Table of contents

The transient response of delaminated smart composite laminates is studied using an improved layerwise laminate theory. The theory is capable of capturing interlaminar shear stresses that are critical to delamination. The Fermi–Dirac distribution function is combined with an improved layerwise laminate theory to model a smooth transition in the displacement and the strain fields of the delaminated interfaces during 'breathing' of delaminated layers. Stress free boundary conditions are enforced at all free surfaces. Continuity in displacement field and transverse shear stresses is enforced at each ply level. In modeling piezoelectric composite plates, a coupled piezoelectric–mechanical formulation is used in the development of the constitutive equations. Numerical analysis is conducted to investigate the effect of nonlinearity in the transient vibration of bimodular behavior caused by the contact impact of delaminated interfaces. Composite plates with surface-bonded or embedded sensors, subject to external loads, are also investigated to study the effects on transient responses due to various sizes and locations of delamination.

Analytical solutions are obtained for the bending deformation of antisymmetric angle-ply laminated plates with thickness–shear piezoelectric actuators. The laminated plates possess two opposite edges that are simply supported, the remaining two edges have any possible combination of boundary conditions: free, clamped, or simply supported. The displacement field of the laminated plates follows the first-order shear deformation theory. The Lévy method, in conjunction with the state-space approach, is used to analytically determine the bending solutions of plates with various boundary conditions. Six layer laminates are used to numerically demonstrate the analytical solutions and to investigate the laminates' static behavior. Interesting deflection patterns are generated by the shear piezoelectric actuators for laminates of various boundary conditions. These findings suggest promising potential for exploiting the considered laminates in many engineering applications. The effects of the composite ply angle and the piezoelectric ply angle on the laminate deflection are also investigated. It is observed that increasing the piezoelectric ply angle always magnifies the deflection, while increasing the composite angle provides concave downward curves for the deflection variation with the angle.

This paper focuses on a geometry optimization methodology based on a lumped-parameter mathematical model, which accepts the voltage as the input, and bending angle and bending moment as the outputs, for a trilayer bending-type polymer actuator. An analogy is made between thermal strain and the real strain in the actuator to establish the mathematical model, which is solved using the finite element method in order to obtain theoretical results. The polypyrrole (PPy) actuator, which consists of five layers of three different materials, operates in a non-aquatic medium, i.e., air, as opposed to its predecessors. With reference to its operation principle, the movement or propagation of dopant ions and solvent molecules into the PPy layers is mimicked with a temperature distribution model to improve the accuracy of the model. Theoretical and experimental results presented suggest that the model is valid to predict the bending angle and bending moment outputs of the PPy actuators quite well for a range of input voltages and actuator thicknesses. The model has been employed to determine the actuator geometry, resulting in improved/higher bending angle and bending moment outputs. The geometry optimization results for an actuator with a constant length and width demonstrate that the thicker is the root of the actuator, where it is clamped, the higher is the bending moment, as compared to an actuator with a uniform thickness.

Torsional vibration control can be crucial for applications of smart materials and structures. In this paper, the problem of topology optimization of collocated piezoelectric sensor/actuator (S/A) pairs for torsional vibration control of a laminated composite plate is directly addressed. Both isotropic and anisotropic PZT S/A pairs are considered and it is highlighted that the torsional vibration can be more effectively damped out by employing the topological optimal design of the S/A pairs than by using the conventional designs. To implement this topology optimization, a genetic algorithm (GA) based on a bit-array representation method is presented and a finite element (FE) simulation model based on the first-order shear theory and an output feedback control law is adopted. Numerical experiments are used to verify the present algorithm and show that the present optimal topology design can achieve significantly better active damping effect than the one using a continuously distributed PZT S/A pair, which was often adopted by many other researchers. Together with the progress in laser cutting and micromachining techniques, topology optimization of piezoelectric sensors and/or actuators would be promising in active vibration control of smart structures.

In this paper, an adaptive resonant controller is used to attenuate multi-mode vibrations in a flexible cantilever beam structure with varying loading conditions. This controller is particularly designed for structures that are exposed to previously unmodelled dynamics. On-line estimation of the structure's natural frequencies is used to update the adaptive resonant controller's parameters. The estimation of the natural frequencies is achieved using a parallel set of second-order recursive least squares estimators, each of which is designed for a specific vibration mode of concern. To achieve the desired estimation accuracy for each mode frequency, a different sampling rate suitable for that mode is used for the corresponding estimator. Experiment results show that the proposed adaptive strategy can achieve better performance, as measured by attenuation level, over its fixed-parameter counterpart for a range of unmodelled dynamics.

This paper presents a new microfabrication technique for bender-type electromechanical actuators made of conducting polymers. The technique is based on a computer-controlled deposition of the active material with a microsyringe. The paper describes the developed microfabrication system and proposes a simple deposition model used for an accurate control of the thickness of deposited layers. The realization of solid-state bimorph bender actuators made of polyaniline and a solid polymer electrolyte is presented. Prototype actuators fabricated with the new technique and stimulated in air with square wave potential differences ranging between −0.5 and +1 V showed bending angles higher than ± 60°.

As the application of fibre reinforced polymer composites (FRP) becomes more widespread there is a desire to add functionality beyond that of simple mechanical properties in order to facilitate the development of 'smart' materials. Magnetic FRP material has been developed which utilizes hollow glass fibres filled with magnetic material. This paper will discuss the manufacture, optimization and applications of magnetic FRP materials. The magnitude of magnetic performance that can be currently achieved is controlled by the availability of suitable magnetic materials in fine powder form, and the volume of magnetic material that can be incorporated within the fibres.

