bluuebunny/crossref_metadata_2025 huggingface dataset:
Active Vibration Control of Intelligent Composite Laminate Structures Incorporating an Electro-Rheological Fluid
Authors: Choi Seung-Bok , Park Yong-Kun , Cheong Chae-Cheon
Published: August 2009

This paper addresses an active vibration control of intelligent composite laminate structures containing an electro-rheological (ER) fluid. Firstly, complex shear modulus of the ER fluid itself is obtained as a function of imposed electric fields and excitation frequencies through a rotary oscillation test. By incorporating the measured complex modulus with a conventional sand wich beam theory, elastodynamic properties of the structures are then predicted. Subsequently, an experimental investigation is undertaken in order to identify modal characteristics such as damped natural frequencies, damping ratios, and mode shapes of the structures. As for the validation of the modeling methodology, the comparison between the predicted elastodynamic properties and the measured ones is performed. Characteristics of the ER fluid actuator explicitly representing the relationship between elastodynamic properties and imposed electric fields are also inferred. A control system model is then formulated by combining the actuator characteristics into a phenomenological governing equation of a finite element form. Based on the field-dependent frequency responses of the structures, an active control algorithm for accomplishing desired responses of the tip deflection is established. In addition, in order to validate the proposed control strategy, the measured desired responses by means of an experimental implementation are compared with the predicted ones through the proposed model in the frequency domain. Finally, the effectiveness of the proposed control model for avoiding resonance to variable disturbances is evaluated by presenting the controlled tip deflection of the employed composite structures with respect to control gain in the time domain.
Optimal Location of Redundants for Prestressing Adaptive Trusses
Authors: Jalihal P. , Utku S. , Wada B. K.
Published: August 2009

This paper describes the location selection of minimunt number of actuator mounted redundant bars for complete prestressing of a determinate truss. Two computationally simple algorithms are presented to obtain the optimal locations of the redundants. The optimal bar prestresses are then obtained by using the least squares solution for the redundant bar forces, knowing the desired list of bar prestresses. The paper then proposes the use of a positive scale parameter. to prevent local buckling/rupture of individual bars of the resulting indeterminate truss and its global buckling. The procedure is illustrated on a simple two-dimensional truss.
Modeling and Analysis of a Shape Memory Alloy-Elastomer Composite Actuator
Authors: Wu W. , Gordaninejad F. , Wirtz R. A.
Published: August 2009

A theoretical model of the stress-strain-temperature response of a thermally driven. shape memory alloy (SMA) composite actuator under applied load is developed. The actuator is assumed to be constructed from a thin layer of SMA bonded to a layer of elastomer. The model is developed by considering an energy balance on the SMA and force equilibrium for both SMA and the composite. It includes the martensite fraction of the SMA as a state variable which describes the phase transition process and the constitutive relation of the SMA. Closed-form solutions for the stress-strain-temperature response are obtained by assuming that heat conduction in the axial direction is negligible. Parametric studies are conducted to show how the material properties of the elastomer and geometric dimensions of the actuator affect the thermal and stress responses of the actuator. Finally, the actuation force as a function of the heating power is predicted by the model.
Basic Observations on Electro-Rheological Fluids
Authors: Stangroom J. E.
Published: August 2009

The early observations which lead to the "Water Bridge" theory of ER fluids are described. The key features are, firstly that a very wide range of materials show some ER response, and secondly, that although the electric field evokes the inter-particle force, it can be shown that the latter is not purely electrostatic.
Composite Structure Analysis of a Hollow Cantilever Beam Filled with Electro-Rheological Fluid
Authors: Berg C. D. , Evans L. F. , Kermode P. R.
Published: August 2009

Unwanted vibrations within structures can become an ever increasing problem as structural components are made lighter with the use of advanced materials and tighter design tolerances. Increased operating bandwidth further compounds the problem resulting in the build up of unwanted vibrations within optimally designed structures. The alteration of the spectral signature of a structural component will enable the aforementioned design criteria to be satisfied. The use of a hollow structural component filled with Electro-Rheological fluid will enable the spectral signature of the component to be altered electrically.

Experimental data obtained for a hollow cantilever beam filled with Electro-Rheological fluid is presented in this paper. Analysis of the data is carried out to determine heuristic values for the beams effective stiffness and damping coefficient. The effects of applying an electric field to the ER fluid are outlined from the results obtained. Comparison of the results is then made with those predicted by a model of an oscillating composite structure cantilever beam. Differences between the predicted and the heuristic data is then examined with regard to a hypothesis based on the behaviour of the induced ER fluid's microscopic structure.
Liquid Dielectric with Dispersed Particles as an Active Medium for an "Acoustic" Laser
Authors: Zavtrak S. T.
Published: August 2009

