bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Control of Flexible Structures Using Nonlinear Modal Coupling: Forced and Free Vibration
Authors: Khajepour Amir , Golnaraghi M. Farid
Published: August 2009

This paper is an experimental study of free and forced vibration suppression in a piezoceramic actuated flexible beam via the nonlinear Modal Coupling Control (MCC). The method is based on transferring the oscillatory energy from the plant to an auxiliary second order system (controller), coupled to the plant through nonlinear terms. The proposed controller produces an input that can be utilized by unidirectional actuators. Unidirectional actuators do not generate symmetric power during an application. Shape memory alloys, thrusters and cable based actuators are examples of this class of actuators. Existing control methods assume a symmetric actuation and therefore application of unidirectional actuators call for new control techniques. Current control techniques implement a bias in utilizing unidirectional actuators. However, the amount of the bias is variable and depends on the control effort. Moreover, the use of a bias changes the system equilibrium point and introduces a steady state error. The proposed controller is used to control the first mode of a flexible beam. The results show that the method is more effective than conventional control approaches in conjunction with unidirectional actuators.
Thermomechanical Constitutive Modeling in Shape Memory Polymer of Polyurethane Series
Authors: Tobushi H. , Hashimoto T. , Hayashi S. , Yamada E.
Published: August 2009

In order to describe the thermomechanical properties in shape memory polymer of polyurethane series, a thermomechanical constitutive model was developed by modifying a standard linear viscoelastic model. The model involved a slip element due to internal friction and took account of thermal expansion. In order to describe the variation in mechanical properties due to the glass transition, coefficients in the model were expressed by a single exponential function of temperature. Several kinds of thermomechanical tests were carried out. The proposed theory expressed well the thermomechanical properties of the material, such as shape fixity, shape recovery and recovery stress. The proposed model is useful for design of shape-memory polymer elements, in which the amount of recovery deformation, the tightening force and the working start and completion temperatures are specified.
Power and Energy Characteristics of Solid-State Induced-Strain Actuators for Static and Dynamic Applications
Authors: Giurgiutiu Victor , Rogers Craig A.
Published: August 2009

The power and energy characteristics of solid-state induced-strain actuators are studied. Piezoelectric (PZT), electrostrictive (PMN) and magnetostrictive (TERFENOL) actuators are considered. The principles and internal construction of solid-state induced-strain actuators are briefly reviewed. Typical performance curves are presented and discussed. The basic equations of piezoelectricity and piezomagnetism are presented. A linearization procedure is adopted whereby apparent values for the piezoelectric and piezomagnetic constants are derived from full-stroke ven-dor data using the secant approximation principle. Values for the apparent electromagnetic conversion coefficient for full-stroke operation are obtained.

The static analysis considers the one-directional operation of the induced strain actuators against an external spring load. It is found that the maximum energy output from the induced-strain actuator is obtained when the internal and external stiffnesses are matched. Expressions for the maximum energy output, and the energy densities per unit volume, mass, and cost are derived. Numerical examples and comparative charts are given for a number of piezoelectric, electrostrictive and magnetostrictive actuators. The influence of casing and pre-stress mechanism on the overall energy density values is also highlighted. The electromechanical conversion efficiency is studied, and two separate expressions are derived, one for the best efficiency, and another for the conversion efficiency at the stiffness match point.

The dynamic analysis considers the cyclic motion of the induced-strain actuators about a midpoint bias position. The dynamic full-stroke is found approximately one-half the static full-stroke. The correspondingly maximum output energy and energy densities under dynamic conditions are calculated. The dynamic energy conversion efficiency is studied and the influence of bias voltage or current is included. Numerical examples and comparative charts are given for a number of piezoelectric, electrostrictive and magnetostrictive actuators operating under dynamic conditions.
Design of Robust Controllers for Smart Structural Systems with Actuator Saturation
Authors: Butler Robert , Rao Vittal , Sana Sridhar
Published: August 2009

The design and implementation of robust controllers on smart structural systems is often constrained by available control force of the actuators. The Lead Zirconite Titanate (PZT) actuators which are used for the control of flexible structures have limited control authority. The performance of the smart structural systems is often limited by the control effort constraint instead of the closed loop stability and performance. Due to the limited availability of control effort, it is desirable to utilize all of the control force in order to obtain the best performance. The research results described in this paper integrate robust control design methodologies with constrained actuator techniques for designing controllers for smart structural systems. In order to implement the proposed controllers, a two-dimensional lattice structure is designed and fabricated. The robust controllers in this paper have been designed for this test article. We have also developed the uncertainty modeling for this test article. An H2/H. controller has been designed and implemented on the lattice structure. The experimental results of the closed-loop system and the verification of the robustness properties are also presented.
Adjustment Procedure of a High Precision Deployable Mesh Antenna for MUSES-B Spacecraft
Authors: Tabata Masaki , Natori M. C. , Tashima Takanori , Inoue Toshio
Published: August 2009

