bluuebunny/crossref_metadata_2025 huggingface dataset:
Controllable Misaligned Journal Bearings, Lubricated with Smart Fluids
Authors: Nikolakopoulos P. G. , Papadopoulos C. A.
Published: August 2009

The controllable rheological behaviour of Electro-Rheological Fluids (ERF) is useful in engineering systems where variable performance is required. In particular the ERF have properties which are changed by an imposed electric field. In this paper a generalised Reynolds equation is solved using finite element techniques in order to simulate the behaviour of misaligned journal bearings lubricated with ERF. The Bingham plastic model is used to described the behaviour of the ERF, when the fluid is in flow mode. It is found that the applied electric field has a substantial influence on the load carrying capacity and the misaligned attitude of the journal bearings. It is concluded that the electric field imposed on the electro-rheological lubricant tends to align the journal in the bearing, making thus the misalignment angle smaller. Thus by changing the electric field it is possible to control the dynamic behaviour of rotor-bearing systems.
An Object Oriented Modeling Approach to Intelligent Variable Geometry Trusses
Authors: Huang Shengyang , Natori M. C. , Umetani Y. , Nakai Shoichi , Katukura Hiroshi
Published: August 2009

Since an intelligent variable geometry truss (IVGT) is usually equipped with large numbers of redundant actuators for the sake of providing adaptivity, a distributed control is considered a promising approach to dealing with its motion control. In this case, a modeling approach and an integrated model is a key to constructing distributed control systems from both hardware and software. To this end, this paper proposes an object-oriented modeling approach. Through decomposing the control problem domain underlying VGTs into objects, an object model can be obtained to represent various object abstractions and the relationships among these objects. It is shown in this paper that an object model of VGTs is exactly the integrated model for their knowledge organizations as well as the control architectures. Two control schemes resulting from the object models-a hierarchical distributed control and an autonomous distributed control-are discussed in particular. To verify the concepts addressed in this paper, an experimental prototype of IVGTs was manufactured, with a two-level hierarchical distributed control system equipped. With this prototype, an experiment is carried out, simulating a self-construction of space structures with IVGTs in a null gravity space.
Fabrication Methods for High Aspect Ratio Microstructures
Authors: Watanabe Satori , Esashi Masayoshi , Yamashita Yoshio
Published: August 2009

Two methods for fabricating high aspect ratio (depth/width) microstructures were developed and compared. The first method is a modified deep X-ray lithography process with thick negative resist. For preventing pattern collapse caused by surface tension while the rinse liquid is evaporated, some post-rinse drying processes were investigated. The second method is a directional etching of polyimide by 02 reactive ion etching (RIE). The advantage of the latter method is that the surface tension of liquids does not affect the microstructure in a dry atmosphere. In both methods, aspect ratio of 10 was achieved in polymer molds for electroplating at pattern width of 5,um without collapse.
Multiplexing Embedded Nitinol Actuators to Obtain Increased Bandwidth in Structural Control
Authors: Srinivasan A. V. , Mcfarland D. Michael , Canistraro Howard A. , Begg Eric K.
Published: August 2009

A wide variety of applications of shape memory alloys is seen in devices where the response required of them is essentially quasi-static. At the same time, the high damping intrinsic to the alloys known as "quiet metals," such as Nitinol, have led to their use as passive distributed dampers. However, it is generally felt that the frequency response of SMA actuators is too slow to permit their use for structural control where they need to supply a time-dependent force at the natural frequency of a structure.

In many applications the response time of SMA actuators is ultimately limited by heat transfer. Typically, very rapid heating can be achieved but the time needed for cooling is long compared to the vibratory period of typical mechanical or civil structures. A unique approach has been found suitable to overcome this inherent limitation. The approach is based on using several Nitinol wires as actuators in parallel and energizing subsets of these during successive cycles of structural motion, effectively trading reduced control authority for increased frequency response. Thus, with an array of actuators an effective bandwidth can be achieved that is demonstrated to be greater than the bandwidth possible with a single actuator.

This technique of multiplexing several actuators was established in principle by the senior author of this paper in 1990. Most recently, upon completion of the effort reported here, the authors learned that Wilson et al. (1990) had employed a similar approach to obtain a higher frequency bandwidth. The approach has now been extended to demonstrate its validity by applying it to a robust box beam made of steel. Furthermore, successful performance of the multiplexing scheme has led to the analysis, design, fabrication and testing of a composite beam in which NiTiNOL fibers were embedded. A series of vibration tests were conducted on the composite beam along with temperature measurements using an infrared camera. With the multiplexing approach, the first two modes of the composite beam, at 23.5 Hz and 144 Hz respectively, were excited. This unique approach can now be developed further to design structural systems of interest to industry and build smart composite structures. This serves the eventual goal of controlling vibration at frequencies higher than was thought possible with this material.
Model-Independent Vibration Control of Flexible Beam-Like Structures Using a Fuzzy Based Adaptation Strategy
Authors: Cohen K. , Weller T. , Levitas J. , Abramovich H.
Published: August 2009

The present study deals with an AFCA (Adaptive Fuzzy Control Algorithm) for an Euler-Bernoulli approximation of a two-dimensional version of a cantilever beam-like orthogonal tetrahedral space truss. Transient disturbances, modeled as a unit impulse, excite all the modes of the beam. The resulting transverse displacement at the free end of the beam and its corresponding rate are observed by sensors placed there, and active control of the beam is provided by a collocated force actuator.

