Interdigitated electrodes are used to obtain an in-plane d₃₃ coupling from patch actuators. Existing design tools do not take into consideration the three dimensional effects of polarization reorientation. This work presents a 3-D finite element code that utilizes a micromechancial constitutive law with full ferroelectric switching. The code is used to explore the design of interdigitated electrode devices. The results point to several parameters that are important to the design of these devices. These include electrode spacing, electrode width, specimen thickness, and specimen depth.

A discrete phase model is used to simulate evolution of domain structures in ferroelectric materials. The discrete phase model balances the structural energy against local mechanical and electrical energies. Devonshire theory is used to model the structural energy while a finite element framework using scalar potential theory computes the local electric field and stress.

A constitutive model for rate dependent behavior of ferroelectric materials is developed from a one-dimensional switching model [Ikeda et al., Proc. SPIE, 7289 (2009), 728905]. The one-dimensional switching model has the following three features. (i) Several ferroelectric variants can be considered, such as 0-degree, 90-degree, 180-degree, and initial mixed variants. (ii) Required switching energy is approximated as a sum of two exponential functions of volume fraction of the variants. (iii) A specimen is assumed to be comprised of grains with infinitesimal size, and relationship between two grains regarding the required switching energy is unchanged independently of switching directions. Accordingly, the switching proceeds one-dimensionally. To take into account loading rate effects, a function of volume fraction rate is added to the required switching energy. That makes energy barrier higher at higher rates. To verify validity of the present model, electro-mechanical behavior of a thin PZT plate is measured at various loading rates and simulated using the present model. Result shows the present model can capture the influence of electric loading rate on responses of electric displacement and strain, such that remnant polarization decreases and coercive field increases with increasing the loading rate.

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.

The mechanical and physical properties of materials change with time which can be due to the viscoelastic effect and/or due to hostile environmental conditions and electromagnetic fields. An experimental study on active fiber composites (AFCs) having PZT5A fibers dispersed in epoxy shows that the mechanical response of AFC depends on time, temperature, and mechanical loading. We examine the time-dependent response of the AFC, where the polymer constituent undergoes pronounced viscoelastic deformations at different temperatures and mechanical loadings. A micromechanical model is used for predicting effective time-dependent response in active fiber composites with thermal, electrical, and mechanical coupling effects. The micromechanical model is derived based on a simplified unit-cell model in which limited information on the local field variables in the fiber and matrix constituents can be incorporated in predicting overall performance of active composites. We compare the overall stress relaxation response of the active composites determined from the micromechanical model with those from available experimental data. We found that the viscoelastic behavior of the matrix constituent can significantly influence the electro-mechanical coupling response of the AFC and elevated temperatures accelerate the relaxation process of the epoxy matrix and the AFCs.

Composites with multiple (bi-) interpenetrating phases are ideally placed to realise multi-functionality and certain multifunctional and smart materials may be modeled as bi-continuous two-phase composites. This paper estimates the mechanical properties of such materials using finite element analysis and homogenization. The effect of phase volume fraction and contiguity on the properties is investigated for a range of microstructures with triply periodic minimal P interfaces between the two phases. The results show that the properties of the composite depend on not only the overall volume fraction but also the contiguity of the constituent phases.

Recent studies showed that the active piezoelectric structural fiber (PSF) composites may achieve significant and simultaneous improvements in sensing/actuating, stiffness, fracture toughness and vibration damping. These characteristics can be very important in the application of civil, mechanical and aerospace structures. The PSF is fabricated by coating the piezoceramic onto the silicon carbide core fiber with electrophoretic deposition (EPD) process to overcome the fragile nature of the monolithic piezoelectric materials. The PSF composite laminates are made of longitudinally poled PSFs that are unidirectionally deployed in the polymer binding matrix. The PSF laminate transducer has electrical inputs/outputs that are delivered through a separate etched interdigital electrode layer. This study analyzed the electromechanical properties with the generalized dilute scheme for active PSF composite laminate by considering multiinclusions. The well-known Mori-Tanaka approach was used to evaluate the concentration tensor in the multi-inclusion micromechanics model. To accurately predict the transverse properties, the extended role of mixtures were applied by considering the inclusions' geometry and shape. The micromechanical finite element modeling was also conducted with representative volume element (RVE) to compare with the micromechanics analysis on the electromechanical properties. The micromechanics analysis and finite element micromechanical modeling were conducted with varied fiber geometry dimensions and volume fractions. These comparison studies indicate the combined micromechanics models with the generalized dilute scheme can effectively predict the electro-elastic properties of multi-inclusion PSF composites.

Army combat operations have placed a high premium on reconnaissance missions for micro air vehicles (MAVs). An analysis of insect flight indicates that in addition to the bending excitation (flapping), simultaneous excitation of the twisting degree-of-freedom is required to manipulate the control surface adequately. By adding a layer of angled piezoelectric segments to a Pb(Zr,Ti)O₃ (PZT) bimorph actuator, a bend-twist coupling may be introduced to the flexural response of the layered PZT, thereby creating a biaxial actuator capable of driving wing oscillation in flapping wing MAVs. The present study presents numerical solutions to governing equations for quasi-static three-dimensional bending of functionally-modified bimorph designs intended for active bend-twist actuation of cm-scale flapping wing devices. The results indicate a strong dependence of bimorph deflection on overall length. Further, the width and angle of orientation of the angled piezoelectric segments may be manipulated in order to increase or decrease the length effects on bimorph deflection. The relationships of geometry and orientation of the angled segments with bimorph flexural response are presented.

Biological processes and electromechanical function in ionic polymers share ion transport as the fundamental processes for sensing, actuation and energy harvesting. Inspired by the similarity in protein-bound cell membranes and polypyrrole membrane (an ionic polymer), our group is developing a hybrid device that provides the template for integrating biology and electronics. The integrated device, referred to as a bio-derived ionic transistor (BIT), consists of a bilayer lipid membrane (BLM) formed on a polypyrrole membrane and has two inputs that regulates the output of the device. This proceedings article will discuss the constructional features of proposed actuator, fabrication procedure of a prototype actuator and discuss a modeling framework for analyzing the dynamics of the ionic response.

Azobenzene liquid crystal polymer networks have recently drawn significant attention due to their novel photomechanical material behavior for developing remotely actuated adaptive structures. The photoisomerization of this material leads to large polymer network deformation since the liquid crystals are synthesized within the network. The amount of deformation may also be changed by applying polarized light and rotating the polarization relative to the liquid crystal orientation. A nonlinear photomechanical shell model is developed to understand polarized light induced bending deformation and structural dynamics of these photomechanical films. The large deformation finite element shell model within the Finite Element Analysis Program (FEAP) is extended to accommodate nonlinear liquid crystal photomechanics and structural dynamics. Nonlinear light-induced bending strain is incorporated into the model as a function of angle dependent light reflection and absorption and nonlinear liquid crystal absorption. The results illustrate changes in light induced bending deformation with respect to the incident angle of light with the material surface for moderate to large bending angles. A set of material parameters are identified to compare the static and structural dynamic model predictions with measurements given in the literature.

