Table of contents

The field of power harvesting has experienced significant growth over the past few years due to the ever-increasing desire to produce portable and wireless electronics with extended lifespans. Current portable and wireless devices must be designed to include electrochemical batteries as the power source. The use of batteries can be troublesome due to their limited lifespan, thus necessitating their periodic replacement. In the case of wireless sensors that are to be placed in remote locations, the sensor must be easily accessible or of a disposable nature to allow the device to function over extended periods of time. Energy scavenging devices are designed to capture the ambient energy surrounding the electronics and convert it into usable electrical energy. The concept of power harvesting works towards developing self-powered devices that do not require replaceable power supplies. A number of sources of harvestable ambient energy exist, including waste heat, vibration, electromagnetic waves, wind, flowing water, and solar energy. While each of these sources of energy can be effectively used to power remote sensors, the structural and biological communities have placed an emphasis on scavenging vibrational energy with piezoelectric materials. This article will review recent literature in the field of power harvesting and present the current state of power harvesting in its drive to create completely self-powered devices.

Large flexible space structures are complex in structural dynamic characteristics. The control method based on custom control theory and modern control theory is difficult to solve for the complex problem. The fuzzy controller is not dependent on the accurate model. But the precision of a conventional fuzzy controller is not good, and the adaptive ability of a conventional fuzzy controller is limited. The fuzzy controller can make the system surge. Scaling universes of discourse is an effective method to improve the performance of the fuzzy controller. This paper is aimed at the difficult problem of designing a stable adaptive controller based on scaling universes of discourse, and letting input membership function and output membership function be denoted as input universes of discourse and the center value of output membership function, respectively. A kind of Lyapunov function, designed as an adaptive law of input universes of discourse and the center value of output membership function, was then adopted. A kind of stable self-adaptive fuzzy controller based on scaling universes of discourse is designed in this paper for the vibration control of a large flexible space truss driven by piezoelectric sensors and actuators (PZTs).

The finite layer method is the most efficient numerical method for three-dimensional analysis of simply supported rectangular plates. In this method, the plate is divided into a number of finite layers. Within each finite layer, trigonometric functions are used for the in-plane interpolations of displacements, whereas polynomials are employed for the interpolations in the thickness direction. Thus, the three-dimensional analysis is transformed into a series of one-dimensional analyses, and the efficiency is enhanced significantly. In the present study, a new finite layer approach is proposed for the three-dimensional static, vibration and stability analysis of piezoelectric composite plates. In this approach, Lagrangian polynomials are employed for the interpolations of all the generalized displacement components in the thickness direction. Thus, higher-order interpolations can be selected in order to yield improved accuracy over any existing higher-order shear deformation theories. Numerical results are presented to demonstrate the accuracy and efficiency of the proposed method. The static, vibration and stability behaviors of some piezoelectric laminates are also investigated through numerical examples.

The direct elastomagnetic effect in composite materials, made of ferromagnetic micro-magnets inside an elastomeric matrix, consists in their relative elastic deformation (10⁻⁴–10⁻³) under the action of an external magnetic field, dependent on the equilibrium between the magneto-mechanical moments and the internal elastic reaction, but independent of the standard magnetostriction. This investigation is focused on the evaluation of the strain linearity with the excitation field in view of the application of these materials for MEMS devices. The studied composite is made of permanently magnetized Sm₂Co₇ microparticles uniformly dispersed inside a silicone matrix. The field-induced strain is measured using a fiber Bragg grating sensor and, at the same time, theoretically evaluated from the model of the direct elastomagnetic effect. The linearity and reversibility of the material response are experimentally verified up to a threshold value of the magnetic field corresponding to the break in the coupling between the particles' magnetic moments and their body and to the passage from the linear magnetization to the non-linear regime accompanied by irreversible magnetization processes.

The suppression of vibrations in structures is commonly considered a useful measure for the extension of their lifetime, when high amplitude vibrations are observed. In the experiments presented in this work, the modification of the stiffness of a beam as a means to suppress vibrations due to resonance is proposed as an alternative to the introduction of discrete damping devices. The stiffness of a beam is modified by applying an electric field between the main element of the structure and additional stiffening elements applied to its surface, thus coupling the latter to the former by transfer of shear stresses. The effect of electrostatic tuning of the bending stiffness (and consequently of its eigenfrequencies) of a large size GFRP–CFRP beam is shown by the shift of the resonance peak for the first bending mode to higher frequencies. The discrete character of the stiffness increase in multi-layer beams (n≥3) is postulated.

IPMC (ionic polymer–metal composite) actuators produce large bending displacements under low input voltages and are flexible enough to be implemented for biological and/or biomimetic applications. In this study, IPMC was considered for the development of a natural muscle-like linear actuator. For the purpose of design, numerical analysis was utilized to predict free strain and blocked stress of IPMC-based linear actuators, which we considered as the important parameters of a muscle-like actuator. An elementary unit composed of an IPMC and the base polymer, Nafion^TM, was proposed for an effective linear actuator. In order to find an optimal design and evaluate the actuation characteristics of the proposed elementary unit, actuation displacement and force were numerically calculated. The calculated maximum free strain of the optimal elementary unit was 25% under an applied 2 V input. Also, brief experimental results are provided.

