This paper presents the open-loop hover testing of a Mach- scaled (1/7-scale) rotor with piezoelectric bender actuated trailing-edge flaps. The flap motion generates new unsteady aerodynamic loads, which if correctly phased can be used to achieve active vibration suppression. The objective of the present tests is to demonstrate the open-loop control authority of the actuator-flap system. The model rotor was tested in hover condition on the University of Maryland rotor test rig. These tests were conducted using a Bell-412 Mach- scaled rotor hub. Trailing-edge flap deflections of ±5 to ±10 degrees were achieved in the 1 - 4/rev frequency range at 1800 RPM. The associated oscillatory rotor thrust per blade for 3/rev flap excitation was ±6.9 lbs (40% of steady rotor thrust per blade at 8 degrees collective). These results demonstrate the open-loop effectiveness of the actuator-flap system. Future work will include closed-loop control tests conducted in forward flight in the Glen L. Martin wind tunnel.

The present research experimentally investigates the feasibility of a trailing-edge flap mechanism actuated in a helicopter rotor by piezoelectric stacks in conjunction with a dual-stage mechanical stroke amplifier to actively control vibration. A new mechanical leverage amplification concept was developed to extend the capability of a simple lever-fulcrum stroke amplifier. A refined prototype actuator and flap mechanism were designed and fabricated using five piezostacks. The bench-top test of the actuator showed 73.7 mils of free stroke and uniform displacement output up to a frequency of 150 Hz. Spin testing was performed in the vacuum chamber to evaluate the performance in rotating environment, and the refined prototype actuator showed approximately 13% loss in actuation stroke at 710 g of full-scale centrifugal loading. In the Open-Jet wind tunnel testing to simulate the aerodynamic loading environment, the peak-to-peak flap deflections above 8 degrees for freestream velocity of 120 ft/sec were obtained at different excitation frequencies. It demonstrated the capability of the refined prototype actuator in rotating environment to potentially reduce helicopter vibration.

The development and testing of a new actuator for helicopter rotor control, the Double X-Frame, is described. The actuator is being developed for wind tunnel and flight testing on an MD-900 helicopter. The double X-frame actuator has a number of design innovations to improve its performance over the original X-frame design of Prechtl and Hall. First, the double X-frame design uses two X-frames operating in opposition, which allows the actuator stack preloads to be applied internally to the actuator, rather than through the actuation path. Second, the frames of the actuator have been modified to improve the actuator form factor, and increase the volume of active material in the actuator. Testing of the double X-frame piezoelectric actuator was conducted in order to determine its performance (stroke and stiffness) and robustness. In general, stiffness test data compared well with the analytical predictions. The actuator stroke was about 15% less than expected, probably due to the stack output being less in the actuator than as measured in single stack segment testing in the lab. The actuator was also tested dynamically, to determine its frequency response. Actuator robustness was evaluated by measuring its performance when subjected to the effects of blade bending, vibration, and centrifugal loading. Blade elastic bending and torsion deformations were simulated by shimming of the actuator mounts. To assess the impact of the blade vibrations, the actuator and bench test rig were mounted on a hydraulic shaker and subjected to flapwise or chordwise accelerations up to 30 g. To assess the impact of centrifugal force loading, the actuator and bench test rig were spun in the University of Maryland vacuum chamber, so that the actuator was subjected to realistic accelerations, up to 115% of nominal. Results showed that actuator output (force times stroke) was largely unaffected by dynamic and steady accelerations or elastic blade deformations.

On-blade smart structure actuators are capable of actively altering the aerodynamic loads on rotor blades. With a suitable feedback control law, such actuators could potentially be used to counter the vibrations induced by periodic aerodynamic loading on the blades with lower weight penalties than the previous actuation methods and without the bandwidth constraints. This paper covers the development and testing of a new, robust individual blade control (IBC) methodology for rotor vibration suppression using piezo actuated trailing edge flaps and active twist tip rotors. The controller uses a neural network to learn to actuate the trailing edge flap thus adaptively suppressing the blade or hub vibrations. In this application, no off-line training is performed. Instead, a neural network is used in real time to adaptively command the actuator deflections thus reducing vibrations. Closed loop experimental tests with piezo actuated scale rotor systems were conducted on the University of Maryland hover test stand. The results include two different Mach scale smart rotor systems (trailing edge flaps and active tip twist) that were controlled by the same adaptive neurocontrol algorithm. These tests demonstrate the controller's robust ability to successfully learn to control the rotor vibrations with no a priori information about the blade/actuator structure or the aerodynamic loading.

Reducing the external noise is becoming a major issue for helicopter manufacturers. The idea beyond this goal is to reduce or even avoid the blade vortex interaction (BVI), especially during descent and flights over inhabited areas. This can be achieved by changing locally the lift of the blade. Several strategies to reach this goal are under investigation at EUROCOPTER such as the control of the local incidence of the blade by a direct lift flap. AEROSPATIALE MATRA Corporate Research Centre and AEROSPATIALE MATRA MISSILES proposed an actuator system able to answer EUROCOPTER's needs for moving a direct lift flap. The present paper describes the definition, manufacturing and testing of this new actuator system. This actuator is based on an electromagnetic patented actuation system developed by AEROSPATIALE MATRA MISSILES for missile and aeronautic applications. The particularity of this actuator is its ability to produce the desired force on its whole range of stroke. The flap is designed to be fitted on a DAUPHIN type blade produced by EUROCOPTER and the actuator system was designed to fit the room available within the blade and to produce the right amount of stroke and force within the required frequency range. Other constraints such as centrifugal loading were also taken into account. This paper describes briefly the specifications and the major characteristics of the actuating system and presents some results of its behavior on a representative composite test-bed manufactured by EUROCOPTER when subjected to realistic mechanical loads.

Another solution to the helicopter blade-tracking problem has been investigated. A discrete, blade-installed actuator utilizing shape memory alloy (SMA) torsion tubes has been developed to enable in-flight rotor tracking. SMA torsion tubes from three materials were tested and one was selected for its cyclic stability. Improved tube fabrication, heating, end attachment methods, and locking schemes were developed. The final prototype actuator employed two bi-axial SMA tubes for actuation/bias; a SMA activated lock for power off operation, and integrated microprocessor control electronics. Tests under static and dynamic loading showed that actuation requirements, except for bandwidth, were met. Increased bandwidth, were met. Increased bandwidth may be obtained by improved control algorithms or cooling. The developed SMA actuator enables an in-flight, real-time adjustment of a blade-tracking tab. Projected payoffs are reduced maintenance cost as well as reduced helicopter vibrations and improved performance.

Experimental and analytical investigations conducted into active control of longitudinal and flexural waves transmitted through a cylindrical gearbox strut are presented in this article. The development of an experimental model of a finite length active cylindrical strut instrumented with sensors, piezoelectric, and magnetostrictive actuators is described. The strut is included in an experimental arrangement where vibratory loads are applied along the strut's longitudinal and transverse directions while it is subjected to an axial static loading. Modal analysis studies are carried out in the frequency range of 10 Hz to 5 kHz with a finite element model of the cylindrical strut and the experimental model. During wave transmission through the strut, coupling between different types of modes is predicted by analysis and observed in the experiments. Actuator and sensor systems issues are discussed with relevance for control of vibrations transmitted through helicopter gearbox struts.

Aeromechanical stability plays a critical role in helicopter design and lead-lag damping is crucial to this design. In this paper, the use of segmented constrained damping layer (SCL) treatment and composite tailoring is investigated for improved rotor aeromechanical stability using formal optimization technique. The principal load-carrying member in the rotor blade is represented by a composite box beam, of arbitrary thickness, with surface bonded SCLs. A comprehensive theory is used to model the smart box beam. A ground resonance analysis model and an air resonance analysis model are implemented in the rotor blade built around the composite box beam with SCLs. The Pitt-Peters dynamic inflow model is used in air resonance analysis under hover condition. A hybrid optimization technique is used to investigate the optimum design of the composite box beam with surface bonded SCLs for improved damping characteristics. Parameters such as stacking sequence of the composite laminates and placement of SCLs are used as design variables. Detailed numerical studies are presented for aeromechanical stability analysis. It is shown that optimum blade design yields significant increase in rotor lead-lag regressive modal damping compared to the initial system.

Recent development of a smart structures module and its successful integration with a multidisciplinary design optimization software ASTROS* and an Aeroservoelasticity (ASE) module is presented. A modeled F-16 wing using piezoelectric (PZT) actuators was used as an example to demonstrate the integrated software capability to design a flutter suppression system. For an active control design, neural network based robust controller will be used for this study. A smart structures module is developed by modifying the existing thermal loads module in ASTROS* in order to include the effects of the induced strain due to piezoelectric (PZT) actuation. The thermal-PZT equivalence model enables the modifications of the thermal stress module to accommodate the smart structures module in ASTROS*. ZONA developed the control surface (CS)/PZT equivalence model principle, which ensures the interchangeability between the CS force input and the PZT force input to the ASE modules in ASTROS*. The results show that the neural net based controller can increase the flutter speed.