Piezoelectric fibres are finding increasing application in a variety of piezoelectric composites, including active fibre composites (AFCs). This paper describes the manufacture and characterization of lead zirconate titanate (PZT) fibres manufactured by viscous plastic processing (VPP). The manufacturing method will be described along with a systematic characterization of the macrostructure, microstructure, phase composition and low and high field piezoelectric properties. A comparison with other available PZT fibres will be made, which demonstrates that the VPP PZT fibres display high piezoelectric coefficients.

Two kinds of sensor protection system for fibre optic sensors (FOS), an embedded type and a surface-mountable type, have been developed in the work described this paper. Extrinsic Fabry–Perot interferometric (EFPI) and fibre Bragg grating (FBG) sensors protected by the designed protection systems have been used to monitor the cure progress and structural health status of concrete cylinders. Experimental results indicate that the sensor protection systems for the FOS perform adequately and effectively in a concrete environment. The protected fibre optic sensors are suitable for achieving structural health monitoring in practice. It is also revealed that there is excellent correlation between the results obtained from the protected FOS and reference electrical resistance strain gauges.

This paper presents the concept of an intelligent reinforced concrete structure (IRCS) and its application in structural health monitoring and rehabilitation. The IRCS has multiple functions which include self-rehabilitation, self-vibration damping, and self-structural health monitoring. These functions are enabled by two types of intelligent (smart) materials: shape memory alloys (SMAs) and piezoceramics. In this research, Nitinol type SMA and PZT (lead zirconate titanate) type piezoceramics are used. The proposed concrete structure is reinforced by martensite Nitinol cables using the method of post-tensioning. The martensite SMA significantly increases the concrete's damping property and its ability to handle large impact. In the presence of cracks due to explosions or earthquakes, by electrically heating the SMA cables, the SMA cables contract and close up the cracks. In this research, PZT patches are embedded in the concrete structure to detect possible cracks inside the concrete structure. The wavelet packet analysis method is then applied as a signal-processing tool to analyze the sensor signals. A damage index is defined to describe the damage severity for health monitoring purposes. In addition, by monitoring the electric resistance change of the SMA cables, the crack width can be estimated. To demonstrate this concept, a concrete beam specimen with reinforced SMA cables and with embedded PZT patches is fabricated. Experiments demonstrate that the IRC has the ability of self-sensing and self-rehabilitation. Three-point bending tests were conducted. During the loading process, a crack opens up to 0.47 inches. Upon removal of the load and heating the SMA cables, the crack closes up. The damage index formed by wavelet packet analysis of the PZT sensor data predicts and confirms the onset and severity of the crack during the loading. Also during the loading, the electrical resistance value of the SMA cable changes by up to 27% and this phenomenon is used to monitor the crack width.

This paper presents a pulse base effect on the Brillouin gain spectrum that can be obtained by Brillouin optical time-domain analysis (BOTDA), which uses a pump–probe system. For theoretical analysis of the pulse base effect, we propose a theoretical model in which the interaction between the pulse base and probe light is taken into consideration. Strain underestimation caused by the pulse base is demonstrated by experiments and theoretical simulations.

Fiber Bragg grating (FBG) sensors are one of many fiber optic sensor technologies that are currently being used in structural health monitoring systems. The sensors operate by detecting a shift in the wavelength of the reflected maxima due to applied strain. This paper studies a new fiber Bragg interrogation method that combines a swept wavelength laser in combination with wavelength references. These include a gas cell which is used as the long term wavelength standard and an etalon used for accurate interpolation of peak wavelengths. An etalon is essentially a filter that has a periodic response over a broad wavelength range. Since its wavelength response spacing is smaller than the gas cell, it can be used to determine the intermediate wavelengths between two gas cell absorption lines. Peak location is a key element of this interrogation method and several detection algorithms are investigated. It was determined that polynomial peak fitting is the most computationally efficient method and yields a resolution of better than 0.5 pm with signal to noise ratios of 30:1 or better. With higher signal to noise ratios, polynomial peak fitting can yield a resolution of better than 0.25 pm. Using a tunable laser, a hydrogen cyanide (HCN) gas cell and an etalon with maxima every 140 pm, static load tests have demonstrated a resolution of 1 pm and an accuracy of less than 5 pm. Also, this accuracy will be maintained over a long period of time as it is based on absorption lines in the gas cell. The results of this study demonstrate that absolute accurate strain measurements can be obtained with the use of wavelength references in conjunction with a suitable peak location algorithm.

Dynamic stall and flow separation induced vibration alleviation is investigated using single crystal and soft piezoceramic-induced shear actuation. PZT-5H performs well to reduce vibration at cruise speed (about 50%) but fails to achieve a substantial vibration reduction (about 20%) at high speed forward flight because dynamic stall and flow separation require a larger stroke for vibration reduction. -induced shear actuation is found to generate a larger stroke and eventually a higher vibration reduction (about 60–70%) at both cruise and high speed flight. It is observed that the controller performs satisfactorily up to a noise level of 20% in the sensed data. Optimum placement of actuators along the span, as well as the eventualities of actuator failure and degradation are also addressed.