Dielectric Electroactive Polymers (DEAP) will undergo large deformations when subject to an electric field making them an attractive material for use in novel actuator systems. There are many challenges with successful application and design of DEAP actuators resulting from their inherent electromechanical coupling and non-linear material behavior. FE modeling of the material behavior is a useful tool to better understand such systems and aid in the optimal design of prototypes. These modeling efforts must account for the electromechanical coupling in order to accurately predict their response to multiple loading conditions expected during real operating conditions. This paper presents a Finite Element model of a dielectric elastomer undergoing out-of-plane, axisymmetric deformation. The response of the elastomer was investigated while it was subjected to mechanical and electric fields and combined electro-mechanical actuation. The compliant electrodes have a large effect on the mechanical behavior of the EAP which needs to be taken into consideration while modeling the EAP as a system. The model is adapted to include the effect of electrode stiffness on the mechanical response of the actuator. The model was developed using the commercial Finite Element Modeling software, COMSOL. The results from the mechanical simulations are presented in the form of forcedisplacement curves and are validated with comparisons to experimental results. Electromechanical simulations are carried out and the stroke of the actuator for different electrode stiffness values is compared with experimental values when the EAP is biased with a constant force.

The system of Poisson and Nernst-Planck (PNP) equations is used to describe the charge transport in ionic polymer-metal composite (IPMC) materials. This process is a key mechanism for the electromechanical transduction of the material. As the system coupled with elastostatic equations is nonlinear and for a domain with two electrodes, the charge concentration differences occur in a very narrow region near the boundaries, the required computing power for a full scale finite element (FE) model is, especially in 3D, rather significant. Furthermore, it is challenging to find a mesh that would be optimal in terms of calculation time, required computing resources, and calculation accuracy. Most of the commercially available FE software for multi-physics problems has rather strict restrictions in terms of element types, mesh types, and choice of polynomial degrees. In this paper, we explore the option of using hp-FEM modeling to solve the PNP and elastostatic equation system. First, we demonstrate how the multi-meshing and the time dependent adaptivity help to control the error of the solution and also how the problem size is reduced. This is done by studying Poisson-Nernst-Planck system of equations in a 2D domain with different hp-adaptivity types. Both 2D and 3D versions of the model are implemented in Hermes which is a space- and space-time adaptive hp-FEM solver. Full mathematical derivation of the weak formulation of the system of equations is presented. Furthermore, we show how the features of Hermes can be useful in modeling more complicated full scale actuation of IPMC.

Liquid crystal polymer networks exhibit a large number of field-coupled mechanical characteristics including light induced deformation, flexoelectricity, thermal shape memory, electrostriction, and chemically induced deformation. Light induced deformation has received considerable attention recently due to its unique functionality for morphing structure applications since light can be considered clean energy and electrodes and wiring are not needed for actuation. Azobenzene liquid crystals that are synthesized within a glassy liquid crystal network (LCN) in a main chain configuration are considered here under time-dependent deformation from light stimuli. A photomechanical constitutive model, coupled with viscoelasticity of the host polymer network, is developed and compared with light induced blocked stress measurements using a blue light emitting diode (LED). It is shown that the rate of change of stress in the main chain azobenzene liquid crystal is strongly dependent on the rate of change of the liquid crystal microstructure. Additional comparisons to side chain azobenzene LCNs is modeled and compared with data in the literature which illustrates the importance of viscoelastic creep of the polymer network.

Light induced bending of photochromic liquid crystal polymer (LCP) thin films sandwiched with some transparent polymer substrates is studied. Kirchhoff plate model is analyzed. We found that under the irradiation of light with suitable wavelength, an effective bending moment of the composite film will be produced and has two contributions, the opto moment and the bi-film moment. The opto moment is due to the inhomogeneous distribution of the light induced contraction resulted from the light absorption decay. It acts as a bending moment for single layered LCP film as well and has been studied by many authors. The bi-film moment, on the hand, is resulted from the homogeneous contraction induced by light and will act only to the composite similar to the well-known bi-metal bending. By utilizing the two contributions, the magnitude of the total effective moment and the bending curvature can be enhanced largely. Moreover, the bending direction can be well controlled by suitable design of the multilayered structures. The variational formulation of the bending equation is derived, according to which any commercial finite element code can be used to simulate the light induced bending behavior under various boundary conditions. Some interesting bending patterns of the film composites are shown to be possibly produced by patterned layer structures.

Ferroelectric and ferromagnetic actuators are being considered for a range of industrial, aerospace, aeronautic and biomedical applications due to their unique transduction capabilities. However, they also exhibit hysteretic and nonlinear behavior that must be accommodated in models and control designs. If uncompensated, these effects can yield reduced system performance and, in the worst case, can produce unpredictable behavior of the control system. In this paper, we address the development of adaptive control designs for hysteretic systems. We review an MRAC-like adaptive control algorithm used to track a reference trajectory while computing online estimates for certain model parameters. This method is incorporated in a composite control algorithm to improve the tracking capabilities of the system. Issues arising in the implementation of these algorithms are addressed, and a numerical example is presented, comparing the results of each method.

Recently, the theoretical framework of fracture mechanics of piezoelectrics has been extended to include electrostatically induced mechanical tractions in crack models yielding a significant crack closure effect.^1-3 However, these models are still simple, neglecting e.g. the piezoelectric field coupling. In this work, an extended model for crack surface tractions is presented yielding some interesting effects. In particular, it is predicted that the Mode-I stress intensity factor is influenced by both a collinear normal stress parallel to the crack faces and a Mode-II shear loading. Also, the direction of electric field vs. poling direction is clearly manifested in the calculated crack loading quantities.

Excellent properties like low density, high mechanical stiffness as well as an outstanding thermal and electrical conductivity make researchers focusing on carbon nanotubes (CNTs) since years. Beside that it is found that structures made of CNTs can be actuated when they are set up like a capacitor. Usually two dimensional (2D) CNT-papers with randomly oriented CNTs, called Bucky-papers, are used. They are charged and divided by an electrically insulating but ionic conductible electrolyte. Experiments demonstrate low voltages for actuation (±1V). Although the mechanism of CNT-actuation is still an open issue theoretical studies suggest a charge and ion induced lengthening of the C-bonds, which predict theoretical strains up to 1%. These characteristics make CNTs a potential candidate for lightweight and powerful actuators of future adaptive aerospace applications. The presented work gives an overview of possible CNT-actuator configurations. Comprehensive analysis tools for 2D mats of randomly oriented CNTs have been developed to guarantee a consistent data base for the comparison of different CNT-configurations. It is focused on the electro-mechanical properties with respect to the processing and configuration of CNT-actuators. For a more efficient use of the mechanical advantages of the CNT-geometry a new aligning manufacturing approach is presented, to get highly oriented 2D CNT-papers. Their properties are compared with randomly oriented CNT-papers. Finally a new test set-up will be introduced, which enables deflection measurements directly on the top of vertically aligned CNTs (CNT-arrays). The buildup and necessary prework are shown, as well as results of the first experiments. The method of measuring along the axis of aligned CNTs qualifies this set-up to get a deeper understanding about the actuation mechanism of CNTs. Vertically aligned CNTs promise to be a more efficient actuator configuration because of their high stiffness in direction of actuation.