In this paper, a precise on-ground adjustment procedure of a high precision deployable space antenna which has to keep the required surface accuracy in space environment, such as zero gravity, high vacuum, etc., is investigated. For space structure systems in the relatively near future the active shape control technology in orbits is still not matured, and it is important to predict their in-orbit performance before launch. Especially for flexible systems precise mathematical models are necessary to compensate the gravity effects in their assembly and adjustment phases on ground. Those models must include sufficient characteristic changes caused by environmental deferences in space. One attempt of such adaptive adjustment procedures in the development of a high precision deployable space antenna planned by the Institute of Space and Astronautical Science (ISAS) is introduced.
Feasibility Study of Delamination Detection with Embedded Optical Fibers
Authors: Elvin Niell , Leung Christopher
Published: August 2009

In this paper, we describe a novel approach for delamination detection, which involves (1) the application of a moving load on the composite member, and (2) measurement of total extension in embedded optical fiber(s). A theoretical study indicates that a single loading test can provide sufficient information to deduce the delamination location (in both the length and thickness directions) as well as the delamination size.
Can a Coupling Coefficient of a Piezoelectric Device be Higher Than Those of Its Active Material?
Authors: Lesieutre George A. , Davis Christopher L.
Published: August 2009

An electromechanical coupling coefficient is a measure of the effectiveness with which a piezoelectric material (or a device employing such a material) converts the energy in an imposed electrical signal to mechanical energy, or vice versa. There are different kinds of material and device coupling coefficients, corresponding to different modes of excitation and response. Device coupling coefficients are properties of the device and, although related to the material coupling coefficients, are generally different from them. It is commonly held that a device coupling coefficient cannot be greater than some corresponding coupling coefficient of the active material used in the device. A class of devices was recently identified in which the apparent coupling coefficient can, in principle, approach 1.0, which corresponds to the limit of perfect electromechanical energy conversion. The key feature of this class of devices is the use of destabilizing mechanical pre-loads to counter inherent stiffness. The approach is illustrated for a symmetric piezoelectric bimorph device: theory predicts a smooth increase of the apparent coupling coefficient with pre-load, approaching 1.0 at the buckling load. An experiment verified the trend of increasing coupling with pre-load: a load corresponding to 50% of the buckling load increased the bimorph coupling coefficient by more than 40%. This approach provides a way to simultaneously increase both the operating displacement and force of a piezoelectric device, distinguishing it from alternatives such as motion amplification. and may allow transducer designers to achieve substantial performance gains for some actuator and sensor devices.
Analysis and Optimization of Electromechanical Devices Based upon a Kinematic Model
Authors: Ruan Xiaoping , Chou Tsu-Wei , Danforth Stephen C. , Safari Ahmad
Published: August 2009

The purpose of this paper is two-fold. First, an effective method for analyzing the electromechanical responses of piezoelectric devices is developed based upon a kinematic model. The predictability of the model is validated by comparing it with the results obtained from finite element analysis. Next, an example of optimization of the design of electromechanical devices is carried out. By using an alternate configuration of polarization, a one-fold increase in device performance has been realized. The model devices considered are an oval flextensional actuator and a moonie actuator with PZT ceramics. The results of this research effort benefit the design and fabrication of electromechanical devices, which now can be produced in increasing complexity using SFF techniques.
Shape Matching with Smart Material Structures Using Piezoceramic Actuators
Authors: Fitzpatrick Ben G.
Published: August 2009

In this paper, we consider the problem of driving a flexible structure from an "unforced" equilibrium position to a given desired shape. Within the context of smart materials, we focus on piezoceramic actuators as controls. Our approach is to base the choice of input voltages on a physical model of the structure, with "good" voltage choices being those whose modelbased displacements "'closely" match the desired shape. This shape matching problem is posed as a least squares problem in a Hilbert space that represents the displacement component of the state space of the flexible structure model. Here we treat the structure as a distributed parameter system, so that the state space is infinite dimensional. Thus, we must examine questions of existence of solutions and convergence of approximations. To illustrate our techniques, we give some numerical examples.
System Identification of Smart Structures Using Neural Networks
Authors: Yang S. M. , Lee G. S.
Published: August 2009

A composite smart structure embedded with piezoelectric sensor/actuator is fabricated and its piezoelectric effectiveness is validated by static test and modal testing. Instead of identifying the structural parameters of the smart structure, system identification is conducted by estimating the connective weights of a backpropagation neural network with an adaptive learning rate. Experimental verification shows that the [6-7-2] neural network, a neural network with 6 input neurons, 7 hidden layer neurons, and 2 output neurons, is capable of representing the system dynamics both in time domain and in frequency domain. In addition, it is fault tolerant. All simulations are validated by experiments. Integration of smart structure and neural network not only avoids the complexity introduced by other traditional analytical or computational methods but also lays the corner stone for effective neural controller design.
Piezoelectric Fiber Composites with Interdigitated Electrodes
Authors: Bent Aaron A. , Hagood Nesbitt W.
Published: August 2009

