This PDF file contains the front matter associated with SPIE Proceedings Volume 7644, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Phase field modeling in ferroelectric materials is used to study the formation and evolution of domain structures. These domain structures evolve in a manner that reduces the free energy of the system. An important goal of phase field modeling is to develop computational techniques that can be used in the design of materials with improved properties. This requires accurate determination of each of the terms used in the Time-Dependent Ginzburg Landau equation. This work presents a discussion of the crystal structure and the gradient terms used in phase field models and proposes several modifications that will be implemented in the near future. This includes a discussion of why a constitutive law written in terms of quadratic electrostriction is appropriate and a suggestion that the Ginzburg term (energy proportional to the square of the gradient) has some overlap with the dipole-dipole interaction term.

Material modeling techniques for active materials include a broad number of approaches that are often focused on predicting a specific field-coupled constitutive relation. This field-coupled material behavior may include electro-mechanical, magnetostrictive, thermal or light induced phase transformations, or ionic deformation. Limited work has been conducted on developing a unified theory. Such theories are useful for quantifying underlying field-coupled mechanics concepts that may otherwise be neglected in phenomenological models. The theoretical approach presented here employs nonlinear continuum mechanics coupled to a set of microscale order parameters that describe microstructure evolution and phase changes. Unifying concepts are obtained which illustrate how material constants such as piezoelectric coefficients depend on the choice of the order parameter and mechanical energy function without introducing explicit phenomenological coupling parameters.

Proper orthogonal decomposition (POD) is a basis reduction technique that allows simulations of complicated systems to be calculated at faster speeds with minimal loss of accuracy. The reduced order basis is created from a set of system data called snapshots. The speed and information retention of POD make it an attractive method to implement reduced-order models of smart material systems. This can allow for the modeling of larger systems and the implementation of real time control, which may be impossible when using the full-order system. There are times when the dynamics of a system can change during a simulation, and the addition of more information to the set of snapshots would be beneficial. The implementation of control on a system is a time when adding new snapshots to the collection can increase the accuracy of the model. Using updates allows more flexibility when trying to balance the accuracy and the speed of the simulation. By updating the POD basis at specific times throughout the interval, we can increase the accuracy of the model and control by using a greater amount of the information given by the snapshots, while we can increase the speed of the simulation during times when using less information will still result in sufficient accuracy.

Stresses and electric fields induced in the poling processes of both polycrystalline and single crystal thick walled cylinders are investigated and compared using a finite element analysis together with a micromechanical ferroelectric constitutive law. The analysis reveals that the polarization process begins at the inner diameter and spreads outward through the cylinder as the applied electric potential is increased. The piezoelectric strain and the remnant strain produce strain fields that are not compatible with the geometry. In the single crystal material the poling is not uniform. It is affected by the angle between the crystal orientation and the electric field direction.

Imaging of domains is a key step in understanding the microstructure and hence the properties of ferroelectric single crystals. This understanding is essential for exploiting engineered domain configurations to achieve enhanced performance. In this paper, single crystals of Barium Titanate are observed by reflection topography using unfocussed monochromatic synchrotron X-ray light. A 10 x 10 mm polished surface of an unpoled crystal was mapped to form a composite image, indicating a fine structure of a- and c-domains. By making use of the angular separation of the diffracted reflections and specimen rocking, the relative tilts between adjacent domains about two orthogonal axes were found. Angular resolution better than 0.1mrad in tilt measurements allowed the local elastic curvature of lattice planes to be observed. The resulting composite images show well defined boundaries between regions of distinct microstructure, and give an indication of the proportion of the domain types present. Over large regions of the crystal the domain structure was finer than the X-ray camera resolution of 6.5μm; AFM and SEM imaging of domains was then used to confirm the typical domain spacing. The results are interpreted in the context of models of compatible microstructure in tetragonal crystals using microscopy of etched crystals to assist the interpretation. The technique shows promise for mapping fine microstructure in single crystals, through the use of high resolution X-ray cameras, and is successful in revealing lattice orientation information that is not normally available in optical or AFM measurements.

The equilibrium domain arrangements of ferroelectric single crystals are significantly affected by loads and boundary conditions. Domain structures evolve towards a minimum energy state. In this paper, a variational method, which minimizes a functional based on free energy and dissipation, is developed to model the evolution of several typical rank-2 laminate domain patterns in the tetragonal crystal system. Periodic laminates which satisfy compatibility at every domain wall are studied. These domain patterns include herringbone and vortex array structures. The unit cells for both types of domain pattern dictate a set of domain walls whose positions may vary while maintaining the same topology. The positions of domain walls are treated as thermodynamic variables in the formulation, and the total dissipation rate is then a function of the velocities of the domain walls. By using this model, many features normally observed in ferroelectric single crystals can be reproduced, such as the dielectric hysteresis loop and butterfly loop. The characteristics of the hysteresis loop for different topologies, as well as under different applied loads and boundary conditions are discussed. The model can readily be extended to higher rank laminate structures and other crystal systems.

Piezoceramic materials have attracted much attention for sensing, actuation, structural health monitoring and energy harvesting applications in the past two decades due to their excellent coupling between energy in the mechanical and electrical domains. Among all piezoceramic materials, lead zirconate titanate (PZT) has been the most broadly studied and implemented, in industrial applications due to its high piezoelectric coupling coefficients. Piezoceramic materials are most often employed as thin films or monolithic wafers. While there are numerous methods for the synthesis of PZT films, the sol-gel processing technique is the most widely used due to its low densification temperature, the ease at which the film can be applied without costly physical deposition equipment and the capability to fabricate both thin and thick films. However, the piezoelectric properties of PZT sol-gel derived films are substantially lower than those of bulk materials, which limit the application of sol-gel films. In comparison, single crystal PZT materials have higher piezoelectric coupling coefficients than polycrystalline materials due to their uniform dipole alignment. This paper will introduce a novel technique to enhance the piezoelectric properties of PZT sol-gel derived ceramics through the use of single crystal PbZr_0.52Ti_0.48O₃ microcubes as an inclusion in the PZT sol-gel. The PZT single crystal cubes are synthesized through a hydrothermal based method and their geometry and crystal structure is characterized through scanning electron microscopy (SEM) and X-ray diffraction (XRD). A mixture of PZT cubes and sol-gel will then be sintered to crystallize the sol-gel and obtain full density of the ceramic. XRD and SEM analysis of the cross section of the final ceramics will be performed and compared to show the crystal structure and microstructure of the samples. The P-E properties of the samples will be tested using a Sawyer-Tower circuit. Finally, a laser interferometer will be used to directly measure the piezoelectric strain-coupling coefficient of the PZT sol-gel ceramics with and without PZT cube inclusions. The results will show that with the integration of PZ_0.52T_0.48 crystal inclusions the d33 coupling coefficient will increase more than 200% compared to that of pure PbZr_0.52Ti_0.48O₃ sol-gel.