A design methodology for the closed-loop control algorithm that is independent of an exact mathematical model (space-state model, F.E.M., etc.) of plant dynamics and which is based on fuzzy logic is presented. First, the behavior of the open-loop system is observed. Then, the control force applied to the system emulates the behavior of a dynamic vibration absorber which is tuned to the measured fundamental frequency. This approach not only assures inherent stability associated with passive absorbers, but also circumvents the phenomenon of modal spillover. The damping and the mass ratios of the absorber adapt themselves by using a fuzzy decision-making process. This results in relatively quick settling times, low overshoots and dying out of vibration within a few seconds.

When the control force is turned off after a mere 16 seconds, almost all the vibrational energy is dissipated. In addition, the performance of the AFCA is insensitive to varying initial conditions. To demonstrate the robustness of the control system to changes in the temporal dynamics of the cantilever beam, the transient response to a considerably perturbed plant is simulated. The Young's modulus of the beam was raised as well as lowered substantially, thereby significantly perturbing the natural frequencies of vibration. The mode shapes, however, remain unchanged. For these cases, too, the AFCA provides similar settling times and rates of vibrational energy dissipation.
Active Damping Enhancement of Composite Plates with Electrode Designed Piezoelectric Materials
Authors: Han Jae-Hung , Lee In
Published: August 2009

The characteristics of the actuation effectiveness of piezo-laminated plates have been investigated. Finite element procedures based on the first order shear deformation theory have been developed. The actuation effectiveness of each portion of a piezoelectric material has been obtained. For a twisting mode, a large amount of cancel out effect is observed. The first order perturbation analysis shows that in case of direct negative velocity feedback, control performance increases when the cancel out effect decreases. A simple and effective electrode design method has been suggested with the idea of electrode shaping such as a combination of subareas without cancel out effects for the modes under consideration. In the present study, a cantilevered plate with piezoelectric polymer on both surfaces is considered. Best electrode shapes which have extremum values for each cost function are obtained.
Design of Shape Memory Alloy Actuators
Authors: Liang C. , Rogers C. A
Published: August 2009

This paper describes the design of shape memory alloy force and displacement actuators based upon the thermomechanical constitutive relations previously developed by the authors. Numerical simulations and design case studies are presented which show the utility and advantages of this method over design methods currently being used. The types of actuators described and analyzed include bias spring actuators, differential force actuators, and their hybrid systems. The design approach includes coupling between the one-dimensional thermomechanical constitutive relations and a lumped capacitance transient thermal analysis. The design approach described herein will provide a practical and convenient method for use in the design of shape memory alloy actuators.
Determination of Design of Optimal Actuator Location and Configuration Based on Actuator Power Factor
Authors: Liang C. , Sun F. P. , Rogers C. A.
Published: August 2009

In this paper, a new design algorithm is proposed for optimization of the inducedstrain actuator location and configuration for active vibration control based on an actuator performance index, namely the actuator power factor. The concept of actuator power factor, developed recently by the authors, describes the capability of an integrated induced strain actuator, such as PZT or Terfenol, to transfer the supplied electrical energy into structural mechanical energy (kinetic or potential energy of the mechanical system). A system optimized based on the actuator power factor will guarantee the highest energy efficiency for single frequency and broad-band applications. This paper will also show that a higher energy efficiency corresponds to higher mechanical performance. The approach introduced in this paper is much more convenient to use than the conventional modal domain optimization approach. Furthermore, since the power factor approach can include the electrical parameters from the power system, it will allow a system optimization design including the power electronics and energy consumption.

The basic concept of the actuator power factor will be introduced first in this paper. Its utility in the system optimization will be discussed using a PZT actuator-driven simply-supported beam. The optimization of actuator location, length, and thickness will be discussed through numerical examples. This paper will also discuss how to use the actuator energy density and actuator power factor to estimate the dynamic response of a system.
Vibration Control of a Composite Plate with Embedded Optical Fiber Sensor and Piezoelectric Actuator
Authors: Yang S. M. , Jeng J. A.
Published: August 2009

