The future of molecularly based Smart Materials hinges on the development of integrated technologies addressing synthesis, assembly, shaping etc and some of these are now becoming clear. Even in the bolt on era new technologies will allow issues of commensurate engineering to be addressed.

This paper summarizes the experience of the DLR in various subdisciplines of smart structures technology and shows how this joint experience is gathered in the development of smart structures. Some smart structural systems which are currently under investigation are presented.

The recent upsurge of research activity in smart materials and structures stresses the interest in materials possessing both direct and inverse electromechanical transduction properties. Three different classes of polymers appear to be particularly interesting in relation to their electromechanical properties: piezoelectric polymers, polyelectrolyte gels and doped electron conducting polymers. In the last decade there has been an impressive growth in research and development in the field of sensor technology. Some advances have also occurred, albeit less substantial, in the field of actuation. Although the largest part of the new physical sensors and actuators make use of inorganic materials and transduction elements, increasing attention is nowadays being paid to functional polymers. In this paper the sensing and actuation properties of these polymers are briefly discussed.

Advanced technology has become too much complicated for general public to understand. Very limited expert can understand and treat this sort of complicated technology. Advanced technology is losing close contact to most people. The present speaker characterize this phenomenon as technomonopoly. Unless people accept and support technology, environmental issues cannot be solved. Intelligent materials have to be developed to simplify technology in order to recover friendship to general public. When general public understand technology, feel satisfied with technology and think technology of their own, technodemocracy is thus achieved.

Hydrogels are materials which will swell in water but not dissolve. They are a large family of materials rather than a single entity. Indeed much of living tissue comprises hydrogel and the variety and function of this class presents the scope for the development of synthetic materials which can perform many so-called 'Smart' functions. The action of muscles, the selectivity of membranes and the contraction and expansion of various sphincters and the control of blood flow in veins and arteries might all be simulated with synthetic analogues. Such materials are now being demonstrated and systems which undergo large dimensional changes with changes in hydrogen ion or other ionic concentration have been reported while hydrogels which bend when subjected to an electrical potential difference have been made. Hydrogels can be incorporated into devices which can act as transducers, as sensors and as accurately controlled timing devices for the release of drugs and in other potential applications. This paper will illustrate a selection of these applications utilizing hydrogels developed in our laboratories and based on crosslinked poly (ethylene oxide). The dry form of the hydrogel will be referred to as a xerogel and the term hydrogel will refer to the material swollen to some degree with water.

This paper describes one possible way forward for smart structures in the domain of fault detection and classification using neural networks and genetic algorithms. Consideration is given to the incompatibility between numerical training data sets and real structures and how this may be ameliorated using optimization procedures for determining the number and location of transducers required to locate and classify a fault.

This paper describes a cellular automaton based on adaptive function of living systems. We simulated the behavior on a computer giving each cell local rules such as 'death', 'birth', and 'division' like an organism. The computational results showed that the model generates a clear framed structure for a mechanical condition. We also reported on diverse topological structures inhered in the system.

'Large scale' is one of major trends in the research and development of recent engineering, especially in the field of aerospace structural system. This term expresses the large scale of an artifact in general, however, it also implies the large number of the components which make up the artifact in usual. Considering a large scale system which is especially used in remote space or deep-sea, such a system should be adaptive as well as robust by itself, because its control as well as maintenance by human operators are not easy due to the remoteness. An approach to realizing this large scale, adaptive and robust system is to build the system as an assemblage of components which are respectively adaptive by themselves. In this case, the robustness of the system can be achieved by using a large number of such components and suitable adaptation as well as maintenance strategies. Such a system gathers many research's interest and their studies such as decentralized motion control, configurating algorithm and characteristics of structural elements are reported. In this article, a recursive architecture concept is developed and discussed towards the realization of large scale system which consists of a number of uniform adaptive components. We propose an adaptation strategy based on the architecture and its implementation by means of hierarchically connected processing units. The robustness and the restoration from degeneration of the processing unit are also discussed. Two- and three-dimensional adaptive truss structures are conceptually designed based on the recursive architecture.

Two possible neural network methods for fault detection in a vibrating mechanical structure, are presented. Results are given for preliminary tests carried out using data from a simple model of a clamped cantilever beam.

This paper describes the experimental verification of a technique to ensure that the raw sensor data base meets integrity confidence levels required for initiating critical operating decisions associated with aircraft structures. Neural Network techniques are used to characterize the spectral response of sensor arrays to known sensor faults, thus discriminating between structural and sensor anomalies.

In this paper, a fuzzy neural network applied to in-process error compensation on CNC machine tools is proposed. The system is designed by a linguistic rule-based fuzzy controller and trained by a back propagation neural network to adjust and develop the control rules.

