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Showing papers in "Smart Materials and Structures in 2003"


Journal ArticleDOI
TL;DR: In this paper, the authors present a detailed description of various techniques and experimental procedures in manufacturing ionic polymer-metal composites (IPMCs) that can be used as effective biomimetic sensors, actuators and artificial muscles as well as fully electroded with embedded electrodes for fuel cells.
Abstract: This paper, the second in a series of four review papers to appear in this journal, presents a detailed description of various techniques and experimental procedures in manufacturing ionic polymer–metal composites (IPMCs) that, if fully developed, can be used as effective biomimetic sensors, actuators and artificial muscles as well as fully electroded with embedded electrodes for fuel cells. The performance of IPMCs manufactured by different manufacturing techniques are presented and compared. In particular, a number of issues such as force optimization using the Taguchi design of experiment technique, effects of different cations on electromechanical performance of IPMCs, electrode and particle size and distribution control, manufacturing cost minimization approaches, scaling and three-dimensional (3D) muscle production issues and heterogeneous composites by physical loading techniques are also reviewed and discussed.

600 citations


Journal ArticleDOI
TL;DR: In this paper, the authors report the results of an analytical and experimental study to develop, calibrate, implement and evaluate the feasibility of a novel vision-based approach for obtaining direct measurements of the absolute displacement time history at selectable locations of dispersed civil infrastructure systems.
Abstract: This paper reports the results of an analytical and experimental study to develop, calibrate, implement and evaluate the feasibility of a novel vision-based approach for obtaining direct measurements of the absolute displacement time history at selectable locations of dispersed civil infrastructure systems such as long-span bridges. The measurements were obtained using a highly accurate camera in conjunction with a laser tracking reference. Calibration of the vision system was conducted in the lab to establish performance envelopes and data processing algorithms to extract the needed information from the captured vision scene. Subsequently, the monitoring apparatus was installed in the vicinity of the Vincent Thomas Bridge in the metropolitan Los Angeles region. This allowed the deployment of the instrumentation system under realistic conditions so as to determine field implementation issues that need to be addressed. It is shown that the proposed approach has the potential of leading to an economical and robust system for obtaining direct, simultaneous, measurements at several locations of the displacement time histories of realistic infrastructure systems undergoing complex three-dimensional deformations.

315 citations


Journal ArticleDOI
TL;DR: In this paper, the authors evaluate the dynamic behavior of two-dimensional cellular structures, with the focus on the effect of the geometry of unit cells on the dynamics of the propagation of elastic waves within the structure.
Abstract: Cellular structures like honeycombs or reticulated micro-frames are widely used in sandwich construction because of their superior structural static and dynamic properties. The aim of this study is to evaluate the dynamic behavior of two-dimensional cellular structures, with the focus on the effect of the geometry of unit cells on the dynamics of the propagation of elastic waves within the structure. The characteristics of wave propagation for the considered class of cellular solids are analyzed through the finite element model of the unit cell and the application of the theory of periodic structures. This combined analysis yields the phase constant surfaces, which define the directions of waves propagating in the plane of the structure for the assigned frequency values. The analysis of iso-frequency contour lines in the phase constant surfaces allows the prediction of the location and extension of angular ranges, and therefore regions within the structures where waves do not propagate. The performance of honeycomb grids of regular hexagonal topology is compared with that of grids of various geometries, with the emphasis on configurations featuring a negative Poisson's ratio behavior. The harmonic response of the considered structures at specified frequencies confirms the predictions from the analysis of the phase constant surfaces and demonstrates the strongly spatially-dependent characteristics of periodic cellular structures. The numerical results presented indicate the potentials of the phase constant surfaces as tools for the evaluation of the wave propagation characteristics of this class of two-dimensional periodic structures. Optimal design configurations can be identified in order to achieve the desired transmissibility levels in specified directions and to obtain efficient vibration isolation capabilities. The findings from the presented investigations and the described analysis methodology will provide invaluable guidelines for the prototyping of future concepts of honeycombs or cellular structures with enhanced vibro-acoustics performance.