Smart structures, structures containing sensor(s) and actuator(s) along with computational and control capabilities, are considered one of the best candidates for vibration control applications. A [0/90]6s glass-fiber composite plate embedded with one optical fiber and six piezoelectric elements has been fabricated, analyzed, and experimentally validated. It is shown that by using the in-situ optical fiber as a Michelson interferometer to detect the structural displacement and the piezoelectric elements as actuator, bending vibrations of the composite laminated plate can be effectively reduced.
Vibration Characteristics of Sandwich Beams Partially and Fully Treated with Electro-Rheological Fluid
Authors: Haiqing Gong , King Lim Mong
Published: August 2009

This experimental study investigated the vibrational properties of a sandwiched beam clamped at both ends and fully or partially treated with an electro-rheological (ER) fluid layer. Frequency response function curves were obtained and analysed in the frequency range between 10 to 1000 Hz. Three factors were investigated for its effect on the ER sandwich beam system, i.e., electric field strength, length of the ER fluid layer and applied excitation gain. It was found that the electric field strength has little effect on loss factors and resonant frequencies of the fully treated beam, except for reduced vibration in some off-resonance regions. For the partially treated beam, the length of the ER fluid layer has a significant effect on resonant frequencies, but little effect on loss factors. As the length of the ER fluid layer increases, the resonant frequencies become higher in the entire frequency range considered. It was also observed that both partially and fully treated ER sandwich beams are almost linear systems, i.e., when different excitation gain levels are applied to the beams, the frequency response function curves are unchanged.
Wind Tunnel Test of a Smart Rotor Model with Individual Blade Twist Control
Authors: Chen Peter C. , Chopra Inderjit
Published: August 2009

The objective of this research is to develop a smart rotor with active control of blade twist using embedded piezoceramic elements as sensors and actuators to minimize rotor vibrations. A 1/8 Froude-scale (dynamically scaled) bearingless helicopter rotor model was built with banks of torsional actuators capable of manipulating blade twist at frequencies from 5 to 100 Hz. To assess the effectiveness of the torsional actuators and vibration suppression capabilities, systematic wind tunnel testing was conducted in the Glenn L. Martin Wind Tunnel. Using accelerometers embedded in the blade tip, the oscillatory blade twist response was measured. The changes in rotor vibratory loads due to piezo-induced twist were determined using a rotating hub balance located at the rotor hub. Experimental test results show that tip twist amplitudes on the order of 0.5 degrees are attainable by the current actuator configurations in forward flight. Although these amplitudes were less than the target value (I to 2 degrees for complete vibration suppression control), test results show that partial vibration reduction is possible. Using open-loop phase shift control of blade twist at the first four rotor harmonics, changes in rotor thrust of up to 9% of the steady-state values were measured.
Piezothermoelastic Solution for Angle-Ply Laminated Cylindrical Panel
Authors: Dumir P. C. , Dube G. P. , Kumar Satish
Published: August 2009

A three dimensional solution is presented for simply supported, angle-ply laminated hybrid cylindrical panel under cylindrical bending. The differential equations with variable coefficients are solved by the modified Frobenius method. Numerical results are presented for sinusoidal loads to illustrate the effect of the thickness parameter and the lamination angle. The two dimensional classical lamination theory and first order shear deformation theory are assessed by comparison with the three dimensional solution.
Modeling of the Thermomechanical Response of Active Laminates with SMA Strips Using the Layerwise Finite Element Method
Authors: Lagoudas D. C. , Moorthy D. , Qidwai M. A. , Reddy J. N.
Published: August 2009

A study on the effective thermomechanical response of a composite laminate with shape memory alloy (SMA) layers based on the implementation of the layerwise laminate theory in the finite element method is carried out in this paper. The SMA thermomechanical constitutive response is based on a thermomechanical model recently developed by Boyd and Lagoudas. The numerical implementation of the constitutive model is based on a return mapping integration algorithm which is employed in studying the SMA response characteristics in the composite laminate under thermal loading. In modeling the laminate, a displacement based finite element approach is used in conjunction with the layerwise laminate theory of Reddy, incorporating piecewise continuous distribution of transverse strains through the thickness. As an illustrative example, the deformations caused by two prestrained SMA strips placed symmetric to the mid-plane of an elastic plate, when thermally activated are studied. The top SMA strip starts transforming from the martensitic into the austenitic state upon actuation through resistive heating, simultaneously recovering the prestrain, thus causing the laminate to bend. A parametric study investigating plane strain and generalized plane strain is carried out, and the accuracy of the results is compared with the commercial finite element code ABAQUS. The main feature of the presented methodology is an accurate evaluation of actuation stresses in the SMA strips, efficiently combining the layerwise geometry with the finite element method.
A Superelastic Shape-Memory-Alloy Beam Model
Authors: Auricchio Ferdinando , Sacco Elio
Published: August 2009

The present paper proposes a simple shape-memory-alloy beam model, based on the classical Euler-Bernoulli beam theory.

Due to restrictive kinematical assumptions, a one-dimensional constitutive equation is used. Thus, the material behavior is described through a simple l-D phenomenological model, which allows for different material responses in tension and compression as well as for different elastic properties between austenite and martensite.