In the last decades researchers in the field of structural engineering have challenged the idea of facing natural hazard mitigation problems by adding to structures particular systems which are designed to protect buildings, bridges and other facilities from the damaging effects of destructive environmental actions. Among most protective systems and devices, active structural control, although having already reached the stage of full-implemented systems, still need theoretical investigation to achieve a complete exploitation of its capacity in reducing structural vibrations. In most of the operating systems (e.g. Soong and Reinhorn, 1993), linear control laws based on some quadratic performance function criteria are used since the design process for these linear strategies are fully developed and investigated. Moreover, the performances of structural systems controlled by linear techniques bring about some question concerning the complete and wise utilization of the capacity of control devices. Indeed, some of these inefficiencies are evident such as the inability to produce a significant peak response reduction in the first cycles of recorded or simulated time histories. (e.g. Reinhorn et al., 1993). Realizing that the expected maximum value for the required control force is a fundamental parameter in all processes to design the complete control system, in this paper it is shown that appropriate nonlinear control laws can significantly enhance the reduction of the system response under the same constraints imposed on the control force. Energy evaluation on the performance of different kinds of nonlinearities are reported such that a common base is built to perform comparative studies. These techniques have been successfully experimented on a structural model with ground excitations supplied by shaking table (e.g. Gattulli et al., 1994).

Recently piezoelectric materials have been used as actuators or sensors in some simple adaptive structures. Thin polarized piezoceramics were bonded to the top and bottom surfaces of simple plate-like passive structures. The piezoelectric layers work as actuators or sensors by means of the converse of the direct piezoelectric effect. In both cases the interaction mechanism between the active layer and the passive structure plays a fundamental role in the response of the overall structure [1,2,3]. Aim of the present paper is to study the stress distribution that is generated in the interaction between a simple (plate) structure and a piezoelectric actuator. A closed form solution is obtained for a given displacement assumption, based on a power series technique. The displacement form allows the interlaminar stress continuity at the interfaces between the actuator layer and the structure [4].

We consider the linearized elasticity system for a class of periodic structures made by very thin bars (as cranes for instance) . There are three small parameters which characterize these structures: their global width (or thickness) e, the size of the period and the thickness €6 of the bars composing the structure. More precisely, we consider a domain consisting of four vertical bars of length L and of cross section eö/2 x e6/2. These bars are linked with horizontal thin bars of length e and cross section eö/2 x 6 and periodically distributed (with period e) along the vertical direction.

Piezoelectric materials are highly attractive as actuator elements for Adaptive Structures since they have material-inherent actuatoric and sensoric functions and can easily be electrically controlled. This paper describes the possible fields of applications and deduces research needs.

Abstract not available.

The physical basis of shape memory alloy (SMA) behavior is outlined and a general one-dimensional constitutive law is reviewed, which is incorporated into a finite element procedure. A demonstration of two applications is given: a SMA pipe connector and a composite beam with embedded SMA wires. Another example is concerned with the use of SMAs for active control of a magnetic mechanical spring system which is currently under investigation for vibration isolation purposes.

'Smart' structure are an emerging technology which will provide the possibility of engineering structures with enhanced functionality for a wide range of applications. In most current Smart Structural Concepts a mechatronic or 'Frankenstein' approach is adopted where separate sensors, signal processing and actuators are 'bolted-together' to produce a 'Smart' system response. In the majority of these concepts the sensors and actuators are integrated within the host structure itself, and many of the sensor and actuator materials are familiar from other more conventional sensing/actuation applications. Amongst the materials used/proposed for actuators are Shape- Memory Alloys (SMAs) since these materials offer a range of attractive properties, including the possibility of high strain/stress actuation. The literature-base on the integration of SMA actuators into composite structures is not extensive. However, their use has been investigated for vibration [1], acoustic radiation [1,2], damage [3], buckling [1,2], and shape [1] control. An interesting feature of this work has been a heavy bias towards modelling, with only limited attempts to experimentally verify the calculated results. Previous work has also failed to produce a systematic database on one other key issue. This is the durability of SPA hybrid composites. The present work was therefore undertaken to provide a preliminary appraisal of the durability issues associated with the use of SMA hybrid composites. This work addressed a number of issues including (i) the effect of actuator fraction on strain outputs, (ii) the effect of actuator fraction and maximum strain on the cyclic stability of shape changes, and (iii) the effect of these variables on damage accumulation within the hybrid structures.

Among the potential materials for embedded actuators in composite smart structures are shape memory alloys (SMA). They have the advantage of being relatively high authority actuators and can be drawn into wires which may be aligned with fibers in a host composite. Interest has been shown in their use in variable geometry aerofoils/hydrofoils and shape control of composite plates has already been investigated. Preliminary studies have also been completed to assess the use of SMA in active damage control. Although the results of these studies appear promising, the durability of the material has not been fully assessed. One aspect of durability which must be considered is the ability of the SMA wire to generate the same force each time it is actuated. The force depends on the amount by which the wire has been prestrained, and optimum prestrain will be that which produces the maximum repeatable force without creating damage in the host composite. This paper describes the results of an initial study of the effects of prestrain on the performance of embedded SMA wires under repeated actuation cycles.

The majority of wavefront disturbances of space reflector and space telescopes are due to external thermal fields variations and the optical surface deformations. Two principal methods of disturbances compensation exist: a thermostabilization by temperature gradients decreasing and the mirror surface active thermodeformation. This can be accomplished only by some thermal methods: either by temperature gradients elimination or by keeping some given temperature field. The latter method is carried out by a system of heaters and sensors located on mirror elements /1,2/. Thermal deformation correction of distortions of optical and structural elements surface is possible, too, in accordance with control system responses. A thermo-optical compensation system (TOCS) consists of individual control units which contain heaters and sensors fixed to respective mirror elements as well as electronic measurement and control units (MCU) interfaced to them Fig. 1. The MCU are made constructively of unified printed circuit boards which can be functionally divided into various zones for interfacing of input/output, memory and supply circuits.

