Proceedings Volume 4699

Smart Structures and Materials 2002: Active Materials: Behavior and Mechanics

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Proceedings Volume 4699

Smart Structures and Materials 2002: Active Materials: Behavior and Mechanics

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Volume Details

Date Published: 11 July 2002
Contents: 12 Sessions, 56 Papers, 0 Presentations
Conference: SPIE's 9th Annual International Symposium on Smart Structures and Materials 2002
Volume Number: 4699

Table of Contents

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Table of Contents

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  • Ferroelectric Materials
  • Reliability of Ferroelectrics
  • Characterization of Ferroelectrics
  • Characterization and Modeling of Active Materials
  • SMA and MSMA Materials I
  • SMA and MSMA Materials II
  • Actuators and Actuator Technology
  • Modeling of SMA
  • Coupled Construction Behavior: SMA
  • Magnetostrictive and Ferromagnetic Materials
  • Navy Transducer Materials and Design
  • Transducer Materials
  • Coupled Construction Behavior: SMA
  • Transducer Materials
Ferroelectric Materials
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Behavior of relaxor single crystals
The constitutive behavior of relaxor rhombohedral single crystal is discussed in terms of the constitutive behavior of crystal variants. The domain engineered cut gives rise to a stable domain state. Resulting crystal behavior is described. The cut and poled single crystal should display the volume average behavior of single domain crystal variants, but comparison of a crystal variant model with measured properties leads to the identification of inconsistencies. Several possible reasons for these inconsistencies are discussed.
Thermodynamically and microscopically motivated constitutive model for piezoceramics under uniaxial loading
Marc Kamlah, Qing Jiang
Our aim is the motivation of a macroscopic constitutive model for engineering reliability analysis of piezoceramic components designed for so-called ``smart'' electromechanical sensor and actuator applications. Typically, such components are made of ferroelectric ceramics, mostly PZT or modified PZT ceramics, which exhibit significant history-dependent nonlinearities such as the well known dielectric, butterfly, and ferroelastic hystereses due to domain switching processes. Following an approach proposed previously by the authors (Smart. Mater. Struct. 9(1999), 441 - 459), we first propose a constitutive framework capable of representing general thermo-electromechanical processes. This framework makes use of internal variables and is thermodynamically consistent with the Clausius-Duhem inequality for all admissible processes. Next, we focus on uni-axial electromechanical loadings and introduce microscopically motivated internal variables and their evolution equations. In order to verify the underlying assumptions, we discuss the numerically calculated model response to standard electromechanical loading paths. This model is capable of reproducing the aforementioned typical hysteresys phenomena and mechanical depolarization as well as other nonlinear electromechanical coupling phenomena. Furthermore, the model response exhibits rate-dependence, which is typical in the response of ferroelectric ceramics.
Constitutive and finite element modeling of ferroelectric repolarization
Hannes Kessler, Marc Kamlah, Herbert Balke
Our aim is the motivation of a macroscopic constitutive model for engineering reliability analysis of piezoceramic components designed for so-called 'smart' electromechanical sensor and actuator applications. Typically, such components are made of ferroelectric ceramics, mostly PZT or modified PZT ceramics, which exhibit significant history-dependent nonlinearities such as the well known dielectric, butterfly, and ferroelastic hystereses due to domain switching processes. Following an approach proposed previously by the authors, we first propose a constitutive framework capable of representing general thermo-electromechanical processes. This framework makes use of internal variables and is thermodynamically consistent with the Clausius-Duhem inequality for all admissible processes. Next, we focus on uni-axial electromechanical loadings and introduce microscopically motivated internal variables and their evolution equations. In order to verify the underlying assumptions, we discuss the numerically calculated model response to standard electromechanical loading paths. This model is capable of reproducing the aforementioned typical hysteresys phenomena and mechanical depolarization as well as other nonlinear electromechanical coupling phenomena. Furthermore, the model response exhibits rate-dependence, which is typical in the response of ferroelectric ceramics.
New finite element formulation for electromechanics
A new finite element formulation for the solution of electromechanical boundary value problems is presented. As opposed to the standard formulation that utilizes a scalar electric potential as nodal variables, this new formulation implements a vector potential from which components of electric displacement are derived. For linear piezoelectric materials with positive definite material moduli, the resulting finite element stiffness matrix from the vector potential formulation is also positive definite. If the material is nonlinear in a fashion characteristic of ferroelectric materials, it is demonstrated that a straightforward iterative solution procedure is unstable for the standard scalar potential formulation, but stable for the new vector potential formulation. Finally, the method is used to compute fields around a crack tip in an idealized non-linear ferroelectric material, and results are compared to an analytical solution.
Reliability of Ferroelectrics
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Fatigue effect in bulk ferroelectrics
Vladimir Ya. Shur, Evgenii L. Rumyantsev, Ekaterina Nikolaeva, et al.
We have used a kinetic approach to the fatigue phenomenon in ferroelectrics for the analysis of the evolution of switching current and strain hysteresis loops in bulk PZT ceramics and the switching current in PZN-PT single crystals during cyclic switching. It is proposed that fatigue is due to a redistribution of the local internal bias field during cycling (spatially non-uniform imprint effect). The model considered is based on the fact that during cycling the ratio of the states with opposite direction of polarization ranges over the sample area. The local value of this ratio defines the change of the internal bias field at the given point during the switching cycle considered. Thus the spatial distribution of the internal bias field depends on the domain evolution prehistory. We have investigated by computer simulation the self-consistent change of the internal bias field distribution function with cycling, which leads to fatigue. The mathematical treatment of the switching current data allows us to extract the information about the evolution of the field distribution function. The fatigue-induced change of the strain loops is explained by a strong unipolarity of the growing frozen domain area, which has been predicted by our simulations. The analysis of experimental data confirms the validity of our model.
Observation of fatigue crack growth in ferroelectrics under electrical loading
Jay Shieh, Norman A. Fleck, John E. Huber
Fatigue crack growth is studied in PZT-5H and PLZT 8/65/35 ferroelectric ceramics under purely electrical cyclic loading. The growing cracks are intergranular and exhibit features such as bifurcation, tunneling, arrest and bursts of rapid growth. Two ferroelectrics show different cracking behaviors once the crack growth commences - the crack growth rate in PZT-5H decreases with the number of cycles, whereas for PLZT 8/65/35, a period of rapid steady-state crack growth is typical. A band of damaged material forms around the crack and propagates through the ceramic. The thickness of this band of damaged material is directly proportional to the strength of the applied electric field. Crack growth measurements are presented for two ferroelectric compositions under varying load amplitude and with varying frequency and test geometry. Potential mechanisms underlying the fatigue behavior include cracking at local stress concentrations due to inhomogeneity at the grain length scale, a wedging mechanism in the crack wake, the action of the crack as a field intensifier, and the degradation of a actuating mechanism.
Modeling of electrode-ceramic interaction in a multilayered ferroelectric actuator
Xianwei Zeng, R. K. Nimal D. Rajapakse
Introduction of electrode termination between neighboring ceramic layers in multilayer stack actuators leads to incompatible deformation between the active and inactive parts of ceramic layers and results in highly concentrated electric and stress fields at an electrode tip, which promote the nucleation and propagation of cracks around an electrode tip as revealed in previous experiments. To understand the mechanism of cracking around an embedded electrode tip, the singular electroelastic field at an embedded electrode tip in a multilayer ferroelectric actuator is studied using the extended Leknitskii's formalism together with the analytic continuation technique. It is found that both mode-I and mode-II stress intensity factors vanish at an electrode tip and consequently the singular near-tip electric and stress fields can be uniquely characterized by an electric field intensity factor. Furthermore, the effect of polarization switching on near- tip electroelastic field is also estimated in this study with the aid of a fundamental solution for a semi-infinite electrode at the interface of two-bonded half-planes interacting with transformation strains and polarization. Due to domain switching, the magnitude of near-tip field can be increased or decreased by as much as seventy percent depending on the angle between an applied electric field and the poling direction of ceramic layers. The elevated stress field developed at an electrode-ceramic due to an applied electric field can lead to interfacial debonding and segmentation cracking.