The theoretical scheme of an "acoustic" laser is suggested. A liquid dielectric wiith dispersed particles is considered as an active medium. Pumping is created by an oscillating electric field that deforms dispersed volumes or by a piezoelectric emitter of a piston type. Two types of resonators (rectangular and cylindrical) are considered for this laser. Phase bunching of initially incoherent emitters (dispersed particles) is realized by acoustic radiation forces. The generation conditions for this "acoustic" laser are evaluated. It is shown that two types of losses must be overcome in order for generation to begin. The first type results from the energy dissipation in the active medium and the second one is caused by radiation losses at the boundaries of the resonator. The possibility of the creation of an "acoustic" laser with an extraordinary active medium (liquid helium with free electrons) is discussed.
Effect of the Electric Field on Wave Motion in a Thin Suspension Layer Flowing Over an Inclined Plane
Authors: Selezov I.
Published: August 2009

Stability of surface gravity waves in an inclined layer of rheological fluid in the presence of an arbitrarily oriented electric field is considered to investigate the effect of electric fields on wave stability. Rheological equations used for a dilute suspension of the rigid dielectric ellipsoids take into account the influence of electric fields on a particular orientation. The evolution equation is derived as a long-wavelength approximation which includes a set of nondimensional parameters responsible for the behaviour of the suspension. Solution of the evolution equation is obtained in the form of a nonlinear wave with the amplitude and phase slowly varying in time in such a way as to allow determination of the curves of neutral stability, bifurcations, suband supercritical instabilities. The results of calculations show that the electric field can both stabilise or destabilise waves.
Boundary Lubrication Characteristics of Silica-Based Electro-Rheological Fluids
Authors: Park W. C. , Choi S. B. , Cheong C. C. , Suh M. S. , Yeo M. S.
Published: August 2009

This experimental study presents friction and wear characteristics under boundary lubrication associated with silica-based ER (Electro-Rheological) fluids. Various types of base liquids (silicone oil, olive oil, transformer oil) and corresponding silica-based ER fluids are adopted as lubricants. As a first step, yield shear stresses of the ER fluids are measured as a function of imposed electric fields. Pin-on-disc wear testings are then performed with the lubricants by evaluating wear rates of the pin specimens. The governing relationship between the wear rate and the fielddependent yield stress is established for the application guideline of the ER fluids. Microscopic observations of worn surfaces of the pin specimens are also analyzed in order to validate the measured wear characteristics. In addition, friction coefficients of the ER fluids are experimentally evaluated with respect to normal loads.
Additional Magnetic Dispersed Phase Improves the Mr-Fluid Properties
Authors: Kordonsky W. I. , Demchuk S. A.
Published: August 2009

The main characteristics of the MR-fluid are the stability and sensitivity of its effective viscosity to an applied magnetic field. Such systems must be well fluid outside the applied field, as the viscosity increases many times in the magnetic field. A method is proposed for improving the MR-fluid properties by adding an additional high-dispersed magnetosolid powder to it. A relatively small content of magnetosolid particles causes a more than 9-fold increase of the MR-fluid viscosity in the magnetic field.
Correlation between Electrical and Rheological Properties of Electrorheological Fluids
Authors: Foulc J. N. , Atten P. , Boissy C.
Published: August 2009

We present results of simultaneous measurements of shear stress and current flowing through a cellulose/mineral oil suspension subjected to shear and DC electric field. Single curves for the variation of apparent viscosity and normalised current are obtained when taking a simplified Mason number as variable. The different regimes observed are discussed in terms of the degree of structuration of the suspension reflected by the Mason number.
Nucleation Theory of Structure Evolution in Magnetorheological Fluid
Authors: Zhu Y. , Gross M. , Liu J.
Published: August 2009

A phenomenological model of nucleation-controlled structure evolution in dilute magnetorheological (MR) fluid is suggested. We find that the critical diameter of column nuclei is related to the external magnetic field Ho, the increase in permeability Att of the nuclei, and to the nucleus surface tension a, by a relation of the form D, = 2a/[JAg I + (I /87r)(H' -H2)(A/t/lI)]. The growth rate of columnar structure, and the field and volume fraction dependencies of the separation between the columns are calculated, and found to be given respectively by d -t d -H314, and d - 1/7. These results fit the experimental data in ferrofluid emulsion systems very well.
On the Role of Conductivities and Frequency in the Electrorheological Effect
Authors: Boissy C. , Atten P. , Foulc J. -N.
Published: August 2009

The aim of this investigation is to establish in the case of DC field or low frequency field the role of conductivities of both suspending liquid and particles in the electrorheological (ER) effect. We approach the problem in considering the case a, < UL and the case ar > UL. For aS > UL we estimate an upper limit for a5 to obtain stable chains. We also investigate the question of the transition between a behaviour determined by the conductivities of the constituents and the behaviour determined by their permittivities.
The Numerical Analysis of Channel Flows of ER Fluida
Authors: Jang Y. J. , Suh M. S. , Yeo M. S. , Choi S. B.
Published: August 2009