A momentum-wheel installed to provide attitude-control torque actually produces undesirable force or torque disturbances owing to wheel imbalance and imperfection of the ball-bearings. To improve the pointing performance of observation satellites, a vibration isolator is used to isolate observation devices from these disturbances. This paper compares three types of semi-active isolators that consist of a piezoelectric material and a switch-controlled passive circuit. Since this isolation is implemented by controlling a circuit switch no external energy is supplied to the system, and so the system is stable even when a malfunction occurs in control. We propose a simple but effective isolation method that needs to know only one velocity value instead of the full state of the system. Numerical simulations with a simple model of an observation satellite demonstrated that the proposed isolator works well to isolate an observation device from disturbances caused by the momentum-wheel, without causing any degradation in the attitude control of satellites.

The primary purpose of this paper is to provide a comprehensive review on the response time of magnetorheological (MR) dampers. Rapid response time is desired for all real-time control applications. In reviewing the literature, a detailed description of the response time of semi-active dampers is seldom given. Furthermore, the methods of computing the response time are not discussed in detail. The authors intend to develop a method for the definition and the experimental determination of the response time of MR dampers. Furthermore, parameters affecting the response time of MR dampers are investigated. Specifically, the effect of operating current, piston velocity, and system compliance are addressed. Because the response time is often limited, not by the response of the fluid itself, but by the limitations of the driving electronics and the inductance of the electromagnet, the response time of the driving electronics is considered as well. The authors define the response time as the time required to transition from the initial state to 95% of the final state. Using a triangle wave to maintain constant velocity across the damper, various operating currents ranging from 0.5 to 2 A were applied and the resulting force was recorded. The results show that, for a given velocity, the response time decreases as the operating current increases. Results for the driving electronics show the opposite trend: as current increases, response time increases. To evaluate the effect of piston velocity on response time, velocities ranging from 0.1 to 4 in s⁻¹ were tested. The results show that the response time decreases exponentially as the velocity increases, converging on some final value. Further analysis revealed that this result is an artifact of the compliance in the system. To confirm this, a series of tests was conducted in which the compliance of the system was artificially altered. The results of the compliance study indicate that compliance has a significant effect on the response time of the damper.

This paper describes the implementation of an autonomous switching resistor–inductor (R–L) shunt circuit for the control of structure vibration. The resulting switch shunt circuit, compared to present shunt circuit techniques, does not require a power for its operation and is almost as effective. Moreover, experiments show that the damping performance is robust against temperature variations due to environmental conditions, whereas present shunt circuits lose their damping performance. The proposed autonomous switching R–L shunt circuit requires a small number of electronic components, therefore making it a viable and effective solution for the control of structural vibration.

This study demonstrates the isolation performance of a variable-damping isolator using a bio-metal fiber (BMF) valve to enhance the pointing performance of observation satellites by isolating disturbances induced by reaction wheel assemblies. Vibration isolation tests of the variable-damping isolator were performed using an air-floating wheel disturbance detector to investigate whether the isolator can actually isolate flywheel vibration. In this paper, we first present a recently developed variable-damping isolator with low power consumption, and a reaction wheel disturbance detector, fabricated in a previous study, which detects low-frequency disturbances. Next, we describe the effectiveness of the variable-damping isolator based on flywheel vibration isolation test results.

Recently, electrorheological fluids (ERFs) have emerged as a potential technology for implementing semi-active control in smart structure and vehicle applications to efficiently suppress vibration. The rheological behavior of ERFs under an electric field is important in engineering application. The work described here involves experimental research into the rheological behavior, under a variety of electric fields, of three kinds of ERF: (C₆H₁₀O₅)_n, TiO₂–CeCl₃, and SrTiO₃/PANI (PANI = polyaniline). We aim to design a high-performance ERF and display an ER effect. Results show that different kinds of ERF have different yield properties, especially under the conditions of both post-yield and higher shear rates. In terms of the trend in behavior of the ER effect shown in the experimental curves, the expression for the relation between dynamic shear stress and static yield stress has also been investigated. Both the highest negative and the highest positive differential values have been obtained. We also show that apparent viscosity shows three different trends in behavior, based on at-line start, non-linear power-law and Bingham power-law (Sisco) flow behavior. The relative variation values of ERFs at low and high shear rates, respectively, are shown.

Biomedical engineering applications of ionic polymer–metal composites such as motion devices for endoscopy, pumps, valves, catheter navigation mechanisms and spinal pressure sensors make it important to properly model IPMCs for engineering design. In particular, IPMC continuum models and their electric equivalent circuit representation are critical to a more efficient design of IPMC devices. In this paper, we propose a new continuum electromechanical model to understand and predict the electrical/mechanical behavior of the IPMC. An IPMC lumped-parameter circuit is derived from its continuum model to predict the relationship between its voltage and current signals. Although based on previous works of Shahinpoor and Nemat-Nasser, our model was derived on a macroscopic level, the water effects were assumed negligible when compared with the electrical effects of mobile ions for the IPMC motion, the model parameters were clearly identified in their physical meaning, and an equivalent-circuit IPMC model was determined from the established continuum electromechanical model. Experiments are done with two IPMC pieces having different dimensions, which were previously immersed in a sodium solution. The IPMCs are current driven, the transverse displacement and voltage signals being measured for different current values, avoiding the water electrolysis phenomenon. Simulations using the analytic models derived are compared with the experimental results and they are found to predict the electrical and mechanical relations very accurately.

