Journal of Intelligent Material Systems and Structures recent issues

Biaxial Constrained Recovery in Shape Memory Alloy Rings

Videnic, T., Kosel, F., Sajn, V., Brojan, M. — 2008-07-25

In this article biaxial constrained recovery in a thick-walled shape memory alloy (SMA) ring with a rectangular cross-section is modeled using the theory of generalized plasticity, which is developed by Jacob Lubliner and Ferdinando Auricchio. As a mechanical obstacle that delays free recovery in a SMA ring, a steel ring is used. The result of constrained recovery is the generation of high stresses in both the rings. All equations are written in a closed form in terms of infinite series. Theoretical results are compared with experimental findings and good agreement is found when SMA rings are in the domain of recoverable strains.

FE Modeling of an Innovative Vibration Control Shunt Technique

Ciminello, M., Ameduri, S., Concilio, A. — 2008-07-25

The possibility of simulating and predicting the dynamic behavior of controlled structural systems is a challenging goal because of the complexity of the related architectures. As a matter of fact, obtaining accurate information on system response in pre-design and design phases may reduce both computational and experimental efforts. In this study, the numerical simulation of a specific family of semi-active vibration control devices is taken into account: piezoelectric acting in the synchronized switched shunt architecture (SSSA). Different from the classic shunt inductive architecture, the SSSA is characterized by a switch component adaptively synchronized with the structural response to be controlled, whatever it is. The ability of controlling low range frequencies without large limitations in terms of inductive components represents, together with the adaptive skill, the main advantage of this technique. The reference structure is represented by an isotropic plate, clamped on the edges; the active system is made of an isolated PZT patch, located at the center. A dedicated simulation tool has been realized and implemented to predict piezo effectiveness for the considered configuration. Related matrices have been suitably integrated within the complete model. The switching state of the electrical circuit causes the matrices elements to be time-variant; the related problems have been dealt with in a Newmark-Beta-based integration solver. The integrated structural system has been fully and simultaneously simulated, considering at the same time the structural dynamics, the nonlinear behavior of the electrical device, and the piezoelectric electromechanical response. Results have been presented in terms of time response. The innovative contribution reported in this study concerns the application of the FE approach to the design of a SSSA integrated within MDOF structural systems. A characteristic of the approach is the ability of interacting with commercial FE codes, like MSC-Nastran, in designing and simulating the SSSA control action. References reported in this study face the SSSA control problem applied to single DOF systems (not directly applicable to complex systems, but through modal analysis reduction operations) or deal with FE simulation of classical inductive shunt (not switched). The details of this statement are fully reported in the Introduction.

Integrated Optimization of Material Layout and Control Voltage for Piezoelectric Laminated Plates

Zhan Kang, , Liyong Tong, — 2008-07-25

Topology optimization techniques have recently been successfully applied to the design of piezoelectric smart structures. However, in previous formulations, the material layout is optimized under the condition of given electric actuation voltages. This imposes a restriction to the design problem and may consequently limit application of these approaches, particularly in complex shape control problems. The present article investigates the integrated optimization of structural topology and control voltage of piezoelectric laminated plates. The finite element analysis formulation of laminated plates with surface bonded piezoelectric layers is introduced first. The optimal design problem is then formulated based on an artificial material model with penalization for both mechanical and piezoelectric properties. In the formulated problem, the topologies of both host and actuation layers are optimized simultaneously with spatial distribution of control voltage. Several special cases of the proposed design problem are considered, and numerical techniques for sensitivity analysis and optimal solutions are proposed. Numerical examples are presented to demonstrate the validity and applicability of the proposed methods.

Single-Walled Carbon Nanotubes -- Ionic Polymer Electroactive Hybrid Transducers

Akle, B. J., Leo, D. J. — 2008-07-25

Ionic electroactive polymers, sometimes referred to as artificial muscles, have the ability to generate large bending strain and moderate stress at low applied voltages. Typical types of ionic electroactive polymer transducers include ionic polymers, conducting polymers, and carbon nanotubes. Preliminary research combining multiple types of materials proved to enhance certain transduction properties. Bennett and Leo (Materials Research Society Symposium Proceedings, vol. 785, 2003b) showed that the speed of response, maximum strain, and quasi-static actuation are improved by adding a layer of conducting polymer on an ionic polymer transducer. In this work, a recently developed fabrication method called the direct assembly process (DAP) plating is used to build SWNT/RuO₂ hybrid transducers. The DAP consists of mixing a conducting powder with an ionomer solution. This technique has demonstrated improved response time and strain output as compared to previous methods. Electrodes applied using this new technique of mixing RuO₂ (surface area 45—65 m²/g) particles and Nafion^TMdispersion provided 5x the displacement and 10x the force compared to a transducer made with conventional methods. Furthermore, previous studies demonstrated that the response speed of the transducer is optimized by varying the composition of metal in the electrode (Akle, B.J., Bennett, M.D., Leo, D.J., Wiles, K.B. and McGrath, J.E. 2007. "Direct Assembly Process: A Novel Fabrication Technique for Large Strain Ionic Polymer Transducers,'' Journal of Mat. Sci., 42:7031—7041). For RuO₂, the optimal loading was approximately 45vol%, while carbon nanotubes electrodes have an optimal performance at 30vol%. Due to low percolation threshold, carbon nanotubes actuators perform better at a lower loading compared to other conducting powders. The addition of single-walled carbon nanotubes (SWNT) to the electrode increases both the strain rate and the maximum strain of the hybrid actuator. The strain rate of the transducer increased proportional to the ratio of SWNT to RuO₂ in the electrode. A maximum peak-to-peak strain of 10.6% (±2V) is attained in a 15vol% SWNT/30 vol% RuO₂ hybrid transducer. The maximum strain rate of 2.7%/s is generated by a 20vol% SWNT/25 vol% RuO₂ hybrid transducer.

