Proceedings Volume 5053

Smart Structures and Materials 2003: Active Materials: Behavior and Mechanics

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Proceedings Volume 5053

Smart Structures and Materials 2003: Active Materials: Behavior and Mechanics

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Volume Details

Date Published: 13 August 2003
Contents: 13 Sessions, 65 Papers, 0 Presentations
Conference: Smart Structures and Materials 2003
Volume Number: 5053

Table of Contents

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Table of Contents

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  • Active and Bioactive Polymers and Polymer Composites
  • Multifunctional Materials and Actuators I
  • Multifunctional Materials and Actuators II
  • Shape Memory Alloys and Magnetic Shape Memory Alloys I
  • Shape Memory Alloys and Magnetic Shape Memory Alloys II
  • Shape Memory Alloys and Magnetic Shape Memory Alloys III
  • Shape Memory Alloys and Magnetic Shape Memory Alloys I
  • Shape Memory Alloys and Magnetic Shape Memory Alloys III
  • Modeling of Active Materials I
  • Modeling of Active Materials II
  • Modeling of Active Materials III
  • Piezoelectric and Magnetic Materials I
  • Piezoelectric and Magnetic Materials II
  • Piezoelectric and Magnetic Materials III
  • Poster Session
  • Shape Memory Alloys and Magnetic Shape Memory Alloys III
  • Poster Session
Active and Bioactive Polymers and Polymer Composites
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Electrical and electrochemical characterization of electroconductive PPy-p(HEMA) composite hydrogels
Sean I. Brahim, Gymama E. Slaughter, Anthony Guiseppi-Elie
Two groups of polymers that have been the focus of widespread research are hydrogels and conducting electroactive polymers (CEPs). 'Intelligent' hydrogels are highly hydrophilic, cross-linked polymers possessing hydration properties that change in response to specific environmental stimuli such as pH, ionic strength, chemical species, magnetic fields, etc. Conducting electroactive polymers such as polypyrrole, polyaniline and polythiophene are highly conjugated, redox-active polymers with electrical and optical properties that change through many orders of magnitude depending upon redox state (doping). We have formed composites of inherently conductive polypyrrole within highly hydrophilic poly(hydroxyethyl methacrylate)-based hydrogels. These materials retain the hydration characteristics of hydrogels as well as the electroactivity and electronic conductivity of CEPs and are thus called 'electroconductive hydrogels'. The electrical and electrochemical properties of these polymer composites have been investigated. The electrochemical characteristics observed by cyclic voltammetry suggest less facile reduction of PPy within the composite hydrogel compared to electropolymerized PPy, as shown by the shift in the reduction peak potential from -472 mV for electropolymerized polypyrrole to -636 mV for the electroconductive composite gel. The network impedance magnitude for the electroconductive hydrogel remains quite low, ca. 100 Ohms, even upon approach to DC, over all frequencies and at all offset potentials suggesting retained electronic (bipolaronic) conductivity within the composite.
Electromechanical modeling of charge sensing in ionic polymers
A model for charge sensing due to imposed deformation in ionic polymer materials is presented. The basic concept of this model is that mechanical deformation induces charge at the surface of the polymer and produces a measureable discharge of current as the material is deformed. This discharge of current occurs when a short-circuit electrical boundary condition is applied across the material electrodes. An expression for charge density, electric field and electric potential under short-circuit conditions is developed from the electrostatic field equations. The solution for charge density is coupled with the mechanical deformation through a proportionality constant. Expressions for induced charge and current flow are then derived from the equations for electric displacement at the surface of the material. Experimental results support the basic form of the model and also demonstrate that the geometric scaling predicted in the model agrees with measured data. Analysis of the length scale predicted by the model produces qualitative agreement with previously published results but also points to the need for a greater understanding of the interfacial mechanics in the ionic polymer transducers.
Temperature- and magnetic-field-induced phase transformation in bulk and composite Gd5Si2Ge2
A -1300ppm strain has been obtained in a [0-3], resin binder, Gd5Si2Ge2 particulate composite. The strain is a result of a temperature induced phase transformation from a high volume (high temperature, low magnetic field) monoclinic phase to a low volume (low temperature, high magnetic field) orthorhombic phase. The particles used in the composite were ball-milled from a bulk sample and were sieved to obtain a size distribution of <600micron. Bulk Gd5Si2Ge2 was manufactured via arc melting and subsequently annealed at 1300°C for 1 hour to produce a textured, polycrystalline sample. The transformation temperatures of the bulk sample, as measured using a Differential Scanning Calorimeter (DSC), were Ms=-9.3°C, Mf=-14.6°C, As=-4.4°C, and Af=-1.2°C. The bulk sample was magnetically characterized using a SQUID magnetometer, and found to undergo a paramagnetic to ferromagnetic transition during the phase transformation, consistent with published results. The bulk sample was also found to possess a -8000ppm volume magnetostriction, agreeing well with measured unit cell parameters of the different phases.
Conformational mechanics of stimulus-responsive polypeptides
Alexei Valiaev, Robert L. Clark, Ashutosh Chilkoti, et al.
Stimulus-responsive polymers and polypeptides (SRPs) experience a significant entropic response when exposed to an environemental stimulus, such as a change in temperature. This phase transition directly affects polymer conformation and can potentially be harnessed for force generation in actuation devices on nano- and micro-scales. While interfacial applications of SRPs have been prototypically demonstrated, a systematic investigation of the phase transition behavior at the solid-liquid interface and on the single-molecule level is lacking. In this paper we present results from force-spectroscopy measurements probing the force-extension and conformational behavior of one SRP, elastin-like polypeptides (ELP), below and above their transition temperature. The results indicate that there is no signficant difference in the force extension behavior at intermediate and large extensions, but the behavior is dramatically different at small extensions. Results also demonstrated that above the phase transition temperature large, unspecific adhesion forces often gave way to constant force steps upon extension, indicating a collapsed, potentially entangled, hydrophobic state of the ELP. The extension behavior below the phase transition temperature, however, closely followed that of random polymer coil, without any significant unspecific adhesion forces. The excellent fit of a simple extended freely jointed chain model to the data at intermediate and large extension suggests that the ELP is in a random conformational state without significant secondary structure. Forces associated with a phase transition therefore arise likely from entropic conformational changes associated with a hydrophobic collapse.
Ferroelectric fluoro-terpolymers with high dielectric constant and large electromechanical response at ambient temperature
T. C. Chung, Atitsa Petchsuk
This paper discusses a new family of ferroelectric polymorphs fluoro-terpolymers comprising vinylidene difluoride (VDF), trifluoroethylene (TrFE), and a chloro-containing third monomer, including vinyl chloride (VC), 1,1-chlorofluoroethylene (CFE), chlorodifluoroethylene (CDFE), chlorotrifluoroethylene (CTFE), with narrow molecular weight and composition distributions. The slightly bulky chlorine atom serves as a kink in the polymer chain, which spontaneously alters the chain conformation and crystalline structure. Comparing with the corresponding VDF/TrFE copolymer, the slowly increasing chlorine content (< 8 mol% of ter-monomer) gradually changes the all-trans chain conformation to tttg+tttg- conformation, without significant reduction of overall crystallinity. Curie (F-P) phase transition temperature between the mixed ferroelectric phases and paraelectric phase (tg+tg- conformation) also gradually reduced to near ambient temperature, with very small activation energy. Consequently, the terpolymers show high dielectric constant (>80) and large electrostrictive response (>5%) at ambient temperature, and exhibiting common ferroelectric relaxor behaviors with a broad dielectric peak that shifted toward higher temperatures as the frequency increased, and a slim polarization hysteresis loop at ambient temperature.
Thin films of light-responsive polymers for sensing and surface patterning
The kinetics of electrostatic layer-by-layer adsorption of a weakly charged polycation, poly(allylamine hydrochloride), PAH, and a polyanion containing an azobenzene chromophore, P-Azo, was studied using UV-vis spectroscopy and ellipsometry. The thickness of the multilayer films was first measured over the adsorption pH range of 3 to 11, and the growth of multilayers was examined as function of time and concentration. Films assembled in bath pH near that of their pKa value produced both the thickest films, and displayed remarkably rapid adsorption isotherms. In some PAH/P-Azo films a significantly large thickness was achieved in less than 5 seconds, which is more than two orders of magnitude faster than what is usually observed. We show that this anomalously rapid adsorption is a consequence of the weak acid-base nature of the layers. Self-assembled polymer films containg azobenzene groups are interesting materials as the chromophores can be addressed as light-responsive groups for surface patterning and sensing.
