Table of contents

This paper discusses the investigation of vibration suppression capabilities of magnetorheological (MR) materials in adaptive structures. Homogeneous three-layered adaptive beams with MR materials sandwiched between two elastic layers were considered. By varying the externally applied magnetic field level over the MR layer, the stiffness and damping properties of the adaptive beam can be varied. These variations in the damping and stiffness properties can be used to tune the vibration characteristics of the adaptive beams such as natural frequencies, vibration amplitudes, mode shapes and loss factors. In this study, theoretical investigation of the MR adaptive beams vibration behavior based on the energy approach is accomplished. Experiments were performed to observe the theoretically predicted vibration responses in real time. From both studies, vibration suppression capabilities of MR adaptive beams were observed in the forms of shifts in natural frequency values, variations in loss factors, and vibration amplitudes.

The paper develops approximate closed-form equations for the torsional stiffness of several variable rectangular cross-section flexure hinges for macro-scale and MEMS applications. Specifically, corner-filleted, elliptic, parabolic and hyperbolic flexure configurations, either longitudinally symmetric or non-symmetric, are studied. The model gives the tools for a preliminary assessment of the static/modal response of flexure-based devices that deform torsionally. Several numerical simulations are conducted based on the model, which indicate that, for similar values of the geometric parameters, the hyperbolic flexure is the stiffest, followed by the parabolic, corner-filleted and elliptic configurations. The modal response is studied for a two-flexure torsional micro-mirror by sequentially considering four different pairs of longitudinally symmetric flexure designs. The results of the simulation confirm the stiffness predictions and are also in agreement with finite element analysis results.

The non-destructive evaluation technique using a piezoceramic (PZT) as an actuator–sensor has a potential to efficiently detect structural damage. In this technique, a PZT actuator–sensor patch is bonded on a structure. Through the measurement of its electrical impedance, which is related to the mechanical impedance of the structure being bonded, the change in structural properties due to damage can be detected. This paper presents the use of a PZT actuator–sensor in conjunction with numerical model-based methodology in structural health monitoring to quantitatively detect damage of bolted joints. The structure used in this study consists of two aluminium beams connected by a bolted joint. The damage was simulated by loosening the bolts. To quantitatively monitor the damage, a numerical model of the structure was formulated. A spectral element method (SEM), based on a wave propagation approach, was used to model the structure. A bonded-PZT beam and a bolted joint element were developed by using the SEM. The equations of motion were derived by using Hamilton's principle and then the spectral element matrices were formulated. Experimental results show the effectiveness of this method to detect the damage. By using the proposed model, the loosening of bolts can be quantitatively identified as the change in stiffness and damping at the bolted joint, indicating a high potential of this method in order to quantitatively monitor structural damage.

Maintaining the surface shape of precision structures such as spacecraft antenna reflectors has been a challenging task. Surface errors are often introduced by thermal distortions due to temperature differences. This paper presents numerical and experimental results of active compensation of thermal deformation of a composite beam using piezoelectric ceramic actuators. To generate thermal distortion of the composite beam, two film heaters are bonded to only one side of the beam using thermally conductive materials. To correct thermal deformation caused by the film heaters, PZT (lead zirconate titanate), a type of a piezoelectric ceramic material, is used in the form of patches as actuators. These PZT patches are bonded on the other side of the beam. First, finite-element analyses are conducted with consideration of the coupled effects of structural, electric and thermal fields on the composite beam. These analyses include static coupled field modeling of the beam deformation with PZT actuation, transient modeling of the beam under thermal loading, and static coupled field modeling of the composite beam with thermal distortion and simultaneous PZT actuation to correct this distortion. Then, experiments are conducted to study the thermal effect, the PZT actuation effect and active thermal distortion compensation using PZT actuators with a proportional, integral and derivative feedback controller. Finite-element modeling and experimental results agree well and demonstrate that the proposed method can actively perform structural shape control in the presence of thermal distortion.

