Table of contents

Active fiber composites (AFC) composed of lead zirconate titanate (PZT) fibers embedded in an epoxy matrix and sandwiched between two interdigitated electrodes provide a thin and flexible smart material device which can act as a sensor or actuator. The thin profiles of AFC make them ideal for integration in glass or carbon fiber composite laminates. However, due to the low tensile limit of the PZT fibers, AFC can fail at strains below the tensile limit of many composites. This makes their use as a component in an active laminate design somewhat undesirable. In the current work, tensile testing of smart laminates composed of AFC integrated in glass fiber laminates was conducted to assess the effectiveness of different packaging strategies for improving AFC sensor performance at high strains relative to the tensile limit of the AFC. AFC were encased in carbon fiber, silicon, and pre-stressed carbon fiber to improve the tensile limit of the AFC when integrated in glass fiber laminates. By laminating AFC with pre-stressed carbon fiber, the tensile limit and strain sensor ability of the AFC were significantly improved. Acoustic emission monitoring was used and the results show that PZT fiber breakage was reduced due to the pre-stressed packaging process.

In this work, a periodic 4 × 4 lay-out of resistive inductive (RL) shunted piezoelectric transducer (PZT) patches is designed and applied to achieve broadband vibration reduction of a flexible isotropic plate over tunable frequency bands. Each surface-bonded PZT patch is connected to a single independent RL circuit and all shunt circuits are tuned at the same frequency. A finite element-based design methodology is used to predict the attenuation properties of the unit cell that characterize the periodic assembly. The predictions are experimentally validated by measuring the spatial average harmonic response of the plate. Significant broadband attenuation is obtained over frequency bands centered at the resonance frequency of the shunting circuit.

In this paper, we analytically and experimentally study the energy harvesting capability of submerged ionic polymer metal composites (IPMCs). We consider base excitation of an IPMC strip that is shunted with an electric impedance and immersed in a fluid environment. We develop a modeling framework to predict the energy scavenged from the IPMC vibration as a function of the excitation frequency range, the constitutive and geometric properties of the IPMC, and the electric shunting load. The mechanical vibration of the IPMC strip is modeled through Kirchhoff–Love plate theory. The effect of the encompassing fluid on the IPMC vibration is described by using a linearized solution of the Navier–Stokes equations, that is traditionally considered in modeling atomic force microscope cantilevers. The dynamic chemo-electric response of the IPMC is described through the Poisson–Nernst–Planck model, in which the effect of mechanical deformations of the backbone polymer is accounted for. We present a closed-form solution for the current flowing through the IPMC strip as a function of the voltage across its electrodes and its deformation. We use modal analysis to establish a handleable expression for the power harvested from the vibrating IPMC and to optimize the shunting impedance for maximum energy harvesting. We validate theoretical findings through experiments conducted on IPMC strips vibrating in aqueous environments.

Corrosion is a representative modality of damage in metallic structures serving in humid or corrosive environments, and examples include petroleum pipelines immersed underwater or buried underground. To facilitate awareness of corrosion at its initial stage is a key measure to prevent further deterioration and failure of these structures. A damage identification approach capitalizing on the fundamental anti-symmetric Lamb wave mode (A₀) and in terms of a pulse-echo measurement scheme was developed for evaluating corrosion in submerged structures. However the presence of a coupled fluid medium and changes in its properties exert influence on the propagation characteristics of the A₀ mode in the structures at a phenomenal level, leading to erroneous identification without appropriate rectification. Allowing for this, the effect arising from fluid coupling on the A₀ mode was investigated and calibrated quantitatively, whereby rectification and compensation were applied to the identification. The proposed approach was numerically and experimentally validated by evaluating through-thickness hole and chemical corrosion in submerged aluminium plates, with the assistance of a probability-based diagnostic imaging approach. Identification results have demonstrated the necessity of rectification and compensation for the medium coupling effect when applying Lamb-wave-based damage identification to structures with coupled media.

The concept of vibration controllability with smart fluids within flexible structures has been of significant interest in the past two decades. Although much research has been done on structures with embedded electrorheological (ER) fluids, there has been little investigation of magnetorheological (MR) fluid adaptive structures. In particular, a body of research on the experimental work of cantilever MR beams is still lacking. This experimental study investigates the controllability of vibration characteristics of magnetorheological cantilever sandwich beams. These adaptive structures are produced by embedding an MR fluid core between two elastic layers. The structural behaviour of the MR beams can be varied by applying an external magnetic field to activate the MR fluid. The stiffness and damping structural characteristics are controlled, demonstrating vibration suppression capabilities of MR fluids as structural elements. MR beams were fabricated with two different materials for comparison purposes. Diverse excitation methods were considered as well as a range of magnetic field intensities and configurations. Moreover, the cantilever MR beams were tested in horizontal and vertical configurations. The effects of partial and full activation of the MR beams were outlined based on the results obtained. The controllability of the beam's vibration response was observed in the form of variations in vibration amplitudes and shifts in magnitudes of the resonant natural frequency.