A numerical analysis is performed on the flow characteristics of an electrorheological (ER) fluid when fully developed ER fluid flow in a channel is instantly subjected to electric fields. The Bingham plastic model is used to describe the ER fluid behavior. The flow field is assumed to be incompressible and isotropic. The SIMPLER algorithm with staggered grid system is employed to solve the momentum and continuity equations governing the steady state, laminar flow. The effects of electric field intensity and upper wall velocity changes on velocity profiles are investigated.
Large-Amplitude Rotary Induced-Strain (LARIS) Actuator
Authors: Giurgiutiu Victor , Rogers Craig A.
Published: August 2009

Induced-strain materials can produce very large forces and, hence, large energy density, but small actual displacements. A new concept for obtaining large-amplitude rotary displace-ments from small linear displacements generated by induced-strain material stacks is proposed. The concept utilizes the theory of twist-warping coupling in thin-wall open tubes. The theory of the proposed solid-state axial-to-rotary converter-amplifier, together with the appropriate bibliographical references, is given. A simple formula is generated for estimating the axial-to-rotary conversion-am-plification coefficient from the geometrical length, L, and enclosed area, A, of the open tube. A large-displacement induced-strain rotary (LARIS) actuator proof-of-concept demonstrator was built and tested to verify and validate the theoretical developments. The LARIS actuator consisted of a 28 mm diameter, 1.2 m length open tube and a 120,um, -1000 V PZT translator. The experimental set-up and the excitation and measuring equipment are fully described in the paper. A maximum rotary displacement of 80 was measured, and the linear relationship between the rotation coefficient, the tube length, L, and the inverse of the enclosed area, A, was verified. An improved theoretical model, that accounts for the experimentally observed zero off-set, is also given. The theoretical developments and experimental tests presented in this paper show that the proposed LARIS actuator, based on a novel solid-state axial-to-rotary converter-amplifier utilizing the warp-ing-torsion coupling of an open tube, is a viable design option, of great constructive simplicity and very low parts count. This concept can be successfully used in a series of aerospace and mechanical engineering applications, as for example in the actuation of adaptive control surfaces for aircraft wings and helicopter blades. The 80 rotary displacement capabilities measured on the proof-of-concept demonstrator can be easily scaled to other values to meet the operation requirements of specific applications. For very large angles (40-50o), conventional electromechanical actuators (e.g., stepper-motors and ball-screws assemblies) can be used.
Mathematical Modelling of the Dynamic Response of Electro-Rheological Fluid
Authors: Firoozian R.
Published: August 2009

The dynamic response of electro-rheological (ER) fluid is studied and it is shown that the current response to a change in the applied voltage can be modelled accurately by a simple nonlinear RC network. Various models proposed in the literature are studied and are compared with the simple model. When the voltage is applied across the electrode of an ER device the yield stress changes from a zero to a finite value. It is concluded that the dynamic response of the yield stress cannot be measured from test in flow mode. However, by employing a simple signal processing technique the dynamic response can be estimated in shear mode. The dynamic response of the yield stress is modelled by a second order transfer function characterized by a natural frequency and a damping ratio.
A Discrete-Time Sliding Mode Control of Flexible Smart Structures with Piezofilm Actuators
Authors: Choi Seung-Bok , Cheong Chae-Cheon , Kim Myoung-Suk
Published: August 2009

In this study, a new discrete-time sliding mode controller is proposed and applied to active vibration control of a flexible smart structure featuring a piezofilm actuator. After deriving the governing equation of motion for the smart structure, a discrete-time control model with system uncertainties is constructed in a state space. A stable sliding surface is then designed followed by the formulations of a discrete-time sliding mode controller which consists of a discontinuous part and an equivalent part. For the design of the discontinuous part, a time-varying control gain is adopted to increase system robustness to the uncertainties. In the design of the equivalent part, a so called equivalent controller separation method is employed to achieve faster reaching to the sliding surface without extension of the sliding region in which undesirable vibration chattering may be arisen. Controlled responses of transient and forced vibrations are evaluated through computer simulation and experimental realization.
A Sensor for Measuring Gel Phase-Transition Temperature, with Potential as a Metal Ion Detector
Authors: Jackson Deron K. , Leeb Steven B. , Mitwalli Ahmed , Fusco Dahlene , Wang Changnan , Tanaka Toyoichi
Published: August 2009

This paper describes a sensor employing a gel formed from an interpenetrating polymer network of poly(vinyl alcohol) and a copolymer of N-isopropylacrylamide and acrylic acid. This gel exhibits a continuous volume-phase transition that is strongly dependent on the presence of polyvalent metal ions in the gel solvent. A sensor apparatus has been constructed that estimates, in real time, the transition temperature of a gel. When this sensor is loaded with a gel sensitive to metal ions, it could be used to detect the presence and identity of metal ions in a solution.
An Improved Reissner-Mindlin-Type Model for the Electromechanical Analysis of Multilayered Plates Including Piezo-Layers
Authors: Carrera Erasmo
Published: August 2009