Finite Element Charts and Active Vibration Suppression Schemes for Smart Structures Design

Ghasemi-Nejhad, M. N., Russ, R., Kougen Ma, — 2008-07-25

This article employs a finite element method to introduce Displacement-Load-Sensor voltage-Actuator voltage (DLSA) Design Charts and associated vibration suppression schemes; namely, Constant Voltage (CV), Optimum Voltage (OV), Corresponding Voltage (COV), and Truncated Corresponding Voltage (TCOV), to develop actuator control voltages with amplitude and phase information for the design of smart structures with piezoelectric sensors and actuators for active vibration suppression. These techniques can be used to (a) design the location, size, and number of actuators without resorting to complex control strategies or formal optimization techniques, (b) investigate the actuation effectiveness of surface-mounted versus embedded piezoelectric patches in similar composite structures, and (c) determine actuator control voltages analogous to a feedforward open-loop control technique. Guidelines are presented for the development of DLSA Design Charts. In addition, closed form analytical equations that can replace DLSA Design Charts, are developed and presented due to their ease of use. An Active Composite Panel (ACP) with a surface-mounted piezoelectric patch actuator for lateral vibration suppression and an Active Composite Strut (ACS) with a piezoelectric stack actuator for axial vibration suppression are considered. The ACP and ACS are employed to demonstrate the applications of the introduced DLSA Design Charts and the vibration suppression schemes for vibration suppression and actuator placement optimization. The vibration suppression of both ACP and ACS is significant over a frequency range encompassing several resonances, and is indicated by the Suppressed Vibration Energy (SVE) index. This investigation shows that the optimum location of the actuator depends on the structural mode shape, based on the criteria of maximum SVE and minimum actuator power. In general, the actuator should be placed on the panel on a sub-area, where the sum of normal strains is maximum. However, a preferred location can be determined over a range of frequencies that encompass more than one natural frequency.

Modal Analysis on Macro-strain Measurements from Distributed Long-gage Fiber Optic Sensors

Suzhen Li, , Zhishen Wu, — 2008-07-25

In a recent study by the authors, an advanced structural health monitoring (SHM) strategy based on distributed fiber optic sensing techniques has been proposed to utilize the strain responses throughout the full or some partial areas of structures to detect the arbitrary and unforeseen damages. As one of the essential components, a two-level scheme based on modal parameters from distributed dynamic macro-strain responses has been developed for damage locating and quantifying. This work further investigates the superiority and some concerns of using distributed long-gage fiber optic sensing technique for vibration based SHM through a theoretical modal analysis on the dynamic macro-strain distribution. Modal testing is also carried out to verify the performance of macro-strain frequency response function (FRF) and identify the modal parameters including resonant frequency, damping ratio, and modal macro-strain vector (MMSV). From the SHM point of view, their applications are summarized finally.

Vibration Control of Smart Composite Laminated Spherical Shell using Neural Network

Kumar, R., Mishra, B., Jain, S. — 2008-07-25

This study presents a neural network approach for the identification and control of a smart composite laminated spherical shell. The spherical shell is in the form of a layered composite shell having a sensor and an actuator layer. The vibratory response of the shell is modeled using FEM. A degenerate shell element is implemented to model composite laminated spherical shell. Modeling is based on the first-order shear deformation theory and linear piezoelectricity theory. The mode superposition method has been used to transform the coupled finite element equations of motion in the physical coordinates into a set of reduced uncoupled equations in the modal coordinates. The reduced uncoupled equations are transformed into discrete state space form. An identifier neural network has been trained using the results of the FEM program to predict the future response of the structure from the immediate history of the system's response. Then a controller neural network has been trained with the aid of the identifier neural network so that the overall behavior of the controlled system can be described by a prescribed reference model. Numerical results have been presented for the vibratory response of the laminated composite spherical shell. The controlled response of the shell is found to exactly follow the reference model.