The concept of microwave-driven smart material actuators was envisioned and developed as the best option to alleviate the complexity and weight associated with a hard-wire-networked power and control system for smart actuator arrays. The patch rectenna array was initially designed for high current output, but has undergone further development for high voltage output devices used in shape control applications. Test results show that more than 200 V of output were obtained from a 6 × 6 array at a far-field exposure (1.8 m away) with an X-band input power of 18 W. The 6 × 6 array patch rectenna was designed to theoretically generate voltages up to 540 V, but practically it has generated voltages in the range between 200 and 300 V. Testing was also performed with a thin layer composite unimorph ferroelectric driver and sensor and electro-active paper as smart actuators attached to the 6 × 6 array. Flexible dipole rectenna arrays built on thin-film-based flexible membranes are most applicable for NASA's various missions, such as microwave-driven shape controls for aircraft morphing and large, ultra-lightweight space structures. An array of dipole rectennas was designed for high voltage output by densely populating Schottky barrier diodes to drive piezoelectric or electrostrictive actuators. The dipole rectenna array will eventually be integrated with a power allocation and distribution logic circuit and microbatteries for storage of excessive power. The roadmap for the development of wireless power drivers based on the rectenna array for shape control requires the development of new membrane materials with proper dielectric constants that are suitable for dipole rectenna arrays.

This paper illustrates various dynamic characteristics of open cell compliant polyurethane foam with auxetic (negative Poisson's ratio) behaviour. The foam is obtained from off-the-shelf open cell polyurethane grey foam with a manufacturing process based on mechanical deformation on a mould in a temperature-controlled oven. The Poisson's ratio is measured with an image processing technique based on edge detection with wavelet methods. Foam samples have been tested in a viscoelastic analyser tensile test machine to determine the Young's modulus and loss factor for small dynamic strains. The same samples have also been tested in an acoustic impedance tube to measure acoustic absorption and specific acoustic resistance and reactance with a transmissibility technique. Another set of tests has been set up on a cam plastometer machine for constant strain rate dynamic crushing analysis. All the tests have been carried out on auxetic and normal foam samples to provide a comparison between the two types of cellular solids. The results from the experimental tests are discussed and interpreted using microstructure models for cellular materials existing in the literature. The negative Poisson's ratio foam presented in this paper shows an overall superiority regarding damping and acoustic properties compared to the original conventional foam. Its dynamic crushing performance is also significantly superior to the normal foam, suggesting a possible use in structural integrity compliant elements.

The extremely small size of the micro-electromechanical systems (MEMS) makes them widely suitable for some special applications. The simplicity of the piezoelectric micro-generators is attractive for MEMS applications, especially for remote systems. In this paper, a general concept of the piezoelectric energy conversion is first given. A simple design modeling and analysis of the '31' transverse mode type piezoelectric micro-generator is presented. The output power is taken as the indicated parameters for the generator. The energy conversion efficiency of the generator, which is dependent on the operation frequency, is expressed in the frequency domain. A case study of laminated type micro-generators using PZT-PIC 255 for MEMS applications is given and the use of single crystal PZN-8%PT is also studied for comparison. Some design guidelines are presented based on the simulation results.

Active control of the vibration of laminated circular cylindrical composite shells has been demonstrated using optimally placed patches of active constrained layer damping (ACLD) treatment. A finite element model has been derived to formulate the dynamics of the composite shells integrated with the patches of ACLD treatment. Optimal placements of the patches are determined by employing a modal controllability criterion to control the first two modes of vibration. The optimal size of the patches located at the optimal places has been determined on the basis of a frequency constraint. The performance of these patches in enhancing the damping of the symmetric cross-ply and angle-ply laminated shells has been illustrated with frequency response functions of the shells.