Multifunctional Materials and Actuators I
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Overview of multifunctional materials
Multifunctional design has evolved over the past decade, moving away from discrete unifunctional subsystems with clearly defined boundaries, to produce systems design and materials design methods that blend performance in new and innovative ways. This presentation looks at the development of multifunctional design from a systems and a materials perspecitve. A classification of multifunctional desings is presented, in terms of the decreasing scales at which the boundaries of subsystems, components and material are blurred. Guidelines for identifying multifunctional opportunities at the system and material scale are also discussed.
Effective properties of three-phase electro-magneto-elastic multifunctional composite materials
Coupling between the electric field, magnetic field, and strain of composite materials is achieved when electro-elastic (piezoelectric) and magneto-elastic (piezomagnetic) particles are joined by an elastic matrix. Although the matrix is neither piezoelectric nor piezomagnetic, the strain field in the matrix couples the E field of the piezoelectric phase to the B field of the piezomagnetic phase. This three-phase electro-magneto-elastic composite should have greater ductility and formability than a two-phase composite in which E and B are coupled by directly bonding two ceramic materials with no compliant matrix. A finite element analysis and homogenization of a representative volume element is used to determine the effective electric, magnetic, mechanical, and coupled-field properties of an elastic (epoxy) matrix reinforced with piezoelectric and piezomagnetic fibers. The effective magnetoelectric moduli of this three-phase composite are, however, less than the effective magnetoelectric coefficients of a two-phase piezoelectric/piezomagnetic composite, because the epoxy matrix is not stiff enough to transfer significant strains between the piezomagnetic and piezoelectric fibers.
Initial investigation in actuator design using high-temperature shape memory alloy
The need for shape memory alloys (SMA) with high transformation temperatures is urgent. SMA actuators may then be designed that will demonstrate two important attributes: (i) actuation in a high temperature environment and (ii) high actuation frequency in a moderate temperature environment. Copper-Aluminum-Nickel (CuAlNi) single crystal alloy is a promising candidate due to favorable characteristics such as wide range of transformation temperatures, large actuation stress and strain, and lack of plastic deformation under cyclic loading. These characteristics point to the possibility that CuAlNi single crystal high temperature SMA (HTSMA) actuators can be developed that will demonstrate the attributes mentioned above. An initial investigation of these possibilities is carried out computationally by analyzing a HTSMA-actuated airfoil. An existing rate-independent thermomechanical model is calibrated to describe the CuAlNi material behavior. Time-dependent thermomechanically-coupled parametric studies are carried out to yield information about the airfoil stroke (trailing edge deflection), the actuation energy required and the actuation frequency possible for cyclic actuation, all as a function of transformation temperatures. For comparison purposes, a similar parametric study is also carried out for NiTi polycrystalline SMA. The analysis indicates that a CuAlNi HTSMA actuated airfoil will demonstrate a cooling time two to six times lower than its NiTi SMA counterpart.
A bio-inspired high-authority actuator for shape morphing structures
Dana M. Elzey, Aarash Yusefzadeh Nagh Sofla, Haydn N. G. Wadley
Lightweight structures capable of changing their shape on demand are of interest for a number of applications, including aerospace, power generation, and undersea vehicles. This paper describes a bio-inspired cellular metal vertebrate structure which relies on shape memory alloy (SMA) faces to achieve fully reversing shape change. The resulting vertebrate actuators can be combined with flexible face sheets to create a load-bearing, shape morphing panel. Performance of the vertebrate actuator in terms of maximum curvature and moment is analyzed and discussed. A recently constructed, prototype shape morphing airfoil is used to illustrate the concept.
Multifunctional Materials and Actuators II
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Bistable shape memory thin film actuators
Tobias Sterzl, Bernhard Winzek, Martina Mennicken, et al.
Shape memory alloys (SMA) are able to provide high work output when they undergo the martensitic transformation. Therefore, they present a favorable actuation mechanism for microsystems, e.g. for microvalves, switches or microgrippers. Sputter deposited thin SMA films are already in use as free-standing films or as composites in combination with a substrate. In the case of a composite, the substrate works as a bias spring and enables the SMA actuator to show a two way behavior. To enlarge the potentialities of shape memory based actuators a bistable principle is presented. This is realized by the combination with a polymer exhibiting a glass transition temperature (Tg) between the hysteresis loop of the shape memory composite. The fabrication of this composite is described with a special emphasis on the development of suitable polymer samples.
SMA-thin film composites providing traveling waves
Bernhard Winzek, Sam Schmitz, Holger Rumpf, et al.
Actuators providign traveling waves are attractive for several industrial applications, like active skins for turbulent drag reduction or transport devices for assembling processes. Traveling waves require a flexible structure in contrast to standing waves which contain knots without vertical motion. Therefore, different concepts to realize these waves have been developed. This work presents the functional principle of wave generation by means of shape memory allow (SMA) thin film composites and the conditions that have to be considered for the performance of traveling waves with continuous wave flow. Devices using temperature inhomogeneities, an arrangement of separately addressed SMA composites as well as structures using different SMAs have been investigated and their feasibilty is discussed.
3D finite-element simulation of a shape memory microgripper
Berthold Krevet, Manfred Kohl
A shape memory alloy (SMA) microgripper for manipulation of microparts is presented, which is made of a monolithic SMA device of 2 × 5.8 × 0.1 mm3 size comprising various integrated functional units like two microactuators for active closing and opening, gripping jaws and an optical slit for position sensing. Recently, the design and fabrication technology of the SMA microgripper have been developed. The present work concentrates on the mechanical and thermal performance. A 3D macromodel and its implementation in a coupled finite element (FEM) routine is introduced, which allows simulation of mechanical, electrical and thermal fields in shape memory actuators of arbitrary shape. The mechanical behavior is described by a two-phase macromodel taking into account material nonlinearity and history effects. The spatial distribution of electrical heating power is determined from simulation of the electrical potential distribution. For simulation of temperature profiles a heat transfer model is used, which takes the distribution of electrical heating power and the effects of latent heat, of heat conduction and of heat convection into account. The simulation results are compared with experimentally determined characteristics. Mechanical tests reveal spring constants of the microactuators in austenitic condition of 1600 N/m, which are confirmed by the simulations. The stroke of the gripping jaws is between 250 and 300 μm depending on the maximum prestrain. The maximum gripping force is determined to 35 mN. Typical heat transfer times are about 100 ms upon heating and 150 ms upon cooling, which are in quantitative agreement with experimentally determined time constants.
Characteristics of magnetic force control device with magnetostrictive and piezoelectric laminate composite
Toshiyuki Ueno, Jinhao Qiu, Junji Tani
A magnetic force control device with laminate composite of giant magnetostrictive material (GMM) and piezo-electric material (PZT) is proposed. This magnetic force control is based on inverse magnetostrictive effect of a magnetic material, whereby the variation of stress applied on the material is converted to that of magnetic force via magnetic circuits. For the purpose of realizing the method in practical applications, disks of GMM and PZT are laminated to control the stress of GMM by electric field on PZT. Due to the capacitive properties of PZT, the device requires little electric energy hence generates no heat to maintain constant force. Furthermore compared with conventional electromagnetics, the device can be fabricated easily and in small size to be suitable for microactuators. This paper presents the principle of the magnetic force control by the lamination of GMM and PZT and investigates the static and dynamic characteristics of several devices to demonstrate their capabilities of the magnetic force control.
Carbon nanotubes as actuators in smart structures
Carbon Nanotubes have diameters in nanometer scale, are up to tens of microns long and can be single- or multi-walled (SWNT and MWNT). Compared with carbon fibers, which typically have a Young's modulus of up to 750 GPa, the elastic modulus of Carbon Nanotubes has been measured to be approximately 1-2 TPa. The strength of Carbon Nanotubes has been reported to be about two order of magnitude higher than current high strength carbon fibers. Additionally especially SWNT show excellent actuator behaviour. Electromechanical actuators based on sheets of SWNT show to generate higher stress than natural muscles and higher strains than ferroelectrics like PZT. Unlike conventional ferroelectric actuators, low operating voltages of a few volts generate large actuator strains. Thus, this paper will give a brief overview of the current activities within this field and show some recent results of the Carbon Nanotube actuator development at the DLR-Institute of Structural Mechanic suggesting that optimized SWNT sheets may eventually provide substantially higher work densities per cycle than any previously known material.