In this study, the numerical model of a shape memory alloy hybrid composite (SMAHC) plate was constructed. The model was based on the effective coefficient of thermal expansion (ECTE) model of the shape memory alloy (SMA) material. The embedded SMA wires were modeled as an integrated composite layer in conjunction with the host composite lamina. The tailored design feature of laminated composite plates allows the flexibility of orienting the SMAHC layer along different directions. The response of the SMAHC plates with and without a central cutout, having certain geometric imperfections, subjected to an initial in-plane compressive loading and a subsequent elevated thermal load, were investigated numerically and experimentally. It was established that the positive attribute of the SMA material could be used to successfully suppress the post-buckling deflection of the SMAHC plate under an elevated temperature, when the SMA wires were properly oriented. The variation of stress concentration around the cutout of the SMAHC plate was also investigated. It was found from this study that the orientation of SMA wires had a significant influence on the suppression of the lateral deflection. The extent of such a positive attribute was found to be influenced by the boundary condition of the SMAHC plate.

Magnetotheological (MR) dampers have emerged recently as potential devices for vibration mitigation and semi-active control in smart structures and vehicle applications. These devices are highly nonlinear and thus accurate models of these devices are important for effective simulation and control system design. In the current literature, the Bouc–Wen model is coupled with linear elements to describe these MR devices both in simulation and control. In this paper, we propose the friction Dahl model to characterize the dynamics of a shear mode MR damper. This leads to a reinterpretation of the MR damper behavior as a frictional device whose friction parameters change with the voltage. An identification technique for this new model is proposed and tested numerically using an experimentally obtained model. A good match has been observed between the model obtained from experiments and the Dahl based model of the MR device.

Ionic polymer metal composites are a class of electro-active polymers that are gaining importance as smart actuators due to their large bending deflection. The property of generating high strains with low actuation voltage makes ionic polymer metal composites (IPMC) suitable for applications requiring large motion such as in large deflection vibration suppression. In this paper we propose an application of IPMC as an active damper for large deflection vibration control of a flexible link. The modes of vibration for a long flexible link are derived using the modal approach and two IPMC patches are placed to suppress the vibration. A distributed PD controller is designed to suppress the vibration of the flexible link for the desired positioning of the tip. Simulations are first done to demonstrate effective vibration suppression and the results proved that the proposed method can suppress vibration effectively. Experiments are conducted to verify the application of IPMC for active vibration suppression. The performance of the proposed distributed PD controller is also found to be better than a single PD controller loop.

Hybrid damping of structural vibration using a combination of active and passive layers is found to have high application potential due to the requirement of a lower power supply and guaranteed stability. Use of hard-coating layers as a passive damping treatment is found to be industrially acceptable for turbine blades etc, due to the high damping capacity and large service temperature range. However, such damping materials also have high strain dependence. In a way that is similar to active constrained layer damping, by using an active material the strain in the passive damping can be controlled, and thereby the damping performance of the passive layer. This paper proposes a semi-analytical method to estimate structural damping in such a system and obtain the response of a smart hybridly damped system. The paper delves into the closed-form solution of all common boundary conditions of a vibrating beam, namely cantilever, hinged–hinged, free–free, hinged–free, and fixed–fixed beams. It also compares the damping performance of a beam with only a passive damping layer to that of beams comprising both active and passive damping layers.

The objective of this paper is to study the bending behavior of 2–2 multi-layered piezoelectric curved actuators. Unlike the traditional investigations based on the elementary theory of elasticity, the governing equations of a curved actuator are solved based on the general theory of elasticity and piezoelectricity. The Airy stress function method is utilized and both the piezoelectric coefficient and the thickness for different layers are taken as variables in the analysis, which makes it easy to consider the effect of elastic layers or electrodes on the bending behavior of the actuators. By introducing several recurrence formulae, the exact solutions are obtained. Furthermore, good agreement is shown by comparing the theoretical results with numerical ones.

Matrix cracking in composite laminates is the first macroscopic damage mode to be readily detected. Polarimetric sensors embedded in composite laminates can detect the development of this damage and they have an advantage over other sensors in being able to sense damage over long gauge lengths (potentially, many metres). In this paper, the sensitivity of a polarimetric sensor manufactured from Hi-Bi PANDA fibre has been measured experimentally and a phase-strain model available in the literature has been used to determine the characteristic parameters of the sensor. The sensitivity of such sensors embedded in unidirectional composites is shown to be in good agreement with theoretical predictions, allowing for material non-uniformity. In the case of cross-ply laminates, which are transversely anisotropic, it is shown that sensor sensitivity is dependent on the relationship of the sensor axes to the composite axes, as well as on the degree of sensor twist. Maximum sensitivity is obtained for a combination of low twist angle and congruence between the sensor optical axes and the composite axes. Twist angles of greater than 90° give rise to sensitivities, which, although lower, are reasonably constant and approximately the same as the sensitivity of the sensor in a unidirectional composite.