Piezoelectric Fiber Composites were previously introduced as an alternative to monolithic piezoceramic wafers for structural actuation applications. This manuscript was an investigation into the improvement of piezoelectric fiber composite performance through a nonconventional electroding scheme. Two microelectromechanical models were developed that predict the composite properties. These models were used to examine the trends of composite properties versus fiber volume fraction for various constituent materials. Several etched electrode PZT fiber composites, with fiber volume fractions ranging from 7% to 58%, were manufactured and tested. Experimental measurements showed excellent agreement with both the trends and magnitude of model predicted values. The maximum fiber volume fraction composites demonstrated a capacitance (E3 /Eo) of 550, piezoelectric free strain constants (d33 and d31) of 150 pm/V and-70 pm/V, and piezoelectric clamped stress (e33) of 5 C/m2, showing a substantial improvement over previous piezoelectric fiber composites with uniform electrodes. Maximum strain values of 1700 ppm were measured, indicating higher in-plane actuation than monolithic piezoceramics.
Spatially Convolving Wave Propagation Sensors for Structural Control-Part I: Analytical Development for One-Dimensional Structures
Authors: Pines Darryll J. , von Flotow Andreas H.
Published: August 2009

A novel method for sensing actual disturbance information which can propagate along one-dimensional structural waveguides is developed. The motivation for this work arises from the inability to realize most active wave control designs using output information from physical measurements such as deflection, slope, curvature and internal shear force. Often the use of actual physical measurements leads to instability and suboptimal performance of certain active wave control loops. Thus, there is a desire to develop wave-propagation filters which can extract magnitude and direction of structural disturbances along dispersive and non-dispersive members. In this work a distributed wave sensing scheme is reported which exploits the characterization of 1-dimensional structural motion in terms of traveling waves. This form of the solution is then combined with distributed sensors to convolve future and past measurements into a single temporal signal to overcome the problem of causality and spatial aliasing inherent in discrete sensor approaches. Thus, by imposing specific shapes to spatially convolving sensors, it is possible to combine the output of these sensors with point measurements to observe directional propagating wave components. Because this method requires some approximation of the spatial domain, there will be errors due to spatial discretization and truncation. This work addresses these issues and presents analytical results for one-dimensional structural elements.
Finite Element Free Vibration Analysis of Smart Laminated Composite Beams and Plates
Authors: Bhattacharya P. , Suhail H. , Sinha P. K.
Published: August 2009

The present paper deals with the development of a finite element method for the free vibration analysis of smart laminated composite beams and plates. The structure consists of a laminated composite substrate to which are surface bonded or embedded a set of piezoelectric layers, one of which is a sensor while the others are actuators. The analysis considers the linear piezoelectric constitutive relations and the first order shear deformation behaviour. An eight noded quadratic isoparametric piezoelectric element is developed to discretize the analysis domain, and the same shape functions are used to describe the electrical field, the charge density, the structural geometry as well as the structural displacements. Numerical results are obtained to study the effects of (1) stacking sequences of the composite laminae and piezoelectric layers, (2) geometric boundary conditions and (3) application of electrical voltages on the free vibration frequencies.
Electrorheological Fluids Response under Mechanical Testing
Authors: Vieira Sheila Lopes , de Arruda Antonio Celso Fonseca
Published: August 2009

In most research, ER fluids have been studied and characterized as if they were extremely viscous liquids. In this work, electrorheological fluids were characterized as solids and their mechanical properties in tensile, compression and shear tests were determined. Two different fluids were studied: one of them was made of starch in silicone fluid and the other was composed of carboxymethylcelullose (CMC) in silicone fluid. From the results we concluded that fluids made of CMC have a better performance than those made of starch and also that ER materials are more resistant to compression, tensile and shear stress, in this order. More precisely, ER fluids made of CMC have an elasticity modulus similar to that of rubber. They have tensile strength 600 to 104 times lower than that of LDPE (low density polyethylene) and static yield stress 1 O4 times lower than that of ABS (acrylonitrile-butadiene-styrene terpolymer).
Study of Electrorheological Fluids Behavior under Fatigue Tests
Authors: Vieira Sheila Lopes , de Arruda Antonio Celso Fonseca
Published: August 2009