A Unifying Perspective on the Quasi-steady Analysis of Magnetorheological Dampers

Hong, S.-R., John, S., Wereley, N. M., Choi, Y.-T., Choi, S.-B. — 2008-07-25

A magnetorheological (MR) fluid, modeled as a Bingham plastic (BP) material, is characterized by a field dependent yield stress, and a (nearly constant) postyield plastic viscosity. Based on viscometric measurements, such a BP model is an idealization to physical MR behavior, albeit a useful one. A better approximation involves modifying both the preyield and postyield constitutive behavior as follows: (1) assume a high viscosity preyield behavior when the shear stress is less than the transition stress, and (2) assume a power law fluid (i.e., strain rate dependent viscosity) when the shear stress is greater than the transition stress. Assuming a power law fluid in postyield allows the model to account for shear thinning behavior exhibited by MR fluids at higher strain rates. Such an idealization for MR fluid constitutive behavior is called an viscous-power law model, or a Herschel—Bulkley (HB) model with preyield viscosity. This study develops a quasi-steady analysis for such a constitutive MR fluid behavior applied to an MR flow mode damper. Closed form solutions are developed for the fluid velocity, as well as key performance metrics, such as damping capacity and dynamic range (ratio of field-on to field-off force). For the given fluid properties and flow mode damper geometry, the fluid velocity profile and gradient, and the relationship of the damper force and piston velocity are analyzed. In addition, specializations to existing models, such as the HB, biviscous, and BP models, are shown to be easily captured by this model when physical constraints (idealizations) are placed on the rheological behavior of the MR fluid.

Damping Behavior of Semi-passive Vibration Control using Shunted Piezoelectric Materials

Guyomar, D., Richard, C., Mohammadi, S. — 2008-07-25

Piezoelectric transducers in conjunction with appropriate electric networks can be used as mechanical energy dissipation devices. Semi-passive vibration control devices using nonlinear methods have experienced significant development in recent years, due to their performance and advantages compared with passive and active techniques. More precisely, synchronized switch damping (SSD) and derived techniques, which have been developed in the field of piezoelectric damping, lead to a very good trade-off between simplicity, required power supply, and performance. This technique consists of nonlinear processing of the piezoelement voltage which induces an increase in electromechanical energy conversion. The control law consists of triggering the inverting switch on each extremum of voltage (or displacement). The purpose of this study is the experimental observation of piezoelement damping sensitivity to variations of amplitude and frequency of excitation force. In addition, the effect of the size of piezoelement area on the vibration damping in high and low values of these parameters has been studied using SSDI method. The proposed method for switching sequence is based on statistical evaluation of the structural deflection.

Tailoring Piezoresistive Sensitivity of Multilayer Carbon Nanotube Composite Strain Sensors

Loh, K.J., Lynch, J.P., Shim, B.S., Kotov, N.A. — 2008-07-08

In recent years, carbon nanotubes have been utilized for a variety of applications, including nanoelectronics and various types of sensors. In particular, researchers have sought to take advantage of the superior electrical properties of carbon nanotubes for fabricating novel strain sensors. This article presents a single-walled carbon nanotube (SWNT)-polyelectrolyte (PE) composite thin film strain sensor fabricated with a layer-by-layer (LbL) process. Optimization of bulk SWNT-PE strain sensor properties is achieved by varying various LbL fabrication parameters, followed by characterization of strain-sensing electromechanical responses. A resistor and capacitor (RC)-circuit model is proposed and validated with electrical impedance spectroscopy to fit experimental results and to identify equivalent circuit element parameters sensitive to strain. Experimental results suggest consistent trends between SWNT and PE concentrations to strain sensor sensitivities. Simply by adjusting the weight fraction of SWNT solutions and film thickness, strain sensitivities between 0.1 and 1.8 have been achieved. While SWNT-PE strain sensitivity is lower than some metal-foil strain gauges ($2), the LbL method allows for precise tailoring of the properties (i.e., strain sensitivity, resistivity, among others) of a high-capacity (±10,000 µm m^-1) homogeneous multilayer strain sensor.

Loop Shaping Control of a Model-Story Building Using Smart Materials

Sethi, V., Gangbing Song, , Franchek, M. A. — 2008-07-08

This research concerns active vibration control of a two-story model structural frame by using the method of loop shaping. Piezoceramic smart materials, in particular the PZT (Lead Zirconate Titanate) in the form of patches, are surface-bonded on the structure and function as actuators and sensors. Sensitivity charts are introduced to assist the control system design. A nonparametric system identification is performed to obtain the frequency response function of the model building. A loop-shaped controller is designed using sensitivity charts. The effectiveness of the designed controller is demonstrated by shaker table tests where data from four earthquakes is used for excitation of the structure. The experimental results clearly show that the loop shaping based controller reduces the vibrations experienced by the structure during seismic activities.

Modal Synthesis of Flexible Mechanisms for Airfoil Shape Control

Campanile, L.F. — 2008-07-08

The use of `compliant' or flexible mechanisms constitutes a very promising option for the successful realization of shape-adaptable airfoil structures. Achieving large deformations by exploiting structural flexibility instead of employing conventional mechanisms with moveable parts offers several advantages: absence of backlash and wear, no need for lubrication, reduced noise, smooth geometry changes, a lighter design, and reduced manufacturing costs. As a counterpart, compliant systems are more complex to analyze and design due to their inherent coupled behavior. Established design procedures, developed in the framework of kinematics design, are of limited use for application to shape-adaptable structures due to differences in requirement priorities. This study presents a novel synthesis procedure for compliant shape-adaptable airfoils. Initially devised for the so-called belt-rib airfoils, the procedure can be extended to the general case of compliant airfoils with an external flexible skin (optionally reinforced by frames) and a system of internal stiffeners. After the description of the core synthesis algorithm, which is based on a modal approach, its integration in a global design procedure is discussed. Application to the case of a belt-rib airfoil is then considered. The compliant structure resulting from the procedure combines the characteristic qualities of a compliant system (smooth deformation pattern, absence of moveable parts, low weight) with the low load-dependence of kinematics which is typical of conventional mechanisms.