Two numerical procedures are developed for the determination of the cross-section response together with a time-step integration algorithm. Then, the implementation of the shape-memory-alloy beam model within a finite-element framework is addressed.

Several numerical examples are investigated to assess both the performance of the beam model and the procedure developed. The complex behavior of a typical cross section is emphasized. The results obtained from the simulation of three and four-point bending tests are compared both with experimental results and with numerical solutions obtained from a three-dimensional finite-element scheme.
Static and Dynamic Testing of Large-Amplitude Rotary Induced-Strain (LARIS Mk 2) Actuator
Authors: Giurgiutiu Victor , Rogers Craig A. , Mcneil Shane
Published: August 2009

A new concept for obtaining large-amplitude rotary displacements from small linear displacements generated by induced-strain active material stacks is considered. The concept utilizes the theory of twist-warping coupling in thin-wall open tubes. A large-displacement induced-strain rotary actuator, LARIS Mk 2, was built and tested under static and dynamic conditions. A rotary displacement of 60 was measured over a 0-50 Hz frequency range. The frequency response was found to be flat up to 40 Hz, and then increasing in the 40-50 Hz frequency range.

The theoretical development of the torsional vibration response for the LARIS Mk 2 actuator is also given. The derivation is performed in a general format for a body with distributed elastic and inertia parameters, and with generic boundary conditions consisting of root stiffness and tip angular deflection. The results of this theoretical analysis are confirmed by experimental measurements. The theory presented is versatile and can be used for the analysis of other torsional vibration devices with specific root and tip boundary conditions.

This LARIS concept presented in this paper 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, or as rotary vane actuators in the control of turbomachinery exhaust flow for active reduction of turbulence, vibrations, and noise.
Optimal Design of Intelligent Composite Structures
Authors: Kalamkarov A. L. , Drozdov A. D.
Published: August 2009

Basic aspects of the mechanical modeling, design and optimization of intelligent structures are formulated and discussed. Governing equations describing the mechanical behavior of a smart elastic composite structure incorporating sensors and actuators are developed and the major optimal design problems are formulated. Theory is illustrated by three examples of intelligent structures of practical interest, which represent three basic classes of optimization problems, on account of residual stresses, material properties, and the geometry of a structure.
CASTOR Active Damping Experiment, Preliminary Flight Results
Authors: Bousquet P. W. , Guay P. , Mercier F.
Published: August 2009

The experiment "'CASTOR" (French acronym for Characterization of Structures in ORbit) is dedicated to the analysis of the structural dynamic modes of the MIR station, and to the investigation of the dynamic behaviour-in zero g conditions-of a truss mock-up with various damping technologies. This project has been developed under CNES management in less than three years. The work in orbit was performed by a French cosmonaut within the frame of the CASSIOPEE mission in MIR at the end of August 1996.

This paper is dedicated to the active damping systems for CASTOR's truss structure. They consist essentially of three piezoelectric members, and one reaction mass actuator. Both systems use collocated sensors and actuators. Their development and flight tests are part of CNES' general activities whose aim is to improve, demonstrate the efficiency, and prepare the application of active control techniques for future space missions. Typical applications include optical systems with high stability requirements, large antennas, sensitive microgravity payloads, spacecrafts with flexible appendages, and large orbital infrastructures.

In Bonus (1995), we presented the motivations behind the test in zero g conditions, and a full description of the equipment. In this paper, we briefly recapitulate upon the design of the active systems, before summing-up the recent development activities. The operations in flight are then presented. A few zero-g measurements are shown without much interpretation considering the short time available between flight and conference. The active systems exhibited excellent performances in flight. Preliminary conclusions are drawn with respect to the CASSIOPEE mission and to further activities.
A Shape Memory Alloy Model for Uranium-Niobium Accounting for Plasticity
Authors: Govindjee Sanjay , Kasper Eric P.
Published: August 2009

In this paper we present a 1-D model for the behavior of U-Nb shape memory alloys that accounts for the effect of plastic deformations on recovery strains. In particular, we account for the erasure of memory effect that occurs with increasing plastic strains. An algorithmic approximation to the model is discussed in detail and a comparison to some experimental results is shown.
Active Damage Detection in Filament Wound Composite Tubes Using Built-In Sensors and Actuators
Authors: Beard Shawn , Chang Fu-Kuo
Published: August 2009

This paper presents a concept for active damage detection in a filament wound composite tube using a built-in diagnostic system. The proposed method uses piezoelectric transducers to generate and detect propagating stress waves. The diagnostic waves interact with structural defects and are scattered in all directions. These scattered waves carry information about the damage to the sensors. Extracting and interpreting this information is vital to the development of a robust structural health monitoring system. An experiment is described in which the location of damage is found by measuring the arrival times of the scattered waves. A method to estimate the size of the damage and the associated material degradation is also introduced.
Performance of Optical Sensors in the Control of Flexible Structures
Authors: Mrad Nezih , Melton Robert G. , Kulakowski Bohdan T.
Published: August 2009

