Experimental investigations conducted into active control of longitudinal waves transmitted through a hollow cylindrical strut are presented in this article. Following along the lines of our previous work, an active strut of finite extent length, instrumented with sensors, piezoelectric, and magnetostrictive actuators, is studied in the frequency range of 10 Hz to 2 kHz. Single and multiple actuator arrangements are employed in open loop control investigations, and the effectiveness of the control effort in minimizing longitudinal harmonic disturbances transmitted through the strut is experimentally investigated. Initial efforts towards development of feedforward and feedback boundary control algorithms for reducing longitudinal vibratory loads in finite length cylinders is also presented. For the feedback controller development, the strut-actuator ensemble is modeled by using the one dimensional wave equation and the direct method of Liapunov is used. The feedforward control algorithm is based on the previous model of the active strut and relies on measurements of axial strains and accelerations at the strut ends. The influence of the boundary conditions and static forces applied to the strut are also investigated. The relevance of the current work to control of structure-borne helicopter cabin interior noise is also discussed.

A membrane primary mirror in a space-based imaging system has the ability to overcome current payload constraints and meet evolutionary needs of the future. The challenge of membrane optics in space is the process of implementing adaptive optics technology to the membrane surface that will provide at least rough order of magnitude imaging, where small aberrations can be removed downstream in the system. The objective of this research was to develop a system to categorize surface properties of optical quality membrane material with the ability to interpret membrane mirror deformation. Coincident with this objective was the design and construction of membrane mirrors and associated test tooling, the design and application of in-plane zonal control for piezopolymer actuated membrane mirrors, and mirror deformation analysis. The system provides wavefront analysis with both optical interferometry and Shack-Hartmann wavefront sensing, with good correlation, which compares favorably to Zygo interferometer data. Results from membrane static testing will be presented. They demonstrate deflection of tens of wavelengths is possible.

Replacing articulated flight control surfaces with adaptive controls reduces surface discontinuities, and enhances low observability. Actuation of the aerodynamic surfaces is achieved by an electric field applied to PZT actuators embedded in the top and bottom skins, creating differential strain and shear (torsion) in the host substrate. The torsion of the torquebox was modeled in the presence of a full complement of air-loads by extending the Bredt-Batho theorem. This was accomplished through modifying Libove's method, using a thin-walled, linearly elastic, fully anisotropic, trapezoid cross-section beam. The linear tip twist angles due to a uniform cross-sectional moment were verified using the isotropic Bredt-Batho theorem, and published anisotropic results by applying isotropic, then anisotropic laminate elastic properties. The isotropic solutions were within 3.1%; the anisotropic results were within 6.9-10.9% of the published angles. The PZT actuation of the host structure was achieved by substituting PZT- composite laminate elastic properties into the derived solution and inducing strain and shear of the PZT lamina by composite laminate elastic properties into the derived solution and inducing strain and shear of the PZT laminae, the angular twist as a function of the host lamina orientation angle and applied voltage was recorded. The amount of twist ranged between 0.03 and 0.40 degrees, and 0.12-1.04 degrees for the AFC and G-1195 PZT laminae respectively.

The present research investigates the feasibility of a compact piezoelectric actuator mechanism to oscillate the rotorblade trailing-edge flap for active vibration suppression. The main components of the actuator are two piezostack segments and a dual-stage stroke amplifier. Each piezostack segment is fabricated by bonding five identical piezostacks. A bidirectional double-lever amplification concept is developed, that involves an extended dual-stage lever-fulcrum stroke amplifier and two parallel rows of piezostacks. Both design and fabrication of the trailing-edge flap actuator are addressed. The designed actuator is of size 8-inch length (spanwise), 1.25-inch width (chordwise), 0.75-inch height, and the weight of the prototype is 1.05 lbs. The bench-top test showed 94% of ideal displacement output. To validate the feasibility of the designed actuator, the spin test in the vacuum chamber is planned to evaluate the performance in rotating environment up to 700g of centrifugal loading.

This paper presents research aimed at actively altering the twist distribution of a tiltrotor blade between hover and forward flight. Three different concepts-extension-twist coupled composites, bimoment actuation and discrete SMA torque tube actuation - are considered, and the torque tube appears the most feasible. Parametric design of the torque tube and attachment technique is presented with actuation torque, heat transfer and bandwidth issues being considered to arrive at the configuration of the tube. The effect of heat treatment of the SMA in tuning the actuation characteristics is discussed. A dramatic improvement in the actuation cooling time is demonstrated through the use of active cooling using thermodelectric modules. An extension of the one-dimensional formulation of Brinson's model to the torsional case is presented. The model is shown to have good correlation with room temperature characteristics. The criterion for impedance matching between the actuator and the host structure is derived. The torsional actuator is tested both under no load and acting against a restoring spring and shows repeatable actuation characteristics.

Low power laser diode sources were used in conjunction with electronically controllable time delays and fiber optic delivery arranges as a phased array to produce an electronically steerable ultrasonic source. Delays between the array elements of up to 520nS allowed steering of the fundamental longitudinal mode to be achieved at angles of up to 18 degree(s), whilst low pulse powers of 3.6(mu) J ensured that the testing mechanism was non-destructive. Beamsteering has been demonstrated for aluminium plates demonstrating great potential as a tool for structural assessment.

Smart materials and actuators meet a noticeable infatuation for the shape control of aerodynamic surfaces. This interest is borne as well to reduced scale where space is limited for the machining of models allowing to demonstrate the merits of some advanced concepts as to full scale prototypes, where these novative mechanisms are supposed to replace advantageously hydraulic or classical electro-magnetic solutions. These new devices are even supposed to provide in some cases several benefits for integrity improvement of the structure itself. The extrapolation from one to the other is nevertheless not straight forward and must take into account the distinct specifications if only the avionability constraints and the cost. If bulk and multilayered electro-active materials and integrated adaptive systems issued from them are convenient for dynamic control, shape memory alloys are only suitable for slow but quite significant geometry changes. After a brief survey of the most outstanding properties, the availability and the limitations of usual materials, actuators and electronic controllers, easily provisionable on the market, the paper deals with some technological applications experimented on models. The subjects investigated concern the flap deflection, the twist of rotor blades and the swelling of a wing profile. The last part of presentation points out some fast started-up and economical developments, to promote these actuators in the near term in order to compensate topical deficiencies, and first actions already undertaken to this end.

Scalable rotary actuators are being developed with the help of Shape Memory Alloy (SMA) wires. Subjected to elevated temperatures SMA wires deliver large strains and high stresses. Yet their bandwidth is limited because of the time required for cooling. Bandwidth can be enhanced by miniaturizing the actuating system, which results in higher cooling rates. Using SMA wires with diameter of about 100 micron, several miniature actuators have been designed and fabricated. For example, a rotary joint with bi-directional actuation, which is about 4mm wide, 9mm long and 3mm high, can achieve angular deflection of around +/- 60 deg. Based on this bi-directional actuator, SMA ratchet mechanisms with minimum feature sizes of about 200 micron have been developed. The ratchet mechanisms can transform angular motion to continuously rotating motion. SMA wires are embedded into polyurethane structures using Shape Deposition Manufacturing (SDM). SDM is a layered manufacturing process capable of building complex 3D parts through the combination of material addition and subtraction. A key advantage of this process is the ease by which process interruption may occur to embed sensors and actuators into components. SDM can also fabricate functional mechanisms in an assembled configuration eliminating the need for assembly. The present article will describe design and manufacturing processes which enable the fabrication of the scalable rotary actuators. System performance and behavior of the SMA actuators will be also discussed in this contribution.

Piezoelectric actuators have been used for active vibration control, noise suppression, health monitoring, etc. The large appeal in using smart material actuators stems from their high mechanical energy density. A relatively new actuator (THUNDER) has overcome the displacement hurdles that have plagued traditional piezoelectric based actuators. It is capable of providing a displacement on order of 0.5 cm. This allows the actuator to be used in some underwater applications, such as propulsion. To date the electrical power consumption and electromechanical efficiency of these actuators has not been quantified; specifically, applied as underwater propulsors. Some of the challenges in obtaining this information stems from the actuator's non traditional actuating architecture, high voltage requirements, and its electrical non-linearity. The work presented experimentally determines the electrical power consumption and mechanical displacement of THUNDER actuators used as underwater propulsors. It is found that the electrical power consumption of the clamshell actuator investigated is significantly less than that consumed by other autonomous under water vehicles. The potential thrust generated by such a device remains to be quantified.