Sound Wave Transmission Reduction through a Plate using Piezoelectric Synchronized Switch Damping Technique

Guyomar, D., Richard, T., Richard, C. — 2008-07-08

Wave control and development of anechoic systems in air are of major interest to improve acoustic comfort. Currently, passive control techniques, which consist in using absorbing materials are effective at high frequency, but the principal limitation of this approach is mass and volume, particularly in the low-frequency range. Active control techniques (like the use of antinoise, which uses interference of sound waves) have been successfully applied to reduce the noise level, but their main drawback is the complexity of the global system and global power requirements. Another approach is to reduce the noise transmission by a proper control of transmitting structure oscillations. The aim of this study is to develop a technique of noise reduction by using piezoelectric elements. The device considered is a large clamped plate, equipped with piezoelements. Sound transmission through this plate is strongly related to the various resonances. Vibration damping devices implemented on this plate results in the reduction of the plate resonances and therefore of the correlated transmitted sound. The synchronized switch damping technique (SSD) is implemented. In this semi-passive approach, the piezoelements are continuously switched from the open circuit state to a specific electric network synchronously with the strain. Owing to this switching mechanism, a phase shift appears between the strain induced by an incident acoustic wave and the resulting voltage, thus creating energy dissipation. As many techniques using piezoelements, in this non-linear process, damping performances directly depend on the electromechanical coupling coefficient of the system. An analytical model and a finite element model are proposed in this study to obtain optimal size and location of piezoelectric inserts. Using this design, an attenuation of 19 dB on the plate oscillations and 15dB on the transmitted wave pressure can be obtained.

Numerical and Experimental Comparison of the Adaptive Feedforward Control of Vibration of a Beam with Hybrid Active-Passive Damping Treatments

Vasques, C.M.A., Rodriques, J. D. — 2008-07-08

This article concerns the adaptive feedforward control of vibration of a freely supported beam with two distinct surface mounted hybrid active—passive damping treatments. The first configuration concerns the use of an Active Constrained Layer Damping (ACLD) patch alone, where the piezoelectric constraining layer is actively utilized to increase the shear deformation of the sandwiched passive viscoelastic layer and at the same time to apply forces and moments into the structure, which will balance the power flows into the structure, and is denoted by ACLD configuration. The second configuration regards the use, as an active element in the control, of the piezoelectric patch alone, denoted by Active Damping (AD), and since the constraining layer of the ACLD treatment also bonded on the other side of the beam is not actively utilized, a Passive Constrained Layer Damping (PCLD) treatment is utilized in combination with an AD one, yielding an AD/PCLD configuration. A finite element model of the beam with the damping treatments is used for the simulation of the adaptive feedforward controller which is also implemented and tested in real-time. The aims are to compare the predicted and measured damping performances of the two treatments in terms of vibration reduction, control effort, stability and robustness, when a filtered-reference LMS algorithm is used to cancel the effects of a broadband voltage disturbance applied into a third surface mounted piezoelectric patch which is used to excite the beam.

In Vitro Atherosclerotic Plaque Characterization by Acoustic Impedance Monitoring, Part I: Sensor Modeling, Design, and Fabrication

Dugnani, R., Chang, F.K. — 2008-07-08

This investigation aims at developing a technique to diagnose the presence of plaque in arteries by measuring the variations of the electromechanical impedance of a piezoelectric (PZT) sensor in contact with the arterial surface. The proposed technique makes use of either one or multiple PZT sensors integrated on a balloon and used prior to percutaneous transmural angioplasty interventions. The system we envision consists of two components: the active, miniaturized PZT sensors (surface-mounted on an angioplasty balloon), and the computer and software. In the proposed technique, the angioplasty balloon with the wall-mounted sensor(s) is inflated in the artery to make contact with the plaque. Initially, low pressure is used not to disrupt the plaque. The diagnostic test feeds an electrical signal that excites the sensors; by analyzing the sensors' response, information on features and properties of the plaque is obtained. Doctors will use this information to recognize unstable plaque prior to full pressurization of the angioplasty balloon. The first part of the article describes the procedure used in designing a sensor for the detection of unstable plaque by the impedance method. Both finite element methods and an analytical model — a modified version of the Krimholtz—Leedom—Matthaei model (Krimholtz et al., 1970) — are utilized in the design of the sensor. An appropriate fabrication technique for manufacturing small-scale PZT sensors is also proposed for use in smaller arteries such as the coronary arteries. Experimentation and verification of the proposed technique is presented in the second paper stemmed from this investigation.

