy. This paper uses a type of pre-stressed PZT-5A Unimorph called Thunder®, to actively convert mechanical vibrations into useable power. The effects of temperature, 20-100°C, pressure, 138-345kPa, frequency, 2-5Hz, and load resistance, 0.47-2.0M&OHgr;, on the energy harvesting potential of the device are studied. The data obtained is analyzed using statistical techniques that assess the significance of the factors being studied. Results showed that the effect of temperature by itself on the voltage, AC or DC, and power generation was seen to be not significant. In combination with other factors such as pressure, frequency, and load resistance however, the temperature effect becomes statistically significant. These interaction effects tend to reduce voltage and power conversion. The maximum DC voltage and power were calculated as 108V and 11641&mgr;W at 20°C, 275.8kPa, 2.5Hz and 2M&OHgr;. Similarly the greatest peak to peak AC voltage of 338V was also measured at 20°C and 2.5Hz. Based on the geometry of the piezoelectric diaphragm the most power density was evaluated to be 15&mgr;W/mm³.

A superlattice is formed in a piezoelectric substrate by intervallic polarizing oppositely along one direction. Wave propagation in this structure is studied with plane-wave expansion method. The polariton behavior in the superlattice is obtained by solving Newton's equations of motion and Maxwell's equations simultaneously. Significant coupling between mechanical and electromagnetic energy occurs in the vicinity of the center of the first Brillouin zone. At the frequency bands of strong coupling, part of the excitation electromagnetic energy will convert into mechanical energy in the superlattice or radiating into free space as EM waves. By measuring the S parameters, the coupling behavior is observed and the frequency bands corresponding to different kinds of energy conversion can be identified.

The polarization switching characteristics of lead-free a(Bi_1/2Na_1/2)TiO₃−bBaTiO₃−c(Bi_1/2K_1/2)TiO₃ (abbreviated as BNBK 100a/100b/100c) ferroelectric ceramics are investigated. This is achieved through examining their polarization and strain hystereses inside and outside the morphotropic phase boundary (MPB). The total induced electrostrain (&egr;_33,total) and apparent piezoelectric charge coefficient (d₃₃) first increase dramatically and then decrease gradually as the BNBK composition moves from the tetragonal phase to the MPB and then to the rhombohedral phase. The measured polarization hystereses indicate that the BNBK compositions situated near the rhombohedral side of the MPB typically possess higher coercive field (E_c) and remanent polarization (P_r), while the compositions situated near the tetragonal side of the MPB possess higher apparent permittivity. Adverse effects on the ferroelectric properties are observed when BNBK is doped with donor dopants such as La and Nb. On the contrary, intricate hysteresis behaviors are observed when acceptor dopant Mn is introduced into BNBK. Under an alternating electric field of ±5.0 MVm^-1, BNBK 85.4/2.6/12, a composition well within the MPB, exhibits an &egr;_33,total of ~0.14%, an apparent d₃₃ of 295 pCN^-1, an E_c of 2.5 MVm^-1 and a Pr of 22.5 &mgr;Ccm^-2. These notable ferroelectric property values suggest a candidate material for lead-free actuator applications. The present study provides a systematic set of hysteresis measurements which can be used to characterize the switching behaviors of BNBK-based lead-free ferroelectrics.

Bone is a smart, self-adaptive and also partly self-repairing tissue. In recent years, many researchers seek to find how to give the effective mechanical stimulation to bone, because it is the predominant loading that determines the bone shape and macroscopic structure. However, the trial of regeneration of bone is still under way. On the other hand, it has been known that electrical potential generates from bone by mechanical stimulation (Yasuda, 1977; Williams, 1982; Starkebaum, 1979; Cochran, 1968; Lanyon, 1977; Salzstein, 1987a,b; Friedenberg, 1966). This is called "stress-generated potential (SGP)". The process of information transfer between "strain" and "cells" is not still clear. But, there is some possibility that SGP has something to do with the process of information transfer. If the electrical potential is more clear under some mechanical loadings, we will be able to regenerate bone artificially and freely. Therefore, it is important to investigate SGP in detail. The aim of present study is to investigate the electric reaction arising in dry bone subjected to mechanical loadings at high amplitude and low frequency strain. Firstly, specimen is fabricated from femur of cow. Next, the speeds of wave propagation in bone are tried to measure by laser ultra sonic technique and wavelet transform, because these have relationship with bone density. Secondary, 4-point bending test is conducted up to fracture. Then, electric reaction arising in bone is measured during loading. Finally, cyclic 4-point bending tests are conducted to investigate the electric reaction arising in bone at low frequency strain.

This paper presents an experimental study to investigate the actuation performance of LIPCA (Lightweight Piezo- Composite unimorph Actuator) with different loading cases. High value of the manufacturing-induced compressive stress in PZT layer of LIPCA helps avoiding potential in-service failure, however, it may cause a reduction in strain due to the induced piezoelectric effect. High compressive prestress makes the domains aligned and constrained perpendicular to the stress direction. Consequently, fewer domains can be reoriented to contribute to polarization and strain output. The unimorph actuator is thus designed and operated such that the compressive stress in piezoceramic material is large enough to avoid failure in working condition but small enough to allow larger amount of non-180o domain switching. To compensate the high designed compressive stress state in the piezoceramic attention should be paid on the loading configuration when the actuator is working in-service condition. Experimental results show that the actuator should be arranged in a manner such that the stress state within the PZT wafer is in as more tension as possible to compensate the high compressive induced stress in the piezoceramic due to the manufacturing process.

The performance and reliability of piezoceramic patches based on Lead-Zirconate-Titanate (PZT) wafers were investigated under both quasi-static and cyclic loading conditions in sensor and actuator applications. A 4-point bending setup was used to study the patches' loading limits and damage behavior under mechanical tensile and compressive loading at varied strain levels. The patches' performance under electric actuation was tested in a bending actuator setup. As opposed to irreversible damage by cracking of the PZT wafers under tensile loading (strain at failure: ca. 0.35 %), no mechanical damage was observed under compressive loading at strain levels of up to -0.6 %. Instead a partly reversible degradation of the piezoceramic's electromechanical properties was noted. A strain-cycle diagram was established for tensile loading at room temperature. Finite-element analyses were performed using 3D material modeling with electro-mechanical coupling behavior. Very good predictability of the sensor and actuator performance was achieved by FE-simulation. Through numerical investigations the degradation of the patches' sensor performance under tensile loading could be correlated to the increasing number of cracks in the PZT wafers.