The aim of this study was to modify conventional reinforcing E-glass fibres to enable them to act as optical waveguides and subsequently as sensor devices. This required the glass fibres to be coated with a relatively homogeneous coating with a corresponding refractive index that was lower than the E-glass fibre (1.56). Although a range of coating materials are available, this study focused on using materials that are generally used as sizing agents for glass fibres to improve the adhesion to the matrix. Two different methods based on conventional sol–gel processing were used to obtain crack-free coatings. In the first method, tetraethoxysilane (TEOS) and polyvinyl alcohol were used as precursors. In the second method, acid-catalysed solutions of TEOS mixed with 3-glycidoxypropyltrimethoxysilane were used as precursors. UV–visible transmission results showed that the films had low absorption and high transparency in the visible range. The refractive indices of the films were found to be a function of the molar fractions of the major chemical components. A simple impregnation procedure was used to apply the coating to the E-glass fibre bundles. The light transmission characteristics of the coated fibres along with their mechanical properties were evaluated. The sol–gel coatings were shown to be effective in converting the conventional E-glass fibres into light guides.

An analytical model is developed for a segmented unimorph actuator consisting of electrostrictive P(VDF-TrFE) copolymer. The segmented actuator consists of individually controlled segments of the active polymer so that varying curvature along the length can be achieved. The analytical model incorporates large deflections and can be used to predict the free deflection and blocked force along the length of the actuator. The target application is active instruments for minimally invasive surgery (MIS), where steerable tool tips are needed to increase dexterity and provide nonlinear access. Results are presented to illustrate predicted free deflection and blocked force for various electric fields. An optimization procedure is also employed to design an actuator for maximum tip deflection, blocked force and out-of-plane stiffness. The predicted deflection performance of the optimized design is shown to be suitable for application to minimally invasive surgery.

Experimental studies on vibration control of a composite beam with a piezoelectric actuator and an extrinsic Fabry–Perot interferometer (EFPI) have been performed using a neural network controller. Because of their interferometric characteristics, EFPI sensors show non-linearity as dynamic amplitude increases. Within the linear range of EFPI, conventional control algorithms can be applied without serious difficulty. However, closed-loop control may make the target system unstable when sensor non-linearity gets high. Therefore, we examine the effects of the non-linearity of the sensor on the control stability and performance, and investigate any simple method applicable to the vibrations beyond the linear range. For this purpose, a neural controller is adopted and its performance is experimentally investigated. The neuro-controller showed good performance and adaptiveness to the sensor's non-linearity. Although the present neuro-controller is not a fundamental solution to vibration control of structural systems, it can be a simple practical choice for systems with sensor non-linearity.

Magnetorheological (MR) and electrorheological (ER) dampers are known to exhibit nonlinear behaviour which can make it difficult to predict their performance, particularly when they are integrated into engineering structures. As a result it can be impossible to properly assess the feasibility of using such semi-active devices to solve practical engineering problems.

In this paper, a new model format is proposed which represents an extension of earlier work by the authors. The proposed model is more general and yet maintains the physical significance of key parameters. A novel model updating (or system identification) technique is developed so that the model can account for the behaviour of various configurations of device without the need for prior knowledge of the fluid properties. The technique relies upon the iterative adjustment of the model's stiffness parameter so that the quasi-steady behaviour of the device can be estimated. Correlation between a bi-viscous model and the estimated quasi-steady behaviour is used as the criterion for choosing the most suitable value of stiffness. The modelling technique is completed by establishing empirical shape relationships between the pre-yield parameters, post-yield parameters, yield force and the applied excitation conditions.

The modelling and identification procedures are applied to an MR damping device and the results are validated by comparing predicted and experimental responses under both non-sinusoidal and broadband excitation conditions.

A brief description of the theory of passive and active absorbers is presented followed by details of an experimental study of a new design of adaptive absorber. The absorber is a single-layer planar structure based upon the topology of a Salisbury screen, but in which the conventional resistive layer is replaced by an active frequency selective surface (FSS) controlled by PIN diodes. The resulting structure has superior reflectivity–bandwidth characteristics compared to conventional passive absorbers of corresponding thickness. Experimental results are presented and compared to those obtained from a transmission line model, and show that the reflectivity response of the absorber can be dynamically controlled over the frequency band from 9 to 13 GHz.