This paper demonstrates the use of embedded single-mode optical fibers in the active control of smart structures. The experimental prototype structure, a composite lattice configuration fashioned from graphite/bismaleimide laminate, exhibits complex bending and torsional modes, and forms a sub-scale model of a similar structure being analyzed at the Air Force Astronautics Laboratory. Simulations that include effects of Gaussian observation and process noise on a linear quadratic regulator/ loop transfer recovery (LQG/LTR) controller for active vibration damping are presented. The fiber-optic sensor demonstrates advantages over conventional strain gage sensors in terms of reduced sensitivity to sensor placement, reduced problems with observation and control spillovers, and improved control stability.
On the Realisation of GHM Models in Viscoelasticity
Authors: Friswell Michael I. , Inman Daniel J. , Lam Margaretha J.
Published: August 2009

A useful method of modeling viscoelastic effects in structures for transient response analysis is to treat the frequency dependence of the usual damping model through the introduction of extra dissipation co-ordinates. These new co-ordinates require a curve fit to loss factor data over a range of frequencies. One such method called the Golla-Hughes McTavish method, or GHM method, is examined here. The standard GHM approach has only three parameters per second order term in the approximation to the material properties, whereas the four parameters used in this paper gives the most general curve fit. Thus, for the same number of extra degrees of freedom, more accurate predictions from a finite element model with viscoelastic components is possible. This paper also reformulates the series used in the GHM modeling in terms of the high frequency stiffness, rather than the standard low frequency stiffness.
Dynamic Characteristics of Sandwich Beam with Embedded Electro-Rheological Fluid
Authors: Lee Chun-Ying , Cheng Chih-Chien
Published: August 2009

In this study, the measured dynamic constants of the Electro-Rheological (ER) fluid using parallel-plate fixture are plugged into the finite element formulation for the sandwich beam with embedded ER fluid derived in a previous work. The resonance frequency and damping loss factor of the sandwich beams in the cantilevered and the simply-supported boundary conditions are obtained by solving the finite element equation in the frequency domain. The simulated results are compared with the experimental measurements from swept-sine technique. It is found that, in both boundary conditions, the finite element formulation accurately predicts the effect of the applied electric field strength and the vibration amplitude on the dynamic characteristics of the ER sandwich beam.
Adaptive Vibration Control by Using Magnetostrictive Actuator
Authors: Shaw Jinsiang
Published: August 2009

In the paper an experimental study on vibration attenuation by using magnetostrictive actuator with Terfenol-D rod is presented. A magnetostrictive actuator is used to provide a negating force to an external excitation for suppressing vibrational response of the disturbed system. A simple and easy-to-implement adaptive plant disturbance canceling scheme is developed and applied for vibration attenuation, when the system is subjected to a sinusoidal disturbance. The plant disturbance canceler consists of an actuation emulator and an inverse actuator (acts as a controller), which are in the forms of linear finite impulse response (FIR) filters. Impulse response of the actuation system and inverse property of the inverse actuator are utilized for obtaining the FIR filters for the actuation emulator and inverse actuator. A signed-f LMS algorithm is developed and employed for on-line adaptive tuning of the inverse actuator. Experimental results indicate that over 96.6% (or 29.3 dB) of the vibrational displacement amplitude of the disturbed system is attenuated in a tested frequency range of 50-70 Hz, thus demonstrating the validity and effectiveness of the plant disturbance canceler.
Experimental Investigation of the Pseudoelastic Hysteresis Damping Characteristics of Shape Memory Alloy Wires
Authors: Wolons David , Gandhi Farhan , Malovrh Brendon
Published: August 2009

An experimental investigation was conducted to determine the pseudoelastic hysteresis damping characteristics of Ni-Ti Shape Memory Alloy (SMA) wires. The comprehensive study examines the effects of cycling, oscillation frequency, strain amplitude, temperature, and static strain offset on the pseudoelastic stress-strain hysteresis of SMA wires under axial loading. Experimental data are obtained for complete austenite-martensite transformation hysteresis as well as partial transformation hysteresis. The results indicate that as the frequency of excitation increases, the reverse phase transformation from detwinned martensite to austenite commences at higher stress levels, and the area of the hysteresis loop decreases. This results in a rapid initial decrease in energy dissipation, but approaches a stable level by about 10 Hz. The energy dissipation at 10 Hz was found to be about 50% of that observed at very low frequencies. The energy dissipated at higher temperatures was found to be up to 40% lower than that observed at 90'F. The energy dissipated per cycle was found to be larger when lower values of static strain offset were used.
Shape Fixity and Shape Recovery in a Film of Shape Memory Polymer of Polyurethane Series
Authors: Tobushi H. , Hashimoto T. , Ito N. , Hayashi S. , Yamada E.
Published: August 2009