281 citations


Journal ArticleDOI
TL;DR: In this paper, a fiber-optic system based on fiber Bragg grating sensors is proposed to detect ultrasonic Lamb waves in aircraft structures, in particular aircraft structural structures.
Abstract: This paper describes a fiber-optic system which is able to detect ultrasound in structures. The aim of the sensing system is to monitor structures, in particular aircraft structures, by detecting ultrasonic Lamb waves. This type of monitoring technique has recently become a key topic in structural health monitoring. Most common approaches use piezoceramic devices to launch and receive the ultrasound. A new way of fiber-optic detection of Lamb waves is based on fiber Bragg grating sensors. In addition to the well known advantages of fiber-optic sensors, this new interrogation scheme allows the use of Bragg gratings for both high-resolution strain and high-speed ultrasound detection. The focus of the paper is on the ultrasonic part of the system. The theoretical approach and the implementation into a laboratory set-up are elaborated. Experiments have been carried out to calibrate the system and first results on simple structures show the feasibility of the system for sensing ultrasonic Lamb waves.

280 citations


Journal ArticleDOI
TL;DR: In this article, the damped free vibration of a system composed of a magnetorheological elastomer and a mass was tested in order to obtain the dependence of the natural frequency and the damping ratio of the structure on the applied magnetic field.
Abstract: This paper presents an experiment testing the damped free vibration of a system composed of a magnetorheological elastomer and a mass. The goal of this experiment was to obtain the dependence of the natural frequency and the damping ratio of the structure on the applied magnetic field. The shear properties, including the shear storage modulus and the damping factor, were therefore determined. The experimental results revealed that the shear storage modulus could reach a value of 60% of the zero-field modulus and was dominated by the magnetic field, but the change in the damping factor could be neglected. Furthermore, when the field was moderate and saturation did not occur, the shear storage modulus increased proportionally with the applied field. This interesting phenomenon was analysed, and it is suggested that the subquadratic field dependence, which arises from the saturation of the magnetization near the poles of closely spaced pairs of spheres, must be taken into consideration.

250 citations


Journal ArticleDOI
TL;DR: In this paper, the local interaction simulation approach for Lamb wave propagation modelling in metallic structures is applied to analyze two-dimensional wave interactions with slot-type defects, and the results show the potential for complex modeling of acousto-ultrasonic waves in damage detection applications.
Abstract: Lamb waves have shown great potential for structural health monitoring The technique is based on guided ultrasonic waves introduced into a structure at one point and sensed at a different location Damage in a structure is identified by a change in the output signal However, previous studies show that even simple structural configurations can lead to complex response signals Therefore a knowledge and understanding of wave propagation can ease the interpretation of damage detection results This paper reports an application of the local interaction simulation approach for Lamb wave propagation modelling in metallic structures The focus of the analysis is on two-dimensional wave interactions with slot-type defects The method shows the potential for complex modelling of acousto-ultrasonic waves in damage detection applications

221 citations


Journal ArticleDOI
TL;DR: In this paper, the design and development of composite thin films of polymethylmethacrylate (PMMA) with multi-walled carbon nanotubes (CNTs) and surface modified multiwalled CNTs for gas-sensing applications are presented.
Abstract: The design and development of composite thin films of polymethylmethacrylate (PMMA) with multiwalled carbon nanotubes (CNTs) and surface-modified multiwalled carbon nanotubes (f-CNTs) for gas-sensing applications are presented in this paper. The responses of these composites for different organic vapors were evaluated by monitoring the change in the resistance of thin films of composite when exposed to gases like dichloromethane, chloroform, acetone, methanol, ethyl acetate, toluene and hexane. It was observed that the f-CNT/PMMA composite showed a higher response. There was an increase in resistance of the order of 102–103, due to surface modification, when exposed to dichloromethane, chloroform and acetone. The sensing mechanism is explained on the basis of volume expansion and polar interaction of various vapors on the CNT surface.