Dealing with multilayered plates including piezo-layers, this paper presents a mechanical model which allows an accurate description of both the in-plane displacement (zig-zag effect is included) and the transverse shear stress fields (interlaminar equilibrium is fulfilled). Moreover, it preserves the computational advantages of the standard Reissner-Mindlin finite element formulation. The electrical stiffnesses are taken into account through assuming a quadratic distribution along the thickness for the voltage field. Von K'ármán-type nonlinearities are considered. The weak form of the coupled system of governing equations, in the dynamic case, has been written by employing the principle of the virtual displacements. Approximate governing equations in the form of nonlinear systems of algebraic equations have been obtained for the particular case of finite element applications. Newton-Raphson linearization technique has been applied and the consistent tangent matrix has been derived. Explicit forms of the derived electromechanical arrays have been quoted in the form of an Appendix. Some numerical results are given to furnish a preliminary assessment of the novel model.
One-Dimensional Thermomechanical Constitutive Relations for Shape Memory Materials
Authors: Liang C. , Rogers C. A.
Published: August 2009

The use of the thermoelastic martensitic transformation and its reverse transformation has recently been proposed and demonstrated for several active control applications. However. the present constitutive models have lacked several important fundamental concepts that are essential for many of the proposed intelligent material system applications such as shape memory hybrid composites.

A complete, unified, one-dimensional constitutive model of shape memory materials is developed and presented in this paper. The thermomechanical model formulation herein will investigate important material characteristics involved with the internal phase transformation of shape memory alloys. These characteristics include energy dissipation in the material that governs the damping behavior, stress-strain-temperature relations for pseudoelasticity, and the shape memory effect. Some numerical examples using the model are also presented.
Design of Shape Memory Alloy Springs with Applications in Vibration Control
Authors: Liang C. , Rogers C. A.
Published: August 2009

Shape memory alloys (SMAs) have several unique characteristics, including their Young's modulus-temperature relations, shape memory effects, and damping characteristics. The Young's modulus of the high-temperature austenite of SMAs is about three to four times as large as that of low-temperature martensite. Therefore, a spring made of shape memory alloy can change its spring constant by a factor of three to four. Since a shape memory alloy spring can vary its spring constant, provide recovery stress (shape memory effect), or be designed with a high damping capacity, it may be useful in adaptive vibration control. Some vibration control concepts utilizing the unique characteristics of SMAs will be presented in this paper.

Shape memory alloy springs have been used as actuators in many applications although their use in the vibration control area is very recent. Since shape memory alloys differ from conventional alloy materials in many ways, the traditional design approach for springs is not completely suitable for designing SMA springs. Some design approaches based upon linear theory have been proposed for shape memory alloy springs. A more accurate design method for SMA springs based on a new nonlinear thermomechanical constitutive relation of SMA is also presented in this paper.
Coupled Electro-Mechanical Analysis of Adaptive Material Systems-Determination of the Actuator Power Consumption and System Energy Transfer
Authors: Liang C. , Sun F. P. , Rogers C. A.
Published: August 2009

This article presents a coupled electromechanical analysis of piezoelectric ceramic (PZT) actuators integrated in mechanical systems to determine the actuator power consumption and energy transfer in the electromechanical systems. For a material system with integrated PZT actuators, the power consumed by the PZT actuators consists of two parts: the energy used to drive the system, which is dissipated in terms of heat as a result of the structural damping, and energy dissipated by the PZT actuators themselves because of their dielectric loss and internal damping. The coupled analysis presented herein uses a simple model, a PZT actuator-driven one-degree-of-freedom spring-mass-damper system, to illustrate the methodology used to determine the actuator power consumption and energy flow in the coupled electromechanical systems. This method can be applied to more complicated mechanical structures or systems, such as a fluid-loaded shell for active structural acoustic control. The determination of the actuator power consumption can be very important in the design and application of intelligent material systems and structures and of particular relevance to designs that must be optimized to reduce mass and energy consumption.
Modelling of the Two-Way Shape Memory Effect
Authors: Zhang X. D. , Rogers C. A. , Liang C.
Published: August 2009

After detailed analyses ofthe microstructural mechanism and training methods ofthe two-way shape memory effect, a further refinement of the transformation kinetic expressions for shape memory alloys (SMAs) is derived. A one-dimensional thermomechanical constitutive model for the two-way effect which undergoes thermoelastic martensitic transformation and its reverse transformation is presented based on the one-way effect model of Liang and Rogers. This model reflects the essence of SMAs in a very simple form and therefore is easy to use in engineering design. It is revealed that the material parameters required by this model can be calculated or measured using standard material testing apparatus. The computer simulation results are in agreement with the experimental data that has been published in the open literature. It is demonstrated that the theory developed can quantitatively predict and describe the behaviour of SMAs and be imposed on the two-way shape memory effect.
Integration and Design of Piezoceramic Elements in Intelligent Structures
Authors: Zhou S. , Liang C. , Rogers C. A.
Published: August 2009