Recently, the lead free piezoelectric material, which should be used for medical devices, such as health monitoring system (HMS) and drug delivery system (DDS), is strongly required. In this study, we discovered a newly designed MgSiO₃ thin film, as a biocompatible piezoelectric actuator, by using the first-principles calculation and process crystallography simulation algorithm. At first, crystal structure was calculated by using the first-principles density functional theory. Secondly, the best substrate for MgSiO₃ was searched by using the process crystallography simulation. Next, MgSiO₃ thin film was generated in our laboratory by using the RF magnetron sputtering apparatus. Finally, crystallographic orientation was obtained by using X-ray diffractometer and the piezoelectric property of thin film was measured by the ferroelectric measurement system. As a result, lattice parameters of MgSiO₃ with tetragonal structure were obtained as a=b=0.3449nm and c=0.3538nm, and its aspect ratio was 1.026. Au(111) was chosen as the best substrate, on which MgSiO₃ thin film with minimum total energy could be grown. Then, MgSiO₃(111) was generated on Au(111)/SrTiO₃(110) by using the RF magnetron sputtering apparatus. The piezoelectric strain constant d₃₃ of MgSiO₃ thin film generated at 400°C was measured as 219.8pm/V and it was higher than one of the existing piezoelectric material BaTiO₃. Consequently, we succeeded the generation of a new biocompatible MgSiO₃ piezoelectric thin film, which can be applied to medical devices in the future.

Shape memory polymers (SMPs) are an emerging class of active polymers that have dual-shape capability, and are therefore candidate materials for multifunctional reconfigurable structures (i.e., morphing structures). However, the SMPs have not been fully tested to work in relevant environments (variable activation temperature, fuel and water swell, UV radiation, etc.) required for Air Force missions. In this study, epoxy-based SMPs were conditioned separately in simulated service environments designed to be reflective of anticipated performance requirements, namely, (1) exposure to UV radiation for 125 cycles, (2) immersion in jet-oil at ambient temperature, (3) immersion in jet-oil at 49°C, and (4) immersion in water at 49°C. The novel high-temperature indentation method was used to evaluate the mechanical properties and shape recovery ability of the conditioned SMPs. Results show that environmentally conditioned SMPs exhibit higher moduli in comparison to an unconditioned one. During free recovery, the indentation impressions of all SMPs disappeared as temperature reached above T_g, indicating that the material's ability to regain shape remains relatively unchanged with conditioning.

Previously, we reported an undersea unmanned vehicle (UUV) termed as JetSum, inspired by the locomotion of medusa jellyfish, [12]. The propulsion of JetSum was based on shape memory alloy (SMA) wires replicating the contraction-relaxation cycle of natural jellyfish locomotion. In this paper, we report modified design of JetSum that addresses problems related to electrical isolation and power consumption. The modifications lead to significant improvement in functionality, providing implementation of a full continuous bell, bolstering critical sealing junctions, and reducing the overall power requirement. A LabVIEW controller program was developed to automate and optimize the driving of JetSum enabling reduction in power consumption for full contraction of SMA. JetSum locomotion in underwater conditions was recorded by using a high-speed camera and analyzed with image processing techniques developed in MatLab. The results show that JetSum was able to achieve velocity of 7 cm/s with power consumption of 8.94 W per cycle.

When McKibben artificial muscle actuators are applied to robotic joints, the joints are driven by pairs of actuators located antagonistically to increase the joint stiffness. However, the force for shape fixity is not large. Therefore, the objective of this study is to develop a McKibben artificial muscle using a shape-memory polymer (SMP). SMPs can be deformed above their glass transition temperature (T_g) by applying a small load. They maintain their shape after they have been cooled to below T_g. They then return to the predefined shape when heated above T_g. Exploiting these characteristics, we coated the braided mesh shell of a commercial McKibben artificial muscle and made a prototype of the actuator using the SMP. When this new actuator is warmed above T_g, the SMP deforms. Then, when the internal bladder is pressurized, the actuator shortens and/or produces a load. After the actuator becomes the desirable length, the actuator is cooled to below T_g and the SMP is fixed in a rigid state even without the air supply. Consequently, this actuator can maintain its length more rigidly and accurately. The experimental results conducted on this prototype confirm the feasibility of this new actuator.

We discuss a relatively simple and computationally inexpensive model that has recently been developed to study phase transformations and shape memory effects in finite nanostructures. Our major focus is given to nanowires of finite length and other nanostructures where size effects are pronounced. The main tool used here is based on mesoscopic models developed with the phase-field approach which we and other authors have applied before to study ferroelectrics at the nanoscale. We study the cubic-to-tetragonal transformations in which case the 2D analogue of the model describes the square-to-rectangle phase transformations. The actual model is based on a coupled system of partial differential equations and is solved with a combination of the Chebyshev collocation method and the extended proper orthogonal decomposition. The developed model and its numerical implementation allow us to study properties of nanostructures and several representative examples of mechanical behavior of nanostructures are discussed.

NiTi alloy wires were embedded during the infusion processing of woven carbon fibre reinforced plastic (CFRP) composite plates with the purpose to passively increase their damping. Two types of NiTi wires, having the same diameter of 203 μm, were considered, one superelastic at room temperature, the other one martensitic. For the first one, a martensitic transformation was induced by applying a pre-strain of 2.5% before embedding the wires. The coexistence of austenite and martensite should provide damping through the mobility of boundaries between the two phases. For the second type of wires, the enhancement of damping was based on the presence of martensite. The passive damping effect produced by the shape memory alloy (SMA) wires was evaluated from free vibration tests on composite plates, neat or with 5% of volume fraction of SMA wires. Resonance frequency and damping ratio were measured as a function of temperature. Improvement in damping was verified, at room temperature, for both types of SMA wires and was observed to be dependent on vibration amplitude. For small-amplitude free vibrations, pre-strained superelastic wires presented more interest as they provided a damping increase of around 87%. The effect however depends on temperature.

The potential use of Shape Memory Alloys (SMAs) as micro-actuators promotes study of the behaviors of these materials at small length scales. The recovery of micro-indentations due to the shape memory effect has recently become an area of particular interest. Experimental observation indicates promising microactuation ability in SMAs subject to indentation. In order to better understand the mechanisms underlying this phenomenon, 3- D Finite Element Analysis incorporating a new SMA transformation-plastic yield constitutive model is used to simulate a unique experimental indentation procedure. This process involves the indentation of an SMA material and the planarization of the material surface to remove all visible traces of the indent region; upon subsequent heating, a protrusion (exdent) is created in the indented zone. Key results of an analysis that simulates this experimental procedure are discussed, along with possibilities for future work.