In pipe vibration the n = 2 (ovalling mode) axial propagating wave causes a large increase of strain in the pipe wall at frequencies greater than its cut-on frequency (the frequency at which the wave starts to propagate axially). This wave readily propagates structure-borne noise and is difficult to control by passive means. In this paper, the active control of this wave is investigated. An n = 2 PVDF (polyvinylidene fluoride) modal sensor and PZT (lead zirconate titanate) modal actuator are used to selectively sense and control the wave. PVDF elements are shaped in the form of sine and cosine functions similar to the n = 2 mode shape of the pipe to form the modal sensor and the modal actuator is constructed from a set of PZT elements bonded to the pipe. Using these transducers the n = 2 wave can, in principle, be completely suppressed. Because this wave is dominant for a few tens of hertz after cut-on, this control strategy is extremely effective over a limited frequency range. Theoretical models for the actuator and sensor are described and experimental results demonstrating the effectiveness of the control system are presented.

The phase transformation behavior in hybrid shape memory alloy (SMA) composites under moderate compressive dynamic loads is being investigated. A hybrid SMA composite is described as a morphological or compositional arrangement of an SMA, and one or more passive or active materials. In this study, the hybrid SMA composite under consideration is assumed to be obtained by filling the pores of a porous SMA matrix with a polymeric material. Finite element simulations of a split Hopkinson bar test are performed to assess the effective hybrid SMA composite behavior under compressive strain rates of . The actual mesostructure of the material is incorporated in the analyses by synthesizing statistical information from x-ray computed micro-tomography (XCMT) images and utilizing it in probabilistic algorithms to insert representative pores in finite element meshes. A parametric study based on the volume fraction of pores and epoxy material is carried out for hybrid epoxy–SMA composite and plain porous SMA, respectively, and a comparison is performed.

The effectiveness of piezoelectric fiber reinforced composite (PFRC) material in the development of new actuators as elements of smart structures has been theoretically investigated. The piezoelectric fibers considered in this study are longitudinally oriented to yield the bending mode of actuation. Micromechanics is used to predict the effective mechanical properties and the effective electromechanical constant of such composites which gives rise to actuation in the fiber direction when subjected to an electric field transverse to the fiber direction. These effective properties are useful for the analysis of smart beams. A micromechanics study reveals that beyond a critical fiber volume fraction, this electromechanical constant is improved over that of the piezoelectric material alone. The performance of this new material used as distributed actuators has been investigated through active constrained layer damping (ACLD) of laminated composite beams in which the constraining layer is made of piezoelectric fiber reinforced composite. A finite element model has been developed to describe the dynamic behavior of a laminated composite beam coupled with active constrained layer damping (ACLD) treatment. The controlled response is illustrated through plots of frequency response functions. The results indicate that these new piezoelectric composites may be superior candidate materials for use in developing lightweight smart structures, as compared with the existing piezoelectric materials alone.

In this paper a signal processing technique is developed to detect delamination on composite structures. In particular, a wavelet-based signal processing technique is developed and combined with an active sensing system to produce a near-real-time, online monitoring system for composite structures. A layer of piezoelectric patches is used to generate an input signal with a specific wavelet waveform and to measure response signals. Then, the response signals are processed by a wavelet transform to extract damage-sensitive features from the original signals. The applicability of the proposed method to delamination identification has been demonstrated by experimental studies of a composite plate under varying temperature and boundary conditions.

A piezoelectric strip of finite width and thickness is placed on top of an isotropic elastic half-space. It operates in actuator mode and a time harmonic voltage is thus applied across it. The piezoelectric material is of type 6mm oriented so that a 2D antiplane (scalar) problem results. By Fourier series expansions the problem is solved exactly and this result is compared to the case when the piezoelectric strip is replaced by an effective boundary condition, which is derived by series expansions in the thickness coordinate in the piezoelectric strip. At low frequencies the results agree very well and this corresponds to the situation usually met in practice. In general, the effective boundary condition should be easier to apply and it is in particular noted that this is the case when using a FEM program where the option of a piezoelectric material is usually not available.