The belt-rib concept for lifting surfaces with variable camber evolved at DLR recently as one of the most promising solutions for the adaptive wing. With the belt-rib idea the adaptive wing issue is approached in a new way: instead of a 'mechatronic' solution with hinges or linear bearings a 'structronic' solution is chosen, where defined, distributed flexibility allow the desired shape changes. The new concept evolves from the classical wing structure. The classical rib, which is in charge of the wing section's stiffness, is replaced by a 'belt rib,' which allows camber changes within given limits while leaving the remaining in-plane stiffness properties of the section widely unchanged. The evolution of the belt-rib concept was accompanied by experimental tests on different prototypes. The last developments concern the construction of a model with solid-state hinges, realized as hybrid glass fiber -- carbon-fiber reinforced composite structure. The model is actuated mechanically by Bowden cables, which can be replaced by shape memory wires in the next development stage. In this paper, the fundamentals of the concept and the most relevant results of the first developments are reported. A description of the new belt-rib design follows, which was implemented in a new prototype. The description of the experimental strength proof and an outline of further development work conclude the paper.

Active structures concepts for the design of aircraft have been investigated for several years. Concerning static aeroelastic applications, all concepts known to the authors are trying to improve the design of aircraft wings. In the case of wings however, the design space for active structures concepts is limited by a multitude of functional requirements. Empennage surfaces on the other hand only have to meet two basic requirements: sufficient stability and maneuverability for the longitudinal and lateral motion of the aircraft. In the case of vertical tails, the aerodynamic effectiveness for the side force and for the rudder yawing moment are usually reduced by the flexibility of the structure. This causes a weight increase for the structure, which is especially unpleasant for tail surfaces because of the rearward shift of the center of gravity. Today, multidisciplinary structural optimization methods can be used to minimize the weight penalty for static aeroelastic effectiveness requirements. But an amount of penalty still remains. A smart solution for additional weight savings, if possible below the conventional basic strength design of the structure, would therefore be very welcome for any new aircraft design. The paper will describe a new design approach for vertical tails. The concept is based on a smart system for the attachment of the complete tail surface to the fuselage. If properly designed, the variable stiffness of this system will provide improved aerodynamic effectiveness of the tail at any flight condition compared to the rigid aircraft. In a first step, the structure for the vertical tail of a fighter aircraft is designed for static strength and buckling stability by means of a structural optimization program, which is based on finite element methods. The impacts of static aeroelastic effectiveness and flutter stability criteria on the structural design are shown. A modified structural model is then used to incorporate the active system for the attachment. The stiffness properties for this system are optimized for improved aerodynamic effectiveness while maintaining sufficient flutter stability and structural strength for the complete tail.

An integrated structures/controls optimization is developed for vibration suppression of a composite box beam with surface bonded piezoelectric actuators. The penalty approach is used to perform the multi-objective hybrid optimization to enhance damping of the first lag, flap, and torsion modes while minimizing control input. The objective functions and constraints include damping ratios, and natural frequencies. The design variables include ply orientations of the box beam walls, and the location and size of the actuators. Two box beam configurations are investigated and the results are compared. In the first, piezoelectric actuators are bonded to the top and bottom surfaces and in the second, actuators are bonded to all four walls for additional in-plane actuation. Optimization results show that significant reductions in control input and tip displacement can be achieved in both cases, however, improved response trends are obtained with in- plane actuation.

In the scanning electron microscope (SEM), specially designed microrobots can act as a flexible assembly facility for hybrid microsystems, as probing devices for in-situ tests on IC structures or just as a helpful teleoperated tool for the SEM operator when examining samples. Several flexible microrobots of this kind have been developed and tested. Driven by piezoactuators, these few cubic centimeters small mobile robots perform manipulations with a precision of up to 10 nm and transport the gripped objects at speeds of up to 3 cm/s. In accuracy, flexibility and price they are superior to conventional precision robots. A new SEM-suited microrobot prototype is described in this paper. The SEM's vacuum chamber has been equipped with various elements like flanges and CCD cameras to enable the robot to operate. In order to use the SEM image for the automatic real-time control of the robots, the SEM's electron beam is actively controlled by a PC. The latter submits the images to the robots' control computer system. For obtaining three-dimensional information in real time, especially for the closed-loop control of a robot endeffector, e.g. microgripper, a triangulation method with the luminescent spot of the SEM's electron beam is being investigated.

Robot manipulators with parallel kinematics chains and two or more robots manipulating an object form closed kinematics chains. When revolute joints are used in the construction of such robotic manipulation systems, the presence of closed chains and their associated kinematics nonlinearity demands high harmonic motions in at least a number of the actuated joints. This is the case even if all the links are relatively rigid and attempt is made to synthesize the joint motions with minimal harmonic content. The presence of high harmonic components in the actuated joint motions is undesirable since as the operating speed is increased, their frequencies would rapidly increase and move beyond the dynamic response limitations of the actuating drives, thereby causing vibration and control problems. The performance of the system in terms of cycle time, tracking precision and the like would therefore suffer. This is particularly the case since the dynamics of such systems is also highly nonlinear and require higher harmonic components in the actuating torques (forces). In this paper, a systematic method is presented for optimal integration of smart (active) materials based actuators into the structure of cooperating robots and robot manipulators with parallel kinematics chain for the purpose of eliminating the high harmonic components of their actuated joint motions. As the result, the potential excitation of the natural modes of vibration of such systems and their related control problems can be greatly reduced. The resulting robotic systems should therefore be capable of operating at higher speeds with increased precision.

The operating speed and precision of computer controlled machines such as robot manipulators are limited mostly by the dynamic response limitations of their primary actuators. The dynamics of systems such as robot manipulators with revolute joints, even when the structural flexibility is not considered is highly nonlinear. The presence of dynamics nonlinearity places an even greater demand on the dynamic response of the prime actuators. This is the case since due to the nonlinear dynamics of such systems, the actuating torques (forces) required for accurate tracking of the desired motions must contain higher harmonics of the joint trajectory harmonics. Such higher harmonic components of the actuating torques become increasingly more significant as the operating speed of the system is increased and can cause serious vibration and control problems. In this paper, a systematic method is presented for optimal integration of smart (active) materials based actuators into the structure of robot manipulators for the purpose of minimizing the high harmonic components of the required actuating torques (forces). The proposed approach is based on the Trajectory Pattern Method (TPM). It is shown that with properly synthesized low harmonic motion trajectories and by minimizing the high harmonic components of the required actuating torques with properly sized and placed smart actuators, such computer controlled machines can operate at higher speeds, greater tracking precision and minimal vibration and control problems.

Changes in elastic moduli of between 0.4 - 18% are common in ferromagnetic materials such as nickel and iron when their magnetization is changed. However, extremely large moduli changes of up to 160% are observed in the rare earth-iron compounds R - Fe₂, which can be advantageously utilized in design of smart structure systems. A nonlinear, hysteretic and magnetoelastically coupled model is presented and used to quantify the changes in resonance frequency exhibited by a loaded magnetostrictive transducer under varied bias magnetizations. The model is constructed in three steps. In the first, the magnetization of the magnetostrictive material is quantified by considering the energy lost to hysteresis as the magnetic field and operating stresses vary. In the second step, a quartic law is used to quantify the magnetostriction arising from domain rotations in the material. The material response, of the type found in linearly elastic solids, is considered in the final step by means of force balancing in the magnetostrictive material. This yields a PDE system with magnetostrictive inputs and boundary conditions given by the transducer-load characteristics. The solution to the PDE system provides displacements and accelerations in the material. Fast Fourier Transform (FFT) analysis is then used to quantify the frequency-domain acceleration response from which the transducer's resonance frequency is calculated. Model results are compared with published experimental data.

Purpose of the work is to present the formulation of a new experimental procedure to employ in problems of damage analysis of structural elements. The proposed method is based on the acquisition and comparison of Frequency Response Functions (FRFs) of the monitored structure before and after a damage occurred. Structural damages modify the dynamical behavior of the structure and consequently its FRFs making possible to calculate a representative 'Damage Index.' The experimental activity was carried on using two prototypes of magnetostrictive actuators developed within the European Commission funded project named MADAVIC (Magnetostrictive Actuators for Damage Analysis and VIbration Control). Three kinds of damages have been simulated on two beam-like structures: little mass disturbances, partial cuts of the beam sections and constraints yielding. Two Damage Indices expressions representative of the damages were calculated. Much effort was spent in order to assess the reliability of the damages identification by using a 'repetitiveness index' related to the lowest, measurable damage extension and the statistical T-Test, in order to verify if each calculated index was really representative of a structural damage, rather than of unforeseen differences between the FRFs.

A compact rotary motor driven by piezoelectric bimorph actuators was developed for applications in adaptive, conformable structures for flow control. Using a roller wedge (rotary roller clutch) as its central motion rectifying element, the actuator converts electrical power to mechanical power by way of a set of resonating bimorph/mass systems. With this type of resonant drive system, the output mechanical power of the actuator was dramatically improved over previous inchworm-type designs. Also, the actuator cost was kept low by using commercial roller clutches and bimorph actuators instead of PZT stacks. Within an application size constraint of 4 x 4 x 1.75 inches, the unloaded speed was 600 RPM, the stall torque was 0.5 N-m, and the peak output power was nearly 4 watts. The motor is driven by a single frequency sinusoidal input, resulting in significant improvements of the cost, size and complexity over typical piezoelectric actuator drivers. Since the backlash of the roller clutch is a critical parameter in assessing the motor performance, an experimental study was performed to better understand its dynamics.