Recent advances in the production and availability of nanoscale materials has led to a significant interest in the use of nanoscale fillers in order to augment and tailor material performance in nanostructured composites. A specific area of interest is the use of high aspect ratio fillers, such as carbon nanotubes (CNT) and carbon nanofibers (CNF) to augment the damping capacity of nanostructured composites. Previous work has shown the use of high aspect ratio fillers to significantly enhance the damping capacity at low frequency by more than 100%; however, the enhancement achieved has been predicated on strain levels in the composite. Our previous studies have indicated a strong strain dependent response in the nanostructured composites utilizing CNF to augment damping capacity. This is due, in part, to the random distribution of fiber orientations seen in the nanostructured composites. The random distribution of filler orientations is thereby relative to the load applied to the composite that results in a critical shear stress thresholds being surpassed at the nano scale, allowing the filler to slip relative to the matrix, resulting in frictional energy dissipation as heat and thereby inducing damping to the high aspect ratio filler nanostructured composite. In light of the promise this technology holds for use in engineered applications requiring specific damping performance, there remains a fundamental lack in understanding of the precise mechanisms and thereby a lack of ability to accurately predict material performance, which is limiting application of the technology. This study looks at the effect of the random filler orientation of CNF included composites and examines the viscoelastic response of the composite specifically investigating the effect of filler orientation relative to the loading direction and the effect of filler waviness. Furthermore, this study looks at the strain dependent nature of the viscoelastic response and develops an analytical modeling tool to look at the effect of the strain dependent viscoelastic response seen in previous studies with the aim of achieving a better fundamental understanding of the effect of filler orientation and the associated strain dependent nature of the viscoelastic response seen in high aspect ratio nano- filled composites.

The new structures and multifunctional materials is that it can achieve some other special functions while it has ability to carry, such as wave-transparent, absorbing, anti-lightning, anti-heat, anti-nuclear etc. It represents the direction of future development of structural materials. And graphene is the one of two-dimensional atomic crystal free substance only found in the existence and shows great importance for fundamental studies and technological applications due to its unique structure and a wide range of unusual properties. It exhibits great promise for potential applications in chemistry, materials, and many other technological fields. In this paper, we prepare nanopaper through physical vapor deposition (PVD) with a variety in the weight ratio between graphene and nanofiber. Then prepare composite materials with nanopaper and T300/AG80 prepreg by the meaning of autoclave molding. The morphology of nanopaper was characterized by transmission electron microscopy (TEM) and scanning electron microscope (SEM). And the electrical properties and the EMI shielding performances of these nanocomposites have been investigated experimentally by and four-point probe measurement and vector network analyzer. The experimental results indicate that the composites made from graphene and nanofiber nanopaper have highly electric capability, and the EMI shielding value of composites were all up to -15dB. In the same time the conductivity and the EMI shielding performances were improved with increasing the ratio of graphene in nanopaper. We tested the mechanical properties of composite materials at the same time. The average strength of composite materials is about 2000MPa, the elastic modulus is 130GPa above. We are sure that it can be used as the load-bearing structural material which has a multi-functional performance in the aviation field.

The use of piezoelectric materials has become more popular for a wide range of applications, including structural health monitoring, power harvesting, vibration sensing and actuation. However, piezoceramic materials are often prone to breakage and are difficult to apply to curved surfaces when in their monolithic form. One approach to alleviate these issues is to embed the fragile piezoceramic inclusion into a polymer matrix. The flexible nature of the polymer matrix protects the ceramic from breaking under mechanical loading and makes the resulting compoistes easier to apply onto curved structure. However, most developed active ceramic composites have relatively low electroelastic coupling compared to bulk piezoceramics. There are two main methods to improve the eletroelastic properties of piezoceramic composites, namely using higher aspect ratio active inclusions and alignment of inclusions in the electric field direction. In this paper, the dielectric and energy storage property of nanowire composites is significantly enhanced by aligning the nanowires in the direction of the applied electrical field. PZT nanowires are hydrothermally synthesized and solutioncast into a polymer matrix, and then aligned using a shear flow based stretching method. The alignment was evaluated by scanning electron microscopy images and it is shown that the nanowires can be successfully aligned in the PVDF. The dielectric constant and energy density of the nanocomposites were tested using Agilent E4980A LCR meter and Sawyer-Tower circuit. This testing result shows that the dielectric constant and energy density of the composites can be increased by as much as 35.7% and 49.3% by aligning the nanowires in the electric field direction. Piezoceramic composites with enhanced energy storage property could lead to broader applications when using this type of materials for polymer based capacitive energy storage.

This study details the fabrication and foaming of biodegradable polylactide (PLA) and chitin composites. Three types of chitin were examined; as-received, chitin nano-whiskers and chitin nano-whiskers with a compatibilizing agent. The chitin and chitin composite morphology was characterized with transmission and scanning electron microscopy, respectively. The thermal, rheological and mechanical behavior of the PLA-chitin composites was investigated. It was found that Chitin decreases the thermal and rheological stability of the composites. The stiffness of the composites was found to increase with increasing chitin content while the strength was found to decrease as a result of PLA hydrolysis. Biodegradable foams of PLA-chitin composites were produced and the expansion behavior was correlated with the visco-elastic observations. The statistical significance of chitin type and composition dependence on the mechanical properties and foam morphologies were evaluated.

The focus of this study was to experimentally investigate spherically shaped micron-size particles reinforced polymethyl methacrylate (PMMA) and polycarbonate (PC) polymer composites for improving energy absorbing capabilities such as toughness and low-velocity impact resistance. In this study, a solution mixing method was developed to fabricate both PMMA and PC polymer composites with spherically shaped micron-size polyamide- nylon 6 (PA6) particles inclusions. The morphology of the fracture surfaces of polymer composites was examined by using optical microscopy and scanning electron microscopy. Strain-rate dependent response of both PMMA and PC polymer composites was investigated by characterizing tensile and flexural properties. Low-velocity penetration testing was performed for both polymer composites and the key results observed for energy absorption capabilities are discussed in this study.