Shape Memory Alloys and Magnetic Shape Memory Alloys I
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Martensitic transformation behavior under magnetic field in Co-Ni-Al ferromagnetic shape memory alloys
Yuji Sutou, Ryosuke Kainuma, Kiyohito Ishida, et al.
Effect of the magnetic field on the martensitic transformation of Co-Ni-Al single-crystal was investigated by differential thermal analysis (DTA) and the in-situ microstructure observation under magnetic field. The martensitic transformation temperatures Ms and Mf of the Co34.5Ni35.5Al30 single-crystal specimen showing the martensitic transformation from the paramagnetic austenite (B2) to the ferromagnetic martensite slightly increased under the magnetic field and those temperature shifts were about 1.3°C at 1.0T. It was also observed in the Co34.5Ni35.5Al30 single-crystal specimen that the phase boundaries between the austenite and the martensite slightly move by applying the magnetic field of 1.0T. These results are discussed on the basis of a thermodynamic stabilty of the martensite phase under the magnetic field. The martensitic and the magnetic transformation behaviors of the Ni-Al-Co alloys are also reviewed.
Experimental characterization of NiMnGa magnetic shape memory alloy rods under dynamic magnetic fields
Ronald N. Couch, Inderjit Chopra
A comprehensive, experimental characterization of single crystal, NiMnGa rods is the current subject of study. Static tests aimed at characterizing the force-deflection behavior show that the actuator has two stiffnesses, a low stiffness associated with the region of twin boundary motion and a high stiffness when the material is in the fully twinned condition. For a 2×3×16 mm specimen, a block force of 4.35 N and a free strain of 5.02% were determined experimentally. Dynamic test of the material exposed to a 0.85 T peak, AC, inductive field show that the strain and force generated by the actuator consist of mean and dynamic components. For peak performance, the recovery force acting on the NiMnGa actuator must be optimized. Experimental results indicate that NiMnGa has a maximum volumetric energy density of 12.15 kJ/m3 and a maximum weight defined energy density of 1.45 J/kg. Using energy density by weight as a metric, NiMnGa has an energy output on the same order of magnitude as commercial piezostacks.
Effects of growth rate and composition on the microstructure of directionally solidified NiMnGa alloys
Magnetic shape memory (MSM) alloys give recoverable strain when subjected to an applied magnetic field. The strongest MSM effect has been observed in single crystals. The magnitude of the effect and the consistency of behavior over the entire volume of a sample is strongly dependent on the solute and phase distributions in crystals. Samples of stoichiometric and off-stoichiometric Ni2MnGa magnetic shape memory alloys were directionally solidified by a seedless Bridgman method using different rates of growth. The growth conditions used resulted in oriented polycrystals exhibiting a coarse cellular structure. Significant macro-segregation was observed, with the top of the ingot enriched in Mn and the bottom enriched in Ga. Micro-segregation also occurred, resulting in Mn-rich intercellular eutectic or eutectoid structures, and coarse intra- and inter-cellular Mn-rich particles. An increase in the pulling rate during the directional solidification process resulted in finer cellular and eutectic / eutectoid structures, as well as finer particles.
Shape memory effect and magnetostriction-sputtered NiMnGa thin films
Holger Rumpf, Juergen Feydt, Daniel Lewandowski, et al.
NiMnGa thin films have been deposited by magnetron sputtering on Mo substrates using a Ni50Mn30Ga20 powder metallurgical target. Independent from variation of substrate temperature during the sputtering process the deposited films are found to be polycrystalline. X-ray diffraction patterns show a decreasing peak width and a shift to slightly higher Bragg angles with increasing substrate temperature during sputtering, which is even amplified when subsequent rapid thermal annealing is applied. Annealing temperatures above 500°C lead to a remarkable enhancement of the shape memory effect as well as of the magnetostriction. Temperature induced martensitic transformations have been measured by a cantilever deflection technique and a cantilever resonance method. Martensitic start temperatures (MS) range between 50 and 90°C depending on composition and annealing temperature. Stress relief upon the martensitic transformation ranges between 200 and 300 MPa whereas the magnetostrictive coupling constant b is about 2 MPa. Magnetization measurements and Curie temperature determination reveal ferromagnetic behavior within the temperature range of the martensitic transformation.
Shape Memory Alloys and Magnetic Shape Memory Alloys II
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Magnetic field-induced strain in single-crystal Ni-Mn-Ga
Robert C. O'Handley, Samuel M. Allen, David I. Paul, et al.
Field-induced strains up to 10% at room temperature have been observed in magnetic shaep memory alloys based on off-stoichiometric compositions of the intermetallic compound Ni2MnGa. This occurs by the motion of twin boundaries in the ferromagnetic martensitic state under magnetic fields of a few kOe. Some data illustrating the interdependence of strain, stress, and magnetic field are reviewed. Phenomenological models describe many of these observations by minimization of free energy terms including Zeeman energy, magnetocrystalline anisotropy energy, stored elastic energy and fractional twin-boundary distribution. Two important questions have been raised about field-induced strain in FSMAs. They are 1) the role of body forces (due to action of the field on the sample), and 2) the role of magnetostriction (stress/strain in a single variant under magnetization rotation) in the twin boundary motion. These questions are addressed in light of published data and models.
Frequency response of single-crystal Ni-Mn-Ga FSMAs
Christopher P. Henry, Pablo G. Tello, David Bono, et al.
Magnetic-field-induced strain in single crystals of Ni-Mn-Ga magnetic shape memory alloys were studied under cyclic field conditions using a compression spring to reset the sample as H→0. Low frequency actuation strain of 2.5% degraded to about 1.5% at an actuation frequency of 500 Hz. Two resonant-like features appear in the ε(f) data, which appear to correspond to a broad test system resonance (100-200Hz) and a sample longitudinal resonance near 350 Hz. The relative phase of field and strain support the assignment of the 350 Hz resonance to the sample.
Shape Memory Alloys and Magnetic Shape Memory Alloys III
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Grown crystalline Ni-Ti shape memory alloy thin films
Crystallization of sputter deposited Ni-Ti thin film is commonly achieved with high temperature annealing to induce the shape memory effect. High temperature annealing has several disadvantages such as formation of precipitates, exclusion of unstable substrates and increase of residual stress. An attempt has been made to obtain as grown crystallized film by using hot target as a process parameter so that those disadvantages can be overcome. In this paper it will be shown that the transformation properties of sputter deposited as grown NiTi thin films from a hot Ti-rich target on single crystal Si substrate is crystalline in nature and shape memory above room temperature. This is true even though the materials did not undergo crystallization process. X-ray diffraction reveals that as grown films are crystalline and shows a mixture of martensite and rhombohedral phases. Transformation temperatures of the sputtered films are determined by using both differential scanning calorimetry and four point probe technique. Film microstructure has been studied by using transmission electron microscopy. The as deposited films have large sized grains with well defined twinned structure. We believe that the film is crystalline because the composition of the target and the high kinetic energy of the sputtered species create a favorable condition to form crystalline film.
Shape Memory Alloys and Magnetic Shape Memory Alloys I
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Effect of composition on the magnetic and elastic properties of shape-memory Ni-Mn-Ga
Aayush Malla, Marcelo J. Dapino, Thomas A. Lograsso, et al.
The growing interest in ferromagnetic shape-memory Ni-Mn-Ga for implementation in actuator applications originates from the fact that this class of materials exhibits large strains when driven by a magnetic field. Large bidirectional strains up to a theoretical 6% are produced in these materials by twin boundary motion as martensite variants rotate to align respectively parallel or perpendicular to applied magnetic fields or stresses. These strains represent a significant improvement over piezoelectric and magnetostrictive materials. In this paper, we report on experimental measurements conducted on Ni-Mn-Ga cylindrical rods subjected to uniaxial stresses and uniaxial magnetic fields which were applied collinearly along the magnetic easy axis direction of the rods. To this end, a test apparatus was developed which consists of a water-cooled solenoid actuator and a loading fixture. Despite the lack of a readily recognizable mechanism for reversible deformations, bidirectional strains as large as 4300 ppm (0.43%) were observed, or three times the saturation magnetostriction of Terfenol-D. This paper presents room-temperature data including magnetization hysteresis, strain versus field and peak strain versus stress curves collected over a range of stresses between 0-65 MPa. From the latter set of curves, blocking force values are estimated as those for which the strain is 1% of the maximum (zero-load) strain. The results illustrate the sensitivity of material behavior with respect to composition at different driving conditions and offer insight on the choice of material compositions at which maximum actuation performance is achieved.