Of Tanaka-based constitutive models for shape memory alloys (SMAs), the model presented by Liang and then improved by Brinson is the most typical one, although it still lacks some important features appearing in typical SMAs. In this paper, we propose a constitutive model of SMAs to complement the Liang–Brinson model. In the proposed model, we augment the rubber-like effect at temperatures below M_f for certain SMAs and shed light on the V-shape feature of the critical stresses in the stress–strain (S–S) curves around M_s. Through numerically comparing the distinctive features of our model with experimental observations, the proposed model is proved to better simulate the thermomechanical behavior of SMAs in a more extensive temperature range and to generate more accurate prediction.

Coupled electro-thermo-elastic equations applicable for the analysis of smart structures with piezoelectric patches/layers have been derived from the fundamental principles of mass, linear momentum, angular momentum, energy and charge conservation. The relevant constitutive equations have been obtained by using the second law of thermodynamics. The interaction of the electric field and polarization introduces distributed non-linear body force in the piezo material, and in addition renders the stress tensor non-symmetric due to distributed couple. Using the linear equations, and applying a layer-by-layer finite element model, the induced electric potential and mechanical deformations in the piezo and non-piezo core material have been obtained for various cases of actuation and sensing of a smart beam under external mechanical, electrical and thermal loadings. The mathematical formulation and the solution technique have been validated by comparing the results of the present study with those available in the literature. It is also shown that piezo patches can be effectively used for shape control.

Grafted copolymers of poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) were prepared using a Ce^(IV) glucose redox initiator by free radical polymerization. Three grafted copolymers having 20%, 50% and 80% grafting were selected for this study. Thus-modified polymer was characterized by means of Fourier transform infrared spectra, ¹H NMR, gel permeation chromatography, thermogravimetric analysis and universal testing machine approaches. The membranes were prepared by a solution casting method, where the cross-linking process was performed through the in situ addition of glutaraldehyde and hydrochloric acid as the cross-linking agent and catalyst respectively. The following four membranes were prepared: (i) pure PVA; (ii) 20% grafted PVA; (iii) 50% grafted PVA; (iv) 80% grafted PVA. The membranes obtained were employed in the electroactive behavior study under a DC electric stimulus in different concentrations of electrolyte. The equilibrium bending angles (EBA) of these polymers were studied with respect to time, poly(acrylic acid) content, electric voltage applied across the polymer and ionic strength of the electrolyte used. Experimental results show stable reversibility of the bending behavior of these polymers under an applied DC electric field. The EBA increased with increase in the applied electric voltage and poly(acrylic acid) content within the polymer.

This work describes a procedure for detecting the presence of damage-induced nonlinearities in composite structures using only the structure's vibrational response. Damage is assumed to change the coupling between different locations on the structure from linear to nonlinear. Utilizing concepts from the field of information theory, we are able to deduce the form of the underlying structural model (linear/nonlinear), and hence detect the presence of the damage. Because information theoretics are model independent they may be used to capture both linear and nonlinear dynamical relationships. We describe two such metrics, the time delayed mutual information and time delayed transfer entropy, and show how they may be computed from time series data. We make use of surrogate data techniques in order to place the question of damage in a hypothesis testing framework. Specifically, we construct surrogate data sets from the original that preserve only the linear relationships among the data. We then compute the mutual information and the transfer entropy on both the original and surrogate data and quantify the discrepancy in the results as a measure of nonlinearity in the structure. Thus, we do not require the explicit measurement of a baseline data set. The approach is demonstrated to be effective in diagnosing the presence of impact damage in a thick composite sandwich plate. We also show how the approach can be used to detect impact damage in a composite UAV wing subject to ambient gust loading.

We propose and demonstrate methods for suppressing the polarization dependence in the interrogation of birefringent fiber Bragg gratings. A wavelength-swept fiber laser with a polarized output was used as the light source. Two polarization-averaging methods, a depolarization scheme and a polarization scrambling scheme, were investigated and compared. The proposed techniques successfully stabilized the reflection spectrum of a birefringent grating regardless of the polarization state of the source laser and birefringence of the lead fiber. The results of this work eliminate one of the major practical difficulties in current fiber Bragg grating interrogation.

An aluminum prototype of the AMICA (astro-mapper for instrument check of attitude) star tracker support (ASTS) of the AMS_02 (alpha magnetic spectrometer) space experiment has been instrumented with fiber Bragg gratings (FBGs) for the acquisition of strain fields during dynamic tests. The excitation has been provided by an instrumented impact hammer; the mechanical response of the structure was provided by surface bonded FBGs and accelerometers nominally in the same location. All time histories have been recorded, transformed into the frequency domain to retrieve frequency response functions (FRFs)—from accelerometers—and strain frequency response functions (SFRFs)—from FBGs, both providing resonant frequencies and displacement (strain) shapes of the ASTS. Numerical simulations of this structure have been performed to predict the aforementioned dynamic features. Good agreement was found for the two first bending modes between the two approaches and in turn with the numerical analysis.