Today's smaller, more powerful electronic devices, communications equipment, and lighting apparatus required optimum heat dissipation solutions. Traditionally, metals are widely known for their superior thermal conductivity; however, their good electrical conductivity has limited their applications in heat management components for microelectronic applications. This prompts the requirement to develop novel plastic composites that satisfy multifunctional requirements thermally, electrically, and mechanically. Furthermore, the moldability of polymer composites would make them ideal for manufacturing three-dimensional, net-shape enclosures and/or heat management assembly. Using polyphenylene sulfide (PPS) as the matrix, heat transfer networks were developed and structured by embedding hexagonal boron nitride (BN) alone, blending BN fillers of different shapes and sizes, as well as hybridizing BN fillers with carbonaceous nano- and micro-fillers. Parametric studies were conducted to elucidate the effects of types, shapes, sizes, and hybridization of fillers on the composite's thermal and electrical properties. The use of hybrid fillers, with optimized material formulations, was found to effectively promote a composite's thermal conductivity. This was achieved by optimizing the development of an interconnected thermal conductive network through structuring hybrid fillers with appropriate shapes and sizes. The thermal conductive composite affords unique opportunities to injection mold three-dimensional, net-shape microelectronic enclosures with superior heat dissipation performance.

In this paper, we present an application of the Floquet-Bloch theorem in the context of electrodynamics for vibroacoustique power flow optimization by mean of distributed and shunted piezoelectric patches. The main purpose of this work is first to propose a dedicated numerical approach able to compute the multi-modal wave dispersions curves into the whole first Brillouin zone for periodically distributed 2D shunted piezo-mechanical systems. By using a specific indicator evaluating the evanescent part Bloch's waves, we optimize, in a second time, the piezoelectric shunting electrical impedance for controlling energy diffusion into the proposed semi-active distributed set of cells. A 3D modeling of semi-distributed distribution of the optimal smart metamaterial is used for validating the obtained cell design.

The influence of applied stress and the composite geometry on impedance properties of composites containing ferromagnetic microwires has been investigated. The results indicate that the application of tensile stress along the microwire axis and the increase of composite thickness decreased the magneto-impedance (MI) ratio. The stress induced impedance (SI) effect was enhanced with increasing composite thickness reflecting the role of the internal residual stresses. Theoretically calculated matrix-wire interfacial stress from the magneto-impedance profiles is in good agreement with the value of the applied effective tensile stress. This demonstrates a new route to probing the stress conditions of such composites.

When studying composite material systems, mechanical properties, such as stiffness, strength, fracture toughness or damage resistance are the subjects of greatest interest and in most of the cases are considered in the context of simple static loading conditions. However, in almost all applications, composites, like most materials are subjected to dynamic loading which requires that the dynamic response of the composite be analyzed. For structural materials which are linear elastic, the stress-strain response is not dependent on strain rate, and there is no hysteresis or damping. However, this is not the case for viscoelastic materials for which both the stiffness and loss properties directly depend on strain rate and implicitly depend on temperature via time temperature superposition, which in case of harmonic loading leads to frequency dependent response. For viscoelastic composites in which at least one of the constituent materials is viscoelastic, there is great utility in the ability to predict the effective dynamic mechanical properties as a function of the constituent phase properties and geometry. In this paper micromechanical methods combined with the correspondence principle of viscoelasticity are used to obtain the effective damping properties of viscoelastic composites. When materials with different damping properties are present in a composite, the damping properties of the resulting composite are different than that of the constituents. The correspondence principle helps to consider all the frequency dependent properties of the constituent materials and conclude the effective damping vs. frequency. In this study the matrix phase is considered to be viscoelastic and spherical elastic/viscoelastic particles are dispersed into the matrix.

One of the properties of composite materials is the possibility of having phononic band gaps, within which sound and vibrations at certain frequencies do not propagate. These materials are called Phononic Crystals (PCs). PCs with large band gaps are of great interest for many applications, such as transducers, elastic/ acoustic filters, noise control, and vibration shields. Most of previous works concentrates on PCs made of elastic isotropic materials; however, band gaps can be enlarged by using non-isotropic materials, such as piezoelectric materials. Since the main property of PCs is the presence of band gaps, one possible way to design structures which have a desired band gap is through Topology Optimization Method (TOM). TOM is a computational technique that determines the layout of a material such that a prescribed objective is maximized. Functionally Graded Materials (FGM) are composite materials whose properties vary gradually and continuously along a specific direction within the domain of the material. One of the advantages of applying the FGM concept to TOM is that it is not necessary a discrete 0-1 result, once the material gradation is part of the solution. Therefore, the interpretation step becomes easier and the dispersion diagram obtained from the optimization is not significantly modified. In this work, the main objective is to optimize the position and width of piezocomposite materials band gaps. Finite element analysis is implemented with Bloch-Floquet theory to solve the dynamic behavior of two-dimensional functionally graded unit cells. The results demonstrate that phononic band gaps can be designed by using this methodology.

This work presents a new chiral composite composed of copper wires braided with Kevlar and nylon to form conductive coils integrated among structural fiber. To create a fabric, these braids were woven with plain Kevlar fiber. This yielded a composite with all coils possessing the same handedness, producing a chiral material. The electromagnetic response of this fabric was first simulated using a finite element full-wave simulation. For the electromagnetic measurement, the sample was placed between two lens-horn antennas connected to a Vector Network Analyzer. The frequency response of the sample was scanned between 5.5 and 8GHz. The measured scattering parameters were then compared to those of the simulated model. The measured parameters agreed well with the simulation results, showing a considerable chirality within the measured frequency band. The new composite combines the strength and durability of traditional composites with an electromagnetic design to create a multifunctional material.

In this work, we propose a constitutive model to describe the behavior of Piezoelectric Fiber Reinforced Composite (PFRC) material consisting of elasto-plastic matrix reinforced by strong elastic piezoelectric fibers. Computational efficiency is achieved using analytical solutions for elastic stifness matrix derived from Variational Asymptotic Methods (VAM). This is extended to provide Structural Health Monitoring (SHM) based on plasticity induced degradation of flapping frequency of PFRC. Overall this work provides an effective mathematical tool that can be used for structural self-health monitoring of plasticity induced flapping degradation of PFRC flapping wing MAVs. The developed tool can be re-calibrated to also provide SHM for other forms of failures like fatigue, matrix cracking etc.

Ultrasonic Consolidation (UC) is a solid state additive manufacturing process which fabricates three-dimensional objects by ultrasonically joining metal foils together, layer-by-layer, to form a solid part. This study investigates the effect of sonotrode surface texture on the bond strength, interlaminar microstructure and sample surface texture of parts fabricated by UC. White light interferometry was used to characterize the surface of two sonotrodes, textured by Electro-Discharge Machining (EDM). Aluminum 3003-H18 UC samples were fabricated using both sonotrodes under identical processing conditions. The surface texture of the UC samples produced is a reduced amplitude version of the parent sonotrodes texture. Peel testing was used to evaluate the bond strength and failure mode of the samples. The interlaminar microstructure of the parts was examined and linear weld density measured. The rougher sonotrode samples exhibited higher weld strength and brittle failure modes compared to the less rough sonotrode samples which demonstrated ductile failure and lower weld strength. This paper examines the influence of sonotrode texture on interlaminar bonding in UC and how this could be controlled and exploited to optimize bonding in UC.