This work aimed at fabrication and electromechanical characterization of a smart material system composed of electroactive polymer and ceramic materials. The idea of composite material system is on account of complementary characteristics of the polymer and ceramic for flexibility and piezoelectric activity. Our preliminary work included Polyvinylidene Fluoride (PVDF) as the flexible piezoelectric polymer, and Zinc Oxide (ZnO) as the piezoelectric ceramic brittle, but capable to respond strains without poling. Two alternative processes were investigated. The first process makes use of ZnO fibrous formation achieved by sintering PVA/zinc acetate precursor fibers via electrospinning. Highly brittle fibrous ZnO mat was dipped into a PVDF polymer solution and then pressed to form pellets. The second process employed commercial ZnO nanopowder material. The powder was mixed into a PVDF/acetone polymer solution, and the resultant paste was pressed to form pellets. The free standing composite pellets with electrodes on the top and bottom surfaces were then subjected to sinusoidal electric excitation and response was recorded using a fotonic sensor. An earlier work on electrospun PVDF fiber mats was also summarized here and the electromechanical characterization is reported.

The magnetoresistance behavior of the polyurethane composites reinforced with iron nanoparticles which has been heat treated was reported. The flexible nanocomposites were fabricated by the surface-initiated-polymerization (SIP) method. The uniformly distributed nanoparticles within the polymer matrix, well characterized by field emission scanning electron microscopy, favor a continuous carbon matrix formation after annealing, rendering the transition from insulating to conductive composites. The coercive forces reflect strong particle loading and matrix dependent magnetic properties. The obtained nanocomposites possess fairly good giant magnetoresistance (MR), with a MR of 7.3 % at room temperature and 14 % at 130 K. Furthermore, the formed carbon matrix has a 7 wt.% argon adsorption potential for fuel cell applications.

This paper explores a unified energy-based approach to model the non-linear behavior of both magnetostrictive and piezoelectric materials. While the energy-approach developed by Armstrong has been shown to capture the magnetostrictive behavior of materials such as Terfenol-D¹ and Iron-Gallium² along different crystallographic directions, extending this approach to piezoelectric materials presents a considerable challenge. Some piezo-electric materials such as PMN-PT and BaTiO₃ may undergo phase changes under applied electric fields and stress in addition to polarization switching. A modeling approach is developed in this paper to capture these effects. Finally, it is shown that the constitutive behavior for the piezo-electric/magnetostrictive layers, coupled by a simple blocked-force approach, is likely to model the behavior of magneto-electric composites.

Rotational isomeric state (RIS) theory has long been used to predict mechanical response trends in polymeric materials based on the polymer chain conformation it addresses. Successful adaptation of this methodology to the prediction of elastic moduli would provide a powerful tool for guiding ionomer fabrication. Recently, a multiscale modeling approach to the material stiffness prediction of ionic polymer has been developed. It applies traditional RIS theory in combination with a Monte Carlo methodology to develop a simulation model for polymer chain conformation on a nanoscopic level. A large number of end-to-end chain lengths are generated from this model and are then used to estimate the probability density function which is used as an input parameter to enhance existing energetics-based macroscale models of ionic polymer for material stiffness prediction. This work improves this Mark-Curro Monte Carlo methodology by adapting the RIS theory in a way to overcome early terminations of polymer chain while simulating the conformation of polymer chains and thus obtains more realistic values of chain length. One solvated Nafion^® case is considered. The probability density function for chain length is estimated with the most appropriate Johnson family method applied. The stiffness prediction is considered as a function of total molecular weight.

A new methodology has been developed to measure the mechanical integrity of a bilayer lipid membrane (BLM) formed over porous substrates. A custom test fixture was fabricated in which a stepper motor linear actuator drives a piston in order to apply pressure to a BLM in very fine increments. The pressure, monitored with a pressure transducer, is observed to increase until the BLM reaches its failure pressure, and then drop. This experiment was performed on 1-Stearoyl-2-Oleoyl-sn-Glycero-3-Phosphocholine (SOPC) lipid bilayers formed over porous polycarbonate substrates with various pore sizes ranging from 0.05 - 10 &mgr;m in diameter. A trend of increasing failure pressure with decreasing pore size was observed. The same set of experiments was repeated for BLMs that were formed from a mixture of SOPC and cholesterol (CHOL) at a cholesterol concentration of 50 mol%. The presence of cholesterol was found to increase the failure pressure of the BLMs by 1.5 times on average. A model of the characteristic pressure curve from this experiment was developed based on an initially closed fluid system in which pressure increases as it is loaded by a moving piston, and which upon reaching a critical failure pressure allows pressure to decrease as fluid escapes through a porous medium. Since the BLM is formed over many pores, this model assumes that the failure pressure for each micro-BLM follows a normal distribution over all pores. The model is able to accurately predict the major trends in the pressurization curves by curve-fitting a few statistical parameters.

This paper is aimed at to discuss two cases of active composites, (i) ferromagnetic shape memory alloy composites, and (ii) piezoelectric ceramic-shape memory alloy composites. Here we discuss the merits of designing such active composites, for use as possible actuator materials. To optimize the nano-/micro-structures of such composites, we developed analytical models based on Eshelby type modeling. Based on the modeling study; a few cases of optimized active composites are suggested.

Shape memory polymers (SMPs) are receiving increasing attention because of their ability to store a temporary shape for a prescribed period of time, and then when subjected to an environmental stimulus, recover an original programmed shape. They are attractive candidates for a wide range of applications in microsystems, biomedical devices, deployable aerospace structures, and morphing structures. In this paper we investigate the thermomechanical behavior of shape memory polymers due to instrumented indentation, a loading/deformation scenario that represents complex multiaxial deformation. The SMP sample is indented using a spherical indenter at a temperature T₁ (>T_g). The temperature is then lowered to T₂ (g) while the indenter is kept in place. After removal of the indenter at T₂, an indentation impression exists. Shape memory is then activated by increasing the temperature to T₁ (>T_g); during free recovery the indentation impression disappears and the surface of the SMP recovers to its original profile. A recently-developed three-dimensional finite deformation constitutive model for the thermomechanical behavior of SMPs is then used with the finite element method to simulate this process. Measurement and simulation results are compared for cases of free and constrained recovery and good agreement is obtained, suggesting the appropriateness of the simulation approach for complex multiaxial loading/deformations that are likely to occur in applications.