The design of induced strain elements (actuators) is a comprehensive issue, involving not only the materials and geometry of the elements, but also the behaviors of the coupled host structures. In particular, the design of the active elements is essentially related to the prediction of induced strain or stress in the elements. A high stress or strain level in the actuators is useful to excite host structures; however, degradation or fatigue damage of the actuators may take place at the same time. This paper presents a dynamic analytical approach for the design and integration of active piezoceramic (PZT) patch elements locally coupled with host structures. Several critical design issues are addressed. These issues include the determination of the actuator dynamic outputs, the prediction of energy conversion efficiency, the estimation of system power requirement, and the limitation of induced alternate peak stress. A coupled electromechanical analytical model was developed to reveal the inherent connections among these issues. Both the mechanical stress behavior and the thermal stress characteristics of the PZT patch elements were investigated. A system power consumption-based model was developed to estimate the temperature and thermal stress distribution of the elements. The attention in parametric design was directed to the thickness and location of the elements. A simply-supported thin plate with surface-bonded PZT patches was built and tested to directly measure the induced dynamic strain of the PZT element so that the prediction accuracy and ability of the design model has been validated.
Investigation of Shape Memory Polymers and Their Hybrid Composites
Authors: Liang C. , Rogers C. A. , Malafeew E.
Published: August 2009

In this paper, a newly developed polymer, shape memory polyurethane (SMP), will be introduced. The shape memory polymer possesses the same basic shape memory effect and elasticity memory effect as shape memory alloys. Shape memory polymers can change their elastic modulus up to 500 times around their glass transition temperatures. Both the shape memory effect and the elasticity memory effect of shape memory polymers make them a useful candidate for today's intelligent material systems and structures. This paper will introduce some of the basic characteristics of SMPs and the results of some initial investigation of SMP composites.
Flexible Graphite for Sensing Stress/Displacement
Authors: Luo Xiangcheng , Chung D. D. L.
Published: August 2009

Flexible graphite sandwiched by copper, after stabilization by two cycles of compressive stress, is a piezoresistive compressive stress/displacement sensor for stresses (perpendicular to the sandwich plane) up to 4 MPa and displacements up to 25% of the flexible graphite thickness. The stress sensitivity (fractional change in resistance per unit stress) is up to 5.4 MPa-' and displacement sensitivity (fractional change in resistance per unit strain in graphite) is up to 6.2. The sensitivities decrease with increasing stress/displacement. The electrical resistance decreases reversibly upon compression, due mainly to reversible decrease in the contact resistivity between graphite and copper. Stabilization removes most irreversibility.
Proportional Feedback Control of an Electro-Rheological Vibration Damper
Authors: Sims N. D. , Stanway R. , Beck S. B. M.
Published: August 2009

In this paper, the authors derive a quasi-steady model of an electro-rheological damper under proportional feedback control. Using this model it is shown how, through the choice of two gain terms, the input/output characteristic of the closed-loop system can be linearised. Also, through the choice of a third gain term, the slope of the force/velocity line can be determined. A numerical study compares the performance of openand closed-loop schemes and indicates clearly the working range over which linear behaviour can be obtained.
Chemomechanical Polymer Gel with Fish-like Motion
Authors: Ueoka Yasuji , Gong Jianping , Osada Yoshihito
Published: August 2009

A water-swollen polymer gel which swings and undulates water backward was made by applying an electric field and making a reversible assembly-reaction of surfactant on the gel. Using this principle a fish-like soft-machine slowly moving forward by undulating the tail was made. The motion was analyzed and the mechanism was discussed.
Identification of Hysteretic Control Influence Operators Representing Smart Actuators, Part II: Convergent Approximations
Authors: Banks H. T. , Kurdila A. J. , Webb G.
Published: August 2009

In a previous paper, the authors investigated the lower semicontinuity properties of two generalizations of the classical Preisach operator: the smoothed Preisach operator and the Krasnoselskii/Pokrovskii (KP) integral hysteresis operators. In particular, it was demonstrated that the output least squares identification problem for the KP operator is well-posed over compact subsets of the Preisach plane. The identification of the hysteretic control influence operator was shown to be equivalent to the identification of a measure in the space of probability measures taken with the weak* topology. In this paper, a consistent and convergent approximation scheme is introduced for this class of integral hysteresis operator. The Galerkin approximation scheme is shown to be function space parameter convergent. A numerical example is presented that illustrates aspects of the theory derived in this paper.
Analysis and Testing of a Froude Scaled Helicopter Rotor with Piezoelectric Bender Actuated Trailing Edge Flaps
Authors: Koratkar Nikhil A. , Chopra Inderjit
Published: August 2009

This paper presents an analytical model and validation tests of a Froude scaled rotor featuring piezoelectric bender (bimorph) actuated trailing-edge flaps for active vibration suppression. The analytical model for the coupled bimorph actuator trailing-edge flap dynamic response in the rotating environment takes into account the aerodynamic, centrifugal, inertial and frictional loads acting on the actuator-flap system. The linkage arm length associated with the mechanical amplification mechanism is selected to maximize flap performance in the rotating environment. The bimorph clamping is improved to prevent actuator slippage under high centrifugal loads. The analytical model is validated by carrying out a series of bench tests, vacuum chamber tests and hover tests. In hover, flap deflections of ±6 degrees at 4/rev flap excitation are achieved at 900 RPM, thus demonstrating the potential of the piezoceramic bender as a lightweight and compact actuation system for individual blade control purposes. This paper also includes a feasibility study for piezo-bimorph actuation of a trailing-edge flap for a Mach scaled rotor model.
Magnetically Driven Chemomechanical Device with Poly(N-isopropylacrylamide) Hydrogel Containing γ-Fe2O3
Authors: Kato Norihiro , Takizawa Yoshihiko , Takahashi Fujio
Published: August 2009

