Table of contents

The paper presents a novel scheme capable of controlling deflection shapes of laminated beam plates without relying on information of external loads and boundary conditions. Layers of piezoelectric sensors and actuators trimmed to sine shapes are embedded in the laminated beam plate. An adaptive control algorithm is used for achieving expected control effects. Theoretical simulation is formulated and performed to demonstrate its feasibility. Fourier sine series incorporated with Stokes transformation is employed for the simulation of beam-plate deflections. Clamped-clamped and simply supported beam plates are used for illustrative purposes. Simulation results indicate that the scheme is effective.

C-blocks are unique piezoelectric building blocks which can be combined in series or parallel to generate tailorable performance and exploit the advantages of bender and stack architectures. This paper presents a complete theoretical model that predicts the force-deflection behavior for any generic C-block actuator array configuration. An experimental investigation with five case studies is described that validates the model over a broad range of actuator prototypes and performance. This study characterizes the sensitivity of this class of actuator array with respect to material, geometric, and configuration parameters. The paper concludes with a comparison of the generic C-block architecture to the current state of art on a basis of absolute measures such as maximum force, deflection, and work and normalized measures such as effective stress, strain, and work per actuator volume. From this, it is concluded that C-blocks are a highly efficient, mid-range actuation technology.

The sensitivity of the fiber polarimetric system for smart structure applications depends on various parameters such as pre-stress, input azimuth, fiber turns etc. The presence of the smart structure modifies the output characteristics of the highly birefringent (HiBi) fiber due to elastic properties of the structure. This differential lateral strain will produce a change in the birefringence of the fiber over this length, which manifests as the state of polarization change in the fiber output. These concepts are used in the defect detection of smart composite structures. Experimental procedures are repeated for bow-tie HiBi fibers with different optical configurations. A parameter sensitivity factor `Q' is proposed to characterize defects. A significant variation in Q-factor can be attributed to the presence of defects/delamination. This paper deals with the on-line defect detection of smart composites based on such concepts.

This paper demonstrates the feasibility of multiplexing several optical fibre-based Fabry-Perot sensors in series for strain metrology. White-light interferometry was employed using the laser-referenced Michelson interferometer of a standard Fourier-transform spectrometer as a receiving (interrogating) interferometer. The primary aim was to demonstrate that at least six fibre Fabry-Perot transducer interferometers (sensors) can be multiplexed in series. A prerequisite for this sensor system is that each sensor has to have a unique optical cavity length within the multiplex. The resulting differing optical path differences at each fibre Fabry-Perot sensor give rise to sharp correlation features (side bursts) at unique positions in the time domain as observed in the interferogram. An optical cavity length change due to an axial strain perturbation is observed as a change in the position in the time domain of the side-burst feature associated with the optical fibre Fabry-Perot sensor. This paper demonstrates that multiplexed strain metrology in the quasi-static regime using optical fibre Fabry-Perot sensors is possible with a measurement range of typically 0-4000 microstrain and a strain resolution of better than 10 microstrain.

The stayed cables of cable-stayed bridges are the main load-bearing components. The cable tension and its variation are two of the most important criteria for judging if a cable-stayed bridge is in order. Through monitoring the cable tension and its variation, the overall technical condition of a cable-stayed bridge can be estimated and whether the cable socket system and protecting system are functional and whether the steel wires in the stayed cables are rusted can be checked. In this paper the frequency analysis method for in situ measuring of cable tension with polyvinylidene fluoride (PVDF) piezoelectric films is put forward. The relationship between the cable sag and the cable tension is explored and the disadvantages of the traditional measuring method of cable tension with frequency analysis are also represented, as are the explicit error equation and its compensation methods. The simultaneous experimental results on a stayed-cable model and the comparison results measured with the accelerometer are presented.