An integral equation based model for a system of piezoelectric flexible patch actuators bonded to an elastic substrate (layer or half-space) is developed. The rigorous solution to the patch–substrate dynamic contact problem extends the range of the model's utility far beyond the bounds of conventional models that rely on simplified plate, beam or shell equations for the waveguide part. The proposed approach provides the possibility to reveal the effects of resonance energy radiation associated with higher modes that would be inaccessible using models accounting for the fundamental modes only. Algorithms that correctly account for the mutual wave interaction among the actuators via the host medium, for selective mode excitation in a layer as well as for body waves directed to required zones in a half-space, have also been derived and implemented in computer code.

A simple and low-cost long-period fiber grating (LPG) sensor suited for chloride-ion concentration measurement is presented. The LPG sensor is found to be sensitive to the refractive index of the medium around the cladding surface of the sensing grating, thus offering the prospect of development of practical sensors such as an ambient index sensor or a chemical concentration indicator with high stability and reliability. We measured chloride ions in a typical concrete sample immersed in salt water solutions with different weight concentrations ranging from 0% to 25%. Results show that the LPG sensor exhibited a linear decrease in the transmission loss and resonance wavelength shift when the concentration increased. The measurement accuracy for the concentration of salt in water solution is estimated to be 0.6% and the limit of detection for chloride ions is about 0.04%. To further enhance its sensitivity for chloride concentrations, we coated a monolayer of colloidal gold nanoparticles as the active material on the grating surface of the LPG sensor. The operating principle of sensing is based on the sensitivity of localized surface plasmon resonance of self-assembled gold colloids on the grating section of the LPG. With this method, a factor of two increase in the sensitivity of detecting chemical solution concentrations was obtained. The advantages of this type of fiber-optic sensor are that it is compact, relatively simple to construct and easy to use. Moreover, the sensor has the potential capability for on-site, in vivo and remote sensing, and it has potential use as a disposable sensor.

In the past few decades, piezoceramic (PZT) transducers have been used extensively in the vibration and noise control of engineering structures. However, in the last decade, PZT transducers have also been used in electromechanical impedance (EMI) based methods of structural health monitoring (SHM). In the EMI methods, the PZT transducers are either surface bonded using adhesive or wrapped with a protective cover and then bonded or embedded inside the host structure. They are then subjected to excitation in the desired frequency ranges to predict the electromechanical (EM) admittance signatures. These EM signatures serve as an indicator of the health/integrity of the structure. The existing PZT-structure interaction methods consider both the PZT transducer and the adhesive layer to be negligible in mass and are thus ignored. However, for wrapped PZT, the presence of thick adhesive significantly reduces the magnitude of the EM signature. This paper presents the formulation of a three-dimensional (3D) interaction model of a PZT-structure which considers the mass of both the PZT transducers and the adhesive. The model is generic in nature compared to the existing interaction models. The model is verified experimentally and is expected to be applicable to the non-destructive evaluation (NDE) of most engineering structures.

This paper considers the plane stress problem of generally anisotropic piezoelectric beams with the coefficients of elastic compliance, piezoelectric and dielectric impermeability being arbitrary functions of the thickness coordinate. Firstly, the partial differential equations for the plane problem of anisotropic functionally graded piezoelectric materials are derived, which the stress function and electric displacement function satisfy. Secondly, the stress and electric displacement functions are assumed in forms of polynomials of the longitudinal coordinate, so that the stress and electric displacement functions can be acquired through successive integrations. The analytical expressions of axial force, bending moment, shear force, displacements, electric displacements and electric potential are then deduced. Thirdly, the stress and electric displacement functions are employed to solve problems of functionally graded piezoelectric plane beams, with the integral constants completely determined from boundary conditions. Two piezoelasticity solutions are thus obtained, for cantilever beams subjected to shear force and point charge applied at the free end, for cantilever beams subjected to uniform load. These solutions can be easily degenerated into the piezoelasticity solutions for homogeneous anisotropic piezoelectric beams. Finally, a numerical example is presented to show the application of the proposed method to a specific case.

In this paper, 32 × 32 infrared (IR) uncooled focal plane arrays (UFPAs) based on nanostructured vanadium oxide (VO_x) thermally sensitive material are fabricated by micromachining processes. The thermally sensitive element is fabricated on the complementary metal–oxide–semiconductor (CMOS) chip after planarization of its surface. In this paper, silicon dioxide is used as a buffer layer for fabrication of nanostructured VO_x. The interconnection of the CMOS chip and the sensitive array is accomplished by electroless plating of nickel (Ni) metal, which shows good electrical conductivity performance. The IR sensitive testing results illustrate that the response of the microbolometer is obvious and the average responsivity and normalized detectivity are 1.26 × 10⁴ V W⁻¹ and 2.04 × 10⁷ cm W⁻¹ Hz^1/2, respectively.