Within the field of 'smart' structures considerable interest has been shown in the use of piezoelectric materials both as sensors and actuators. One of the best characterized of these materials is the family of Lead Zirconate Titanate (PZT) based ceramics. The use of PZT in intelligent systems has been fairly widespread, the high modulus of the material give high authority actuation, coupled with a wide operational bandwidth and relative ease of control by the application of an applied voltage. The linearity of the actuation response over a limited range has made PZT a popular choice for high precision, relatively low displacement applications. A number of attempts have been made to utilize such actuators for aerospace, using both surface mounting [1] and embedding techniques [2,3]. The effects of actuators on aeroelastic performance has also been investigated for aerospace applications [4,5]. The current practical solution to this problem appears to be the use of spatially distributed actuators [6]. One of the practical limitations of this problem are the large number of actuators required to produce the required degree of static control. In order to ensure accurate shape control, measurements must be taken to ensure there are no significant difference in the actuator element properties due to factors such as batch processing variation. In the past this has proved difficult due to the extremely brittle nature of the actuator material. More specifically the requirement for thinner elements for use in embedded applications has increased this problem. A method by which the static performance of electroceramic actuators could be quickly established would therefore be desirable. This paper presents the results of recent work to develop a test method to define the static electromechanical properties of encapsulated actuator materials in order to assess their suitability as static actuators for aerospace applications. Preliminary results using a standard PZT material are described.

Piezoelectric/electrostrictive materials are a unique class of nonconducting, anisotropic materials which change in dimension due to the application of an electric field and thereby may be used as mechanical actuators. The most widely used actuation materials for acoustic transduction applications are piezoceramics, such as lead zirconate titanate (PZT) and lead magnesium niobate (PMN). Disadvantages of these materials include relatively high creep and hysteresis, the tendency of the ferroelectric dielectric material to retain electric potential after the alternating electric field to which it is subjected reverses polarity, thus causing electrostatic action to lag the applied voltage. The need to study the geometrical, material, and time dependent nonlinear behavior, as well as the interaction effects between sensors and actuators, is increasingly apparent, although a unified approach for modeling the local and global response of a nonlinear active material system has not been accomplished. In this paper we discuss the use of optical fiber-based short gage length Fabry-Perot sensors to experimentally verify an analytical model and allow determination of the nonlinear behavior of actuator elements without affecting their material properties.

This paper details the progress made towards the realization of a robust and user friendly system designed to damp vibration in composite structures. The system relies on polyvinylidene fluoride (PVDF) strain sensors linked to PZT actuators through a simple feedback signal inversion algorithm. The PVDF is coated to reduce charge leakage and the PZT ceramics are encapsulated to provide easy to handle, robust actuators that do not electrically short in CFRP based composites. Details of the system design are presented along with initial results showing vibration control of multimoded CFRP cantilevers.

This paper describes a manufacturing technique for active structures and a displacement measurement concept based on an embedded sensor system, which can both be used for the design of future active fiber reinforced reflector panels.

Aircraft structures made of Carbon Fiber Reinforced Composites (CFRP) are susceptible to impact damage in service. If the damage is of sufficient size, strength and service durability of the structure are degraded. The size and location of the damage are only predictable in a statistical sense; leading to excessive conservatism in design strains. Statistical approaches (1) have been explored, but condition monitoring is increasingly seen as the way forward. Smart materials are an attractive route to condition monitoring, and in the past ten years there has been considerable work to develop optic fiber strain and damage sensing techniques for composites, together with similar work on compliance change, acoustic emission and acoustic injection techniques (2). All of these involve use of discrete sensors, manufactured integral with the composite laminate. Many of the difficulties associated with use of discrete sensors may be overcome by adoption of techniques which rely on changes in the physical properties of the composite as a consequence of damage. A prime candidate is the electrical resistance technique. This relies on changes in electrical resistance, or of potential distributions in the laminate to characterize the damage state.

A new methodology has been developed for structural damage assessment and monitoring based on smart material sensors. The sensors transform to a ferromagnetic phase progressively as a function of strain. The solid-state phase transformation is useful in determining the local structural peak strains in monitored high stress sites. The technology is discussed with applications provided to illustrate the utility of the approach in addressing a range of engineering problems

The concept is developed of a 'self-sensing' composite to enable 'Smart' damage detection. This approach involves monitoring the damage induced change in a global physical property of a composite rather than the use of local sensors. The composite as a whole therefore effectively becomes the 'sensor'. Envisaged benefits of such an approach are reduced parasitic weight and increased reliability. The concept has been examined in terms of monitoring the changes in electrical resistivity of a carbon fiber/epoxy composite due to impact damage. Preliminary results have shown that damage from a 6 Joule impact can be detected and located in a 2 mm thick laminate by an array of voltage sensing, point contacts. Changes in potential distribution have been interpolated as a potential difference surface to give a visual representation of the damage site. The inherent simplicity of the system promises a reliable technique for structural health monitoring.

The experimental feasibility study using fiber optic sensors, strain gauges and speckleinterferometry (ESPI), indicates that delamination in FRP-sandwich structures can be detected by monitoring changes in the vibrational resonance frequencies. The frequencies are also determined analytically.