Morphing structures have the potential to significantly improve vehicle performance over existing fixed component designs. In this paper, we examine new composite material design approaches to provide combined high stiffness and large reversible deformation. These composites employ shape memory polymers (SMP) matrices combined with segmented metallic reinforcement to create materials with variable stiffness properties and reversible accommodation of relatively large strains. By adjusting the temperature of the sample, the storage modulus can be varied up to 200x. We demonstrate the segmented composite concept in prototype materials made using thermoplastic polyurethane SMP reinforced with interlocking segmented steel platelets. Measured storage moduli varied from 5-12 GPa, below SMP T_g, and 0.1-0.5 GPa above SMP T_g. The samples demonstrated more than 95% recovery from induced axial strains of 5% at 80°C. Viscoelastic effects are dominant in this regime and we investigate the rate dependence of strain recovery.

We present a thermodynamic framework to quantify the magnetization and magnetostriction of Galfenol alloys in response to magnetic fields, mechanical stress, and/or stress-annealing. The framework utilizes only physical parameters and thus provides useful information for material characterization. Furthermore, we formulate the model in state-space form, thus facilitating the computational implementation for design and control of dynamic Galfenol devices.

Ferroelectric and magnetic transducers are utilized in large number of applications, including nanopositioning, fluid pumps, high-speed milling, and vibration control/suppression. However, the physical mechanisms which make these materials highly effective transducers inherently introduce nonlinear, hysteretic behavior that must be incorporated in models and control designs. This significantly complicates control designs and limits the effectiveness of linear control algorithms when directly applied to the system. One solution is to employ an exact or approximate inverse model which converts a desired output to the corresponding input. This alleviates the complex input-output relation, allowing a linear control to be applied. Linearization of the actuator dynamics in this manner permits subsequent use of linear control designs to achieve high accuracy, high speed tracking as well as vibration attenuation and positioning objectives.

We report the first measurements of self-healing polymers with embedded shape memory alloy (SMA) wires. Improvements of healed peak loads by up to a factor of two are observed, approaching the performance of the virgin material. Moreover, the repairs can be effected with reduced amounts of healing agent. The improvements in performance of self-healing polymers with SMA wires are due to three effects: i) crack closure, which reduces the crack volume, ii) heating of the curing agent during polymerisation, which improves the cross-linking, and iii) mechanical registration of the two crack faces, which results in a reduced crack volume on closure.

Inspired by natural examples of microvascular systems in a wide variety of living organisms, we perform the computational design of a new class of polymer-based composite materials with the unique ability to heal and/or cool in a completely autonomic fashion, i.e., without any external intervention. The design process combines graph theory to represent and evaluate the microvascular network and Genetic Algorithms (GA) to optimize the diameter of its microchannels. In this work, a multi-objective GA scheme has been adopted to optimize the network topology against conflicting objectives, which include (i) optimizing the flow properties of the network (i.e., reducing the flow resistance of the network to a prescribed mass flow rate) and (ii) minimizing the impact of the network on the stiffness and strength of the resulting composite in terms of the void volume fraction associated with the presence of the microvascular network. The flow analysis of the network is performed based on the assumption of fully established Poiseuille flow in all segments of the network, leading to the classical proportionality relation between the pressure drop along a segment and the mass flow rate. The optimized structures resulting from the optimization can then be manufactured using an automated process ("robotic deposition") that involves the extrusion of a fugitive wax to define the network. Once manufactured, the computer-aided design can then be validated through a comparison with the results obtained from flow tests. This presentation focuses on the results of the optimization of an epoxy-based composite material containing a two-dimensional microvascular network.

In order to provide structures with new and better characteristics, researchers often look to biological systems for inspiration. One trait that many biological system have that conventional structures do not is a circulatory system, which can be used for many purposes, one of which is the transport of structural material. This paper explores the benefits of transporting structural material for the purpose of changing the structure's static and dynamic characteristics. Several scenarios are explored, including the transport of non-load-bearing mass (mass transport) to load-bearing mass (termed stiffness transport). It is argued that stiffness transport, while more complex than simply moving mass within a structure, affords the same features as mass transport, along with several unconventional and particularly useful abilities.

Structural polymer composites are susceptible to premature failure in the form of microcracks in the matrix. Although benign initially when they form, these matrix cracks tend to coalesce and lead in service to critical damage modes such as ply delamination. The matrix cracks are difficult to detect and almost impossible to repair because they form inside the composite laminate. Therefore, polymers with self-healing capability would provide a promising potential to minimize maintenance costs while extending the service lifetime of composite structures. In this paper we report on a group of polymers and their composites which exhibit mendable property upon heating. The failure and healing mechanisms of the polymers involve Diels-Alder (DA) and retro-Diels-Alder (RDA) reactions on the polymer back-bone chain, which are thermally reversible reactions requiring no catalyst. The polymers exhibited good healing property in bulk form. Composite panels were prepared by sandwiching the monomers between carbon fiber fabric layers and cured in autoclave. Microcracks were induced on the resin-rich surface of composite with Instron machine at room temperature by holding at 1% strain for 1 min. The healing ability of the composite was also demonstrated by the disappearance of microcracks after heating. In addition to the self-healing ability, the polymers and composites also exhibited shape memory property. These unique properties may provide the material multi-functional applications. Resistance heating of traditional composites and its applicability in self-healing composites is also studied to lay groundwork for a fully integrated self-healing composite.

A study was performed to develop a novel technique to enhance the bond strength between a piezoelectric (PZT) actuator and a hosting structure. The bond interface has been considered to be a critical linkage between the structure and the surface-mounted actuators. The loss of interface integrity can have a detrimental effect on the performance of the PZT actuators. The key feature of the proposed technique is to embed a high-density array of oriented carbon nanotubes (CNTs film) into the adhesive layer between the structure and the actuators to enhance the interfacial strength. This presentation focuses primarily on the two fabrication techniques that were developed during the investigation: one is to grow the CNTs directly on the PZT surface at elevated temperatures and the other is to grow the CNTs film on a substrate and then transfer it into the bonding layer at significantly lower temperatures. The latter method is a cost-effective and easy technique which has the potential to be used for structural (as the one proposed here) and for high-performance electronic applications. Through a microscopic examination of the adhesive, it was found that CNTs were uniformly dispersed and aligned into the bonding adhesive. Mechanical tests were performed to investigate the shear strength of the adhesive layer with the embedded CNTs film. Preliminary results show that an increase of the bondline strength up to nearly 300% could be achieved. However a wide data dispersion was also observed and might be attributable to the ratio between the length of the CNTs and the actual PZT-structure gap [1].