Thermo-mechanical investigations on a segmented poly(ester urethane) have shown that the material displays triple-shape functionality: gradual heating of programmed specimens leads first to the transformation from shape (A) to shape (B) and later from shape (B) back to permanent shape (C). In the essential two-step programming process, the first deformation state (B) is stabilized by crystallized soft segments at T<T_c, the second one (A) through the polymer's glassy state at T<T_g. The transition temperatures, as analyzed for the permanent-shaped polymer via DSC, are T_g≈−49 °C and T_m(onset)≈34 °C; the material crystallizes when cooled at T_c(onset)≈4 °C. For the characterization of the material's cyclic thermo-mechanical triple-shape properties, maximum deformations of ε_m1 = 100% for shape (B) and ε_m2 = 130% for shape (A) were tested. In cycles N = 2–5 averaged shape fixing abilities of 74% (shape A, −60 °C), 109% (shape B, 23 °C) and shape recoverabilities of 103% (A B) and 96% (B C) could be detected. Values larger than 100% indicate the occurrence of plastic deformation during the second stretching.

Surface-bonded lead zirconate titanate (PZT) transducers have been widely used for guided wave generation and measurement. For selective actuation and sensing of Lamb wave modes, the sizes of the transducers and the driving frequency of the input waveform should be tuned. For this purpose, a theoretical Lamb wave tuning curve (LWTC) of a specific transducer size is generally obtained. Here, the LWTC plots each Lamb wave mode' amplitude as a function of the driving frequency. However, a discrepancy between experimental and existing theoretical LWTCs has been observed due to little consideration of the bonding layer and the energy distribution between Lamb wave modes. In this study, calibration techniques for theoretical LWTCs are proposed. First, a theoretical LWTC is developed when circular PZT transducers are used for both Lamb wave excitation and sensing. Then, the LWTC is calibrated by estimating the effective PZT size with PZT admittance measurement. Finally, the energy distributions among symmetric and antisymmetric modes are taken into account for better prediction of the relative amplitudes between Lamb wave modes. The effectiveness of the proposed calibration techniques is examined through numerical simulations and experimental estimation of the LWTC using the circular PZT transducers instrumented on an aluminum plate.

The aim of this paper is to capture the grain boundary effects taking into consideration the nonlinear dissipative effects of ferroelectric polycrystals based on firm thermodynamic principles. The developed micromechanically motivated model is embedded into an electromechanically coupled finite element formulation in which each grain is represented by a single finite element. Initial dipole directions are assumed to be randomly oriented to mimic the virgin state of the unpoled ferroelectric polycrystal. An energy-based criterion using Gibbs free energy is adopted for the initiation of the domain switching process. The key aspect of the proposed model is the incorporation of effects of the constraint imposed by the surrounding grains on a switching grain. This is accomplished by the inclusion of an additional term in the domain switching criterion that is related to the gradient of the driving forces at the boundary of the grains. To study the overall bulk ceramics behavior, a simple volume-averaging technique is adopted. It turns out that the simulations based on the developed finite element formulation with grain boundary effects are consistent with the experimental data reported in the literature.

Displacement current is associated with the generation of magnetic fields due to time-varying electric fields. The harmonic response of a magneto-electro-elastic axisymmetric cylinder accounting for displacement current is carried out using the semi-analytical finite element method. The non-conservative electric field is represented using a magnetic vector potential. Studies are carried out for the first circumferential harmonics of the shell structure with the clamped–free boundary condition. The contribution made to the magnetic flux density by the electric displacement current is very small at lower frequencies but it becomes significant at higher frequencies.

The elastic properties of Cu–Al–Ni single crystals have been studied during forward and reverse martensitic transformation by dynamic mechanical analysis. Measurements were performed for two alloys, occurring in austenitic (Cu–14%Al–4%Ni) and martensitic (Cu–13.7%Al–3%Ni) phases at room temperature. Investigation of elastic and damping properties was performed for several frequencies of the oscillating force. Evolution of damping in cooling/heating measurements gave information about internal friction during forward and reverse martensitic phase transformations. Characteristic temperatures of martensitic transformation were determined by dynamic mechanical analysis and compared with optical micrographs of samples' surfaces and with previous results from differential scanning calorimetry. In addition, comparison of elastic properties in pure austenitic and martensitic phase during ageing was made. The paper presents a step-by-step analysis of experimental results showing the causes which lead to observed changes of elastic properties at martensitic transformation or with time.