Domain switching near crack tip in piezoceramics
Sureshkumar Kalyanam, Chin-Teh Sun, D. N. Fang
Domain switching near the crack or notch tip is important in the study of fracture in piezoelectric materials. The ABAQUS finite element piezoelectric element was used in conjunction with the domain switching code developed for prediction of domain switch zone by performing a nonlinear analysis. Domain switching zones in the vicinity of the crack tip were obtained using the work and energy density criteria corresponding to combined electrical and mechanical loads. Comparison is made to indicate the differences in the prediction by the two domain switching criteria. Experiments are conducted with uniform single crystal BaTiO3 and notched single crystal BaTiO3. The difference in the intensity of the polarized light is used to identify the out-of-plane domains and the in-plane domains.
Characterization of Ferroelectrics
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Determination of plastic strains from compression tests including the effect of change of Young's modulus
Theo Fett, Marc Kamlah, Dietrich Munz, et al.
Under compressive loading piezoelectric material shows an interesting change of Young's modulus with increasing compressive strain. This effect is of importance for the determination of plastic strain contributions of stress- strain curves in compression test. Two different possibilities are considered to define plastic strain contributions. To obtain Young's modulus, partial unloading test were performed on a soft PZT material. The applied load was measured with a DC load cell and the related strains were obtained by a pair of strain gauges. In addition to the continuously increased external load small pulse-shaped partial unloadings of about 1 MPa were superimposed. Young's modulus was found to be variable during the mechanical test and increased from 40-70 MPa up to about 130-150 Gpa.
Fabrication of high-performance PNN-PZT ceramic using microwave and hot-press hybrid sintering process
Hirofumi Takahashi, Jinhao Qiu, Junji Tani, et al.
It has been reported in the author's previous work that the hybrid sintering process, a combination of 28GHz microwave heating and hot-press, yields higher performance in the sintering of PZT ceramics than conventional technologies. The improvement of properties with the hybrid sintering process is due to the increase in the grain size and due to the suppression of Pb evaporation on account of reduction in sintering time. In this study, the hybrid sintering process was applied to the fabrication of PNN-PZT and the influence of the pressure and sintering temperature on the density, electro-mechanical coupling factor and the piezoelectric constants of the sintered specimens were extensively investigated. In the optimized sintering conditions, the maximum achieved value of the piezoelectric constant d31 was about 390 X 10-12 m/V, which is nearly 26 percent high than 310 X 10-12 m/V, the value of d31 of the conventionally sintered specimen. It can be concluded that the hybrid sintering process is an effective means to improve the performance of the materials of Pb extraction.
Modeling of the dynamic effective characteristics of fiber reinforced transversely isotropic piezoelectric materials
Valery M. Levin, Thomas M. Michelitsch, Huajian Gao
So far the modeling of the effective material characteristics of piezocomposites was mainly studied in the framework of statics. Due to the increasing need of piezocomposites for dynamic applications, e.g. as transducers or ultrasonic applications, the modeling of the dynamic effective material characteristics has become highly desirable. To this end the electroacoustic wave propagation in a piezoelectric medium reinforced by a statistical ensemble of cylindrical fibers is considered. Both, the matrix and the fiber material is assumed to be piezoelectric with transversely isotropic symmetry with symmetry axes parallel to the fiber axes. In this model system for a fiber reinforced piezocomposite, special emphasis is given to the propagation of an electroacoustic axial shear wave polarized parallel to the axis of symmetry propagating in the direction normal to the fiber axis. Using the solution of the scattering problem for one isolated fiber the homogenization problem for a piezoelectric medium containing a random set of fibers is performed in the framework of a self consistent scheme of the effective field method. Closed form expressions for the dynamic characteristics as total cross section, electroelastic moduli, effective wave velocity, effective wave vector and attenuation factor are obtained in the long-wave approximation.
Integration, electrical, and electromechanical properties of PZT and PMN-PT thin films for MEMS applications
Carsten Kuegeler, Marcus Hoffmann, Ulrich Boettger, et al.
Piezoelectric and electrostrictive thin films are potential candidates for actuator functions in micro-electro-mechanical systems (MEMS) offering displacements and forces which outperform standard solutions, e.g. in micro mirrors and micro relays. Within this context the paper reports on the preparation and the integration processes of chemical solution deposited (CSD) PZT and PMN-PT thin films in combination with silicon bulk micro machining technique. The operativeness of the processes is demonstrated by the development of an integrated micro actuator for a micro switch application. Furthermore, the work deals also with the characterization of the integrated materials. For fabrication control and electrical characterizations microscopy, SEM, hysteresis- and CV-, and degradation measurements were performed. Laser interferometry and resonance frequency measurements were used to characterize the electromechanical performance of both materials in comparison to the behavior of the developed micro actuator.
Compression of PZT-5H piezoelectric ceramic at constant electric field: investigation of energy absorption mechanism
This paper presents an experimental and analytical investigation into the mechanical behavior of PZT-5H piezoelectric ceramic. The materia is subjected to cyclic uniaxial compressive stress at a constant electric field bias. The damping characteristics such as fraction of energy absorbed and elastic modulus are evaluated as a function of bias electric field. Increasing the positive electric field increases the specific damping and decreases the elastic modulus. The trend is reversed when the electric field becomes sufficiently high to inhibit the domain wall motion by the mechanical stresses. Measured specific damping values vary form 0.18 to 0.46 depending on the stress amplitude and bias electric field. The corresponding secant modulus varies from 79 to 24 Gpz. The optimum electric field values increase as the stress amplitude increases because the positive electric field and the compressive stress counteract each other in terms of domain wall motion. An analytical model shows that the material's response is proportional to the volume fraction of the domains available for switching and the domain wall pressure difference between positive electric field and compressive stress.
Characterization and Modeling of Active Materials
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Multiaxial response of hard and soft ferroelectrics under stress and electric field
John E. Huber, Jay Shieh, Norman A. Fleck
Samples of soft PZT-5H, hard PZT-4D and Barium Titanate were subjected to multi-axial loading in stress and electric field space. The loading paths were: (1) Poling with electric field, followed by repolarizing with electric field at an angle to the original poling direction. (2) Proportional loading with electric field and coaxial compressive stress, the proportions of stress and electric field being varied between tests. In case (1) the poled material was cut to produce faces angled to the original poling direction. The measured material responses are reported and initial switching surfaces are calculated based on an offset from linear response in electric displacement. The measurements are used to assess the features required in micromechanical or phenomenological models of switching.
Modeling of nonlinear piezoelectric behavior
Ajit Achuthan, Chin-Teh Sun
A finite element model for the nonlinear behavior of piezoelectric material is developed. Important issues in modeling the nonlinear behavior of piezoelectric material at micro-scale is discussed and methods to solve such issues are proposed. A procedure is developed to obtain RVE from the simplified microstructure of the material. The RVE is obtained based on a statistical parameter, which is a measure of the degree of heterogeneity at a point. The material properties at the micro-scale are obtained from the macro-scale properties by rule of mixture approach. A finite element iterative solution procedure is then used to model the material behavior by averaging the local response over the entire RVE. Nonlinear behavior of the material is due to the domain switching phenomenon and is simulated based on internal energy density based switching criterion. A numerical example is given for PZT-4 material and the results agree qualitatively with the experimental results.