Numerical unit cell models of 1-3 periodic composites made of piezoceramic unidirectional cylindrical fibers embedded in a soft non-piezoelectric matrix are developed. The unit cell is used for prediction of the effective coefficients of the periodic transversely isotropic piezoelectric cylindrical fiber composite. Special emphasis is placed on a formulation of the boundary conditions that allows the simulation of all modes of the overall deformation arising from any arbitrary combination of mechanical and electrical loading. The numerical approach is based on the finite element method and it allows extension to composites with arbitrary geometrical inclusion configurations, providing a powerful tool for fast calculation of their effective properties. For verification, the effective coefficients are evaluated for square and hexagonal arrangements of unidirectional piezoelectric cylindrical fiber composites. The results obtained from the numerical technique are compared with those obtained by means of the analytical asymptotic homogenization method for different volume fractions. Furthermore, the results are compared with other analytical and numerical methods reported in the literature.

The free vibrations of simply supported magneto-electro-elastic cylindrical shells are studied. A series solution is assumed in the circumferential and axial directions of the shell to preserve the three-dimensional character of the structure. The constitutive equations of the magneto-electro-elastic medium involving mechanical, electrical and magnetic fields are used to derive the finite element model for the system. The influence of the piezomagnetic effect on the structural frequencies of the cylindrical shell is studied. A comparison is made between a shell with a layered configuration and one with a multiphase system. The study is carried out for a typical shell with simply supported boundary conditions for different ratios of length to radius and radius to thickness to analyse the frequency behaviour.

The large radar cross section of wind turbine generator (WTG) blades combined with high tip speeds can produce significant Doppler returns when illuminated by a radar. Normally, an air traffic control radar system will filter out large returns from stationary targets, but the Doppler shifts introduced by the WTG blades are interpreted as moving aircraft that can confuse radar operators and compromise safety. A possible solution to this problem is to incorporate an active layer into the structure of the WTG blades that can be used to dynamically modulate the radar cross section (RCS) of the blade return. The active blade can operate in one of two modes: first the blade RCS can be modulated to provide a Doppler return that is outside the detectable range of the radar receiver system so that it is rejected; a second mode of operation is to introduce specific coding onto the Doppler returns so that they may be uniquely identified and rejected. The active layer used in the system consists of a frequency selective surface controlled by semiconductor diodes and is a development of techniques developed for active radar absorbers. Results of theoretical and experimental work using a 10 GHz Doppler radar and scale-model WTG are presented.

This paper investigates multimodal vibration control of a three-story model structural frame by using surface bonded PZT (lead zirconate titanate) type piezoceramic patches. Piezoceramic is one of the smart materials. Complete control systems design is synthesized on the model frame using system identification and a pole placement controller. A time domain based subspace system identification is performed to identify the first three modes of the structural frame. A fit of 90% is achieved in identification results. A full-state pole placement feedback controller is designed based on the identified model. To implement the full-state feedback controller, the design of a state estimator is also performed. Experimental results demonstrate the effectiveness of multimodal active control of the smart frame structure using pole placement control.

Squeeze film damping effects are critical issues for nano/microelectromechanical system (NEMS/MEMS) devices. A modified analytical formula for squeeze film damping is proposed, which was derived as an analytical solution of the Poisson equation, a simplified Navier–Stokes equation pertaining to systems with rectangular air capacitors. Silicon on insulator based perforated microscanners were characterized experimentally in air, to verify the squeeze film damping model. The differences of the measured displacements from the numerical analysis are less than 5%. Considering the fabrication-related tolerances in device dimensions, the estimates of the squeeze film damping of the perforated microscanners are very precise and practical, and could be broadly applied in NEMS/MEMS engineering.

Previous NASA work has included fabrication and modeling of hybrid composite (HC) specimens with embedded Nitinol ribbon actuators and thermomechanical testing of the constituents. The Nitinol tensile behavior depended significantly on the thermomechanical condition (TMC). A Nitinol microstructure/mechanical property characterization was conducted on four TMCs. Differential scanning calorimetry and x-ray diffraction were used to rationalize the microstructures present. Tensile tests determined the effect of TMC on the Nitinol tensile behavior and stress state of the microstructure. Three TMCs showed typical shape memory behavior. The TMC that simulated the HC autoclave process on the actuator resulted in an irreversible microstructure. The microstructural constituents and their stress states probably govern the Nitinol stress–strain behavior. The critical stress to achieve an initial stress plateau was dependent on the amount and stress state of R-phase present in the initial microstructure. Thus, prior TMC critically affects the Nitinol tensile behavior. Numerical model inputs must therefore account for these effects on the Nitinol actuator.

Composites of shape memory alloys (SMA) with a matrix have been widely studied to suppress propagating damage of the matrix, where the embedded SMA is used as an actuator. We use the embedded SMA wire in composites both as an actuator and as a strain sensor. The possibilities of using the SMA wire as a strain sensor to obtain an actuation trigger signal for damage suppression were investigated using the variation of the SMA electric resistance. We determined that the electric resistance variation of the SMA wire is correlated with the strain. The temperature dependence of the correlation, which can be reduced by a compensation method, is also discussed.

Self-sensing active vibration damping is advantageous if external sensors cannot be collocated with the actuators or these sensors add too much weight or cost. When self-sensing, electrodynamic actuators are used damping is directly added to an attached structure without the need of potentially destabilizing electronic integrators or differentiators. In this paper self-sensing control with a shunted resistor, positive current feedback and induced voltage feedback are investigated in simulations and experiments. Experiments with a commercial shaker on a clamped plate show that its vibration attenuation is increased from 5 to 15 dB and the control bandwidth is more than doubled when the appropriate control scheme is used.