To investigate the toughness enhancing effect of a floating electrode on an actuator, a conventional actuator and an actuator with a floating electrode are numerically analyzed using the finite element method. Electrostatic analysis is performed for both types of actuators based on an assumption of the mathematical equivalence between out-of-plane deformation and electrostatics. The electric behavior of a ceramic is idealized by the electric displacement saturation model. The numerical results of electric fields and electric displacement fields are obtained from the electrostatic analysis. For both types of actuators, the self-equilibrating stress fields induced by a non-uniform distribution of the electric displacement fields are computed using the finite element method. The stress intensity factors for a flaw-like crack nucleated from the edge of an internal electrode are evaluated for each case. We found that the stress intensity factor for the actuator with a floating electrode is smaller than the factor for the conventional actuator when the length of the flaw-like crack is approximately equal to the grain size. Thus, we conclude that actuators with floating electrodes have higher reliability than conventional actuators.

This paper studies the nonlinear vibration of a clamped–clamped microresonator under combined electric and piezoelectric actuations. The electric actuation is induced by applying an AC–DC voltage between the microbeam and the electrode plate that lies on opposite sides of the microbeam, and the piezoelectric actuation is induced by applying the DC voltage between upper and lower sides of the piezoelectric layer deposited on the microbeam length. It is assumed that the neutral axis of bending is stretched when the microbeam is deflected. The equations of motion are derived using Newton's second law, and are solved using the multiple-scale perturbation method. It is shown that, depending on the value of DC electric and piezoelectric actuations, geometry and the bending stiffness of the system. A softening or hardening behavior may be realized. It demonstrates that nonlinear behavior of an electrically actuated microresonator may be tuned to a linear behavior by applying a convenient DC electric voltage to the piezoelectric layer, and so an undesirable shift of resonance frequency may be removed. If one lets the applied voltage to the piezoelectric layer be equal to zero, this paper would be an effort to tailor the linear and nonlinear stiffness coefficients of two layered electrically actuated microresonators without the assumption that the lengths of the two layers are equal.

Magnetorheological (MR) materials exhibit rapid variations in their rheological properties when subjected to varying magnetic field and thus offer superior potential for applications in smart structures requiring high bandwidth. MR sandwich structures can apply distributed control force to yield variations in stiffness and damping properties of the structure in response to the intensity of the applied magnetic field and could thus provide vibration suppression over a broad range of external excitation frequencies. This study investigates the properties of a multi-layered beam with MR fluid as a sandwich layer between the two layers of the continuous elastic structure. The governing equations of a multi-layer MR beam are formulated in the finite element form and using the Ritz method. A free oscillation experiment is performed to estimate the relationship between the magnetic field and the complex shear modulus of the MR materials in the pre-yield regime. The validity of the finite element and Ritz formulations developed is examined by comparing the results from the two models with those from the experimental investigation. Various parametric studies have been performed in terms of variations of the natural frequencies and loss factor as functions of the applied magnetic field and thickness of the MR fluid layer for various boundary conditions. The forced vibration responses of the MR sandwich beam are also evaluated under harmonic force excitation. The results illustrate that the natural frequencies could be increased by increasing the magnetic field while the magnitudes of the peak deflections could be considerably decreased, which demonstrates the vibration suppression capability of the MR sandwich beam.

The guided wave (GW) field excited by piezoelectric wafers and piezocomposite transducers in carbon-fiber composite materials is experimentally investigated with applications to structural health monitoring. This investigation supports the characterization of the composite long-range variable-length emitting radar (CLoVER) transducer introduced by the authors. A systematic approach is followed where composite configurations with different levels of anisotropy are analyzed. In particular, unidirectional, cross-ply [0/90]_3S and quasi-isotropic [0/45/–45/90]_2S IM7-based composite plates are employed. A combination of laser vibrometry and finite element analysis is used to determine the in-plane wave speed and peak-to-peak amplitude distribution in each substrate considered. The results illustrate the effect of the material anisotropy on GW propagation through the steering effect where the wavepackets do not generally travel along the direction in which they are launched. After characterizing the effect of substrate anisotropy on the GW field, the performance of the CLoVER transducer to detect damage in various composite configurations is explored. It is found that the directionality and geometry of the device is effective in detecting the presence and identifying the location of simulated defects in different composite layups.