Next-generation electroceramic fibers for active control
Pavel Bystricky, Marina R. Pascucci, Harold B. Strock
Lead-based PMN-31PT and lead-free BNBZT fibers in the 250- 500 micrometer diameter range were produced using CeraNova's proprietary extrusion technology. Various recrystallization approaches were investigated, including seeded solid state conversion and self-seeded texturing, with the goal of obtaining single-crystalline or textured macrocrystalline fibers. Grains in excess of 100 micrometers - and exceeding 1 mm in some cases - with surface and bulk coverage approaching 100 percent, were obtained in a narrow temperature range and under carefully controlled atmosphere conditions. Large grain growth in BNBZT required the presence of BaSrTiO3 or SrTiO3 seeds and temperatures in the 1150-1200 degrees C range. In PMN-31PT, nearly compete recrystalline was observed in unseeded material at relatively low temperature and short time, and improved performance was achieved with a two-step sintering schedule and slightly extended time. While conduction effects have not yet allowed compete assessment of recrystalline BNBZT, PMN-31PT fibers have shown excellent piezoelectric properties with remanent polarization in excess of 30(mu) C/cm2 and coercive field of 4.5kV/cm. When incorporated into active fiber composites, the latter fibers' performance of 2000 microstrain in superior to average PZT-based production composites. Efforts are under way to induce preferred orientation in the large crystal in order to maximize performance.
AC magnetic-field-induced strain of single-crystal Ni-Mn-Ga
The dynamic field-induced strain response at 2Hz is reported for a ferromagnetic shape memory alloy (FSMA), Ni49.8Mn28.5Ga21.7. For the d31 actuation mode, longitudinal strain response was measured as a function of longitudinally applied bias stress and transverse applied field. Under a 1.5MPa compressive bias stress, dynamic strains of 2.6% were achieved at fields of 6 kOe. However, dynamic field-induced strain is largely blocked under a compressive bias stress of 4.2MPa. The 'coercive field' hysteresis in the field versus strain loops was observed to be as low as 100kA/m at 1.5MPa and increase linearly at greater stresses. Peak piezomagnetic d31 coefficients measured from these field versus strain loops approached 1.3 X 10-7 m/A. Dynamic stress versus strain loops were recorded for compressive bias stresses from 0 to 4.2MPa. Stiffnesses of approximately 40MPa in the active twinning stress range were recorded, and the stiffness approached 5 times the twinning stiffness beyond the twinning range. The mechanical loss measured in stress versus strain loops, when normalized to the output strain, resulted in a linear increase of 6.84 kJ/m3 per MPa bias stress. Current investigations are attempting to isolate the factors that contribute to the extraordinary behavior exhibited in these properties of the Ni-Mn-Ga system.
Design of ferromagnetic shape memory alloy composites based on TiNi for robust and fast actuators
Yasuhiro Matsunaga, Tetsuya Tagawa, Taishi Wada, et al.
Recently, ferromagnetic shape memory alloys (FSMAs) attracted strong attentions due to their fast actuation with relatively large strain. However, the mechanical properties of popular ferromagnetic shape memory alloys are found to be lower than TiNi alloys. A TiNi has high mechanical performances, large transformation strain and stress capability. On the other hand, the speed of TiNi alloys actuated by changing temperature is usually slow. Thus use of a ferromagnetic material is attractive in utilizing it for induction of magnetic force at high speed. If we combine both merits of TiNi and ferromagnetic material, we can design a new ferromagnetic SMA composite. The actuation modes examined here are plate bending and bar torsion, where the stress and strain across thickness direction change linearly with position. The outer layers that are subject to the larger strain are the superelastic TiNi, which sandwich the inner layer of a ferromagnetic material. The force activated in the ferromagnetic layer from the applied magnetic field causes the phase change in the superelastic TiNi layer, i.e. from austenite to martensite, thus the softening of stiffness of TiNi leads to large displacement.
Thermomechanical characterization and development of SMA-embedded CFRP composites with self-damage control
Byung-Koog Jang, Ya Xu, Ryutaro Oishi, et al.
The focus of this work is the thermomechanical characterization and effect of damage recovery on the pre-strained SMA wire embedded CFRP composites for developing the smart composites with self-damage control. The SMA utilized in this work is a Ni-45at percent Ti wire with a diameter of 0.4 mm. A steel mold was specially designed to embed the pre-strained TiNi wire into CFRP preperg and prevent their recovery during the cure cycle. TiNi/CFRP composites were fabricated by hot-pressing in the temperature range of 150-180 degrees C by controlling the applied pressure. The overall research is divided into four parts: fabrication of SMA wire embedded CFRP composites, experimental characterization of thermomechanical behavior on SMA wire by electrical heating, recovery effect of self-damage control in composites and sensing effect by detecting the electrical resistance at SMA wire. Compressive recovery force induced by thermomechanical actuation of SMA depends on pre-strained level and volume fraction of TiNi. The hot-pressed TiNi/CFRP specimens were loaded under tensile test in order to induce a transverse crack or partial damage. Specially, transverse crack easily happen at 90 degrees stacking CFRP layers. The damage degree due to generation of transverse cracks is quantified by real-time measurements of electrical resistance of SMA in composites during tensile load. After electrical heating, the generated transverse cracks at composites successfully repaired due to compressive force introduced by pre-strained TiNi wires and resulting in the self-damage recovery effect.
Pulsed magnetic field actuation of single-crystalline ferromagnetic shape memory alloy Ni-Mn-Ga
Miguel A. Marioni, David Bono, Robert C. O'Handley, et al.
Ferromagnetic shape memory alloys can exhibit magnetic-field-induced strains of several percent at room temperature. These strains have been shown to correlate with the motion of twin boundaries in the crystals. Twin boundaries advance by the motion of stacking faults along the twin boundary. Such mechanical defects have as an upper limit of their velocity, the speed of sound. It is an important matter to understand the mobility of twin boundaries in ferromagnetic shape memory alloys from a scientific perspective. Namely, how does their velocity depend on field strength, crystal structure and perfection, what are the roles of inertia and threshold field, and does the velocity ever approach anything like the speed of sound. From a practical point of view, it is important to know the twin boundary dynamics in order to understand the bandwidth capabilities of these new active materials as well as their response to different field wave forms that may optimize the response for particular applications. In the present paper we describe a pulse field experimental setup and preliminary results that begin to address the issues raised above.
SMA and MSMA Materials I
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Crystal structure, magnetic anisotropy, and mechanical properties of seven-layered martensite in Ni-Mn-Ga
Magnetic-field-induced strain of about 10 percent is reported in Ni48.8Mn29.7Ga21.5 alloy at ambient temperature in a magnetic field order of 1 T. It was confirmed by different experimental methods that the strain is contributed by twin boundary motion. The crystal structure of thermally-induced martensitic phase in this alloy was found to be close to orthorhombic one in temperature range from 245 K to 333 K with lattice parameters a equals 0.619 nm, b equals 0.580 nm, c equals 0.553 nm (relating to the cubic parent phase coordinates) at ambient temperature. More detailed x-ray studies revealed seven-layer shuffling-type modulation along and directions. High magnetic anisotropy properties were found for this phase. The magnetic measurements revealed that the shortest axis (c-axis) is the axis of easiest magnetization, the longest (a-axis) is the axis of hard magnetization, and b-axis is the intermediate one. The orthorhombic phase has low twinning stresses. The compressive stress applied along a-axis of single-variant sample at most 2 MPa is enough to produce approximately 10 percent strain realized by twin boundary motion. The necessary conditions for observation a giant magnetic-field-induced strain in non-stoichiometric Ni2MnGa alloys based on the new experimental data are discussed.
Model calculation of the stress-strain relationship of polycrystalline Fe-Pd and 3D phase transformation diagram of ferromagnetic shape memory alloys
Robert Liang, Taishi Wada, Tetsuya Tagawa, et al.