208 citations


Journal ArticleDOI
TL;DR: In this article, a broadband active shunt technique for controlling vibration in piezoelectric laminated structures is proposed, which is similar in nature to passive shunt damping techniques.
Abstract: In this paper a broadband active shunt technique for controlling vibration in piezoelectric laminated structures is proposed. The effect of the negative capacitance controller is studied theoretically and then validated experimentally on a piezoelectric laminated simply supported plate. The 'negative capacitance controller' is similar in nature to passive shunt damping techniques, as a single piezoelectric transducer is used to dampen multiple modes. While achieving comparable performance to that of the passive shunt schemes, the negative capacitance controller has a number of advantages. It is simpler to implement, less sensitive to environmental variations and can be considered as a broadband vibration absorber.

208 citations


Journal ArticleDOI
TL;DR: In this paper, an application of the local interaction simulation approach for wave propagation in metallic structures is reported, where the focus of the analysis is on damage detection applications, and the simulated results are validated experimentally.
Abstract: Lamb waves are the most widely used acousto-ultrasonic guided waves for damage detection. The method is generally complicated by the coexistence of at least two highly dispersive modes at any given frequency. Furthermore pure Lamb wave modes may generate a variety of other modes by interacting with defects and/or by crossing different boundaries. Knowledge and understanding of Lamb wave propagation is important for reliable damage detection. However, the theoretical analysis of guided wave scattering forms an extremely difficult problem. This paper reports an application of the local interaction simulation approach for wave propagation in metallic structures. The focus of the analysis is on damage detection applications. The study also involves wave propagation in a piezoceramic actuator/sensor diffusion bond model in which one of the piezoceramics generates the thickness mode vibration. The simulated results are validated experimentally. The results show the potential of the method for wave propagation analysis in damage detection applications.

204 citations


Journal ArticleDOI
TL;DR: In this article, a review of self-assembly in the field of nanotechnology is presented, particularly in the formation of nanostructures using guided molecular self-assembling methods.
Abstract: This paper serves as an introductory review of significant and novel successes achieved in the fields of nanotechnology, particularly in the formation of nanostructures using guided molecular self-assembly methods. Self-assembly is a spontaneous process by which molecules and nanophase entities may materialize into organized aggregates or networks. Through various interactive mechanisms of self-assembly, such as electrostatics, chemistry, surface properties, and via other mediating agents, the technique proves indispensable to recent functional materials and device realizations. The discussion will extend to spontaneous and Langmuir–Blodgett formation of self-assembled monolayers on various substrates, and a number of different categories of self-assembly techniques based on the type of interaction exploited. Combinatorial techniques, known as soft lithography, of micro-contact printing and dip-pen nanolithography, which can be effectively used to up-size nanostructured molecular assemblies to submicrometer and micrometer scale patterns, will also be mentioned.

186 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the actuation of a single-wall carbon nanotube (CNT) mat, an electrically conducting polyaniline (PAn) film and a composite of these two materials.
Abstract: The actuation of a single-wall carbon nanotube (CNT) mat, an electrically conducting polyaniline (PAn) film and a composite of these two materials has been investigated in NaNO3 (1 M), NaCl (1 and 3 M) and HCl (1 M) solutions. The expansion and contraction patterns of the PAn, CNT and CNT/PAn samples are similar in these solutions. Fabrication of the CNT/PAn samples by coating PAn (CNT:PAn = 3:1 by weight) substantially enhanced the actuation strain (0.2?0.5%) of the CNT/PAn composite compared to the low actuation strain (0.06%) of the pure CNT mat. The actuation of PAn and CNT operates via different mechanisms. Non-Faradaic electrochemical charging of the CNT bundles is the main factor behind the expansion of CNT, while the expansion/contraction of PAn is dependent on the redox reactions of the polymer. The displacement pattern of the composite is dominated by the PAn component. However, when a load is applied to the sample (up to 1.2 MPa) the CNT/PAn sample behaves similarly to CNT samples, i.e. the actuation strain is almost independent of the applied loads in contrast to pure conducting polymers. This implies that the reinforcing effect of the CNT component is possibly due to the inherent high Young's modulus of the CNT bundles (~640?GPa).