Magnetorheological (MR) and electrorheological (ER) materials show variations in their rheological properties when subjected to varying magnetic and electric fields, respectively. They have quick time response, in the order of milliseconds, and thus are potentially applicable to structures and devices when a tunable system response is required. When incorporated into an adaptive structural system, they can yield higher variations in the dynamic response of the structure. This study presents a detailed analysis of vibration control capabilities of adaptive structures based on MR and ER materials, and compares their vibration minimization rates, time responses and energy consumption rates. Homogeneous one-dimensional MR and ER adaptive beam configurations were considered. A structural dynamic modeling approach was discussed and vibration characteristics of MR and ER adaptive beams were predicted for different magnetic and electric field levels. In addition to the model predictions, actual MR and ER adaptive beams were fabricated and tested. Both studies illustrated the vibration minimization capabilities of the MR and ER adaptive beams at different rates and environmental conditions. The relative performances of both MR and ER adaptive beams were discussed in detail and their advantages and disadvantages were listed.

The variation of electrical resistance of near stoichiometric NiTi during some thermo-mechanic procedures was studied in this paper. The results show that when the R-phase does not exist in the near stoichiometric NiTi wire, the electrical resistance of NiTi wire increases linearly with the increase of strain at constant temperature. When a phase transformation or martensite reorientation takes place, the slopes of the electrical against strain curves are changed. During the cycles of tensile loading and unloading, electrical resistance of NiTi wire increases as the increase of the cycle numbers, but will stabilize after approximately 15 cycles. Furthermore, the possibility to use NiTi wire as a sensor in the intelligent materials system is discussed.

This paper demonstrates the use of RAINBOW and THUNDER actuators as acoustic control sources in the real-time control of low frequency harmonic interior noise. The former actuator drives a flat acoustic piston while the latter drives a conventional speaker cone. The low-profiled and lightweight nature of these actuators makes them suitable for aircraft applications. The two devices have been used successfully for active noise cancellation inside a duct and a cylindrical enclosure. This paper presents results of the real-time noise control experiments.

The ongoing research and development of cost effective technology for remotely queried sensors for health and usage monitoring of composite structures has lead to the application of electrically conductive thermoplastic adhesive films. This paper intends to provide an in depth overview of a newly developed technology for the design and manufacturing of smart structures by introducing the application of electrically conductive thermoplastic adhesive films. The current technology is discussed and compared with this newly developed technology. It is shown that the structural aspects of this new technology are advantageous to the concept of smart structures as a whole. Fabrication and manufacturing techniques for this new technology is discussed, including the suitability of the process for automation. Specifically, standard tensile testing of the manufactured composite coupons with embedded thermoplastic conductive adhesive films have performed and compared to the test results from copper embedded coupons. The effect of embedded thermoplastic stripes on stiffness as well as strength of the parent laminated structure is evaluated and discussed. Furthermore, fatigue testing was performed at various ultimate failure strength percentiles to determine some degree of the fatigue life of the composite and the embedded conductive and insulting films. The conductive thermoplastic films are found to be structurally superior to copper when embedded in a composite structure, but the electrical conductivity is not as good as copper or other metallic conductors.

A reciprocating mechanism which utilizes two electro-rheological clutches is described. An industrial application of the mechanism is in winding filaments onto bobbins. The required traverse speed is 5 m s^-1 with a turn-round period of 10-20 ms, the traverse length is 250 mm and the turn-round position must be electronically controllable and repeatable within the ±1 mm. These combined criteria of high-speed and controllability makes the use of electro-rheological fluids an attractive proposition. The operation of the reciprocating mechanism and the dynamic model used to simulate the performance are outlined. The simulation is verified by comparison with experimental results from a prototype mechanism. Simulations are made to illustrate the effect of various fundamental electro-rheological fluid characteristics, such as electro-shear stress, time delays and viscosity. These simulations are considered in relation to the requirements for the operation of the high-speed mechanism.

It is now well known that smart fluids (electrorheological (ER) and magnetorheological) can form the basis of controllable vibration damping devices. With both types of fluid, however, the force/velocity characteristic of the resulting damper is significantly nonlinear, possessing the general form associated with a Bingham plastic. In a previous paper the authors suggested that by using a linear feedback control strategy it should be possible to produce the equivalent of a viscous damper with a continuously variable damping coefficient. In the present paper the authors describe a comprehensive investigation into the implementation of this linearization strategy on an industrial scale ER long-stroke vibration damper. Using mechanical excitation frequencies up to 5 Hz it is shown that linear behaviour can be obtained between well defined limits and that the slope of the linearized force/velocity characteristic can be specified through the choice of a controller gain term.