A micromechanics approach is proposed to calculate the stress-strain relationship of a polycrystalline Fe-Pd ferromagnetic shape memory alloy. It is modeled as consisting of spherical grains, which are grouped according to their orientations with respect to the loading axis. Therefore, the internal stress and elastic energy are accumulated as straining proceeds due to the strain differences between differently oriented grains. In the present study, the energy dissipation of the interface movement is also considered. Furthermore, a stress-magnetic field-temperature phase transformation diagram is constructed. The magnetic field induced transformation is found to be insignificant based on thermodynamics model. The cases of Fe-Pd and NiMnGa systems are examined for 3D phase transformation diagram.
Influence of target temperature on sputter deposited Ti-Ni-Cu and Ti-Ni-Pd shape memory alloys
Ti-Ni-Cu and Ti-Ni-Pd films are deposited on Si < 100 > substrate by d.c. magnetron sputtering technique. In this paper, the influence of target temperature on the properties of the film is discussed. The target temperature transitions from a low temperature value to a high temperature value during sputtering. As grown Ti-Ni-Cu films are amorphous and are crystallized by heating at 500 degreesC for 20 minutes in situ prior to removal from the sputtering system whereas, as grown Ti-Ni-Pd films are crystallized at 550 degrees C for one hour. DSC and electrical resistivity measurements are used to determine the transformation temperature whereas, TEM and XRD are used for structural characterization and composition of the film is determined by using EDAX. We find that the transformation temperatures and the shape memory characteristics are strongly influenced by target temperature. The films show more uniform stoichiometry if the target is hot during deposition.
SMA and MSMA Materials II
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Effect of transformation induced plasticity on the mechanical behavior of porous SMAs
Dimitris C. Lagoudas, Pavlin B. Entchev, Eric L. Vandygriff
The fabrication of porous NiTi Shape Memory Alloy (SMA) from elemental Ni and Ti powders using Hot Isostatic Press (HIP) is presented in this work. Porous NiTi alloys with different porosity levels and different mechanical properties are obtained and analyzed. Their behavior under compressive mechanical loading is modeled using a micromechanical averaging model. The model treats the porous NiTi alloy as a two-phase composite: dense SMA matrix and pores. The behavior of the fully dense SMA matrix is modeled using a thermomechanical model with internal state variables. The development of transformation and plastic strains during the martensitic phase transformation is taken into account. The results from the model are compared with the experimental data.
Cobalt-base ferromagnetic shape memory alloys
Corneliu M. Craciunescu, Yoichi Kishi, Marc De Graef, et al.
Single crystalline and polycrystalline CoxNiyGa100-(x+y), 41 < xCo< 62 and 19.3 < yNi < 32.7, Ferromagnetic Shape Memory Alloys have been produced in the range of the Heusler-type composition. Elasto-mechanical properties have been analyzed for the annealed and quenched states, respectively. The mechanical spectroscopy data show the occurrence of martensitic phase transformation with the transition range and characteristics depending on the state and the composition of the alloys. For XCo approximately equals 49 +/- 1 at percent, the Ni/Ga ratio was shown to be in direct relationship with the transition temperature range, from an Ms of -100 degrees C for Ni/Ga approximately equals (21/29) to a +150 degrees C for a Ni/Ga ratio of about (26/25). For Ga approximately equals 27 +/- 0.4 at percent, the Co/Ni ratio is in indirect relationship with the transition temperature, with an Ms of -125 degrees C for a (53/19) ratio to a +175 degrees C for a ratio of about (49/26). Optical and electron microscopy shows that a typical thermoelastic martensitic transformation occurs. The L21 Structurbericht parent phase transforms into monoclinic or orthohombic martensitic upon cooling. The formation of a Co-rich phase has been observed for alloys with lower Ga content and is considered to be one of the reasons for the difference in the transformation range for annealed and quenched alloys.
Microscopic considerations for models of ferromagnetic shape memory actuation
Robert C. O'Handley, David I. Paul, Miguel A. Marioni, et al.
Micro magnetic and analytic models have been sued to describe the equilibrium twin structure and quasistatic actuation behavior of ferromagnetic shape memory alloys. However, these models do not incorporate microscopic aspects of the twin-boundary strain field, interactions with defects or non-equilibrium behavior. A model is described that accounts for the interaction of a 90 degree domain wall with such a twin boundary. Application of a magnetic field can displace the domain wall from a pinned twin boundary with the Zeeman energy being stored elastically in the domain- wall anisotorpy energy. Finally, the departure of the magnetization and twin structure from equilibrium configurations can be incorporated in thermodynamic models to describe AC behavior and hysteresis.
Magnetomechanical behavior of a ferromagnetic shape memory alloy: Fe3Pd
Thomas W. Shield, Jun Cui
The alloy Fe3Pd undergoes a reversible structural phase transformation between FCC and FCT crystal structures at approximately 20 degrees C. The FCT structure has lattice parameters relative to the parent phase with lattice parameter a0, where a/a0 > 1 and c/a0 < 1. In addition the three martensite variants of the FCT structure are also ferromagnetic. Magnetic measurements have shown that the easy magnetic axes correspond to the FCT axes with the lattice parameter a. A new instrument called a Magneto-Mechanical Testing Machine (MMTM) is used to study the magneto-mechanical response of this alloy. This instrument allows a specimen to be loaded mechanically uniaxially, while the magnetic field can be rotated in a plane containing the loading axis. In addition, the temperature of the specimen can be controlled while the microstructure on its surface is observed using an optical microscope equipped to view surface tilt using differential interference contrast (DIC). The results of experiments that control the rearrangement of the martensite variants through applied compressive loading and magnetic field, will be discussed.
Actuators and Actuator Technology
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Pressurized shape-memory micropumps
We propose a multiscale framework to study the behavior of pressurized shape-memory thin films. These alloy films are typically heterogeneous and contain three length scales including film thickness, grain size and microstructure scale. We show that the effective behavior of shape-memory film exhibits strong size effect due to the interaction among these dimensional and material length scales. In addition, we apply the thin-film theory to predict maximum recoverable deflection for various shape-memory diaphragms with different textures. We find that recoverable deflection is not sensitive to common film textures in Ti-Ni films while it is sensitive in Cu-based shape-memory films. It turns out that Cu-based films may have better behavior than sputtered Ti-Ni films in view of large recoverable deflection. We conclude with comparison with experiment.
Performance characterization of active fiber-composite actuators for helicopter rotor blade applications
Viresh K. Wickramasinghe, Nesbitt W. Hagood
The primary objective of this work was to characterize the performance of the Active Fiber Composite (AFC) actuator material system for the Boeing Active Material Rotor (AMR) blade application. The AFCs were a new structural actuator system consisting of piezoceramic fibers embedded in an epoxy matrix and sandwiched between interdigitated electrodes to orient the driving electric field in the fiber direction to use the primary piezoelectric effect. These actuators were integrated directly into the blade spar laminate as active plies within the composite structure to perform structural actuation for vibration control in helicopters. Therefore, it was necessary to conduct extensive electromechanical material characterization to evaluate AFCs both as actuators and as structural components of the rotor blade. The characterization tests designed to extract important electromechanical properties under simulated blade operating conditions included stress-strain tests, free strain tests and actuation under tensile load tests. This paper presents the test results as well as the comprehensive testing process developed to evaluate the relevant AFC material properties. The results from this comprehensive performance characterization of the AFC material system supported the design and operation of the Boeing AMR blade scheduled for hover and forward flight wind tunnel tests.
Orthotropic piezoelectric composite materials actuator and its preliminary application
Ying Luo, Guoqi Zhao, Jianzu Gu, et al.