Recent structural failure and damage associated with earthquakes and pipeline failures have underscored the need for structural integrity monitoring systems using distributed fiber optic sensors. Such sensors must be low-cost, easily installed on new and existing structures, allow rapid assessment of structural integrity, and be capable of surviving and sensing large displacements associated with cracks and deflections in structural members. Experimental results for multimode fiber crack detection sensors based on the orientation angle approach are reported for both longitudinal and transverse crack displacements. In addition, we report results on a novel all-fiber sensor capable of sensing submillimeter cracks while surviving and sensing larger than 100% strains and cm level displacements.

The requirements of sensor monitoring associated with instrumented civil structures poses potential logistical constraints on manpower, training, and costs. The need for frequent or even continuous data monitoring places potentially severe constraints on overall system performance given real-world factors such as available manpower, geographic separation of the instrumented structures, and data archiving as well as the training and cost issues. While the pool of available low wage, moderate skill workers available to the authors is sizable (undergraduate engineering students), the level of performance of such workers is quite variable leading to data acquisition integrity and continuity issues - matters that are not acceptable in the practical field implementation of such developed systems. In the case of acquiring data from the numerous sensors within the civil structures which the authors have instrumented (e.g., a multistory building, roadway/railway bridges, and a hydroelectric dam), we have found that many of these concerns may be alleviated through the use of an automated data acquisition system which archives the acquired information in an electronic location remotely accessible through the Internet global computer network. It is therefore a possible for the data monitoring to be performed at a remote location with the only requirements for data acquisition being Internet accessibility. A description of the developed scheme is presented as well as guiding philosophies.

There exists a need to have a reliable comprehensive software/hardware to monitor the condition of airframe structures and aircraft components. Failure of any structural parts of aircraft are often prohibitively costly and could even lead to loss of life. The existing technologies deal with the use of some of the characteristics of structural vibration and thus resulting in false detections. The use of complete vibration signature measured by an array of embedded (or attached) fiber-optic sensors, which are loaded with multiple laser beams generated by a single optical source, is the focus of this project. The hardware will be light weight, low cost, and effective for monitoring discontinuities, damage, and delamination in both composite and metal airframes.

In a bridge, flexure cracks can be spotted and their mechanical consequences estimated through the automatically measured redistribution of curvature variations under convenient loading and a quick chain application of the classical expression for bending moment in beams. The residual flexural stiffnesses are thus obtained and introduced into a specific structural analysis program to define the new statical system of the bridge. More realistic stresses can then be predicted for any given live loads and at any time intervals.

We have demonstrated that fiber optic intracore Bragg grating sensors are able to measure the strain relief experienced over an extended period of time by both steel and carbon composite tendons within the concrete deck support girders of a recently constructed two span highway bridge. This is the first bridge in the world to test the prospects of using carbon fiber composite tendons to replace steel tendons. This unique set of measurements was accomplished with an array of 15 Bragg grating fiber optic sensors that were embedded within the precast concrete girders during their construction. We have also demonstrated that these same sensors can measure the change in the internal strain within the girders associated with both static and dynamic loading of the bridge with a truck. We are now studying the ability of Bragg grating fiber optic sensors to measure strong strain gradients and thereby provide a warning of debonding of any Bragg grating sensor from its host structure...one of the most important failure modes for any fiber optic strain sensor.

Primarily coated optical fibers for non-destructive monitoring of structures were embedded in cement mortar bodies and, in a separate test series, exposed to concrete-specific chemical attacks. Microstructure studies after four weeks revealed the relative resistance of acrylate-coated and flourine polymer-coated fibers. Polyimide-coated fibers showed serious changes in the coatings after the exposure.

This paper describes the construction and operation of a galvanic sensor which responds to changes in the corrosion intensity of mild steel in carbonated mortars or concretes. The sensor is simple to construct and operate. It is robust and has potential for development as an inexpensive method for long- term, continuous non-destructive corrosion monitoring of steel in concrete. Its range of possible applications include laboratory and field studies of effects of environmental exposure conditions and cement matrix variables on corrosion rates of steel in reinforced concrete structures. Information derived from such investigations is needed to provide basis for service-life prediction.

Fiber optical sensors were applied on a cracked prestressed concrete bridge in Berlin to get the static and dynamic structure response under load. Interferometric sensors (extrinsic Fibre-Fabry-Perot) were adhered on prestressing steels of a tendon opened inside the box girder; Intensity- modulated fiber sensors were tightened over the cracked concrete region. The very high resolution of interferometric sensors ((epsilon) equals +/- 0.024 micrometers /m) simultaneously allowed to measure strain of tendon and dynamic (natural frequency) response. This bridge is the first prestressed concrete structure in Germany to have fiber optic interferometric sensors installed. The optimization of the adhesive bonding and embedment technique are problems that need to be addressed as part of the further development.

In a reinforced concrete wall the deformation during concrete hardening was measured by means of embedded extrinsic fibre-Fabry-Perot-interferometers. The sensors were specifically modified in order to provide a self-calibration cycle and to ensure the functional efficiency under adverse conditions at the building site. The installation was done in the wall's cage of reinforcement before its concreting. The measurement was carried out automatically over a period of 35 days. The measuring results are very satisfactory and give a resolution of 0.1 micrometers /m.

