Table of contents

Vibration control of a plate using an optical fiber sensor and a PZT actuator is considered in this study. An aluminum plate with attached extrinsic Fabry–Perot interferometer (EFPI) and PZT actuator is prepared for experimental investigation. The vibration level of EFPI that can represent the mechanical strain without severe distortion is validated by a forced vibration experiment. A linear time-invariant system model is constructed based on the experimentally obtained frequency responses, and an optimal controller is designed for the multi-modal vibration suppression. Control performance is presented in frequency and time domains. It is found that the vibration level of the first three modes can be greatly reduced. The effect of low-pass filtering used to eliminate high frequency noise on the stability and control performance is also considered.

A mechanical model of a longitudinal oscillation ultrasonic motor and a method of analyzing its frequency–temperature characteristics are presented. The sticking and slipping between the stator and the rotor in the intermittent contact region are analyzed theoretically. An analytical expression for the motor's driving force that undergoes continuous changes is given. The behaviors of the ultrasonic motor (USM), including the revolving speed of the rotor, the output kinetic energy from the rotor to the other object, the input kinetic energy from the beam tip, and the efficiency of the energy transformation, are discussed. The effects of the initial compressive force, driving frequency, load, and the moment of inertia of the motor on the behavior of the motor are examined. In the study of the temperature effect, the course of the vibration of the piezoelectric element inside the USM is expounded, the main factors affecting the frequency–temperature characteristics are analyzed, and the analytical expression for the change of the resonance frequency with respect to the temperature is given. Numerical simulations show that the results obtained in this paper agree with reported experimental results.

In this paper, the numerical modeling of a damaged plate with piezoelectric actuation is presented. Unlike in previous studies, the effects of the defect are considered and embodied by mass and stiffness reductions in the equation of motion. The model is validated using indices related to frequency variation and energy change in both frequency and time domains. A comparison of the tendencies of the measured indices with those of the simulated ones shows a reasonably good agreement. Results show that the energy index is more sensitive to damage than the frequency index. Both square-wave and pseudo-random excitations can be used to assess the energy index variation. For the latter, however, an averaging over time signals is needed to provide more reliable results.

This paper presents a numerical investigation of the thermal behavior of an artificial anal sphincter using shape memory alloys (SMAs) proposed by the authors. The SMA artificial anal sphincter has the function of occlusion at body temperature and can be opened with a thermal transformation induced deformation of SMAs to solve the problem of severe fecal incontinence. The investigation of its thermal behavior is of great importance in terms of practical use in living bodies as a prosthesis. In this work, a previously proposed phenomenological model was applied to simulate the thermal responses of SMA plates that had undergone thermally induced transformation. The numerical approach for considering the thermal interaction between the prosthesis and surrounding tissues was discussed based on the classical bio-heat equation. Numerical predictions on both in vitro and in vivo cases were verified by experiments with acceptable agreements. The thermal responses of the SMA artificial anal sphincter were discussed based on the simulation results, with the values of the applied power and the geometric configuration of thermal insulation as parameters. The results obtained in the present work provided a framework for the further design of SMA artificial sphincters to meet demands from the viewpoint of thermal compatibility as prostheses.

This paper presents a study of an arrangement consisting of two matched pairs of piezoelectric transducers bonded on a cantilever beam for vibration control. A single pair of transducers when used as a matched actuator and sensor in practice, is known not to have a strictly positive real (SPR) response due to coupling between in-plane motion and out-of-plane motion. The stability and performance of the matched single pair are thus limited when direct velocity feedback control is applied. An arrangement using four piezoelectric transducer layers arranged as two matched pairs has been suggested to overcome this problem. Theoretically, when the actuator pair and the sensor pair are connected out-of-phase, the response becomes SPR since in-plane motion cannot be excited. A smart beam with matched double piezoelectric sensor/actuator pairs has been implemented. Triangularly shaped sensors and actuators were bonded on each side of the beam. However, this matched double sensor/actuator pair could not excite pure out-of-plane flexural motion of the beam, due to the direct inter-layer coupling between the sensor and actuator which were bonded directly on to each other. Therefore, the four-layer smart beam does not provide an SPR response.

The results of this study demonstrate that resistance compensation can provide significant improvement in the charging rate, and consequent actuation strain rate, for carbon nanotube sheets operated in an organic electrolyte. The strain rate increased with increasing potential pulse amplitude and a more negative potential limit. The amount of strain produced also increased with longer pulse times. The highest strain rate achieved was 0.6% s⁻¹, producing a strain amplitude of 0.3% in 0.5 s. This performance is significantly better than previously reported. The improvements in strain rate are somewhat offset when large negative potential limits are used due to the introduction of faradaic reactions in the electrolyte medium that do not contribute to actuation. Efficiency of operation is, therefore, reduced under such conditions. Some slight differences were observed between the actuator responses for the negative and positive pulses, which are partly explained by the basic mechanism of actuation and partly by instrumental effects.