A numerical model of a beam structure with a piezoelectric actuator bonded to the surface of the structure and an accelerometer placed on the tip can be obtained in the ANSYS Matlab platform. The validated numerical model and the experimental data allow us to use the obtained finite element model of the complete system (beam, piezoactuator and accelerometer) as a basis for the design and optimization of the electrical shunted circuit elements. The obtained optimal electrical elements of the circuit network have been used in an experimental test to confirm the numerical result. The analysis has been extended to more complex structures, such as the dominant mode of vibration of a chassis subframe of a car.

A self-switching circuit and a resistive circuit are designed and implemented for vibration suppression with a piezo patch in this study. A numerical model is developed for a rectangular beam bonded with a pair of piezo patches. One piezo patch is used to excite the system, the other one being used for vibration damping. Optimal resistances are respectively determined for the resistive circuit and self-switching circuit, and a new switch law is proposed for the switching circuit. These two circuits are implemented in an experimental setup to verify the model. Experimental results show that the vibration of a clamped beam can be effectively damped by using the resistive circuit or switching circuit. Due to the fact that switching is not perfect in practice, the damping performance of the switching circuit is a little different from the simulated result.

This paper presents a micromechanics approach to the study of the vibration of beams with embedded piezoelectric sensors and actuators. The natural frequency of the beam is determined from the variational principle in Rayleigh quotient form. The piezoelectric sensors and actuators embedded in the beam are analysed using Eshelby's equivalent inclusion method. In addition, the Euler–Bernoulli beam theory and Rayleigh–Ritz approximation technique are used in the analysis. Results show that the size, volume fraction and location of the piezoelectric inclusions significantly influence the natural frequency of the beam. The results of the present model agree well with the theoretical results presented in the literature.

Surface bonded piezoelectric ceramic (PZT) transducers are currently the most prominent area of research in structural health monitoring using electromechanical impedance methods. This paper presents a new embedded PZT patch and its interaction with the host sandwiched beam. Durability and protection from surface finish, vandalism and the environment are important features of the embedment. The paper also demonstrates the use of thickness vibration of the PZT patch in electromechanical admittance formulations. This embedded PZT–structure interaction model is based on the new concept of 'average sum impedance'. The formulations used for this model can be conveniently employed to extract the mechanical impedance of any 'unknown' PZT patch embeddable plane structure. The mechanical impedance of the structure is obtained from the admittance signatures of the embedded PZT patch. The proposed model is experimentally verified on sandwiched beams.

This paper presents an integrated formulation for the calculation of the spectral response of a fiber Bragg grating sensor embedded in a host material system, as a function of the loading applied to the host structure. In particular, the calculation of the transverse strain sensitivity of a fiber Bragg grating sensor through the calculation of the change in effective index (or indices) of refraction of the fiber cross-section due to the applied load is presented in detail. For the calculation of the fiber propagation constants, a two-step finite element formulation is used incorporating the optical, geometric and material properties of the cross-section. Once the propagation constants and principal optical axes are known along the fiber, a modified transfer matrix method is applied to calculate the spectral response of the FBG. It is shown that the FE formulation yields close agreement with previous methods for benchmark diametrical compression cases. However, the current method provides the potential to evaluate the effects of high strain gradients across the optical fiber core present in some loading applications.

This paper presents the development of a new class of current sensor based on active materials for high-voltage transmission systems. This current sensor is an innovative design with respect to conventional current measurement transformers. The alternating current signal to be measured induces a magnetic field in an emitter which consists of a magnetostrictive material. The emitter transforms the current magnetic energy into mechanical energy in the form of mechanical waves due to the alternating nature of the induced magnetic field. These waves are transmitted through a dielectric structure until a piezoelectric stack, the receiver, is reached which converts the mechanical energy back into electrical energy. An electronic signal module processes this low electrical current and estimates the primary current to be measured. A numerical model has been developed to evaluate the preliminary design. A small scale prototype has been built and tested to demonstrate the feasibility of the current sensor. Experimental data have been used to fit the damping parameters of the model.

The size reduction of power supplies motivates the research of new elements which could be better candidates for integration. In this field, electromagnetic transformers may be replaced, with significant advantage, by piezoelectric transformers (PT).

In a PT, the input electrical energy is transferred to the output through a mechanical wave using the direct and converse effects of piezoelectric materials. The main advantages of PTs over electromagnetic transformers are: no magnetic noise generation, smaller size, higher power density and higher efficiency.

This paper presents an innovative non-linear processing technique derived from the so-called 'synchronized switch damping' technique (SSD), that was developed to address the structural damping problem. In transformer applications, the power capability of piezoelectric materials is mainly limited by mechanical losses related, in particular, to the mechanical wave amplitude.

This synchronized switch technique provides a strong attenuation of the PT mechanical wave amplitude while preserving the transmitted power level. Thus, the PT efficiency and its power capability are significantly enhanced. Theoretical predictions and experimental results using a PT structure similar to a Langevin transducer show that the power capability may increase over 450%.

A concept demonstrator of the structural health monitoring (SHM) system was developed to autonomously detect the degradation of the mechanical integrity of the standoff carbon–carbon (C–C) thermal protection system (TPS) panels. This system enables us to identify the location of the loosened bolts, as well as to predict the torque levels of those bolts accordingly. In the process of building the proposed SHM prototype, efforts have been focused primarily on developing a trustworthy diagnostic scheme and a responsive sensor suite. In part I of the study, an attenuation-based diagnostic method was proposed to assess the fastener integrity by observing the attenuation patterns of the resultant sensor signals. The attenuation-based method is based on the damping phenomena of ultrasonic waves across the bolted joints. The major advantage of the attenuation-based method over the conventional diagnostic methods is its local sensing capability of loosened brackets. The method can further discriminate the two major failure modes within a bracket: panel-joint loosening and bracket-joint loosening. The theoretical explanation of the attenuation-based method is performed using micro-contact theory and structural/internal damping principles, followed by parametric model studies and appropriate hypothesis testing.