Journal ArticleDOI
TL;DR: In this paper, a new method of impact location in composite materials is proposed based on a classical sensor triangulation methodology and combines experimental strain wave velocity analysis with an optimization genetic algorithm procedure.
Abstract: Impacts, which may occur during manufacture, service or maintenance, are the major cause of in-service damage to composite structures. Many investigations have been undertaken in order to assess and locate impact damage. A new method of impact location in composite materials is proposed in this paper. It based on a classical sensor triangulation methodology and combines experimental strain wave velocity analysis with an optimization genetic algorithm procedure. The method is validated on a composite panel with embedded piezoceramic sensors. The paper shows that the new method has potential for effective impact damage location. Strain data from only three piezoceramic sensors provide good impact location results, avoiding learning and modelling difficulties associated with other techniques.

Journal ArticleDOI
TL;DR: In this article, a new approach to control shape memory alloy (SMA) actuators with hysteresis compensation by using a neural network feedforward controller and a sliding-mode based robust feedback controller is presented.
Abstract: This paper presents a new approach to controlling shape memory alloy (SMA) actuators with hysteresis compensation by using a neural network feedforward controller and a sliding-mode based robust feedback controller. SMA actuators exhibit severe hysteresis, which is often responsible for position inaccuracy in a regulation or tracking system and may even cause instability in some cases. A single SMA wire actuator is used in this research. A testing system, which includes a wire stand, a linear bearing, a bias spring, a position sensor, a programmable current amplifier and a PC-based digital data acquisition and real-time control system, is used to test the SMA wire actuator in both open-and closed-loop fashions. The proposed control includes two major parts: a feedforward neural network controller, which is used to cancel or reduce the hysteresis, and a sliding-mode based robust feedback controller, which is employed to compensate uncertainties such as the error in hysteresis cancellation and ensures the system's stability. The feedforward neural network controller is designed based on the experimental results of open-loop testing of the wire actuator. With the proposed control, tests of the SMA actuator following sinusoidal commands with different frequencies and magnitudes are conducted. The experiments show that the actual displacement of the SMA actuator with the proposed control closely followed that of the desired sinusoidal command.

Journal ArticleDOI
TL;DR: In this paper, the Bingham model of MR damper is introduced, and the formula relating the yielding shear stress and the control current of MR dampers is put forward that matches the experimental data.
Abstract: Semi-active control of buildings and structures with magnetorheological (MR) dampers for earthquake hazard mitigation represents a relatively new research area. In this paper, the Bingham model of MR damper is introduced, and the formula relating the yielding shear stress and the control current of MR dampers is put forward that matches the experimental data. Then an on-line real-time control method for semi-active control of structures with MR dampers is proposed. This method considers the time-delay problem of semi-active control, which can solve distortion of the responses of structures. Finally, through a numerical example of a three-storey reinforced concrete structure, a comparison is made between controlled structure and uncontrolled structure. The calculated results show that MR dampers can reduce the seismic responses of structures effectively. Moreover, the on-line real-time control method is compared with the traditional elastoplastic time-history analysis method, and the efficacy of the on-line real-time control method is demonstrated. In addition, the Levenberg–Marquardt algorithm is used to train the on-line control neural network, and studies show that the algorithm has a very fast convergence rate.