Stacks are a popular form of piezoelectric actuation. Unfortunately with this type of actuation architecture the long lengths normally required to obtain necessary displacements can pose packaging and buckling problems. To overcome these limitations, a new architecture for piezoelectric actuators has been developed called telescopic. The basic design consists of concentric shells interconnected by end-caps which alternate in placement between the two axial ends of the shells. This leads to a linear displacement amplification at the cost of force; yet the force remains at the same magnitude as a stack and significantly higher than bender type architectures. This paper describes the fabrication and experimental characterization of three different telescopic prototypes. The actuator prototypes discussed in this paper mark a definitive step forward in fabrication techniques for complex piezoceramic structures. Materials Systems Inc. has developed an injection molding process that produced a functional, five-tube, monolithic telescopic actuator. A three-tube, monolithic actuator was fabricated using a novel polymerization technique developed at the University of Michigan. As a benchmark, a third actuator was built from off-the-shelf tubes that were joined with aluminum end-caps. Each prototype's free deflection behavior was experimentally characterized and the results of the testing are presented within this paper.

Positioning instruments offering a submicrometric accuracy within a restricted mass budget will become indispensable in future planetary exploration missions. Among the technologies known to date, only the combination of piezoelectric actuators with capacitive displacement sensors meets such specifications. This solution has the advantages of providing a rugged, frictionless, solid-state mechanism, which can be finely controlled due to the high signal to noise ratio that can obtained with the drive electronics. This actuator-sensor combination was applied to the design of an XY stage that could offer 100 x 100 micrometer strokes in a total mass budget of 400g. Since the required stroke was too large to be achieved directly with the piezoelectric material, the amplification technique developed at Cedrat Recherche was employed. Their Amplified Piezoelectric Actuators were chosen over other techniques, such as Hertzian pivots, because of the mass requirement on the system. The design of the stage made it necessary to address issues such as the guiding functions, especially important to reduce parasitic degrees of freedom. Finite element analysis was used intensively. The engineering model built includes eight APA50S actuators and two capacitive displacement sensors. The operating performance was tested and shown to be close to the predicted results. The strokes and parasitic degrees of freedom were measured using a laser interferometer. The stage was tested over the temperature range (-20°+50°C), submitted to random vibrations tests, and its lifetime was tested over more than one million strokes. The results of these tests and other parameters, such as piezoelectric drift and gravity effects on the functional performances, are discussed. This paper focuses on the design aspects of the XY stage, the tools used for this design and the lessons learned from its development.

This paper shows how shape memory alloy (SMA) wires can be used to actively twist a beam or other long slender structural members. This is accomplished by attaching to the beam, a pre- strained SMA strip in its martensite state. The strip is wrapped around the beam in a helical pattern. When heated, the SMA wire transforms into from it martensite state to its austenite state. This causes the wire to shorten in length but since it is attached to the beam it induces a force on the beam that causes the beam to twist. A nonlinear finite element model that incorporates the thermo-structural coupling is used to analyze and study the phenomenon. Results from experiments and finite element analysis are presented and they show that this method can produce large twist angles. This twist can be maintained and reversed without causing any damage to the underlying structure. Several issues involving the method of attachment of the SMA strip to the beam are addressed including a method that allows the SMA wire to 'slide' along the beam. This concept can be used to control the angle of twist of blades of rotor equipment and thereby improve their performance or change their vibratory response.

This paper extends a synchronous averaging technique to incorporate the use of multiple sensors to extract the vibration signals associated with the planet gears of planetary geartrains. The use of multiple sensors mounted along the annulus gear of a planetary gearbox is shown to overcome four limitations of the existing single sensor methodology. First, the constraints on the gearbox geometry in determining whether the technique can be applied are reduced. Second the speed of computation of the technique is increased. Third, the robustness of the methodology to possible sensors failures is enhanced. Finally, susceptibility to noise that is synchronized with the rotation of the carrier is reduced. The methodology is applied to data collected from a miniature planetary transmission system with and without seeded faults. Results indicate that the multiple sensor methodology is able to separate the vibration signals associated with the planet gears in the presence of sensor noise and synchronized disturbances. In addition, the separated vibration signals are analyzed using the continuous wavelet transform to illustrate that planet gear faults can be easily detected after separation.

This paper is concerned with the passive impact detection system based on fiber Bragg grating sensors which can be either embedded or surface mounted on a composite structure. The focus of the paper is the methodology of the intelligent signal processing for the optical fiber sensor data. This methodology is briefly discussed and illustrated using simple examples which utilize the experimental data. The experimental study involves a series of simple impact tests. The composite panel is installed in a loading fame. An instrumented impactor is used to damage the panel at different positions with different energy levels. For each impact the data from optical fiber sensors is digitized, logged and used for signal processing. The paper shows the importance of the intelligent signal processing for impact damage detection based on optical fiber sensors.

Presented here is a newly developed Boundary Effect Detection (BED) method for pinpointing locations of small damage to structures using Operational Deflection Shapes (ODSs) measured by a scanning laser vibrometer. The BED method requires no model or historical data for locating structural damage. It works by decomposing a measured ODS into central solutions and boundary-layer solutions by using a sliding-window least- squares curve-fitting technique. For high-order ODSs without damage, boundary-layer solutions are non-zero only at structural boundaries. For a damaged structure, because damage introduces new boundaries, its boundary-layer solutions are non-zero at damage locations as well as its original boundaries. At a damage location, the boundary-layer solution of slope changes sign, and the boundary-layer solution of displacement peaks up or dimples down. The theoretical background is shown in detail. Experiments are performed on several different structures with different damages, including surface slots, edge slots, surface holes, internal holes, and fatigue cracks. Experimental results show that this damage detection method is more sensitive and reliable for locating small damage than other dynamics-based methods using curvatures or strain energies.

Structural health monitoring for complex systems can contribute significantly to reduced life cycle costs. Many damage detection algorithms have been proposed in the literature for investigating the structural integrity of systems. Changes in modal strain energy have been used to detect the location and extent of damage in structures. In the previous studies, the stiffness matrix is analytically derived and assumed constant even after damage. This paper reports a study on the sensitivity of the modal strain energy method to the stiffness matrix and its accuracy in detecting the location and extent of damage. The modal strain energies for each element of the undamaged structure are computed for each mode using the original analytical matrix and measured modal data. Modal data from the damaged case is used to update the stiffness matrix by a simplified matrix update scheme. This updated matrix is used to correct the elemental matrices for the damaged system. Two case studies are presented in this work. The first is an experimental and analytical model of a cantilever beam and the second, a truss model of the European Space Agency. In the first case three identical aluminum cantilever beams are used. Damage is simulated on two of them by milling 1-inch long slots at two different locations on the beams. Modal data are obtained from experiment using Scanning Laser Vibrometer (SLV) and STAR software to extract the mode shape vectors from the experimental results. These are also compared with finite element simulations of the beams. The second case is an analytical example in which damage is simulated by reducing the area of one of the truss elements hypothetically by 50%. Results from these studies show a slight improved accuracy in determining the location of damage using an updated elemental stiffness matrix. For experimental results however, modal strain energy change method does not give an accurate location of the damages. There is need for further analysis of the application of modal strain energy techniques to damage identification. The results also demonstrate the potential of SLV as a structural health- monitoring tool.

A project to develop non-intrusive active sensors that can be applied on existing aging aerospace structures for monitoring the onset and progress of structural damage (fatigue cracks and corrosion) is presented. The state of the art in active sensors structural health monitoring and damage detection is reviewed. Methods based on (a) elastic wave propagation and (b) electro-mechanical (E/M) impedance technique are cited and briefly discussed. The instrumentation of these specimens with piezoelectric active sensors is illustrated. The main detection strategies (E/M impedance for local area detection and wave propagation for wide area interrogation) are discussed. The signal processing and damage interpretation algorithms are tuned to the specific structural interrogation method used. In the high frequency E/M impedance approach, pattern recognition methods are used to compare impedance signatures taken at various time intervals and to identify damage presence and progression from the change in these signatures. In the wave propagation approach, the acousto- ultrasonic methods identifying additional reflection generated from the damage site and changes in transmission velocity and phase are used. Both approaches benefit from the use of artificial intelligence neural networks algorithms that can extract damage features based on a learning process. Design and fabrication of a set of structural specimens representative of aging aerospace structures is presented. Three built-up specimens, (pristine, with cracks, and with corrosion damage) are used. The specimen instrumentation with active sensors fabricated at the University of South Carolina is illustrated. Preliminary results obtained with the E/M impedance method on pristine and cracked specimens are presented.

The geared servomechanism is an important device used in many industrial applications for transferring power and motion. Over time, the meshing of gear teeth will lead to wear and damage. In this paper, the dynamics of a spur gear pair with damage to a single tooth will be instigated. Damage associated with the formation of a fillet crack and spalling will be simulated. The dynamic forces induced often result in a higher level of noise and vibration within the gear system. The prime direction of the present work is to study the effects of damage on the transient and steady-state vibration response of a spur gear pair. Simulation results indicate that damage significantly affects the response of the system and may accelerate tooth failure.