The shape fixity and recovery in a film of shape memory polymer of polyurethane series were investigated by the thermomechanical cycling tests with loading at various temperatures. The results are summarized as follows: (1) Strain is recovered at temperatures in the vicinity of the glass transition temperature Tg for loading above Tg, but it is recovered at temperatures in the vicinity of the midpoint temperature of glass transition for loading below Tg. (2) The rate of strain fixity is 98% for loading above Tg, while it decreases with increasing cycles for loading below Tg. (3) The rate of strain recovery for loading above Tg is 98% except for the early cycles. (4) The thermomechanical properties of materials with different Tg are quite alike in spite of the difference in Tg.
Stress Stiffening Effects in Laminated Beams with Piezoelectric Actuators
Authors: Oguamanam Donatus C. D. , de Almeida Sérgio Frascino Müller , Hansen Jorn S.
Published: August 2009

The effectiveness of using piezoelectric elements to enhance the mechanical performance of laminated structures by inducing favorable in-plane stresses is investigated. A finite element formulation is presented for the analysis of laminated Timoshenko beams with an arbitrary number of piezoelectric actuators and/or sensors placed along the length of the beam. Von Kdrman nonlinear strain-displacement relations are used and ideal linear behavior is assumed for the piezoelectric actuation. It is shown that if the beam is longitudinally restrained at both ends the piezolectric actuators induce in-plane stresses that significantly affect the mechanical behavior of the beam. It is also shown that stress stiffening is more pronounced for slender beams. A configuration with a piezoelectric actuator at the top of a slender beam and a sensor at the bottom is analyzed. It is demonstrated that neglecting the stress stiffening effects may lead to large errors in both the static and dynamic analyses of this widely used configuration for slender beams. Further, the stiffness of the beam can be piezoelectrically tuned to significantly change the natural frequency; this has interesting applications in active vibration and acoustics control or smart structures.
Embedded In-Line Fiber Etalon/Bragg Grating Hybrid Sensor to Measure Strain and Temperature in a Composite Beam
Authors: Jin X. D. , Sirkis J. S. , Chung J. K. , Venkat V. S.
Published: August 2009

An optical fiber sensor for simultaneous measurement of axial strain and temperature in composite structures is reported. This sensor configuration consists of an in-line fiber etalon (ILFE) cascaded with an in-fiber Bragg grating (BG) and is demultiplexed using a variation of coherence division multiplexing. The strain/temperature sensor is demonstrated by embedding it into a graphite/epoxy composite cantilever beam. Concentric cylinders micromechanics models are developed that enable the optical signals from the embedded sensors to be cast in terms of the composite host strain and temperature without the need for calibration. The fiber optic strain/temperature sensor with a gage length of-1.0 cm is found to agree with traditional strain and temperature sensors to within 5 με and 0.50C, respectively.
Feasibility of Applying Distributed Piezotransducers to Structural Damage Detection
Authors: Kawiecki Grzegorz
Published: August 2009

The purpose of this paper is to demonstrate experimentally the feasibility of nondestructive damage detection by an array of piezotransducers embedded or bonded to the surface of a monitored structure. This paper shows the results of experiments with transmission of elastic waves among systems of piezotransducers surface-bonded to two aluminum specimens: a beam and a plate, and embedded in a concrete block. Structural damages were simulated by masses of various magnitudes placed at the surface of tested specimens. Experimental results obtained so far indicate that there is a strong correlation between the size and location of a simulated and actual damage and the character of signals transmitted among piezotransducers. Anomalies in those signals are repeatable and have distinct characters when they are caused by damage and when they are due to other causes. Piezotransducers used in this study were able to produce and receive signals well above the noise level both when surface-bonded to aluminum specimens and when embedded in a concrete block. The anomalies caused by simulated damages were significant enough to be used for training a neural network.
Electromechanical Tuning of Self-Sensing Piezoelectric Transducers
Authors: Brusa Eugenio , Carabelli Stefano , Carraro Fulvio , Tonoli Andrea
Published: August 2009

The application of a self-sensing piezoelectric transducer included in a bridge readout network is here investigated taking into account the electromechanical interaction. The parametric uncertainties and the piezoelectric device losses as well as the tolerances of the electric components make the balancing of the bridge difficult to achieve in practice. A loss and uncertainties compensation, based on a real-time software implementation of the bridge reference arm is here presented and validated. The standard electrical and the proposed electromechanical balancing are both theoretically and experimentally compared in the case of a simple beam. The bridge output signal that is proportional to the strain rate is then fed back by means of a sharp phase second order low pass filter which is aimed at increasing the damping of the first bending mode of the beam.
Feedback Control Using Shape Memory Alloy Actuators
Authors: Dickinson Carrie A. , Wen John T.
Published: August 2009