Vibration isolation and precision pointing problems using hexapods have been separately investigated by several groups of researchers. Since many applications require simultaneous vibration isolation and precision pointing (e.g., telescopes, laser communication, and laser weapons), it is particularly useful to do both with a single device. A simultaneous control scheme is developed in this paper using acceleration feedback to provide high-frequency vibration isolation, while Cartesian pointing feedback provides low-frequency pointing. The compensation is divided by frequency because pointing sensors often have a low bandwidth, while acceleration sensors often have a poor low-frequency response. Methods for unifying these finite bandwidth joint and Cartesian controls to perform simultaneous pointing and vibration isolation on a single platform are developed and verified. Experiments on the University of Wyoming hexapods show that this scheme provides a viable control bandwidth.

This study is focused on the development effort conducted on a new generation of biorobotic actuators suitable for use in many industrial and biomedical applications. The new robotic actuator herein called the Metal Hydride Anthroform Biorobotic Actuator (MHABA) uses metal hydrides as hydrogen sponge and can be operated both electrically and thermally. A small metal hydride biorobotic actuator has been built using a porous metal hydrice compact of LaNi₅/CU. The reported MHABA has high specific-force (over 100 N/g of metal hydride), and is biomimetic, compact, operationally safe, lubricationless, noiseless, fast and soft actuating, and environmentally benign. The potential for applying the MHABA as electrically/thermally-controllable large force and displacement robotic actuator to industrial, biomedical, and space structures is enormous. The preliminary data shows a great potential for these metal hydride actuators to be used as high power actuators.

Vibration in today's increasingly high-speed vehicles including automobiles severely affects their ride comfort and safety. The objective of this paper is to develop and study automotive suspension systems with magneto-rheological (MR) fluid dampers for vibration control in order to improve the passenger's comfort and safety. A two degree-of-freedom quarter car model is considered. A mathematical model of MR fluid damper is adopted. In this study, a sliding mode controller is developed by considering loading uncertainty to result in a robust control system. Two kinds of excitations are inputted in order to investigate the performance of the suspension system. The vibration responses are evaluated in both time and frequency domains. Compared to the passive system, the acceleration of the sprung mass is significantly reduced for the system with a controlled MR damper. Under random excitation, the ability of the MR fluid damper to reduce both peak response and root-mean-square response is also shown. The effectiveness of the MR suspension system is also demonstrated via hardware-in-the-loop simulation. The results of this study can be used to develop guidelines to effectively integrate automotive suspensions with MR dampers.

There is much current interest in the development of smart fluid clutches for use in the design of high speed machinery. In this paper, the authors employ an ER clutch mechanism in a robotic application. This clutch mechanism consists of twin ER clutches which are driven in opposite directions by two electric motors. By controlling the electric field applied to each clutch, it is possible to control the angular displacement of a robot arm. Before considering control, an established mathematical model is validated. The purpose of this model validation is to help design a control strategy for accurate positioning of the robot arm. Through the use of a Simulink program and a digital controller, both the simulated and experimental angular displacements are compared and shown to be in close agreement. Finally, the displacement response of the ER- driven and DC servo-actuatored robot arm are compared and conclusions are drawn as to the suitability of the ER clutch mechanism as a robotic actuator.

A magnetorheological (MR) fluid-based hydraulic power system is analyzed and experimentally validated by testing a prototype. A set of MR valves is proposed to implement within a Wheatstone bridge hydraulic power circuit to drive a hydraulic actuator using a pump. The MR valves are used in place of conventional mechanical servo valves. The proposed use of MR valves in hydraulic actuator systems has many advantages. First, MR valves have no moving parts, enhancing reliability. Second, the MR valves operate at the same speed as the actuation bandwidth (typically below twenty Hz in our applications). Third, the actuator relies on flow rates for a given pump speed, and avoids, to a large degree fluid compliance. Fourth, if a change in stroke direction is required, the flow through each of the MR valves can be controlled smoothly via changing the applied magnetic field. The performance of the Wheatstone bridge with MR valves is theoretically derived using three different models of the MR fluid behaviors: an idealized model, a Bingham-plastic model and a biviscous model. The analytical system efficiency in each case is compared, and departures from ideal behavior are recognized. The driving force and efficiency will be evaluated in the MR hydraulic power actuator system for both Bingham plastic and biviscous flows. An MR valve is designed using a magnetic finite element analysis. The magnetic flux density developed in the MR valve are verified by analytical and experimental methods. The yield stresses achieved in the MR valve due to the applied current are also measured to validate the design methodology. The overall performance of the MR fluid based hydraulic power system is described using the experimental MR valve performance data.

It is genrally known that tracked vehicles are exposed to severe working environments such as rough road and complex ride behaviors. Therefore, high performance suspension units are required to isolate the vehicle body from terrain induced vibrations. This paper presents a novel type of suspension units utilizing an electro-rheological (ER) fluid. An in-arm type of ER suspension units (ERSU) is modeled and its spring and damping characteristics are analyzed with respect to the intensity of the electric field. Subsequently, a 16 degree-of-freedom model for a tracked vehicle is adopted and aneuro-fuzzy skyhook controller is designed for the semi-active ERSU. In the control algorithm, the vertical speed of the body and the rotational angular speed of the wheel are used as fuzzy variables. Vibration control performances of the tracked vehicle subjected to bump and random excitations are evlauated in both the time and frequency domains. In addition, the mobility of the vehicle with the limited power absorption is investigated with respect to the road roughness.

This Paper demonstrates the possibility of shock wave attenuation propagating through a smart structure that incorporates ER insert. The wave transmission of ER inserted beam is theoretically derived using Mead & Markus model and the theoretical results are compared with the finite element analysis results. To experimentally verify the shock wave attenuation, ER insert in an aluminum plate is made and two piezoceramic disks are used as transmitter and receiver of the wave. The transmitter sends a sine pulse signal such that a component of shock wave travels through the plate structure and the receiver gets the transmitted wave signal. Wave propagation of the ER insert can be adjusted by changing the applied electric field on the ER insert. Details of the experiment are addressed and the possibility of shock wave attenuation is experimentally verified. This kind of smart structure can be used for warship and submarine hull structures to protect fragile and important equipment.

The active vibration with smart material has potential to realize not only distributed actuator and sensor but also simplified and light weight active control methods. Electro-Rheological Fluid can produce shear force according to voltage of electrical field and respond quickly enough to control structure. In this paper, control methods to achieve effective damping are described. The key points are modeling the smart structure with Electro-Rheological Fluid and control methods for reducing vibration. The nonlinear model is derived to identify physical parameters of Electro- Rheological Fluid. The vibration test results of small specimens show that this analytical model can express electro-rheological effect. The analytical model is made for larger specimen in the same manner. The effects of vibration reduction with Electro-Rheological Fluid on the bema structure are investigated as the vibration control system, where the strength of electrical field for input and minimizing the transmissibility of vibratory loads for objective analytically. As the results of this study, it is revealed that smart structure embedded ERF can achieve the expected damping performance. Some technical issues of control method for applying to any actual structures are discussed.

To realize simplified vibration reduction system, Electro- Rheological Fluid will be used. Since there was no suitable ERF for this study, material specification was created. According to this specification, particle-type ERF was manufactured and tested. To evaluate damping characteristics of laminate with ERF, three kinds of specimens were manufactured and tested. Specimen A, 20mm x 200mm, and B, 20mm x 400 mm, were used to evaluate ERF and acquire basic damping data to establish analytical model. Element specimens, 40mm x 500mm, were tested as small part of the actual structure to evaluate performance of the smart structure concept. From technical point of view, this smart structure concept has the ability to reduce vibration well but there are some technical issues to be resolved for applying to actual structures. The specification for applicable ERF and manufacturing method for smart structures are discussed.