The research presented in this paper is motivated by the need for reliable inspection technology for the detection of bolt loosening in carbon–carbon (C–C) thermal protection system (TPS) panels using minimal human intervention. Based on the diagnostic scheme proposed in part I of the study, a new PZT (lead zirconate titanate)-embedded sensor washer was developed to constitute the sensor network. The sensor suite was included in the C–C TPS prototype without jeopardizing the integrity of the original fastening components. The sensor-embedded washer enhances the remote sensing capability and achieves sufficient sensitivity by guiding the diagnostic waves to propagate primarily through the inspection areas. After evolution of the sensor design and appropriate algorithm development, the verification tests were conducted using a shaker which simulated the acoustic environments during the re-entry process. The test results revealed that the proposed system successfully identified the loss of the preload for the bolted joints under loosening and gave the correct diagnostic results. The sensors were found to be durable under cyclic mechanical loads without major failures, and the diagnostic scheme was capable of locating a loosened bracket as well as discriminating major failure modes 1 and 2: panel and bracket loosening in the bracket.

In this paper, microneedle fabrication using the PCT (plane pattern to cross-section transfer) method is summarized. Three types of microneedle array have been developed: the single-tip, quadruplet, and hollow microneedle arrays. A brief introduction to the fabrication process using PCT and detailed design concepts for optimizing the fabrication steps for shape improvement of the three types of microneedle are provided. The microneedle structures have controllable angled sidewalls, exhibiting an extraordinarily geometrical level of accuracy compared to what is achieved using other existing fabrication methods based on deep x-ray lithography by synchrotron radiation. Furthermore, the improvements reported in this work as compared to the results from the existing methods are: sharper tips for the single-tip microneedles, strength improvement for the quadruplet microneedles, and cost reduction for the hollow microneedles. Each type of microneedle was designed to serve a different biomedical need.

Submicron chitosan fibres were prepared using an electro-wet-spinning process. The chitosan solution was ejected into a coagulation medium containing different concentrations of ethyl alcohol in aqueous sodium hydroxide (0, 30, 50 and 70% (v/v)). Submicron chitosan fibres were obtained using a coagulation medium containing 50% (v/v) of ethyl alcohol in an applied electric field of 15 kV with a 10 cm spinning distance. The density of the coagulation medium controlled the uniformity of the resulting fibres. When a swollen chitosan fibre hydrogel was placed between a pair of electrodes, it contracted in an applied electric field and showed a stepwise contraction behaviour that depended on the magnitude of the electrical stimulus. Chitosan fibre hydrogels showed a fast and reversible electroactuation under low applied potentials. This type of fibre has potential application in artificial muscles.

In recent years the use of distributed optical fiber sensors for measurements of strain in beams, by means of the Brillouin scattering effect, has been proposed. Several works pointed out the practical difficulty of this kind of measurement, connected both to theoretical and to experimental problems, e.g. mechanical characterization of optical fibers, decaying of strains in the protective coatings, spatial resolution of the Brillouin scattering, brittleness of the glass core, elastic–plastic response of the polymeric jackets, end effects and the different responses of the fiber for dilatation and contraction. Dealing with each of the above problems still requires a great research effort. However, recent literature shows that distributed optical fiber measurement techniques are extremely useful for finding qualitative responses in terms of strains. Indeed, in spite of the above-mentioned uncertainties, the great advantage of the proposed distributed measurement of strains remains evident for the safety assessment of large structures, such as bridges, tunnels, dams and pipelines, over their whole lifetimes. In view of this, in the present paper the detection of defects or damage in bending beams—by using distributed optical fiber sensors in a method based on time domain stimulated Brillouin scattering—is proposed. In particular, laboratory tests were carried out to measure the strain profile along a steel beam. Two tests were performed: the first one involves an integral steel beam, while the second experiment is performed on a damaged beam. Comparison between these two tests allows the detection of the position and the establishing of bounds on the size of the defect. At the end, the quality and accuracy of the measurements are discussed and a sensitivity analysis of the strain readings taking into account the bonding conditions at the interface between the structure and the fiber is also carried out by means a parametric numerical simulation.

In this paper, a modal approach is realized to define the damping properties of piezoelectric/elastic/piezoelectric beams. This method is based on the classical laminated beam theory and some simple assumptions about the electric fields. This leads to an electromechanical beam constitutive law. The piezoelectric layers play the role of sensor and actuator and two feedback control laws are considered. The equivalent stiffness, eigenfrequencies and loss factors of the whole system beam/control device are obtained.

This paper deals with the analysis of vertically reinforced 1–3 piezoelectric composite materials as the material used for the distributed actuator of smart structures. A micromechanics model has been derived to predict the effective elastic and piezoelectric coefficients of these piezoelectric composites which are useful for the analysis of smart beams. In order to investigate the performance of a layer of this 1–3 piezoelectric composite material as the distributed actuator of smart structures, active constrained layer damping (ACLD) of smart laminated composite beams has been studied. The constraining layer in the ACLD treatment has been considered to be made of this piezoelectric composite. A finite element model has been developed to study the dynamics of the overall beam/ACLD system. Both in-plane and out-of-plane actuations of the constraining layer of the ACLD treatment have been utilized for deriving the finite element model. It has been found that these vertically reinforced 1–3 piezoelectric composite materials which are in general being used as distributed sensors can be potentially used as distributed actuators of smart structures.