The high work to volume ratio and the stress recovery of Shape Memory Alloy (SMA) thin films with temperature makes them an ideal choice for microactuators. However, these materials have not gained widespread acceptance due to issues associated with phase transformation. Primary concerns are rapid change in stress at the transformation temperature giving the actuator a step function like response and a significant shift in transformation temperatures due to a wide hysteresis. In the present research, TiNiCu (53.59at%Ti, 39.05at%Ni), TiNi (50.32at%Ti) and TiNiHf (39.56at%Ti, 48.63at%Ni) composite SMA thin films that display close to linear stress temperature behavior (slope: 2-7 MPa/°C) with high stress recovery (300-550MPa), wide transformation range (60-130°C) and low hysteresis (10-30°C) were fabricated. Properties were achieved through the deposition of SMA thin films with varying composition in a layered (composite) format on Si wafers. The TiNi+TiNiCu composite exhibited a two-step transformation (slopes of 2.5 and 3.9 MPa/°C) without a significant impact on stress recovery. Displaying identical recovery stresses, the TiNiHf film possessed a 65°C transformation range and the TiNiHf+TiNi composite exhibited a wider range of 120°C. A strong correlation between deposition conditions, annealing parameters and transformation characteristics was observed for all the SMA films.

The creep behavior and the phase transformation of Ti₅₀Pd₃₀Ni₂₀ High Temperature Shape Memory Alloy (HTSMA) is investigated by standard creep tests and thermomechanical tests. Ingots of the alloy are induction melted, extruded at high temperature, from which cylindrical specimens are cut and surface polished. A custom high temperature test setup is assembled to conduct the thermomechanical tests. Following preliminary monotonic tests, standard creep tests and thermally induced phase transformation tests are conducted on the specimen. The creep test results suggest that over the operating temperatures and stresses of this alloy, the microstructural mechanisms responsible for creep change. At lower stresses and temperatures, the primary creep mechanism is a mixture of dislocation glide and dislocation creep. As the stress and temperature increase, the mechanism shifts to predominantly dislocation creep. If the operational stress or temperature is raised even further, the mechanism shifts to diffusion creep. The thermally induced phase transformation tests show that actuator performance can be affected by rate independent irrecoverable strain (transformation induced plasticity + retained martensite) as well as creep. The rate of heating and cooling can adversely impact the actuators performance. While the rate independent irrecoverable strain is readily apparent early in the actuators life, viscoplastic strain continues to accumulate over the lifespan of the HTSMA. Thus, in order to get full actuation out of the HTSMA, the heating and cooling rates must be sufficiently high enough to avoid creep.

One and three-dimensional computational models for the dynamical sensing response of Galfenol based magnetostrictive devices are developed. The sensing model calculates the fraction of magnetic moments oriented along each of the energetically preferred directions of the crystal as a function of time, which can then be used to determine the time evolution of the total magnetization. Results from the sensing model are compared to quasi-static loading experiments for validation and extraction of phenomenological parameters. As a sample application, the sensing model is incorporated into an AC energy harvesting circuit to predict the magnetization and energy harvested under dynamical loading conditions.

In this paper an electromechanical network model of a magnetostrictive unimorph structure, acting as solenoid coil core, is developed. For typical applications a non-uniform stress distribution in the magnetostrictive layer results which is simulated via FEM. This phenomenon leads to a spatial varying electromechanical transduction coefficient for large deflections and was taken into account by coupled finite electromechanical network elements. By simplifying the finite network model an easy to use new network model is obtained which enables the fast analysis of the system and optimization of sensor and actor properties.

Rising requirements for a new constructions, devices and machines force engineers to monitor them all day long. An attractive solution seems to be applications of wireless sensors. However, there is a barrier limiting their application, which is the need to supply them with an electrical power over extended period of time without using additional wiring or batteries. The potential solution of this problem seems to be an energy harvesting. Most methods of obtaining the energy from the external sources e.g. vibrations, is to use piezoelectric materials. However, the amount of energy generated by piezoelectric materials is smaller than most electronic devices need. Therefore a new method for generating a pulse of energy and conditioning for other loads devices must be developed. This paper proposes a new energy harvesting device based on magnetostrictive material. In the course of the experiments with using Terfenol-D rods as actuators and sensors it has been observed interesting phenomenon. Mechanical impact (e.g.energy between 1J and 10J in infinite time) to magnetic core based on Terfenol-D rod (diameter 5mm, length 10 mm), NdFeB permanent magnets and coil allowed get electric power signal enough to supply device of 100 Ohm load on their active state (typical low power controller). In comparison to the same magnetic circuit built with other typical ferromagnetic materials e.g. Armco iron, showed effect 10 times lower or none. Tests and experiments showed the important role of coupling Terfenol-D and NdFeB permanent magnets, their configuration and variable coil parameters determined this effect. In regard to the results the authors proposed the construction of a new impulse harvesting method based on Terfenol-D material for low impedance load.

Previous studies did by some scholars proved applying a magnetic field during the manufacture process of polymer-bonded Terfenol-D could orient the magnetic easy direction of the particles along the field direction and form a pseudo-1-3 structure. Compared to the 0-3 composites composed of Terfenol-D particles dispersed randomly in a polymer matrix, pseudo-1-3 magnetostrictive composites present much larger magnetostrictive performance. In this paper, magnetostrictive composites based on Terfenol-D particles in an unsaturated polyester resin matrix were fabricated under different magnetic fields. Magentostriction was tested and compared to get the detail effects of orientation fields on magnetostrictive properties of magnetostrictive composites. Scanning electron microscopy was used to observe their microstructures. Image analysis was applied to describe the microstructures. The distribution of the angles between the major axis of the particles and the magnetic field direction was used to evaluate the arrangement of particles in the matrix quantitatively. The results confirm particle chain-like structures in composites prepared under larger magnetic field, and show that particle arrangement changes with the strength of the orientation field, which is result in the changes of magnetostrictive performance.

In this paper, wireless optical system was developed by using array type TbDyFeNi thin film actuator. The effect of Ni content on the magneto-mechanical properties of the Tb_0.24Dy_0.76Fe₂ system, for wireless micro actuator with the effect of deposited film thickness of TbDyFeNi on silicon substrate, was also investigated. To create the device, array shape silicon substrates were bulk micromachined, and Tb_0.24Dy_0.76Fe_2-xNi_x, (x=0, 0.5, 1.2, 2.0) films were sputter-deposited on the back side of substrate by selective DC magnetron sputtering techniques. After the sputter process, magnetization and effective mgnetoelastic coupling coefficient and magnetostriction of the sample were measured for the magnetomechanical characterizaztion. For the operation, each branch of the array type actuator has different length and out-ofplane motion. Each branch was actuated by externally applied magnetic fields up to 0.5T and motion of the branches made inclined movement. As a result, deflected angle of the actuator due to the movement of array type actuator to external magnetic fields were observed.

In this work we study the unstable phenomena that occur on Magnetic Shape Memory Alloys (MSMAs) during compression tests. Solving the coupled magnetomechanical problem we observe that during the reorientation process the material presents strong non-uniformity, in the form of localized zones, in the distribution of the magnetic, the stress and the strain field. This non-uniformity is due to loss of ellipticity of the coupled problem during the martensitic reorientation and affects significantly the reorientation process. The identification of the stability conditions of the magnetomechanical problem is achieved by performing stability analysis.