Use of surface-mounted piezoelectric actuators to generate acoustic ultrasound has been demonstrated to be a key component of built-in nondestructive detection evaluation (NDE) techniques, which can automatically inspect and interrogate damage in hard-to-access areas in real time without disassembly of the structural parts. However, piezoelectric actuators create complex waves, which propagate through the structure. Having the capability to model piezoelectric actuator-induced wave propagation and understanding its physics are essential to developing advanced algorithms for the built-in NDE techniques. Therefore, the objective of this investigation was to develop an efficient hybrid spectral element for modeling piezoelectric actuator-induced high-frequency wave propagation in thin plates. With the hybrid element we take advantage of both a high-order spectral element in the in-plane direction and a linear finite element in the thickness direction in order to efficiently analyze Lamb wave propagation in thin plates. The hybrid spectral element out-performs other elements in terms of leading to significantly faster computation and smaller memory requirements. Use of the hybrid spectral element is proven to be an efficient technique for modeling PZT-induced (PZT: lead zirconate titanate) wave propagation in thin plates. The element enables fundamental understanding of PZT-induced wave propagation.

In this study, we demonstrate the full-spectral interrogation of a fiber Bragg grating (FBG) sensor at 535 Hz. The sensor is embedded in a woven, graphite fiber–epoxy composite laminate subjected to multiple low-velocity impacts. The measurement of unique, time dependent spectral features from the FBG sensor permits classification of the laminate lifetime into five regimes. These damage regimes compare well with previous analysis of the same material system using combined global and local FBG sensor information. Observed transient spectral features include peak splitting, wide spectral broadening and a strong single peak at the end of the impact event. Such features could not be measured through peak wavelength interrogation of the FBG sensor. Cross-correlation of the measured spectra with the original embedded FBG spectrum permitted rapid visualization of average strains and the presence of transverse compressive strain on the optical fiber, but smeared out the details of the spectral profile.

This paper presents a three-dimensional (3D) nonlinear quasi-static isothermal finite element formulation for single crystals of Ni–Mn–Ga ferromagnetic shape memory alloy (FSMA). This formulation is directly coupled (strong coupling) between the magnetic vector potential and mechanical displacement. As a result this formulation is applicable to general structural configurations, where the mechanical and magnetic behaviour of the entire structural and magnetic system can be computed simultaneously. This finite element formulation has the potential for applications that require accurate prediction of the magnetic field distribution and strain response of Ni–Mn–Ga single crystals. One of the major advantages of this finite element formulation is the ability to predict the behaviour of the material for generalized or complicated shapes and geometries where analytical methods may not be adequate.

The two-dimensional nonlinear finite element analysis computer software MAGSTRAN (magnetic structural analysis) is developed based on this formulation. Numerical results for selected examples are validated against experimental data available in the literature. It is demonstrated that there is reasonable correlation between MAGSTRAN results and experimental data available in the literature.

This paper is devoted to the study of the decentralized guaranteed cost static output feedback vibration control for piezoelectric smart structures. A smart panel with collocated piezoelectric actuators and velocity sensors is modeled using a finite element method, and then the size of the model is reduced in the state space using the modal Hankel singular value. The necessary and sufficient conditions of decentralized guaranteed cost static output feedback control for the reduced system have been presented. The decentralized and centralized static output feedback matrices can be obtained from solving two linear matrix inequalities. A comparison between centralized control and decentralized control is performed in order to investigate their effectiveness in suppressing vibration of a smart panel. Numerical results show that when the system is subjected to initial displacement or white noise disturbance, the decentralized and centralized controls are both very effective and the control results are very close.

The condition of civil infrastructure systems (CIS) changes over their life cycle for different reasons such as damage, overloading, severe environmental inputs, and ageing due normal continued use. The structural performance often decreases as a result of the change in condition. Objective condition assessment and performance evaluation are challenging activities since they require some type of monitoring to track the response over a period of time. In this paper, integrated use of video images and sensor data in the context of structural health monitoring is demonstrated as promising technologies for the safety of civil structures in general and bridges in particular. First, the challenges and possible solutions to using video images and computer vision techniques for structural health monitoring are presented. Then, the synchronized image and sensing data are analyzed to obtain unit influence line (UIL) as an index for monitoring bridge behavior under identified loading conditions. Subsequently, the UCF 4-span bridge model is used to demonstrate the integration and implementation of imaging devices and traditional sensing technology with UIL for evaluating and tracking the bridge behavior. It is shown that video images and computer vision techniques can be used to detect, classify and track different vehicles with synchronized sensor measurements to establish an input–output relationship to determine the normalized response of the bridge.