A hydrid composite comprised of shape memory alloy (SMA) fibers with piezoelectric ceramic is designed to transform thermomechanical energy into electrical energy that can be stored or used to power other devices. SMA fiber, after its shape is memorized and prestrained at martensitic phase, extends to its original length upon heating to austenitic finish temperature. The compressive residual stress of the composite is induced at austenitic phase, and then by cooling to martensitic finish temperature, SMA will shrink and the residual stress will reduce. By direct effect of the piezoelectric matrix material the mechanical energy which was induced by temperature change can be converted to electrical energy. 1-D and 3-D models for the energy harvesting mechanism of the composite have been proposed. Eshelby formulation with Mori-Tanaka mean field theory modification is used to determine the effective thermo-electro-mechanical properties of the composite. Attention is focused on the constrained recovery behavior of SMA phase in this study. Electrical model is examined and the electrical energy stored in the piezoelectric matrix as a result of stress fluctuation is estimated. Numerical example is given that illustrate the ability of the composite to convert the thermomechanical energy into electrical energy.

Currently a carbon/glass fiber, piezoelectric-ceramic composite, LIPCA, is being investigated for use in micro aerial vehicles, micropumps, vibration control systems, and a number of bio-inspired robotic devices. Many of these applications help demonstrate the growing trend in miniaturization that drives innovative developments in products ranging from pacemakers to cell phones. When designing products for our ever shrinking world not only must the size of the principal components of the system be taken into consideration but also the components of the system that afford functionality as a bi-product of their inclusion. To this end we are referring to the mechanical or electrical systems that provide these devices with the necessary energy to perform their tasks. In order to make efficient use of LIPCA in the previously mentioned applications, the ability to forecast power consumption is essential. In the present investigation, a method of modeling the power consumption of piezoelectric devices is presented and evaluated over a range of frequencies and voltages. Effects of variation in actuator dimension, driving voltage, and frequency are presented. Accuracy of the model is assessed and factors leading to inaccuracies are identified.

Cement-based composite filled with nanophase carbon black (CCN) was found the promising strain sensor material candidate. Experimental results showed that temperature had obviously influence on the initial resistivity of CCN, but nearly no effect on the strain-sensing property of CCN. Resistivity of CCN decreases linearly upon compressive strain, and the strain gauge factors measured under various temperatures were all about 55. Strain sensor was made with CCN and applied in concrete beam for strain monitoring, the results monitored by CCN sensor agreed well with that of strain gauge. The results of this paper suggested CCN sensor a practicable strain sensor.

Two types of the electroactive response in polymeric suspensions can be considered - dielectrostriction and piezoresistance. Dielectrostriction is a variation of dielectric properties of a material with deformation while piezoresistance involves a change in conductivity with deformation. Both phenomena have similar microscopic foundation - they arise from variation of local electric field due to the redistribution of polarized or conductive inclusions. Both dielectrostriction and piezoresistance are determined by the pair distribution function of inclusions and are sensitive to a material's microstructure, which renders them effective for material characterization. In this study, dielectrostriction effect of silicone/aluminum oxide (Al₂O₃) and piezoresistance effect in silicone/graphite suspensions during oscillatory shear deformations are detected by a rosette of planar sensors with mutually perpendicular electrodes. In both measurements, the electric responses are found to be scaled with the deformation-induced stresses. Moreover, the variation of dielectrostriction response with suspensions having various particle size distributions indicates the high sensitivity of dielectrostriction to material's microstructure. Dielectrostriction and piezoresistance constitute new approaches to study the rheological properties of suspensions and compliment each other for revealing the microstructure in various systems.

A study of the microwave absorbing properties of polymer (epoxy) based nanocomposites is presented. The ferrite nanoparticles employed as filler materials were produced by a co-precipitation method, which was designed for production of large amounts at low cost. The absorbing properties of different kinds of ferrite nanoparticles, soft (manganese) and hard (cobalt) magnetic nanoparticles, are compared. In addition, the impact of high and low densities of the respective ferrite type has been investigated. Our analysis of the microwave absorbing properties is made over a wide frequency band including both MHz and GHz regions, which is of high interest for a number of different applications both military and civilian.

Designs for future spacecraft have been conceived with very large lightweight apparatus and structures. New techniques of packaging to be stowed into existing launch vehicles are desired. A kind of current deployment techniques is mechanical hinge mechanisms and this results in an increase of weight in structures. In the present study, Partially- Flexible CFRP with SMA embedded (PFC-S) is proposed to be appropriate for the deployable structures. The PFCS consists of two kinds of matrices: high-stiffness resin matrix and low-stiffness rubber matrix, and the SMA are embedded in low-stiffness rubber part. It can be deformed and folded for packaging and it can be deployed with over 80°C due to the SMA embedded. Since the width of PFCS influences the foldable shape, the relationship between width of the PFCS and the curvature of foldable shape is investigated by using specimens with various width of flexible part. Also the effect of SMA embedded and temperature change on bending stiffness in specimen is measured. As a result, it is found that narrow PFCS specimen keeps appropriate shape with comfortable curvature, and SMA embedded and elevated temperature increases bending modulus of the PFCS specimen.

A new actuation mechanism utilizing piezoelectric properties of boron-nitride nanotube (BNNT) for microcantilever beams is proposed here and modeled using a multiple-scale, multi-physic approach. Using the developed model, specific attention is placed on thermal effects on the microbeams made of aluminum and titanium and the results are compared with each other. Different studies are conducted on the microbeams response characteristics such as frequency response, resonance frequency and heat transition effects while the microbeam tip temperature varies. It is found that Titanium microbeam possesses smaller peak frequency response that occurs at lower frequency. Also, it is demonstrated that increasing the temperature will lower resonance frequency in both beams. Finally, the temperature gradient through the beams with respect to time is studied and it is found that Titanium beam can be stabilized in a longer time period.