This paper is a report of an initial investigation into the active control of preload in the joint using a shape memory actuator around the axis of the bolt shaft. Specifically, the actuator is a cylindrical Nitinol washer that expands axially when heated, according to the shape memory effect. The washer is actuated in response to an artificial decrease in torque. Upon actuation, the stress generated by its axial strain compresses the bolted members and creates a frictional force that has the effect of generating a preload and restoring lost torque. In addition to torque wrenches, the system in question was monitored in all stages of testing using piezoelectric impedance analysis. Impedance analysis drew upon research techniques developed at Center for Intelligent Material Systems and Structures, in which phase changes in the impedance of a self-sensing piezoceramic actuator correspond to changes in joint stiffness. Through experimentation, we have documented a successful actuation of the shape memory element. Due to complexity of constitutive modeling, qualitative analysis by the impedance method is used to illustrate the success. Additional considerations encountered in this initial investigation are made to guide further thorough research required for the successful commercial application of this promising technique.

The present work relates to the assessment and testing of a multifunctional intelligent system, based upon the use of piezoelectric devices, devoted both to the active noise and vibration control and to damage detection f the structure. In the control application, the piezoelectric devices (in form of patches) play the role of actuators; their induced secondary vibration field has the target to reduce the primary one through a specific control algorithm and system. In the health monitoring application, the piezo devices play both the roles of actuators and sensors. In fact the developed technique is primarily based upon the evaluation and comparison of the structure Frequency Response Functions (FRF) that intrinsically contains all the information regarding the structural properties whose change may be correlated with incipient damages. The aforementioned application were investigated and experimentally assessed with good results with reference to a typical partial fuselage structure (three frames, eight stringers and the skin panels: 1.2 m x 1.7 m). On the noise control application side, a height sensors/height actuators control architecture was then assessed and experimentally tested whose results may be synthesized in a 30 dB vibration level reduction at sensors locations and more than 20 dB of reduction of the associated noise field. In the optic of a multifunctional intelligent system, the aforementioned set of piezo's was decided to be used also for health monitoring application. As a preliminary activity, an extensive monitoring was performed on the integer structure to verify the sensibility of the system and the stability of the defined Damage Index (DI) in respect to environmental factor not related to structural real modification. To verify the sensibility of the technique to reveal and locate a typical shear clip damage, a set of rivets were successively cut in the area surrounding the frame shear clip, and relative FRF's were acquired and relative DI calculated. The analysis of the data showed a good sensibility of the system to identify the presence of a damage with maximum values of the DI in the sensor closest to the damage location and with an absolute value of the index growing up with damage extension.

A damage detection method was implemented for a simply supported beam structure. The analytical model was compared to experimental results. The theoretical model was obtained from an energy formulation of the problem using the Rayleigh-Ritz method to obtain the equation of motion. Matrices were composed in a State Space model to reproduce the input-output system between actuator and sensor. The damage was modeled with material property variations in a small section of the beam. The experimental set up consisted of an aluminum beam with damage introduced by adding different weights in various locations. Two piezoelectric patches were used to provide the dynamical excitation and output the response. The dynamic changes were investigated and compared with theoretical predictions with good agreement obtained. The Power Spectral Density (PSD) approach was used to obtain information related to the size of damage. The analysis resulted independent of damage location.

The DAMASCOS (DAMage Assessment in Smart COmposite Structures) project is a European Union funded program of work bringing together a number of academic and industrial partners throughout Europe. The aim of Damascos is to apply new ultrasonic detection and generation techniques integrated within the structure, together with advanced signal processing to realize damage assessment and ageing characterization in composite structures. This paper describes the background, experimental findings and future applications of the technology as the project moves into its final phase.

Active sensor wave propagation technique is a relatively new method for in-situ nondestructive evaluation (NDE). Elastic waves propagating in material carry the information of defects. These information can be extracted by analyzing the signals picked up by active sensors. Due to the physical property of wave propagation, large area can be interrogated by a few transducers. This simplifies the process of detecting and characterizing defects. To apply this method, efficient numerical modeling is required to predict signal amplitude and time history of elastic wave scattering and diffraction. In order to construct the model, good understanding of these physical phenomena must be achieved. This paper presents results of an investigation of the applicability of active sensors for in-situ health monitoring of aging aircraft structures. The project set forth to develop non-intrusive active sensors that can be applied on existing aging aerospace structures for monitoring the onset and progress of structural damage such as fatigue cracks and corrosion. Wave propagation approach was used for large area detection. In order to get the theoretical solution of elastic wave propagating in the material, wave functions of axial wave, share wave, flexure wave, Raleigh wave, and Lamb waves were thoroughly investigated. The wave velocities and the motion of these different types of waves were calculated and simulated using mathematical analysis programs. Finite Element Method was used to simulate and predict the wave propagating through the structure for different excitation and boundary conditions. Aluminum beams and plates were used to get experiment results. Structures both pristine and with known defects are used in our investigation. The experimental results were then compared with the theoretical results.

The application of bonded composite patches to repair or reinforce defective metallic structures is becoming recognized as a very effective versatile repair procedure for many types of problems. Immediate applications of bonded patches are in the fields of repair of cracking, localized reinforcement after removal of corrosion damage and for reduction of fatigue strain. However, bonded repairs to critical components are generally limited due to certification concerns. For certification and management of repairs to critical structure, the Smart Patch approach may be an acceptable solution from the airworthiness prospective and be cost effective for the operator and may even allow some relaxation of the certification requirements. In the most basic form of the Smart Patch in-situ sensors can be used as the nerve system to monitor in service the structural condition (health or well-being) of the patch system and the status of the remaining damage in the parent structure. This application would also allow the operator to move away from current costly time-based maintenance procedures toward real-time health condition monitoring of the bonded repair and the repaired structure. TO this end a stand-alone data logger device, for the real-time health monitoring of bonded repaired systems, which is in close proximity to sensors on a repair is being developed. The instrumentation will measure, process and store sensor measurements during flight and then allow this data to be up-loaded, after the flight, onto a PC, via remote (wireless) data access. This paper describes two in-situ health monitoring systems which will be used on a composite bonded patch applied to an F/A-18. The two systems being developed consists of a piezoelectric (PVDF) film-based and a conventional electrical-resistance foil strain gauge-based sensing system. The latter system uses a primary cell (Lithium- based battery) as the power source, which should enable an operating life of 1-2 years. The patch health data is up- loaded by the operator using an IR link. The piezoelectric film-based sensing system is self-powered and has been designed to operate using the electrical power generated by an array of piezoelectric films, which convert structural dynamic strain to electrical energy. These transducers power the electronics which interrogate the piezoelectric film sensors, and process and store the patch health data on non-volatile memory. In this system the patch health data is up-loaded by the operator using a magnetic transreceiver. This paper describes the development and evaluation of the two systems, including issues such as system design and patch health monitoring techniques.

A new method of damage detection using wavelet transforms and curvature mode shapes is proposed in this paper. A damage in the structure results in changing its dynamic characteristics such as natural frequencies, damping, and mode shapes. A number of researchers have investigated structural health monitoring techniques for identifying, locating, and quantifying the damage using the changes in the dynamic response of a damaged structure. Curvature mode shape and wavelet maps are two such methods that have already been used to locate damages. These methods have some limitations in determining the exact location of the damages. We have developed a technique by combining these two methods for enhancing the sensitivity and accuracy in damage location. The mode shapes are double differentiated using the central difference approximation to obtain the curvature mode shape. Then a wavelet map is constructed for the curvature mode shape. It is shown that this method can be used to determine the location of the damages. The proposed method is applied to detect damage in an experimental lattice structure and a cantilever beam with multiple damages. The mode shapes are obtained analytically using finite element analysis and also experimentally using laser vibrometer. The experimental results obtained are satisfactory.

This paper investigates the feasibility of sensing damage emanating from rotating drivetrain elements such as bearings, gear teeth, and drive shafts via airborne paths. A linear phased acoustic array of microphones is evaluated as a potential fault detection scheme for detecting acoustic signatures radiating from gearbox components. Specifically, this paper discusses the minimum spot size for a given linear array geometry and its sensitivity to acoustic sources. In addition, the use of beam focusing and beam steering to track individual tooth mesh dynamics are analyzed. Experimental results for a linear array are presented to illustrate the concepts of adaptive beam steering and acoustic filtering. This feasibility study indicates that the linear array can be used to track the acoustic signatures of gear mesh dynamics at higher harmonics of the mesh frequency.