We report on preliminary experimental trials aimed at assessing the suitability of a distributed water monitor as a means of determining the presence of grout in reinforced tendon ducts of civil engineering structures. This sensing capability is realized through a combination of Optical Time Domain Reflectometry (OTDR) and chemically sensitive water swellable polymers (hydrogels). This form of sensor cable can detect water as a function of linear position along its length with a spatial resolution of a few centimeters^1,2. The experiments carried out here indicate that this approach has considerable potential as a means of providing quality assurance during the grouting procedure.

Various types of active control systems have been proposed in order to reduce wind-induced structural vibrations. The objectives of this control are to keep structures safe from some distorting damages and to avoid sea sick of habitants. The typical type of those kinds of systems is so-called active mass damper system (AMD). This system aims to use controllable inertia forces of the AMD in order to reduce the structural vibrations. However, another problem may be arisen on the AMD systems. It is that dead loads of structures obviously increased by introducing this system. Moreover, the AMD system needs large electric power to shake its additional mass. In order to solve those problems, an active fin system⁽¹,(2)) is proposed by authors as an effective technique of the active control for wind-induced structural vibrations. The concept of this system is based on an idea to use wind force itself as effective damping forces. By changing the angle of the fin according to both wind direction and structural vibration direction, wind resistant forces can be generated arbitrarily. Moreover, the active fin system requires comparatively less electric power than that of the AMD system. In this paper, the effectiveness of two different types of control devices of the active fin are investigated by experimental tests (a wind tunnel is used for this aim). One is a single-fin type and the other is a twin-fin type. Following three items are focused to investigate: (1) Composition of an effective control algorithm for the active fin system, (2) Comparisons of control effects in the case of using the single-fin type and in the case of using the twin-fins type, (3) Estimation for real wind resistance forces acting on the fins.

In this paper, the global and local health monitoring of civil structures using RF antennas and ferroelectric sensors is presented. The sensors are fabricated with interdigital transducers printed on a piezoelectric polymer or ceramic type film. They in turn are mounted onto an ultra thin Penn State's novel RF antenna. The wave form measurements may be monitored at a remote location via the antennas in the sensors and an outside antenna.

In this paper, the results of a feasibility study for developing an efficient and effective design methodology to make systems 'smart by design' is presented. The primary focus is on computer-aided structural design to implement the inter-coupling of modes of vibration and smart devices built in the original design of structures. The conventional add-on elements are replaced by built-in multi tasks components. First, structures are designed so that a major portion of their vibration energy is localized into their non- critical areas and thereby isolate and quieten critical areas. Next, multi tasks smart components are integrated in the most critical locations of the system in order to monitor and maintain the designed vibration characteristics of the system.

This paper looks at the real problems facing engineers today when assessing the durability of structures. The role of monitoring structures to assess their current and long term behavioral characteristics and the enhancement of the safe use of structures is discussed. The capability of existing sensor systems to enable structures to inform engineers as to the onset of problems occurring is highlighted, thus establishing the advent of Smart Structures as a reality of today, rather than an idea of the future.

Severe environmental loads acting upon civil engineering structures can provide a significant hazard. Structural control, first formalized by Yao [10], is one tool that engineers today can use, especially in the retrofit of older existing structures that have been found to be deficient. Few active control strategies, however, can deal adequately with a lack of exact knowledge of system parameter values or nonlinear behavior. One strategy that appears to be effective is fuzzy logic control. Imprecise linguistic descriptions of system conditions (e.g., the velocity is slightly negative and the displacement is somewhat positive, so apply a small force in the negative direction) can be used as the basis for activating control forces through the mathematical rules created by Zadeh [11]. In this paper, we discuss some aspects of the application of fuzzy control to civil engineering problems and we present results from the control of linear, two-degree-of- freedom systems that are subjected to simulated seismic excitation.

A fiber optic smart structure system is proposed for monitoring earth motion that has the potential to substantially enhance our understanding of earthquakes, and volcanic activity through the use of long gauge length strain sensors.

A measuring system adapted to the needs of civil engineering structural monitoring is presented. It is based on low coherence interferometry in standard singlemode fibers and has a resolution of 5 micrometers , an operational range of 7 cm, stability over long periods (at least 1 year) and insensitivity to variations of the fiber losses. The portable reading unit doesn't need to be connected to the sensing fibers permanently and can thus be used to monitor multiple structures reducing the costs of the instrumentation. This paper presents the operating principle of this system and different techniques used to install the sensing fibers in large concrete structures, timber and mixed timber-concrete structures as well as on metals.

The measurement of thermal expansion of a 5 meter length concrete beam by embedded fiber-optic interferometric sensors is reported. The measurement has been done by a scheme which permits to solve the fiber strain-temperature cross-sensitivity by a contemporary reading of both the optical path length and the dispersion parameter of the fiber. The reported experimental data confirm the suitability of the technique for simultaneous detection of absolution strain and temperature.

Intrinsic Optical Fibre Sensors (OFS), in which the fiber is the transducer, are now recognized as good candidates for distributed or quasi-distributed sensing applications. In the particular field of Civil Engineering, this concept will provide powerful means for global and real time monitoring of the structure integrity. Natural phenomena like earthquakes, wind, atmospheric pollutions but also more insidious internal effects such as chemical attack (Alkali problem) yield consequent internal damage for which the embedment of sensor arrays could be of great interest. In our application, the transducer scheme is based on a polarimetric approach in which the two modes of a high birefringent fiber are used to measure a phase shift proportional to the strain state. A quasi-distributed measurement is performed by using the low coherence 'White Light Interferometry' (WLI) to separate the information provided by a linear sensor arrangement. Along the fiber, the sensors are separate each other by intrinsic mode couplers [1,2]. In this paper, we report some experimental results of strain states obtained with concrete test structures. The sensors were embedded in the structure during its manufacturing and tests of elongation and compression were performed.

