Showing papers in "Journal of Intelligent Material Systems and Structures in 1990"

One-Dimensional Thermomechanical Constitutive Relations for Shape Memory Materials

Abstract: The use of the thermoelastic martensitic transformation and its reverse transformation has recently been proposed and demonstrated for several active control ap plications. However, the present constitutive models have lacked several important funda mental concepts that are essential for many of the proposed intelligent material system ap plications such as shape memory hybrid composites.A complete, unified, one-dimensional constitutive model of shape memory materials is developed and presented in this paper. The thermomechanical model formulation herein will investigate important material characteristics involved with the internal phase transformation of shape memory alloys. These characteristics include energy dissipation in the material that governs the damping behavior, stress-strain-temperature relations for pseudoelasticity, and the shape memory effect. Some numerical examples using the model are also presented.

Modelling of Piezoelectric Actuator Dynamics for Active Structural Control

Abstract: The paper models the effects of dynamic coupling between a structure and an electrical network through the piezoelectric effect. The coupled equations of motion of an arbitrary elastic structure with piezoelectric elements and passive electronics are derived. State space models are developed for three important cases: direct voltage driven electrodes, direct charge driven electrodes, and an indirect drive case where the piezoelec tric electrodes are connected to an arbitrary electrical circuit with embedded voltage and current sources. The equations are applied to the case of a cantilevered beam with surface mounted piezoceramics and indirect voltage and current drive. The theoretical derivations are validated experimentally on an actively controlled cantilevered beam test article with indirect voltage drive.

Detailed Models of Piezoceramic Actuation of Beams

Abstract: In this paper, techniques for modeling induced strain actuation of beam-like components of intelligent structures are developed. Two analytical models and one numer ical model describing the detailed mechanics of induced strain actuators bonded to and embedded in one-dimensional structures are presented. The models illustrate the exten sion, bending, and localized shearing deformations induced. The range of parameters for which the simpler analytic models are valid is also established. The specific characteris tics of one type of induced strain actuator, piezoceramic materials, are discussed, and im plications for practical use of piezoceramic actuators are outlined. Experimental results are used to validate the beam actuation models presented.

Vibration Characteristics of a Composite Beam Containing an Electrorheological Fluid

Abstract: The complex moduli of a composite consisting of a hollow beam filled with an electrorheological (ER) fluid were obtained by analyzing the beam's motion in free oscillation. The beam was considered to be a uniform viscoelastic material and was modeled as a damped harmonic oscillator. Hydrous-based ER fluids consisting of either cornstarch-corn oil or zeolite-silicone oil mixtures with varying amounts of solids and water content were employed, along with electric field intensities ranging from 0.0 to 1.7 × 103 kV/m. Rheological data were also obtained for the fluids A linear correlation between the two components of the moduli and fluid strength was observed, which was ex plained in terms of fluid structure and particle polarization

A Concept of Intelligent Materials

Abstract: SCIENCE AND TECHNOLOGY in the twenty-first century will rely heavily on the development of new materials. Based on a concept that differs greatly from that of the so-called structural and functional materials, &dquo;intelligent materials&dquo; will play an important part in materials sciences and development. Intelligent materials may be defined as &dquo;materials which respond to environmental changes at the most optimum conditions and manifest their own functions according to the changes&dquo;. The advent of intelligent materials will undoubtedly mark an epoch-making development in many fields of science and technology such as information science, electronics, computer science, medical treatment, life science, energy transportation, and safety engineering. Individual philosophies and specialties have led scientists to a variety of definitions of intelligent materials. In Japan, from July 1987 to November 1989, the Council for Aeronautics, Electronics, and Other Advanced Technologies of the Science and Technology Agency supported a discussion on intelligent materials. For the first time in Japan, an attempt was made to study this new concept from the perspective of professionals representing a broad range of disciplines. It was hoped that these discussions could provide some direction for the development of research techniques in the field of intelligent materials. In November 1989, a report summarizing the discussion was submitted to the Minister of the Science and Technology Agency. It is hoped that this report will be used in the future development of science and technology in Japan. In order to facilitate world-wide understanding of intelligent materials, Japan hosted the International Workshop on Intelligent Materials (1989), March 15-17, at Tsukuba Science City, Japan [1]. This paper will describe a concept of intelligent materials based on the discussions of the Materials Technology Committee and Subcommittee in the Council for Aeronautics, Electronics, and Other Ad-

Fiber-Optic Strain Sensors for Smart Structures

Abstract: A set of requirements is proposed for fiber-optic strain sensors, and specific criteria are suggested for such sensors in the context of "smart" structures. The suitability of several potential sensor types is evaluated against these criteria, and the characteristics of two particular suitable sensors are presented.

Health Monitoring Aircraft

Abstract: A description is given of the health monitoring aircraft concept, which will incorporate innovative sensors, AI, and advanced analytical techniques to provivide real-time and continual aircraft health assessment. According to this concept, all flight-critical structures will be evaluated for integrity as part of the automated preflight checklist. The pilot will be given a visual display of the health of all systems prior to takeoff. Any in-flight change in the health of the aircraft wil be displayed along with recommended action. In order to achieve these capabilities, state-of-the-art structural integrity computer programs, together with AI/neutral network decision-making software, will be incorporated as part of the aircraft computing capability. The life history of the aircraft will be continually and automaticaly updated so that acccurate structural integrity assessments can be made.