As a technique of diagnosing failure in structures and systems, the method of novelty detection shows considerable merit. The basis of the approach is simple: given measured data from normal condition of the structure, the diagnostic system builds an internal representation of the system normal condition in such a way that subsequent departures from this condition can be identified with confidence in a robust manner. The success or failure of the method is contingent on the accuracy of the description of normal condition. In many cases, the normal condition data may have quite a complex structure: for example, an aircraft may experience a wide range of ambient temperatures in the course of a single flight. Also, the operational loads experienced by the craft as a result of flight manoeuvres may have wide-ranging effects on the measured states. The object of the current paper is to explore the normal condition space for a simple benchmark monitoring system. The said system uses Lamb-wave inspection to diagnose damage in a composite plate. Both short-term and long-term experiments are carried out in order to examine the variations in normal condition as a result of run-in of the instrumentation and variations in ambient temperature. The exercise is not purely academic as the fiber-optic monitoring system is a serious candidate for a practical diagnostic system.

The function and performance of the self-diagnosis composites embedded in concrete blocks and piles were investigated by bending tests and electrical resistance measurements. Carbon powder (CP) and carbon fiber (CF) were introduced in glass fiber reinforced plastics composites to obtain electrical conductivity. The CP composite has commonly good performances in various bending tests of block and pile specimens, comparing to the CF composite. The electrical resistance of the CP composite increases in a small strain to response remarkably micro-crack formation at about 200 μ strain and to detect well to smaller deformations before the crack formation. The CP composite posses a continuous resistance change up to a large strain level near the final fracture of concrete structures reinforced by steel bars. It has been concluded that the self-diagnosis composite is fairly useful for the measurement of damage and fracture in concrete blocks and piles.

Although there have been many researches concerning health monitoring system in the aerospace field, most of such researches relate to aircraft; there are only few that relate to satellite structures. This research first points out merit of the health monitoring system. The health monitoring system usually utilizes optical fiber sensor of which the diameter is 125 micrometer. However, such fiber sensors tend to be perceived as obstacles within the structure, which affects the soundness of the structure. This is especially the case in satellite structure, which utilizes especially thin composite laminates. In view of this problem, this study utilizes small diameter optical fiber, which is less likely to affect the soundness of the structure. The optical fiber is 40 micrometer in cladding diameter, and is embedded in the composite laminate structure. The structure and the optical fiber have been visually observed. Also, tensile test has been conducted on the structure. The result of the study indicates that the small diameter optical fiber can be embedded in the structure without affecting the soundness of the structure. The study further found that compressive destruction of a face sheet of a honeycomb sandwich panel having thin face sheets can be detected by utilizing this optical fiber.

A large variety of applications exist which take advantage of the high dynamic strain and high energy coupling factor exhibited by 'giant' magnetostrictive materials. One such material is the rare earth-iron compound Terfenol-D (Tb_0.3Dy_0.7Fe_1.95), which is being increasingly used in industrial, biomedical and defense applications. In order to fully realize the performance of this material, it is necessary to accurately model magnetostrictive transducer behavior from DC through the low ultrasonic regimes where the material is used. This paper has been motivated by the need for physically-based performance models of magnetostrictive materials as used in transducers. To this end, a recent magnetoelastic model for magnetostrictive transducers is employed to characterize the magnetization and strain behavior of Terfenol-D at frequencies from 1 Hz to 30 kHz. Model simulations were compared to experimental measurements at various drive levels and frequencies of operation, both under magnetically unbiased and biased conditions. The model provides an accurate characterization of the magnetization and strain for all operating conditions studied. However, further progress in strain simulations may be achieved through improvements in minor loop closure techniques and additional parameter identification.

In this paper the dynamic strain response of a piezoelectric material subjected to an electron beam charge input is examined. A piezoelectric material plate (PZT5h) was prepared with a single distributed electrode on one face and the second face subjected to a variety of electron beam inputs. Strain gages were attached atop the electrode to measure the strain response due to the combined effects of the electrode potential and the charge from the electron gun. When the electrode potential is stepped from 0 to 100 volts the strain needs only 1 second to reach steady state position, but when the electrode potential is stepped down it needs almost 1 minute to reach steady state. This phenomenon can be explained as follows: raising the electrode potential increases the energy of the electrons, so the secondary electron yield falls well below one and negative charge builds up quickly. Dropping the electrode potential decelerates the incoming beam, so the secondary yield becomes only slightly higher than one, so the negative charge decreases at a much lower rate, thus it takes longer to reach steady state.

The Space Interferometer Mission (SIM) is required to point each arm of its science interferometer to better than 30 milli-arcseconds (mas) RMS residual jitter using a 0.01 Hz bandwidth optical sensor on the star. We address the residual pointing error due to the spinning spacecraft reaction wheel assemblies which emit disturbances from 2 Hz to 1 kHz. The vibration attenuation strategy for this 'blind' pointing problem is to isolate each reaction wheel assembly with a vibration isolation system and to possibly augment the low bandwidth closed loop system with an internal high bandwidth sensor. Central to estimating the high frequency pointing error is the Micro-Precision Interferometer (MPI) testbed which is a softly suspended hardware model of a spaceborne optical interferometer and is dimensionally representative of SIM. Using the testbed and a transfer function-based performance prediction algorithm, we show that the 30 mas requirement is missed by a factor of six when only employing a six-axis active vibration isolator made by TRW. In preparation for augmenting the vibration attenuation strategy, we also show that the primary contributor to the tip-tilt jitter error is the first optic in the interferometer's optical train.

Adaptive optics correct light wavefront distortion caused by atmospheric turbulence or internal heating of optical components. This distortion often limits performance in ground-based astronomy, space-based earth observation and high energy laser applications. The heart of the adaptive optics system is the deformable mirror. In this study, an electromechanical model of a deformable mirror was developed as a design tool. 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 version of the 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.

An Modal filter based Independent Modal Space Control (IMSC) method is proposed for active damping enhancement of a flexible space intelligent truss structure. Modal Filter (MF) is used to extract modal states from response measurement. The MF is developed for the structures with closely spaced modes, or even repeated frequencies. Modal acceleration can then be extracted form physical acceleration measurements via MF. A modified Leunberger observer is adopted to estimate modal displacement and modal velocity from modal acceleration. The MF-based IMSC method is employed to enhance damping of the space intelligent truss structure with active members. A real- time computer control system is developed to implement the MF- based IMSC strategy. Experimental results demonstrate that the intelligent structure design is successful and the active control method is effective.

So-called magnetorheological (MR) elastomers, comprising rubbery polymers loaded with magnetizable particles that are aligned in a magnetic field, possess dynamic stiffness and damping that can subsequently be controlled by applied fields. Tunable automotive bushings and mounts incorporating these materials and an embedded magnetic field source have been constructed. In this article, the response of these components to dynamic mechanical loading is described. They behave essentially as elastomeric springs with stiffness and damping that is increased by tens of percent with an applied electrical current. Their time of response to a change in current is less than ten milliseconds. In addition to a tunable spring or force generator, these components may also serve as deflection sensors.

Double adjustable shock absorbers allow for independent adjustment of the yield force and post-yield damping in the force versus velocity response. To emulate the performance of a conventional double adjustable shock absorber, a magnetorheological (MR) automotive shock absorber was designed and fabricated at the University of Maryland. Located in the piston head, an applied magnetic field between the core and flux return increases the force required for a given piston rod velocity. Between the core and flux return, two different shaped gaps meet the controllable performance requirements of a double adjustable shock. A uniform gap between the core and the flux return primarily adjusts the yield force of the shock absorber, while a non-uniform gap allows for control of the post-yield damping. Force measurements from sinusoidal displacement cycles, recorded on a mechanical damper dynamometer, validate the performance of uniform and non- uniform gaps for adjustment of the yield force and post-yield damping, respectively.

This paper presents control characteristics of a semi-active magneto-rheological (MR) fluid damper for a passenger vehicle. A cylindrical MR damper is devised and its governing equation is derived. After verifying that the damping force of the MR damper can be continuously tuned by the intensity of the magnetic field, PID controller is employed to achieve the desired damping force. The proposed MR damper is then applied to a full-car model and performance characteristics of the full-car such as vertical acceleration of the body are evaluated via hardware-in-the-loop-simulation (HILS).

Magnetorheological (MR) fluids are characterized by dynamic yield stress with the application of a magnetic field. The Bingham plastic model has proven useful in modeling MR fluid properties, as in flow mode dampers. However, certain MR fluids can exhibit shear thinning behavior, wherein the fluid's apparent plastic viscosity decreases at high strain rates. The Bingham plastic model does not account for such behavior, resulting in over-prediction of equivalent viscous damping. This paper proposes a Bingham biplastic model to account for shear thinning or shear thickening. This approach assumes a bilinear post-yield viscosity, with a critical strain rate specifying the region of high strain rate flow. Furthermore, the model introduces non-dimensional terms to account for the additional parameters associated with shear thinning and thickening. A comparison is made between Bingham plastic and Bingham biplastic force responses to sinusoidal input, and equivalent viscous damping is examined with respect to nondimensional parameters.