The polarimetric fiber optic sensor is embedded in an 8 ply carbon/epoxy composite. The test specimens are exposed to different load conditions such as 3-point bending test. It is demonstrated that if the embedded optical fibers are twisted, the sensitivity to stress transverse to the fiber will decrease.

Different methods using optical fibers for real time inspection of concrete buildings and structures have already been investigated. According to recent progress it becomes more and more possible to obtain reliable punctual strain measurements with sophisticated techniques based on light polarization analysis. Based on knowledges about birefringence measurements in single-mode fibers which shows a fullness of information, this paper presents the difficulty of average strain measurement interpretation from beat length determination in homogeneous zones.

At present, there is an acute need for techniques in monitoring civil engineering structures, and optical fiber sensors are acknowledged to be amongst the best candidates. For more than ten years, interferometric optical fiber sensors have been widely investigated and now provide a rich extended basis for measuring strains experienced by structural elements. However, because of their periodic response, those sensors need extending measuring techniques to fulfill civil engineering requirements. Amongst different methods, Thomson-CSF and the University of Strathclyde have recently employed a microwave subcarrier system [1]. A specific sensor dedication to the arena of large civil engineering structures has been designed and tested.

The crucial components on which helicopter performance and handling qualities depend are the main and tail rotors, which are also strong contributors to the noise and vibration levels. Improvement of these elements leads to an enhancement of the overall rotorcraft quality. In this paper the aspect of smart structures applications chosen for consideration is that of control design concepts, leaving aside the areas of materials, sensor/actuators design, control algorithms, etc. Various design concepts of helicopter rotor control currently under consideration are reviewed, thereby indicating that rotorcraft technology is an area in which research into the application of smart structures may lead to significant improvements.

A method for using the extended Kalman filter to identify the modal parameters of vibration controlled structures has been developed and demonstrated. The closed-loop structural vibration system is excited by a known of unknown excitation signal and the resulting time histories of the closed-loop systems response are analyzed. The present method has the advantage that the physical parameters of the system are directly estimated. The numerical examples showed excellent results and it is expected that the present method can be applied to the on-orbit modal testing of controlled space structures.

The aim of the present paper is to demonstrate the efficiency of an LQG-based controller for the active control of the acoustic field radiated by a rectangular panel. This topic has been of interest for numerous researchers in the past 10 or 15 years, but very little attention has been paid to broadband disturbances occurring in a relatively high frequency range. These are unfortunately common features of noise perturbations in realistic structures such as airplanes or helicopters. The few articles that deal with this problem provide very scarce experimental results and are related to frequency bands where the structure dynamics is rather poor. From the outset, the problem at hand involves numerous difficulties, such as the modeling of the active structure itself and the possible large size of the controller. In the following, the experimental setup is described, then the controller design procedure is developed and finally some experimental results are shown that prove the efficiency of the method.

The potential of Active Damping Control Systems (ADCS) is demonstrated for several satellite applications where active control of satellite disturbances is required. Test results of damping large satellite appendages like solar arrays will be presented.

A proof of concept for the applicability of active structural control on a Vertical Turning Lathe was demonstrated. The effort proved that active damping can reduce chatter in a production machine tool when machining tough materials like nickel. Significant vibration reductions and surface roughness improvements were achieved.

The well known addage 'don't run before you can walk emerging materials. It typically takes ten years before a material is sufficiently well characterized for commercial aerospace application. Much has to be learnt not only about the material properties and their susceptibility to the effects of their working environment but also about the manufacturing process and the most effective configuration related application. No project will accept a product which has no proven reliability and attractive cost effectiveness in its application. The writers firmly believe that smart structures and their related technologies must follow a similar development pattern. Indeed, faced with a range of interdisciplinary problems it seems likely that 'partially smart' techniques may well be the first applications. These will place emphasis on the more readily realizable features for any structural application. Prior use may well have been achieved in other engineering sectors. Because ground based applications are more readily accessible to check and maintain, these are generally the front runners of smart technology usage. Nevertheless, there is a strong potential for the use of smart techniques in space applications if their capabilities can be advantageously introduced when compared with traditional solutions. This paper endeavors to give a critical appraisal of the possibilities and the accompanying problems. A sample overview of related developing space technology is included. The reader is also referred to chapters 90 to 94 in ESA's Structural Materials Handbook (ESA PSS 03 203, issue 1.). It is envisaged that future space applications may include the realization and maintenance of large deployable reflector profiles, the dimensional stability of optical payloads, active noise and vibration control and in orbit health monitoring and control for largely unmanned spacecraft. The possibility of monitoring the health of items such as large cryogenic fuel tanks is a typical longer term of objective.

Active vibration control of smart structural materials has been achieved by using distributed piezoelectric actuators. Numerical simulation and experimental testing have been conducted to investigate vibration suppression of the advanced materials.