This paper presents the development of a microgripper for micro-assembly and micro-operation applications. Two design configurations for a silicon-based microgripper with integrated thermal expansion actuator and microsensor were proposed and studied in this work. The opening distance of the microgripper is up to 120 µm. The microgripper is designed to operate through an integrated thermal or piezoelectric element that is controlled by an electricity supply. Piezoresistive sensors are integrated on the micromachined gripper to detect and feedback the gripping force applied on gripped objects. The two proposed configurations for the microgripper were simulated numerically and compared with one another. The thermal dynamic response of the thermal expansion element was, in particular, studied through finite-element modelling. Finally, a stainless steel prototype of the designed microgripper was fabricated and tested.

Low velocity impact response of glass reinforced polymer composites, which have the potential to self-repair both micro- and macro-damage, has been investigated. This class of material falls under the category of passive smart polymer composites. The self-repairing mechanism is achieved through the incorporation of hollow fibers in addition to the normal solid reinforcing fibers. The hollow fibers store the damage-repairing solution or chemicals that are released into the matrix or damaged zone upon fiber failure. Plain-weave S-2 glass fabric reinforcement, vinyl ester 411-C50 and EPON-862 epoxy resin systems were considered for this study. Different tubing materials were investigated for potential use as storage materials for the repairing chemicals instead of the actual hollow repair fibers and included borosilicate glass micro-capillary pipets, flint glass pasteur pipets, copper tubing and aluminum tubing. composite panels were fabricated by using a vacuum assisted resin transfer molding process. The present investigation addressed fabrication of self-repairing composite panels and some of the parameters that influence the response of self-repairing composites to impact loading. Specific issues addressed by this study include: the processing quality; the selection of storage material for the repairing solution; release and transportation of the repairing solution; the effect of the number, type and spatial distribution of the repairing tubes, specimen thickness, matrix material and impact energy level.

Magnetoelastic thin film sensors can be considered the magnetic analog of surface acoustic wave sensors, with the characteristic resonant frequency of the magnetoelastic sensor changing in response to different environmental parameters. We report on the application of magnetoelastic sensors for remote query measurement of pressure, temperature, liquid viscosity and, in combination with a glucose-responding mass-changing polymer, glucose concentrations. The advantage of using magnetoelastic sensors is that no direct physical connections, such as wires or cables, are required to obtain sensor information allowing the sensor to be monitored from inside sealed containers. Furthermore since it is the frequency response of the sensor that is monitored, rather than the amplitude, the relative orientation of the sensor with respect to the query field is unimportant.

The converse piezoelectric effect is used to suppress the vibrations of a beam stiffened with piezoceramic actuators. The control problem involves the minimization of the dynamic response of the beam by using the voltage applied to the piezoactuators as a control variable. The dynamic response is defined as the vibrational energy of the beam, which is used as the cost functional of the control problem. The piezoactuators are bonded on the opposite surfaces of the beam and placed symmetrically with respect to the middle plane. The control moments are activated by applying out-of-phase voltages. The control voltage is subject to a maximum value constraint and is defined as a modified bang-bang type which can take this voltage as a plus or minus value as well as the zero value. It is found that the optimal active control takes the form of a piecewise constant alternating voltage with varying switch-over intervals.

Piezoelectric materials have been increasingly used in damage mitigation applications and in real-time health monitoring of structures. The key for these is the distributed piezoelectric material within the structure. In cutting down the design time and the cost involved in modeling structures, the finite-element method proves a useful tool. This is more scalable with appropriate usage of the number and type of elements involved in modeling. Before going into the modeling of more complicated structures, for impact and damage mitigation, a basic comparison of the finite-element method and experimental work was carried out by means of active strain transfer from the piezoelectric to the beam.

As a first phase, this current paper focuses on comparing the results from a three-dimensional finite-element method and experimental work with the analytical methods of the two-dimensional finite-difference method and one-dimensional work done by Park and co-workers. The L9 orthogonal array of the Taguchi method is employed to simplify the analysis and realistically compare the strains on the beam and the piezoelectric. To validate the results and compare them on the same scale, the active strain-transfer analysis is carried out with the same field strength for different piezoelectric materials. The results indicate that the finite-element method and experimental methods agree well within the scope of the Taguchi method. The extension of the concept could also be used in shape control applications using smart materials. The paper concludes with discussions on the success of finite-element methods and advantages in modeling, and their scalability towards analysis of complicated structures.