Polyurethane shape memory polymers (PU-SMPs) are active materials that can be transformed into complex shapes with the ability to recover their original shape even after undergoing large deformations. Because of their light weight, large recoverability, low cost, and high compliance, SMPs can be potentially employed as actuators, MEMS devices, temperature sensors, and damping elements to name a few. One of the key challenges in implementing SMPs is the response time which is limited by the method of heating and cooling and the material. Unlike shape memory alloys, SMPs can be activated by multiple stimuli including lasers, resistive heating, electric fields, and magnetic fields. While these methods may provide an efficient way of heating the SMP, they rely on the slow process of passive conduction for cooling. In this paper, a self regulating SMP (SR-SMP) composite is introduced, whereby a novel heating and cooling system consisting of embedded silica capillary tubes in the SMP (DiAPLEX® MP4510: SMP Technologies, Inc.) has been developed. The tubes are used to pump hot/cold fluid through the SMP membrane and hence provide a local temperature source. In order to show the effectiveness and efficiency of the mechanism, the thermomechanical response of the SR-SMP is compared experimentally to a SMP with "conventional" i.e. global heating and cooling mechanisms. It is shown that the SR-SMP has a faster thermomechanical response. It has been demonstrated previously that soft SMPs can be controlled by an electric field while in the rubbery phase, thus taking advantage of the Maxwell stress or electrostatic stress effect. Thermomechanical characterization of PU-SMPs is described for different weight percentages of resin (Diphenylmethane-4, 4'-diisocyanate) and hardener (1,4-Butanediol). Varying the percent hardener reduced the effective cross-link density of the polymer and hence the thermomechanical properties. The electromechanical response of pure SMP and SR-SMP is predicted numerically. The numerical computation indicates that the softer SMPs (resin:hardener = 5:4, 8:7, and 9:8) could be used as electroactive polymers.

We report giant electrical control of magnetic anisotropy in a magnetoelectric polycrystalline Ni thin film and (011)-oriented [Pb(Mg_1/3Nb_2/3)O₃]_(1-x)-[PbTiO₃]x (PMN-PT) heterostructure. The (011) PMN-PT ferroelectric substrate exhibits both linear anisotropic piezoelectric response and unique giant hysteretic response. These important features can significantly tune the magnetization states via strain coupling. Reversible and permanent magnetization reorientation demonstrates an approach for developing magnetoelectric memory devices.

Magneto-active polymers (MAPs), composed of polymer matrices and magnetic filler particles, are smart materials that deform quickly in an external magnetic field. The ability to produce large deformation of MAPs makes these materials promising for actuators and sensors. Due to the viscoelasticity of the polymer matrices, MAPs usually demonstrate ratedependent dynamic properties. However, very few models of coupled magnetic field and viscoelasticity in MAPs exist in the literature, and even fewer are capable of reliable predictions. Starting from nonequilibrium thermodynamics, a field theory is developed to fully couple the finite-deformation viscoelasticity and magnetostatics of MAPs. The theory provides a guideline for experimental characterization of MAPs, and most material laws are readily applicable in this framework. A specific material model is prescribed for an idealized MAP. As demonstrations, numerical examples are implemented on the responses of the MAP in response to both uniform and nonuniform magnetic fields. In the nonviscous limit, our theory recovers a model for elastic MAPs, and is capable of capturing instability phenomena observed in the experiments.

Magnetoelectric materials made from magnetostrictive and piezoelectric constituents are best suited for selfsensing actuators. The relationship between applied magnetic field (force), tip displacement (deflection) and current output (sensing signal) is necessary for the development of self-sensing actuator systems. The dynamic behavior of the constituent magnetostrictive materials and piezoelectric materials independent of each other are well-understood. The coupled dynamic force-strain-sensing behavior of magnetoelectric materials as selfsensing actuators is largely unexplored and provides the motivation for our work in this area. This paper presents theoretical and experimental analysis of the dynamic behavior of a Metglas/PVDF magnetoelectric laminate composite. Experimental results for the mechanical and electrical behavior of a 15mm × 30mm × 75μm Metglas/PVDF cantilever beam across the frequency spectrum are compared to those predicted by an equation of motion developed using the principle of virtual work and Hamiltonian principle. The theoretically developed model predicts the observed displacement and sensing current within 35% and 20% respectively. A parametric analysis is presented to determine the optimum design parameters of the composite for self-sensing actuation.

The Villari effect of magnetostrictive materials, a change in magnetization due to an external stress, is used for sensing applications. For a dynamically loaded sensor, one measures the time-varying magnetization on the material. The question is, from these measurements, could information be extracted about all the applied stresses (the three axial and the three shear) on the material? In a previously developed rate-equation model [P. Weetman and G. Akhras, SPIE Proceedings Vol. 7644, 76440R], essentially the inverse of this problem was discussed where the input was a set of known stresses and the output was the calculated resulting magnetizations. A preliminary conceptual design of a Galfenol based 3D dynamical sensor is presented. In the proposed prototype sensing device, one can measure the time-varying magnetization and its derivative in all three directions. Incorporating the previously developed 3D rate equation model, a new model is developed pertaining to this sensor. It will be shown that, under certain conditions, all stresses can be found from the magnetization measurements. The required calculations are presented and then performed on a sample set of magnetization data for validation. From this model, the implications to future sensing devices are discussed as well as suggestions on improvements to the model and the prototype.

Galfenol is an alloy of iron and gallium which possesses a unique combination of structural strength and significant magnetostriction. This alloy can be machined, welded and extruded into complex geometries opening up avenues for a new class of load-bearing transducers with 3D functionality. This work addresses the development of an advanced modeling tool to aid in the design of Galfenol transducers. The model describes the full nonlinear coupling between the electrical, magnetic and mechanical domains in 3D Galfenol structures, yielding complete system input-output relationships. Maxwell's equations for electromagnetics and Navier's equations for mechanical systems are formulated in weak form. An energy-averaged constitutive model is employed to relate magnetization and strain to magnetic field and stress in the Galfenol domain. The overall system is approximated hierarchically; first, piecewise linearization is used to describe quasi-static responses and magnetic bias calculations. A linear dynamic solution with piezomagnetic coefficients computed at the bias point describes the system dynamics for moderate inputs. Dynamic responses at large input fields and stresses are described through an implicit dynamic solution based on the trapezoidal rule. The model equations are solved on a commercial finite element solver. A case study consisting of a Galfenol unimorph is presented which illustrates the model's ability to describe transient dynamic responses.