Shape memory alloy (SMA) has been considered as an actuator for applications that require large force and displacement. Two factors have hampered the usefulness of such actuators: a hysteretic input-output relation and bandwidth limitations. This paper considers the hysteresis phenomenon from a control point of view. Instead of directly compensating for the hysteresis, which requires an accurate model, we use a closed loop approach which considers the feedback control of the beam strain. A simple lumped temperature and SMA force/displacement model is used for stability analysis. We show that with the SMA wire fixed between rigid surfaces, a proportional force feedback would render the closed loop stable. However, when SMA is coupled to a flexible structure, the resulting system can exhibit instability. We then show that a proportional position feedback is stabilizing, but there would be steady-state error. An adaptation scheme can be further added to remove the steady-state error. The analysis is verified experimentally in a simple experimental setup consisting of a flexible aluminum beam and a Nitinol shape memory alloy wire that applies a bending force to the end of the beam.
Genetic Algorithm Optimization for the Active Control of a Beam by Means of PZT Actuators
Authors: Gaudenzi Paolo , Fantini Enrico , Koumousis Vlasis K. , Gantes Charis J.
Published: August 2009

The aim of this work is to optimize placement and sizing of a given number of piezoelectric (PZT) actuator patches on an Euler-Bernoulli beam, in order to control (or damp) desired modes in an optimal way. A modal approach for the dynamic influence functions is used to take directly into account the position, length and loading of a generic PZT. The optimization problem is solved from a stochastic point of view by means of Genetic Algorithms.
A Simple Micromechanical Model for Pseudoelastic Behavior of CuZnAl Alloy
Authors: Levitas V. I. , Idesman A. V. , Stein E. , Spielfeld J. , Hornbogen E.
Published: August 2009

A simple micromechanical model for thermoelastic martensitic phase transitions (PT) is developed. It is deduced from the local description of PT in transforming particles with subsequent usage of average procedure, based on a model for elastic three-phase materials (austenite, martensite and new infinitesimal nucleus) under assumption of homogeneity of stresses in each phase. In contrast to known approaches, a new local PT criterion and a corresponding extremum principle for PT with dissipation are used. The macroscopic PT criterion obtained is split into two different equations for description of temperature-induced PT and stress-induced PT. To identify the material parameters of the model and to check its validity, simple one-dimensional experiments were carried out for CuZnAl alloy. The experimental values of martensite start and finish temperatures and austenite finish temperature for temperature-induced PT and the stress-strain diagram for stress-induced direct PT at any fixed temperature have allowed to determine six material parameters of the model for the simplest one-dimensional case. Then model prediction is compared with other independent tests. A good agreement is obtained of the calculated stress-strain curves for reverse PT (martensite-austenite) at 01 = 20C and for direct PT at temperature range of 30—80C with experimental data. Finally, the formula for determination of the transformation heat during temperature-induced PT for the given model is derived. It is shown that the predicted transformation heat is close to the experimental one.
Localized and Diffuse Thermoinduced Phase Transformation in 1-D Shape Memory Alloys
Authors: Bekker A. , Brinson L. C. , Issen K.
Published: August 2009

In this paper we further explore the thermoinduced shape memory alloy transformation using a model developed in a previous publication. The problem investigated in detail is that of a semi-infinite SMA rod under uniaxial tension, subjected to boundary cooling or heating. The boundary conditions lead to propagation of a martensite/austenite transformation along the rod starting at the cooled/heated boundary. The mathematical model for the problem is formulated via the energy equation coupled with a one-dimensional constitutive law and phase diagram based kinetics and solved numerically. In this paper, the previous solution technique for boundary cooling is extended to the case of boundary heating, nonuniform initial states are considered, and particular attention is focused on the transition two-phase zone of the transformation. It is shown that even though the problem is formulated using a phase diagram with finite width transformation regions, a localized interface type solution may be obtained. The results have important implications for applications and modeling of SMA behavior.
A Model for Simulating Polarization Switching and AF-F Phase Changes in Ferroelectric Ceramics
Authors: Chen W. , Lynch C. S.
Published: August 2009

A computational micromechanics model for polycrystalline ferroelectric ceramics developed by Chen and Lynch (1997) is modified and applied to the simulation of ferroelectric and ferroelastic switching of the tetragonal and the rhombohedral crystal structures, and to antiferroelectric to ferroelectric phase changes. Interactions between different grains in the ceramic are considered. Two switching criteria are used, one for ferroelectric switching and one or phase changes. Experimental results for both types of materials are simulated.
Optimal Shape Control of Composite Thin Plates with Piezoelectric Actuators
Authors: Tong Daqun , Williams Robert L. , Agrawal Sunil K.
Published: August 2009