In Vitro Atherosclerotic Plaque Characterization by Acoustic Impedance Monitoring, Part II: Experimentation and Validation

Dugnani, R., Chang, F.K. — 2008-07-08

Although coronary atherosclerosis is the leading cause of hospitalization and death in the United States, at present no effective diagnostic technique is available to effectively characterize atherosclerotic plaque in vivo and in real-time. In `Introduction' of this article, we propose the use of an impedance-based technique to diagnose the presence of atherosclerotic plaque. Both analytical and finite element methods are developed to study the effect of a multi-layer substrate in contact with a sensor on the sensor's electro-mechanical impedance. Also a modified version of the Krimholtz, Leedom, and Matthaei (KLM) model is introduced to design the sensor dimension based on a sensor/plaque configuration. An appropriate fabrication technique for manufacturing a small-scale PZT sensor is also proposed for possible use in small arteries. In section `Analytical Model' of the article, we show that the presence of plaque can be accurately predicted by using the proposed impedance-probing technique on samples of human, atherosclerotic tissues. The presence of atherosclerotic plaque in the samples — as predicted by our technique — is confirmed by a histological examination carried out at the Stanford Histology Research Core Lab. The plaque mechanical properties are approximated based on a modified KLM model describing the sensor-artery system. The properties predicted are found to be consistent with the values reported in the literature. A brief study pertaining to the pressure necessary to achieve an acceptable contact between the PZT sensors and the probed artery is presented in the last section of the article. This work suggests that it is possible to characterize atherosclerotic plaque in real-time using the described impedance-based monitoring technique. One future possible application for this technique could be — for instance — the detection of unstable plaque in arteries prior to percutaneous transmural angioplasty (PTA).

Spatial Weighting of Smart Materials for Real-time Measurement of Aerodynamic Forces

Keats-Pullen, D., Hubbard, J. E., Guerreiro, N. M. — 2008-07-08

Spatial weighting techniques are used to determine the apertures of a conformal smart material sensor required to measure aerodynamic forces on an aircraft wing section. Aperture shading with a linear weighting allows for the compilation of an aerodynamic center of pressure sensor. A technique is presented that allows the extraction of sectional aerodynamic forces, such as lift and drag, from appropriately shaped sensor electrodes. An example of the implementation of this sensor aperture weighting technique is given for a wing section with a NACA 0010 airfoil cross-section. It is shown that, given any airfoil cross-section, a unique lift and drag sensor aperture can be derived. Preliminary data from the testing of a prototype center of pressure sensor is presented. This sensor technology enables real-time measurement of aerodynamic forces in a free-flight testing environment.

Model Predictive Control of a Two Stage Actuation System using Piezoelectric Actuators for Controllable Industrial and Automotive Brakes and Clutches

Neelakantan, V. A., Washington, G. N., Bucknor, N. K. — 2008-07-08

High bandwidth actuation systems that are capable of simultaneously producing relatively large forces and displacements are required for use in automobiles and other industrial applications. Conventional hydraulic actuation mechanisms used in automotive brakes and clutches are complex, inefficient and have poor control robustness. These lead to reduced fuel economy, controllability issues and other disadvantages. Recently, a two-stage hybrid actuation mechanism was proposed by combining classical electromechanical actuators like DC motors and advanced smart material devices like piezoelectric actuators. This article discusses the development and implementation of a model predictive control methodology for controlling this two-stage actuation system in tracking various reference inputs. Additionally, this methodology also employs a unit-step delayed disturbance estimate to account for actuator hysteresis, other nonlinearities and unmodeled dynamics in the system. Finally, the article highlights the effectiveness of this control methodology experimentally by tracking various reference inputs.

Design and Analysis of a Superelastic SMA Damper

Zuo, X.-B., Li, A.-Q., Chen, Q.-F. — 2008-05-20

Based on the superelasticity of shape memory alloy (SMA), a superelastic SMA damper is designed, and its analytical model has been established and verified by experimental results. Numerical simulation is carried out to investigate the effects of the damper's parameters on its behaviors, such as groove depth, SMA wire amount, and friction coefficient, temperature and displacement amplitude. Results show that initial stiffness, external force, and dissipated energy of the SMA damper increase linearly with groove depth, SMA amount, and friction coefficient. Under different displacement amplitudes, the shapes of the external force—displacement curve of the damper are polygons, such as triangle, quadrangle, and pentagon, respectively, hence the SMA damper is a variable-stiffness type damper. In addition, experimental results indicate that the model can be used to simulate the mechanical behavior of the damper.

A New Magneto-rheological Fluid Damper for High-mobility Multi-purpose Wheeled Vehicle (HMMWV)

Dogruer, U., Gordaninejad, F., Evrensel, C. A. — 2008-05-20

This study focuses on the design, development, and testing of a new magnetorheological fluid (MRF) damper for high-mobility multi-purpose wheeled vehicle (HMMWV). The new damper is designed to provide controllability while keeping the same geometrical dimensions as the original equipment manufacturer (OEM) damper. To design a fail-safe MRF damper, MRF behavior is simulated using the Bingham Plastic model, and the magnetic field distribution is obtained by a three-dimensional electromagnetic finite element analysis. A fail-safe MRF damper is referred to one which retains a minimum damping capacity comparable to that of OEM damper in the event of a power supply or electronic system failure. The proposed MRF damper is designed to achieve non-symmetrical force characteristics with different force responses at rebound and compression phases. Theoretical predictions and experimental results are presented for the force—displacement and force— velocity behaviors of the damper under different input motions, various magnetic fields, and different MR fluids.