It is well known that barely visible damage is often induced in composite structures subjected to out-of plane impact, and the mechanical properties of the composites decrease markedly. The stiffened composite panels, which are the representative structural elements of airplane, are characterized by different impact damage from that of the coupon level specimens. Therefore, the goal of this study is that small-diameter optical fiber sensors are applied in stiffened composite panels, and it is discussed about the possibility of the detection of impact damage in the structures by the sensors. In this study, both multi-mode optical fibers and fiber bragg grating (FBG) sensors are used for detecting impact load and impact damage in stiffened composite panels. The fibers have polyimide coating and about 40 micrometers in cladding diameter which will have no serious effect on mechanical properties of composites. Impact tests are performed using the stiffened composite panels with embedded optical fibers. The characteristics of impact damage are investigated. The impact load, the strain and the optical responses of the optical fibers are measured as a function of time. And we discuss the relationship among the optical responses, the impact load and the impact damage.

Sandwich structures we are interested in (glass fibers skins foam core) are very sensitive to low velocity impacts. These impacts induce debonding between the skins and the core and a crush of the foam, which are not visible from the outside. We propose a health monitoring system to localize these damages and estimate their size. This system is based on thin piezoelectric discs bonded on the skins and used as transducers, making it possible to generate and detect Lamb waves propagating in the sandwich. Experiments show that it is possible to choose waves having interaction with the particular damages of this sandwich. In order to analyze the interaction of Lamb waves with the defect, and define and optimize identification procedures for these defects, we have done f.e.m. computations which make it possible to obtain theoretical background to the analysis of the experimental data and propose an identification procedure of defects. When applied to numerically simulated experimental data, the identification procedure for defects give quite good results.

This paper reports results of the application of a simple technique that explores the use of piezoelectric actuators and sensors to monitor the growth of surface breaking defects in beams. The method consists in exciting the structure with piezoelectric actuators, subjected to either a single frequency or broad-band signal, while recording the electromechanical response of sensors placed close to the defect. Piezoelectric sensors detect the damage growth by monitoring changes in the dynamic strain field induced by the actuator near the defect. The performance of this methodology was assessed through experiments in beams containing surface breaking fatigue cracks or machined slots. Results have shown that the choice of adequate parameters, such as sensor size and its distance to the crack edge, allows the detection of small changes in defect depth. Finite element simulations were also performed to determine a correlation between sensor response, sensor location, and damage size. Results from tests performed in a three-dimensional framed structure are also presented.

This paper describes a theoretical and experimental investigation concerning embedded piezoelectric transducers employed principally for condition monitoring of engineering composites. Both interdigital transducers (IDTs) and plate transducers are investigated with the aim of assessing their efficiency as uni-modal Lamb wave transmitters. The IDT configuration comprises a piezocomposite layer sandwiched between two flexible printed circuit boards, where the interdigital electrode spacing corresponds to the wavelength of the desired Lamb wave mode. The alternative configuration comprises a thin piezoceramic plate for which the lateral dimensions are chosen to efficiently couple energy into the desired mode. For both types of transducer, finite element models have been successfully employed to establish the design requirements for generating the zero order symmetrical mode (S_o) without simultaneously generating the zero order anti-symmetrical mode (A_o), which exhibits strong velocity dispersion. In this investigation the A_o mode is regarded as coherent noise. Generation of a pure S_o mode is shown to require positioning of the transducer at a depth which is exactly half way between the top and bottom faces of the plate-like structure within which it is embedded. For structural monitoring, the plate-type transducer is shown to be more suitable than the IDT. A scanning laser vibrometer was used to verify many of the theoretical findings.

This paper proposes a new type of piezoactuator-driven valve system. The piezoceramic actuator bonded to both sides of a flexible beam surface makes a movement required to control the pressure at the flapper-nozzle of a pneumatic system. After establishing a dynamic model, an appropriate size of the valve system is designed and manufactured. A sliding mode controller is then formulated in order to achieve accurate tracking control of desired pressure trajectories. The controller is experimentally realized and control performances for various pressure trajectories are evaluated in the presence of the parameter variations.

A plate of PZT5h was prepared with a single electrode on one face connected to a power amplifier. The opposite face was left as bare ceramic material which was then exposed to an electron beam. Sixteen strain gages were attached atop the electrode to measure the strain response and as a function of electrode potential (backpressure voltage). A range of sinusoidal voltage inputs were applied to the electrode and the strain response and current draw through the PZT were recorded. Electrode potentials between -15 and 100 V yield very predictable strain response and extremely small currents (approcimately 10^-7 - 10^-6 microamperes) which appear to be independent of the electrode potential. Below -15 V the current through the PZT suddenly increases to 10 (mu) a. At -15 volts level the strain response is still predictable but, as the electrode voltage decreases the strain signal begins to display significant drift. The root cause of this phenomenon is examined with the aid of the deBroglie-Einstein postulate and the Schr*dinger wave equation.

The piezoelectric telescopic actuation architecture capitalizes upon an internally leveraged amplification technique to produce large actuation forces with amplified displacements. This building-block type actuator consists of interconnected concentric, cascaded cylinders with end cap joints that allow for a telescopic type motion. The internal amplification scheme and building-block nature of the telescopic design allow for efficient, densely packed actuators that yield a high work output for a given volume. This paper presents an experimental investigation of the quasi-static force-deflection performance of three unique telescopic prototypes, each manufactured by different means, from various materials, and in distinct geometries. To accurately predict the observed behavior of this architecture, a full three-dimensional numerical model was constructed for each prototype and was used to revise a previously derived analytical model. These models were refined to include extra compliance factors to account for observed actuation losses, focusing primarily on the bonding layer effects. The revised models captured more accurately the complex actuator behavior observed in the experiments and characterized better the loss mechanisms in the telescopic actuation architecture.

Piezohydraulic actuation is the use of fluid to rectify the motion of a piezoelectric actuator for the purpose of overcoming the small stroke limitations of the material. In this work we study a closed piezohydraulic circuit that utilizes active valves to rectify the motion of a hydraulic end affector. A linear, lumped parameter model of the system is developed and correlated with experiments. Results demonstrate that the model accurately predicts the filtering of the piezoelectric motion caused by hydraulic compliance. Accurate results are also obtained for predicting the unidirectional motion of the cylinder when the active valves are phased with respect to the piezoelectric actuator. A time delay associated with the mechanical response of the valves is incorporated into the model to reflect the finite time required to open or close the valves. This time delay is found to be the primary limiting factor in achieving higher speed and greater power from the piezohydraulic unit. Experiments on the piezohydraulic unit demonstrate that blocked forces on the order of 100 N and unloaded velocities of 180micrometers /sec are achieved.

This paper reports the modeling, design, and dynamic simulation of a piezoelectrically-driven microfabricated valve for high frequency regulation of high 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 paper focuses on the development of a sytematic procedure to arrive at a geometric valve design for given performance requirements. Modeling of the non-linear large deflection behavior of the valve membrane and design of this structure to maintain stresses below critical levels are discussed. Design of the piezoelectric material drive portion of the valve to create a stiffness match with the valve membrane and external hydraulic system is detailed. In addition, this paper presents a dynamic simulation of the active valve, including effects such as valve cap dynamics and fluid damping, that allow for understanding and prediction of valve performance under various loading conditions.

A flextensional transducer consist of a piezoceramic connected to a flexible structure which amplifies and changes the direction of generated piezoceramic displacement. In a previous work[1,2] these transducers were designed by using topology optimization method. In this work, some prototypes of these transducers were manufactured and experimental measurements were performed to characterize them. The prototypes were built by bonding a flexible structure manufactured by using a wire EDM machine to a piezoceramic with epoxy. As a result, the displacements obtained through laser interferometry at a given frequency and the electrical impedance curves are presented. The experimental results were compared with simulated results obtained by using a commercial finite element software (ANSYS), and the predicted amplification rate provided by these transducers were verified.

As hard disk drive areal densities increase at a compound annual growth rate (CAGR) of 60%, disk drives must position the head over increasingly small areas while moving more rapidly to reach the desired position. This results in an increase in vibration disturbance. To meet this demand, many hard disk drive manufactures have created prototype dual-stage actuators employing piezoelectric ceramics for the second stage. These are an attractive means of obtaining higher-bandwidth control due to the low inertia and size of the actuator element. As the technology improves, the next limiting factor will be the amount of displacement obtainable with traditional piezoceramic elements. Under the AXIS (Advanced Crystal Integrated System) Consortium program funded by DARPA, the application of PZN-PT single crystal piezoceramic as a second stage disk drive actuator was studied, based on the fact that the single crystal material provides larger stroke than its traditional PZT counterparts. The transverse (d31) strain of PZN-PT single crystal was measured to be about two times larger than that of PZT-5H ceramic. Both materials were integrated into a disk drive system and compared as second stage actuators. The methodologies used and the servo control techniques applied are also discussed in the paper.