The functionality of a commercially available piezoelectric (lead zirconate–titanate (PZT)) actuator/sensor embedded in a quasi-isotropic graphite/epoxy composite while undergoing a combined electromechanical (E/M) fatigue under the fully reversed, tension–compression fatigue condition was investigated. The applied maximum stress levels ranged from 25 MPa (500 µε) to 87.5 MPa (1750 µε), which were in the range of 0.5–1.75 times its design limit of 50 MPa (1000 µε). At the same time, the embedded PZT was subjected to ac voltages ranging from −100 to 100 V or 100 to −100 V at 10 Hz, giving either in-phase or out-of-phase electrically induced strain with respect to the cyclic mechanical load or strain. The output voltage of embedded PZT was monitored during cycling to determine its health. Failure of the PZT was assumed when a reduction of 30% of the initial output voltage was seen during cycling, even after repoling. Out-of-phase tension–compression E/M fatigue generated greater damage to the PZT than in-phase tension–compression E/M fatigue. This was because the net effective stress/strain experienced by the PZT was lower in the in-phase condition than the out-of-phase condition. Comparisons were also made with the previously available tension–tension E/M fatigue results. In-phase results showed less damage of the PZT in tension–compression tests than in tension–tension tests. This was because in the tension–tension E/M fatigue loading there was no repoling of the PZT, but in the tension–compression case there was a continual repoling during cycling from the applied external voltage. In the out-of-phase E/M fatigue, the tension–compression case was worse for the PZT than the tension–tension E/M fatigue since relatively greater damage was done to the PZT from the tension–compression cyclic loads than tension–tension cyclic loads.

Ferroelectric ceramic samples of PbTiO₃, prepared by a modified oxide-mixing technique, were examined by x-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques for crystalline and microstructural characterization. XRD clearly revealed only a monophasic perovskite of tetragonal symmetry for the reference PbTiO₃, which was established to possess both a–a-and a–c-type 90° domains. The inclination was approximately 2° between the two different domains, as observed by high-resolution TEM. Inductively coupled plasma (ICP) analysis, electron probe microanalysis (EPMA), and x-ray photoelectron spectroscopy (XPS) were employed and the ensuing chemical composition results are discussed. The approximate molar ratios of Pb:Ti were 1:1, 1:1.5, and 1:0.8 as obtained by ICP analysis, EPMA, and XPS, respectively. Corrections for the sensitivity factor (S_Corr) for Pb 4f, Ti 2p and the substitution of the matrix factors for F_Ti,Pb, F_Pb,Ti have been taken into account in obtaining the Pb:Ti ratio of 1:1 by XPS quantification. The sensitivity factor (S_Kratos) given by the instrumental maker was compared with the theoretical one (S_Theo) and the result is also discussed.

This paper deals with a class of functionally graded materials (FGMs) called active FGM that has electro-thermo-elastically graded material phases. The focus is on the characterization of active FGM under electrical and thermal fields. The structure comprises a substrate, an electro-thermo-elastically graded layer and an active layer. Using augmented piezoelectric constitutive law, the effect of temperature on the piezoelectric properties is incorporated in the model. A formulation for exact solutions of the system based on Euler–Bernoulli theory is presented. Polynomial compositional variations of the constituent phases in the graded layer are considered and their performance for a range of stiffness and electrical property ratios of the active and substrate materials is studied under electrical and thermal fields. The effect of temperature dependence of piezoelectric coefficients on the stress distribution in the active FGM is discussed. It is also observed that the compositional variation significantly influences the actuation authority of graded materials depending on the modular ratio of the constituent materials.

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

The effect of the phase of harmonic actuation on the stress intensity factor (SIF) for delaminated composites with embedded piezoelectric (PZT) layers is studied. A plane-stress finite-element model using a four-node quadrilateral element having one active degree of freedom per node is developed. A fracture mechanics-based approach, which uses a general purpose computational scheme to obtain the strain energy release rate and the SIF due to delamination in orthotropic laminated composite, is employed. The performance of the finite-element result is first validated using the results reported in published literature. A composite double cantilever beam specimen with three embedded PZT layers around the tip of the delamination is considered for actuation. Numerical simulations on the effects of actuation voltage and phase on mode-II SIF are carried out. The results show that for a specified voltage amplitude to the embedded actuators, the actuation phase can have a significant influence on delamination growth.