A dynamic measurement method is described for the rapid identification and determination of volatile organic compounds (VOCs) in ambient air. For the qualitative recognition of VOCs, only a single SnO₂-based gas sensor operating in a rectangular temperature-modulation mode is required. The working temperature of the sensor was modulated between 250 and 300 °C and its dynamic responses to different concentrations of propane-2-ol, acetyl acetone and ethanol vapor were measured. The discrete wavelet transform (DWT) was used to extract important features from the sensor response. These features were then input to a (neural) pattern recognition algorithm. The species considered can be discriminated with a 100% success rate using a back propagation network and the concentrations of the organic vapor can also be accurately predicted.

Despite various successful applications of lead zirconate titanate (PZT) material for structural health monitoring (SHM), the fundamental research work of determining the PZT sensing region is still needed. Among a variety of issues in relation to the PZT sensing region, this paper focuses on one of the most important factors, the material and structural damping. The elasticity solution of PZT generated wave propagation is first derived in terms of the wave reflection and transmission matrices. Subsequently, based on the corresponding principle, the viscoelasticity solution is obtained directly from the elasticity solution. Finally, the output voltage of the PZT sensor is calculated according to the PZT–structure interaction effect. In the experiment, an aluminum beam specimen bonded with PZT actuators as well as PZT sensors is tested. The output voltages of sensors are compared with the theoretical predictions to verify the developed model and to determine the reliable sensing region of PZT transducers.

Concrete is a very popular material in civil engineering, although it exhibits some limitations. The most crucial limitation is its low tensile strength, compared to its compressive strength, which results from the propagation of micro-cracks. This may be prevented by using prestrained shape memory alloy wires that are embedded in the concrete matrix. Upon activation, these wires regain their original shape, and consequently initial compressive stresses are transmitted to the concrete matrix. In this study, a thermomechanically micromechanical model of prestressed concrete reinforced by shape memory alloy fibers is presented and examined for different reinforcement aspects. It was found that there is a strong relation between the activation temperature deviation and the behavior of the prestressed concrete. The relation between the fiber's volume fraction and the composite response and the effect of the shape of the reinforcing fibers and residual strain orientations is examined in detail.

A linear array of optical fibers was used to deliver optical power from 8 low power (1.5 W) semiconductor laser sources to an aluminum plate. The optical fibers were arranged to form a linear phased array. Time delays of up to 520 ns were then utilized to adjust the excitation of the elements in the array, thus allowing the direction of the generated ultrasonic beam to be controlled at angles of up to 18° for an array spacing of 8 mm. Excitation was in the form of 3.6 µJ laser pulses and hence was truly non-destructive. Detection was achieved using piezoelectric transducers or interferometric fiber optic sensors.

To fabricate metal clad optical fibres for corrosion sensing, we investigated and compared three techniques of preparing metal cladding on the surface of fibres with cladding removed. The first technique directly deposits iron on the fibre surface by physical vacuum deposition (PVD). The second technique uses nickel on the fibre under the control of a magnetic field in a vacuum environment (MFV). The third technique prepares silver on the fibre by chemical sputtering plating (CP). Finally corrosion-sensitive fibre samples with metal cladding treated as in the above three techniques are electroplated with the materials for monitoring. The metal cladding by the first technique achieved the best quality, and also the desirable material composition and structure as examined by x-ray diffraction analysis. The corrosion parameters of the first metal clad samples, including the change of open circuit potential E_corr and linear polarized resistance R_p with Cl⁻ concentrations, were measured. The fibres prepared by the first technique are shown to satisfactorily monitor corrosion processes in our preliminary experiment.

Magnetically levitated microrobotic systems have shown a great deal of promise for micromanipulation and biomedical applications. This paper discusses the identification of the vertical and horizontal motion models for a large-gap magnetic suspension system developed by the authors. The suspension system consists of six electromagnets attached to a soft iron pole piece, which levitate a small microrobot prototype manufactured from a 10 mm × 10 mm cylindrical neodymium magnet. A modified least squares algorithm is used to identify ARMAX models describing the motion of the system. Due to the unstable nature of open loop vertical position control, the black-box open loop model is extracted from the identified closed loop model by examining the motion of the closed loop poles on a root locus diagram. The identified models are able to reasonably predict the system behaviour.