This paper describes the development of a compact hybrid hydraulic actuation system as a potentially high-authority compact actuator for various applications including actuation of the trailing edge flap of a smart rotor system. The actuation system is divided into two parts, a pump driven by piezostack actuators and an output hydraulic actuator. The present work focuses on the design, analysis and testing of the pump. Analytical models are developed for various elements of the system. Operating the piezostacks at a frequency of up to 250 Hz over a period of five minutes, the pump generated a maximum pressure rise of 180 psi, displacing approximately 100 ml of hydraulic fluid in the process. A maximum temperature of 55 degree(s)C was measured on the piezostack.

A smart structural model is developed to analytically determine the response of arbitrary structures with piezoelectric materials and attached electrical circuitry. The equations of motion are formulated using the coupled piezoelectric formulations. However, rather than solving for strain and electric field, the proposed model solves for the strain and electric charge. The equations of motion are simplified for the case of a composite plate structure using a refined higher order laminate theory. Additional degrees of freedom are then added to describe any attached electrical circuitry. A method is also presented for system simplification using the structural mode shapes and natural frequencies. Results are verified using experimental data for passive electrical shunt damping. The developed model results in a general framework that can be useful in solving a wide variety of coupled piezoelectric-mechanical problems addressing issues such as passive electrical damping, self-sensing and electrical power consumption.

There is a range of NASA experiments, instruments and applications where miniature pumps are needed. To address such needs, a piezoelectrically actuated miniature pump is being developed. This pump employs a novel volume displacing mechanism using flexural traveling waves that acts peristaltically and eliminates the need for valves or physically moving parts. This pump is being developed for planetary instruments and space applications. Finite element model was developed using ANSYS for the purpose of prediction of the resonance frequency of the vibrating mode for the piezo-pump driving stator. The model allows determining simultaneously the mode shapes that are associated with the various resonance frequencies. This capability is essential for designing the pump size and geometry. To predict and optimize the pump efficiency that is determined by the volume of pumping chambers the model was modified to perform harmonic analysis. Current capability allows the determination of the effect of such design parameters as pump geometry, construction materials and operating modes on the volume of the chambers that are formed between the peaks and valleys of the waves. Experiments were made using a breadboard of the pump and showed water-pumping rate of about 4.5 cc/min. The pump is continually being modified to enhance the performance and efficiency.

A recently qualified Honeywell vibration isolation system does two things well. It supports and protects its payload during launch environments, and subsequently provides micro-inch level jitter reduction on-orbit. An elliptical hexapod provides six-degree-of-freedom support and isolation. The fluid-damped D-Strut isolation system maintains its payload optical alignment after vibration and thermal exposure. Vibration tests at one micro-inch input and at one- tenth of an inch input show almost identical damping and isolation responses. The 70-lb test payload was made from wood with an aluminum backbone. The payload provided accurate mounting geometries for the six isolator struts, and precision locations for ten accelerometers and an optical cube. Shock testing, launch-level random vibration, and launch sine vibration were imposed. The system was also subjected to thermal cycling. Functional transmissibility tests were performed before, midway, and after launch environments, at 0.25-g and 2.5-g sine input levels. Honeywell's Matlab Isolator Design Tool predicted transmissibility between 6 degrees-of-freedom inputs and the six rigid body outputs. Another analysis code took these 36 transmissibilities and used optical element transfer functions to calculate an overall jitter number. Finally, 18 measured transmissibility curves from functional tests were fed through the optical jitter code.

Future NASA exploration missions are increasingly seeking to conduct sampling, in-situ analysis and possibly return samples to Earth for further tests. Missions to Mars are the more near term projects that are seeking such capabilities. One of the major limitations of sampling on Mars and other low gravity environments is the need for high axial force when using conventional drilling. To address this limitation an ultrasonic/sonic drilling/coring (USDC) mechanism has been developed that employs an ultrasonic horn driven by a piezoelectric stack. The horn drives a free mass that resonates between the horn and drill stem. Tests have shown that the USDC addresses some of the key challenges to the NASA sampling objectives. The USDC is lightweight (450 g), requires low preload (< 5N) and can be driven at lower power (5W). The device has been shown to drill rocks with various levels of hardness including granite, diorite, basalt and limestone. The hammering action involved with the coring process can produce cores of various shapes, which need not necessarily be round. Because it is driven by piezoelectric ceramics, the USDC is highly tolerant to changes in its operating environment. These actuation materials can be designed to operate at a wide range of temperatures including those expected on Mars and Venus. Although the drill is driven electrically at 20 kHz, a substantial sub-harmonic acoustic component is found that is crucial to drilling performance. An analytical model has been developed to explain this low frequency coupling in the horn, free mass, drill stem and rock.

This research is concerned with the modeling and active vibration control of slewing smart structures. When cantilever beam rotates about axes perpendicular to the undeformed beam's longitudinal axis, it experiences inertial loading. Hence, the beam vibrates during and after slewing. In this paper, the analytical model for a single slewing flexible beam with surface bonded piezoelectric sensor and actuator is first developed using the Hamilton's principle with discretization by the assumed mode method. The theoretical frequency response function is then compared to the experimental open loop frequency response data. It is found from the comparison that the rotor friction should be included in the modeling. A new concept is introduced to incorporate the effect of the friction. As a result, the use of coupling factor is proposed in this paper. The positive position feedback, (PPF) controller is designed for the suppression of residual vibrations after slewing. The experimental results show that it can suppress the vibration effectively but cannot alleviate the vibrations occurred during slewing. This problem is discussed in detail in this paper.

The collaboration of active piezoceramic fibers and passive matrix material compliments the dynamic actuation excellence of piezoelectrica with the tailorability of active and passive anisotropic properties as well as with the potential to realize flexible shaping and structural integration. This material composition with alignment of poling and electric field in fiber direction is examined on the micromechanics level to provide elastic and piezoelectric coefficients for the subsequent investigations. Thin layers of such a compound are joined with assistance of the classical lamination theory. The resulting active laminated composite is employed for the walls of a single-cell closed cross-section beam, which is modeled in Timoshenko fashion with supplementary torsional warping. The principle of virtual displacements is applied to a cantilever configuration and provides the natural boundary conditions and equations of motion. These are solved in conjunction with the stiffness and actuation properties for arbitrary constant and linear load conditions to obtain voltage dependent static displacements and rotations. Focusing on the beam twist different actuation schemes are examined and the interplay of stiffness characteristics and actuation efficiency is analyzed. The results are compared with the outcome of a finite element analysis using layered shell elements with the analogy of piezoelectric and thermal expansion.

A rotary actuator driven by piezoelectric bimorphs has been developed for various smart structure applications. A rotary (roller) clutch rectifies bimorph oscillation into rotational motion to convert electrical to mechanical power. While prototype actuators perform well, they were designed with just engineering intuition. Here, a mathematical model of the actuator is developed. Using empirical data collected from a prototype actuator and a roller clutch, the mathematical model was tuned so that it predicted accurately the performance of the prototype. The model was then used to perform parameter studies and optimize the design of the actuator. The model predicts that performance can be significantly increased by making slight modifications to the prototype. Work to verify these predictions of the mathematical model is underway.

Inflatable structures are effective in space applications, as they are weight, volume and cost competitive. For certain space applications, higher gains are obtained for the antennas by increasing their size. Higher gains often result in increased data throughput. These and other advantages lead to inflatable structures being considered increasingly for building large space structures. However, large inflatable structures are prone to surface errors arising from environmental factors, among others. In this context, piezoelectric films are used for the active and passive control. In this paper, we discuss numerical approaches exploring piezoelectric film. In order to explore the applications of piezoelectric films, a circular diaphragm is subjected to varying pressures and displacements are measured using laser instrumentation. The effects of applying voltage on the shape of the piezoelectric film subjected to pressurization are studied. The piezoelectric film is modeled as a large displacement/large rotation membrane undergoing small strains. This paper presents experience gained in modeling the piezoelectric film subjected to both thermal and pressure loads. The numerical results are presented in the form of graphs. The response is studied for applied steady-state temperatures for various pressurization levels. Certain thermo-structural instabilities were encountered in the modeling and the paper presents procedures used in circumventing such instabilities for the piezoelectric type of thin inflatable membranes.