Experimental Demonstration of H{infty} Control based Active Vibration Suppression in Composite Fin-tip of Aircraft using Optimally Placed Piezoelectric Patch Actuators

Rao, A.K., Natesan, K., Seetharama Bhat, M., Ganguli, R. — 2008-05-20

The goal of this study is the multi-mode structural vibration control in the composite fin-tip of an aircraft. Structural model of the composite fin-tip with surface bonded piezoelectric actuators is developed using the finite element method. The finite element model is updated experimentally to reflect the natural frequencies and mode shapes accurately. A model order reduction technique is employed for reducing the finite element structural matrices before developing the controller. Particle swarm based evolutionary optimization technique is used for optimal placement of piezoelectric patch actuators and accelerometer sensors to suppress vibration. H based active vibration controllers are designed directly in the discrete domain and implemented using dSpace^® (DS-1005) electronic signal processing boards. Significant vibration suppression in the multiple bending modes of interest is experimentally demonstrated for sinusoidal and band limited white noise forcing functions.

Characteristics of Energy Storage Devices in Piezoelectric Energy Harvesting Systems

Guan, M.J., Liao, W.H. — 2008-05-20

Using piezoelectric elements to harvest energy from ambient vibration has been of great interest recently. As the power harvested from the piezoelectric element is relatively low, energy storage devices are needed to accumulate the energy for intermittent use. In this study, the energy storage devices considered include rechargeable batteries and supercapacitors. The traditional electrolytic capacitors are not considered due to their low energy density. The charge/discharge efficiencies of the energy storage devices are of major concern. The equivalent circuit model of the energy storage devices is investigated. It is found that the leakage resistances of the energy storage devices are the dominant factor that influences the charge/discharge efficiency in the piezoelectric energy harvesting systems. A quick test method is proposed to experimentally study the charge/discharge efficiencies of the energy storage devices. The experimental results verify our findings. Adaptability, lifetime, and charging protection circuit of the energy storage devices are also discussed. It can be concluded that supercapacitors are suitable and more desirable than the rechargeable batteries to store the energy in the piezoelectric energy harvesting systems.

Homogenized Strain Model for Ni--Mn--Ga Driven with Collinear Magnetic Field and Stress

Faidley, L. E., Dapino, M. J., Washington, G. N. — 2008-05-20

Prior experimental measurements by the authors demonstrated large reversible strains of ·0.41% along the [001] crystal direction of a cylindrical Ni₅₀Mn_28.7Ga_21.3 rod driven with a magnetic field along the same direction and no external restoring force. The origin of the reversibility is attributed to internal bias stresses generated by impurities absorbed during manufacture of the alloy. This article presents a macroscopic constitutive model for Ni—Mn—Ga strain in collinear field and stress configuration. The switching between two variant orientations in the presence of Zeeman energy and the pinning energy of the impurities is formulated through a Gibbs energy function for the crystal lattice. Inhomogeneous local interaction fields and impurity distributions are addressed through stochastic homogenization techniques. Attributes of the model are illustrated through comparison of model results with strain—field measurements collected at various compressive loads. Constrained optimization is used to determine the necessary parameters and an error analysis is performed to assess the accuracy of the model for various loading conditions. The collinear field and stress configuration can lead to solenoid transducers with enhanced energy density and bandwidth relative to standard electromagnet devices.

Performance Improvement of a Rotary MR Fluid Actuator Based on Electromagnetic Design

Nam, Y.-J., Moon, Y.-J., Park, M.-K. — 2008-05-20

This study presents an electromagnetic design methodology for a rotary magnetorheological (MR) fluid actuator. In order to improve the performance of the MR fluid actuator, the magnetic field should be effectively applied to the MR fluid. Therefore, it is important that the magnetic circuit composed of the MR fluid, the ferromagnetic material for magnetic flux path, and the electromagnetic coil is well designed. For this purpose, two effective approaches are proposed: one is to shorten the magnetic flux path by removing the unnecessary bulk of the yoke in order to improve the static characteristic of the MR fluid actuator, and the other is to increase the magnetic reluctance of the magnetic circuit by minimizing the cross-sectional area of the yoke through which the magnetic flux passes in order to improve the dynamic and hysteretic characteristics. The effectiveness of the proposed design methodology is verified through magnetic analysis and a series of basic experiments.

Electroelastic Analysis of Functionally Graded Piezoelectric Material Beams

Zheng Zhong, , Tao Yu, — 2008-05-20

A general two-dimensional solution is proposed for functionally graded piezoelectric material beams with arbitrary graded material properties along the beam thickness direction. The beam is subjected to normal and shear tractions of polynomial form on the top and bottom surfaces, while the end boundary conditions can be cantilever, simply supported or rigidly clamped. The Airy stress function and the electric potential are expressed in a finite power series, and the corresponding recurrence-governing equations are obtained. Explicit expressions of analytical solution to a specific example for a cantilever beam are obtained to demonstrate the usefulness of the proposed general solution technique. The proposed solution method will be useful in analyzing functionally graded piezoelectric structures with arbitrary variations of material properties, and the obtained results can serve as a basis for establishing simplified theories and numerical methodology of functionally graded piezoelectric material beams.