Journal ArticleDOI
TL;DR: In this paper, the feasibility of the Hilbert-Huang transform (HHT) as a signal processing tool for locating an anomaly, in the form of a crack, delamination, stiffness loss or boundary in beams and plate, based on physically acquired propagating wave signals.
Abstract: This paper illustrates the feasibility of the Hilbert–Huang transform (HHT) as a signal processing tool for locating an anomaly, in the form of a crack, delamination, stiffness loss or boundary in beams and plate, based on physically acquired propagating wave signals. The basis of detection hinges on simple wave propagation concepts using flight times, velocities and frequency changes. The basic concept of HHT is first presented where the empirical mode decomposition must be applied on the signal using a sifting process to obtain intrinsic mode functions before the Hilbert spectral analysis can be meaningfully performed. Some implementation issues are discussed, such as end effects and the criterion to terminate the sifting process, and an alternative criterion is proposed and implemented using MATLAB V6.1. Four examples are used to illustrate the suitability of the technique, namely an aluminum beam with a crack, a sandwiched aluminum beam with an internal delamination, a reinforced concrete (RC) slab with different degrees of damage and a plate with distorted input signal. The results indicate that HHT is able to represent a localized event well and is sensitive to slight distortion in the signal. Crack and delamination in homogeneous beams can be located accurately and damage in a RC slab can be identified if it has been previously loaded beyond first crack. However, the sensitivity of HHT is such that analysis with a distorted signal needs careful interpretation, as illustrated by the aluminum plate example.

Journal ArticleDOI
TL;DR: In this article, the authors provide a summary of recent research activities that will act as a catalyst to expand interest in the development of new health monitoring technologies, including stress-wave methods for the evaluation of structural materials and pavements.
Abstract: Reliable health monitoring, including nondestructive evaluation, is an essential part of the feedback and monitoring system for infrastructures. The goal of this paper is to provide a summary of recent research activities that will act as a catalyst to expand interest in the development of new health monitoring technologies. The paper describes the motivation for developing innovative tools for monitoring the health of the USA's infrastructure. An overview of initiatives sponsored by the National Science Foundation to develop new technologies is presented. The paper includes a review of the state-of-the-art stress-wave methods for the evaluation of structural materials and pavements at the National Institute of Standards and Technology. Finally, efforts at the Federal Highway Administration to develop new technologies for the assessment of the nearly 500 000 bridges along the USA's roads and highways are described.

Journal ArticleDOI
TL;DR: In this article, the authors present the design and experimental results of control of an SMA actuator using pulse width modulation (PWM) to reduce the energy consumption of the SMA wire actuator.
Abstract: Shape memory alloys (SMA), in particular nickel–titanium alloy (or nitinol), have been used as actuators in some astronautic, aeronautic and industrial applications. The future will see more SMA application if less energy is required for actuation. This paper presents the design and experimental results of control of an SMA actuator using pulse width modulation (PWM) to reduce the energy consumption by the SMA actuator. A SMA wire test stand is used in this research. Open-loop testing of the SMA wire actuator is conducted to study the effect of the PWM parameters. Based on test results and parameter analysis of the pulse width (PW) modulator, a PW modulator is designed to modulate a proportional plus derivative (PD) controller. Experiments demonstrate that control of the SMA actuator using PWM effectively saves actuation energy while maintaining the same control accuracy as compared to continuous PD control. PWM also demonstrates robustness to external disturbances. A comparison with a pulse width pulse frequency modulator is also presented.

Journal ArticleDOI
TL;DR: In this article, the thermomechanical recovery behavior of a shape memory polymers (SMP) was examined in three-point flexure for various pre-deformation and recovery conditions.
Abstract: Shape memory polymers (SMPs) have the capacity to recover large strains when pre-deformed at an elevated temperature, cooled to a lower temperature and reheated. The thermomechanical recovery behavior of an SMP is examined in three-point flexure for various pre-deformation and recovery conditions. Results indicate that when pre-deformed well above the glass transition temperature, Tg, the stress–strain response at the pre-deformation temperature governs the relationship between the recovery stress/strain and the corresponding pre-deformation strain/stress. When pre-deformed at a temperature below Tg, the relationship between recoverable stress and strain level in the SMP is not governed by the stress–strain response of the material at the pre-deformation temperature. Rather, a peak recovery stress, which is less than the applied pre-deformation stress, appears near Tg. Higher cooling rates during constraint lower the temperature necessary for complete shape fixity, but increase the recoverable stress level. Higher heating rates during recovery raise the recovery onset temperature and decrease the peak recoverable stress. Ramifications of the results on future research efforts and emerging applications of SMPs are discussed.