A moving load causes the radial displacements of an axi- symmetric shell to be several times higher than that produced by the static application of the same load. The travel velocity of the moving load affects the amplitude of the radial response and a critical velocity above which the shell response becomes unstable can be identified. A finite element model (FEM) is developed to analyze the dynamic response of axi-symmetric shells subjected to axially moving loads. The model accounts for the effect of periodically placing stiffening rings along the shell, on the dynamic response and stability characteristics of the shell. Shape functions obtained from the steady-state solution of the equation of motion for a uniform shell are utilized in the development of the FEM. The model is formulated in a reference frame moving with the load in order to enable studying the shell stability using wave propagation and attenuation criteria. Hence, the critical velocity can be identified as the minimum velocity allowing the propagation of applied perturbations. Such stability boundaries are conveniently identified through a transfer mis formulation. The model is used to determine the critical velocities of the moving load for various arrangements and geometry of the stiffening rings. The obtained results indicate that stiffening the shell generally increases the critical velocity and generates a pattern of alternating stable and unstable regions. The presented analysis provides a viable means for designing a wide variety of stable dynamic systems operating with fast moving loads such as crane booms, robotic arms and gun barrels.

In numerous applications, smart material transducers are employed to actuate upon virtually immovable structures, that is, structures whose stiffness approaches infinity in comparison with that of the transducer itself. Such mechanically blocked transducer configurations can be found in applications ranging from seismic testing and isolation of civil structures, to clamping mechanisms in linear or rotational inchworm motors. In addition to providing high blocking forces, smart materials for this type of applications must often be small in size and lightweight in order for design constraints to be met. This paper provides a characterization of the force produced by a 0.9 cm (0.35 in) diameter, 2.0 cm (0.79i in) long Terfenol-D operated under mechanically blocked conditions. Experimental results are shown for several mechanical preloads as well as various magnetic field intensities, waveforms, and frequencies. Optimal levels are deduced and discussed and the results are compared to published data for a PZT transducer of similar size operated in mechanically blocked configuration. The comparison reveals that the Terfenol-D rod provides higher blocking forces than its PZT counterpart. It is thus feasible to employ small magnetostrictive drivers in applications involving zero or near-zero displacement, particularly those based on hybrid magnetostrictive/piezoelectric designs in which high efficiencies are achieved by driving the two electrically complementary transducer materials at electrical resonance.

A magneto-electric composite element of two functional materials: giant magnetostrictive (GMM) and piezoelectric materials, is developed for coil-less magnetic force control. This force control is based on the inverse magnetostrictive effect of GMM and realized by composing a closed parallel magnetic circuit with a permanent magnet in magnetic yoke. The magnetic force between two yokes can be adjusted by controlling the strain in the magnetostrictive rod. For the purpose of efficiently controlling the strain of the GMM rod, a magneto-electric composite element is constructed, in which the two functional materials: a giant magnetostrictive rod and a stack piezoelectric actuator, are mechanically coupled via strain. The magnetization in the GMM rod can be controlled by adjusting the voltage of the piezoelectric actuator. It is confirmed that this element works to adjust magnetic force and has wide frequency bandwidth. As an application of this element, a magnetic levitation system is proposed and the movable yoke was levitated by simple PD control. This system has advantages of low power consumptions and low heat generation compared with a conventional system with electromagnetic coils.

Active structural flow control has emerged as an effective way to suppress the vibration of large structures by controlling in the vicinity of the disturbances with a limited number of sensors and actuators. This is in contrast with other active structural control strategies which employ distributed sensors and actuators to provide a global control of the modes of the structure. This paper presents theoretical and experimental structural intensity control results, where the instantaneous intensity is completely taken into account in the control algorithm, i.e. all the terms are considered in the real-time control process and, in particular, the evanescent waves are considered in this approach. Moreover, both the flexural and extensional waves are taken into account in the control algorithm. As they are especially well-suited for integration into structures in order to create smart materials, piezoelectric strain sensors (PVDF) are used in the sensing approach. The structural intensity is estimated from the discrete strain measurements using a finite difference scheme. A feedforward filtered-X LMS algorithm is adapted to this energy-based control problem, involving a non-positive definite quadratic form in general. In this respect, the approach is limited to cases where the geometry is such that the intensity component will have the same sign for the control source and the primary disturbance. Experimental validation of the approach is conducted on a structure made of a beam connected to a plate, where the beam is covered with viscoelastic material. A comparison of the proposed approach is made with classical acceleration control and these results show that intensity control using strain sensors allows the error sensors to be placed closer to the control source and the primary disturbance, while preserving a good control performance.

The propagation of waves in cylindrical shells with periodic stiffening rings is analyzed by detecting transient waveforms of longitudinal impulse waves. The detected signals are analyzed in time-frequency domain using the Wavelet Transform. A Spectral Finite Element model is developed to predict structural response and wave dynamics of stiffened shells. The model employs spectral shape functions that accurately replicate the shell's dynamic behavior. Hence, a significantly small number of spectral elements can be used for studying the wave propagation along the structure. The model together with a Fast Fourier Transform algorithm is utilized to predict the shell response in the time domain. The analysis of the transient waveforms in the time domain shows that the stiffening rings partly reflect the propagating impulse. The reflected waveforms interact with the applied impulse and generate a constructive/destructive interference pattern, which produces pass/stop frequency bands typical of periodic structures. The filtering capabilities of periodically stiffened shells are visualized by analyzing the shell axial response using the Wavelet Transform. The Wavelet Transform indicates the location of the stop and pass bands and demonstrates that the filtering capabilities of the shell are enhanced by increasing the number of the stiffening rings. The conclusions of the numerical simulations are confirmed experimentally. Close agreement is achieved between the theoretical predictions and the experimental results. The presented theoretical and experimental techniques serve as effective means for the design of periodically stiffened shells with desirable filtering characteristics.

This paper presents the results of experiments involving jitter suppression of optical components. Acoustic disturbances and structurally transmitted vibration contribute to the jitter of optical systems such as lasers. Active and passive methods must be used to suppress jitter from entering the optical train. An experimental test bed is constructed to study the effects of acoustic disturbances on an optical system. A laser source is directed onto a light-detecting target by way of a turning mirror and fast-steering mirror (FSM). The FSM, actuated by three piezoelectric stacks, provides tilt in both the elevation and azimuth axes. Both mirrors are exposed to an acoustic disturbance. The objective is to use knowledge of the acoustic-structural interaction to design a controller that precisely points the laser. To achieve this, several control methodologies are studied. A servo control loop around the FSM is designed using an H₂ approach. By feeding back the laser beam position to the FSM, the jitter is reduced by a factor of 2.5. Feedforward methods are also explored using microphones and accelerometers as disturbance sensors. Acoustic noise control is studied as a means of reducing the sound pressure level in the proximity of the optics. Sound pressure sensed by a microphone was fed to a loudspeaker and the loop was closed with an H₂ optimal controller.

Active structural control using the ACX QuickPack piezoelectric strain actuators has been proven to be an effective method for controlling vibration. However there are structures where the optimal strain actuator location is either inaccessible or undesirable. Under such circumstances, a solution can be an active isolation system where strain actuators are placed along the direct transmission path of the vibration. The feasibility of an active isolation system was demonstrated using a cantilevered beam with a tip mass. Vertical acceleration at the tip was used as the performance metric, and a force near the clamp as the disturbance source. Thin aluminum flexures sandwiched by QuickPack strain actuators were placed between the beam end and the mass to isolate the mass from the beam. A finite element model was built and a state-space representation derived for the transmissibility between disturbance and performance to optimize the flexures and actuators, as well as to predict performance. Once the system was built, transfer functions were taken and a PPF controller was implemented. The amount of vibration transmitted to the mass was reduced by 22 dB overall, with a 5 dB reduction due to the passive isolation effects, and 17 dB due to the active control.