It is now well known that smart fluids [electrorheological (ER) and magnetorheological (MR)] 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 non-linear, possessing the general form associated with a Bingham plastic. In a previous paper the authors showed that by using a linear feedback control strategy is it possible to produce the equivalent of a viscous damper with a continuously variable damping coefficient. In the present paper the authors illustrate an extension of the technique, by showing how the shape of the force/velocity characteristic can be controlled through feedback control. This is achieved by using a polynomial function to generate a set point based upon the damper velocity. The response is investigated for polynomial functions of zero, 1st and 2nd order. It is shown how the damper can accurately track higher order polynomial shaping functions, while the zero order function is particularly useful in illustrating the dynamics of the closed-loop system.

Coupling adjacent buildings with supplemental damping devices is a developing method of mitigating structural responses due to wind and seismic excitations. The concept is to allow structures, vibrating at different frequencies, to exert control forces upon one another to reduce the overall responses of the system. Previous studies have identified optimal coupled building configurations and have introduced passive, active and 'smart' damping control strategies. This paper will focus on the application of 'smart' dampers as coupling link devices to produce control forces between three tall buildings. Smart dampers are semi-active dampers capable of changing their dynamic characteristics in real-time to allow for a variety of control forces to be produced without requiring significant energy. A clipped optimal control strategy is employed for the smart dampers that can provide increased performance, over a comparable passive control strategy, during moderately severe seismic events.

This paper presents a semi-active seat suspension with a magneto-rheological (MR) fluid damper, which is applicable to commercial vehicles such as a large size of truck. A cylindrical MR seat damper is designed and manufactured by incorporating Bingham model of MR fluid. After evaluating field-dependent damping characteristics, the controllability of the damping force is experimentally demonstrated in time domain by implementing PID controller. A semi-active seat suspension system is then constructed and its governing equation of motion is derived. A skyhook control scheme is formulated in order to reduce vibration level at the driver's seat. The controlled responses such as acceleration transmissibility are evaluated in frequency domain. In addition, performance characteristics of a full-car model installed with the proposed MR seat suspension are evaluated via hardware-in-the-loop simulation (HILS).

It has been shown that piezoelectric materials can be used as electromechanical vibration absorbers when they are shunted by an electrical network. Semi-active piezoelectric absorbers have also been proposed for the purpose of suppressing harmonic excitations with varying frequencies. These semi- active devices can be constructed using a variable inductance or variable capacitance element in the shunt circuit, however both of these implementations have several limitations that restrict their practical use. The design presented here is a high performance alternative to semi-active absorbers that uses a combination of a passive RL circuit and an adaptive feedback law to suppress harmonic excitations with varying frequency. The adaptive tuning is accomplished by simulating a variable inductor using feedback. An equation for the optimal tuning of the piezoelectric absorber on a general MDOF structure is derived. Next, it is illustrated that the performance and robustness of the piezoelectric absorber can be increased by using additional active actions to reduce the circuit resistance and enhance the coupling of the piezoelectric. Two methods for increasing the effective coupling of the absorber are examined -- a negative capacitance shunt and active coupling feedback. Finally, the effectiveness of the proposed algorithm is demonstrated experimentally.

The concept of a built-in structural health monitoring system has attracted great interest as such systems may allow reduced maintenance cost and increased safety. One attractive technique to realize such a system in composites is to use embedded transducers to generate Lamb waves. The damage in the structure is detected by determining the change in the character of the Lamb waves as an effect of damage. In this paper, the performance of embedded piezoceramic transducers used as Lamb-wave generators was investigated. The composite specimens with a piezoceramic transducer embedded in the mid- plane were subjected to tensile and compressive static loading as well as fatigue loading. A surface-attached acoustic emission sensor further detected the Lamb waves. Measurements of the impedance were also performed during static loading to evaluate the electrical conduction of the piezoceramic transducer. During static loading, the embedded piezoceramic transducers functioned near to the final failure of the composite without significant changes in the generated Lamb waves, although the microscopic examination indicated damage. Debonding between the surfaces of the piezoceramic element and the interconnectors as well as failure in the piezoceramic element had occurred. In fatigue, for a stress ratio of -1, the piezoceramic transducers also showed a large working range. The amplitude and frequency of the Lamb waves, generated by the piezoceramic transducers, were not significantly changed after a large number of cycles, around 50,000 - 100,000 cycles at strain levels of ± 0.20%. The changes in terms of amplitude and frequency of the Lamb waves, occurring after a large number of cycles, were associated with increasing matrix cracks in the specimen.

This paper proposes the use of a modern control method, the Kalman filter, to perform dynamic shape estimation of structures. Existing dynamic shape estimation techniques use static estimation techniques at each time step. This approach has been shown to be unsatisfactory, since aliasing of the higher modes, which is largely not seen in the static case, occurs strongly in the dynamic case. In many cases the aliasing produces signal to noise ratios significantly greater than unity. The proposed approach uses a Kalman filter to sift out the desired low frequency modes, since they contribute the most to the displacements, and treats the higher modes as a component of the noise in the system. Also, unlike the static techniques, the Kalman filter allows sensing of a number of modes larger than the number of sensors, and it takes into account the measurement errors. Numerical simulations show that the Kalman filtering technique can reduce the error from a thousand percent down to less than a percent for an ideal cantilever beam. Experimental data, susceptible to modeling and sensing errors, show that the proposed method results in a significant improvement over existing techniques.

This paper describes a manufacturing technique for embedding standard fiber-optic connection hardware in aircraft composite components. Three different concepts for detachable edge connections are presented. Embedding the fiber-optic connection hardware at the edges of the composite components is favorable since it entails easy manufacturing and maintenance. Carbon fiber/epoxy laminates were manufactured with embedded MT-ferrules and FC-ferrules. Using dummies in the manufacturing step solved the difficulty with laminate edge trim, which generally is a problem with edge connectors. The dummies were manufactured by polytetrafluoroethylene and had similar shape and dimensions as the embedded ferrules. The dummies could easily be removed after laminate curing and edge trimming, leaving embedded ferrules at the laminates edges, ready for connection. The manufacturing technique and fiber- optic connection were evaluated by manufacturing and loading a laminate with embedded MT-ferrule and optical fibers with Bragg grating sensors. The fiber-optic connection was confirmed and the strains measured by the Bragg grating sensors were in close agreement with the strains measured by strain gauges.

Health and usage monitoring systems for composite structures based on Lamb wave propagation are one of the most promising systems presently evaluated. Generally, they are constituted of a network of piezoelectric transducers. The various transducers generate and receive the Lamb waves. The diagnostic is based on the perturbation in the propagation of the waves due to the presence of the damage. In view to develop less intrusive actuators/sensors, the possibility of using a fiber optic delivery system for laser generation of Lamb waves is evaluated. 125 μm-dia. optical fibers are embedded in the composite during the process. The energy of the pulses are lower than a mJ allowing a good functioning of the system even after several hundred of thousands pulses. The out-of-plane displacement field on the surface of a carbon-epoxy structure equipped by such a system is reconstructed (B-scan) using point measurement from a very sensitive and wide-band (20 kHz - 30 MHz) interferometric probe. The analysis of typical B-scans by 2-D Fourier transform clearly demonstrates the generation of Lamb waves. Various modes are excited, from the fundamental ones to high order ones. Comparison to theoretical dispersion curves is presented.

This paper reports the design of a piezoelectrically-driven microfabricated valve for high frequency control of large pressure fluid flows. The enabling concept of the valve is the ability to convert the small displacement of a piezoelectric element into a large valve cap stroke through the use of a hydraulic fluid, while maintaining high force capability. The current valve design, with operating frequency of 24 kHz and valve stroke of 40 micrometer, has been tailored for use in microhydraulic actuation and energy-harvesting devices, which require high-frequency regulation of approximately 1 ml/sec fluid flows across pressure differentials of 1-2 MPa.

This paper develops and demonstrates performance analysis of vibration suppression and damage detection control laws on structures with fatigue cracks. State feedback control laws for the individual tasks of vibration suppression and autonomous damage detection are designed based on low-order models of a damaged structure. These control laws are applied to finite-element models of structures with through-surface and surface cracks. The analysis ascertains the ability of feedback control to enhance sensitivity of modal frequency shifts due to realistic damage and the potential for using the same sensors and actuators for implementing vibration damping control laws that are insensitive to damage. In the control model, damage consists of simple reductions in thickness over a small area of the structure. Finite-element models to which control laws are applied are developed using commercial software (ABAQUS) that more accurately models the crack by releasing element connections or by using line spring elements. Results show that feedback control laws can be designed for either crack detection or vibration suppression using identical hardware. In addition, we demonstrate that simple models of damaged structures are suitable for designing control laws for detecting more complex damage conditions, and we demonstrate the use of commercial software for model-based simulation of controlled structures.

A new theory is developed to model the hysteresis relation between polarization and electric field of piezoceramics. An explicit formulation governing the hysteresis is obtained by using a saturation polarization, remnant polarization and coercive electric field. A new form of elastic Gibbs energy is proposed to address the coupling relations between electrical field and mechanical field. The nonlinear constitutive relations are derived from the elastic Gibbs energy and are applicable in the case of high stroke actuation. The hysteresis relations obtained using the current model are correlated with experimental results. The static deflection of a cantilever beam with surface-bonded piezoelectric actuators is analyzed by implementing the current constitutive relations. Numerical results reveal that hysteresis is an important issue in the application of piezoceramics.