Traditional 1-D and 2-D composite materials have excellent in-plane properties. However, they are susceptible to interlaminar crack and crack growth leading to delaminations and catastrophic failure of the composite structures. To remedy these problems, researchers have developed 3-D composites using through-the-thickness stitching and/or braiding. However, these two techniques have their own problems. For braiding, the part thickness should be known a priori, which is not practical. Besides the fiber architecture is not arranged orthogonally. For the stitching, it has been shown that while through-the-thickness properties increase, in-plane properties decrease. Here, we explain a novel technique, developed by the authors and co-workers, to develop 3-D multifunctional hierarchical nanocomposites with superior properties. In this approach, multi-walled carbon nanotubes (MWCNTs) are grown vertically over 2-D microfiber woven fabric cloth, without altering the 2-D cloth architecture, to create nano-forests coating of MWCNTs in the thickness direction to yield 3-D orthogonal fiber architechture. The 3-D nano-forest woven cloths are later impregnated with the resins and are subsequently stacked, vacuum bagged, and cured to give 3-D multifunctional hierarchical nanocomposites. Since MWCNTs have superior mechanical, thermal, and electrical properties, the hierarchically developed 3-D multifunctional nanocomposites have enhanced mechanical, thermal, thermomechanical, damping, and electrical properties by many folds.

Changing dielectric properties of an elastically deformed solid material is called dielectrostriction. This physical response enables a concept of self-sensing in dielectric materials such as polymers and polymeric composites. In addition, dielectrostriction response is governed by same material parameters as the electrostriction effect which is suitable for self-actuation applications. Designed planar capacitor sensor is employed for monitoring dielectrostriction effect without mechanical contact with a loaded specimen. Such sensor can also be arranged in a rosette to directly obtain the principal values of the stress/strain and the principal directions. This study investigates dielectrostriction and electrostriction effects in carbon nanotube (CNT) composites. Preliminary results show tenfold increase in dielectrostriction response of nanocomposites having 2 vol. % of randomly distributed CNTs. Current study targets CNT composites having microstructure modified using applied electric field for optimizing sensing and actuation performances.

Increasingly materials and systems are being tailored to achieve multifunctional properties where they can combine active, sensory, adaptive, and autonomic capabilities. Toward the development of these material capabilities there is a critical need to develop methodologies and devices for in situ self-sensing. The expansion of processing techniques that enable structuring materials at the nanoscale combined with development of new methods for analysis should enable optimization of material structure to achieve systems that satisfy specific functional requirements. In this research we demonstrate that conducting carbon nanotube networks formed in an epoxy polymer matrix can be utilized as highly sensitive sensors for both strain and damage accumulation in advanced fiber composites.

This paper demonstrated the physical properties of a layer-by-layer (LBL) assembled single-walled carbon nanotubes (SWNTs) - polymer composite thin film. The superior mechanical and electrical properties that originate from SWNTs were successfully incorporated into a polymeric thin film by hydrogen bonding-directed LBL assemblies. The electrical conductivities and mechanical strength of a LBL composite are 8.5*10³ S/m and 160 MPa with only 8±2wt% SWNT loading. The combination of high electrical and mechanical properties of SWNT-polymer LBL thin films makes this material unique, opening the way for a wide range of applications from flexible electronics to space telescopes and biomedical implantable devices.

Cellulose based Electro-Active Paper (EAPap) is attractive due to advantages in terms of biodegradable, lightweight, dry condition, large displacement output, low actuation voltage and low power consumption. However, its output force and actuating frequency band should be enhanced to realize its potential applications. Thus, MWNTs are mixed with cellulose solution in this paper. To fabricate the cellulose solution, cellulose fibers are dissolved with LiCl/N,N-dimethyl- acetamide (DMAc) by heating at 150°C. Carboxyl groups functionalized MWNTs (F-MWNT) were used to make well-dispersion of MWNTs in cellulose matrix. F-MWNTs are dispersed in cellulose solution by sonication for 2 hours. The suspension is spin-coated and pressurized to fabricate an F-MWNT/cellulose EAPap. The prepared F-MWNT/ cellulose EAPap is tested in terms of bending displacement and output force. The actuating performance is compared with MWNT/cellulose EAPap and EAPap only.

Unlike widely-used carbon nanotubes, boron nitride nanotubes (BNNTs) have shown to possess stable semiconducting behavior and strong piezoelectricity. Such properties along with their outstanding mechanical properties and thermal conductivity, make BNNTs promising candidate reinforcement materials for a verity of applications especially nanoelectronic and nanophotonic devices. Motivated by these abilities, we aim to study the buckling behavior of BNNT-reinforced piezoelectric polymeric composites when subjected to combined electro-thermo-mechanical loadings. For this, the multi-walled structure of BNNT is considered as elastic media and a set of concentric cylindrical shell with van der Waals interaction between them. Using three-dimensional equilibrium equations, Donnell shell theory is utilized to show that the axially compressive resistance of BNNT varies with applying thermal and electrical loads. The effect of BNNT piezoelectric property on the buckling behavior of the composites is demonstrated. More specifically, it is shown that applying direct and reverse voltages to BNNT changes the buckling loads for any axial and circumferential wavenumbers. Such capability could be uniquely utilized when designing BNNT-reinforced composites.

Cellulose Electro-Active Paper (EAPap) has potential as a smart material due to its advantages of biodegradability, lightweight, air actuation, large displacement output, low actuation voltage and low power consumption. However, improvement of its small output force and low actuating frequency band still remain as drawbacks. In this study, asymmetrical arrangement of Multi-Walled Carbon Nanotubes (MWNTs) in cellulose matrix was investigated to resolve drawbacks. Corona discharging technique was used by means of DC electrophoresis of MWNTs in cellulose matrix. To make MWNTs mixed cellulose EAPap, cellulose fibers were well dissolved in 8%(w/w) LiCl/DMAc (N,N-dimethyl acetamide) by swelling procedure followed by solvent exchange technique. MWNTs were well dispersed in the cellulose solution by sonication for 2 hours, and the suspension was spin-coated on an ITO (Indium tin oxide) coated glass, and high DC electric field was given to the spincoated suspension for 3 hours at 40°C. The structure of MWNT/Cellulose film was characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). It was seen that most of MWNTs were moved and biased toward cathode, and film having double layer-like structure was made.