Magnetic heating was applied to convert magnetic energy into chemomechanical work by using poly(N-isopropylacrylamide), poly(NIPAAm) gel, exhibiting a reversible swellingshrinking property. y-Fe2O3, which can generate heat by itself due to hysteresis loss in the presence of an alternating magnetic field, was immobilized within poly(NIPAAm) gel. The shrinking rate of the hydrogel accelerated when the inner temperature of the gel was increased over 34°C, the lower critical solution temperature (LCST). The initial rate of the temperature increase, which was in proportion to the amount of immobilized ferromagnetic powder, was 0.2°C/s in the gel immobilized 24% of the y-Fe2O3 weight under the alternating magnetic field (effective value 830 Oe, maximum value 1,170 Oe, 2.08 kHz). Cylindrical poly(NIPAAm) gel rods immobilized 24% y-Fe2O3, which was crosslinked by 5% N,N'-methylenebisacrylamide, were able to generate mechanical force. Five gel rods whose cross-area was 1.5 x 10-1 cm2 at 22°C could lift 20 g of weight up and down repeatedly by using contractile property of the gels. Shrinking of the gel rods was completed within 2 min. The hybrid poly(NIPAAm) gel containing the ferromagnetic powder could generate heat from inside and shrink spontaneously in the presence of the magnetic field. The magnetically driven chemomechanical device, which can convert magnetic energy into mechanical work, was studied using the hybrid hydrogel which was applied under the magnetic induction heating.
Experimental Study and Modeling of a TiNi Shape Memory Alloy Wire Actuator
Authors: Benzaoui H. , Lexcellent C. , Chaillet N. , Lang B. , Bourjault A.
Published: August 2009

Shape memory alloys (SMA) are often used as actuators in miniature articulated devices. In this paper, a single TiNi SMA wire loaded by a mass is studied as a basic actuator controlled by Joule's effect. First, we describe an experimental study of the wire (150,m in diameter) under coupled stress and temperature actions for different thermal input velocities in order to analyze its dynamical behavior. In the case of static loadings, modeling is performed with a macroscopic description of the thermomechanical behavior preformed by Leclercq and Lexcellent (1996). Then, the heat equation integration is sufficient to take into account the thermal input velocities. Comparison between experiment and modeling is fairly correct.
Active Damping of Thermally Induced Vibrations
Authors: Friswell Michael I. , Inman Daniel J. , Rietz Ralph W.
Published: August 2009

The prospect of using active damping in a smart structure to suppress thermally induced vibration is investigated. Here smart structure refers to an aluminum structure with an integrated active control system consisting of piezoceramic sensors and actuators. A simply supported aluminum beam is used to illustrate the nature of thermally induced vibrations caused by a suddenly applied heat flux. A distributed piezoelectric self-sensing sensor/actuator pair is implemented to actively suppress the motion caused by thermal disturbances. The effect of large temperature changes on the structure and actuator are taken into account in the control system design. A proportional-derivative controller, a linear quadratic regulator and a positive position feedback filter are considered. Simulation results show that thermally induced vibrations can be damped using currently available smart structure technology, provided temperature effects are properly accounted for in the control law.
Residual Stiffness and Actuation Properties of Piezoelectric Composites: Theory and Experiment
Authors: Hagood Nesbitt W. , Pizzochero Alessandro
Published: August 2009

This work attempts to characterize and model the effective stiffness and actuation properties of active composite materials under high uniaxial tensile loads. The motivations for this undertaking are to obtain effective material properties as damage accumulates in the active element and to identify the mechanisms affecting stiffness and actuation to improve the material. A unified model with predictive capability for overall laminate effective material properties was developed. Key model assumptions include a constant linear elastic fiber recovery length and a Weibull form for fiber strength. A one dimensional shear lag model was employed to characterize the load transfer between the composite's layers. In order to validate this model several experiments were conducted on interdigitated electrode piezoelectric fiber composites embedded in E-glass laminae. Actuation data were obtained by performing active tests: specimens were subjected to increasing tensile loads and measurements of actuation under load were taken at selected strain levels. Stiffness data was collected during actuation tests. Very good correlation was demonstrated in most cases between predicted behavior and experimental results.
Vibration Control System Using Electromagnetic Forces
Authors: Matsuzaki Yuji , Ishikubo Daisuke , Kamita Toru , Ikeda Tadashige
Published: August 2009