Underwater acoustical imaging techniques and the inverse analysis of acoustic scattering problems have now found many important engineering applications. Most of the inverse techniques use the backscattering signals in the acoustical far field to retrieve the shape and size information of an underwater object, such as the ramp response technique. This paper addresses a modified ramp response technique, which could be used to reconstruct the 3D image of an object for the bistatic case. This technique shows that the bistatic ramp response is proportional to the profile function of an underwater object based on the small bistatic angle assumption. The numerical examples demonstrate that the bistatic ramp response technique is still valid to obtain an excellent profile function even for the bistatic case with a fairly large bistatic angle. The numerical results also suggest that, if the object is of a more slender shape, then its bistatic ramp response will be closer to the exact profile function for a larger bistatic angle. Finally, a 3D image of a spheroid with a/b = 5 has been reconstructed using the bistatic ramp response signals in three incident directions. This bistatic ramp response technique allows us to reconstruct the 3D image of an underwater object with only one receiver.

This paper studies three-dimensional (3D) static responses of a multilayered anisotropic piezoelectric structure due to a point force and point charge. The materials in each layer are homogeneous, generally anisotropic, and linearly piezoelectric, and in general different from one another. The interfaces between adjacent layers are perfectly bonded. The generalized Stroh formalism and two-dimensional (2D) Fourier transforms are employed to find the responses in terms of a 2D integral. For a layered structure made of ten alternating layers of piezoelectric AlN and InN on an InN substrate, we show that the responses due to the point force and point charge are greatly influenced by the material layering, showing complicated patterns through the layer thickness. Furthermore, the responses exhibit the asymptotic behavior in the case of homogeneous infinite space/half-space in a very short distance to the point source, about one tenth of the layer thickness. The complicated responses due to the layered heterogeneity dictate the need for a general 3D analysis in the design of such smart structures.

A piezoelectric wafer has been widely used as a key component of actuators or sensors of a layer type. According to recent research, the piezoelectric wafer behaves in a nonlinear way under excessive electro-mechanical loadings. In the present paper, a simple one-dimensional model for the nonlinear behaviour of a piezoelectric wafer near a poled state is proposed, based on the principles of thermodynamics and a simple viscoplasticity theory. The constitutive model is rate-dependent as well as nonlinear. The predictions of the developed model are compared with experimental observations.

It was observed that the polyurethane shape memory polymer (SMP) loses its shape fixing capability after being exposed in the air at room temperature for several days. A significant indication for this change is the continuous decrease of the glass transition temperature (T_g) of polyurethane. Accompanying the decrease of T_g, the uniaxial tensile behaviour also changes. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) tests were carried out to find the cause behind this phenomenon. Moisture was concluded as the main reason. A mathematical expression was obtained for the relationship between T_g and the moisture. Moreover, the polyurethane shape memory polymer can fully regain its original properties after being heated at temperatures above 180 °C, which is the melting temperature of this SMP.

Adaptive composites, which consist of carbon fiber reinforced plastics (CFRP) and shape memory alloy (SMA) wires, have attracted much attention recently in the aerospace industry, etc. In the fabrication of such adaptive composites, CFRP and SMA wires must be cured at specific temperatures, either at 130 or 180 °C depending on the kind of matrix resin used. Since the curing temperature is much higher than the A_s (reverse transformation start) temperature of SMA, inconvenient special fixture jigs had to be used to keep SMA wires in the martensitic phase during the curing process, and thus restricted the shape and size of smart composites. Recently the present authors developed a new method for fabricating adaptive composites without using such fixture jigs. Although the method could be used for the curing temperature of 130 °C, it could not resolve the problem of the curing temperature of 180 °C. In the present paper we present a newer method, which has overcome the problem of the curing temperature of 180 °C by utilizing heavily cold-drawn ultrathin wires and low temperature heat-treatment.