This paper presents a Finite Element Analysis (FEA) of an adaptive structure that uses multiple Shape Memory Alloy (SMA) wires for actuation. The commercially available FEA program ABAQUS was used to simulate the displacement of an adaptive nozzle structure which is actuated by controlling the power to six SMA wires simultaneously. The SMA wires were modeled within the user material (UMAT) feature using a mesoscopic free energy model [1] to accurately describe their thermomechanically coupled actuator behavior. During simulations, the required heat input, wire temperature, phase fraction changes, resulting strains, stresses, and the mechanical interactions with the structure were determined for each SMA wire. Second order effects of wire coupling were also observed and analyzed. The results from the simulation were compared with experimental measurements taken with the current adaptive nozzle prototype.

The focus of the present work is to study the effect of stress and temperature on the accumulated residual strain during the thermomechanical cycling of Shape Memory Alloys (SMAs). NiTi wires were pseudoelastically trained at different temperature above the austenitic finish temperature, up to different maximum applied stress levels. The total residual strain recorded during each training experiment was decomposed into the contributing plastic strain and retained martensite. The quantity of retained martensite in the trained wire was determined by a flash heating the trained SMA and recording the recovered strain. Preliminary observations from the thermomechanical test results suggest that the retained martensite formation is dependent on the maximum applied stress level during the thermomechanical test and is not dependent on the transformation plateau stress level of the SMA. On the contrary the transformation plateau stress level or consequently the test temperature is a critical parameter in dictating the irrecoverable plastic strain generated during the thermomechanical cycling of SMAs.

Current strategies in modeling shape memory alloy (SMA) behavior follow either the concept of classical irreversible thermodynamics or the methodology of phenomenological approaches at the micro as well as at the macro space scale. The objective of the present study is to show a new approach in modeling SMA's by using a statistical physics concept without the requirement of evolution equations for internal variables. Thermodynamic principles in connection with the mathematical apparatus of statistical physics allow deriving relevant system properties in analogy to the formalism used for paramagnetic-ferromagnetic systems. As a result the macroscopic strains and the volume fractions of the martensitic variants and their rates are obtained. The multi-block-spin approach further maps the tension compression asymmetry of multivariant SMA's.

Multifunctional materials and structures possess the ability to perform multiple tasks by combining structural integrity with sensing and actuating capabilities. Recent progress in the development of such materials/structures has made concepts like load-bearing antennas or load-bearing batteries feasible and formed new research possibilities. Load-bearing antenna structures are multifunctional sensing and actuating devices integrated with a load-bearing structure, i.e. they can simultaneously function as a mechanical structure and an electromagnetic antenna. Such an antenna structure is subjected to mechanical forces, temperature gradients, and electromagnetic fields, giving rise to highly-coupled nonlinear thermo-electro-magneto-mechanical (TEMM) behavior. The current research focuses on modeling and characterizing the nonlinear 3-D coupled behavior of TEMM materials, consistent with first principles. This theoretical framework is specifically aimed at modeling and analysis of load-bearing antenna structures. In this paper we demonstrate the development of analytical techniques and computational tools for multiscale, multi-physics modeling of load-bearing antenna structures. The mathematical model, based predominantly on first principles, employs the thermomechanical governing equations coupled with Maxwell's equations. Our modeling has identified 92 nondimensional numbers which quantify the competition between physical effects in the operation of load-bearing antenna. A fixed relative ordering of all competing effects determines a regime of antenna/environment interaction. In this work, we demonstrate a comprehensive framework to derive the 3-D governing equations for a given regime. For thin geometries, these equations are further reduced to 2-D model, using series expansion and perturbation techniques. Mathematical modeling of thin electro-magneto-mechanical plates can have applications like design and optimization of load-bearing antennas structures. This framework can be extended to model various regimes of behavior of any device/material with coupled electro-magentomechanical capabilites.

One of the main selling points of smart materials is the potential to exploit their multi-functional capabilities. For example, a shape memory alloy (SMA) wire can be used as a positioning actuator by heating the wire to induce contraction and as a positioning sensor by measuring the resistance across the length of the wire. While SMA's have found application in many on-off type applications, their ability to 'sense' their own change in length has not been fully exploited. This is because when coupled with a compliant structure, SMA wires exhibit non-linear, hysteretic behavior that depends not only on the phase transformation within the material, but also the thermal and force interactions between the wires and structure itself. If the resistance across an SMA can be reliably mapped to wire strain, a closed-loop controller can easily vary the length of the wire by changing the amount of electrical power put into the wire that causes Joule heating. This paper analyzes the fidelity of different mapping schemes when employed in a closed-loop controller. The schemes are tested in the context of a dual-joint flexible nozzle that is designed to control both the release position and trajectory of an emitted fluid flow. The mapping methods include consideration of the force coupling that results from opposing SMA actuators. The challenges of practical implementation issues are discussed alongside the results to develop the best mappingcontrol scheme for this application. Results show that simple linear-mapping solutions offer 2D nozzle tip position tracking with errors of 2 mm over a range of 12 mm on both axes, with minimal investment of calibration time, while more involved solutions that include force coupling and account for hysteresis can bring positioning errors to less than 500 um.

The capability of Shape Memory Alloys (SMAs) to modify the reference configuration of an SMA-composite through martensitic transformation is explored. It is intended that through careful selection of a thermomechanical loading path the composite can be "processed" such that the constituent phases are in a preferential reference configuration. Specifically, for materials which have preferred loading conditions (i.e., compression versus tension), such processing results in a residual stress state which takes advantage of the improved properties. The composite under investigation is assumed to be composed of an SMA phase and an elasto-plastic second phase. For analysis of such a composite, a Finite Element (FE) mesh based on a realistic microstructure is constructed by using the results of X-ray tomography. The resultant microstructure is analyzed using FE techniques. It is shown that through an isobaric loading path, transformation generates plastic strains in the elasto-plastic phase which modify the composite reference configuration. The effect of different applied loads is considered.

Magnetic shape memory alloys (MSMAs) have recently drawn considerable research interest due to their ability to produce magnetic field-induced strains (MFIS) , at least one order of magnitude higher than those of ordinary magnetostrictive materials. In the present work microstructure dependence of martensitic phase transformation and reorientation is taken into account by introducing internal variables into the model. The magneto-thermomechanical constitutive equations are derived in a thermodynamic consistent way. A 3-D stress-field-temperature phase diagram is predicted using the model for the case of field induced phase transformation (FIPT).