This paper presents the concept of a new vibration control system in which motions of an Al-Fe alloy thin beam/plate with magnetized segments can be suppressed or activated through electromagnetic forces induced by an applied electric current. Analytical evaluation of the induced electromagnetic forces acting both on the electric current applied and on the magnetized segments are derived from an electromagnetic consideration. To examine the feasibility of the proposed vibration control system, we have formulated a simple regulator problem in which the disturbed motion of the thin alloy beam caused by an impulsive force is suppressed.
Planar Motion of a Cable-Supported Beam with Feedback Controlled Actions
Authors: Gattulli V. , Paolone A.
Published: August 2009

Active tendon control for slender and flexible structural systems such as guyed mast and cable-stayed bridge, is an innovative methodology to contain their oscillations. In this paper, a simple cable-supported cantilever beam is controlled by means of an imposed longitudinal displacement at the grounded end of the cable aiming to stabilize planar oscillation amplitudes of both cable and beam. The equations of motion of this system are obtained including cable elasticity through finite strain. Analytical eigensolutions of the linearized equations are used to investigate influences of mechanical characteristics on a family of structural systems and to derive a nonlinear discrete model by classical Galerkin method. A one mode model is used to design linear and nonlinear feedback control laws. Comparisons on the effectiveness of different strategies are made on the basis of both control intensity and system response amplitudes.
Control Experiments of a Docking Mechanism Composed of a Planar Variable Geometry Truss
Authors: Murotsu Yoshisada , Senda Kei , Mitsuya Akira , Kawano Hidefumi , Andot Akihiro
Published: August 2009

This paper addresses an experimental docking system using a variable geometry truss (VGT), which is a kind of intelligent adaptive structures. The experimental system is composed of a docking mechanism, a frictionless table system, a computer system, and a vision sensor system. By using the developed experimental system, a PD-control and a computed torque method (CTM) are examined. The dynamics-based control, CTM, shows the superiority over the kinematics-based PD control. This paper proposes a resolved acceleration control (RAG), i.e., a position control, with redundancy considering. The proposed control scheme can avoid a bad condition caused by the redundancy. The CTM and the RAC use the efficient formulation of inverse dynamics that was proposed for real time controls by the present authors. Feasibility and effectiveness of those methods are examined by numerical simulations and experiments.
Impact-Induced Damage of Laminated Graphite/Epoxy Composites Monitored Using Embedded In-Line Fiber Etalon Optic Sensors
Authors: Chang Chia-Chen , Sirkis Jim
Published: August 2009

This paper describes the use of fiber optic sensors embedded into laminated graphite/epoxy composites for low velocity impact-induced damage assessment. The sensor system uses in-line fiber etalon (ILFE) sensors interrogated with path-matched differential interferometry (PMDI) and demodulated with a "single channel phase tracker." Uncoated and coated copper ILFE sensors were embedded at the mid-plane of [902/04/OF(O)/04/902] composite plates subjected to transverse impact (The OF(0) denotes an optical fiber orientation of zero degree). The ILFE sensor response was compared to a resistance strain gage bonded to the back side of the specimen and to the load cell mounted on the impactor. The strain measured with the metal coated ILFE sensor and the load cell response were used to plot a hysteresis strain-load curve to assess the impact-induced damage. The result shows that the-1 J impact energy starts to initiate the composite damage, and that the area contained within the hysteresis loop area is approximately proportional to the delamination area evaluated by X-ray radiographs. X-ray NDE indicates that the embedded ILFE sensor does not alter the structural integrity based on the macro-scale observations. In addition, the impact test showed that the sensor embedded in the middle layer had higher survivability than the resistance strain gage bonded to the rear surface of the plate.
Characterisation of Anisotropic, Non-Homogeneous Beam Sections with Embedded Piezo-Electric Materials
Authors: Ghiringhelli G. L. , Masarati P. , Mantegazza P.
Published: August 2009

The paper discusses the problem of the characterisation of untwisted, untapered, anisotropic and non-homogeneous straight beams with embedded piezo-electric devices. The determination of the section properties, i.e., the generalised electro-elastic stiffness and compliance matrices, is performed through an in-plane discretisation in a finite element way, in which the axial dependence of the unknown is handled in analytical form. This leads to a semi-analytical formulation that allows the solution of both the "central" and the "extremity" problems, namely, the indefinite and the boundary solutions. The piezo-electric generalisation implies the modelling of electro-static potential field. The peculiar bound for piezo-electric devices, the conductive laminae that allow sensing and actuation, implies a distributed non-holonomic constraint to the related electric variables. The section finite element discretisation allows detailed stress and electric displacement recovery, thus, giving the designer a powerful analysis tool. A Finite Volumes formulation is used in order to simplify the determination of the three-dimensional beam properties. This technique leads to punctual stiffness matrix evaluation, skipping numerical integration, and is intrinsically locking free. A complete set of numerical simulations and comparisons with three-dimensional models demonstrate the effectiveness and soundness of the proposed formulation.
Design, Simulation and Fabrication of Doped TiO2-Coated Surface Acoustic Wave Oxygen Sensor
Authors: Atashbar Massood Z. , Wlodarski Wojtek
Published: August 2009