Shape Memory Alloys and Magnetic Shape Memory Alloys III
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Thermomechanical properties of Ni60%weightTi40%weight
60-NiTinol (60% Nickel 40% Titanium content by weight) was developed by the US Naval Ordnance Laboratory in the 1950s as a structural form of NiTinol. Due to 60-NiTinol's extreme brittleness the application development was abandoned. Nitinol Technology Inc. successfully produced cutting instruments with this material in the early 90's. Subsequent work demonstrated that with the proper heat treatment the material exhibits a strong, stable, shape memory response. Unlike other Nitinol alloys, 60-Nitinol does not require cold work. Initial testing of this material shows that the transition temperature is a strong function of the heat treatment. Therefore the same ingot of material can produce samples with superelastic and shape memory effect. Samples with different heat treats exhibited transition temperatures varying from -55 C to +60 C. Additionally, appropriate heat treatment allows the material to exhibit extreme hardness (Rc 63) or a two-way shape memory effect. This paper provides the first study of the thermomechanical properties, including stress-strain curves and thermal cycling, of axially loaded slender 60-Nitinol samples. The samples were tested at extremely high stress level greater than 695 MPa (100 ksi) with recoverable strain of 2.5%. In addition, flexures designed with potential for aerospace applications were tested. This initial research shows that 60-Nitinol has some enticing advantages over 55 Nitinol, however further study is required.
Composition and annealing effects on the mechanical properties of superelastic thin film nickel titanium
This work examines the influence of annealing temperature on the transformation temperatures, stress necessary to induce martensite (sAM), and the Young's modulus of superelastic NiTi of two different compositions--47.5 at.% Ni and 50.5 at.% Ni. The films were sputter deposited, crystallized, and annealed for two hours at three different temperatures of 400°C, 500°C, and 600°C. Isothermal tensile tests at the austenite finish temperature (Af) were performed for evaluating the mechanical response. For the 47.5 at.% Ni film, increasing the annealing temperature from 400°C to 500°C decreased sAM by 55 MPa, while the film annealed at 600°C failed to demonstrate complete superelastic behavior. For the 50.5 at.% Ni film, increasing the annealing temperature from 400°C to 600°C decreased sAM by 138 MPa. Results were explained using the transformation temperatures and the Clausius-Clapeyron relationship.
Shape memory alloys characterization by different methods
Shape Memory Alloys (SMA) are metal materials that show the property to return to a previously defined shape or dimension when they are subjected to a variation of temperature. These alloys can be largely deformed at some relatively low temperatures and when they are brought to some higher temperatures return to their original shape. Materials that show shape memory only by means of heating are called “one-way shape memory alloys”; materials that also show the phenomenon during the cooling, are called “two-way shape memory alloys”. Changing in shape or dimension is generally associated to a generated load, so that the pieces could be employed as actuators. Today Copper based alloys and Nickel-Titanium alloys are employed by exploiting this property. The property of these materials is referred to a temperature called “transition temperature”. The knowledge of this temperature is very important in order to an appropriate use of the material. In this research, microstructure of a Cu-Al-Ni SMA has been studied to detect martensitic and austenitic phases, while simple tooling for experiments have been set up in order to apply the main methods to find out the transition temperatures of different Ni-Ti alloys; the results, discussed and compared, shown a very good overlapping even employed several simplifications of the tooling that make very easy the experimental procedures.
Low-cost high-quality Fe-based shape memory alloys suitable for pipe joints
Setsuo Kajiwara, Albert L. Baruj, Takehiko Kikuchi, et al.
By addition of small amount of Nb and C to the conventional Fe-Mn-Si based shape memory alloys, shape memory properties are greatly improved in such an extent that the costly 'training' heat treatment is no more necessary. The key to this remarkable improvement of shape memory effect is to produce small NbC precipitates of about several nm in size in austenite. In order to generate such very small NbC particles, the sample is firstly rolled at 870 K and then aged at 1070 K. An example of Fe-28Mn-6Si-5Cr-0.53Nb-0.06C (mass %) alloy is shown; 95% shape recovery for initial strain of 4% is obtained and the shape recovery stress of about 300 MPa is attained for the sample pre-rolled 14%, which is well above the criterion for industry application of pipe jointing. A pipe jointing with this material is demonstrated.
Modeling of Active Materials I
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Micromechanical approach of stress-induced phase transformation
Stress-induced martensitic phase transformation is responsible of very important phenomena like superelasticity or two-way shape memory in shape memory alloys. These phenomena are at the origin of many innovative products in industrial fields like aerospace or biomedical applications. To reach the best design is a very difficult task for applications using shape memory alloys: due to the existence of a phase transformation, these materials can no longer be considered as homogeneous and macroscopic approaches failed to give an accurate description of their behavior. The recent trend using SMA thin film as microactuator in microdevice increase the need of reliable design tools. Moderns concepts developed in micromechanics and finite element analysis are well adapted to deal with these problems. Intra and intergranular stresses building from transformation strain incompatibilities in bulk materials or thin films are well accounted using these tools, even when complex loading conditions or different initial crystallographic texture are considered.
Sharp phase front model of phase transformation and micro-macro transitions in shape memory alloys
This paper deals with the micro-macro transition in shape memory alloy thin films using a recently developed sharp phase front-based 3D constitutive model outlined by Stoilov (2002), and originally proposed in the 1D context by Stoilov and Bhattacharyya (2002). The key ingredient in the model is the recognition of austenite and/or martensite variants as separate phases in a SMA domain. Evolution of the interface between these phases is taken as an indicator of a phase transformation in progress. A generalized Clausius-Clapeyron (CC) equation is derived from the continuity of chemical potential at the interface. The implications of the CC equation on the initiation of phase transforamtion are studied for various mechanical loading modes. Finally, the issue of micro-macro transition is examined in the context of stress-strain-temperature response of a CuAlNi SMA thin film.
Numerical studies of wave propagation in polycrystalline shape memory alloy rods
Dimitris C. Lagoudas, Peter Popov
Shape Memory Alloys (SMAs) have recently been considered for various applications involving dynamic loading. An SMA body subjected to external dynamic loading will experience large inelastic deformations that will propagate as phase transformation and/or detwinning shock waves. The wave propagation problem in a cylindrical SMA is studied numerically. An adaptive Finite Element Method (FEM) is used to solve several model problems representing various boundary conditions and thermomechanical paths. The mesh adaptivity is based on the Zienkiewicz-Zhu (ZZ) error estimator. Convergence studies are performed demonstrating the ability of the adaptive FEM to accurately and efficiently capture solutions with moving shock discontinuities. The energy dissipation capabilities of SMA rods are evaluated based on the numerical simulations. Correlations with existing experimental data on impact loading of NiTi SMA bars are also performed.
Modeling the hysteresis of a simple SMA wire actuator with a load-dependent Preisach-type operator
William S. Galinaitis, Jeremy W. Poling
To accurately position an object with an actuator that exhibits load dependent hysteresis requires a hysteresis model that is capable of adjusting to a change in load. In this paper we investigate the specific problem of modeling the hysteresis of a simple shape memory alloy wire that is operated under changing tensile loads. A Preisach operator that incorporates load dependent parameters in the Preisach density function is proposed as the hysteresis model. In support of this selection, a relationship between the Preisach density function and the wire's thermal coefficient of expansion is established. It is then shown that the load dependent Austenite-Martensite transition temperatures of the wire can be used to estimate the parameters of the density function. Based on these findings a load dependent Preisach operator is defined. To test this approach, a bivariate density function that incorporates two load dependent parameters is substituted for the Preisach density function. Two load dependent linear estimators are developed from experimental data and used to estimate the parameters of the density function. These estimators and the load dependent Preisach operator are then used to estimate the length of a SMA wire that is operated under several tensile loads. The estimates are compared to experimental data and a discussion of the effectiveness of this approach is given.