Magnetic Shape Memory Alloys (MSMAs) are materials that respond to a change in either compressive stress or magnetic field, and can be used for applications such as actuation, sensing, and power harvesting. MSMA prismatic specimens are usually loaded magneto-mechanically by a compressive stress applied along the longest side of the specimen and by a magnetic field applied normal to the direction of the compressive stress. Karaman et al. proved the viability of using MSMAs, specifically NiMnGa single crystals, for energy harvesting applications using up to 5 Hz of cyclic stress. The group proposed a simple mathematical model to predict electrical voltage output generated by the material during the shape recovery process. The voltage output predicted by the model matched well with experimental results recorded at low frequencies¹. The magnetization reversal responsible for the voltage output has been approximated by Karaman et al. does not use the constitutive relations for the magneto-mechanical behavior of the material, such as that proposed by Kiefer and Lagoudas^2,3. This work presents simulated and experimental results describing the electromotive force (EMF) producing capabilities of a NiMnGa magnetic shape memory alloy (MSMA) at frequencies of up to 10 Hz. Unlike previous work, the current paper uses the constitutive model developed by Kiefer and Lagoudas^2-4 and the corresponding magnetization relations to theoretically predict the voltage output of the material. COMSOL Multiphysics 3.5a and Simulink were used to generate the simulated results for different constant bias magnetic fields and frequencies of excitation, partial reorientation strains and stress amplitudes. Simulated results are compared to experimental data and the reasons for data match/mismatch are discussed.

This work investigates the electromechanical response of piezoelectric macro-fiber composites (MFCs) under tension. Nonlinear three dimensional finite element model incorporating the polarization switching mechanism was used to predict the electromechanical fields near interdigitated electrode (IDEs) in the piezoelectric MFCs. The lead zirconate titanate (PZT) fibers in the MFC are partially poled. The electric field-induced strain was then measured, and test results were presented to validate the predictions.

Bilayer actuators comprising of MWCNT (Multi-walled carbon nanotubes) and Graphene oxide (GO) were studied for their actuation performance by using induction heating system. A simple fabrication method namely, filtration of the colloidal suspensions of MWCNT and GO through an Anodisc membrane was used to fabricate the actuators. In case of bilayer actuators, sequential filtration of MWCNTs and Graphene oxide dispersions through a membrane filter membrane was used. Morphological studies by SEM showed that the bilayer paper did not delaminate at the macro-scale and a certain degree of adhesion between MWCNT and GO can be achieved even without any functionalization of either of the constituents of bilayer actuators. Actuation was tested by using the induction heating system, operated at different current densities. Substantial degree of deformation, as much as 0.128 mm^-1 at 300 A was measured. The degree of actuation was defined in terms of bending curvature, because the deformation was too large to be detected by conventional displacement laser sensors. An attempt has been made to explain the basic mechanism of bilayer actuator in terms of the differential thermal expansion rates and eddy current which was confirmed from images obtained from thermal camera wherein the variation in bilayer actuator's surface temperature were monitored. Finally the deformation trend under different pulses is also examined.

The recent progress in creation of materials with negative refractive index inaccessible for natural substances show all-important role of the multi-phase materials in modern technology. In the present work the approach for calculating of effective properties is considered for multi-component composite materials with variable configurations and concentration of inclusions [1]. The approach is based on interpolation formulas obtained between the rigorously calculated limiting borders [2]. The general merit of the model is the ability to obtain algebraic formulas for complicated properties with the vectors of electrical, thermal, magnetic, etc. fields directed along the different axes [3]. The examples of application of the above model are given for the analysis of multi-phase states in the vicinity of pressure-induced phase transition. The model was used for a set of semiconductor compounds like PbX, SmX (X - Te, Se, S), iron ore, etc. [4]. The program for calculation of different electrical, thermal, mechanical etc. properties of n-phase systems with variety of configuration and concentration of phase inclusions has been created, which may be applicable for real multiphase systems.

Firstly, two types of CFRP tubes are designed using the filament-wound forming technology. These tubes are winded by carbon fibers with a filament winding pattern of [(900/00)2]S. The compression and tensile test are also carried out to investigate the stress-strain relationship, ultimate strength and macroscopic failure mode of the former CFRP tube. The results demonstrate that the former CFRP tube has a much larger ultimate tensile stress and strain than compressive stress and strain. However, the elastic modules of CFRP tubes under tension and compression are similar and the failure mode of these CFRP tubes is brittle under compression and tension. Secondly, the stress and strain analysis method of filament-wound CFRP tube is investigated according to anisotropic elasticity theory and lamination theory of composite material. Then, the strength of carbon-fiber-reinforced plastic tubes is obtained. In addition, the comparison of theoretical analysis results and experimental results shows that the theoretical analysis results are reliable.

In the present work, an unsymmetric laminated plate with surface bonded piezoelectric sensors, and actuators has been considered. Piezoelectric sensor were used to monitor the load and deformation bifurcation occurs. Monitoring the shape and load of a morphing structure is essential to ascertain that the structure is properly deployed and it is not loaded excessively ,thus, preventing structural to failure. A piezoceramic actuator is used to provide activation load and to force the structure to change its stability state from one to another. A non-linear finite element model based on the layerwise displacement theory considering the electro-mechanical coupling effects of piezoelectric elements has been developed for simulation purposes. A control mechanism is also employed to actively control the shape of the structure. It is observed that, utilizing multistable composite to design a morphing structure may significantly reduce the energy required for changing the shape. Further controlling the buckling phenomena using piezoelectric sensor and actuator along with an ON/OFF controller can effectively and efficiency enhance the performance of the morphing structure during manoeuver.

There are five kinds of plane waves in a general piezoelectric solid, three of them are quasi-acoustic waves and the other two are quasi-electromagnetic waves. When these plane waves propagate from interior of a half space to the solidvacuum interface, electromagnetic waves in vacuum are induced. For the same input power, the power of EM waves in the free space induced by quasi-acoustic waves is much smaller than that induced by quasi-electromagnetic waves. That is, the EM waves are hardly to be generated mechanically in piezoelectric materials. Piezoelectric superlattice formed by intervallic polarizing oppositely along one direction can have significant coupling between phonon and photon in the vicinity of the first Brillouin zone center. Since the acoustic energy and electromagnetic energy of polaritons in the piezoelectric superlattice can be very close, the free space EM waves excited by polaritons can be expected. LiNbO₃ is adopted as an example. Once LiNbO₃ is polarized intervallic oppositely, the power ratio increases significantly. The free space electromagnetic field coupled with polaritons can extend very far from the solid -vacuum interface.

We study the behavior of ferroelectric material (BaTiO₃) for the design of a nano-generator to convert mechanical into electrical energy. The investigations consider an electro-mechanical phase-field model with polarization as state variable. This widely accepted model has its origins in the work of^1-3 and is fully developed by Landis and coworkers.^4,5 We use a finite element model to simulate tetragonal regions of ferroelectric material sputtered on substrate. Different geometries as well as various mechanical and electrical boundary conditions are considered. The model parameters are normalized to achieve better computational conditions within the stiffness matrix. The major objective of this contribution is the fundamental understanding of domain switching caused by a cyclic electrical field. The corresponding hysteresis loops of the overall polarization cannot be achieved by using a two-dimensional model because the domain topologies evolve in three dimensions. The three-dimensional nature of the domain structure evolution is even true for flat regions or thin films.⁶ We show some examples of three-dimensional domain topologies, which are able to break energetically unfavorable symmetries. Finally, the computational model of a tetragonal nano-generator with dimensions 10 x 60 x 10 nm is presented. The specific ratio of height to width and the mounting on substrate is essential for its performance and principle of energy harvesting. We discuss the challenges and scopes of such a system.