ER fluids made of starch and CMC in silicone fluid were submitted to fatigue tests in a Material Testing System (MTS). Wohler curves were determined and the behavior of the electric current was studied. We concluded that it is possible to treat data on fatigue life of ER fluids by means of Weibull distribution and that it is possible to determine the time the "snap" begins in an ER material by monitoring the electric current. The ER fluids studied have fatigue lives similar to those of some polymers like polypropylene and polyethylene.
Polymer Surfaces, Interfaces and Computer Modelling: An Investigation of New Intelligent Materials for Sensing Application
Authors: Talaie A. , Taguchi T. , Adachi K. , Zivdar M. , Romagnoli J. A.
Published: August 2009

The discovery of new sensing materials and electrodes has greatly expanded the range of scientific methods including electrochemical techniques. Conducting polymers such as polypyrrole and polyaniline represent a new class of organic polymers that are capable of molecular interactions and being able to interact, chemically or electrochemically, with the species of interest for detection. Although these conductive materials have unique properties they have their specific problems with respect to their reproducibility and reusability. Problems exist due to the dynamic nature of these polymers thereby mitigating against their successful applications as novel sensors. This has also hindered the production of analytical useful, sensitive, and reversible signals using these polymers. This paper has sought to examine the problems due to the lack of useful analytical, sensitive, reversible and re-usable signals through the introduction of new series of integrated artificial intelligence/conducting polymer based sensors. In these type of sensors analytical responses, which look irreversible and non reproducible, are combined by an artificial intelligence trained computer by which reproducible output can be predicted based on the created model and pattern by the computerized system.
Magnetic Thrust Bearing Concepts: Tests and Analyses
Authors: de Weese R. T. , Palazzolo A. B. , Chinta M. , Kascak A.
Published: August 2009

The rotor/stator configurations considered are washer-shaped laminate stack (WL), tape-wound laminate stack (TL), U-shaped laminate stack (UL), solid metal (S), and solid wedge pieces. Since preloading reduces rotor vibration, the effects of preloading a WL rotor and TL stator system on the flux density/input current transfer function magnitude and phase are determined from tests. Since eddy currents result in power loss and phase lag, tests are performed on four rotor/stator pairs, i.e., WL/TL, TL/TL, TL/UL, and S/S, to find the one with minimal eddy currents. For S/S, the test results are compared with those obtained from a two-dimensional finite element analysis, for Silicon-Iron and Hiperco-27. Since overhanging the rotor beyond the stator is a common practice, the effect of this on the fringing of magnetic flux is studied using finite element analysis.
Adaptive Base Isolation System for the Control of Seismic Energy Flow into Buildings
Authors: Şener Murat , Utku Senol
Published: August 2009

Passive base isolation is an effective system for reducing earthquake induced damage to buildings. The effectiveness of the passive base isolation system can be further improved by combining it with an active vibration control system. This "hybrid" base isolation system can actively adapt to seismic excitation to minimize the induced damage to the structure. In this study an "adaptive base isolation" system which utilizes passive base isolation devices and strain inserting actuators is proposed. Strain inserting actuators are placed horizontally between the structure and the foundation in order to isolate the structure from the horizontal components of the ground motion. The proposed system is designed to minimize the earthquake induced forces imposed on the structure, in order to control the seismic energy flow into the building.
Damage Identification of Chordwise Crack Size and Location in Uncoupled Composite Rotorcraft Flexbeams
Authors: Lakshmanan K. A. , Pines Darryll J.
Published: August 2009

The appearance of cracks and delaminations in composite rotocraft flexbeams can lead to degradation in flapwise and lagwise performance of the rotor blade. In addition, cracks in composite rotorcraft flexbeams under cyclic loading can result in rapid fatigue failure of these elements. A novel detection strategy, which attempts to use structural waves to locate damage in the form of a crack, is evaluated in this work. Previous approaches have focused on modal response and damage detection methods. These techniques are incapable of detecting small defects or flaws in structures. However, a continuum mechanics description of the local structural dynamics provides greater resolution in the ability to detect small flaws. Such a model is employed here to determine the location and depth of a crack by examining the frequency domain properties of the scattering coefficient. The magnitude and phase of this parameter contains properties that capture the size and location of the crack. The modeling technique can also be applied to beams under rotation. The additional centrifugal force is modeled as an increase in the stiffness and the analysis is repeated. The analysis captures the trends observed experimentally. A least squares optimization is performed to determine both crack depth and location. Analytical predictions are confirmed on an experimental [0/90]s uncoupled graphite epoxy flexbeam of approximately 16 inches in length. Analytical and experimental results indicate that this approach is able to locate the crack and approximate depth under centrifugal loading. The model predicts the location within 7% and approximates the depth to within 20% under various rotation rates.
An Adaptive Neurocontroller for Vibration Suppression and Shape Control of a Flexible Beam
Authors: Spencer Michael G. , Sanner Robert M. , Chopra Inderjit
Published: August 2009