Consider a stacked actuator of nominal (free-stroke) displacement UISA, and internal stiffness k,. During static operation, the total induced energy, EISA, gets divided between the internal and external subsystems: part of it, Ee, is transmitted to the external application, while the rest, E, remains stored in the internal compressibility of the stack. The value of EISA, and its repartition between Ee and E1, depends on the stiffness ratio r = kik

The Challenger aircraft fleet of the Canadian Forces will fly demanding missions, requiring the implementation of a fatigue management program based on the monitoring of in-flight aircraft load conditions. Conventional sensing techniques experience problems arising from severe electromagnetic interference (EMI). This paper describes the development of an EMI- insensitive smart-structure sensing concept for loads monitoring. Fiber-optic strain sensors, incorporated at critical structural locations, are used to monitor the fatigue life of the aircraft wing, fuselage, and empennage. A fiber-optic accelerometer is also incorporated in the system. A long-term plan is presented for the development of an advanced smart-structure concept which can support the continuous monitoring of fatigue-prone components, and provide the aircraft with near real-time damage location and assessment.

Smart structures research has focussed upon the many different subsystems making up the smart structure with the exception of the power/communication interface. In the case of embedded fiber optic sensors, an acceptable solution has yet to be found. A preferred solution would not involve physical interconnection between the power/interrogation subsystem and any embedded electronics. One method which offers promise to provide this solution is based upon inductive coupling between a surface mounted interrogation coil and an embedded coil connected to some local system. In this paper, a description of such a system is provided detailing its basic operating principles, the design/performance of a pc based demonstration system, results from sensors embedded in composite coupons and a discussion of how the system may properly be called a smart subsystem.

The performance of passive quadrature demodulated fiber-optic interferometric strain gauges is investigated, which are used for monitoring the strain on the surface of rods and plates made from Carbon fiber composites under dynamic load variations and in the presence of strong vibrations during flight tests.

Fiber Bragg grating strain sensors have been embedded in carbon fiber composite beams at BAe. A program of work to develop sensory structures is addressing issues of fiber sensor embedding, multiplexing, optical connection, and temperature compensation.

Of importance in building designed to posses adaptive and responsive relationships with their environment is the design of their control mechanisms, whose dynamics should be structurally congruent with the prevailing environment around the building element.

In developing some initial ideas on inexpensive 'smart structures' which could sense, indicate, record and respond, it became apparent to us that a cheap, lightweight, flexible and versatile display mechanism would be of considerable commercial utility for this and many other applications. We therefore initiated a probe to look at what might be possible, focussing mainly on electrochromic systems.

The detection of prosthesis loosening in total hip replacement remains a problematic issue. Common techniques such as radiography and arthrography have not been shown to be very effective. Although originally developed for the assessment of fracture healing, vibration analysis was proposed as a method for the detection of loose prostheses [1,2]. In this paper, we will discuss the principles used in the vibration analysis in relation with the detection of loose prothesis and discuss the potential and limitations.

It is generally acknowledged that technologies diffuse through industry and that the rate of diffusion varies both within different industries and according to the circumstances. Innovation is a process involving risk, especially during the adoption and adaptation of a powerful new technology. Central to a consumer products success using new technology is the quality of their designs and the nature of their forms. Form is of prime importance in influencing the purchasing decisions of consumers and it is also influential in determining the relationships between people in its use environment. The acceptance of a new product into the world is often unduly ad hoc. Many failures are created for each success and there are few guidelines to assist the formulation of a strategy for creating an appropriate form. It is suggested below that success of consumer products incorporating 'smart structures' may be determined not only by the function of products and systems, but also by the form they take. The definition of a desirable product form depends entirely on the point of view taken: technological, commercial, ecological, cultural, and social. However any design using new will incorporate the old and the new. The probability of acceptance of a new product is enhanced by maintaining a fine balance between imaginative and creative form and that with which people are familiar and prefer: a new design may be rejected if it is too novel and unfamiliar, or too traditional. The acceptance of a new product and its subsequent development depends on the success designers and engineers have when dealing with the initial forms, particularly using new technology such as 'smart structures'.

Specially prepared thin single-crystal plates rigidly fastened to the sample surface area are shown to be effective as sensor elements (indicators and detectors) of the deformation damage of multi-phase commercial alloys under fatigue and static loading. It is proposed to estimate the lifetime and the strain of basic material by monitoring the geometric characteristics of band patterns on the detector surface. It is shown that density, direction of deformation bands and fractal dimension of band patterns on surfaces of indicators correlate with the number of cycles, maximum applied stress (fatigue loading) and plastic strain, temperature (static loading).

This paper describes the design and development of a low cost indicator mechanism that is triggered by overloading. The method is applied to Flexible Bulk Containers (FIBCs) and detects overloading during handling.

Homeostasis refers to the process by which living organisms maintain internal bodily balance and equilibrium. For buildings, to embody the principles of homeostasis gives them a potential of becoming truly energy efficient and thus effective.

The subject of this research is the enhancement of properties beyond that available in an original hardened material by the release of 'healing' chemicals such as adhesives from hollow fibers into cementitious matrices in response to loading. Thus, the sensing of a crack by the fibers or the breaking of coating starts the activation of a remedial process (i.e., the release of a sealing or adhering chemical). This capacity for self-healing occurs whenever and wherever cracks are generated. In terms of fracture mechanics, this research concerns the repair of cracks and rebonding of fibers by chemicals released from hollow fibers at the fiber wall and into the adjacent cracks. The overall property change is an increased flexural toughening. The mechanisms for that appears to be an adhesive rebonding of the fibers and a crack-filling with adhesives which causes the material to become stronger when it is bonded inside cracks or pores.