Continuous polyacrylonitrile (PAN) nanofibers fabricated via the electrospinning process and commercially available silica nanoparticles were investigated and compared for their impact mitigating effects when incorporated into composite materials. The nanofibers were introduced at ply interfaces using two different approaches while the nanoparticles were mixed into the matrix material. Behavior was experimentally characterized by determining the fracture toughness of flat carbon-fiber composite coupons using the double cantilever beam (DCB) test according to ASTM D5528. The nanofibers were introduced to the composite coupons by directly electrospinning the fibers onto the ply surfaces or transferring the fibers from an interim substrate, or "nanomat", while the nanosilica particles were mixed into the resin system during vacuum bagging hand layup. Testing facilitated the calculation of Mode I strain energy release rates. Preliminary results show that when compared to a baseline coupon without nanoreinforcement, there is a 54.5%, 43.1%, and 26.9% reduction in Gavg for the nanomat, nanosilica, and directly deposited nanomaterial coupons, respectively. Directly deposited nanofibers outperformed the nanosilica reinforcement by 16.2% and the nanomat approach by 27.6%. Basic materials (carbon-fiber ply material and matrix system) and incomplete composite consolidation were cited as contributors to poor test coupon quality and detrimental to Mode I performance.

An appropriate continuum theory to predict the behavior of flexible magnetic or electrically polarized materials undergoing large deformations is explained. The formulation treats the angular momentum as an explicit complementary principle including net-couples from magnetic resp. electric fields. As a consequence non-symmetric Cauchy stresses are mandatory for equilibrium, which is unlike in classical theories. However, the micropolar model is in accordance with classical phenomenological modeling parameters but with the feature to cover large deformations and non-classical types of loading. The formulation considers rotational degrees of freedom to appear in the kinematical equations as exact rotations in SO(3). This is a source of nonlinearity in the model but allows easily for large deformation as well as for net-couples. A simple example is the torque of a compass needle to explain the effect of materials with remanent magnetization within a magnetic field. The twisting moment becomes a maximum for remanent magnetization being perpendicular to an outer magnetic field. It vanishes if both fields are parallel. We investigate magnetic structures using finite element simulations. The development of active materials on the micro-level is in the focus.

In this study, the road snow-melting system consisted of CNFP thermal source, AlN/Epoxy-based insulated-encapsulated layer and MWCNT/cement-based thermal conductive layer, was fabricated. The carbon nano-fiber paper (CNFP) taken excellent thermal and electrical properties was integrated into snow-melting system as the high-efficient thermal source. The remarkable electro-thermal and resistive properties of CNFP with the thickness of 0.38mm were investigated, and verified much higher efficiency electro-thermal property than other papery materials. The linearly temperature-dependent effect of CNFP resistivity was founded in certain temperature scope and met the line model as a function of temperature. Carbon nanotubes (CNT) attracted many filed scholars' focus based on its unique thermal conduction as a strong thermal-transferring candidate since it was founded. A new approach, named electric repulsion/high-frequency oscillatory dispersion, was proposed to fabricate the MWCNT/cement-based composites. The sample, filled with 3% MWCNT by the amount of cement, presents the significant improvement of thermal conductive property in contrast with other fillers and dispersing methods, which was integrated into snow-melting system with other parts as the thermal conductive layer material. The AlN/Epoxy-based composite, filled with 20% micron-AlN by the weight of mixture as the best candidate of insulated-capsulation material, would be used to guarantee the insulation. Due to the snow-melting field test, the snow-melting characteristics of integrated snow-melting system, dependent on the ambient temperature, wind speed, heat flux density and snow thickness, were investigated. The results not only verified the high-efficient, stable, feasible and economic properties, but also provided the valuable parameters for further snow-melting or ice-deicing investigation.

The design of a piezocomposite transducer is accomplished by such advanced modeling technique as finite element method (FEM). However, accurate analysis of a 1-3 piezocomposite transducer enforces three dimensional (3D) modeling that requires very finemeshing of the transducer structure, which is frequently over affordable calculation resource capacity. In order to simplify the FEM model for complicated underwater transducers, the 1-3 piezocomposite needs to be simulated with a single phase material of equivalent properties. The 1-3 piezocomposite material in this study is made of the PMN-PT single crystal as the active material and urethane as the matrix material. Theoretical models for the calculation of new material parameters of 1-3 composites having fine lateral periodicity have been derived. For the validation of the equivalent properties, TE (thickness extensional), LE (length extensional), LTE (length thickness extensional), and TS (thickness shear) FEM models have been built to compare the impedance-frequency spectra of the 1-3 composite material and an equivalent material. Through the simulation with the models, all the equivalent elastic, dielectric and piezoelectric constants of the single phase material are determined. Further, 3D and axis-symmetric 2D FEM models of a multi-mode Tonpilz transducer have been constructed with the equivalent material properties. The equivalent material provides a very good correlation between the 2D and 3D transducer models, which is not easily attainable with the full 1-3 piezocomposite model. This result confirms the efficacy of the equivalent material properties of the 1-3 piezocomposites.

A method for homogenization of an elastic composite with periodic microstructure is presented, focusing on the Floquet-type elastic waves. The resulting homogenized frequency-dependent elasticity and mass-density then automatically satisfy the overall conservation laws and by necessity produce the exact dispersion relations. The method is used to calculate the dynamic effective parameters for a layered composite by using the exact solution.

In this manuscript, we reported the preparation and characterization of Fe₃O₄/Epoxy nanocomposites. Structural characterizations were given by powder X-ray diffraction. The magnetic performance of pure Fe₃O₄ nanoparticles in the resulting composites was investigated by vibrating sample magnetometer. The coercivity of Fe₃O₄ nanoparticles in the composites has no obvious change, while the saturation magnetization of pure Fe₃O₄ nanoparticles in the composites increased from 42 emu/g to 60 emu/g with its content increasing. Such content-dependent behavior in the saturation magnetization is attributed to the 'Fe₃O₄-Epoxy' interfacial interaction and 'Fe₃O₄-Fe₃O₄'interparticles magnetic interaction.

We report on the production of thin films of titanium nickelides (TiNi) shape memory alloy, prepared via Current- Activated Tip-based Sintering (CATS), a new localized powder sintering process. Mechanically alloyed equi-atomic TiNi powder was tip-sintered at varying currents and cycles of current exposure time. The effect of processing conditions on the developed localized microstructure and properties are discussed. The number of cycles of current exposure time and current magnitude were studied. Both number of cycles and current magnitude in general result in an increase micro-hardness and a reduction in residual porosity in the sintered thin films.