In this paper, the laminated piezoelectric composite materials with orthotropic properties, the structures, performances of orthotropic piezoelectric actuation elements are studied. Orthotropic piezoelectric composite materials present remarkable differences in two primary directions perpendicular to each other. As actuation chips, the laminated orthotropic piezoelectric composite materials present opposite deformation tendencies in two primary directions, which conforms to the deformation law of common engineering materials. This property presents merit in the control of structure shape and displacement and as the actuation element around self-adaptive structures compared with the common piezoelectric actuation materials. It follows from the practical test that the longitudinal induced strain of OPCM actuation element is 1.28 times of PZT actuation element, and 1.30 times of the traverse induced strain, together with opposite directions. Experimental researches are carried out respectively for bending and torsion actuation of cantilevers by using 1-1 type OPCM and PZT actuation elements. The results show that the actuation efficacy of OPCM element is 1.68 times that of PZT. In torsion actuation experiment, the actuation efficacy of OPCM actuation element is 2.1 times that of PZT actuation element. The above-mentioned advantages of the laminated orthotropic piezoelectric composite materials make them play important rules in self-diagnosis and self-adaptive structures.
Spring-based actuators
A new concept of a spring actuator based on the ferromagnetic shape memory alloy (FSMA) is presented. The coil spring made by a FSMA is activated by the attractive magnetic force produced by electromagnets, which is usually not uniform. When the magnetic field is applied, each turn of the spring comes into contact with the neighboring turns one by one, stacking from the turn closer to the yoke of the electromagnet. As a result, entire shrinkage of the spring accompanied by large liner stroke is achieved. This actuator is energy-efficient, since almost all magnet flux originated from electromagnet discharges into the ferromagnetic spring. The performance of the spring actuator, i.e. the output force and stroke, depends on many factors, such as the diameter and the pitch of the spring or the dimension of the cross section of the spring wire, and so on. We processed successfully a spring actuator driven by a hybrid magnet based on the above principle by using polycrystalline FePd alloy. Since the stiffness of the FePd coil spring become softer due to the martensite phase transformation, the movement of the actuator is accelerated during actuation.
Active piezoelectric diaphragms
Robert G. Bryant, Robert T. Effinger IV, Isaiah Aranda Jr., et al.
Several active piezoelectric diaphragms were fabricated by placing unelectroded piezoelectric disks between copper clad films patterned with Inter-Circulating Electrodes (ICE). When a voltage potential is applied to the electrodes, the result is radially distributed electric field that mechanically strains the piezo-ceramic along the Z-axis, rather than the expected in-plane direction. Unlike other out of plane piezoelectric actuators, which are benders, these Radial Field Diaphragms strain concentrically yet afford high displacements while maintaining a constant circumference. This paper covers the fabrication and characterization of these diaphragms as a function of poling field strength, ceramic diameter and line spacing, as well as the surface topography, the resulting strain field and displacement as a function of applied voltage ranging from DC to 10 Hz.
Experimental performance evaluation of lightweight piezo-composite curved actuators
Ki-hoon Park, Yongbum Kim, Young Sung Kim, et al.
This paper is concerned with the performance evaluation and comparison for several kinds of LIPCA device system. LIPCA device system is composed of a piezoelectric ceramic layer and fiber reinforced light composite layers, typically a PZT ceramic layer is sandwiched by a top fiber layer with low CTE and base layers with high CTE. To investigate the effect of lay-up structure of the LIPCA system, four kinds of actuator with different lay-up stacking sequence have been designed, manufactured, and tested. The performance of each actuator was evaluated using an actuator test system consisted of an actuator supporting jig, a high voltage actuating power supplier, and a non-contact laser measuring system. From the comparison of the performance of the LIPCA prototypes, it was found that the actuator with larger actuation moment arm length and lower total flexural stiffness can generate larger actuating displacement.
Modeling of SMA
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Effects of thermomechanical history on the tensile behavior of Nitinol ribbon
Cynthia L. Lach, Travis L. Turner, Karen M. Taminger, et al.
Shape memory alloys (SMAs) have enormous potential for a wide variety of applications. A large body of work exists on the characterization of the microstructure and stress-strain behavior of these alloys, Nitinol (NiTi) in particular. However, many attributes of these materials are yet to be fully understood. Previous work at NASA Langley Research Center (LaRC) has included fabrication of hybrid composite specimens with embedded Nitinol actuators and modeling of their thermomechanical behavior. An intensive characterization effort has been undertaken to facilitate fundamental understanding of the stress-strain behavior of this alloy in relation to its microstructure and to promote implementation of Nitinol in aerospace applications. Previous work revealed attributes of the Nitinol ribbon that were not easily rationalized with existing data in the literature. In particular, tensile behavior at ambient temperature showed significant dependence on the thermomechanical history prior to testing. The present work is focused on characterizing differences in the microstructure of Nitinol ribbons exposed to four different thermomechanical histories and correlation of the microstructure with tensile properties. Differential scanning calorimetry (DSC) and x-ray diffraction (XRD) analysis were employed to rationalize the microstructures present after exposure to various thermomechanical histories. Three of the Nitinol ribbon conditions were reversible upon heating (in the DSC) through the reverse transformation temperature (Af) to transform the microstructure to austenite. However, the prior thermomechanical conditioning for the Nitinol ribbon that reflected the entire fabrication procedure was found to have an irreversible effect on the microstructure, as it remained unchanged after repeated complete thermal cycles. Tensile tests were conducted to determine the effect of prior thermomechancial conditioning on both the tensile behavior of the Nitinol ribbons and the stress state of the microstructure. The stress-strain behavior of the Nitinol actuators appears to be governed by the interplay between two major variables: namely, microstructural constituents such as the R-phase and the martensite; and the stress state of these constituents (whether twinned with low residual stresses, or detwinned with high residual stresses). The most significant difference in the stress-strain behavior of the four conditions, the critical stress required to achieve an initial stress plateau, was found to depend on both the amount and stress state of R-phase present in the initial microstructure. Thus, the effect of prior thermomechanical processing is critical to the resulting tensile behavior of the Nitinol actuator. For numerical modeling inputs one must take into account the entire fabrication process on the Nitinol actuator.
One-dimensional constitutive model of stress-induced transitions between Ms and Mf in shape memory alloys
Yun Luo, Takeshi Okuyama, Toshiyuki Takagi
Traditionally smart material actuation has been reserved for high technology industries such as space and aerospace; however, as the field matures more and more instances are found in low-cost, high production areas. This paper describes one such instance - the application of shape memory alloys to auxiliary functions in appliances. This investigation focused on lid locks for washing machines because it is representative of several other applications found in appliances including valves, dispensers, locks, brakes, etc. Several competing concepts for SMA actuated lid locks are discussed including simple analytical design models and experimental characterization of proof-of-concept prototypes. A comparison of these designs based on performance (force, response times), energy (power requirements) and economic metrics is given. From this study, a final concept was developed based upon the best attributes of the different concepts. The resulting proof-of-concept prototype demonstrated improved performance over the current state with a potential for cost reduction.
Thermomechanical representation of the multiaxial behavior of shape memory alloys
Dirk Helm, Peter Haupt
A thermomechanically consistent material model representing the multiaxial behavior of shape memory alloys is proposed in this article. The constitutive equations describe the one-way and two-way shape memory effect as well as pseudoelasticity, pseudoplasticity and the transition range between pseudoelasticity and pseudoplasticity. The material model is based on a free energy function as well as evolution equations for internal variables. In detail, the free energy function is introduced in order to describe the energy storage during thermoelastic processes, the energy difference between the regarded phases (austenite and martensite) as well as the energy storage due to the evolution of the residual stresses. In contrast to this, the evolution equations for the internal variables represent the observed inelastic behavior of shape memory alloys as well as the related thermomechanical coupling effects. Due to the description of the energy storage and release during the martensitic phase transitions by means of a mixture theory, one internal variable is the fraction of martensite. Others are the inelastic strain tensor and internal variables describing residual stresses. The viscous material behavior of NiTi shape memory alloys, which is experimentally observed, is represented by an inelastic multiplier of Perzyna-type. Numerical solutions of the developed constitutive equations for isothermal and non-isothermal strain and stress processes demonstrate that the material model represents the main effects of shape memory alloys. Additionally, the material model is able to depict the multiaxial material behavior as observed. Numerical solutions are compared with uniaxial and in particular biaxial experimental observations on NiTi shape memory alloys.