A continuum thermodynamics formulation for micromagnetics coupled with mechanics is devised to model the evolution of magnetic domain structures in magnetostrictive materials. The theory falls into the class of phase-field or diffuse-interface modeling approaches. In addition to the standard mechanical and magnetic balance laws, a set of micro-forces their associated balance laws are postulated. Thereafter, the second law of thermodynamics is analyzed to identify the appropriate material constitutive relationships. The general formulation does not constrain the magnitude of the magnetization to be constant, allowing for the possibilities of spontaneous magnetization changes associated with strain and temperature. The approach is shown to yield the commonly accepted Landau-Lifshitz-Gilbert equations for the evolution of the magnetization when the magnetization magnitude is constant. Within the theory a form for the free energy is postulated that can be applied to fit the general elastic and magnetic properties of a ferromagnetic shape memory material near its spontaneously magnetized state.

A unified thermodynamic model is presented which describes the bulk magnetomechanical behavior of singlecrystal ferromagnetic shape memory Ni-Mn-Ga. The model is based on the continuum thermodynamics approach, where the constitutive equations are obtained by restricting the thermodynamic process through the Clausius-Duhem inequality. The total thermodynamic potential consists of magnetic and mechanical energy contributions. The magnetic energy consists of Zeeman, magnetostatic, and anisotropy energy contributions. The microstructure of Ni-Mn-Ga is included in the continuum thermodynamic framework through the internal state variables domain fraction, magnetization rotation angle, and variant volume fraction. The model quantifies the following behaviors: (i) stress and magnetization dependence on strain (sensing effect), and (ii) strain and magnetization dependence on field (actuation effect).

This paper investigates the nano-macro transition in magnetic shape memory alloy(MSMA) thin films using a recently developed sharp phase front-based three-dimensional (3D) constitutive model outlined by Stoilov (JSMS 2007), and originally proposed in the 1D context by Stoilov and Bhattacharyya (Acta Mat 2002). The key ingredient in the model is the recognition of martensitic variants as separate phases in a MSMA domain. Evolution of the interface between these phases is taken as an indicator of the process of reorientation in progress. A formulation of the Helmholtz free energy potential based on Ising model has been derived. The implications of the external magnetic field on the initiation of phase transformation are studied for various mechanical loading modes.

High-temperature shape memory alloys in the NiTiPd system are being investigated as lower cost alternatives to NiTiPt alloys for use in compact solid-state actuators for the aerospace, automotive, and power generation industries. A range of ternary NiTiPd alloys containing 15 to 46 at.% Pd has been processed and actuator mimicking tests (thermal cycling under load) were used to measure transformation temperatures, work behavior, and dimensional stability. With increasing Pd content, the work output of the material decreased, while the amount of permanent strain resulting from each load-biased thermal cycle increased. Monotonic isothermal tension testing of the high-temperature austenite and low temperature martensite phases was used to partially explain these behaviors, where a mismatch in yield strength between the austenite and martensite phases was observed at high Pd levels. Moreover, to further understand the source of the permanent strain at lower Pd levels, strain recovery tests were conducted to determine the onset of plastic deformation in the martensite phase. Consequently, the work behavior and dimensional stability during thermal cycling under load of the various NiTiPd alloys is discussed in relation to the deformation behavior of the materials as revealed by the strain recovery and monotonic tension tests.

The focus of this paper is the study of tensile work characteristics and the transformation behavior of a High Temperature Shape Memory Alloy (HTSMA) by thermomechanical characterization at temperatures ranging from 200 to 500°C. In order to investigate the above issues, a nominal composition of Ti₅₀Pd₄₀Ni₁₀ HTSMA was used. The alloy was fabricated using a vacuum arc melting technique. The melt was cast and hot rolled followed by cutting of tensile specimen using Electrode Discharge Machining (EDM). A high temperature experimental setup was developed on a load frame to test the material at high temperatures under constrained actuation conditions. The stability of the material response under cyclic actuation was also investigated. The observations from the tests are presented in this paper. Microprobe analysis was performed on the as-cast and rolled material to study the composition. The material was also studied by X-ray diffraction (XRD) and optical microscopy before and after testing. Certain key observations about the material response are discussed specifically, in terms of transformation behavior, recoverable strains under various applied total strains, and cyclic thermomechanical behavior.

This study concerns the superelasticity of Shape Memory Alloys (SMA) under cyclic loading. A particular attention is paid to the evolution of residual strain with number of cycles (like ratcheting in cyclic plasticity of classical metals). To study the phenomenology of the cyclic behavior and to identify the origin of the developed residual strain a series of cyclic uniaxial tensile tests on copper based alloys wires has been realized. A macroscopic model describing the cyclic behavior of superelastic SMA has been proposed. The originalities of the model are, on the one hand, the definition of a particular elasticity domain when the material is in a two phased state and, on the other hand, an ad hoc kinetic of transformation strain taking into account a residual strain evolution. The proposed model has been identified using our experimental data base and has been used to simulate various cyclic multiaxial loadings.

This study concerns the pseudoelasticity of Shape Memory Alloys (SMA). A series of tests under tension-compression-torsion multiaxial loadings is used to show the validity of a conjecture concerning the relation between the volume fraction of martensite and the equivalent transformation strain. It is shown that the proportionality between an ad doc equivalent transformation strain and the volume fraction of martensite is confirmed under multiaxial proportional and nonproportional loadings.

A process for inducing uniaxial anisotropy in 18.4 at% Galfenol has been developed, applied, and proven to be reliable. The stress annealing procedure that produces the most consistent results and induces the highest uniaxial anisotropy in FSZM Galfenol (6.35 mm &nullset;) is one modified from previous works by the Magnetic Materials Group at Naval Surface and Warfare Center (NSWC) - Carderock. Further modification in which applied stress is lowered and temperature is raised has proven most successful for stress annealing Bridgman Galfenol (20.83 mm &nullset;) and, in addition, has produced an increase in saturation magnetostriction. Model calculations show predicted tensile operation ranges, on average, of 69 MPa for research grade and 40 MPa for production grade FSZM 18.4 at% Galfenol in which full magnetostriction can be utilized.

We investigate a micro bending actuator based on unimorph, lamination of Galfenol (Iron-gallium alloy) and non-magnetic material. Galfenol C-shape yoke bonded with stainless plates (lamination) is wound coils, and is composed close magnetic loop with connected an iron plate. The magnetostriction in longitude direction is constrained by the stainless, thus, the laminations yield bending deformation with the current flowing. The advantage of the actuator is simple, compact and ease of assembling including winding coil, and high tolerance against bending, tensile and impact. We machined the yoke from a plate of 1mm thickness of polycrystalline Galfenol (Fe_81.4Ga_18.6 Research grade) using ultra high precision cutting technique. The prototype, thickness of 1mm and length of 10mm, was observed the displacement 13&mgr;m and 1st resonance at 1.6 kHz, and the high bending (tensile) tolerance withstanding suspended weight of 500g.