Journal ArticleDOI
TL;DR: In this paper, a wavelet technique was used in an active system for the damage detection of aerospace composites, which was based on the generation and reception of Lamb waves by embedded piezoceramic transducers.
Abstract: A wavelet technique was used in an active system for the damage detection of aerospace composites. The active system was based on the generation and reception of Lamb waves by embedded piezoceramic transducers. The wavelets were used to decompose the Lamb-wave response into wavelet coefficients. The decomposition performance was improved by utilizing more adapted wavelets, based on the recurrent waveforms of Lamb waves. The changes in the Lamb waves interacting with damage in the plate were successfully characterized by this wavelet technique, through the amplitude change of the wavelet coefficients. The wavelet technique also showed great sensitivity in detecting damage of small sizes. This technique was found to be straightforward for detection of impact damage and evaluation of the damage size.

Journal ArticleDOI
TL;DR: In this article, a method for online adaptation of the shunting impedance of a piezoelectric transducer with an electrical impedance is presented. But the method is limited to a randomly excited beam.
Abstract: Piezoelectric shunt damping systems reduce structural vibration by shunting an attached piezoelectric transducer with an electrical impedance. Current impedance designs result in a coupled electrical resonance at the target modal frequencies. In practical situations, variation in structural load or environmental conditions can result in significant changes in the structural resonance frequencies. This variation can severely reduce shunt damping performance as the electrical impedance remains tuned to the nominal resonance frequencies. This paper introduces a method for online adaptation of the shunting impedance. A reconstructed estimate of the RMS strain is minimized by varying the component values of a synthetic shunt damping circuit. The techniques presented are applied in real time to tune the component values of a randomly excited beam.

Journal ArticleDOI
TL;DR: In this paper, an analytical-numerical method is presented for analyzing dispersion and characteristic surface of waves in a circular cylinder composed of functionally graded piezoelectric material (FGPM).
Abstract: An analytical–numerical method is presented for analyzing dispersion and characteristic surface of waves in a circular cylinder composed of functionally graded piezoelectric material (FGPM). In this method, the FGPM cylinder is divided into a number of annular elements with three-nodal lines in the wall thickness. The elemental mechanical as well as electrical properties are assumed to vary linearly in the thickness direction so as to better model the spatial variation of the mechanical and electrical properties of FGPM. The associated frequency dispersion equation is developed and the phase velocity and slowness as well as the group velocity and slowness are established in terms of the Rayleigh quotient. Six characteristic wave surfaces are introduced to visualize the effects of anisotropy and piezoelectricity on wave propagation. The calculation examples provide a full understanding of the complex phenomena of elastic waves in FGPM cylinders.

Journal ArticleDOI
TL;DR: In this article, two modes of a simply supported beam are successfully damped using a capacitance modified shunt circuit, and a low inductance multi-mode circuit is also studied and experimentally verified.
Abstract: Structural vibration can be reduced by shunting an attached piezoelectric transducer (PZT) with an electrical impedance. Current shunt circuit designs, e.g. a single-mode inductor–resistor network, typically require large inductance values of up to thousands of henries. In practice, discrete inductors are limited in size to around 1 H. By placing an additional capacitance across the terminals of the PZT, shunt circuit inductances can be drastically reduced. To justify our claims, we present a theoretical analysis of the damped system and identify the influence of the additional capacitance. Two modes of a simply supported beam are successfully damped using a capacitance modified shunt circuit. A low inductance multi-mode circuit is also studied and experimentally verified.

Journal ArticleDOI
TL;DR: In this paper, the fabrication process of FG piezoelectric bending actuators is developed and the characteristics of the fabricated actuators are investigated, and the results show that the durability of the FG actuator is much higher than that of the traditional bimorph actuator.
Abstract: A new type of functionally graded (FG) piezoelectric bending actuator was proposed by the present authors in their former study and the advantage of the new actuator over the traditional bimorph and unimorph actuators in internal stress distribution was illustrated by simulation results. In this study, the fabrication process of FG piezoelectric bending actuators is developed and the characteristics of the fabricated actuators are investigated. The material compositions with different dielectric and piezoelectric constants were selected from the Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 family and used as the four layers in the new FG piezoelectric actuator. The piezoelectric constant and dielectric constant were graded oppositely in the thickness direction. The durability of the fabricated FG piezoelectric actuators was measured in a vibration test and compared with that of the traditional bimorph actuator to evaluate the improvement of performance. The results show that the durability of the FG piezoelectric actuators is much higher than that of the bimorph actuator.