Subtle interaction between shape-memory polymer and cellulose fibers within fabrics remains a critical issue for understanding their thermal–mechanical properties and thus the shape-memory behavior in cotton fibers. We demonstrate here the efficacy of Raman spectroscopy to probe the induced stresses in warp and weft fibers, presenting physicochemical features for cellulose fibers finished with macromolecule polyurethane and small-molecule dimethyloldihydroxyethyleneurea. Accordingly, a possible mechanism for transfer of the shape-memory effect to fabrics is proposed. Forming as a coating on the fiber surface after the finishing process, the shape-memory polymer takes a critical role in reducing the residual stress in weft fibers, establishing the prerequisite for reserving the shape-memory effect to fabric. In addition, this work has demonstrated that Raman spectroscopy is able to probe the residual stresses in cotton fabrics after being treated by chemicals in addition to that due to physical deformation. Our result provides clear evidence that in the finishing process strength reduction in fibers in general is not only caused solely by a chemical reaction, but also by a physical modification of the cotton structure.

This paper is concerned with static analysis of simply supported antisymmetric angle-ply plates integrated with a layer of piezoelectric fiber reinforced composite (PFRC) material undergoing nonlinear deformations. The Von Kàrmàn type nonlinear strain displacement relations and first-order shear deformation theory are used to formulate the variational model of this electromechanical coupled problem. Subsequently, the Galerkin method is employed to derive the nonlinear algebraic governing equations which are solved by employing the Newton–Raphson method. The results suggest the potential use of PFRC material for distributed control of nonlinear deformations of smart antisymmetric angle-ply composite plates. Particular emphasis has been placed on investigating the effect of variation of piezoelectric fiber orientation on the actuating capability of the PFRC layer for counteracting the nonlinear deformations of the smart antisymmetric angle-ply composite plates.

Small-diameter fiber Bragg grating (FBG) sensors were applied to the debonding monitoring of composite repair patches. The target of the monitoring consists of carbon fiber reinforced plastic (CFRP) patches and an aluminum substrate. The specimens were prepared through simple means: the tabular patches adhered to both sides of the aluminum substrate using epoxy adhesive films. Under cyclic loading conditions, the debonding progressed between the aluminum substrate and the adhesive layers. Before the embedding of the FBG sensors, the embedding location was determined using the calculation of the sensor signals, also called the reflection spectra. When the cyclic loading was stopped at a pre-determined numbers of cycles, the reflection spectra were measured at stress conditions of both 0 and 200 MPa. The newly appearing peak in the reflection spectrum indicated the arrival of debonding at the FBG sensors. As the debonding length increased, the intensity of the peak was found to increase. The relationship between the spectral change and the debonding length was verified by the simulated spectra and the strain distributions calculated by finite element (FE) analysis. As a result, the debonding length could be evaluated quantitatively by the spectral changes in the FBG sensors.

In this paper the two-way shape memory effect (TWSME) of a Ni–51 at.% Ti alloy is investigated and a numerical model is developed, which allows real time simulations of its hysteretic behaviour strain versus temperature. The two-way shape memory effect (TWSME) was induced through a proper thermo-mechanical training, carried out at an increasing number of training cycles and for two values of training deformation. The TWSME was measured under different applied stresses and the hysteretic behaviour in the strain–temperature response was recorded. In order to evaluate the thermal stability of the hysteresis loops the material was subjected to many cycles, by repeated heating and cooling, between A_f (austenite finish temperature) and M_f (martensite finish temperature). The numerical method is based on a phenomenological approach and was developed in a Matlab^® function, which calculates the model parameters from a set of experimental data, and a Simulink^® model, which is efficient enough for use in real time applications. The accuracy of the proposed model was analysed through systematic comparisons between experimental measurements and numerical predictions.

A model on the basis of transformation kinetics is developed in this paper in which magnetic-field-induced stress is introduced and the equivalence principle is employed for mechanical and magnetoelastic deformation. An exponential expression is given to describe the field dependence of magnetization for martensitic variants. A good agreement between the theoretical calculations and the experimental results is achieved for the non-stoichiometric Ni₂MnGa alloys. The proposed simple model is acceptable for describing magnetization and magnetic-field-induced strain behavior of ferromagnetic shape memory NiMnGa alloys.

This paper investigates the static bending, free vibration, and dynamic response of monomorph, bimorph, and multimorph actuators made of functionally graded piezoelectric materials (FGPMs) under a combined thermal-electro-mechanical load by using the Timoshenko beam theory. It is assumed that all of the material properties of the actuator, except for Poisson's ratio, are position dependent due to a continuous variation in material composition through the thickness direction. Theoretical formulations are derived by employing Hamilton's principle and include the effect of transverse shear deformation and axial and rotary inertias. The governing differential equations are then solved using the differential quadrature method to determine the important performance indices, such as deflection, reaction force, natural frequencies, and dynamic response of various FGPM actuators. A comprehensive parametric study is conducted to show the influence of shear deformation, temperature rise, material composition, slenderness ratio, end support, and total number of layers on the thermo-electro-mechanical characteristics. It is found that FGPM monomorph actuators exhibit the so-called 'non-intermediate' behavior under an applied electric field.