Inner loops of pseudoelastic hysteresis of shape memory alloys: Preisach approach
Yuji Matsuzaki, Ken Funami, Hisashi Naito
Shape memory alloys (SMA) show very complicated thermomechanical behavior due to phase transformations and rearrangements, including large bounding hysteretic stress-strain loops as well as their inner loops. In our previous analyses, incorporating the phase interaction energy function (PIEF) as a dissipation potential with the free energy of the alloy, we proposed a macroscopic model of SMA for the pseudoelasticity and shape memory effect. Analytical bounding loops derived could accurately model experimental results of a wire subjected to cyclic loads up to 1Hz, including the temperature change. In the present paper, to further extend the concept of the PIEF, we propose a microscopic approach by taking into account the pseudoelastic hysteresis in single crystal grains of polycrystalline SMA. In each grain, we assume that the hysteretic behavior is represented by the Preisach model. Again, incorporating the PIEF with the free energy of the grain, and summing up over the whole material, we have derived the stress-strain relationship in which the Cauchy distribution function is used for the probability of the martensitic and the reverse transformation. We will show that the analytical stress-strain model which has been determined using experimental data of a bounding loop can well describe its inner loops.
Coupled Construction Behavior: SMA
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Evaluation of phase transformation in ferromagnetic shape memory Fe-Pd alloy by magnetic Barkhausen noise
Yasubumi Furuya, Shizuka Tamoto, Takeshi Kubota, et al.
The possibility to detect the phase transformation with martensites by heating or cooling as well as stress-loading in ferromagnetic shape memory Fe-30at percent Pd alloy thin foil by using magnetic Markhausen noise sensor was studied. MBHN is caused by the irregular interactions between magnetic domain and thermally activated martensite twins during magnetization. In general, the envelope of the MBHN voltage versus time signals in Fe-29at percent Pd ribbon showed two peaks during magnetization, where secondary peak at intermediate state of magnetization process decreased with increasing temperature, while the MBHN envelopes in pure iron did not change with increasing temperature. The variety of MBHN due to the phase transformation was apt to arise at higher frequency part of spectrum during intermediate state of magnetization process and it decreased with disappearance of martensite twins. Besides, MBHN increased monotonically with increasing loading stress and then, it decreased with unloading, however MBHN showed large hysteresis between loading and unloading passes. Based on the experimental results from MBHN measurements for both thermoelastic and stress-induced martensite phase transformations in Fe-30at percent Pd ribbon samples, MBHN method seems a useful technique to non-destructive evaluation of martensite phase transformation of ferromagnetic shape memory alloy.
Deformation behavior of TiNi shape memory alloy under strain- or stress-controlled conditions
Hisaaki Tobushi, Kayo Okumura, Masato Endo, et al.
The deformation properties of TiNi shape memory alloy subjected to strain control and stress control were investigated experimentally. The result obtained are summarized as follows. In the case of full loop, the stress- strain curves under stress-controlled condition are similar to those under strain-controlled condition with high strain rate. The overshoot and undershoot do not appear at the start points of the stress-induced martensitic transformation in these curves. In the case of subloop under stress-controlled condition, temperature decreases and therefore strain increases owing to the martensitic transformation at the early stage in the unloading process. At the early stage in the reloading process, temperature increase and therefore strain decease owing to the reverse transformation. In the case of subloop under stress- controlled condition, the starting stresses of the martensitic transformation and the reverse transformation in the loading and unloading processes coincide with the transformation stresses under strain-controlled condition with low strain rate, respectively. The deformation behaviors for subloop under stress-controlled condition are prescribed by the condition for progress of the martensitic transformation based on the transformation kinetics. The deformation behaviors subjected to cyclic loading under stress-controlled condition at constant temperature are also prescribed by the condition for progress of the martensitic transformation.
Constitutive model for shape memory alloys and its use in design and finite element analysis
Sudip Bose, Sridhar Santhanam
A constitutive model for predicting the thermomechanical behavior of Shape Memory Alloys (SMAs) has been developed and validated. The model uses an approach similar to Brinson, Liang and Rogers, and Tanaka. It links key thermomechanical variables: stress, strain, temperature, and martensite fraction. A basic differential form for the SMA constitutive behavior, developed by Tanaka, forms the foundation of the model. The model is completed with a definition of the rules governing the behavior of martensite fraction. Like Brinson, the model distinguishes between de-twinned and twinned martensite. The phase transition temperatures are assumed to be a linear function of applied stress. The forward and reverse phase transformations are described by piecewise exponential functions. There are a number of parameters in the model that need to be determined using experimental data. The critical transformation temperatures are determined by resistivity measurements. All other parameters are determined by mechanical tension testing followed by nonlinear least-squares estimations. Mechanical testing consisted of displacement controlled, tension tests on Nitinol wires at several temperatures. The effectiveness of this model is demonstrated by its use in the design of an SMA actuated robotic arm. The constitutive model is used in conjunction with a lumped heat transfer model, a kinematic model, and a dynamic model to predict the behavior of the arm. Comparison between predictions and experimentally observed behavior is very good indicating a sound constitutive model. The model is also built into a finite element code that simulates pseudoelastic SMA behavior. The code considers geometric and material nonlinearities. The behavior of a simple pseudoelastic device is shown to be well predicted by the finite element code.
Energy-absorbent composites featuring embedded shape memory alloys
W. Zhang, M. Davis, Nikhil A. Koratkar
Shape Memory Alloy (SMA) wires, were integrated within E-glass composite beams. The fiber volume fraction of the SMA material was 10 percent. Several baseline beams were also fabricated. Both the baseline and SMA reinforced composite beams were tested to failure in tension. The SMA reinforced beams were tested in both the martensite phase (room temperature) as well as the austenite phase (75 deg C). The test results indicated that SMA reinforced composites can offer significant increase in the strain-energy absorption prior to failure thereby improving the fracture toughness and crashworthiness for such systems. Significant increase in damping was also observed for the SMA reinforced composite when the wires were transformed from the martensite to the austenite phase by resistive heating.
Magnetostrictive and Ferromagnetic Materials
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Modern magnetostrictive materials: classical and nonclassical alloys
Arthur E. Clark, Marilyn Wun-Fogle
Magnetostrictive materials have not changed greatly from their discovery by Joule in 1842 through the 1960's. Their saturation strains remained small and their magnetomechanical couplings were only moderate. The separation of the rare earth elements during World War II and the subsequent measurement of their magnetic properties, created the groundwork for the development of 'giant' magnetostrictive materials during the 1960's. Magnetically anisotropic Tb and Dy became the generators of unprecedented classical magnetostrictions of nearly 1 percent. Coupling factors increased to approximately 0.8. During the same period, a remarkable 5-fold increase of magnetostriction of commonplace b.c.c. Fe with concentrations of Al near 1 18 percent was discovered. More recently, measurements in b.c.c. Fe-Ga alloys have shown a still greater enhancement of the magnetostriction, yielding strains of nearly 400 X 10-6 over the wide range in temperature from 4 K to far above room temperature. In the Fe alloys, as well as in the rare earth alloys, there is no known stress limit to the magnetostriction. Power output is limited by magnetic field generation and mechanical sample failure. Within the last few years, a new class of magnetostrictive materials, ferromagnetic shape memory alloys (FSMA's), have been introduced. These materials have huge magnetically induced strains. However, unlike the classical magnetostrictive alloys, these strains may be stress limited. While all the above materials have been introduced primarily for their high power electrical to mechanical energy conversion capability, they also function in the reciprocal mode, as magnetomechanical sensing materials.