Calculation of the onset and progress of the martenistic transformation using tensorial measures for transformation kinetics
The description of the transformation kinetics during a martensitic phase transition in solids is usually performed by scalar variables for both the thermodynamic force and flux. In a local description at the phase boundary, the movement of the boundary during the martensitic transformation can be described in terms of the second order Eshelby Tensor (or asymmetric chemical potential tensor) and the local orientation of the phase boundary. Transferring this local consideration to a macroscopic description by applying appropriate homogenization techniques, the Eshelby Tensor is introduced as the macroscopic thermodynamic driving force for the phase transformation. Consequently, a second order tensor is introduced as the associated thermodynamic flux. This tensorial description collapses to the classical case for a hydrostatic stress state. A constitutive relation between these tensorial variables is postulated based upon the assumption of the maximization of the dissipation and the existence of a threshold value for the thermodynamic force. Considering shape memory alloys, the onset and progress of the transformation for various thermomechanical loading path is calculated. The influence of the direction and magnitude of the stress and the temperature on the transformation is investigated. Furthermore, restrictions on the choice of the parameters of the model are derived.
The effective electromechanical moduli of ferroelectric crystals with engineered domain configurations
Jiang Yu Li, Dan Liu
We present a micromechanical analysis to explain the enhanced electromechanical properties of ferroelectric single crystals with engineered domain configuration. The theory starts with energy-minimization approach, where all possible energy minimizing domain configurations are characterized as the convex hull of the ferroelectric energy wells, and are constructed by multi-level laminations. The effective electromechanical moduli of ferroelectric single crystal with engineered domain configuration can then be determined exactly by the homogenization theory. Using this approach, we analyzed the engineered domain configuration in tetragonal single crystal BaTiO3 poled in <111> direction, where d33 70% higher than those poled in <001> direction has been demonstrated, consistent with experimental observation. It is also found that the two-variant domain configurations have higher enhancement than three-variant systems, suggesting an optimal domain configuration for the enhanced piezoelectric properties. The theory reveals the fundamental property enhancement mechanism in ferroelectric single crystals with engineered domain configuration, and offers insight on the design and optimization of ferroelectric single crystals with superior functional properties.
Modeling of Active Materials II
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Micro-electromechanically informed phenomenological constitutive models for ferroelectrics
Chad M. Landis, Jianxin Wang, Jianshun Sheng
Accurate phenomenological constitutive laws for ferroelectric ceramics that can be rapidly integrated are required for finite element models aiming to resolve the complex fields in ferroelectric devices. At best, phenomenological theories can provide a framework within which thermodynamic restrictions are satisfied and undetermined functions exist for "fitting" material behavior. The ultimate challenge in deriving a final constitutive law is to capture the physics of the material deformation and polarization processes within these undetermined functions. A number of micro-electromechanical models exist in the literature. These models are bases on domain switching events at the domain/grain level and then are generalized to polycrystalline behavior by averaging over many different domain/grain orientations. In this work it will be shown how information obtained from these micro-electromechanical models can be incorporated directly into the undetermined functions of a phenomenological theory.
Crystal-variant-based modeling of relaxor single crystals
Rhombohedral relaxor single crystals are a class of materials that includes PZN-xPT and PMN-xPT in a certain range of compositions. This work presents an approach to predicting the physical properties of engineered domain state crystals. A model based on the properties of the crystal variants and volume averaging provides a method for determining a full set of the piezoelectric coefficients for the rhombohedral <111> single domain. The model suggests there is a large d15 and the existence of d16 for the <111> orientation cuts of PZN-PT and PMN-PT crystals. The approach has led to the identification of engineered domain states with properties optimized for specific applications such as the large transverse piezoelectric coefficients of the <110> orientation. This cut has optimal properties for actuator and sensor applications that utilize the transverse mode piezoelectric coupling coefficients (d31 and d32).
A micro-electromechanical model of ferroelectric materials with thermal and rate effects
A micro-electro-mechanical model of the behavior of piezoelectric ceramics including thermal, and rate effects is presented and compared to experimental data. Results include analytical and numerical investigations of the behavior of piezoelectric ceramics. The model is based on physical mechanisms and includes elastic, dielectric, and piezoelectric anisotropy. Moreover, the model is based on an internal energy approach so that work-energy relations may be directly applied. Results from the model give insight into material behavior.
Modeling large strain electrostriction of ferroelectrics under combined electromechanical loads
Wei Zhang, Kaushik Bhattacharya
A computational model for investigating domain switching and macroscopic electromechanical properties of ferroelectric materials is developed. Various aspects of domain nucleation and growth, and their effects on macroscopic hysteresis are examined. The model is validated against recent experimental observations. It is thus validated as a design tool to investigate various aspects of a novel thin film ferroelectric microactuator in future work.
Modeling of Active Materials III
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New approach to solving crack tip stress fields for piezoelectric materials
A new technique has been developed which solves the anisotropic stress fields in piezoelectric materials. The technique utilizes orthotropy rescaling by rescaling the coordinate axes in terms of certain elastic, piezoelectric and dielectric material coefficients to obtain the biharmonic equation. The steps which lead to the biharmonic equation require decoupling the stress and electric field components. It is shown that for a certain ratio of dielectric and piezoelectric coefficients, an applied electric field does not change the stress field near a crack tip. The new technique is compared to Stroh's formalism and to finite element modeling.
Polarization switching of ferroelectric polycrystals: finite element modeling and simulations
Sang Joo Kim
A 3D constitutive model for polarization switching in ferroelectric ceramics is presented and implemented into a finite element code. The developed code is used to investigate the nucleation and growth of new domains in a ferroelectric thin film, which is pulsed upward initially and whose bottom electrode is grounded. Then a point on the top surface of the film is subjected to a constant positive electric potential for a certain period of time, leading to a polarization switching downward. The distribution of electric field and polarization are not homogeneous within the film. The evolution of switched zone is calculated and qualitatively compared with experimental observations.
Influence of the fracture process zone in ferroelectrics on the effective fracture toughness
Andreas Ricoeur, Meinhard Kuna
A model is presented to calculate the influence of ferroelectric/ferroelastic domain switching near a crack tip on the effective fracture toughness of piezoelectric ceramics. The switch-toughening effect is quantified in terms of intrinsic field intensity factors accounting for residual fields within the fracture process zone which are due to constraints at the boundary of the switching zone. The intrinsic field intensity factors themselves depend on the external electromechanical loading of the cracked body and thus can clearly be expressed in terms of the intensity factors of the applied loading. These can also account for the effects of an electrical permeability of the crack. The extension of the process zone is calculated using closed-form solutions for the asymptotic crack tip fields in connection with a domain switching criterion. Subsequently, the amount of switch-toughening is calculated applying a weight function technique. Therefore, crack weight functions have been derived for the real anisotropy in piezoelectrics.
Fully three-dimensional incremental model of magneto-elastic hysteresis in terfenol-D
The paper presents an incremental hysteretic magneto-elastic constitutive description of pseudo-cubic ferro-magnetostrictive alloys, which may be used to predict the magneto-elastic response of these materials under quite general applied magnetic field and stress processes. These processes may include fully saturated major loop, unsaturated minor loop or more general types of magnetic field processes. Local stress and domain wall pinning non-uniformities assumed in the development of the model result in smooth and continuous hysteretic magnetization and magnetostriction curves which follow the magnetization and magnetization anhysteretics with a non-constant offset. Comparisons between model results and a set of high quality measurements show that the model is agrees well with experimental curves when the magnetization response is dominated by inhibited domain wall motion.
A general FEM technique to model wave propagation in cellular periodic structures
The paper describes a finite element based technique to model the propagation of elastic waves in cellular periodic structures. The technique can be applied to predict the dynamic response of repetitive structural assemblies, such as honeycombs, network grids part of deployable antennas and space trusses. In the proposed method, the unit cell of the structure is modeled using conventional elements available in commercial finite element codes. The cell finite element model is then duplicated to obtain a representation of real and imaginary fields of the propagating wave. Instead of imposing the Bloch wave conditions using complex number relations between cell edge nodes, a set of equivalent real equations is established as constraint relations to couple real and imaginary domains. This approach is effective and flexible as it can be easily implemented into the meta-parametric languages of commercial finite element codes. Existing Lanczos routines can be used to calculate the phase constant surfaces, the modes of the repeating cells as well as the structure's harmonic response.