Various configurations of piezoelectric high strain actuators are available in the market. The influence of humidity at high temperature is not well documented, even though it is an important consideration for actuator performance. This paper describes the testing and results of two different families of actuators; QuickPack products and multilayer actuators, tested under two environments; room temperature low humidity and elevated temperature and humidity (80°C/80%RH). A constant DC load was applied to the QP10N andand QP10Ni products in free condition, while positive only AC field was applied to multilayer actuators, under pre-stressed condition. High field IR was used as the main tool to determine the health of QuickPack products, whereas, in-situ displacement was measured to monitor the health of multilayer actuators. As expected, in both families of actuators, it was shown that the actuator life is significantly reduced when specimens are exposed to humidity at elevated temperature. Improvement of the humidity barrier, thus less moisture penetration, even when electrodes do not contain silver, is expected to prolong life of actuators.

A preliminary investigation of a novel transducer proposed for digital loudspeaker technology is presented. The transducer comprises a piezoelectric, helicoidal structure that wraps round an inflated, elastomeric torus with a lightweight cylindrical core element mounted on the inside. As the helix is deformed by application of an electric field along its length, linear motion of the core is actuated. An axisymmetric finite-element model is presented to account for inflation of the torus against the outer helix and to demonstrate core motion. The interaction of surfaces in contact is studied in a hyperelastic framework using a double cylinder model, which produces favorable predictions of the actuating forces from finite element analysis. A finite-element model of the helix demonstrates primary aspects of deformation that are utilized in formulating a much simpler single-layer analysis by a variational strain-energy approach; a correlation to experiment is observed.

The main advantages of piezoelectrical actuators as compared with conventional actuation concepts are their high precision, unsurpassable resolution in motion (sub μm-range) and in particular their excellent dynamic behavior. Especially the very short response time of solid state actuators gives rise to new opportunities in developing high dynamical systems with unsurpassable characteristics. Very compact systems with parallel motion and high accuracy in high displacements can be realized by integration of piezoelectric actuators into special mechanical frames with lever transmission systems made of solid state hinges. For the design of such dynamical actuation systems, the knowledge of significant parameters such as resonance frequency, stiffness and damping as a function of the additional load is important. This problem can be reduced to the determination of a few general system parameters, which is outlined in detail. As a result of the complexity of compact electromechanical actuation systems this determination is not a simple calculation by means of commonly given material specific parameters or by the actuator moved masses. Exact acquisition of the characteristics of the complete transducer-system requires the use of a known mathematical model of piezoelectrical transducers and appropriate measurements. Essential parameters and characteristic values of piezoelectrical actuators are presented in order to develop a suitable measuring technique for general characterization of system parameters.

The mechanical behavior of a cylindrical, finger-like shaped, piezoelectric actuator with Functionally Graded Microstructure (FGM) was modeled by our analytical model and FEM. Different layers or lamina of different piezoelectric volume fraction in a polymer matrix were stacked to create FGM. Although the bimorph plate exhibit reasonably high out-of-plane displacement, induced stress field remains very high limiting its long life use. FGM piezoelectric plates have been developed to increase the out-of-plane displacement while reducing the stresses where the electro-elastic properties are graded through the plate thickness. Finger-like shape piezo actuators are developed where the properties are graded in the radial direction. FGM piezoelectric type actuator showed promising results in that the deflections to any direction can be obtained by manipulating the magnitude and direction of the applied electric field. Analytical modeling in computing the deflection of the finger-like actuator and stress field induced in each lamina was developed and compared to FEM modeling. The theory of cylindrical FGM is based on lamination theory in which the coordinate system is changed from the rectangular to cylindrical one and from infinite to finite plate.

In a joint research project of 5 Fraunhofer institutes, composite materials with piezoelectric fibers (diameter about 30 μm) and interdigitated electrodes are being developed. In this paper, finite element simulation techniques for this class of material are discussed. On the micromechanical level, the simulation techniques are based on the concept of the unit-cell method and allow the prediction of effective (smeared) properties of the composite as a function of the fiber and matrix properties, the fiber content, the fiber distribution, the placement of the electrodes and other microstructural details. The analyses are restricted to quasielectrostatic behavior and to linear piezoelectricity. The resulting effective properties serve as input data for the structural modeling on the macroscopic level. Four structural applications are presented: The response of a composite plate with integrated piezoelectric fiber impact sensors is simulated under quasistatic and under dynamic loading. The second application involves adaptive passive vibration damping and noise reduction with the help of externally shunted piezofibers. Possible applications to adaptive optical systems are then discussed. The fourth application is a peristaltic micropump. For this last application, only a virtual prototype exists up to now.

Much research in this decade has concentrated on the application of modal space to simplify control design and system monitoring. This investigation will address the fidelity limitations of the modal filter based classical control strategies. Specifically, when the eigen-parameters shift, in concert with semi-global changes in the systems structural properties resulting in similar mode shape but dramatic shift in frequency. Expressly, this examination will concentrate on two spatially similar five bay box trusses of exactly the same geometry (connections and element lengths) and different materials (steel and plastic) and some shift in cross-sectional dimension. The limitation of these parameter shifts should present a practical bound for future application. The investigation incorporated both analytic and experimentally based models of the structural frequency response and residue matrices to analytically model the control problem. The control is investigated for the lower frequency modes due to experimental model limitations. Investigation includes single and multi-mode control.

The impedance method predicts the response of a structure to piezoelectric patch actuators. The drawback has always been that the structure's impedances had to be calculated analytically. This work uses fmite element analysis (FEA) to generate the structure's impedances from eigenvectors. This approach allows for the method to be applied to a much wider variety of structures than before, as for many structures of interest the necessary closed form expressions do not exist. At present, the method has been used with two-dimensional structures, though it should be extendable to any structure that can be accurately modeled by FEA. From a single fmite element run, multiple actuator and response locations can be examined. The equations to recover the impedances and structure's response from a FEA normal mode analysis are developed. The method is then experimentally verified for plates with different boundary conditions, material types, and actuator orientations. Comparisons are made between calculating the impedances using just the eigenvectors at the center points of the patch sides and using a shape function to describe the eigenvectors along the patch sides. The method is found to accurately predict the plate's response. In several cases the predicted response fell within the range of experimentally recovered responses.

In active vibration control, the modeling of the mechanical structure is generally done using the finite element method. The model obtained must be reduced to compute the controller. Model reduction must achieve two objectives: the reduced model must keep its initial dynamic behavior in the frequency range of interest; and the influence of neglected dynamics must be minimized to limit the risk of spillover. In this paper, we propose an original criterion for the selection of the controlled dynamics. This criterion has the great advantage to be independent of the placement of actuators and sensors. First, the structure is successively reduced to only one mode. For each one, it is obvious to find the optimal location of one actuator and one sensor. Thus, we obtain as many SISO systems of second order as the number of modes. Then, the Hinfinity norms of these systems are computed and the modes are sorted regarding to their influence in the global response of the system. To show the efficiency of the method, it is applied to an experimental structure: an LQR controller is designed and several tests are performed. A comparison is also done with other classical techniques of reduction.

A methodology has been developed to monitor the quality and performance of Lead Zirconate Titanate (PZT) active fibers manufactured by CeraNova Corporation (Franklin, MA) in a diameter range of 80 to 500 μm for use in Active Fiber Composites (AFC) for structural control applications. Single fiber P-E loop tests (induced polarization versus applied electric field) and density measurements are conducted on samples from each fiber production run. Results are correlated with AFC pack quality, determined by measuring actuation performance (composite strain versus applied electric field) and peak capacitance. Single fiber piezoelectric properties are comparable to those of bulk PZT-5A, i.e. remanent polarization P_r in excess of 30 μC/cm² and coercive field E_c on the order of 14 kV/cm. Sintered fiber density is consistently greater than 95% of theoretical. AFC packs routinely exhibit actuation in excess of 1200 microstrain at 2.5 kV/mm applied field. Fiber characterization techniques and quantitative single fiber behavior versus composite performance correlations are discussed.

Previous papers by these authors presented an effort to develop a prototype boring tool, utilizing a piezoelectric actuator and photosensitive detectors to actively control a cutting insert. This paper describes an effort to redesign the system using an integrated structural/control methodology. The purpose of the micro-positioner is to improve precision by: (1) isolating the finish cutter from tool vibrations, (2) absorbing energy from the tool during rough cuts, and (3) compensating for small geometric or thermal errors. These characteristics enable tools with large length to diameter ratios (L/D) without loss in machining precision, and facilitate automated tool changes. The integrated structural/control design variables consist of the structural shape of the mechanism, including the piezoelectric actuator, and the controller feedback gains. The design variables are determined simultaneously in a single optimization problem. The objective and constraints equations quantify system performance, stability, actuator saturation, and life expectancy as explicit functions of the design variables. The proposed integrated methodology both simplifies the design process of the prototype boring tool, and improves the performance over the original design, as shown by simulation results.