This paper presents research into an adaptive nonlinear neural network control algorithm that can be used with smart structure actuators and sensors to control the shape and suppress the vibrations of flexible beams. The algorithm presented couples an explicitly model-based adaptive component, which employs time-varying estimates of the beam material properties, with an adaptive neural network, learning in real-time, which is used to estimate the additional actuator moments needed to offset the effects of periodic external disturbances. Experimental results are given for a thin beam, with bonded piezoceramic sensors and actuators, demonstrating the ability of the algorithm to track desired bending profiles and reject the vibrations caused by external disturbances, as well as to maintain this performance despite changes in the material properties of the structure or in the properties of the external disturbance.
Shear Control and Analytic Solutions for 2-D Dynamic Smart Beam Theory
Authors: Cai Duxing , Gao David Yang
Published: August 2009

Analytic solutions are presented for the boundary control of 2-dimensional dynamic smart beam model with shear actuators on the top and bottom of the beam. By using Fourier Series method, the vibration control, optimal location of actuators, and shape control of smart beam are obtained. Applications are also illustrated.
Power Flow Analysis of Electrostrictive Actuators Driven by Switchmode Amplifiers
Authors: Zvonar Gregory A. , Lindner Douglas K.
Published: August 2009

In this paper we analyze the power flow between stacked electrostrictor actuators and a pulse-width-modulated switching amplifier. The amplifier and actuator are analyzed as components of a smart skin whose function is underwater acoustic echo cancellation. An integrated model is developed which includes a dynamic structural model of the actuator, a dynamic model of the power electronics and a nonlinear electromechanical coupling mechanism of the electrostrictor actuation material. Using a linearized version of this model, the mechanical admittance of the actuator as seen by an external force is analyzed. It is shown that an outer acoustic control loop can modify this mechanical admittance and optimize the power coupling between the actuator and an external fluid medium by impedance matching. With the nonlinear model, the power flow between the electrical and mechanical systems is analyzed through simulation. The flow of power is traced from the power injected by the external force, through the amplifier and into the electrical bus. It is shown that effective power flow occurs only when the frequency of the external force is within the bandwidth of the amplifier. This analysis also reveals that the electrical power flow through the actuator is two orders of magnitude larger than the external mechanical power extracted by the actuator. This analysis shows that one main requirement on the amplifier design is to manage the charge flow through the actuator.
Parametric Investigation of the Deflection Performance of Serial Piezoelectric C-Block Actuators
Authors: Moskalik Andrew J. , Brei Diann
Published: August 2009

This paper presents an investigation of the deflection performance of serial configurations of C-block piezoelectric actuators. To conduct the investigation both a theoretical and an experimental approach were used. A theoretical model was derived and experimentally verified with six different case studies. These experimental case studies were used to explore the effect on the deflection performance by modifying the geometric, material, and configuration parameters. The results demonstrate the wide versatility possible with serial C-block actuation architectures.
Control of Low Frequency Structurally Radiated Noise with an Array of Weak Radiating Cells: An Experimental Study
Authors: Ross Bradley W. , Burdisso Ricardo A.
Published: August 2009

The concept of a weak sound radiating cell to reduce low frequency radiated noise from structures is proposed. The cell consists of two mechanically coupled surfaces such that, when placed on a vibrating structure, the responses of the two surfaces are nearly out-of-phase and of equal strength over a wide frequency range. The cell thus behaves as an acoustic dipole and thus a therefore poor sound radiating source. The control of low frequency structurally radiated noise is achieved by covering the structure with an array of these weak radiating cells, i.e., surface treatment. Thus, the surface treatment essentially transforms the response of the structure to that of a distributed array of dipoles yielding a low sound radiating structure. For the implementation of the concept one surface of the cell is rigidly linked to the vibrating structure while the second surface is obtained by attaching a plate to the structure through a flexible mounting system. A dipole acoustic source is formed by designing the system so that the radiated sound from the plate is out-of-phase with the radiated sound from the rigidly linked surface. Experimental verification was performed by applying an array of weak radiating cells to a vibrating rectangular plate excited with white noise from 0-1600 Hz. An overall sound power level reduction of 10.2 dB was achieved between 100-1600 Hz with maximum reductions of 25 dB at discrete frequencies. These results demonstrate the potential of the weak radiating cell concept to reduce low frequency structurally radiated noise.
Helicopter Blade Response and Aeromechanical Stability with a Magnetorheological Fluid Based Lag Damper
Authors: Marathe Sameer , Gandhi Farhan , Wang K. W.
Published: August 2009