Piezoelectric and Magnetic Materials I
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Prestressed curved actuators: characterization and modeling of their piezoelectric behavior
Pre-stressed curved actuators consist of a piezoelectric ceramic (lead zirconate titanate or PZT) sandwiched between various substrates and other top layers. In one configuration, the substrates are stainless steel with a top layer made with aluminum (THUNDER). In another configuration, the substrates and top are based on fiberglass and carbon composite layers (Lipca-C2). Due to their enhanced strain capabilities, these pre-stressed piezoelectric devices are of interest in a variety of aerospace applications. Their performance as a function of electric field, temperature and frequency is needed in order to optimize their operation. During the processing steps, a mismatch between the properties of the various layers leads to pre-stressing of the PZT layer. These internal stresses, combined with restricted lateral motion, are shown to enhance the axial displacement. The goal is to gain an understanding of the resulting piezoelectric behavior over a range of voltages, and frequencies. A nonlinear model, which quantifies the displacements generated in THUNDER actuators in response to applied voltages for a variety of boundary conditions, is developed. The model utilizes a hysteretic electric field-polarization relationship and predicts displacements based on the geometry and physical characteristics of the actuator components. The accuracy of the model and associated numerical method is demonstrated through comparison with experimental data.
Large-stroke low-profile single-crystal piezoelectric actuators
Xiaoning Jiang, Paul W. Rehrig, Wesley S. Hackenberger, et al.
TRS single crystal plates with special crystal orientations and dimensions of 10×5×0.5mm were prepared, and the in-plane strain-electric field behavior was measured using a modified Sawyer-Tower circuit with an LVDT. A d32 coefficient as high as -1600 pm/V was observed which is 60-75% higher than d31 in the conventional cut crystal. The increased performance of this cut can be directly applied to bending mode actuators and other devices that utilize the d31 mode. The strain response was both linear and non-hysteretic up to 15 kV/cm. Large stroke and highly directional strain was also achieved from a quasi-d33 mode single crystal plate with interdigital electrodes (IDE). These were prepared with plate thickness of 0.2 mm, and an effective d33>1000 pC/N was obtained under 10 KV/cm driving field. Both types of plate actuators show at least 5 times larger piezoelectric coefficient than the d31 of PZT materials. Amplified out-of-plane stroke could be easily achieved by integrating the developed thin plate actuators into unimorph, bimorph, or moonie structures.
High-performance tonpilz transducers utilizing d32-cut piezoelectric single crystals
Paul W. Rehrig, Wesley S. Hackenberger, Xiaoning Jiang, et al.
High frequency sonar is becoming ever more important to the Navy through expanded use of unmanned underwater vehicles (UUV). Proposed missions for many UUV's involve shallow water operation where broad bandwidth is required making these applications ideal candidates to use single crystal piezoelectrics. In addition, many UUV sonar systems have commercial uses including oceanographic research, oil and mineral prospecting, salvage, and undersea equipment inspection and maintenance. The properties of single crystal piezoelectrics were exploited for broad bandwidth, high frequency sonar. Crystal sonar investigations based on Tonpilz transducers utilizing the '33' resonance mode have shown limitations on bandwidth due to less than ideal resonator aspect ratio. This is a result of the crystals' low elastic stiffness, which leads to short resonators with large lateral dimensions. To address this issue an alternative design was proposed utilizing the '32' resonance mode with the resonating length oriented along a special crystallographic cut. 'Crystals with this orientation are known to have high properties; d32 values as high as 1600 pC/N have been observed. Since prestress for such a design is applied perpendicular to the poling direction, '32' mode Tonpilz elements exhibit lower loss and higher reliability than '33' mode designs. The feasibility of such '32' mode Tonpilz resonators will be presented as determined through property measurements and finite element analysis. The targeted application for this work is broadband (>100%), high frequency (45 kHz) synthetic aperture arrays for unmanned underwater vehicles.
Characterization of loaded prestressed piezoelectric actuators
Karla M. Mossi, Lisa A. Scott, Shivan Haran
Over the past few years, actuators have been characterized and analyzed under several different boundary conditions. One of these conditions is loading, which plays a critical part in any application where the actuator is used in a structure. This study concentrated on comparing the displacement under load for different types of actuators of the same length and width, but having different layer compositions. The same load and excitation frequency was used at different voltages. Eleven different groups of devices were tested with metal thickness ratios (MTR - ratio of metal thickness to the total thickness) varying between 0.3 and 0.44. The metals used were stainless steel and brass. The results indicated that the devices with an MTR between 0.31 and 0.37 were able to lift a load of 76 grams. All the devices with this MTR had a ceramic thickness of 0.38mm and stainless steel or brass backing. It was also observed that the positive and negative peak displacements were equal for most devices except for the devices with a metal to PZT thickness ratio of 1 showing a negative peak displacement more than 65% higher than positive peak displacement. This may be due to differences in location of the neutral axis, distribution of pre-stresses, and deformations of the devices under load. It was found that the maximum displacement per applied voltage per mm of ceramic thickness was produced by the devices, which had an MTR of 0.33 to 0.37, with no top, and with a ceramic thickness of 0.38mm.
Nonlinear behavior of piezoelectric lead zinc niobate-lead titanate single crystals under AC electric fields
Wei Ren, Shi-Fang Liu, Binu K. Mukherjee
The nonlinear behavior of the dielectric and piezoelectric resopnse of <001> oriented Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT) single crystals for x=4.5% and x=8% have been investigated as a function of AC electric fields and DC bias field. At relatively low applied fields, the polarization and strain of PZN-PT single crystals poled along the <001> direction show little hysteresis and have a linear dependence on the applied field, which is a consequence of engineered domain stability. Hence, the dielectric and piezoelectric coefficients of the material do not exhibit any field dependence. However, when the applied electric field exceeds a threshold value, the strain and dielectric responses become nonlinear. The dielectric and piezoelectric constants are a function of the applied field, and hysteresis loops are observed. The results suggest that the observed nonlinear behavior in the PZN-PT single crystals is caused by domain motion/switching in response to the large AC fields. Applying a positive DC bias can effectively stabilize the domain configuration in the crystals and enhance linear responses. The threshold field, at the onset of nonlinearity, is found to have a linear relation with DC bias field in the field range investigated.
Adhesive characterization in prestressed piezoelectric laminates
Pre-stressed piezoelectric laminates, consisting of one or more metal layers and a piezoelectric material bonded together with an adhesive, have been widely studied over the past few years, both numerically and experimentally. Most of the current research has concentrated on the effect of the metal layers, types and geometry, along with variations in the active layer of the laminate. Historically, the adhesive layer has been neglected as a contributing factor in the overall performance of the final device. This paper attempts to address the effect of the adhesive line thickness and its influence on the performance of pre-stressed piezoelectric laminates under specific boundary conditions. All laminates tested were constructed with the following lay-up: 0.354 mm thick stainless steel, adhesive, 0.381 mm PZT ceramic, adhesive, and a 0.0254 mm aluminum layer. The devices having an adhesive line thickness of 0.169 mm were classified as group A, and group B were the devices with an adhesive line thickness of 0.036 mm. The adhesive line thickness for group A was approximately 21% more than the line thickness of group B. The devices were tested in a simply supported, free-free condition under a series of loads at a constant frequency of 5 Hz over a voltage range from 400 to 800 Volts peak-to-peak. Displacement was measured using loads of 25, 50, 75, 100, and 200 grams for each actuator. The data from each group was averaged and compared. The results showed group B generated more displacement at the same "arm weight" applied as compared to group A. However, only three samples for group B were measured since the rest of the samples failed during testing. Failure of the devices of group B may be due to the ultimate stress of the devices and their ability to lift a load under those conditions. The study demonstrated that adhesive layer thickness, along with the manufacturing process, has to be taken into account when developing an application that requires load-bearing capabilities. Even though no direct mechanical property measurements were taken to verify this theory, the results demonstrated that the adhesive does play a critical role in the performance of the device as an actuator and should be factored into both experimental and numerical studies to obtain more accurate predictions of the ultimate behavior of these devices.
Fabrication of piezoelectric fibers with metal core
Jinhao Qiu, Junji Tani, Naoki Yamada, et al.