This paper presents the results of theoretical modeling and experimental characterization of PiezoSystems Jena P-177-00 large stroke piezoelectric actuator and of Etrema AA-140J025-ES1 large stroke/large power magnetostrictive actuator. An improved smart-material actuators measurement method suited for static and low frequency actuation was devised. Analytical and finite element modeling (ANSYS) of the experimental setup to determine stiffness component characteristics was performed. The output displacements of the active material actuators were recorded in quasi-static and dynamic regimes, under varied pre-stress level, voltage and frequency values. The measurements indicated a strong dependence of the actuator stiffness and piezoelectric properties on the electromechanical loading conditions. The study also identified and calculated the parameters of the induced strain actuators electro-mechanical model. These parameters are necessary for performing design optimization to achieve maximum energy transfer and minimum power requirements. Experimentally verified data characterizing piezoelectric and magnetostrictive actuators in the full stroke/full power regime required for designing an effective airborne induced strain activated aerodynamic control system for air and space vehicles is provided.

The capability of periodic structures to act as filters for propagating waves is used to control the propagation of waves in shells. The shells are stiffened by periodically- placed rings in order to generate periodic discontinuities in the stiffness and inertial spatial distribution along the longitudinal axes of these shells. Such discontinuities result in attenuation of the wave propagation over certain frequency bands called Stop Bands. A distributed-parameter approach is used to derive a spectral finite element model of the periodically stiffened shell. The model accurately describes the dynamic behavior of the shell using a small number of elements. The stiffening rings, modeled using the curved beam theory, are considered as lumped elements whose mass and stiffness matrices are combined with those of the shell. The resulting dynamic stiffness matrix of the ring-stiffened shell element is used to predict the wave propagation dynamics in the structure. In particular, the shell propagation constants are determined by solving a polynomial eigenvalue problem, as a numerically robust alternative to the traditional transfer matrix formulation. The study of the propagation constants shows that the discontinuity introduced by the stiffeners generates the typical stop/pass band pattern of periodic structures. The location and width of the stop bands depend on the spacing and geometrical parameters of the rings. The existence of the stop bands, as predicted from the analysis of the propagation constants, is verified experimentally. Excellent agreement between theoretical predictions and experimental results is achieved. The presented theoretical and experimental techniques provide viable means for designing periodically stiffened shells with desired attenuation and filtering characteristics.

Recent advances in fiber optic sensors have shown the great potential for Bragg gratings to be used as strain sensors. Optical fiber Bragg gratings offer significant advantages over traditional resistance foil strain gages, including a high degree of multipexibility, compact size, immunity to electromagnetic noise interference, and resistance to most chemicals. However, Bragg grating strain sensors have met only limited success in real-world applications. Two reasons for their limited presence is the inherent temperature sensitivity of the dual-parameter Bragg grating and the lack of experience of engineers with fiber optic sensors. This paper describes the development of a fiber Bragg grating strain sensor that attempts to address both of these issues. The flat-pack strain sensor incorporates a pair of Bragg gratings into a single package. One grating is bonded tightly to the pack and acts as a combined thermal-mechanical strain sensor. The second Bragg grating is packaged loosely within the sensor and is used to measure only temperature, which can then be subtracted from the tight grating, providing a temperature-compensated strain reading. By packaging the two gratings into a configuration that is similar to resistance strain gages, we expect that many of the technical and practical implementation issues of optical sensor technology will be overcome. This paper describes the details of the design and experimental testing of prototype sensor packages to validate the functionality of the fiber optic strain gage.

Advanced composites are being extensively used for aerospace structures due to the high stiffness to weight and high strength to weight ratios. Measuring internal strings of composite structures is of great interest with respect to the structural integrity of aerospace structures. A large number of sensors are required for large-scale structures such as aircraft. Fiber Bragg grating (FBG) sensor system based on the wavelength division multiplexing (WDM) technology offers a versatile and powerful one for strain monitoring of large structures due to the advantage of multiplexing capability. In this paper, we present an improved FBG sensor system using a wavelength-swept fiber laser (WSFL). The WSFL provides unique and powerful output characteristics useful for a large number of sensor interrogations without any other expensive optic devices such as optical switches. As a practical application of aircraft structures, we demonstrate 24 FBG sensors were used to monitor strains of the smart composite wing box model in the bending test. 3 sensor lines are embedded into upper skin and 1 sensor line is embedded into front spar of composite wing box. Each sensor line has 6 FBG for the strain sensing and 1 reference FBG for temperature compensation. Experimental results are compared with finite element analytical results. The structural bending behavior of composite wing box monitored by FBG sensors shows an almost same tendency with the analytical result. All strain data can be real-timely visualized and saved in PC.

A nonlinear active vibration absorber to control the vibrations of plates is investigated. The absorber is based on the saturation phenomenon associated with dynamical systems with quadratic nonlinearities and a two-to-one internal resonance. The technique is implemented by coupling a second-order controller with the plate's response through a sensor and an actuator. Energy is exchanged between the primary structure and the controller and, near resonance, the plate's response saturates to a small value. Numerical results are presented for a cantilever rectangular plate. Modal analysis is used to solve for the plate displacement. Finite-element methods are used to extract the eigenmodes of the system. A numerical study is conducted to optimize the location of the actuators to maximize its controllability. In this regard, the control gain is maximized for the PZT actuators. Furthermore, a more general method is introduced, which is based on a global measure of controllability for linear systems.

We are carried out the tests for the sound and vibration control of the CFRP square panel. 500Hz bandwidth noise through two speakers is applied to the CFRP panel. Our objects are to improve the structural damping of the panel and attenuate the sound power radiated from the panel using piezoelectric sensors and actuators. The dimensions of the CFRP plate are 600.0 mm x 600.0mm in area and 1.8mmt in thickness. Eighteen piezoelectric elements (40.0 x 20.0 x 0.3mmt) are bonded on the surface of the panel by epoxy adhesive. The panel is driven using some piezoelectric elements as actuators. The vibration of the panel is monitored using piezoelectric elements as sensors. We can get the strain of the panel from the voltage induced by piezoelectric elements. The signals are sent to digital signal processor (DSP) through filters and the control signal are sent to the power amplifiers. The amplified signals drive the piezoelectric actuators. The vibration and the radiated sound power of the panel are suppressed. We try to apply two methods for the control which are the gain control and the reduced LQG control. In the case of the gain control, the strain is reduced as much as 10-20 dB at some resonant peaks and the radiated sound pressure level as much as 1-15 dB. The radiated sound power is reduced by 1.59dB in the 0-500Hz frequency range. In the case of the LQG control, the strain is reduced as much as 7-10dB at some resonant peaks and the radiated sound pressure level as much as 1-7dB. The radiated sound power is reduced by 0.7dB in the 0-500Hz frequency range.

The active vibration control of composite shell structure has been performed with the optimized sensor/actuator system. For the design of sensor/actuator system, a method based on finite element technique is developed. The nine-node Mindlin shell element has been used for modeling the integrated system of laminated composite shell with PVDF sensor/actuator. The distributed selective modal sensor/actuator system is established to prevent the effect of spillover. Electrode patterns and lamination angles of sensor/actuator are optimized using genetic algorithm. Continuous electrode patterns are discretized according to finite element mesh, and orientation angle is encoded into discrete values using binary string. 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 the second mode vibration control of singly curved cantilevered composite shell structure are designed with the method developed on the finite element method and optimization. For verification, the experimental test of the active vibration control is performed for the composite shell structure. Discrete LQG method is used as a control law.

Piezoceramic actuator placement is investigated to minimize structurally radiated noise of flat and curved panels subjected to a uniform random acoustic disturbance. The flat panels use traditional PZT actuators, while the curved panels incorporate anisotropic macro fiber composite (MFC) PZT actuators. A linear quadratic regulator (LQR) feedback control augmented with acoustic radiation filters is used to minimize the radiated noise. A coupled finite element model is used in conjunction with a genetic algorithm to determine the optimum actuator location for two PZT actuators. Experiments are conducted to verify analytical simulation results.

In recent years, there has been a surge of interest in using piezoelectric patches attaches to optical surfaces in hope of attaining high precision of optical mirrors with minimal additional weight. Based on results from preliminary investigations, the configuration of thin piezoelectric strip actuators placed in the radial and circumferential line directions of a circular plate (host structure of the mirror) is chosen to control the surface error of the mirror. The major challenges here is the two dimensional actuation effect of the actuator patches, which could induce high order modal deformations and increase the difficulty of surface error control. The purpose of this research is to investigate such effects and propose solutions. A simple model is first developed through Hamilton's principle and discretized using Galerkin's method, thus giving a set of differential equations describing the coupled mechanical and electrical systems. Form the equations, the coupling between the electrical and structural systems for each mode shape can be calculated, thus giving a means to maximize the coupling between the actuator and the mode shapes of interest by changing the actuator's properties. Likewise, the properties can be tailored such that excitation of the unwanted modes can be avoided or reduced. A more comprehensive finite element model is also derived to validate the observations obtained from the simple model. From the analysis, it si found that decoupling of the circumferential action from the radial action of the piezoelectric patches can dramatically improve the performance of the controller, thus achieving a greater reduction in the surface error. Methods to decouple the circumferential strain from the radial strain are then proposed.