A matrix formulation is presented for the solution of frictionless contact problems on arbitrarily multilayered piezoelectric half-planes. Different arrangements of elastic and piezoelectric materials with hexagonal symmetry within the layered medium are considered. A generalized plane deformation is used to obtain the governing equilibrium equations for each individual layer. These equations are solved using the infinite-Fourier-transform technique. The problem is then reformulated using the local/global stiffness method, in which a local stiffness matrix relating the stresses and electric displacements to the mechanical displacements and electrical potentials in the transformed domain is formulated for each layer. Then it is assembled into a global stiffness matrix for the entire half-plane by enforcing interfacial continuity of traction forces and displacements. This local/global approach not only eliminates the necessity of explicitly finding the unknown Fourier coefficients, but also allows the use of efficient numerical algorithms, many of which have been developed for finite-element analysis. Unlike finite-element methods, the local/global stiffness approach requires minimal input. Application of the mixed boundary conditions reduces the problem to a singular integral equation. This integral equation is then numerically solved for the unknown contact pressure using a collocation technique. Knowledge of the contact pressure and electrostatic distributions is very important for applications where piezoelectric layers are used as sensors and/or actuators. One example includes the active deformation and shape control of support surfaces.

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

The application of the impedance method and the transfer function method to detect disbonds in bonded repairs has been investigated using finite-element analysis. The damages simulated are typical disbonds that can occur in bonded repairs. This paper shows that both the impedance method and the transfer function method can be used to detect disbond growth under the repair patch within the limitations set out. By strategically locating the sensor and actuator pair, the location, type and severity of a disbond in a repair patch can be determined.

Shape memory alloy (SMA) wires were integrated within E-glass composite beams. The fiber volume fraction of the SMA material was 10%. Several baseline beams (without SMA reinforcement) were also fabricated. Both the baseline and SMA-reinforced composite beams were tested to failure in tension. The SMA-reinforced beams were tested in both the martensite phase (room temperature) and the austenite phase (75 °C). The test results indicated that SMA-reinforced composites can offer significant increase in the strain energy absorption prior to failure, thereby improving the fracture toughness and 'crashworthiness' of such systems. A significant increase in damping was also observed for the SMA-reinforced composite when the wires were transformed from the martensite to the austenite phase by resistive heating.

Finite element formulations are derived for static and dynamic analysis and the control of functionally graded material (FGM) plates under environments subjected to a temperature gradient, using linear piezoelectricity theory and first-order shear deformation theory. The multi-input–multi-output (MIMO) system with four collocated sensors and actuators is applied to provide active feedback control of the integrated FGM plate in a closed loop system. The distributed piezoelectrical sensors monitor the structural deformation due to the direct piezoelectrical effect and the distributed actuators control the deformation via the converse piezoelectrical effect. Numerical results for the static and dynamic control have been presented for the FGM plate, which consists of zirconia and aluminum. The purpose of the examples, which consist of a FGM plate with four collocated sensors and actuators used as MIMO system, is to determine the optimum configurations of the sensor/actuator pairs under various thermal and mechanical load fields.

BaTi₅O₁₁ powders with microwave dielectric application potentials were synthesized using the homogeneous precipitation method and characterized. The precursor of the powders was prepared by co-precipitation of a solution of barium and titanium species with oxalic acid at a temperature of 80 °C and subsequent calcination at different temperatures. The phase evolution and characteristics of the samples were studied using differential thermal analysis, Fourier transform infrared spectroscopy, x-ray diffractometry, and transmission electron diffraction. The results show that formation of BaTi₅O₁₁ starts around 700 °C and continues until 1100 °C in air, and in this calcination temperature range all powders appear to be single-phase, monoclinic BaTi₅O₁₁. Scanning electron microscopy and transmission electron microscopy observations reveal that the sizes of the particles, nearly round in shape, formed due to agglomeration, are about 100 nm at a calcination temperature of 700 °C, and 600 nm at 1100 °C.

This note assesses the impact of the quality of the bonding layer on the sensing capability of plane piezoelectric patches. The bonding layer between the piezoelectric material and the main structure is assumed to be elastic, having a finite stiffness and considerable thickness as compared to the thickness of the piezoelectric sensor. The equations governing the mechanical equilibrium are simplified by assuming a pure shear stress state in the bonding film. The equilibrium equations are derived, the associated functional is obtained and, subsequently, the finite-element method is employed to solve the problem in two dimensions. The displacements found are those occurring on the contact surface between the bonding film and the piezoelectric sensor. The numerical solution obtained in terms of displacements allows the calculation of the effective voltage 'observed' by the piezoelectric sensor. This investigation addresses shear lag effects and shows that end-bonding must be carefully assessed in order to enhance the quality of the sensing output.