Simulation Analysis on Intelligent Structures with Magnetorheological Dampers

Guo, Y.-Q., Fei, S.-M., Xu, Z.-D. — 2008-05-20

The magnetorheological (MR) damper, a shock absorption device, can be used to reduce vibration or dynamic response of controlled systems. Its parameters can be adjusted in real-time by updating its control current, therefore, it is critical to determine the control current of the MR damper accurately and quickly. This study proposes a fuzzy control strategy based on a neural network forecasting model of the building structure with MR dampers, in which a neural network forecasting model is developed to predict dynamic responses of the system with MR dampers and a fuzzy controller is then designed to determine control currents of MR dampers. A five-floor steel structure with MR dampers using the proposed fuzzy control strategy is simulated by using Simulink. Simulation results of the fuzzy control system are compared with those of the bi-state control system, the passive-on control system, the passive-off control system, and the uncontrolled system. Analysis results demonstrate that the fuzzy control strategy can determine control currents of MR dampers accurately and quickly; furthermore, the fuzzy control strategy reduces seismic responses of structures more effectively than the passive-on control strategy, the passive-off control strategy, and the bi-state control strategy.

Synthesis of Reference Signal in Adaptive Feedback Controller for Structure Vibration Suppression

Yang, S.M., Sheu, G.J., Li, C.C. — 2008-05-20

Adaptive control has been known to be desirable to accommodate the system parameter variations and adapt to operational requirements in smart (intelligent) structures. Conventional feedforward controller requires both the reference sensor to measure the disturbance and the error sensor to measure the residual vibration; however, the reference sensor measurement may be impractical because the disturbance is often not known a priori in structural vibration. This study presents an adaptive feedback controller design in which the reference signal is synthesized by the error sensor measurement and the system dynamics identification, which is a prerequisite also in adaptive feedforward controller design. The infinite impulse response (IIR) adaptive filter for system identification and the finite impulse response (FIR) adaptive filter for feedback controller are implemented on digital signal processor for effective on-line vibration suppression. Experimental results show that the controller performance is strongly influenced by the accuracy of system identification. The controller achieves broadband attenuation and remains robust under parameter variations.

Dynamic Stability of Beam-type Vibratory Angular Rate Sensors Subjected to Rate Fluctuations

Asokanthan, S. F., Cho, J. — 2008-05-20

Dynamic stability behavior of a beam-type vibratory structure, for applications in a class of vibratory angular rate sensors is investigated. A suitable mathematical model for a rotating beam perturbed by periodic velocity fluctuations is developed. The natural frequency variations due to the gyroscopic coupling present in the system are characterized. When the system is considered to be under an influence of periodic perturbations in the input angular speed, the dynamic stability is investigated. The method of averaging is employed for this purpose, and closed-form stability conditions are obtained. The analytical results are verified by direct numerical integration of the system equations.

Constitutive Model of Shape Memory Alloys for Asymmetric Quasiplastic Behavior

Ikeda, T. — 2008-05-14

A simple constitutive model of shape memory alloys for analyses of tension—compression quasiplastic behavior is derived. Here, three martensitic variants are considered; namely, thermal-induced, tensile stress-induced, and compressive stress-induced martensitic variants. Reorientation from one variant to another variant is assumed to take place according to a reorientation energy criterion based on grain-based micromechanics. Stress—strain hysteresis loops for a bar under tension—compression cyclic loading are simulated and they are compared with available experimental data. Results show that this constitutive model can capture asymmetric stress—strain behavior for tension and compression and a strain rate effect on stress—strain—temperature relationship quite well.

Modeling of Shape Memory Alloys Based on Microplane Theory

Kadkhodaei, M., Salimi, M., Rajapakse, R.K.N.D., Mahzoon, M. — 2008-05-14

A three-dimensional microplane constitutive model utilizing statically constrained formulation with volumetric—deviatoric split is presented for shape memory alloys (SMAs). Shear stress within each microplane is described by resultant shear component on the plane. One-dimensional stress—strain laws are used for normal and shear stresses on microplanes by considering suitable adjustments between the macroscopic and the microscopic quantities. The behavior of SMAs under simple and complicated loadings is studied. The model represents interaction between the stress components and the deviation from normality in the case of nonproportional loadings. The results are in good agreement with the existing theoretical and experimental findings.

Performance of MRE-based Vibration Absorbers

Lerner, A. A., Cunefare, K.A. — 2008-05-14

The purpose of this work is to use magnetorheological elastomers (MREs) as field-dependent springs within three vibration absorber configurations, and to determine their vibration absorption characteristics. Magnetorheological elastomers are fabricated from silicone gel and iron microparticles, and implemented as tunable springs in three vibration absorber configurations, which excited the MREs in shear, squeeze mode, and compression. Each vibration absorber configuration exploits different magneto-mechanical properties, achieving very different results. The MRE iron concentration is varied to find the largest natural frequency shift for the squeeze-mode absorber due to an applied magnetic field. Absorbers with MREs containing 35% iron by volume exhibits the largest natural frequency shift, 507%. MREs containing 35% iron are placed into shear and longitudinal mode vibration absorber devices, which exhibit 470% and 180% frequency increases, respectively.