Emerging technologies in microsensing, microactuation, active airfoils, turbine blades, and large, lightweight, flexible space structures can benefit from piezoelectric actuators for active shape control. Piezoelectric materials develop strain under applied voltage which induces structural deflection. This article presents analytical models, FEM solution, and optimal shape control of composite thin plates with piezoelectric actuators surface embedded or bonded in a biomorph arrangement. A 2D FEM approach is developed which is accurate, plus simpler and more efficient than existing 3D solutions. Three optimal shape problems are presented: applied voltage, actuator layout, and actuator number optimizations. For the latter two problems, a novel method is introduced using a vector of binary variables.
The Fractional Order Elastic-Viscoelastic Equations of Motion: Formulation and Solution Methods
Authors: Escobedo-Torres Javier , Ricles James M.
Published: August 2009

The equations of motion of structures with elastic and viscoelastic materials in the time domain are derived. The development is consistent with the finite element formulation and leads to a system of equations where the matrices are symmetric, real, and composed of constant coefficients. A four-parameter fractional derivative model is used to model the frequency dependence of the linear viscoelastic material since experimental data can be fitted successfully over a wide frequency range. The resulting equations of motion are known as the elastic-viscoelastic equations of motion. Numerical procedures for solving the elastic-viscoelastic equations of motion in the time domain are developed, and a procedure based on the central-difference method that incorporates fractional derivatives is presented. The numerical stability of the procedure is presented, and criteria for selecting the size of the time step are given.

The closed-form, steady state solution of a single degree of freedom system is obtained in the frequency domain and is utilized to validate the results obtained by using the numerical procedures. The proper selection of the stiffness for viscoelastic dampers placed in elastic structural systems is discussed in order to ensure that the damper is effective in reducing dynamic amplification of the structure. The dynamic response of a multi-degree of freedom structure, obtained by using the numerical procedures, is used to demonstrate the effectiveness of the dampers in reducing the structural response to dynamic loading.
Combining Modeling Methodologies for Improved Understanding of Smart Material Characteristics
Authors: deGiorgi V. G. , Lindner D. K. , McDermott S. H.
Published: August 2009

Smart materials are complex materials that contain both active and passive components. The system performance depends not only on active component performance capabilities but the synergistic response of the smart material and companion structure. Behavior is a result of interaction between diverse subsystems including, but not limited to, sensors, actuators, drive amplifiers and connecting digital electronics. An integrated model is developed which incorporates structural characteristics of a smart material and companion structure with a dynamic model of the amplifier used to power the smart material. Actuators are modeled using nonlinear constitutive laws and integrated with the dynamic model of the amplifier. The actuators have a significant structural influence on the smart material response. This interaction is obtained through a detailed finite element model used to determine the structural response of the smart material. Calculated displacements are compared for the dynamic model and the static finite element response model. The two analysis methodologies are used in conjunction to obtain a better understanding of the smart material performance.
Single Actuator and Multi-Mode Acceleration Feedback Control
Authors: de Noyer Maxime P. Bayon , Hanagud Sathya V.
Published: August 2009

The objective ofthe paper is to develop avibration control design procedure that uses a single actuator to suppress vibrations in many structural modes simultaneously by using acceleration feedback control theory. In this paper, a new technique, based on the crossover point design of the compensator, has been developed to compute optimal design parameters to achieve modal vibration reduction without introducing any new natural frequencies in the closed loop system. The new technique has been validated by both experimental studies and simulation studies. The new design procedure has also been compared experimentally and analytically to a previous design of acceleration feedback controller by using critically damped compensators. Then, experimental and analytical investigations are directed to control more than one mode of a cantilevered beam with a single actuator. This is demonstrated by using piezoceramic wafer actuators and an accelerometer sensor on the beam structure.
Maximizing the Power Output of Air-Acoustic Actuator Arrays
Authors: Leo Donald J.
Published: August 2009

The maximization of radiated sound power from baffled vibrating structures is studied as a means of examining the structural-acoustic control authority of point force and distributed moment actuators. The relationship between the structural vibration and radiated sound power is expressed as a quadratic function of the modal velocities and the structural mode shapes. The sound power model is nondimensionalized through geometric transformations. The problem of computing the maximum radiated acoustic power using an array of actuators is shown to reduce to a generalized eigenvalue analysis. A term denoting the power efficiency, which is defined as the ratio of maximum radiated power normalized with respect to the maximum achievable radiated power, is stated and a series of numerical simulations are performed. The numerical simulations examine the physical mechanisms of maximizing the sound power output of structures. The expressions for the modal coefficients of point force and distributed moment actuators are used to determine actuator locations that influence only the efficient radiator modes. Power efficiency studies illustrate the relationship between the modal velocities and the direction of the maximizing force input. The numerical studies indicate that a group of properly placed point force actuators can achieve broadband power efficiency over the frequency range studied, whereas distributed moment actuation exhibits lower power efficiency at high frequencies. This difference is attributed to the magnitude and phasing of the array modal velocities. The simulations also demonstrate the utility of the eigenvalue technique for determining optimal placement and sizing of a multiple transducer air-acoustic actuator array.