Simultaneous active control of flexural and extensional waves in beams

Abstract: The simultaneous active control of flexural and extensional vibrations in elastic beams is experimentally investigated. The results demonstrate that using pairs of piezoceramic transducers, whose elements are symmetrically located and independently controlled by a multichannel adaptive controller, enables the high attenuation of both flexural and extensional response. This capability is due to the nature of the piezoceramic element, which when bonded to the surface of the structure and electrically excited, exerts a surface strain on the structure. This strain enables input of both shear forces and moments into the structural system. The results are applicable to many situations where extensional vibrations couple to large flexural vibrations and subsequently radiate significant sound levels.

Active Vibration Control Using NiTiNOL and Piezoelectric Ceramics

Abstract: The results of a study recently completed by Boeing Aerospace & Elec tronics to investigate the use of NiTiNOL Shape Memory Metals as the sensor and actua tor components of active vibration suppression systems are presented. Two different test set-ups consisting of aluminum cantilever beams with NiTiNOL wires fastened along both sides were developed. The test article for the first set-up was a very flexible, low frequency beam which utilized NiTiNOL wires for both sensing and actuation. The test article for the second set-up was a much stiffer, high frequency beam which utilized NiTiNOL wires for sensing and piezoelectric ceramics for actuation. The settling times of both beams were significantly reduced through the use of the NiTiNOL wire sensors and actuators. Analytical simulations were developed which correlated well with the experimental results. The results of the study demonstrated the feasibility of using NiTiNOL sensors and actuators for active vibration control of structural members.

Active control of a flexible structure using a modal positive position feedback controller

Abstract: The feasibility of a new Modal Positive Position Feedback (MPPF) strategy in controlling the vibration of a complex flexible structure using a single piezo-electric active structural member is demonstrated. The control strategy generates its control forces by manipulating only the modal position signals of the structure to provide a damping action to undamped modes. This is in contrast to conventional modal controllers that rely in their operation on negative feedback of both the modal position and velocity. The proposed strategy is very simple to design and implement as it designs the controller at the uncoupled modal level and utilizes simple first order filters to achieve the Positive Position Feedback effect. The performance of the new strategy is enhanced by augmenting it with a time sharing strategy to share a small number of actuators between larger number of modes. The effectiveness of the new strategy is validated experimentally on a flexible box-type structure that has four bays and its first two bending modes are 2.015 and 6.535 Hz respectively. A single piezo-electric actuator is utilized as an active structural member to control several transverse bending modes of the structure. The performance of the active control system is determined in the time and the frequency domains. The results are compared with those obtained when using the Independent Modal Space Control (IMSC) of Meirovitch. The experimental results suggest the potential of the proposed strategy as a viable means for controlling the vibration of large flexible structures in real time.

The Dynamics of Helical Shape Memory Actuators

Abstract: This paper presents an experimental and theoretical study of the dynamic and thermal characteristics of SHAPE MEMORY ALLOY (SMA) actuators. The actua tors are made of a NIckel-TItanium (NITINOL) wires formed in the shape of helical coils that are capable of generating large deflections when subjected to low voltage excitations. The deflections produced are accompanied by significant forces resulting from the unique phase transformation of the NITINOL alloy as it is heated past its transition temperature.

Advantages of Slewing an Active Structure

Abstract: The slewing control of an active flexible structure is considered by examin ing the equations of motion of an integrated actuator/structure system containing both the actuator and structure dynamics. These equations are derived using a Hamiltonian ap proach. The system under consideration is a slewing flexible structure, a thin aluminum beam, torque driven by an armature controlled DC electric motor and actuated by a piece- wise distributed piezoceramic actuator. An improvement in performance is gained by 1) including the effects of motor actuator and beam dynamic interaction and 2) using a piezo electric device, layered on the structure, for direct vibration suppression of the structural dynamics. A comparison is made using simulations, to point out the advantages of slewing an active structure versus slewing a passive structure. This presents a multi input slewing control problem which is implemented using a standard linear quadratic regulator control design.

Technology Development and Forecast of Dynamical Intelligent Building (D.I.B

Abstract: The Dynamical Intelligent Building takes a new horizon with derivation from the conventional earthquake resistant building structures. The author has proposed and expanded this new concept and has been promoting its research and development. The ultimate goal aims at the intelligent structure which reacts actively to earthquake taking an initiative with the building itself, in contrast with the passive design philosophy which is to endure the fatal disturbance The author realizes the actual building as a first stage of a Dynamical Intelligent Building with an Active Mass Driver (AMD) system and also has been carrying out the development of an Active Variable Stiffness (AVS) system. It is thought that still more development of this innovative technology has progress steadily and the specific plans for the respective applications will be reviewed extensively hereafter.