A model has been developed to predict the magnetic induction, elastic and magnetostrictive strain and mechanical stress in a laminated structure with ferromagnetic and non-magnetic layers and subjected simultaneously to mechanical stress and magnetic field. This model was obtained by coupling classical laminated plate theory to an energy-based statistical magneto-mechanical model. The model can accommodate in-plane axial and shear forces as well as bending and twisting moments and can predict both in-plane axial and shear strains and stresses. A stress-dependent Young's modulus combined with an iterative algorithm was used to obtain non-linear magneto-mechanical response from a unimorph actuator and sensor. The effect of tensile and compressive bias force on actuator performance and the effect of DC magnetic bias field on sensor performance were studied. Possible applications areas for the model have been proposed.

A homogenized energy model was implemented in a model-based nonlinear control design to accurately track a reference displacement signal for high frequency magnetostrictive actuator applications. Rate dependent nonlinear and hysteretic magnetostrictive constitutive behavior is incorporated into the finite-dimensional optimal control design to improve control at high frequency. The integration of the rate-dependent nonlinear and hysteretic magnetostrictive constitutive model in the control design minimized the amount of feedback required for precision control. The control design is validated experimentally and shown to accurately track a reference signal at frequencies up to at least 1 kHz.

In recent years, influence of volume, size and shape of particulate, stiffness of the polymeric matrix and mechanical preload on the magetostrictive property of polymer-bonded Terfenol-D composites have been investigated by several papers, however, few studies on the effects of the blending soft magnetic particles. In this study, polymer-bonded Terfenol-D composites composed with 20% volume fraction of Terfenol-D particulate and different volume percentage of carbonyl iron particle (i.e. 0, 10%, 20%, 30% and 40%) are fabricated. The changes of magnetostriction and magnetic permeability with changing applied field are tested. The experimental results indicate that with increases of fraction of carbonyl iron particle, the permeability of the composites increases, but the magnetostrictive property declines. The change of permeability is explained based on two ideal models, while the change of magnetostriction is explained from the perspective of energy transforming and mechanical property of matrix.

Magnetostrictive Galfenol (Fe-Ga) is a promising new active material. Single crystals of Galfenol have been shown to exhibit up to 400 ppm magnetostrictive strains with saturating fields of several hundred oersteds. Its robustness and ability to actuate in either tension or compression allows for new actuator and sensor designs. However, due to the high permeability of Galfenol, it needs to be in thin sheet form for many device applications to minimize eddy current losses. Work is underway to develop conventional rolling processes to produce large quantities of thin Galfenol sheet, while retaining a preferred <100> crystallographic texture to optimize magnetostrictive performance. Knowledge of deformation behavior at elevated temperature is crucial to understanding formability and crystallographic texture evolution during rolling. In this work, the high-temperature plasticity and the deformation behavior of polycrystalline Galfenol were investigated using conventional axial compression tests and rolling experiments. As the temperature increased, significant softening of the material occurred in the temperature range from about 450°C to 800°C. The results also suggested that significant dynamic recovery and recrystallization occurred during deformation at above 800°C.

This paper presents the results of an analytical and experimental investigation in fatigue crack growth behavior of piezoelectric ceramics under electromechanical loading. Static fatigue tests are performed in three-point bending with the single-edge precracked-beam piezoelectric specimens under electric fields. Time-to-failure under different mechanical loads and electric fields are measured, and the effect of applied electric fields on the energy release rate vs lifetime curves are discussed, with combination with the finite element method. Cyclic crack growth tests are also conducted on the same piezoelectric specimens under electric fields, and the fatigue crack growth rate vs maximum energy release rate curves are examined.

An improved two-dimensional constitutive model for Shape memory alloys (SMAs), which can describe both the shape memory effect (SME) and super elasticity effect (SE) of the SMAs, is developed based on the previous work of Boyd and Lagoudas, who used the thermodynamics theories of free energy and dissipation energy to derive the constitutive law of SMAs. The improved model, which will combine the ideas of Brinsion's one-dimensional constitutive law and the concepts of Boyd and Lagoudas' two-dimensional one, has a simple but accurate expression. The results of the simulations show that the developed constitutive model can qualitatively describe the thermo-mechanical behaviors of two-dimensional SMAs and can be used in the analysis of structures actuated by SMAs.

Magnetorheological fluids have great potential for engineering applications due to their variable rheological behavior. These fluids find applications in dampers, brakes, shock absorbers, and engine mounts. However their relatively high cost (approximately US$600 per liter) limits their wide usage. Most commonly used magnetic material "Carbonyl iron" cost more than 90% of the MR fluid cost. Therefore for commercial viability of these fluids there is need of alternative economical magnetic material. In the present work synthesis of MR fluid has been attempted with objective to produce low cost MR fluid with high sedimentation stability and greater yield stress. In order to reduce the cost, economical electrolytic Iron powder (US$ 10 per Kg) has been used. Iron powder of relatively larger size (300 Mesh) has been ball milled to reduce their size to few microns (1 to 10 microns). Three different compositions have been prepared and compared for MR effect produced and stability. All have same base fluid (Synthetic oil) and same magnetic phase i.e. Iron particles but they have different additives. First preparation involves organic additives Polydimethylsiloxane (PDMS) and Stearic acid. Other two preparations involve use of two environmental friendly low-priced green additives guar gum (US$ 2 per Kg) and xanthan gum (US$ 12 per Kg) respectively. Magnetic properties of Iron particles have been measured by Vibrating Sample Magnetometer (VSM). Morphology of Iron particles and additives guar gum and xanthan gum has been examined by Scanning Electron Microscopy (SEM) and Particles Size Distribution (PSD) has been determined using Particle size analyzer. Microscopic images of particles, MH plots and stability of synthesized MR fluids have been reported. The prepared low cost MR fluids showed promising performance and can be effectively used for engineering applications demanding controllability in operations.