The unique characteristic of magnetic field induced phase transformation of NiMnCoIn magnetic shape memory alloys (MSMAs) lies in the generation of large transformation strains under high constant stress levels. Motivated by experiments, a constitutive model is proposed to take into account magnetic field induced phase transformation from austenitic to martensitic phase. The working principle of such materials is described by the deformation of continua due to mechanical and magnetic forces. The cross coupling of mechanical and magnetic variables is captured by introducing nonlinear kinematics. In the present work, microstructure dependence of martensitic phase transformation is taken into account by introducing internal variables into the model. The constitutive response is derived in a consistent thermodynamic way.

A magnetoelectric self-sensing cantilever actuator is under investigation for use as a remotely driven self-sensing actuator. The cantilever is fabricated from Galfenol and Lead Zirconate Titanate strips as a laminate composite. An applied magnetic field generates strain in the magnetostrictive layer, thereby creating a bending moment in the composite and generating an electrical signal in the piezoelectric layer. A force-deflection model and equation of motion for the self-sensing magnetoelectric material in cantilever configuration is developed in this paper. An equivalent mass and stiffness matrix derived for the cantilever in terms of generalized coordinates is used to predict the bending behavior of the cantilever in its linear range of operation. In addition, the electrical boundary condition of the piezoelectric layer is varied to determine its influence on the actuation properties of the cantilever tool. Cantilever specimens measuring 40mm x 20mm and 20mm x 10mm are excited using a remote magnetic field of up to 2.8x10⁴ A/m and free tip displacements of 200μm and 60 μm are observed, respectively. The model predicts the slope of the magnetic field/tip displacement curve with an error of 7% and 33%, respectively. The sensing current generated by the smaller specimen is 5x10^-7 A.

In this work, the magnetoelectric cantilever composed of a layer of Galfenol and a layer of PZT-5H is studied for novel applications such as surgical ablation tools and cutting tools for machining applications. For developing a suitable model for the magnetoelectric cantilever, an energy based approach for the non-linear constitutive behavior of the magnetostrictive material and linear piezoelectric constitutive equations will be coupled with Euler Bernoulli model for composite beams. The cantilever is held in a uniform magnetic field and the magnetic field is measured by a Gaussmeter. The tip-deflection of the cantilever is detected by a laser triangulation sensor. The piezoelectric response can be studied with low noise preamplifier. Four PZT-5H layers with different thickness are separately bonded on the top of the same Galfenol layer and characterized to study the thickness ratio effects on the quasistatic actuation and sensing behavior of the composite cantilever.

The converse magnetoelectric effect of an asymmetric Piezo-fiber/Metglas bilayer laminate composite subjected to mechanical prestress is presented. The mechanical prestress is applied by either dc electric voltage bias or direct mechanical load bias. It is found that a mechanical prestress strongly influences the converse magnetoelectric coupling response. The optimum dc magnetic field bias shifts with different prestress and compressive stress requires higher dc magnetic field bias. Additionally, an optimum prestress exists to maximize the converse magnetoelectric response under certain dc magnetic field bias ranges. Therefore, in order to integrate magnetoelectric composite into actual structures, a proper prestress needs to be employed to maximize the CME coefficient.

Consisting of charged network swollen with ionic solution, polyelectrolyte gels are known for their salient characters including ion exchange and stimuli responsiveness. The active properties of polyelectrolyte gels are mostly due to the migration of solvent molecules and solute ions, and their interactions with the fixed charges on the network. In this paper, we extend the recently developed nonlinear field theory of polyelectrolyte gels by assuming that the kinetic process is limited by the rate of the transportation of mobile species. To study the coupled mechanical deformation, ion migration, and electric field, we further specialize the model to the case of a laterally constrained gel sheet. By solving the field equations in two limiting cases: the equilibrium state and the steady state, we calculate the mechanical responses of the gel to the applied electric field, and study the dependency on various parameters. The results recover the behavior observed in experiments in which polyelectrolyte gels are used as actuators, such as the ionic polymer metal composite. In addition, the model reveals the mechanism of the selectivity in ion transportation. Although by assuming specific material laws, the reduced system resembles those in most existing models in the literature, the theory can be easily generalized by using more realistic free-energy functions and kinetic laws. The adaptability of the theory makes it suitable for studying many similar material systems and phenomena.

Hydrogels are 3-D network polymeric materials that exhibit a large volume phase-transition due to a of change in their environment so that the response causes the hydrogel to swell or shrink. Since hydrogels have been found to be useful for chemical sensing and delivery, there is a growing interest in their use for medicine. This ,requires a thorough understanding of the hydrogels characteristic response to pH. The hydrogel response can be explained by various physical equations which are often challenging to solve. We discuss the simulation of such phase-transitions in steady-state conditions emphasizing the response to solvent pH and other environmental stimuli. We demonstrate a method for simulating pH response of hydrogels and describe numerical model and its implementation in detail. Though a few models have been developed for simulation of these hydrogel characteristics, these have been based on custom programs implemented in individual laboratories and often not generally accessible. Hence, our modeling effort is implemented using the generic finite element software COMSOL and the method can be used with any software having similar capabilities. The effect of buffer solution concentration, fixed charge density, the solution pH on the swelling characteristics are studied. Results are compared with published experimental data.

Poly-AMPS (PAMPS) gel was fabricated and its electroactive behavior was studied. A weakly cross-linked anionic PAMPS gel was produced by radical polymerization using 2-acrylamido-2-methylpropane sulfonic acid (AMPS) monomers, where N,N'-methlenebisacrylamide (MBAA) and α -ketoglutaric acid were used as a cross-linking agent and a radical initiator, respectively. The polymerization was carried out at 55°C for at least 24 hours. Density and the degree of swelling of gel samples were investigated as physical properties. Also, swelling experiments were conducted in a surfactant solution using 1-dodecylpyridinium chloride hydrate. The chemo-mechanical properties of PAMPS gel were studied in a dilute surfactant solution under the electric field. The effect of material parameters on the bending deformation was investigated. As design parameters, sample thickness, current density, ion concentration of the surfactant solution, and cross-linking degree of gel were chosen, and the effect of these parameters on the actuation was studied.

Different materials provide a mechanical-electrical energy conversion and are thus interesting candidates for piezoelectric sensors and actuators. Beside ferroelectric ceramics and polymers, also polymer foams, so-called ferroelectrets, are developed as piezoelectric active materials. Their piezoelectricity originates from optimized structural and elastic-foam properties accompanied with an optimized charge trapping at the polymer layers within the foam structure. The piezoelectric activity arises if mechanical stimuli lead to a thickness variation of the electrically charged voids which results in an electrical signal between the connected electrodes on the film surfaces due to the change of internal electric fields. The concept of such a piezoelectric transducer was developed by investigating cellular polypropylene films with different foam structures and thus different elastic properties. Recently, ferroelectrets were prepared from other polymers following the same concept. Different kind of new foaming procedures are developed in order to broaden the range of usable materials as well as to optimize the adjustment of piezoelectric and ultrasonictransducer properties. The paper provides an overview about ferroelectrets, their underlying working mechanism as well as their preparation possibilities. In detail, piezoelectric properties of polypropylene ferroelectrets are described which are usable for pushbutton or touch-pad applications as well as in ultrasonic-transducer applications.