This paper presents real-time control characteristics of an electrorheological (ER) suspension system via a fuzzy sliding mode control algorithm which is formulated in a discrete-time manner by considering the sampling rate of an electronic control unit for a vehicle system. A quarter-vehicle system consisting of sprung mass, spring, tire and a cylindrical ER damper (shock absorber) is constructed for the real-time control. After deriving the governing equation of motion of the proposed system, a discrete-time control model with system uncertainties is formulated. A stable sliding surface is then designed and followed by the formulation of the discrete-time sliding mode controller which consists of a discontinuous part and an equivalent part. In the controller formulation, the fuzzy control algorithm is also adopted to enhance system robustness to the mass variation and reaching time to the sliding surface. The controller is then experimentally realized for the manufactured quarter-vehicle ER suspension system. Control performances such as vertical acceleration are evaluated under various road conditions and presented in both time and frequency domains.

In this paper we consider vibration control of tensegrity structures under stationary and nonstationary random excitations. These excitations may be representative of many physical loading conditions, such as earthquake, wind, aerodynamic and acoustic excitations. The optimal control theory based on H₂ and controller with full state and limited state feedback is used for the control. The response of the tensegrity structure is represented by the zero lag covariance matrix and the same is obtained by solving the matrix Lyapunov equation. The force generated by the electro-mechanical coupling of the piezoelectric actuator is used in the formulation. A tensegrity structure of class-1 comprising of two modules, with 24 pretension cables and six struts with piezoelectric actuators, is considered.

Two experimental test programs are conducted to collect data and simulate the dynamic behavior of CuAlBe shape memory alloy (SMA) wires. First, in order to evaluate the effect of temperature changes on superelastic SMA wires, a large number of cyclic, sinusoidal, tensile tests are performed at 1 Hz. These tests are conducted in a controlled environment at 0, 25 and 50 °C with three different strain amplitudes. Second, in order to assess the dynamic effects of the material, a series of laboratory experiments is conducted on a shake table with a scale model of a three-story structure that is stiffened with SMA wires. Data from these experiments are used to create fuzzy inference systems (FISs) that can predict hysteretic behavior of CuAlBe wire. Both fuzzy models employ a total of three input variables (strain, strain-rate, and temperature or pre-stress) and an output variable (predicted stress). Gaussian membership functions are used to fuzzify data for each of the input and output variables. Values of the initially assigned membership functions are adjusted using a neural-fuzzy procedure to more accurately predict the correct stress level in the wires. Results of the trained FISs are validated using test results from experimental records that had not been previously used in the training procedure. Finally, a set of numerical simulations is conducted to illustrate practical use of these wires in a civil engineering application. The results reveal the applicability for structural vibration control of pseudoelastic CuAlBe wire whose highly nonlinear behavior is modeled by a simple, accurate, and computationally efficient FIS.

In this paper, an electro-active shape memory fibre was fabricated successively by incorporating multi-walled carbon nanotubes (MWNT). The shape memory polyurethane (SMP–MWNT) composite was prepared by in situ polymerization and the SMP–MWNT fibre was prepared by melt spinning. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations of the morphology revealed that the MWNTs are axially aligned and homogenously distributed in the SMP matrix, which is helpful for the fibre's electrical conductivity improvement and for the electro-active shape memory effect. At 6.0 wt% MWNT content, the prepared shape memory fibre shape recovery ratio was 75% and the fixing ratio was 77%.

A free vibration analysis of an annular plate with an electrorheological (ER) fluid core and a constraining layer is presented in this study. A discrete finite element method is used to investigate the vibrational characteristics of the sandwich annular plate. The extensional and shear moduli of the ER fluid layer are described by complex quantities. Complex eigenvalues are then found numerically, and from these, both frequencies and loss factors are extracted. When applying an electric field, the rheological properties of the ER fluid materials, such as viscosity, plasticity, and elasticity can be changed. When the electric field is applied to the sandwich structure, the damping of the system is more effective. The ER fluid core is found to have a significant effect on the vibrational behavior of the sandwich annular plate. The effects of ER layer thickness, constraining layer stiffness and thickness on natural frequencies and modal loss factors are also presented.

The theory of the strain field (SF) method using Brillouin optical fiber sensing (BOFS) is proposed for structural damage identification in this paper. Field test verification of this method was carried out by implementing a destructive loading test to an existing prestressed concrete bridge. A series of structural damage scenarios were thus produced for identification. A sub-matrix featuring the damage scenarios was first extracted from the space–time matrix to obtain the strain field distribution in space–time coordinates. Furthermore, other feature extraction operations, including row vector extraction, column vector extraction and boundary extraction, were performed to characterize the structural damage behavior and damage evolution patterns. Finally, damage localization and quantification were successfully implemented in both space and time domains in terms of a damage index vector array. The investigation results demonstrated the SF method using BOFS is a feasible and efficient approach for structural damage identification.