Experimental study of electrical point shorts in laminated Terfenol-D
It is well known that laminating TERFENOL-D drivers for high frequency operation reduces eddy current losses. However, there are questions regarding the effectiveness of the lamination if there is an electrical short between two adjacent laminae. Because of the high electrical resistivity of the epoxy used for lamination, these electrical shorts are most likely caused by metal particles or other impurities penetrating the epoxy layer, referred to here as 'point shorts'. The effects of electrical point shorts between adjacent laminae in TERFENOL-D drivers have been investigated. TERFENOL-D drivers with specific configurations of point shorts were fabricated and tested. The drivers were tested in two simple configurations, the first with its resonant frequency below the eddy current critical frequency for the lamina thickness, 7 kHz, and the second with its resonance above the critical frequency, 19 kHz. A comparison of solid drivers with completely shorted drivers show that the effect of laminating the TERFENOL-D is not nullified by the presence of an electrical short. In fact, comparing a completely shorted driver with a perfectly laminated driver indicates that there is very little, if any, performance degradation due to the presence of electrical shorts.
Manufacturing and testing of [1-3] nickel/polymer composites
A 15 percent nickel composite was manufactured and tested under a sinusoidally applied magnetic field at a frequency of 0.3 Hz around a DC bias of 0kA/m without an external mechanical load. The particulate are obtained from a process known as spark erosion, resulting in particulate that are nearly spherical in shape. Parameters that were recorded include strain, magnetic field, and magnetic flux. Experimental strain output values were comparable to strain measured from a single crystal nickel along the axis. However, the effects of the epoxy are non-negligible and results regarding texturing of the composite are inconclusive.
Dynamic magnetomechanical behavior of Terfenol-D/epoxy 1-3 composite
This paper presents an experimental investigation of the dynamic behavior of a 1-3 type magnetostrictive composite, with emphasis on the evaluation of fundamental material properties pertinent to device design. The fabricated 1-3 magnetostrictive composite comprises 51 percent volume fraction of Terfenol-D particulates embedded and magnetically aligned in a passive epoxy matrix. The dynamic magnetomechanical properties of the composite are measured as functions of bias field, drive field, and frequency. These properties include Young's moduli at constant magnetic field strength (EH3) and at constant magnetic flux density (EB3), magnetomechanical coupling coefficient (k33), dynamic relative permeability (ur33), dynamic strain coefficient (d33), mechanical quality factor (Qm), and the ratio of the dynamic strain coefficient to the dynamic susceptibility. Dependence of material properties on applied fields and frequency is observed with no evidence of eddy current losses. The observed eddy current effect agrees with the prediction of classical eddy current theory. This suggests that the composite can provide superior high-frequency performance as compared to monolithic Terfenol-D and laminated Terfenol-D systems. Implications for high-frequency applications of the material to resonance devices are also described.
Equation of state for ferromagnetic transducers
An equation of state based upon magnetization scaled to its saturation value, m equals M/Ms, applied magnetic field scaled to its coercive value, h equals H/Hc, distribution of coercivities, and reversible susceptibility Xrev of magnetization and applied stress, scaled to its initial value is proposed for ferromagnetic transducers. Reversible susceptibility divided by the initial susceptibility is the anisotropy function of domain magnetization, decreasing for Terfenol-D nearly linearly with scaled magnetization from one in the demagnetized state to zero at saturation. Measurements of reversible susceptibility, initial, anhysteretic and saturate magnetization curves, and loops for Terfenol-D show that differential magnetic susceptibility is the product of the reversible susceptibility and a cooperative function due to domain interactions. This function is roughly triangular in magnetization having the same slope from each reversal for magnetization magnitude up to half of saturation, at which the onset and decay of cooperation occur. This cooperative function causes parabolic Rayleigh minor loops and sigmoid major B(H) curves truncated by stress demagnetization. Anhysteretic reluctivity increases linearly with the root sum square of shape and stress demagnetizations, the latter added to the anisotropy function. Magnetization loops under stress are modeled and the d* transducer constant dB/ds is derived as a function of stress and magnetization.
Magnetorheological fluids exploiting nanometer-sized particles
Magnetorheological(MR) fluids are suspensions of magnetic particles in a carrier fluid. The rheological properties of MR fluids undergo changes on application of magnetic field. MR fluids made using nanometer sized soft magnetic iron particles were studied for their benefits vis-a-vis flow characteristics and settling properties. Three kinds of MR fluids were synthesized using the microwave process (1) 30 micrometers sized iron particles (2) 26.5 nm sized iron particle (3) a mixture of micron and nanometer sized iron particles . The fluids were suspensions of micron, nanometer as well as a mixture of nanometer and micron sized powders. Standard static and dynamic yield stress measurements were performed using a parallel disc oscillatory rheometer. The flow properties of these fluids were then characterized using the Bingham-Plastic, Eyring-Plastic and the Herschel-Buckley models. This paper investigates the rheological properties of these fluids and assesses their advantages and disadvantages. The pure micron powder yielded an MR fluid with highest yield stress, but had the most rapid settling. The nano sized powders overcame the problem of settling because of the predominance of thermodynamic forces at that scale, but they yielded a considerably lower yield stresses. A hybrid combination of micron and nano sized powders was an effective compromise to exploit the high yield stress provided by the micron powders and the self dispersing properties of the nano sized powders. We characterized these mixtures using existing rheological models. A key conclusion is that it may be possible to synthesize MR fluids with significant yield stress, while mitigating settling through the use of nanoscale powders.
Navy Transducer Materials and Design
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Material challenges for transducer designers in the 21st century
Jan F. Lindberg
The modern U.S. Navy is rapidly evolving to meet the challenges of operating in the littorals. This focus changes the rules, especially to the designers of sonar systems that now need to aggressively engage quiet diesel electric submarine threats and neutralize sophisticated underwater mines. These new responsibilities dictate that new concepts be developed. To meet these new demands on the sonar system, transducer designers are being tasked to design transducers and to utilize new materials to address performance requirements that were never even imagined a decade ago. Sensor needs are no longer limited to pressure types but now have to sense velocity or acceleration. Sources are challenged to both frequency extent and power levels. The need to physically move sources off of submarines and surface combatants and onto vehicles with limited energy capabilities prompt the challenge of efficient bandwidth and high coupling. These are the needs of the 'next Navy'; the needs of the 'Navy after next' will present an even more demanding scenario. The future will demand revolutionary technology at the micro level with devices utilizing new power sources and new materials.
Time-dependent behavior in a Terfenol-D actuated visco-elastic polymer matrix composite
William D. Armstrong, Cosmina S. Hogea
The present paper develops a one dimensional magneto-elastic model of a magnetostrictive fiber actuated polymer matrix composite material which accounts for a strong visco-elastic response in the polymer matrix. The visco-elastic behavior of the composite polymer matrix is modeled with a three parallel Maxwell element visco-elastic model, the magneto-elastic behavior of the composite fibers is modeled with an anhysteric directional potential based domain occupation theory. Example calculations are performed to identify and explain the dynamical behavior of the composite. We observed that the increasing and decreasing limbs of the magnetization and magnetostriction loops are offset at middle levels of applied field. This offset is a consequence of the interaction of the time varying fiber stress caused by matrix viscosity with a multi-domain state in the fiber. The small increase in fiber longitudinal compressive stress due to matrix viscosity under increasing field inhibits the occupation of domains with magnetization orientations near the fiber longitudinal direction. As a consequence, the summed longitudinal magnetization and magnetostriction is reduced as compared to the decreasing field limb. This results in an apparent hysteresis loop in the magnetization and magnetostriction curves even though the model does not include magneto-elastic hysteresis in the fibers.