Materials with an internal mechanism for damage repair would be valuable in isolated environments where access is difficult or impossible. Current work is focused on characterizing neat polymers with reformable cross-linking bonds. These bonds are thermally reversible, the result of a Diels-Alder cycloaddition between furan and maleimide monomers. Candidate polymers are examined using modulated differential scanning calorimetry (DSC) to confirm the presence of reversible bonding. One polymer, 2MEP3FT, was expected to have these bonds, but none were observed. A second polymer, 2MEP4FS, with a modified furan monomer does exhibit reversible bonding. Further DSC testing and dynamic mechanical thermal analyses (DMA) are conducted to determine material properties such as glass transition temperature, storage modulus and quality of the polymerization. Healing efficiency is established using the double cleavage drilled compression (DCDC) fracture test. A column of material with a central hole is subjected to axial compression, driving cracks up and down the sample. After unloading, the cracks are healed, and the sample is retested. Comparing the results gives a quantitative evaluation of healing.

Recent research on overcoming inherent limitations on the electromechanical properties of polyvinylidene fluoride (PVDF) and copolymers has been directed towards adding nanoinclusions to take advantage of their scale and properties. This research shows that adding single walled carbon nanotubes (SWNTs) creates a quadratic electromechanical response in PVDF. Enhanced effective dielectric constant and formation of polar microstructure suggests an electrostrictive response. Contributions from Joule heating will be assessed next, as they may be significant at higher SWNT content.

This paper was presented at the SPIE conference indicated above and has been withdrawn from publication at the request of the authors.

Poly(vinylidene fluoride) (PVDF) is a piezoelectric polymer material. In general, it is necessary to give large stretch to PVDF film when PVDF film is used as sensor or actuator element. However, we recently found that PVDF shows piezoelectricity without large stretch if nano-clays are uniformly dispersed into it. The aim of present study is to investigate the possibilities of nano-clay/PVDF composite film as sensor and actuator element. Firstly, PVDF films and nano-clay/PVDF composite film are fabricated by solvent casting. Also, commercial PVDF film is prepared as comparative material. Secondarily, we investigate the change of electrical displacement according to the input voltage of triangle wave by using Sawyer-tower bridge circuit for PVDF films and nano-clay/PVDF composite film. Then, the change of impedance is also measured at broad frequency by using impedance analyzer. Thirdly, we apply the voltage of sine wave to fabricated films, and measure the output oscillation generated from films. Finally, we discuss the possibilities of nano-clay/PVDF composite film as sensor and actuator element.

Future adaptable applications require electro-mechanical actuators with a high weight-related energy. Among modern multi-functional materials carbon nanotubes (CNTs) have some special characteristics which give them the potential to solve this demand. On the one hand raw CNTs have excellent mechanical properties like their low density (1330kg/m³) and very high estimated stiffness of about 1TPa. On the other hand CNTs have the ability under presence of ions, wired like a capacitor and activated by a charge injection to perform a dimensionchange (length of C-C bondings). Calculations and experiments present achievable active strains of 1% at low voltage of ±1V what qualifies CNT-based materials for leightweight powerful actuators. In this paper the former work done with actuators using CNT-containing mats and Nafion as solid electrolyte is evaluated by analyzing the two main-components in more detail. On the one hand the CNT-based modelmaterial SWCNT-mats called Bucky-paper (BP) and on the other hand ion donating electrolytes in liquid-phase like a NaCl-solution and its solid equivalent Nafion as thin-foils are tested. Additional methods of fabrication, preparation and characterization of the CNT-powder and the manufactured BPs containing randomly oriented single-walled carbon nanotubes (SWCNTs) are presented which provide a deeper system-understanding. Both materials (BPs and Nafion-foils) are intensively investigated in different deflection-test-rigs due to their structural assembly. This paper presents a method for electro-mechanical measurements of BPs in an in-plain test set-up which avoids sensing secondary effects like thermal expansion or mass-transport and confirm that BP-deflection should only be a capacity-driven effect. Nafion as solid electrolyte will be tested in an out-of-plane facility to measure its possible actuation within the lamellar-direction. With this approach the dependencies of each component and their individual characters on the deflection can be estimated. The active response can be referred to the internal structure of both components as well as of the whole structural assembly. The results give a certain direction to a BP-optimization referring to active strain, density, structural integrity and conductibility. In addition to these facts the active character of BPs using CNTs of different suppliers and Nafion is analyzed. These investigations are of particular importance for detection of global dependencies and using both materials in a hybrid-assembly like solid actuators which are needed for structural applications.

Currently aircraft structural composites are commonly protected using approaches such as laying of metallic meshes and foils. However, these are not ideal solutions because they add significant weight and may be difficult to repair. In this paper, we used multi-walled carbon nanotubes(MWNTs) and short carbon fiber(SCF) as reinforcement, and epoxy resin as matrix, prepared conductive nanocomposites for lightning protection of aircraft. MWNTs and SCF as conductive filler, they via acidification and surface treatment, mechanical milling, ultrasonic dispersion method, the CNTs/SCF Epoxy (EP) conductive nanocomposites were prepared by casting method. The characterizations of materials microstructure, electrical and mechanical properties were investigated by scanning electron microscope (SEM), resistance instrument, and tensile test machine and indentation experiments. Result proved that surface treatment carbon nanotubes and short carbon fiber can be evenly spread over the epoxy matrix, and form three-dimensional conductive network in the epoxy matrix. This makes the resistance of composite materials greatly reduced, improved conductive performance. The characterization of materials mechanical properties also showed that the addition of nano-conductive filler, but also significantly enhanced the material elastic modulus and hardness.

Although a number of hypotheses have been presented to explain the enhanced electromechanical performance observed in electroactive polymer nanocomposite materials, many of the underlying mechanisms responsible for this behavior remain unclear. In this report, electric force microscopy (EFM) is used to investigate the near surface morphology of an electroactive polyimide-based nanocomposite film containing SWNTs in an effort to gain insight into the electrical interactions occurring at the polymer-electrode interface. As a means of measuring the proximity of SWNTs to this interface, the depths of SWNTs buried beneath a processing-induced polymer skin layer are determined using EFM measurements derived from a sample standard. In this way, evaluation of the ability for embedded SWNT structures to behave as extensions of surface electrodes is possible, a scenario that could potentially reduce the applied field required to elicit electromechanical actuation.

Macro Fiber Composite (MFC) actuators utilize PZT fibers embedded in an epoxy matrix for structural actuation. Due to their construction, they are lightweight and provide broadband inputs. Significant advantages of MFC actuators are their high performance, durability, and flexibility when compared to traditional piezoceramic actuators. They are presently being considered for a range of applications including positioning of membrane mirrors and structural control in the aerospace and automotive industry. However, they exhibit varying degrees of hysteresis and constitutive nonlinearities throughout their operating range that must be incorporated in models to achieve the full capabilities of the materials. In this paper, hysteresis is modeled using the homogenized energy model. The inverse model is then used to construct an inverse compensator framework suitable for subsequent control design. The performance of the inverse compensator is illustrated through a numerical example.