The active control of a structure in order to reduce its vibration or sound radiation, which may be termed active vibro-acoustic control, has previously been achieved with multiple actuators and sensors and fully-coupled feedforward or feedback controllers. In this paper local velocity feedback using multiple miniature accelerometers will be investigated, together with either collocated force actuators or piezoceramic actuators placed under each sensor. With ideal force actuators, the plant response is passive for such an arrangement of collocated actuator/sensor pairs and so decentralized (local) feedback is guaranteed stable. This property is shown to extend to collocated velocity sensors and piezoceramic actuators over the bandwidth of interest and so multiple local feedback loops are also predicted to be stable. The performance of such a system is simulated in controlling the vibration and sound transmission through a thin plate, excited by an acoustic plane wave, with a 4 x 4 array of such actuator/sensor pairs, which are connected together with 16 local feedback control loops. Using force actuators, significant frequency-averaged reductions up to 1kHz in both the kinetic energy (28dB) and transmitted sound power (18dB) can be obtained with an appropriate feedback gain in each loop. These reductions are not so great with piezoelectric actuators (12dB and 9dB respectively) but their use allows the controller to be fully integrated in the structure.

The effects of crack damage on the vibrations of a beam is examined using wave propagation methods. A scattering matrix is developed which explores the relationship between incoming and outgoing structural waves at a crack. Near field waves are examined as an indicator of crack damage. Trends can be seen which would be helpful in determining the presence of a crack in a damage detection scheme. Experimental results show that near field waves increase as a result of crack damage.

The aim of the present paper is to illustrate the configuration and the performances of a charge feedback amplifier to drive a piezoelectric transducer in self-sensing operation, i.e. to use the same transducer as sensor and actuator at the same time. A suitable balancing procedure of the self-sensing circuit allows to obtain an output signal proportional to the displacement of the mechanical structure. Experimental tests show that the proposed charge feedback amplifier simplifies the balancing procedures needed to obtain a useful output signal from the self-sensing readout circuit, this is attributed to the increased stability of the electric parameters of the piezoelectric that can be achieved with charge control.

Experimental results on mechanical behavior of Extrinsic Fabry-Perot Interferometric Fiber Optic Strain Sensors (EFPI-FOSS) are presented in this paper. The goal of this study was to determine the accuracy, strength characteristics, and durability properties of both bare (non-embedded) EFPI sensors, and embedded EFPI optical fiber sensors in either a neat resin or aerospace grade composite laminate. Experimental results suggest that the embedded EFPI sensors provide reliable strain measurements for values exceeding 10,000 (mu) (epsilon) under static loading conditions. A major portion of this study focused on evaluating the long term tension-tension fatigue behavior of optical fiber sensors. Test data suggest the EFPI sensors provide reliable data up to 1 million cycles at fatigue strain levels below 3,000 (mu) (epsilon) . For fatigue strain levels above this value, failure of the fiber optic sensor was observed. While the sensor failed it did not influence the strength and fatigue life of the composite coupons. Considering the design strains used in aerospace components, these results provide evidence that the EFPI sensors will survive during the life of typical aerospace structures.

The variability of Young's modulus (the (Delta) E effect) in giant magnetostrictive Terfenol-D has a significant impact on the performance and modeling of Terfenol-D transducers. While elastic modulus variability introduces nonlinearities in the transducer input/output relationship that are often deemed undesirable, it also affords opportunities for achieving novel device performance attributes. In this investigation, Terfenol-D's modulus of elasticity is characterized under controlled thermal, magnetic, and mechanical loading conditions. Quasi-static cyclic compressive stress testing methods are used to quantify the variability in Young's modulus over a wide range of d.c. applied magnetic fields and stresses. Elastic modulus changes of four-fold or more are demonstrated through the variation of a d.c. applied magnetic field. The effect of decreasing cyclic stress amplitude giving rise to an increase in Terfenol-D's apparent elastic modulus is also examined. The thermally controlled transducer used throughout this investigation is described. This conference paper is a shortened version of the paper titled Experimental Investigation of Terfenol-D's Elastic Modulus that has been submitted for peer reviewed journal publication.

The control of Terfenol-D's operational elastic modulus offers opportunities for novel devices and applications capitalizing on real time changes in material stiffness. This work describes the development and testing of a Terfenol-D transducer employed as a wide-band variable frequency mechanical resonator. The design and construction of such a wide-band mechanical resonator for testing under controlled thermal, magnetic and dynamic mechanical load conditions are described. Changes in Terfenol-D's elastic modulus, the (Delta) E effect, approaching 266% are demonstrated in the mechanical resonator utilizing a range of d.c. applied magnetic field levels of less than 61.0 kA/m. The elastic modulus and damping characteristics of Terfenol-D critical to the successful design of devices employing the (Delta) E effect are examined. This conference paper is a shortened version of the paper titled Wide band tunable mechanical resonator employing the (Delta) E effect of Terfenol-D that has been submitted for peer reviewed journal publication.

The transonic aerodynamic field around a wing section is characterized by a large number of peculiarities, which strongly influence the airfoil performance. In particular, a shock wave located on the wing upper surface strongly interacts with the boundary layer, causing a drag increase. Moreover, wave oscillations may give rise to the undesired aeroelastic phenomenon of buffeting. Aerodynamic studies have pointed out that shape airfoil modifications may lead to performance improvements. The aim of the work is to present a procedure to design and realize a tailored and integrated composite actuator made of an aluminium alloy sheet. The geometry of the skin element is modified by the combined action of a uniform pressure load producing static deformations, and tangential piezoelectric ceramic patches bonded through a laminate connection layer, towards one direction, preferably. Glass fiber/epoxy was selected to this target. The design procedure is made of a first part, devoted at the definition of the sheet thickness law (taking into account the ceramics contributions) that assures the deformed shape following the specific aerodynamic requirements, and a second part, applied to optimize the structure-actuators configuration. Analytical and numerical extensions of available models, able to predict the strain actuation on composite elements with variable thickness under different boundary conditions complete the proposed methodology. According to the obtained results and indications, an experimental bump prototype was realized. An experimental campaign is being carried out in order to compare the real behavior of the skin element with the theoretical predictions: static and dynamic bump deflected shape was measured.

With the trend towards longer span and thus lower frequency floors, human induced vibration and human-structure interaction has received more and more concern about structural serviceability. When subjected to vertical vibration, a human behaves as a mass-spring-damper system rather than solely as a mass on the structure. The interaction between the human body and the structure results in a significant increase in the damping of the human-structure system. In order to study human-structure interaction, mathematical model for this system is established. The human body and the slab are simulated as a SDOF model respectively. Through laboratory experiment with 30 human samples, the parameters of the SDOF human model were obtained. The result shows that the human resonant frequency is 5.24 +/- 0.40Hz, and damping ratio is 39%+/- -0.05. By combining experimental data and simulation, the human body's damping effect on vibrating floor was quantified in terms of energy absorption. During vibration, human absorbed most of the input energy.

Piezoelectric actuators and motors promise to deliver useful work at power densities an order of magnitude greater than that of their electromagnetic counterparts. The circuit concept developed is for a resonant, regenerative switching piezomotor drive amplifier that would efficiently transfer electrical energy that could be coupled into mechanical work through a piezoelectric actuator. The motor/amplifier system would operate at both electrical and mechanical resonances for the system. The amplifier's efficiency is estimated to be greater than 80% when driving a 1mF piezoelectric load with a 500 Vpk-pk signal. The available output power should be greater than 20 watts continuously from DC to 2.0 kHz. A prototype amplifier with +50% power efficiency is presently undergoing design debug and testing. Once operational, future amplifier refinements can focus on improved analog computation methodologies, mitigation of alignment and calibration difficulties, while trying to reduce sensitivity to actuator capacitance and improvements to output waveshape fidelity.