2.5-kHz magnetostrictive Tonpilz sonar transducer design
Stephen C. Butler
Naval Undersea Warfare Center has fabricated and tested a 2.5 kHz magnetostrictive sonar transducer to validate various modeling techniques. The transducer selected is a longitudinal vibrator Tonpilz type consisting of Terfenol-D driver, tail mass, radiating head mass, and stress rod bolt with 21 MPa (3000 psi) prestress. The Terfenol-D drive rod is interlaced with three samarium cobalt magnets, one in the center and one on either end magnetically biasing the Terfenol to 60 kA/m (750 Oe). Both the Terfenol-D rods and magnets were laminated to reduce eddy currents. The magnetic circuit is comprised of pole piece discs on each end of the Terfenol-D magnet assembly and an external magnetic cylinder (return path) made of a high-permeability, high-resistivity, high-saturation powdered metal 'T2'. The transducer has a 25 cm (9.8in) diameter radiating face (piston), is 28 cm (11 in.) long, and weighs 15 kg (32 lb.) without the housing. It is 41 cm (16 in.) long and 25 kg (56 lb.) with the underwater housing. The measured results are compared to a finite element model using 'ATILA' and distributed plane wave element equivalent circuit model. The coupling coefficient, permeability and mechanical loss effects for different prestress loads were measured on a resonant Terfenol 'dumbbell' device. The in-water measured results indicate a mechanical Q of 2.5, an effective coupling coefficient of 0.36, an electro-acoustic efficiency of 60 percent, beam pattern directivity index of 6 dB, a maximum Source Level of 214.6 dB re 1uPa/m at 15 Amps AC drive and bandwidth of 2 kHz to 5.4 kHz +/- 1.5 dB.
Transducer Materials
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Stress-dependent behavior of d33 and Y33E in Navy Type III and VI ceramics
Rachel S. Levinson Fisher, Elizabeth A. McLaughlin, Harold C. Robinson
Study of the mechanical stress dependence of hard and soft active ceramic properties is important because many submarine sonar transducers include a compressive mechanical prestress throughout ac electrical activation. The level of prestress to which a ceramic in a transducer is subjected also depends in part on operational factors, such as the level of ac activation and depth of the submersible. This investigation builds upon prior work by Yang et al. by examining the time dependence and the uniaxial stress dependence of the average, differential and dynamic d33 and Y33E of Navy Type III (PZT8) and Navy Type VI (PZT5H) lead zirconate titanate ceramics. This research adds higher levels of prestress and various mid-level ac stress cycles. Under short-circuit conditions, large and small compressive stresses are applied to the samples while measuring dielectric displacement and strain. The piezoelectric coefficient, d33, is evaluated using the direct method as a function of time, prestress level, and ac stress magnitude. The constant-field modulus is calculated from the slope of the corresponding stress-strain curves. Intrinsic and extrinsic contributions to these properties are discussed.
Frequency dependence of PMN-PT ceramics under electrical bias
It is a well-known fact that electrostrictive materials, such as lead magnesium niobate-lead titanate (PMN-PT) ceramics, exhibit significant frequency dispersion in their small signal dielectric constant below their dielectric maximum temperature Tm. The frequency dispersion in several PMN-PT compositions will be examined in this study using two independent measurement methods: dc biased resonance and large signal quasistatic measurements conducted on NUWC Division Newport's SDECS. From these measurements, the coupling factor, piezoelectric constant and Young's modulus are compared as a function of the applied bias and frequency. Both the DC biased and SDECS measurements were performed on the same 3:1 aspect ratio samples. Finite element calculations will show that the error in determining the Young's modulus and piezoelectric constant from resonance using these samples is less than 5 percent. It will be shown that when frequency dispersion exists it remains even with the application of dc bias, and that the degree of deviation between these quantities increases the further below Tm the temperature drops. It will also be shown that, like the dielectric constant, the coupling factor, piezoelectric constant and Young's modulus in PMN-PT ceramics above Tm are non-dispersive.
Magnetoelastic thin films and multilayers for high-frequency applications
Alfred Ludwig, Michael Frommberger, Christel Zanke, et al.
Magnetoelastic and magnetic high-frequency properties of single and multilayer thin films are investigated with respect to applications in micro-inductors and as remote-interrogated sensors for mechanical quantities. The basic structure is a thin film inductor incorporating a magnetic material in order to enhance the inductance. In case of a sensor the inverse magnetostriction is used to change the permeability of the magnetic material and thus the inductance of the device. Materials properties like saturation magnetization, anisotropy field, resulting domain structures, electrical resistivity as well as the stress state of the films have to be adjusted carefully in order to meet certain requirements like high cut-off frequencies combined with low losses, and a high and controllable inverse magnetostrictive effect. In this paper (Fe-Co/Fe-Co- B-Si) multilayers are investigated in terms of their magnetic, high-frequency, and structural properties. (Fe50Co50Cp80B20) multilayers, e.g., have been fabricated which show ferromagnetic resonance frequencies up to 5 GHz while exhibiting a high inverse magnetostrictive effect up to the GHz frequency range. The obtained results for first LC circuits realized using (Fe50Co50/Co80B20) multilayers are discussed.
Coupled Construction Behavior: SMA
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Image-based dynamic modeling of phase transformation in hybrid SMA
Muhammad A. Qidwai, Virginia G. DeGiorgi
The main interest of this study is to investigate phase transformation behavior in hybrid SMA under moderate dynamic loads. A hybrid SMA is described as a two-component composite made of dense SMA matrix with pores, and a passive or active material that fills the pores. The dynamic behavior of hybrid SMA under strain rates of 1000 /s is investigated by incorporating the porous mesostructure in the finite element analysis. X-ray computed micro tomography (XCMT) images are employed to synthesize statistical information and probabilistic algorithms are utilized in obtaining suitable representative finite element meshes. The effective constitutive response of hybrid SMA is obtained by simulating the split Hopkinson bar test of the finite element specimen. A parametric study based on volume fraction of the filler material is carried out. A comparison of hybrid SMA and porous SMA is also performed.
Transducer Materials
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Optimizing work output in Ni-Mn-Ga and other ferromagnetic shape memory alloys
Present article briefly summarizes the mechanism of magnetic shape memory, main modeling principles and most important information about the main structural, magnetic and mechanical properties related to a family of non- stoichiometric Ni-Mn-Ga alloys. We also first consider in details the problems of energy balance, energy losses, optimization of work output and estimation of thermodynamic efficiency for Ni-Mn-Ga based MSMAs.
Fabrication of TiNi/CFRP smart composite using cold drawn TiNi wires
Ya Xu, Kazuhiro Otsuka, Nobuyuki Toyama, et al.
In recent years, pre-strained TiNi shape memory alloys (SMA) have been used for fabricating smart structure with carbon fibers reinforced plastics (CFRP) in order to suppress microscopic mechanical damages. However, since the cure temperature of CFRP is higher than the reverse transformation temperatures of TiNi SMA, special fixture jigs have to be used for keeping the pre-strain during fabrication, which restricted its practical application. In order to overcome this difficulty, we developed a new method to fabricate SMA/CFRP smart composites without using special fixture jigs by controlling the transformation temperatures of SMA during fabrication. This method consists of using heavily cold-worked wires to increase the reverse transformation temperatures, and of using flash electrical heating of the wires after fabrication in order to decrease the reverse transformation temperatures to a lower temperature range again without damaging the epoxy resin around SMA wires. By choosing proper cold-working rate and composition of TiNi alloys, the reverse transformation temperatures were well controlled, and the TiNi/CFRP hybrid smart composite was fabricated without using special fixture jigs. The damage suppressing effect of cold drawn wires embedded in CFRP was confirmed.