Journal ArticleDOI
TL;DR: In this paper, two devices using fiber Bragg grating (FBG) sensors have been developed for temperature-compensated strain measurement, which are named hybrid sensor and laminate sensor, respectively.
Abstract: For accurate strain measurement by fiber Bragg grating (FBG) sensors, it is necessary to compensate the influence of temperature change. In this study two devices using FBG sensors have been developed for temperature-compensated strain measurement. They are named 'hybrid sensor' and 'laminate sensor', respectively. The former consists of two different materials connected in series: carbon fiber reinforced plastic (CFRP) and glass fiber reinforced plastic. Each material contains an FBG sensor with a different Bragg wavelength, and both ends of the device are glued to a structure. Using the difference of their Young's moduli and coefficients of thermal expansion, both strain and temperature can be measured. The latter sensor is a laminate of two 90° plies of CFRP and an epoxy plate, and an FBG sensor is embedded in the epoxy plate. When the temperature changes, the cross section of the optical fiber is deformed by the thermal residual stress. The deformation of the fiber causes the birefringence and widens the reflection spectrum. Since the temperature can be calculated from the spectrum width, which changes in proportion to the temperature, the accuracy of the strain measurement is improved. The usefulness of these sensors was experimentally confirmed.

Journal ArticleDOI
TL;DR: In this article, the behavior of fiber Bragg grating sensors subjected to transversal as well as axial strains is characterized, both in the case of low-birefringent and polarization-maintaining singlemode optical fibres.
Abstract: In this paper, the behaviour of fibre Bragg grating sensors subjected to transversal as well as axial strains is characterized, both in the case of low-birefringent and polarization-maintaining single-mode optical fibres. Two configurations are considered. Firstly, diametrical compression is studied and the results compared to those previously obtained in the literature. Secondly, the sensors are embedded in an epoxy specimen and their response monitored when the latter is subjected to biaxial loading. In both cases, the experimental results are compared to those obtained by means of finite-element simulations and an appropriate analytical description of the opto-mechanical response of polarization-maintaining fibres.

Journal ArticleDOI
TL;DR: In this paper, fiber Bragg gratings (FBGs) were applied to measure dynamic strains inside a subscale wing under real-time wind tunnel testing, and two re-coated FBGs were embedded in the wing skin.
Abstract: In this paper, fiber Bragg gratings (FBGs) were applied to measure dynamic strains inside a subscale wing under real-time wind tunnel testing. Two re-coated FBGs were embedded in the wing skin. The FBG sensor system includes a wavelength swept fiber laser with a wavelength indicator and fast signal processing modules. The agreement among the three kinds of sensor inside the subscale wing (FBG, electric strain gauge and PZT sensor) was confirmed in the bench test. The optical fiber strain sensors had an excellent resolution (< 5μe) in the time domain and could detect a frequency response up to 100 Hz. Through the wind tunnel test of the subscale smart wing, the flutter was experimentally detected using FBG sensors and their usefulness as an in-flight health monitoring system was demonstrated.