A new approach to the design and control of shape memory alloy (SMA) actuators is presented. SMA wires are divided into many segments and their thermal states are controlled individually as a group of finite state machines. Instead of driving a current to the entire SMA wire and controlling the wire length based on the analog strain–temperature characteristics, the new method controls the binary state (hot or cold) of individual segments and thereby the total displacement is proportional to the length of the heated segments, i.e. austenite phase. Although the thermomechanical properties of SMA are highly nonlinear and uncertain with a prominent hysteresis, segmented binary control is robust and stable, providing characteristics similar to a stepping motor. However, the heating and cooling of each segment to its bi-stable states entail longer time and larger energy for transition. In this paper, an efficient method for improving the speed of response and power consumption is developed by exploiting the inherent hysteresis of SMA. Instead of keeping the extreme temperatures continuously, the temperatures return to intermediate 'hold' temperatures closer to room temperature but sufficient to keep constant phase. Coordination of the multitude of segments having independent thermal states allows for faster response with little latency time even for thick SMA wires. Based on stress dependent thermomechanical characteristics, the hold temperature satisfying a given stress margin is obtained. The new control method is implemented using the Peltier effect thermoelectric devices for selective segment-by-segment heating and cooling. Experiments demonstrate the effectiveness of the proposed method.

The shape-memory effect (SME) is demonstrated to occur for the solid solution of lead magnesium niobate with lead titanate for the molar ratio 70:30. Since the material is an insulator, it was possible to apply an electric field to influence and investigate the SME. It is shown that electric field can be used for enhancing the shape strain produced by the bending load, although some fraction of the shape strain becomes irrecoverable on repeated SME cycling under the combined effects of mechanical and electric loads. An explanation is offered for this and other observations, invoking the relaxor-ferroelectric nature of the ceramic. Such materials have potential for use as 'actuators with a memory' in smart structures.

A nonlocal continuum mechanics model is developed and applied to study the vibration of both single-walled nanotubes (SWNTs) and double-walled nanotubes (DWNTs) via elastic beam theories. The small-scale effects on vibration characteristics of carbon nanotubes are explicitly derived through a complete mechanics analysis. A qualitative validation study shows that the results based on nonlocal continuum mechanics are in agreement with the published experimental reports in this field. Numerical simulations are conducted to quantitatively show the small-scale effect on vibrations of both SWNTs and DWNTs with different lengths and diameters.

In this note, we present an alternative in situ approach to determine the phase transformation temperatures of sputter deposited NiTi based shape memory thin films atop a substrate. Reflection in three thin films upon thermal cycling was measured with a reflection spectrometer in a wavelength range from 360 nm to 2 µm. Subsequently, the relationship of the reflection change versus temperature was obtained, which shows obvious hysteresis, clear evidence of the phase transformation. Hence, the transformation temperatures were determined and then compared with the result of the differential scanning calorimeter test; good agreement was observed. Additionally, we started modeling the phenomenon by identifying and quantitatively estimating four potential contributors to the change of reflection during phase transformation in deposited shape memory thin films.

Ferrites with the general formula Li_0.5Ni_0.75−x/2Cd_x/2Fe₂O₄ (where x = 0, 0.1, 0.3, 0.5, 0.7 and 0.9) were prepared by the standard double sintering ceramic method. X-ray diffraction analysis confirmed the single phase spinel structure of the samples. The variation of saturation magnetization (M_s) was studied as a function of Cd content. The dielectric constant (ε') and dielectric loss tangent (tanδ) were measured at room temperature as a function of frequency in the range 100 Hz–1 MHz. These parameters decrease with increasing frequency for all of the samples. The compositional variation of ε' and ρ_DC show an inverse trend of variation with each other.

A fibre-optic-based humidity sensor has been developed and used for the measurement of moisture absorption in concrete. The sensor was fabricated using a fibre Bragg grating (FBG) coated with a moisture sensitive polymer. To investigate the use of this sensing technique for the detection of moisture ingress in concrete, the sensor was embedded in various concrete samples of different water to cement ratios which were then immersed in a water bath. A direct indication of the humidity level within a sample is given by the shift of the Bragg wavelength caused by the expansion of the humidity-sensitive material coated on the fibre. The sensor itself exploits the inherent characteristics of the FBG, with its operation being based on the strain effect induced in the Bragg grating, through the swelling of the polymer coating.

It was found that optical-fibre-based humidity sensors of this type form a basis for determining the changes in the moisture content in different concrete samples, indicating potential new applications of the sensor system to ensure the integrity of civil engineering structures in which they are used.

Smart heteromicrostructures of a new kind, composed of SiO₂ microspheres and ZnO branches, have been prepared hierarchically for the first time. Such heteromicrostructures have been characterized by means of x-ray diffraction and field emission scanning electron microscopy. Suggesting a possible formation process has been tackled. This type of smart branched heteromaterial is expected to have applications in fields of nanomedicine such as clearing clogged arteries, breaking aggregated amyloids and delivering drugs.