The field of fiber optic smart structures has recently been an active area of research with many important advances in sensors, manufacturing and structural reliability. These areas of fiber optic smart structures have progressed independently to the level that separate design criteria are beginning to be formulated. As has been emphasized time and again, fiber optic smart structures is a multidisciplinary field that requires an integrated approach to system design and testing. This paper describes one such integrated design approach for composite material-based fiber optic smart structures. Both design for sensor performance and structural reliability are considered. The design for sensor performance presents a rational design philosophy for choosing the appropriate combination of sensors and demodulators to faithfully record the target strain in a smart structure. The design for structural reliability provides a rational approach for ensuring that the structure will support its design loads.

Fiber Bragg grating sensor arrays fabricated during optical fiber drawing have been embedded in fiber-resin composite panels made by the Continuous Resin Transfer Molding^TM (CRTM^TM) process. The sensors accurately measure stain induced during both curing and bending tests.

We describe a multiplexed nine element Bragg grating array used for strain mapping over a plate which is subjected to deflection forces. The system comprises two sub arrays of gratings which are sequentially addressed, and read via a single interrogation system into a PC. Real time strain distributions of the plate are determined and displayed.

For control of structures with aeroelastic loads, torsion and bending must be sensed and controlled independently. Tailored piezoelectrics with skewed sensing axes can provide decoupled sensing of both bending and twist using the same set of sensors. This paper discusses the use of a finite element model to evaluate the effectiveness of anisotropic piezoelectric sensors for shape control sensing. Using a finite element representation for a plate-like structure covered by PVDF laminates, it is shown that integral sensors can accurately capture system independent bending and torsion displacement by measuring the induced electric charges without any additional signal processing efforts. The contribution of this work is to suggest an expression that relates sensed output from anisotropic sensors to plate of lifting surface bending and twist. An expression for the bending and torsion is tested with the finite element model. It is found that bending slope is accurately measured, but that twist is less likely to be accurately approximated by the sensor output.

An eight element time-division multiplexed fiber Bragg grating sensor array is demonstrated using an unbalanced integrated-optic discriminator to facilitate demodulation of Bragg wavelength shifts in the return signals. The system exhibits a wide sensing range with a detection capability of <1 (mu) - strain/(root)Hz rms at low frequencies.

A new fiber optic stress/strain sensor, utilizing near-infrared SPATE, is reported which is suitable for monitoring hot materials. The fiber is merely arranged to collect the grey body emission from a heated metal sample. When the sample is subject to transient stresses, the radiation is modulated because of the adiabatic changes in the temperature of the material surface. The modulation of the light is monitored, via a silica optical fiber, using a near-infrared GaInAs photo-detector. This is also believed to be the first demonstration of SPATE in the near infrared region of the spectrum.

Thin films of ferroelectric ceramic and epoxy composites with 0-3 connectivity have been produced by dispersing a ceramic powder in a thermosetting epoxy resin. Calcium Modified Lead Titanate [PTCa] powder with grain size of less than 10 micrometers was mixed with an epoxy resin and curing agent and then formed into thin films of approximately 100 micrometers . The pyroelectric behavior of these composites with 50% and 60% volume loading of ceramic is reported in this present work.

New type of fiber optic sensor of electrostatic field is considered. Using the interferometric detection technique the sensitivity of about 0.2 (V/m)/(root)Hz was achieved. Theoretical evaluation yields the thermal fluctuation limit of sensitivity of about 2.5 X 10^-4 (V/m)/(root)Hz.

An optical fiber sensor system to interrogate point sensors (Bragg gratings) and optical path length between point sensors is discussed. The paper describes interrogation schemes capable of measurement resolutions better than 100 microstrain based on simple optics, telecommunications electronics and sophisticated signal processing.

Micromechanical Finite Element (FE) analysis was used to model stress and strain fields in and around embedded optical fibers (EOFs) in flexural test coupons of carbon fiber composite. The coupons were used in studies of EOF effects on macroscopic laminate properties. The FE method allows complex material inhomogeneities, laminate boundaries, and load conditions to be modelled.

The problem of chemical and biological sensing, i.e., identification of components of various media and measuring their concentrations, is of extreme importance in science, technology, medicine, environmental monitoring, etc. Principally, the problem could be solved by means of purely optical methods, particularly, tunable diode laser spectroscopy [1]. Due to the spectral resolution by an order or two of magnitude higher than Doppler width of spectral lines, it provides ideal selectivity and suitable sensitivity in gas sensing. However, such techniques require bulk, expensive laboratory equipment and qualified personnel. This results in a very high cost of analysis and makes the method unsuitable from the commercial standpoint

Finite element analysis has been performed to determine the local stress field in a tensile loaded composite specimen with an embedded EFPI-sensor. The sensor/coating and the coating/composite interfaces have been distinguished as the sites where failure is initiated due to stress concentrations caused by the cavity in the EFPI-sensor. An increase in the strength of the interfaces is an important task to improve the reliability of embedded sensors.