Active deformable sheets are integrated smart planar sheet structures performing off-plane deformations under computer actuation and control, to take up a desired dynamic morphology specified in CAD software or obtained by 3-D scanning of a solid surface. The sheet prototypes are implemented in the laboratory by elastic neoprene foil layers with embedded asymmetric grids of SMA wires (Nitinol), which upon electrical contraction bend the sheet to the necessary local curvature distribution. An analytical model of such prototypes, consisting of an electrical, a thermal, a material and a mechanical module, as well as a more complex finite element thermomechanical simulation of the sheet structure have been developed and validated experimentally. Besides open-loop control of the sheet curvatures by modulation of the SMA wire actuation current, a closed-loop control system has been implemented, using feedback of the wire electrical resistance measurements in real time, correlating to the material transformation state. The active deformable sheets are intended for applications such as reconfigurable airfoils and aerospace structures, variable focal length optics and electromagnetic reflectors, flexible and rapid tooling and microrobotics.

Displacement-amplifying mechanisms can be systematically designed using topology optimization. Due to the special need of large displacement amplification for piezoelectric stacked actuators, the objective function should be formulated properly. Among output stroke, magnification factor and work ratio, magnification factor better describes the design goal of displacement amplifier and is thus adopted in this work. To depict the dynamic operation of displacement amplifier, undamped harmonic response is used in the formulation. The design problem is thus posed as a material distribution problem, which maximize the dynamic magnification factor by varying the thickness of 2-D domain. Plane stress solid is assumed for the design domain. Stiffness of the actuator and the workpiece is included in the analysis. The design problem is solved by Method of Moving Asymptotes or MMA. To show the viability of this design methodology, two examples of magnification mechanism for printer head driven at different excitation frequency are presented.

In this paper, a method based on finite element technique is developed for the design of sensor/actuator system of the active vibration control of shell structure. To prevent the adverse effect of spillover, distributed modal sensor/actuator system is established using PVDF film. Although shell structure is three-dimensional structure, the PVDF sensor/actuator system can be treated as two-dimensional. The electrode patterns and lamination angle of PVDF sensor/actuator are optimized to design the modal sensor/actuator system. Finite element programs are developed to consider curved structures having PVDF modal sensor/actuator. The nine-node shell element with five nodal degree of freedoms is used for finite element discretization. Electrode patterns and lamination angles of PVDF sensor/actuator are optimized using genetic algorithm. Sensor is designed to minimize the observation spillover, and actuator is designed to minimize the system energy of the control modes under a given initial condition. Modal sensor/actuator for the first and second modes of singly curved cantilevered shell structure are designed using above mentioned methods. For the demonstration, numerical simulation of the closed loop system is performed. Discrete LQG method is used as a control law.

A rigorous multi-objective optimization procedure, is developed to address the integrated structures/control design of composite plates with surface bonded segmented active constrained layer (ACL) damping treatment. The Kresselmeier- Steinhauser function approach is used to formulate this multidisciplinary problem. The goal is to control vibration without incorporating a weight penalty. Objective functions and constraints include damping ratios, structural weight and natural frequencies. Design variables include the ply stacking sequence, dimensions and placement of segmented ACL. The optimal designs show improved plate vibratory characteristics and reduced structural weight. The results of the multi- objective optimization problem are compared to those of a single objective optimization with vibration control as the objective. Results establish the necessity for developing the integrated structures/controls optimization procedure.

The paper introduces a novel transducer technology, called the solid-state micro-hydraulic transducer, currently under development at MIT. The new technology is enabled through integration of micromachining technology, piezoelectrics, and microhydraulic concepts. These micro-hydraulic transducers are capable of bi-directional electromechanical energy conversion, i.e., they can operate as both an actuator that supplies high mechanical force in response to electrical input and an energy generator that transduces electrical energy from mechanical energy in the environment. These transducers are capable of transducing energy at very high specific power output in the order of 1 kW/kg, and thus, they have the potential to enable many novel applications. The concept, the design, and the potential applications of the transducers are presented. Present efforts towards the development of these transducers, and the challenges involved therein, are also discussed.

Being high Q devices, low frequency underwater transducers often lack bandwidth. Variable resonance frequency transducers offer the double advantage of increased effective bandwidth and maximum response at all frequencies within the bandwidth. This paper presents and evaluates a technique to vary the first resonance frequency of some widely used underwater acoustics transducers: flexural piezoceramic bars and disks. DC bias electric fields are added to the AC driving field and used to generate in-plane tensile or compressive loads. These loads modify the flexural rigidity of the transducer, which in turn affects its resonance frequencies. Theoretical investigations show that the frequency shift per DC field is linked to the ratio of the in-plane blocked force to the critical buckling load of the transducer. This ratio depends on the type of piezoceramic material and coupling, the boundary conditions, the length to thickness ratio of the transducer, and the piezoceramic thickness and coverage. Calculations show that both significant frequency shifts per DC field and acceptable device coupling coefficients may be achievable in practice. A flexural bar transducer using k₃₁ coupling was built and tested. The experimental frequency shift per DC field and coupling coefficient were lower than predicted. Measurements show the existence of a polarization switch due to a combined compressive stress and negative field effect at -400 V/mm DC field. This polarization switch limits the range of useful negative DC fields, therefore limiting the total frequency shift, and also results in a permanent reduction of the polarization level, therefore reducing the amount of frequency shift per DC field. In the case of k₃₁ coupling, one must determine the safe stress and field region for the material and try to operate within the corresponding DC field range. In the case of k₃₃ coupling, compressive stresses and negative fields do not occur simultaneously, and the available DC field range should be much higher.

The feasibility of utilizing piezoelectric actuators for air flow control of low-power fuel cells is assessed using an electromechanical model of the actuator and a steady-state model for compressible flow. Expressions for electromechanical efficiency are derived using one-dimensional transducer equations of a piezoelectric actuator coupled to the pressure- volume relationships for an ideal gas. The derivation demonstrates that the mechanical power output and electrical power requirements of the system are a function of the input- output force ratio, the input force normalized to the blocked force of the actuator, and the piezoelectric coupling coefficient. The mechanical efficiency of the closed cycle is constant at 28.6% and the electrical efficiency varies from less than 1% for a coupling coefficient of 0.1 to approximately 8% for a coupling coefficient of 0.5. Expressions for the force, displacement, and work performed during each process of the four-stroke cycle are derived. A numerical example of a 50 Watt fuel cell demonstrates that only 219 mW of real mechanical power is required to deliver the necessary air flow to the fuel cell. Operating frequencies are approximately 600 Hz for actuators with 1 mm free displacement. Dissipation in the power electronics is between 6 and 19 Watts for linear amplifiers but can be reduced to less than 2 Watts for more efficient switching-type power conditioners. This example demonstrates that piezoelectric actuators are a viable technology for fuel cell air flow control when they are used in conjunction with efficient power electronics.

Three different piezoelectric stacks (PI, NEC, and Marco stack) were characterized in this paper. Their mechanical and electrical properties were first evaluated including Young' modulus, piezoelectric constants, and effective permittivity under mechanical preloads up to 69 MPa (10 ksi) at 2 MV/m. Test result shows that the PI stack generated the highest strain output (2087 με) under a mechanical preload of 55 MPa (8 ksi) at 2 MV/m. As electric field and frequency increased, piezoelectric stack was heated. Heating is mainly caused by power dissipated due to dielectric loss. The power density of the piezoelectric stack was measured under different frequencies, electric fields, and mechanical loads based on a factorial experimental design. Test results indicate that operational frequency influenced the power density more significantly than other parameters.

Recent research in smart wing technology has led to the identification of a need for large displacement (0.1 to 10 mm), high force (10 to 2000 N) actuators that function over low to intermediate frequency bands (0.1 to 200 Hz). A hybrid piezohydraulic pump is under development for this smart structures application. Piezoelectric stack actuators are capable of producing large forces at higher bandwidth, but the stroke is too small. Shape memory alloys are capable of producing a larger stroke, but the bandwidth is too low. Step and repeat piezoelectric devices, such as inchworm motors, increase the power output of the actuators and have the potential to produce large forces and large displacements simultaneously. The piezohydraulic pump makes use of the step and repeat capability. A preliminary piezoelectric stack actuator driven hydraulic pumps system was constructed. The pump was connected to a hydraulic actuator and the actuator driven at 1 cm/sec with a 490 N (110 lb) blocking force. To achieve this, the stack actuator was driven at 10 Hz. Two subsequent generations of the piezohydraulic pump achieved intermittent actuation rates of 10 cm/sec. This work presents efficiency considerations and design modifications utilized in the subsequent generations of the piezohydraulic pump. The relationship between the diameter of the hydraulic actuator, actuation rate, and blocking force are discussed. Effective use of accumulators to increase actuation rate and control bias pressure is also discussed.

A structural health monitoring method for determination of damages in structural system is developed using state variable model. A time-domain identification method, the subspace system identification algorithm, is first applied to get a state-space model of the structure. The identified state-space model is then transformed to two special realization forms, for determination of the equation of motion of multiple- degrees-freedom of the structure. The parameters of equation of motion, mass and stiffness matrices or damage indices are used to determine the location and extent of the damage. This method is also extended for the health monitoring of substructural system. Unlike the health monitoring of the whole structure, the health monitoring of substructure uses localized parameter identification which only involves the measurement of substructure parameters. Using this method, the number of unknown parameters and the computational requirement for each identification can be significantly reduced, hence the accuracy of estimation can be improved. Illustrative cases studies using both numerical and experimental structures are presented.