A study on the fabrication of Pb(Nb,Ni)O3-Pb(Zr,Ti)O3 (PNN-PZT) piezoelectric ceramic fibers with a metal core is introduced. The green fibers were fabricated by extruding a mixture of PNN-PZT powder and organic solvent together with a 50 mm Pt core. The fibers of 250 mm in diameter and a few centimeters long are obtained without any cracks after sintered at 1200°C. The core is precisely located at the center of the fibers. The boundary of the PNN-PZT ceramics and the Pt core was investigated by cutting the fiber along the cross-section and the longitudinal direction, and observing them with a scanning electron microscope. The ferroelectricity and piezoelectricity of a single fiber was confirmed. The polarization versus electric field relationship was measured by a Radiant RT-6000 and the result exhibits the typical ferroelectricity of the PNN-PZT material. The strain versus electric field relationship also shows the typical hysteresis of piezoelectric materials due to the d31 effect.
Extended-temperature-range piezoactuator system with very large movement
Paul M. Weaver, Andrew Ashwell, Yulan Zheng, et al.
The Servocell planar bimorph actuator employs a very simple novel construction which provides a very large movement (up to 3mm) in a compact profile. It provides solid state actuation for high volume, cost sensitive applications e.g. valves, locks and circuit breakers. Thermal variations in the piezoelectric properties usually result in a compromise in performance, particularly at low temperature. This paper presents new data on the effects of thermal variations in piezoelectric properties on actuator performance. These data are used to devise a control regime which takes advantage of thermal variations in piezo activity to provide a wide operating window across the temperature range -40 to +125°C. It is shown how the stroke of the actuator can actually be increased at lower temperatures. The system is very simple and can thus be implemented using a very low cost microcontroller. The use of the system is illustrated by real life applications in optical switching, valves, locks, and trip mechanisms.
Piezoelectric and Magnetic Materials II
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Microdomains and averaged symmetry in poled Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals
Dwight D. Viehland, Benjamin Ruette, Jie Fang Li
Diffraction investigations have been performed ojn poled 0.75Pb(Mg1/3Nb2/3)O3-0.25PbTiO3 crystals of cubic shape, where each cube face was oriented along a (001)-type plane. Contour small area reciprocal space scans of the three (001) faces of the cube were found to be in-equivalent. The results demonstrate a high micro-domain density within the poled condition, where micro-domain averagign produces monoclinic symmetry.
Dependency of electric field and mechanical stress on piezoelectric strain of PZT 3203HD
Sung Hoon Jang, Young Sung Kim, Sang Ki Lee, et al.
In this paper, material nonlinear behavior of PZT wafer (3202HD, CTS) under high electric field and tensile stress is experimentally investigated and the nonlinearity of the PZT wafer is numerically simulated. In the simulation, new definitions of the piezoelectric constant and the incremental strain are proposed. Empirical functions that can represent the nonlinear behavior of the PZT wafer have been extracted based on the measured piezo-strain under stress. The functions are implemented in an incremental finite element formulation for material nonlinear analysis. With the new definition of the incremental piezo-strain, the measured nonlinear behavior of the PZT wafer has been accurately reproduced even for high electric field.
Measurement of all the elastic, piezoelectric, and dielectric properties of PMN-PT single crystals
Sang-Han Lee, Su-Sung Lee, Yongrae R. Roh, et al.
PMN-PT single crystals have rhombohedral 3m symmetry. In this paper, all the elastic, piezoelectric, and dielectric constants of the PMN-PT single crystals wre measured by the resonance method. For the rhombohedral symmetry, a total ot twelve independent material constants were measured such as six elastic compliance constants at constant electric field, two dielectric constants at constant stress, and four piezoelectric constants d. Seven sets of the crystal samples of each different geometry were prepared for the measurement of length-thickness extensional, thickness extensional, radial, length extensional and thickness shear modes of vibration, respectively. In order to check the validity of the measurement method, the same technique was applied to the characterization of common PZT ceramics. Experimental impedance spectrum of the PZT ceramics was compared with numerical impedance spectrum calculated with measured material constants. The good agreement between the two spectra confirmed validity of the characterization method in this paper.
Analysis of the influence of tiny mirrors and mechanical holder in the interferometric measurements of piezoceramic displacements operating in a kHz range
Gilder Nader, Alessandro Barbosa Shirahige, Emilio C. N. Silva, et al.
Analysis of piezoceramics by using optical systems usually requires reflective surfaces. The usual solution to mirror the piezoceramic surface are the optical polishing with gold deposition, or sticking small rigid mirrors. The former solution is difficult to apply in surface with complex shapes. In the latter solution, by sticking a 200um mirror to the piezoceramic surface, it was detected that when piezoceramic are excited in the kHz range, it behaves as unilaminar actuator. In addition, usually not to much attention is paid to the way the piezoceramic is held in the laser interferometer. However, it was noticed that the measured displacements are also highly affected by the mechanical boundary conditions defined by the piezoceramic holder design. Therefore, in this work, both influences are analyzed by combining experimental and computational techniques, and it is discussed how these problems can be solved by using simple solutions. The experimental results are obtained by using laser interferometer and electrical admittance analysis techniques. These results are compared with computational simulations done by using finite element method in ANSYS software. This comparison was very important since it allowed us not only to detect these problems but also to check and evaluate the experimental set up during tests. Simulations and tests are conducted by considering piezoceramics with and without mirror. These problems are isolated, and separately simulated and studied. Experimental measurements are conducted by considering static and transient (one 10kHz sine cycle) piezoceramic excitation. Experimental and simulated data comparison shows a good agreement, and the effect of the mirror and mechanical holder are successfully understood.
Piezoelectric and Magnetic Materials III
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Computation of fracture toughness of giant magnetostrictive material
Magnetostrictive materials such as Terfenol-D are increasingly being considered for demanding applications such as active noise damping, sonar devices and reactive structures, due to their large strain capability. A limiting factor for the use of magnetostrictive material slies in their inherent susceptibility to brittle fracture. The present study applies finite element technology in support of experimental investigations to assess the mode II fracure toughness of magnetostrictive materials. In this exploratory effort, the fully coupled non-linear behavior of the material is not considered. Rather, a methodology for converting the applied magnetic field to an equivalent mechanical load, based on the material's magnetostrictive properties, is devised and applied. The DSA-VAST finite elemtn software is emlpoyed to model the cylindrical, pre-cracked test specimen using both conventional solid elements and enriched twenty-noded solid fracture elements. Two load cases are investigated, namely one in which a mechanical load is applied to the specimen in the absence of a magnetic field, and a second case in which both a magnetic field and a mechanical load are applied to the specimen. In the absence of an applied magnetic field, the mode II fracture toughenss is found to be approximately 4.497 MPa√m, a value comparable to that reported for ceramic-like materials. On the other hand, in the presence of an applied magnetic field (simulated by an equivalent compressive prestress), the mode II fracture toughness is reduced to 2.768 MPa√m, a significant reduction from the 'zero-field' value. FE results indicate significant specimen bending and an appreciable mode III component to the fracture behavior, both of which are consistent with observed crack growth patterns in laboratory specimens.
Mechanical properties of magnetostrictive iron-gallium alloys
Rick A. Kellogg, Alan M. Russell, Thomas A. Lograsso, et al.
Single crystal specimens of Fe-17 at. % Ga were tested in tension at room temperature. Specimens with a tensile axis orientation of [110] displayed slip lines on the specimen faces corresponding to slip on the {110}<111> with a critical resolved shear stress of 220 MPa. Yielding began at 0.3% elongation and 450 MPa. An ultimate tensile strength of 580 MPa was observed with no fracture occurring through 1.6% elongation. The Young’s modulus was 160 GPa in the loading direction with a Poisson’s ratio of -0.37 on the (100) major face. A specimen with a tensile axis orientation of [100] showed slip lines corresponding to slip on the {211}<111> with critical resolved shear stress of 240 MPa. Discontinuous yielding began at 0.8% elongation, which was thought to result from twinning, kink band formation, or stress-induced transformation. The Young's modulus was 65 GPa in the loading direction with a Poisson’s ratio of 0.45 on the (001) major face. A maximum tensile strength of 515 MPa was observed with fracture occurring after 2% elongation. A sizeable elastic anisotropy of 19.9 was identified for Fe-27.2 at. % Ga accompanied by a Poisson's ratio of -0.75 to produce a large in-plane auxetic behavior.
Poster Session
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High-field behavior of piezoelectric fiber composites
Luke J. Nelson, Chris R. Bowen, Ron Stevens, et al.