Mathematical Model of Drum-type MR Brakes using Herschel-Bulkley Shear Model

Farjoud, A., Vahdati, N., Yap Fook Fah, — 2008-05-14

Most of the commercially available magnetorheological (MR) fluids are only tested up to 1200 1/s shear rates but with no magnetic field. Data are rarely available at high shear rates with magnetic field applied. In most of the applications where MR fluids are used, such as MR rotary brakes or MR translational dampers, the shear rates can be in the order of thousands and in some applications, the shear rates could be in the order of ten thousands (1/s) and higher. At these high shear rates, most MR fluids will be shear thinning and Bingham model will be inappropriate to use. The focus of this study is on the mathematical modeling of a drum-type MR rotary brake using the Herschel-Bulkey model.

Multimodal Vibration Control of a Flexible Structure using Piezoceramic Sensor and Actuator

Sethi, V., Gangbing Song, — 2008-05-14

This study presents results of multimodal vibration suppression of a smart flexible cantilever beam with piezoceramic actuator and sensor by using a pole placement controller. Piezoceramic PZT (lead zirconate titanate) patches are surface-bonded on the beam and function as actuator and sensor. Nonparametric identification for the dynamics of the first three modes is carried out. From the nonparametric model, a parametric model is identified to assist the control system design. The identified model is used for state estimation and development of control algorithm. A linear pole placement controller is designed and simulated using the identified model. Experimental results demonstrate the effectiveness of observer-based multimodal active vibration control of the structure using piezoceramic smart materials.

Experimental Investigation of Terfenol-D's Elastic Modulus

Kellogg, R., Flatau, A. — 2008-05-14

The variability of Young's modulus (the E effect) in giant magnetostrictive Terfenol-D has a significant impact on the performance and modeling of Terfenol-D transducers. In this investigation, Terfenol-D's modulus of elasticity is characterized under controlled thermal, magnetic, and mechanical loading conditions. Quasistatic cyclic compressive stress testing methods are used to quantify the variability in Young's modulus over a wide range of DC applied magnetic fields and stresses. Apparent elastic modulus changes of four-fold or more are demonstrated through the variation of a DC applied magnetic field. The effect of decreasing cyclic stress amplitude giving rise to an increase in Terfenol-D's apparent elastic modulus is also examined.

Actuator Designs using Environmentally Responsive Hydrogels

Westbrook, K. K., Qi, H. J. — 2008-05-14

Environmentally responsive (ER) hydrogels are hydrogels that can experience an abrupt volume change and hence hold or release a large amount of water under the change of certain environmental conditions, such as temperature, pH, or an electric field. Because of their unique capability to achieve a large yet reversible volume change, hydrogels have been widely used in microfluidics and biomedical applications, such as hydrogel sensors and actuators for microfluidic channels, novel drug delivery systems, and scaffolding materials for tissue engineering. In most applications, ER hydrogels are used to create an isotropic volume change or one-dimensional motion by constraining the hydrogel in the other two directions. In this study, using finite element based simulations, actuator designs are demonstrated that can generate a variety of shape changes by carefully patterning ER hydrogels on a non-ER hydrogel matrix. In these designs, as the environment changes, the ER hydrogels undergo volume change under the constraints imposed by the non-ER matrix, causing an eigenstrain (mismatch strain) and hence the deformation of the non-ER matrix. By properly controlling the locations of the ER hydrogel sections with respect to the non-ER hydrogel matrix, one can achieve a desired deformation of the composite structure. As examples, designs of a single material actuator, one linear spring composite actuator, and two coil composite actuators are demonstrated. The feasibility to produce these actuators and the possible applications are discussed at the end of the article.

Shape Memory Alloy Hybrid Composite Plates for Shape and Stiffness Control

Daghia, F., Inman, D. J., Ubertini, F., Viola, E. — 2008-05-14

Shape memory alloy hybrid composite plates are `intelligent' structures whose shape or stiffness is actively modified by embedded shape memory alloy fibers. In this work, the behavior of such structures is investigated numerically and experimentally. A finite element model which separately represents the host structure and the fibers in a two-dimensional setting is proposed as a simple tool to predict the structural behavior in stiffness and shape control. The shape control configuration is used to validate the model experimentally since it is the most sensitive to the choice of the geometrical and mechanical model parameters.

Electrical Equivalent Circuit of Multi-mode Flexible Beams with Piezoelectric Elements

Saghafi, M., Meghdari, A. — 2008-05-14

Surface mounted piezoelectric sensors and actuators on elastic structures are often connected to electrical networks. The coupled equations of motion of the elastic structure with piezoelectric elements are already well known. However, due to complex behavior of some electrical elements in the electrical network, it is not an easy task to obtain the integrated equations of the whole system. A good remedy for this problem is to take advantage of an equivalent electrical circuit (EEC) representation of the mechanical part, leading the entire system to be represented as an electrical circuit. In this study, the authors propose a new method for constructing the EEC. This method is based upon the multimode analysis of vibrating structures. Utilizing modal analysis, the equations are converted to tridiagonal form which is shown to be appropriate for constructing the EEC. In contrast to previous works, no restrictive approximations are made in its development. This method can also be used in similar applications, such as power harvesting from vibrating structures.