Precision inflatable space structures promise revolutionary change in spacecraft design over the next decade. Given the variety of previous applications and the potential of future concepts, development of advanced design tools is underway. Validation of these models requires experimental analysis of both ground and orbiting test articles. The present study examined the suitability of piezoelectric polymer materials (namely PVDF) to excite an inflated structure for modal testing. Experiments were undertaken using both a conventional electrodynamic shaker and a small sheet of PVDF bonded to an inflated torus. In addition, a linear finite element model of an inflated torus is compared to the experimental results. The results demonstrate the potential for PVDF to excite inflatable ground test articles.

This paper presents the use of piezoceramic transducers, PZT actuators and PVDF sensors, for experimental modal testing of a simply supported plate. A series of rectangular shape of PVDF films are evenly distributed over the plate and act as the sensing devices instead of traditional acceleration sensors. The rectangular PZT patches that are adhered to the opposite surfaces of the plate and activated 180° out- of-phase for pure bending excitation are adopted as the actuator. The theoretical formulation of frequency response functions (FRFs) of the piezoceramic transducers is developed. The mode shape functions of the PZT actuator and the PVDF sensor are identified, respectively. Experiments are performed to obtain a column of FRF matrix. The structural modal parameters, including natural frequencies, modal damping ratios and mode shapes, can then be extracted by a modal parameter extraction method. Results show the modal parameters can be properly obtained and physically interpreted in comply with theoretical results. This paper presents the concepts of smart structural testing (SST) with the use of piezoceramic transducers and leads to the applications of smart structures to health monitoring of structural systems.

Current applications in active vibration control mainly use piezoceramic actuators (PZT). With the aim of improving vibration absorption, electrostrictive actuators have been elaborated. These electrostrictive ceramics show very attractive properties for active vibration control applications. Yet, their non linear electromechanical behavior tempers these numerous advantages and considerably complicate their use. In usual active vibration control applications, dynamic electric fields with varying magnitudes and frequencies are applied to the ceramic. Earlier measurements, performed at ONERA, show that the ceramic behavior is strongly sensitive to operating parameters (electric field magnitude and excitation frequency, and surrounding temperature). It is demonstrated in this article that this sensitivity can, in fact, be reduced to a sensitivity of the material to its own temperature. Indeed, a significant heating of electrostrictive ceramics occurs when they are subjected to a sinusoidal electric field. This heating turns out to be, itself, dependent on operating parameters. An experimental electric model of stressfree electrostrictive patches is presented, which is then used to develop constitutive relations of these materials. A simplified, dynamical, electromechanical coupled model of distributed electrostrictive patches bonded on a generic thin plate host structure is finally briefly discussed.

A three-dimensional model of a structurally integrated optical fiber sensor into a composite patch bonded over a cracked metallic structure is built using ANSYS finite elements analysis program. Composite patch is modeled assuming three- dimensional epoxy matrix with embedded cylindrical carbon fibers and optical fiber sensors. The latter is composed from two different materials to represent the core/cladding and the protective coating. The whole patch is perfectly bonded over a cracked aluminum sheet. External loads are applied only on the metal structure, as in a real repair case. The primary loading axis of the metal is parallel to the direction of the optical and the carbon fibers. However, because of the different nature of the materials that form the composite patch, complex mechanical interactions between the fibers and the surrounding material occur, resulting in a complicated strain field along the optical fiber sensor, which causes significant sensing variations. Different crack lengths are assumed in order to study their effect on the strain field of the optical fibers at different points across its radius, as well as the variation of the stress field along the optical sensor and the corresponding plots were produced.

Occupant safety and severity of vehicle damage are important factors in automotive vehicle design. Smart automobiles of the future could potentially use distributed smart material sensors and actuators in order to identify impact and take appropriate evasive or mitigative actions. This provides the motivation for this study. The first part of this study is focused on detecting the location and magnitude of impact, particularly for the case where the automotive structure is subjected to minimal damage. This is accomplished by developing a generalized algorithm using the Reissner-Mindlin plate theory, the Rayleigh-Ritz energy approach, and the Lagrangian-Hamilton principle. The level of performance of this methodology is demonstrated for impacts on a simply supported rectangular plate. Different case studies for static as well as impact loading with point as well as area contacts are presented. An algorithm using deconvolution for identifying impact location and magnitude has been developed and implemented. Additionally, the influence of damage on the structural vibratory content is studied via a frequency analysis. The modal analysis for undamaged and damaged plates, with nine different damage locations and six different damage sizes are performed. Changes in frequency and mode shapes are observed in regard to the severity of the damage.

A high-speed traversing mechanism using two electro- rheological clutches is described. An application of the traversing mechanism is in winding filaments onto bobbins. The traverse speed is 5 m/s; the required turn round period is 10 to 20 milli-seconds; the traverse length is 250 mm; the turn round position must be controllable and repeatable within +/- 1 mm; and the traverse requires to be controlled to shape the resulting bobbin. These combined criteria of high speed and controllability makes the use of electro-rheological fluids an attractive proposition. The paper considers the optimization of the traversing mechanism; both geometric and fluid parameters are considered. The limiting performance of the mechanism is detailed together with the effects on the precision of the mechanism. The paper also outlines control aspects of the mechanism and uses this to indicate important areas for consideration in the future development of electro- rheological fluids.

Conventionally electroded surface-bonded piezoceramic elements are incapable of controlling torsional motions because the in- plane isotropic actuation strain is orthogonal to the surface shear strain pattern associated with torsional deformations. For devices with in-plane orthotropic properties, however, such as those with interdigital electrodes (IDE), sensing and controlling torsion is possible, allowing damping by passive or active means. An electromechanical model is developed for orthotropic piezoceramic devices bonded to the surfaces of beams or tubes in torsion; expressions for mechanical compliance, actuator authority, electromechanical coupling, and passively attainable damping for the combined system are derived in terms of geometric and material parameters and orientations. Optimization of the actuator orientation and geometry is addressed, with specific attention to the width, spacing, and angle of interdigital electrodes. Experimentally determined damping ratios are presented for torsional IDE piezoceramic devices with passive shunts, along with considerations for future improvements.

Application of smart materials technology in nuclear industry offer new opportunities in this industrial sector for safety enhancement, reduced personal exposure, life-cycle cost reduction, and performance improvement. However, the radiation environments associated with nuclear operations represent a unique challenge to the testing, qualification and use of smart materials. The present study assesses the physical limitations of smart materials applications to nuclear industry and identifies areas of where such technologies could be reliably used. In our investigation, we considered a spectrum of smart materials technologies and a variety of irradiation environments. A literature survey to identify prior experimental data related to irradiation effects on smart-materials showed significant irradiation induced alterations in performance. However, the available database was limited and additional tests will be required before smart materials technologies can be introduced in most radiation environments. This paper summarizes a test program that was developed for the Accelerator Production of Tritium project. This program was designed to identify specific irradiation areas where the application of smart materials technologies is practical.

In this paper, the authors present vibration mode identification of rectangular plates by using discrete piezoelectric materials. The novelty in this study stems from the fact that only spatial information is used. The analytical development and numerical simulation results of the method are also included. For the structural vibration control community, identification of the dominant vibration has been an important issue. If the dominant vibration modes are successfully identified, the control engineers can choose a proper control gain set which has been pre-tuned for the identified vibration mode. As the development of piezoelectric materials progressed, vibration mode identification techniques step into a new stage. Several papers reported vibration mode identification by using distributed piezoelectric modal sensors. Unfortunately, the spatially filtering methods need specially designed configuration corresponding to the geometry of the structures. These difficulties hinder the application and development of modal sensing and vibration control technology. In this paper, the authors develop a new method of the mode identification, and present analytical simulations for rectangular plates and circular plates. Finally, experimental verification of the method is also presented.

Active magnetic bearings are a proven technology in turbomachinery applications and they offer considerable promise for improving the performance of manufacturing processes. The Active Magnetic Bearing (AMB) is a feedback mechanism that supports a spinning shaft by levitating it in a magnetic field. AMBs have significantly higher surface speed capability than rolling element bearings and they eliminate the potential for product contamination by eliminating the requirement for bearing lubrication. In addition, one of the most promising capabilities for manufacturing applications is the ability of the AMB to act concurrently as both a support bearing and non-invasive force sensor. The feedback nature of the AMB allows for its use as a load cell to continuously measure shaft forces necessary for levitation based on information about the magnetic flux density in the air gaps. This measurement capability may be exploited to improve the process control of such products as textile fibers and photographic films where changes in shaft loads may indicate changes in product quality. This paper discusses the operation of AMBs and their potential benefits in manufacturing equipment along with results from research addressing accurate AMB force sensing performance in field applications. Specifically, results from the development of enhanced AMB measurement algorithms to better account for magnetic fringing and leakage effects to improve the accuracy of this technique are presented. Results from the development of a new on-line calibration procedure for robust in-situ calibration of AMBs in a field application such as a manufacturing plant scenario are also presented including results of Magnetic Finite Element Analysis (MFEA) verification of the procedure.