A micromechanical analysis which is capable of predicting the nonlinear behavior of multiphase composites in which one or more phases are electrostrictive materials is proposed. In view of the nonlinear behavior of the electrostrictive constituents, an incremental procedure in conjunction with a tangential formulation is developed. As a result of the micromechanical analysis, the instantaneous electromechanical concentration tensor and thermal-pyroelectric vector are established. These readily provide the current electromechanical effective constants, coefficients of thermal expansion and the associated pyroelectric coefficients. Results are given that show the effects of electrical, mechanical and thermal loadings on the behavior of electrostrictive porous materials, and the capability for sensing by tagging of electrostrictives in a polymer matrix composite is illustrated.

Smart materials such as piezoceramics are being used as actuators and sensors to achieve active control of elastic deformations of structures. Intelligent structures, with highly distributed actuators and sensors, can be designed with intrinsic vibration and shape control capabilities. Piezoceramics can be integrated with a structure either by being embedded within or bonded onto the structure. Particularly for the case of surface bonding, it is important to have an effective strain transfer from the smart material to the metallic substrate through the adhesive layer.

In this paper, study of the strain transfer of piezoceramic actuators bonded to the surface of a structure with a finite-thickness adhesive bond is presented. A structure with actuators bonded to the top and bottom surfaces of a cantilever beam, which can deform in either bending or extension, is analysed. A detailed two-dimensional model of the structure is developed to study this strain transfer through an adhesive layer using the finite-difference method to solve the equations of elasticity, with appropriate boundary conditions.

The resulting strains in the actuator and those induced in the substructure are compared with a finite-element model and two existing one-dimensional analytical models. The limitations of the simplified analytical models are brought out. The uniform-strain analytical model was found to be in agreement with the numerical models only for the case of extension actuation. The Bernoulli-Euler analytical bending model agreed with the numerical models only at points near the center of the structure. The finite-difference and finite-element models were in agreement in almost all cases. For the case of bending actuation, the finite-difference and finite-element methods differed in their predictions of induced strains.

An electromechanical model of a deformable mirror was developed as a design tool for adaptive optical systems. The model consisted of a continuous, mirrored face sheet driven with multilayered, electrostrictive actuators. A fully coupled constitutive law simulated the nonlinear, electromechanical behavior of the actuators, while finite element computations determined the mirror's mechanical stiffness observed by the array. Static analysis of the mirror/actuator system related different electrical inputs to the array with the deformation of the mirrored surface. The model also examined the nonlinear influence of internal stresses on the active array's electromechanical performance and quantified crosstalk between neighboring elements. The numerical predictions of the static model agreed well with experimental measurements made on an actual mirror system. The model was also used to simulate the systems level performance of a deformable mirror correcting a thermally bloomed laser beam. The nonlinear analysis determined the commanded actuator voltages required for the phase compensation, and the resulting wavefront error.

In this study, we developed a simple electromechanical, lumped parameter model to simulate the dynamic performance of a deformable mirror driven by electrostrictive actuators in an adaptive optics system. Positioned behind the mirror, the multilayered actuator array dynamically controls the mirror's surface shape for optical phase compensation. Our analysis approach combined the linear mechanical impedance of the mirror with a nonlinear representation of an actuator in the array. We used a nonlinear constitutive law for the electrostrictive material to accurately characterize prestress and bias voltage effects on the actuator's induced strain behavior. The model examines the effect of the mirror's impedance on the actuator's resonance characteristics, and predicts the dynamic range limitation imposed by the mechanical structure of the device. The nonlinear behavior of the actuator material created super-harmonics that limited the operational bandwidth of the deformable mirror. However, the analysis showed that tuning the actuator's bias voltage significantly reduced or eliminated these super-harmonics. The model also clearly demonstrated that this tuning does not adversely affect the device's displacement output, power consumption or efficiency.