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 of particular importance in various civil, mechanical and aerospace structures. This study firstly conducted the micromechanical finite element analysis to predict the elastic properties and piezoelectrical coupling parameters of a special type of an active PSF composite laminate. The PSF composite laminates are made of longitudinally poled PSFs that are unidirectionally deployed in the polymer binding matrix. The passive damping performance of these active composites was studied under the cyclic force loadings with different frequencies. It was found that the passive electric-mechanical coupling behavior can absorb limited dynamic energy and delay the structure responses with minimum viscoelastic damping. The actuating function of piezoelectric materials was then applied to reduce the dynamic mechanical deformation. The step voltage inputs were imposed to the interdigital electrodes of PSF laminate transducer along the poled direction. The cyclic pressure loading was applied transversely to the composite laminate. The electromechnical interaction with the 1-3 coupling parameter generated the transverse expansion, which can reduce the cyclic deformation evenly by shifting the response waves. This study shows the promise in using this type of active composites as actuators to improve stability of the structure dynamic.

The role of Smart Magnetic Materials (SMM) is still increasing. One type of SMM are Giant Magnetostrictive Materials (GMM) which can be represented by i.e. Terfenol-D. The biggest difficulty with mechanical application of GMM is its brittleness. On the other hand, increase of frequency generate meaningfully eddy currents. These disadvantages tend to search new solutions in a form of composite materials with giant magnetostriction (GMMC). The matrix for GMMC most often is an epoxy resin with magnetostrictive material inside (in a form of powder, flakes or tiny rods made of i.e. Terfenol-D). Several composites, with outstanding magnetostrictive properties, have been synthesized combining an epoxy resin with polycrystalline powders of Terfenol-D. Application of appropriate way of compression allowed to achieve composites consisting near 70% volume fraction of Terfenol-D powder in comparison with about 48% volume fraction of reinforcement in traditional production way. Composites had random and preferential grain orientation which was obtained by curing the material respectively with or without a magnetic field. The quasistatic magnetomechanical properties of the composites were investigated and compared with monolithic Terfenol-D alloy. The highest response was obtained for a perpendicular polarized composite. Investigated composite are promising magnetostrictive material enable to create a new type of actuators and magnetic field sensor.

Previous studies into the possibility of a plasmonic medium of a coiled conductor array in air have shown promise. This work serves to evaluate the possibility of creating a mechanically-tunable composite filter at low frequencies. Copper springs were created with varying starting pitches using a coil winder. These springs were then embedded into a flexible host polymer. The mechanical and electromagnetic properties of each spring design were predicted and tested. Two horn antennas were used to characterize the overall electromagnetic (EM) properties of the composite. The pitch of each spring was increased mechanically through application of force to the entire polymermetal composite at equal intervals, with an EM test completed at each step. Using an Agilent 8510C Vector Network Analyzer (VNA), the frequency spectrum within the microwave range was scanned. Relative amplitude and phase measurements were taken at equal frequency and pitch steps. With no polymer surrounding the springs, plasmon turn-on frequencies were observed to span the microwave bands as the pitch of the springs were increased. Similar results are expected with the springs embedded in a polymeric matrix. These results suggest a method of creating a mechanically-tunable composite filter for use at low frequencies.

The voltage creep behavior on actuation performance of cellulose based electro-active paper (EAPap) has been studied. Because the actuation of EAPap is originated from both the inner ionic movement in cellulose and its piezoelectric behavior, the actuation can be affected by the external field. When the external field applied, cyclic hysteresis of P-E loop is observed. In order to investigate the detail of actuation behavior of EAPap actuator, the detail actuation response - called voltage creep- is required. The voltage creep which can reduce the response and the actuating accuracy of actuator is one important issue in order to control the micro/nano scaled positioning of smart material devices. In this paper, we present the voltage creep phenomena of EAPap, which will give more detail information to understand EAPap as well as other polymer based smart materials.

The Finite Element Analyze (FEA) methods have proven to be applicable for modeling the basic transduction sheets(cantilevers) of ionic polymer-metal composite (IPMC). Physical models can simulate ion transport and corresponding strain. More complicated models also add the effect of the electrode, both surface and electrochemical ones. In this work we propose a FEA model for IPMC materials of different shapes. The new model is three dimensional. When dealing with 3D transduction, the electrode surface geometrical properties of IPMC becomes more important as well. For instance, there are several ways how to attach the electrodes to a cylindrical IPMC to get various deformation modes. The proposed model considers the electrode placement and provides sufficiently accurate transduction estimate for more complicated IPMC structures.

Several researchers are actively studying Ionomeric polymer transducers (IPT) as a large strain low voltage Electro- Active Polymer (EAP) actuator. EAPs are devices that do not contain any moving parts leading to a potential large life time. Furthermore, they are light weight and flexible. An IPT is made of an ion saturated polymer usually Nafion, sandwiched between two electrodes made of a mixture of Nafion and electrically conductive particles usually RuO2 or platinum. Nafion is an acid membrane in which the cations are mobile while the anions are covalently fixed to the polymer structure. Upon the application of an electric potential on the order of 2V at the electrodes the mobile positive ions migrate towards the cathode leading to bending strains in the order of 5%. Our earlier studies demonstrate that the cations develop thin boundary layers around the electrode. Later developments in this finite element model captured the importance of adding particles in the electrode. This study presents the electromechanical coupling in ionic polymer transducers. Since all our earlier models were restricted to the electro-chemical part, here we will introduce the chemomechanical coupling. This coupling is performed based on previous studies (Akle and Leo) in which the authors experimentally showed that the mechanical strain in IPTs is proportional to a linear term and a quadratic term of the charge accumulated at the electrode. The values of the linear and quadratic terms are extracted from experimental data.

Compact actuation that is integrated into a structure's material system has the potential to provide rapid structural reconfiguration while reducing weight. The effect of scale (diameter, overall length and segment length) on the performance of cylindrical fiber-reinforced McKibben-like Rubber Muscle Actuators (RMA) was investigated. An "activation" pressure was observed for all actuators at a value that depended upon the actuation construction. Upon pressurization past the activation threshold, the overall force, stroke, and work capacity increased with increasing actuation length and diameter. The actuation force per unit RMA cross-sectional area was predicted, and experimentally observed, to be roughly constant after activation. By segmenting a longer actuator, a larger contraction and lower actuation force could be achieved. Though actuation forces decreased as actuator diameter and length decreased, the force per unit actuator volume was shown to increase with decreasing diameter including a roughly 4-fold increase in force/volume between the 0.5" and 0.05" actuators. However, due to the small amount of total contraction for the smaller diameter actuators, the relative work per actuation volume was decreased by roughly 35% in comparing those same actuators. Thus, small diameter RMAs have great potential to provide needed linear actuation force within adaptive material systems.