A shape memory alloy (SMA) with a composition of Ni₆₀Ti₄₀ (wt%) was chosen for the fabrication of active beam elements intended for use as cyclic actuators and incorporated into a morphing aerospace structure. The active structure is a variable-geometry chevron (VGC) designed to reduce jet engine noise in the take-off flight regime while maintaining efficiency in the cruise regime. This two-part work addresses the training, characterization and derived material properties of the new nickel-rich composition, the assessment of the actuation properties of the active beam actuator and the accurate analysis of the VGC and its subcomponents using a model calibrated from the material characterization.

The characterization performed in part I of this work was intended to provide quantitative information used to predict the response of SMA beam actuators of the same composition and with the same heat treatment history. Material in the form of plates was received and ASTM standard tensile testing coupons were fabricated and tested. To fully characterize the material response as an actuator, various thermomechanical experiments were performed. Properties such as actuation strain and transformation temperatures as a function of applied stress were of primary interest. Results from differential scanning calorimetry, monotonic tensile loading and constant stress thermal loading for the as-received, untrained material are first presented. These show lower transformation temperatures, higher elastic stiffnesses (60–90 GPa) and lower recoverable transformation strains (≈1.5%) when compared to equiatomic NiTi (Nitinol). Stabilization (training) cycles were applied to the tensile specimens and characterization tests were repeated for the stable (trained) material. The effects of specimen training included the saturation of cyclically generated irrecoverable plastic strains and a broadening of the thermal transformation hysteresis. A set of final derived material properties for this stable material is provided. Finally, the actuation response of a structural beam component composed of the same material given the same thermomechanical processing conditions was assessed by applying a constant bias load and a variable bias load as thermal actuation cycles were imposed.

A shape memory alloy (SMA) composition of Ni₆₀Ti₄₀ (wt%) was chosen for the fabrication of active beam components used as cyclic actuators and incorporated into morphing aerospace structures. The active structure is a variable-geometry chevron (VGC) designed to reduce jet engine noise in the take-off flight regime while maintaining efficiency in the cruise regime. This two-part work addresses the training, characterization and derived material properties of the new nickel-rich NiTi composition, the assessment of the actuation properties of the active beam actuator and the accurate analysis of the VGC and its subcomponents using a model calibrated from the material characterization.

The second part of this two-part work focuses on the numerical modeling of the jet engine chevron application, where the end goal is the accurate prediction of the VGC actuation response. A three-dimensional (3D) thermomechanical constitutive model is used for the analysis and is calibrated using the axial testing results from part I. To best capture the material response, features of several SMA constitutive models proposed in the literature are combined to form a new model that accounts for two material behaviors not previously addressed simultaneously. These are the variation in the generated maximum actuation strain with applied stress level and a smooth strain–temperature constitutive response at the beginning and end of transformation. The accuracy of the modeling effort is assessed by comparing the analysis deflection predictions for a given loading path imposed on the VGC or its subcomponents to independently obtained experimental results consisting of photogrammetric data. For the case of full actuation of the assembled VGC, the average error in predicted centerline deflection is less than 6%.

Electromagnetic (EM) energy harvesting seems to be one of the most promising ways to power wireless sensors in a wireless sensor network. In this paper, FR4, the most commonly used PCB material, is utilized as a mechanical vibrating structure for EM energy harvesting for body-worn sensors and intelligent tire sensors, which involve impact loadings. FR4 can be a better material for such applications compared to silicon MEMS devices due to lower stiffness and broadband response. In order to demonstrate FR4 performance and broadband response, three moving magnet type EM generator designs are developed and investigated throughout the paper. A velocity-damped harvester simulation model is first developed, including a detailed magnetic model and the magnetic damping effects. The numerical results agree well with the experimental results. Human running acceleration at the hip area that is obtained experimentally is simulated in order to demonstrate system performance, which results in a scavenged power of about 40  µW with 15 m s⁻² acceleration input. The designed FR4 energy scavengers with mechanical stoppers implemented are particularly well suited for nearly periodic and non-sinusoidal high- g excitations with rich harmonic content. For the intelligent tire applications, a special compact FR4 scavenger is designed that is able to withstand large shocks and vibrations due to mechanical shock stoppers built into the structure. Using our design, 0.4 mW power across a load resistance at off-resonance operation is obtained in shaker experiments. In the actual operation, the tangential accelerations as a result of the tire–road contact are estimated to supply power around 1 mW with our design, which is sufficient for powering wireless tire sensors. The normalized power density (NPD) of the designed actuators compares favorably with most actuators reported in the literature.