Perovskite structures in the PZ–PNN system with formula (1−x)PbZrO₃–xPb(Ni_1/3Nb_2/3)O₃ with x = 0.0–0.5 are synthesized via the columbite precursor technique. The formation of the perovskite phase in the calcined powders has been investigated as a function of calcination conditions by using thermogravimetric and differential thermal analysis (TG-DTA) and x-ray diffraction (XRD) techniques. The complete solid solutions of the perovskite phase of PZ–PNN ceramics were obtained over a wide compositional range. It was observed that for the binary system (1−x)PbZrO₃–xPb(Ni_1/3Nb_2/3)O₃, the change in the calcination temperature is approximately linear with respect to the PNN content in the range x = 0.0–0.5. With increasing x, the calcination temperature shifts forward to high temperatures. It is seen that optimization of the calcination conditions can lead to a 100% yield of PZ–PNN in a pseudo-cubic phase. The P–E hysteresis loop measurements demonstrated that the ferroelectric properties of the ceramics in the PZ–PNN system changed gradually from normal ferroelectric behavior to relaxor ferroelectric behavior with increasing PNN concentration. In addition, the squareness of the hysteresis loop (R_sq) decreased quasi-linearly as the molar fraction of PNN increased. The maximum spontaneous polarization (P_s) and remanent polarization (P_r) for the x = 0.1 composition were 31.6 µC cm⁻² and 27.8 µC cm⁻², respectively. These results clearly show the significance of PNN in controlling the electrical responses of the PZ–PNN system.

This paper is concerned with the development of a cantilever transducer patched with a piezoelectric element for evaluating the characteristics of a temperature-sensitive polymer gel membrane. The transducer consists of an aluminum cantilever beam patched with a piezoelectric ceramic and a probe coated by a polymer gel membrane. The probe can be easily attached to the cantilever transducer with double-sided sticky tape. The piezo-cantilever transducer is first simulated with the aid of a finite element method and the relation between the natural frequency change of the transducer and the absorbed mass on the polymer gel membrane is obtained theoretically. For measuring the temperature characteristics of the polymer gel membrane, the experiments are conducted in liquid and out of liquid. The temperature-sensitive poly(N-isopropylacrylamide) gel membrane hydrophilic–hydrophobic characteristics can be explained clearly by the results. Furthermore, two kinds of membrane coating method were proposed. The results indicate that the coating gel membrane has a better effect than the pasted gel membrane. The results also show that the piezo-cantilever transducer has a potential application for detecting polymer gel membrane characteristics conveniently and accurately.

A micromechanical model for smart composite shells with periodically arranged embedded piezoelectric actuators and rapidly varying thickness is developed. The pertinent mathematical framework is that of asymptotic homogenization. The model enables the determination of both local fields and effective elastic and actuation coefficients of smart composite sandwich shells made of generally orthotropic materials. Orthotropy of the constituent materials leads to a significantly more complex set of local problems and is considered in the present paper for the first time. The effective coefficients are determined by means of a set of four simpler problems called 'unit-cell' problems. The actuation coefficients, for example piezoelectric or magnetostrictive, characterize the intrinsic transducer nature of active smart materials that can be used to induce strains and stresses in a co-ordinated fashion.

The theory is illustrated by means of examples pertaining to hexagonal honeycomb cored and hexagonal–triangular mixed cored smart sandwich shells made of orthotropic materials. The effective elastic and piezoelectric coefficients for these structures are calculated and analyzed. It is shown that the model can be used to tailor the effective properties of any smart shell to meet the requirements of a particular application by changing some geometric or material parameters.

Nowadays, some compositions of Cu–Zn–Al alloys are commercially available with the potential to present shape memory properties after a suitable thermomechanical treatment. Applied as sensor and/or actuator, the smallest product of Cu-based shape memory alloys (SMA) are wires 0.5 mm in diameter. This paper focuses on Cu–25.3Zn–4.0Al (wt%) wires, 0.5 mm in diameter, that were supplied by Societé Tréfimetaux (France) in a cold drawn condition, without any martensitic transformation. After betatization heat treatment of the SMA wires, physical characterization was carried out through an optical micrograph, DSC and x-ray diffraction while the thermomechanical behavior of the samples was verified by thermal cycling under a constant load. The results obtained have demonstrated the appearance of a two-step transformation which causes an important change in the strain–temperature behavior. This phenomenon is rarely observed in these Cu–Zn–Al SMA.

This work proposes a new piezoelectric shunt damping methodology to control the vibration of a computer hard disk drive (HDD) disk-spindle system. The first part of this work (part I) deals with dynamic modeling of the piezoelectric shunted drive, while the second part of this work (part II) covers experimental implementation of the proposed shunt circuits. In the modeling, a target vibration mode which significantly restricts the recording density increment of the drive is determined by analyzing the dynamic characteristics of the conventional drive. This is achieved by undertaking both modal testing and finite element (FE) analysis. In order to effectively suppress the unwanted vibration of the target mode, a piezoelectric bimorph is then designed and integrated to the drive by considering the mode shapes of the target vibration mode. The mechanical impedance of the shunted bimorph is derived from lamination theory and piezoelectric constitutive equations. In this derivation, the electromechanical coupling coefficient of the shunted drive is analytically incorporated with the mechanical impedance. Using the coupling coefficient, the shunt damping performance for the target vibration mode is predicted and evaluated by presenting the displacement transmissibility.