This paper explores the feasibility of using Magnetorheological (MR) fluid-based dampers for lag damping augmentation in helicopters. An MR damper model is integrated with a rotor aeromechanical model. Two different control schemes are presented-namely the On-Off scheme and the Feedback Linearization scheme. In the On-Off scheme, two criteria are used to obtain equivalent linear damping for the nonlinear MR damper as a function of the size of perturbation and the applied field. The Feedback Linearization scheme uses a feedback controller to linearize the force output of the MR damper. The two control schemes are compared for lag transient response in ground resonance and their ability to reduce periodic damper loads in forward flight. It is shown that an MR damper of a size comparable to an elastomeric damper can provide sufficient damping for ground resonance stabilization and can significantly reduce periodic damper loads with ajudicious choice of operation scheme.
Improved Operation of Micromechanical Comb-Drive Actuators through the Use of a New Angled Comb Finger Design
Authors: Rosa Michel A. , Dimitrijev Sima , Harrison H. Barry
Published: August 2009

An original design for a new comb finger structure to be used in electrostatically driven actuator devices is presented and experimentally demonstrated. The new design is seen as one viable alternative to the already prevalent rectangular comb finger design and can be considered as a crossbreed between a conventional comb finger design (0 = 0 a parallel-plate design (0 = 900). The design topology is verified both analytically, to show the validity of fundamental effects, and experimentally. Experimental results show the fabricated device based on the new comb finger design achieves twice the displacement of a standard rectangular comb finger based device under equal operating conditions, hence demonstrating twice the force generation capability, while at the same time maintaining overall device stability.
LQR Control of Thin Shell Dynamics: Formulation and Numerical Implementation
Authors: del Rosario R. C. H. , Smith R. C.
Published: August 2009

A PDE-based feedback control method for thin cylindrical shells with surface-mounted piezoceramic actuators is presented. Donnell-Mushtari equations modified to incorporate both passive and active piezoceramic patch contributions are used to model the system dynamics. The well-posedness of this model and the associated LQR problem with an unbounded input operator are established through analytic semigroup theory. The model is discretized using a Galerkin expansion and basis functions constructed from Fourier polynomials tensored with cubic splines, and convergence criteria for the associated approximate LQR problem are established. The effectiveness of the method for attenuating the coupled longitudinal, circumferential and transverse shell displacements is illustrated through a set of numerical examples.
Calculation of Pseudoelastic Elements Using a Non-Symmetrical Thermomechanical Transformation Criterion and Associated Rule
Authors: Gillet Y. , Patoor E. , Berveiller M.
Published: August 2009

There are relatively few applications in the market that utilize SMA considering the large number of patents filed. This can be partly explained by the lack of design tools able to correctly predict SMA behavior. Due to the highly non-linear behavior of SMA, classical methods of design are inefficient. Furthermore, SMA behavior is strongly temperature dependent and exhibits hysteresis. The aim of this study is to give a method of measurement adapted to SMA. The definition of a constitutive equation describing the superelastic behavior and its application to structure calculation based on the classical beam theory assumptions is presented. Numerical results obtained in this way are compared with experimental measurements performed on Cu-based alloys.
Thermomechanical Response of SMA Composite Beams with Embedded Nitinol Wires in an Epoxy Matrix
Authors: White S. R. , Berman J. B.
Published: August 2009

Nitinol shape memory wires were embedded in epoxy beams to study their thermomechanical behavior in the embedded state. Beams were made with ten wires placed below the geometric mid-plane. A room temperature cure epoxy was used to minimize residual stresses acting on the wires. The beams were placed in an oven and heated from room temperature to a temperature well above the austenitic finish temperature of the wires. The beams were photographed through a window in the oven door at periodic intervals during the experiment. The photographs were analyzed to measure beam deflections during the experiment resulting from thermal and shape memory transformational strains. A beam model was developed and predictions of beam curvature were compared to the experimental data. The results show that agreement between the model and the experimental data is dependent, and extremely sensitive to, an accurate knowledge of the thermomechanical properties of both the nitinol and epoxy phases. Large deflections of the beams were obtained and some evidence of a transformation front propagation from the edges to the center of the beam is shown.
Micromechanics of Magnetoelectroelastic Composite Materials: Average Fields and Effective Behavior
Authors: Li Jiang Yu , Dunn Martin L.
Published: August 2009

A micromechanics approach is developed to analyze the average fields and effective moduli of heterogeneous media that exhibit full coupling between stationary elastic, electric, and magnetic fields. Exact relations regarding the internal field distribution inside a heterogeneous magnetoelectroelastic solid are first established, followed by exact connections between the effective magnetoelectroelastic and thermal moduli of two-phase composites. The Mori-Tanaka mean field approach is then applied to obtain closed form expressions for the effective moduli of fibrous and laminated composites. Finally, numerical results for BaTiO3-CoFe2O4 composites are presented and discussed.
An Analytical Description of Slow Hysteresis in Polarized Ferroelectric Ceramic Actuators
Authors: Huang L. , Tiersten H. F.
Published: August 2009