This paper analyses strain and polarisation responses of 1-3 composites, which are related to the fibre and matrix properties. The validity of equations that predict the strain and polarisation of fibres from composite responses, and associated errors at high electric driving fields, are discussed. Surface profile measurements of single PZT rods in a polymer matrix, subjected to a static voltage, were made to investigate the effect of fibre aspect (diameter to length) ratio. Surface profiles, which show the active PZT rod extending from the passive polymer matrix, agree well with predictions made using finite element analysis. The results show that for a 1-3 composite to be treated as a homogeneous medium the fibre aspect ratio needs to be low. Commercially available PZT-5A composition fibres fabricated using four production methods were incorporated into 1-3 composites with fibre volume fractions ranging from 0.02 to 0.72, and with various aspect ratios, were evaluated. Strain-field and polarisation-field curves for the composites were obtained by testing the composites under electrical field cycles of ±2 kVmm-1. From these curves the strain and polarisation response of the fibres have been extracted using appropriate analytical equations. The saturation strain, saturation polarisation and coercive field values are reported for the four fibre types. The Viscous Plastic Process (VPP) and Viscous Suspension Spun (VSSP) fibres develop strains of approximately 4000 ppm. Reduced piezoelectric activity is seen in extruded fibres, which develop strains of 3000 ppm.
Modeling and measurement of piezoelectric fibers and interdigitated electrodes for the optimization of piezofibre composites
Luke Nelson, Chris Bowen, Ron Stevens, et al.
Commercially available PZT-5A composition fibres fabricated using four production methods were incorporated into 1-3 composites with fibre volume fractions ranging from 0.02 to 0.72. Measurements of the piezoelectric induced strain constants (d33 and d31), relative dielectric constants (e33), longitudinal coupling factors (k33) and stiffness' (s33) of the varying volume fraction composites are compared to analytical expressions in order to extract the fibre properties. Results show 1-3 composite data accurately follows the analytical trends. The Viscous Plastic Process (VPP) fibres are found to exhibit optimum material properties, which approach bulk material values. Reduced piezoelectric activity in extruded fibres is thought to be associated with a small grain size and high porosity. A second study, an optimisation of interdigitated electrode design, was performed using the finite element software ANSYS. The effect of the IDE geometry (electrode width and spacing) and PZT substrate thickness on the strain output of bulk PZT substrates was modelled. Results show optimal actuation occurs at electrode widths equal to half the substrate thickness, and for thin substrates the electrode finger spacing can be reduced to enable lower driving voltages.
Direct numerical simulation of active fiber composite
Seung Jo Kim, Joon Seok Hwang, Seung Hoon Paik
Active Fiber Composites (AFC) possess desirable characteristics for smart structure applications. One major advantage of AFC is the ability to create anisotropic laminate layers useful in applications requiring off-axis or twisting motions. AFC is naturally composed of two different constituents: piezoelectric fiber and matrix. Therefore, homogenization method, which is utilized in the analysis of laminated composite material, has been used to characterize the material properties. Using this approach, the global behaviors of the structures are predicted in an averaged sense. However, this approach has intrinsic limitations in describing the local behaviors in the level of the constituents. Actually, the failure analysis of AFC requires the knowledge of the local behaviors. Therefore, microscopic approach is necessary to predict the behaviors of AFC. In this work, a microscopic approach for the analysis of AFC was performed. Piezoelectric fiber and matrix were modeled separately and finite element method using three-dimensional solid elements was utilized. Because fine mesh is essential, high performance computing technology was applied to the solution of the immense degree-of-freedom problem. This approach is called Direct Numerical Simulation (DNS) of structure. Through the DNS of AFC, local stress distribution around the interface of fiber and matrix was analyzed.
Comparison of martensite transformation temperatures in a NiMnGa alloy determined with hot/cold stage optical microscopy and differential scanning calorimetry
Calvin V. Hyatt, Shannon P. Farrell, Bob Armstrong, et al.
The martensite transformation temperatures of both as-grown and heat-treated specimens removed from a Bridgman grown boule of off-stoichiometric Ni2MnGa were determined by differential scanning calorimetry (DSC) and hot/cold stage microscopy. The work showed that martensite start and austenite finish transformation temperatures determined by the hot/cold stage microscope technique were in agreement with those determined by the DSC method. The hot/cold stage microscope technique was shown to be useful for characterizing variations of transformation temperature across a specimen. The results revealed that residual stress, deformation and boule composition variations produce artefacts in DSC traces which need to be identified, understood and controlled. Transmission electron microscope results suggest that the possible contribution of a premartensitic transformation to the high temperature edge of the martensite peak on DSC scans needs further investigation.
Effect of crystal structure on magnetic-field-induced strain in Ni-Mn-Ga
Magnetic shape memory materials are expected to have a high potential in practical applications. Several ferromagnetic materials exhibiting the large magnetic-field-induced strain have been found in recent years. The largest field-induced strain is observed in Ni-Mn-Ga system. The most important experimental results on crystal structure, magnetic anisotropy and twinning stress of martensitic phases in Ni-Mn-Ga having tetragonal five-layered, orthorhombic seven-layered and tetragonal non-layered crystal structures are reported. Depending on the martensite crystal structure Ni-Mn-Ga alloys are able to show a really giant strain response (approximately 6% in tetragonal five-layered or 10% in orthorhombic seven-layered martensitic phase) in a magnetic field less than 1 T. Contrary to these two phases, a detectable field-induced strain is not observed in non-layered tetragonal martensitic phase in Ni-Mn-Ga system. Effect of crystal structure is in a good agreement with calculation of the magnetic-field-induced strain based on the model developed by authors. The effect of composition on appearance of undesirable non-layered tetragonal martensitic phase in Ni-Mn-Ga system is discussed based on the new experimental results.
Elasticity of austenitic and martensitic NiMnGa
Liyang Dai, Jun Cui, Manfred R. Wuttig
The elasticity of both the austenite and martensite states of a NiMnGa Heusler alloy was investigated by using a continuous wave method. A magnetic field was used to detwin the martensite. The symmetrized elastic constants of both austenite and martensite were determined by exiting different modes of wave propagation. In austenite, the shear elastic constant (C11-C12)/2 equals 7Gpz, which means the alloy is very soft as is typically the case in near second order shape memory alloys. Similarily, in martensite, (C11-C12)/2 equals 9GPa. Moreover, in the martensitic state the two rhombohedral elastic constants, C44 and C66, equaling 51GPa and 49GPz, respectively are almost the same.
Shape Memory Alloys and Magnetic Shape Memory Alloys III
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Dynamic response of a frame with SMA bracing
Shuangshuang Sun, R. K. Nimal D. Rajapakse
This paper investigates the dynamic response of a frame structure with pre-strained SMA bracing elements. The constitutive model proposed by Brinson is used to simulate the axial response of SMA bracing elements. A non-linear transient finite element model incorporated with Newmark's time integration scheme is used to analyze the dynamic response of a structure. The time histories of displacements and hysteresis loops of SMA tendons are computed under harmonic loading. The effect of forcing amplitude and initial pre-strains of SMA tendons on transient dynamic response of a structure is discussed. The suitability of pseudoelastic SMA for energy dissipation is briefly discussed.
Poster Session
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Dynamic deformation in MR elastomer driven by magnetic field
Gang Yi Zhou, Zhen Yu Jiang
Magnetorheological Elastomer (MRE) is a new class of smart materials, whose modulus can be controlled by applied magnetic field. In this paper, we first show the field-dependent dynamic mechanical properties including shear and stretch of the MRE, cured by ourselves. By white light speckle method for deformation analysis, we present the dynamic deformation progress (the vector diagram of displacement or the whole-field quantitative displacement distribution, at various times) of the MRE and the elastomer-ferromagnetic composite (EFC) while the magnetic field turns on. The real-time deformation progress gives us a deep understanding to MRE and EFC.
Fatigue life characterization of shape memory alloys undergoing thermomechanical cyclic loading
Olivier W. Bertacchini, Dimitris C. Lagoudas, Etienne Patoor
This paper presents a study on the fatigue life of shape memory alloy actuators undergoing thermally induced martensitic phase transformation under various stress levels. A microstructural study characterizing specific damage patterns is conducted in the current work. A highly stressed state with formation of different types of microcracks has been observed, showing a superficial micro cracking, responsible for the growth of circular cracks localizing the failure of the specimens. The influence of the interactions between the micro cracking pattern and the corrosion occurrence is also studied. Finally, a spallation oxidation occurring at the surface of the actuator, which damages its properties, is also investigated. The failure pattern observed provides information necessary to introduce a correction to the classical Wohler curve for fatigue life of a material undergoing cyclic loading.