Fly ash, which consists of hollow particles with porous shells, was introduced into polyurea elastomer. A one-step method was chosen to fabricate pure polyurea and the polyurea matrix for the composites based on Isonate® 2143L (diisocyanate) and Versalink® P-1000 (diamine). Scanning electron microscopy was used to observe the fracture surfaces of the composites. Particle size and volume fraction were varied to study their effects on the tensile properties of the composites. The tensile properties of the pure polyurea and fly ash/polyurea (FA/PU) composites were tested using an Instron load frame with a 1 kN Interface model 1500ASK-200 load cell. Results showed that fly ash particles were distributed homogeneously in the polyurea matrix, and all of the composites displayed rubber-like tensile behavior similar to that of pure polyurea. The tensile strength of the composites was influenced by both the fly ash size and the volume fraction. Compared to the largest particle size or the highest volume fraction, an increase in tensile strength was achieved by reducing particle size and/or volume fraction. The strain at break of the composites also increased by using fine particles. In addition, the composites filled with 20% fly ash became softer. These samples showed lower plateau strength and larger strain at break than the other composites.

The use of ceramics as energy absorbents has been studied by many researchers and some improvements in the ballistic performance of ceramic tiles have been made by coating them with different classes of materials (e.g. E-glass/epoxy, carbon-fiber/epoxy, etc.). Using ceramics for energy absorbing applications leads to a significant weight reduction of the system. Therefore, any modification to the ceramic configuration in the system which leads to more energy absorption with the same or less areal density is significant. On the other hand, polyurea has been proved to be an excellent energy dissipating agent in many applications. Inspired by this, we are studying the effect of coating ceramics with polyurea and other materials, on the energy absorption and ballistic performance of the resulting ceramic-based composites. In this study, we investigate the effect of polyurea on ballistic efficiency of ceramic tiles. To this end, we have performed a set of penetration tests on polyurea-ceramic composites. In our experiments, a high velocity projectile is propelled to impact and perforate the ceramic-polyurea composite. The velocity and mass of the projectile are measured before and after the penetration. The change in the kinetic energy of the projectile is evaluated and compared for different polyurea-ceramic configurations (e.g., polyurea on front face, polyurea on back face, polyurea between two ceramic tiles, etc.). The experimental results suggest that polyurea is not as effective as other restraining materials such as E-glass/epoxy and carbon-fiber/epoxy.

The work presents an analytical three-dimensional solution for simply supported angle-ply piezoelectric (hybrid) laminated cylindrical shells in cylindrical bending with interlaminar bonding imperfections, in an electro-thermomechanical loading environment. The jumps in displacements, electric potential and temperature at the imperfect interfaces are modeled using linear spring-layer model. The solution includes the case when, besides at inner and outer surfaces, electric potentials are prescribed at layer interfaces also for effective actuation/sensing. The entities for each layer are expanded in Fourier series in circumferential coordinate to satisfy the boundary conditions at the simply supported ends. The resulting ordinary differential equations in thickness coordinate with variable coefficients are solved by the modified Frobenius method. Numerical results are presented for hybrid composite and sandwich shells with varying imperfection compliance. The effect of location of imperfect interface on the response is studied for cross-ply panels while the effect of ply angle on the sensitivity towards imperfection is studied for angle-ply panels. The effect of weak bonding at actuator/sensor interface on the actuation/sensing authority is investigated. The presented results would also help assessing 2D shell theories that incorporate interlaminar bonding imperfections.

Thermal protection system is one of the key technologies of reusable launch vehicle (RLV). The ARMOR TPS is one of important candidate structure of RLV. ARMOR TPS has many advantages, for example: fixing easily, longer life, good properties, short time of maintenance and service. In comparison with traditional TPS, the ARMOR TPS will be the best selection for all kinds of RLV. So the ARMOR thermal protection system will be used in aviation and spaceflight field more and more widely because of its much better performance. ARMOR TPS panel is above the whole ARMOR TPS, and the metal honeycomb sandwich structure is the surface of the ARMOR TPS panel. So the metal honeycomb sandwich structure plays an important role in the ARMOR TPS, while it bears the flight dynamic pressure and stands against the flight dynamic calefaction. Because the active environment of metal honeycomb sandwich structure is very formidable, it can produce interface connection defects which can exist in the process of manufacture as well. Tensile mechanical properties of the metallic honeycomb sandwich structure with defects are analyzed to obtain damage tolerance of the structure. The effect of shape, dimension and location of defects on the tensile mechanical properties is conducted by experimental study. Then finite element analysis is performed to validate the experimental results. Haynes214 which is a kind of super alloy materials with high performances is chosen as both face sheet and core in this paper.

In addition to the preparation of carbon nanotube (CNT)/epoxy shape memory composites, the thermo-mechanical properties of the composites are focused on. Furthermore, the factors which would influence thermo-mechanical properties of the composites are studied too. Four types of test were carried out, namely, differential scanning calorimetry (DSC), dynamic mechanical analyzer (DMA) test, quasi-static tension test and shape memory behavior. The results of DSC show that CNT decreases the glass transition temperature of the composites. From DMA test, a sharp drop can be found in each composite, which indicates that the composites are typical shape memory polymer materials. And elastic ratio of the composites decreases with increasing CNT content. Tensile test indicates that tensile strength increases and then decreases with the increasing CNT content ranging from 1 wt% to 3 wt%. Study on shape recovery behaviors of the composites showed that each composite can reach a shape recovery ratio near 99%.

In this paper, a method for preparing tri-layer nano stealth composite film is proposed. Using H₂SO₄, HNO₃ mixture for MWCNTs carboxylation, dispersant CTAB is added into surface-treated CNTs, nano Fe and nano Fe₃O₄ respectively. These three mixtures are dispersed by ultrasonic vibration so that they form homogeneous films in epoxy matrix. Vector network analyzer is utilized for EMI SE measurements. According to experiment data, EMI shielding performance curves are generated when CNTs vary from 5%-10%wt, nano Fe 10%-15%wt, nano Fe₃O₄ 10%-15%wt respectively in the frequency bands of 3.22-40GHz. Simultaneously, variation trends of these curves are analyzed. A new type of multilayer nano stealth composite film is fabricated by superposing the three films prepared above. The tri-layer nanocomposites of which matching layer of is 15%wt nano Fe₃O₄ or 15%wt nano Fe, absorbing layer is 5%wt CNTs and reflecting layer is 10%wt CNTs has good EMI shielding performance. The peak values of the two layered material all achieve more than -100dB.

This work presents the nonlinear bending response of magnetostrictive/piezoelectric laminated devices under electromagnetic fields both numerically and experimentally. The devices are fabricated using thin Terfenol-D and PZT layers. The magnetostriction of the Terfenol-D layer bonded to the PZT layer is measured, and a nonlinear finite element analysis is performed to evaluate the second-order magnetoelastic constants in Terfenol-D layer using measured data. The deflection, internal stresses and induced voltage/magnetic field for the laminated devices under magnetic/electric fields are then discussed in detail.