Recently, an existing system of electroelastic equations was extended to account for slow hysteretic effects in polarized ferroelectric ceramic plates by employing an internal variable in a thermodynamic state function. All material irreversibility was taken to be a consequence of the ferroelectric polarization-electric field irreversibility. Since only the slowest possible hysteresis is of concern, the evolution equation is ignored and the known irreversible thickness polarization-electric field saturation curve is taken as the starting curve. Since all experimental data available to us are from strain measurements on a thin wide beam forced by voltages applied to very thin polarized ferroelectric ceramic actuators on the surfaces, the linear strain, plane-stress version of the equations is employed in the description of the actuator. The new irreversible material coefficients for the case of plane-stress are obtained from data on one major hysteresis loop along with the coefficients in the saturation polarization-electric field relations. These now known coefficients are then used to calculate other hysteresis loops, which are shown to agree quite well with measurement.
Hysteresis Modeling of SMA Actuators for Control Applications
Authors: Webb Glenn V. , Lagoudas Dimitris C. , Kurdila Andrew J.
Published: August 2009

Active material actuators, sometimes referred to as "smart" actuators, are gaining widespread use for control actuation. Many of these actuators exhibit hysteresis to some degree between their input and output response. There exists an extensive body of research concerning the modeling of hysteresis for the linearization, or compensation, of these hysteresis nonlinearities. However, the models have typically been identified off-line and mainly used in open-loop compensation. When the identified models do not exactly match the actuator nonlinearities, the compensation can create an error between the desired and actual control output. The hysteresis for several of these actuators has been shown to evolve over time, and can render a fixed hysteresis model inadequate to linearize the hysteretic nonlinearities. This paper presents an adaptive hysteresis model for on-line identification and closed-loop compensation. Laboratory experiments with a shape memory alloy wire actuator provide evidence of the success of the adaptive identification and compensation. In addition, the means of determining the saturation of the SMA using updated information from the adaptive hysteresis model is provided.
Shaping of Piezoelectric Sensors/Actuators for Vibrations of Slender Beams: Coupled Theory and Inappropriate Shape Functions
Authors: Irschik Hans , Krommer Michael , Belyaev Alexander K. , Schlacher Kurt
Published: August 2009

Flexural vibrations of smart slender beams with integrated piezoelectric actuators and sensors are considered. A spatial variation of the sensor/actuator activity is achieved by shaping the surface electrodes and/or varying the polarization profile of the piezoelectric layers, and this variation is characterized by shape functions. Seeking shape functions for a desired purpose is termed a shaping problem. Utilizing the classical lamination theory of slender composite beams, equations for shaped sensors and actuators are derived. The interaction of mechanical, electrical and thermal fields is taken into account in the form of effective stiffness parameters and effective thermal bending moments. Self-sensing actuators are included. From these sensor/actuator equations, shaping problems with a practical relevance are formulated and are cast in the form of integral equations of the first kind for the shape functions. As a practical interesting aspect of these inverse problems, shape functions which fail to measure or to induce certain structural deformations are investigated in the present paper. Such inappropriate shape functions are termed nilpotent solutions of the shaping problems. In order to derive an easy-to-obtain class of such nilpotent solutions, the homogeneous versions of the integral equations for the shaping problems are compared to orthogonality relations valid for redundant beams. Hence, by analogy, the presented nilpotent solutions are shown to correspond to solutions of the basic theory of thermoelastic structures, namely to thermally induced static bending moment distributions. This result beautifully reflects the close connection between the theory of thermally loaded structures and the theory of smart structures. A particular result for a nilpotent shape function previously investigated in the literature is explained in the context of the present theory, and examples of nilpotent shape functions for various structural systems are presented.
MEMS-Based Control of Structural Dynamic Instability
Authors: Berlin Andrew A. , Chase J. Geoffrey , Yim Mark , Maclean Brian J. , Olivier Marc , Jacobsen Stephen C.
Published: August 2009

This paper describes the design, analysis and characterization of a prototype active column that applies distributed MEMS technology to the active stabilization of a buckling compressive member. The axial load bearing capacity of structural members can be increased by actively controlling the dynamic instability of buckling. Effective active stabilization is dependent on three primary factors: sensor precision, actuator authority, and control system bandwidth. A networked array of MEMS sensors, filamentary PZT actuators, and recently developed optimal control strategies are combined to demonstrate active control of an inherently unstable column. The active system, designed and simulated using finite element and optimization methods, stabilizes an experimental column for compressive axial loads up to 2.9 times the critical buckling load. Additionally, the system is stable for all loads in the range from tension to this maximum compressive axial load.
A Semi-Active Suspension Using ER Fluids for a Commercial Vehicle Seat
Authors: Choi S. B. , Choi J. H. , Nam M. H. , Cheong C. C. , Lee H. G.
Published: August 2009