An analytical prediction of dynamic performance for piezoelectric bimorph structures was investigated. A damping ratio was assumed and employed to determine dynamic peak amplitudes at resonances by finding the frequency with of the peak amplitude. Finite element simulations were used to validate the proposed improvement strategy. Results show that the peak amplitude determination method is good enough to predict the dynamic performance of piezoelectric bimorphs. The effects of bonding layers were also analysed by both static and dynamic methods. The bonding influence can be minimized by selecting appropriate bonding materials and dimensions of structures.

Modal analysis is now mature and well accepted in the design of mechanical structures. It determines the vibration mode shapes and the corresponding natural frequencies. However, the validity of modal analysis is limited to structures showing a linear behaviour. In non-linear structural dynamics, it is well known that mode shapes are no longer useful for the characterization of the dynamic response. The purpose of the present paper is to define new features which efficiently capture the dynamics of a non-linear structure. The proposed methodology takes advantage of auto-associative neural networks to compute one-dimensional curves which allow for non-linear dependences between the coordinates. Synthetic data sampled from a non-linear normal mode motion are used to illustrate the method and to develop intuition about its implementation.

The problem of shape control and correction of small displacements in composite structures using piezoelectric actuators glued or embedded was addressed. A finite element model based on Mindlin plate theory was used to characterize the behaviour of the structure and the one of the actuators. Emphasis was put on the development of an efficient and general methodology, based on genetic algorithms, for the determination of the optimal actuation voltages needed to apply to the piezoelectric actuators in such a way that a pre-defined shape of the structure is achieved. The model was investigated numerically and verified experimentally. Measurements were carried out using electronic speckle pattern interferometry. Good agreement was found between simulation results and the optically measured values.

Shape memory alloy (SMA) actuators have attractive advantages such as high power to volume ratio. However, they also have hard nonlinearities including backlash-like hysteresis and saturation. These nonlinearities result in steady-state errors and limit cycle problems when conventional controllers are used for trajectory control. In this paper, time delay control (TDC) is applied to SMA actuators. The TDC is a well-known robust nonlinear controller and does not require a precise mathematical plant model. The dynamics of an SMA actuator was derived based on Liang's model. This dynamics does not only describe the characteristics of SMA actuators very effectively but also helps tune the TDC gains. A control strategy for the SMA actuator was established and examined from the point of view of the influence of an anti-windup scheme and high gain tuning on the control performance. We also conducted experiments on the position control of the SMA actuator and show the results of the TDC in comparison with other control schemes.

Oxidized multiwalled carbon nanotubes (CNT) were functionalized with polydimethylsiloxanes (PDMS) by opening epoxide groups of PDMS under ultrasonic irradiation and the acidic condition provided by ion-exchange resin. The final product is a uniform solution and allowed the wet-casting of thin film. Photoinitiator and sensitizer were added for UV curing using the Penn state microstereolithography (MSL) system which has a wavelength close to 364 nm.

A simple and novel method was developed for efficient synthesis of 2D quasi-aligned multiwalled carbon nanotubes by a catalytic chemical vapour deposition technique. The CNT alignment and in depth analysis of structures has been studied by scanning electron microscopy and transmission electron microscopy. The growth rate and the purity of the product have been found to be affected by the flow rates of the gases as well as the nature of the support used.

The influence of applied electric field on fracture toughness and cyclic electric field induced fatigue crack growth behaviour was characterized for an actuator piezoelectric ceramic under the combined loading of a high electric field and a mechanical stress. Results show that there exists a strong anisotropic effect on fracture toughness and electric field induced fatigue crack growth in polarized PZT. It is found that the apparent fracture toughness in the orientation parallel to the polarization direction is much higher than that in the transverse orientation. Under a positive electric field, increasing the electric field intensity reduces the fracture toughness in the transverse orientation but enhances that in the parallel orientation. However, the reverse is true under a negative electric field. A sphere cavity model in dielectrics was employed to characterize the effect of the external applied electric field on the evolution of cracking in an indentation. The results also show that low electric field intensity does not result in fatigue crack growth in PZT. For a relatively high applied electric field, the cracks initially grow quickly and then are arrested. This result is very significant for the long-term durability of PZT actuators.