Through summarizing and analyzing the physical corrosion theories of polymer, a theoretical model is constructed to depict the relationship between relaxation time with temperature, stress and humidity. The correlation between physical corrosion behavior and external factors is predicted from semi-experimental profile. In sequence, the morphology of polymer and fiber was investigated by the scanning electron microscopy (SEM) in comparison with that of nonimmersed samples. The dynamic mechanical thermal analysis (DMTA) methods were used to study the evolution of thermomechanical properties against immersed time. It is found that the glass transition temperature (T_g) and storage modulus were significantly reduced with immersion time increase. Then the hardness, tensile strength and bending strength of GFRP were tested by their corresponding mechanical measurements.

Shape memory alloy (SMA) tube is an perfect candidate used to design the torsion actuator in the self-adaptive wings. In this paper, the thermo-mechanical property of SMA torsion thin-walled tube is investigated based on Zhou's threedimensional constitutive model of SMA, which include the three-dimensional phase transformation equation and the three-dimensional mechanical constitutive equation, and material mechanics. The phase transformation equation describing the relationship between torque and martensitic volume fraction of SMA torsion thin-walled tube is established based on Zhou's three-dimensional phase transformation of SMA. The mechanical equation is established to express the relationship of torque, temperature and torsion angle of the SMA torsion thin-walled tube based on Zhou's three-dimensional mechanical constitutive equation and material mechanics. The thermo-mechanical behaviors of SMA torsion thin-walled tube are numerically simulated by using the established mechanical equation and phase transformation equation together. Numerical results show the established mechanical equation and phase transformation equation well predict the thermo-mechanical behaviors of SMA torsion thin-walled tube.

The behavior of piezo-metal-compounds made of laminar piezo-modules and sheet metal which are formed by various forming processes is simulated. To evaluate the formability of the piezo-modules strains and stresses have to be known. Otherwise finite element models with a discretization in the dimension of the piezomaterial are not suitable for forming simulation concerning the size of the model. The simulation method of unit cells is used to homogenize the material parameters. In order to achieve the real strains and stresses of the piezomaterial the strains/stresses obtained with the homogenous material parameters are superimposed with the phase concentrations from the unit load cases.

The objective of this study is to design and characterize a piezoelectric composite and evaluate its suitability for viscosity-measuring applications, i.e., monitoring the coagulation rate of blood. The composite is manufactured of a platinum-core lead zirconate titanate (PZT) fiber inserted into an aluminum matrix. This study characterizes the described composite by testing its impedance, capacitance, voltage sensitivity response to vibrational inputs, and deformation due to electrical input. As actuators, different voltage inputs are fed into the probes and displacement is measured with results on the range of nanometers. As sensors, the devices are used to monitor cantilever beam vibrations. The probe's response is in the mV range and follows the same pattern as an accelerometer. Additional tests in air, water, and deionized water are carried out to evaluate the sensor's suitability for measuring viscosity using two probes: one as an actuator and the other as a sensor. Results of the gain and phase between the two probes indicate that the phase shift may be used as an indicator of viscosity changes. The first significant phase shift was measured as 2.45, 2.77, and 4.065x10⁷Hz, for water, air, and oil, respectively, which is directly proportional to the kinematic viscosity of each fluid.

Biological systems in ocean environment provide all the desired features required for design of unmanned undersea vehicles. We noticed the uniqueness and simplicity in the design of rowing medusa and have successfully demonstrated working prototypes of Aurelia Aurita. In this study, we demonstrate the effect of bell joints in reducing the contraction force required for deformation. The study is based on observations made for the sub-umbrella features of jellyfish. Artificial jellyfish unmanned undersea vehicle (UUV) was fabricated consisting of silicone as the matrix material and shape memory alloy (SMA) as the actuation material. UUV was characterized for its performance and tailored to achieve vertical motion. SMAs were selected for actuation material because they are simple current-driven device providing large strain and blocking force. However, electrical power requirements were found to be quite high in the underwater conditions. It was identified that by including "joints" in the structural material forming the bell, the overall power requirement can be reduced as it lowers the resistance to compression. An analytical model was developed that correlates the deformation achieved with the morphology of the joints. Experiments were conducted to characterize the effect of both joint shapes and structural materials on the motion. Results are compared with that of natural medusa gastrodermal lamella and analyzed using the theoretical model. By including the features inherently present in natural jellyfish, the required compression force was found to be decreased.

Micro-electro-mechanical systems (MEMS) switches for radio-frequency (RF) signals have certain advantages over solid-state switches, such as lower insertion loss, higher isolation, and lower static power dissipation. Mechanical dynamics can be a determining factor for the reliability of RF MEMS. The RF MEMS ohmic switch discussed in this paper consists of a plate suspended over an actuation pad by four double-cantilever springs. Closing the switch with a simple step actuation voltage typically causes the plate to rebound from its electrical contacts. The rebound interrupts the signal continuity and degrades the performance, reliability and durability of the switch. The switching dynamics are complicated by a nonlinear, electrostatic pull-in instability that causes high accelerations. Slow actuation and tailored voltage control signals can mitigate switch bouncing and effects of the pull-in instability; however, slow switching speed and overly-complex input signals can significantly penalize overall system-level performance. Examination of a balanced and optimized alternative switching solution is sought. A step toward one solution is to consider a pull-in-free switch design. In this paper, determine how simple RC-circuit drive signals and particular structural properties influence the mechanical dynamics of an RF MEMS switch designed without a pull-in instability. The approach is to develop a validated modeling capability and subsequently study switch behavior for variable drive signals and switch design parameters. In support of project development, specifiable design parameters and constraints will be provided. Moreover, transient data of RF MEMS switches from laser Doppler velocimetry will be provided for model validation tasks. Analysis showed that a RF MEMS switch could feasibly be designed with a single pulse waveform and no pull-in instability and achieve comparable results to previous waveform designs. The switch design could reliably close in a timely manner, with small contact velocity, usually with little to no rebound even when considering manufacturing variability.

When a high electric field is applied across a dielectric electro-active polymer, the stiffness, in the in-plane direction, decreases. This change in stiffness can be used to generate linear actuation in the out-of-plane direction if the dielectric electro-active polymer (DEAP) is subject to a suitable bias force. This bias force is commonly provided by a linear spring, but a recent research work suggests the use of so-called negative-rate bias springs (NBS) to increase the achievable stroke. These systems are geometrically non-linear systems with bi-stable mechanical characteristics with a negative stiffness between equilibrium points that can be efficiently matched to the DEAP load/deformation behavior. This paper provides an overview of current work performed using NBS and discusses why NBS provide more displacement output. In addition, this paper presents a simple analytical model and a FE simulation of a negative-rate bias spring (NBS). The simple model is introduced to explain the non-linear snap-through behavior of the bi-stable NBS. FE simulated results obtained with bi-stable buckled beam are examined and compared with a linear spring model. The beam buckling and stiffness are identified to be analogous to the simple linear spring model's pre-compression and spring stiffness. These parameters can be used to tune a mechanism to appropriately match with a DEAP film. Future work includes NBS mechanism design and their coupling with circular DEAPs.