This paper presents control performances of a semi-active suspension using ER (electro-rheological) fluids for a commercial vehicle seat. A cylindrical ER seat damper is designed and manufactured by incorporating Bingham model of an arabic gum-based ER fluid. After evaluating field-dependent damping characteristics of the ER seat damper, a sliding mode controller is formulated to control the seat vibration due to external excitations. The controller is then experimentally realized and controlled responses are presented in both time and frequency domains. In addition, a full-car model consisting of primary, cabin and seat suspensions is established and the hardware-in-the-loop simulation (HILS) is undertaken to demonstrate a practical feasibility of the proposed seat suspension system showing ride comfort quality under various road conditions.
Electro-Rheological Fluid Controllers
Authors: Ivanescu Mircea , Stoian Viorel
Published: August 2009

The paper proposes two new fluid controllers based on the properties ofthe ER fluids. The first controller is a modulated width pulse system in which the control variable is not the amplitude of the input, but rather the duration of the input signal with constant amplitude. An ER valve with an on/off function assures the pulse-width modulated signal. This valve operates as a hydraulic semiconductor controlled by a high-voltage signal. A processor defines the control algorithm and computes the pulse width. A special circuit assures the high-voltage pulse-width modulated signal that controls the ER valve. The dynamic equations of this system are deduced, the transfer functions of each component are obtained and the classic parameters of this controller are computed. It is shown that the proportional and integral coefficients of this controller can be easily implemented from the model parameters. The second controller is a new control system based on the viscosity control of ER fluids by an electrical field. It is shown that the motion control can be divided into two parts: a conventional control determined by the second Lyapunov method for the pressure control of the ER fluid and a non-conventional control obtained by the viscosity control. It is shown that the stability of the motion on a switching manifold is assured if some constraints determined by the non-linear elements of the system are verified. Two control methods are proposed. The first is determined by a simultaneous control of the viscosity on the overall system, a lumped control. The second method is defined by a distributed control of the viscosity associated with a decomposition of the system in a finite number of lower dimension problems. These procedures are applied to a special manipulator, a tentacle arm, and several numerical simulations are presented.
Urethane Modified Polyethers as Homogeneous Electrorheological Materials
Authors: Minagawa Keiji , Okamura Hirokazu , Masuda Seizo , Tanaka Masami
Published: August 2009

Urethane modified polyethers having hard-soft-hard or soft-hard-soft structure were prepared by addition of isocyanate compounds and polyether glycols. It was found that a hard-soft-hard polymer prepared from polypropylene glycol and naphthalene diisocyanate shows an increase of viscosity in an electric field (positive electrorheological effect), while a soft-hard-soft polymer prepared with the same starting materials shows a decrease of viscosity (negative electrorheological effect). Viscosity measurements and NMR relaxation analyses of monodisperse model compounds were also performed to consider the mechanism of these opposite effects. Comparison of 'H-NMR relaxation times of modified and unmodified polyether indicated that the rapid mode of molecular motion is enhanced by the modification while the slow mode is restricted. The change of molecular movement by the modification of polyether is considered to play some role in the enhanced electro-responsive property.
Reynolds Number Effects in the Flow of an Electrorheological Fluid between Fixed Surfaces of Revolution
Authors: Walicki Edward , Walicka Anna
Published: August 2009

The steady laminar flow of electrorheological fluid (ERF) through a narrow space between two fixed surfaces of revolution is considered. The ERF is modeled as a viscoplastic fluid. This problem is described by boundary layer equations. Using the method of averaged inertia one obtains the formulae expressing the pressure distributions. Numerical examples of pressure distributions between parallel disks and between concentric spherical surfaces are presented.
Magnetic Field Sensitive Polymeric Actuators
Authors: Zrinyi M. , Szabo D. , Barsi L.
Published: August 2009

This paper reports on the magnetoelastic properties of a recently developed soft and wet material; the magnetic field sensitive polymer gel. It is a polymer network swollen by a ferrofluid. The peculiar magnetoelastic properties may be used to create a wide range of motions and to control the shape change and movement. An understanding of magnetoelastic coupling in gels will hasten the application of gel engineering to switches, sensors, micromachines, biomimetic energy-transducing devices and controlled delivery systems.
The Permanent Freezing of ER Fluids at Room Temperature
Authors: Winslow Willis M.
Published: August 2009

Over a duration of time, films of certain all-liquid electrorheological (ER) fluids between stationary electrodes charged only with alternating current voltage will freeze. The word freeze is used here to describe a lock which extends beyond the time the electrodes are charged. In other words, the electrodes are not moveable even when the voltage is removed. This freeze is in addition to the instantaneous lock in between charged electrodes that occurs with either alternating current or direct current. With either current, this instantaneous lock breaks when voltage is removed. However, continued application of alternating current over time with stationary electrodes will induce a permanent freeze. While this permanent freeze lasts indefinitely, it immediately breaks into a liquid when the electrodes are pried apart.