Journal ArticleDOI
TL;DR: In this article, three models of shape memory alloy behavior have been presented and re-investigated, attributed to Tanaka, Liang and Rogers, and Brinson, and have been used extensively in the literature for studying the static or dynamic performance of different composite material structures with embedded SMA components.
Abstract: In this paper three models of the shape memory alloy behaviour have been presented and re-investigated. The models are attributed to Tanaka, Liang and Rogers, and Brinson, and have been used extensively in the literature for studying the static or dynamic performance of different composite material structures with embedded shape memory alloy components. The major differences and similarities between these models have been emphasised and examined in the paper. A simple experimental rig was designed and manufactured to gain additional insight into the main mechanics governing the shape memory alloy (SMA) mechanical properties. Data obtained from the experimental measurements on Ni-Ti wires have been used in the numerical simulation for validation purposes. It has been found that the three models all agree well in their predictions of the superelastic behaviour at higher temperatures, above the austenite finish temperature when shape memory alloys stay in the fully austenitic phase. However, at low temperatures, when the alloys stay in the fully martensitic phase, some difficulties may be encountered. The model developed by Brinson introduces two new state variables and therefore two different mechanisms for the instigation of stress-induced and temperature-induced martensite. This enables more accurate predictions of the superelastic behaviour. In general, it can be recommended that for investigations of the shape memory and superelastic behaviour of shape memory alloy components the Brinson model, or refinements based on the Brinson model, should be applied.

Journal ArticleDOI
TL;DR: In this article, a neural network approach is used for detection of structural damage in a helicopter rotor blade using rotating frequencies of the flap (transverse bending), lag (in-plane bending), elastic torsion and axial modes.
Abstract: A neural network approach is used for detection of structural damage in a helicopter rotor blade using rotating frequencies of the flap (transverse bending), lag (in-plane bending), elastic torsion and axial modes. A finite element method is used for modeling the helicopter blade. Radial basis function (RBF) neural networks are used and several combinations of modes are investigated for training and testing the neural network. Using the first 10 modes of the rotor blade for damage detection yields accurate results for the soft in-plane hingeless rotor considered in this study. Using a parametric study of the blade rotating frequency in conjunction with the neural network, it is found that a reduced measurement set consisting of five modes (the first two torsion modes, the second lag mode and the third and fourth flap modes) also gives good results for damage detection. Furthermore, taking only the first four flap modes also results in good damage detection accuracy. Three rotating frequency sets are therefore identified in this paper for structural damage detection in a helicopter rotor using RBF neural networks.

Journal ArticleDOI
TL;DR: In this article, the authors explored the role of steady-state dynamic analysis in the vibration-based structural health monitoring field and proposed a geometric portrait of system dynamics to extract information about the steady state response of the structure to sustained excitation.
Abstract: This work explores the role of steady-state dynamic analysis in the vibration-based structural health monitoring field. While more traditional approaches focus on transient or stochastic vibration analysis, the method described here utilizes a geometric portrait of system dynamics to extract information about the steady-state response of the structure to sustained excitation. The approach utilizes the fundamental properties of chaotic signals to produce low-dimensional response data which are then analyzed for features which indicate the degree to which the dynamics have been altered by damage. A discussion of the fundamental issues involved in the approach is presented along with experimental evidence of the approach's ability to discriminate among several damage scenarios.

Journal ArticleDOI
TL;DR: In this article, a co-reduction process is developed for plating ionic polymer materials with precious and non-precious metal electrodes, which reduces the use of expensive precious metals such as platinum and gold in the development of ionic polymers.
Abstract: A co-reduction process is developed for plating ionic polymer materials with precious and non-precious metal electrodes. The purpose is to develop a process that reduces the use of expensive precious metals such as platinum and gold in the development of ionic polymer transducers. Previous results obtained by Bennett and Leo (2001 12th Int. Conf. on Adaptive Structures and Technologies pp 208–19) have demonstrated that oxidation is the key issue associated with the use of non-precious metal electrodes. The present work overcomes this problem through the use of a co-reduction process in which an alloy of platinum and copper is deposited in an impregnation/reduction process. A thin (~50 nm) layer of gold is then deposited to increase the surface conductivity of the electrode. Actuators developed using this process are tested for longevity for approximately 250 000 cycles. The results demonstrate the stability of the electrode, although multiple tests reveal that variations in the process produce variations in the electrode stability. The transducers made in this study are also quantified in terms of their electromechanical coupling. Results demonstrate that their performance is comparable to those of ionic polymer materials made using other methods and to other types of smart material.