This paper reports on the design, simulation and fabrication of Surface Acoustic Wave (SAW) devices using lithium niobate (LiNbO3) as a substrate. Sol-gel prepared doped TiO2 thin films have been deposited onto the SAW devices by spin-coating. Modelling and simulation has been performed to predict the performance of a SAW oxygen sensor using a high frequency electronics computer software package (HP-EEsof TM). Experimental work has been carried out for the purpose of evaluating the accuracy of the simulated results. Resistivity of doped TiO2 thin films has been found to decrease 47 fold when the oxygen concentration is decreased from 1% to 1 ppm at a working temperature of 200'C. The SAW oxygen sensor registered a 180 kHz frequency shift for the same changes in oxygen concentration. Our preliminary experiments highlighted that the doped TiO2-coated SAW sensors can detect oxygen in the concentration range of 1 ppm-l%.
Practical Design and Verification of LQG Controllers as Applied to Active Structures
Authors: Charon Willy
Published: August 2009

Many mechanical engineers find difficulty in applying LQG controllers to active mechanical structures. Answers to frequently asked questions are provided here, describing in detail the procedure as applied to a ca. 2 m x 0.5 m panel where vibrations are to be actively damped. This application was chosen because of the number of difficulties it can throw light on, while remaining simple enough to be understood with common sense. From another point of view, LQG controllers, as applied to mechanical structures with a theoretical infinity of degrees of freedom, have a bad reputation concerning stability. However, mechanical understanding of the reasons for the behavior helps to find very practical solutions. After reviewing the most important equation sets, a method for designing an LQG-controller is given. It mainly includes the design of the observer filter and the design of a feedback gain matrix considering the ideal knowledge of the system state vector. The test bed and its instrumentation is described. Physical measurements and computations are outlined as well as the integration of both theoretical and practical data into the same procedure aiming to determine system parameters. In the first step, only bending is considered. The experimental behavior shows a spillover due to bending modes not considered. Two methods are proposed in order to suppress this spillover. The first considers the sensor signal given by the uncontrolled dynamics as a noise. The second improves the estimation of the structural state without changing the controller gains. Both have advantages and disadvantages that are outlined. Finally, torsion is included in order to improve the behavior.
A Review on the Modelling of Piezoelectric Sensors and Actuators Incorporated in Intelligent Structures
Authors: Chee Clinton Y. K. , Tong Liyong , Steven Grant P.
Published: August 2009

The main objective of this article is to present an overview of the modelling that has been proposed by various workers in the field of smart or intelligent structures. Before the main discussion on the various models, some background information will be presented in relation to intelligent structures and the types of adaptive materials that are available. Although there are several categories of materials that can be implemented in intelligent structures, this article will focus on models that use piezoelectric materials as sensors and/or actuators (S/A). The modelling of the intelligent structures can be categorised in terms of the structural configuration (e.g., rod composites, fibre composites, monolithic structures, etc.) and also according to the type of modelling whether by finite element modelling or by analytical exact solutions.

Models in this field of work had incorporated concepts from different background including three-dimensional linear elastic theory and dielectric theory to give rise to the linear piezoelectric model. Rules of Mixture and methods for calculating effective properties of fibre composites were extended to include piezoelectric fibre composite models. Classical Laminated Plate Theory was also adopted in laminated composite models where some laminae were piezoelectric materials. Exact solutions were applied to simple models and illustrated the potential of using piezoelectrics. Finite element techniques were used for more complicated problems that included complex geometries, nonlinear behaviour and dynamic control of the structure. The difference between induced strain and actuation strain is usually not addressed when using FE techniques, instead the piezoelectric strain can be regarded as an equivalent external force/moment or incorporated into the strain energy. In regard to control algorithms, the most common form applied by investigators in this field seems to be the negative velocity feedback control with single input and single output and some included linear quadratic control. More advanced control algorithms such as using multiple input and multiple output or even neural networks are less established.
Dynamic Modeling and Neural Control of Composite Shells Using Piezoelectric Devices
Authors: Chandrashekhara K. , Smyser C. P. , Agarwal S.
Published: August 2009

A modal dynamic model was developed for the active vibration control of laminated doubly curved shells with piezoelectric sensors and actuators. The dynamic effects of the mass and stiffness of the piezoelectric patches were considered in the model. Finite element equations of motion were developed based on shear deformation theory and implemented for an isoparametric shell element. The mode superposition method was used to transform the coupled finite element equations into a set of uncoupled equations in the modal coordinates. A robust controller was developed using Linear Quadratic Gaussian with Loop Transfer Recovery (LQG/LTR) design methodology to calculate the gain and actuator voltage requirements. A Neural Network controller was then designed and trained offline to emulate the performance of the LQG/LTR controller. Numerical results have been presented for a flat plate and a spherical shell showing the variation in initial conditions and structural parameters. The neural network controller was shown to effectively emulate the LQG/LTR controller.