In this study, we implemented resin flow monitoring by using an optical fiber sensor during vacuum assisted resin transfer molding (VaRTM).We employed optical frequency domain reflectometry (OFDR) and fiber Bragg grating (FBG) sensor for distributed sensing. Especially, long gauge FBGs (about 100mm) which are 10 times longer than an ordinary FBG were employed for more effective distributed sensing. A long gauge FBG was embedded in GFRP laminates, and other two ones were located out of laminate for wavelength reference and temperature compensation, respectively. During VaRTM, the embedded FBG could measure how the preform affected the sensor with vacuum pressure and resin was flowed into the preform. In this study, we intended to detect the gradient of compressive strain between impregnated part and umimpregnated one within long gauge FBG. If resin is infused to preform, compressive strain which is generated on FBG is released by volume of resin. We could get the wavelength shift due to the change of compressive strain along gauge length of FBG by using short-time Fourier transformation for signal acquired from FBG. Therefore, we could know the resin flow front with the gradient of compressive strain of FBG. In this study, we used silicon oil which has same viscosity with resin substitute for resin in order to reuse FBG. In order to monitor resin flow, the silicon oil was infused from one edge of preform, the silicon oil was flowed from right to left. Then, we made dry spot within gauge length by infusing silicon oil to both sides of preform to prove the ability of dry spot monitoring with FBG. We could monitor resin flow condition and dry spot formation successfully using by FBG based on OFDR.

Metal foams are expected to find use in structural applications where weight is of particular concern, such as space vehicles, rotorcraft blades, car bodies or portable electronic devices. The obvious structural application of metal foam is for light weight sandwich panels, made up of thin solid face sheets and a metallic foam core. The stiffness of the sandwich structure is increased by separating the two face sheets by a light weight metal foam core. The resulting high-stiffness structure is lighter than that constructed only out of the solid metal material. Since the face sheets carry the applied in-plane and bending loads, the sandwich architecture is a viable engineering concept. However, the metal foam core must resist transverse shear loads and compressive loads while remaining integral with the face sheets. Challenges relating to the fabrication and testing of these metal foam panels remain due to some mechanical properties falling short of their theoretical potential. Theoretical mechanical properties are based on an idealized foam microstructure and assumed cell geometry. But the actual testing is performed on as fabricated foam microstructure. Hence in this study, a detailed three dimensional foam structure is generated using series of 2D Computer Tomography (CT) scans. The series of the 2D images are assembled to construct a high precision solid model capturing all the fine details within the metal foam as detected by the CT scanning technique. Moreover, a finite element analysis is then performed on as fabricated metal foam microstructures, to calculate the foam mechanical properties with the idealized theory. The metal foam material is an aerospace grade precipitation hardened 17-4 PH stainless steel with high strength and high toughness. Tensile and compressive mechanical properties are deduced from the FEA model and compared with the theoretical values for three different foam densities. The combined NDE/FEA provided insight in the variability of the mechanical properties compared to idealized theory.

This paper is concerned about an investigation of mechanical and electrical conductive properties of carbon fiber fabric reinforced shape memory polymer composite (SMPC). The shape memory polymer (SMP) is a thermoset styrene-based resin. SMP is a promising smart material, which is under intensive investigation at present. Its primary advantages over other smart materials are the high strain capacity (200% reversible strain), low density and low cost etc.. But its major drawbacks are low strength, low modulus and low recovery stress. So the fiber reinforced SMPC was naturally considered to be investigated in this paper, which may overcome the disadvantages mentioned above. The investigation was conducted with experimental methods: Dynamic Mechanical Analyzer (DMA), static and mechanical cycle loading tests, microscope observation of microstructural deformation mechanism, conductivity and shape recovery tests. Results indicated that SMPC showed higher glass transition temperature (T_g) than neat SMP and improved the storage modulus, bending modulus, strength and resistance against relaxation and creep. Both fiber microbuckling and fracture of SMPC were observed after the static 3-ponit bending test at the constant room temperature. SMPC showed favorable recovery performances during thermomechanical cycles of the bending recovery test and the fiber microbuckling was obvious. Moreover, the conductive SMPC of this study experienced low electrical resistivity and performed a good shape memory effect during numerous thermomechanical cycles.

This paper is concerned about the synthesis of shape memory styrene copolymer and the investigation of the influence of cross-linking degree on its shape memory effect. As one of novel actuators in smart materials, shape memory polymers (SMPs) have been investigated intensively. Styrene copolymer with proper cross-linking degree can exhibit shape memory effect (SME). In this paper, the influence of cross-linking degree on shape memory effect of styrene copolymer was investigated through altering the dosage of cross-linking agent. The cross-linking degree of styrene copolymer was determined by measuring the gel content. The glass transition temperature (Tg) of styrene copolymer, which is determined the cross-linking degree, was measured by Dynamic Mechanical Analysis (DMA). The shape memory performance of styrene copolymer with different cross-linking degrees was also evaluated. Results indicated that the shape memory polymer (SMP) was synthesized successfully. The T_g increased from 55°C to 80.7°C followed by increasing the gel content from 0% to 80% through increasing the dosage of cross-linking agent from 0% to 4%. Moreover, the SMP experienced good SME and the largest reversible strain of the SMP reached as high as 150%. When heating above T_g+30°C (different copolymers performed different T_g), the shape recovery speed of the copolymers increased with increasing the gel content. However, the recovery speed decreased with increasing the gel content at the same temperature of 95°C.

Applications of piezoelectric actuators have increased dramatically during the past decade, focusing mainly on stack-type actuators. Some applications would, however, benefit from bending actuators with improved performance, particularly within the valve industry. Noliac engineers have developed and patented a novel design of multilayer bender actuators which doubles the performance of bending actuators. The design is based on an innovative electrode structure. Theoretical and experimental results based on several different actuator designs are presented. As a result, more compact actuators can be designed, thereby reducing the application volume and costs.

Recently, we developed hot-pressing method to enhance the actuating force of ionic polymer-metal composite(IPMC) by increasing the thickness of IPMC membrane and proved it to be effective in the previous research. In the present work, water-uptake and mechanical properties of the hot-pressed Nafion membrane were measured and compared with those of bare Nafion. We observed slight change of mechanical properties with respect to the increase of laminated Nafion films and assumed the property change of the hot-pressed Nafion is due to the interlayers between laminated Nafion films. Then we applied classical laminated plate theory assuming the existence of interlayer in the hot-pressed Nafion and the analytic results agreed well with the experimental results.