This paper presents the experimental implementation of piezoelectric shunt damping for an HDD disk-spindle system. Prior to evaluating the shunt damping performance of the drive, the piezoelectric bimorph designed in part I is optimally redesigned so as to satisfy desirable shunt damping performance. The electrical admittance of the bimorph is derived from the piezoelectric constitutive equation and stress–strain relationship. Subsequently, in order to maximize the electrical admittance two electrodes of the bimorph are formed on an annular piezoelectric disk by considering the target vibration mode. The sensitivity analysis method is then employed to determine the optimal design parameters. After manufacturing the piezoelectric bimorph with optimally obtained design parameters, the vibration control performance of the proposed shunt damping for the HDD disk-spindle system is empirically evaluated in the frequency domain by changing the impact and measuring points.

This paper presents exact solutions of the dynamic responses of a fully coupled hybrid piezoelastic cylindrical shell with piezoelectric shear actuators (PSAs). The fundamental response quantities of each layer in the shell are expanded into a double Fourier series. A state-space method is used to represent the response quantities using eight first-order homogeneous ordinary differential equations with variable coefficients. The solutions are then obtained by the Frobenius method. Numerical examples are presented to show the effects of thickness ratio and location of PSAs on the transverse response of the shell subjected to mechanical and electric loadings. Finally, an active vibration control model for a simply supported laminated cylindrical shell with piezoelectric shear sensor and actuator layers is established using the negative velocity feedback control strategy. Numerical results are presented to verify the feasibility of the control model.

This paper describes how post-buckled precompressed (PBP) piezoelectric bender actuators are employed in a deformable wing structure to manipulate its camber distribution and thereby induce roll control on a subscale UAV. By applying axial compression to piezoelectric bimorph bender actuators, significantly higher deflections can be achieved than for conventional piezoelectric bender actuators. Classical laminated plate theory is shown to capture the behavior of the unloaded elements. A Newtonian deflection model employing nonlinear structural relations is demonstrated to predict the behavior of the PBP elements accurately. A proof of concept 100 mm (3.94^'') span wing employing two outboard PBP actuator sets and a highly compliant latex skin was fabricated. Bench tests showed that, with a wing chord of 145 mm (5.8^'') and an axial compression of 70.7 gmf mm⁻¹, deflection levels increased by more than a factor of 2 to 15.25° peak-to-peak, with a corner frequency of 34 Hz (an order of magnitude higher than conventional subscale servoactuators). A 1.4 m span subscale UAV was equipped with two PBP morphing panels at the outboard stations, each measuring 230 mm (9.1^'') in span. Flight testing was carried out, showing a 38% increase in roll control authority and 3.7 times greater control derivatives compared to conventional ailerons. The solid state PBP actuator in the morphing wing reduced the part count from 56 down to only 6, with respect to a conventional servoactuated aileron wing. Furthermore, power was reduced from 24 W to 100 mW, current draw was cut from 5 A to 1.4 mA, and the actuator weight increment dropped dramatically from 59 g down to 3 g.

A series of low molecular weight poly(ethylene glycol)–polycaprolactone–poly(ethylene glycol) (PEG–PCL–PEG) biodegradable block copolymers were successfully synthesized using isophorone diisocyanate (IPDI) as the coupling agent, and were characterized using ¹H NMR and Fourier transform infrared spectroscopy. The aqueous solutions of the PEG–PCL–PEG copolymers displayed a special thermosensitive gel–sol transition when the concentration was above the corresponding critical gel concentration. Gel–sol phase diagrams were recorded using the test-tube-inversion method; they depended on the hydrophilic/hydrophobic balance in the macromolecular structure, as well as some other factors, including the heating history, volume, and the ageing time of the copolymer aqueous solutions and dissolution temperature of the copolymers. As a result, the gel–sol transition temperature range could be altered, which might be very useful for application in injectable drug delivery systems.

The paper presented the effectiveness of a shape memory alloy hybrid composite. It was designed to actively suppress stress intensity in the vicinity of a crack-tip. A shape memory alloy (SMA) TiNi fiber reinforced epoxy composite was fabricated based on the proposed design concept and its material and mechanical properties were investigated by photoelastic examinations. The stress intensity factors, K_I and K_II, at a crack-tip decreased temperatures greater than A_f under mixed mode. The phenomenon was caused by the recovery force of the TiNi fiber. The relationship of the stress intensity factors with the prestrain in the SMA fiber as well as with the ambient temperature in an isothermal furnace was clarified. On this basis, the active control for stress intensity by a shape memory composite was discussed.