Active Control of Seismic Response of Structures

Abstract: A new closed-open-loop optimal control algorithm is proposed that has been derived by minimizing the sum of the quadratic time-dependent performance index and the seismic energy input to the structural system. This new control law provides feasi ble control algorithms that can easily be implemented for applications to seismic-excited structures. We developed optimal control algorithms, taking into account the nonlinearity of the structural system for applying a control force to a structural system subjected to gen eral dynamic loads. The formulation of a predictive control law has been developed in which emphasis is placed on compensation for the time delay due to measurement process and the control action. These optimal algorithms are simple and reliable for on-line con trol operations and effective for a structural system with a base isolation mechanism. The control efficiency affected by two weighting matrices included in the performance index is investigated in detail. Numerical examples are worked ou...

Mathematical Models of Dynamical Martensitic Transformations in Shape Memory Alloys

Abstract: HE SHAPE MEMORY effect is a physical property characteristic of numerous solids, including various metallic alloys and non-metallic solid materials like polymers. This property consists in an ability of a solid, subject to plastic deformation, to recover its original shape after an appropriate thermal treatment (possibly complemented by a mechanical loading). The effect had already been discovered in the mid-thirties, but an explosive development of interest in it, as well

Overview. of Nondestructive Evaluation Projects and Initiative at NSF

Abstract: Infrastructure of public works In the world is deteriorating. Nondestructive evaluation (NDE) is essential for condition assessment for repair, retrofit, rehabilitation, and replacement (if needed) to Insure the public safety. In this paper an overview of nondestructive evaluation projects, including a new initiative on Quantitative NDE for Large Structural Systems, is presented.

Inverse dynamics of adaptive structures used as space cranes

Abstract: As a precursor to the real-time control of fast moving adaptive structures used as space cranes, a formulation is given for the flexibility induced motion relative to the nominal motion (i.e., the motion that assumes no flexibility) and for obtaining the open loop time varying driving forces. An algorithm is proposed for the computation of the relative motion and driving forces. The governing equations are given in matrix form with explicit functional dependencies. A simulator is developed to implement the algorithm on a digital computer. In the formulations, the distributed mass of the crane is lumped by two schemes, vz., 'trapezoidal' lumping and 'Simpson's rule' lumping. The effects of the mass lumping schemes are shown by simulator runs.

A Comparison of Actuators for Vibration Control of the Planar Vibrations of a Flexible Cantilevered Beam

Abstract: The methods and results of an analytical study comparing the effectiveness of four actuators in damping the vibrations of a planar clamped-free beam are presented. The actuators studied are two inertia-type actuators, the proof mass and reaction wheel, and two variable geometry trusses, the planar truss and the planar truss proof mass (a combination variable geometry truss/inertia-type actuator). Actuator parameters and loca tions used in the models were chosen based on the results of a parametric study. A full- state, LQR optimal feedback control law was used for control in each system. Numerical simulations of each beam/actuator system were performed in response to initial condition inputs. These simulations provided information such as time response of the closed-loop system and damping provided to the beam. This information can be used to determine the "best" actuator for a given purpose.

Optimum Adaptation of Intelligent Truss Structures

Abstract: Intelligent structures that can actively change their geometric configura tions, as well as their mechanical properties, are developed to meet various space mission requirements. In this paper, opt...

Seismic Damage and Damage-Control Design for RC Frames

Abstract: A review is performed of some of the seismic damage models that were more recently developed, taking into consideration the effect of cumulative damage. One of these models derives a local damage index in the form of a modified Miner's rule. This index is then used to develop the automated damage-control design procedure so that the design, while satisfying the necessary building design code, is optimized in the sense that it spatially distributes the damage as uniformly as possible.

Effect of Joint Imperfections on Static Control of Adaptive Structures as Space Cranes

Abstract: Effect of imperfections in the joints of an adaptive structure on its slow (no inertia forces) motion along a prescribed trajectory as a space crane is studied. Two mathematical models to predict the effect of joint imperfections are proposed. The two models are used to obtain estimates of the deviations of the node of the space crane to which the end-effector is attached, from its prescribed trajectory. An application of the models to a two-section space crane is given.

Aseismic Hybrid Control System for Building Structures under Strong Earthquake

Abstract: Two aseismic hybrid control systems recently proposed for protecting tall buildings against strong earthquakes are investigated and evaluated. The hybrid control system consists of a base isolation system connected to either a passive or active mass damper. The base isolation system, such as elastomeric bearings, is used to decouple the horizontal ground motions from the building, whereas the mass damper, either active or passive, is used to protect the safety and integrity of the base isolation system. The per formance of the proposed hybrid control systems is compared with that of an active control system. It is shown from the theoretical/numerical investigations that the proposed hybrid control systems are very effective in reducing the response of tall buildings under strong earthquakes. Likewise, the practical implementation of such hybrid control systems is easier than that of an active control system alone.

Intelligent Materials for Future Electronics

Abstract: Until now, electronic devices have been made using materials with given characteristics. In the future, however, materials should be designed to give the desired characteristics to electronic devices. As may be inferred from the widespread use of semi conductors in electronic devices, semiconductors are at present indispensable to the elec tronics industry. However, if we rely exclusively upon semiconductors, we run the risk of material shortages. Consequently, there is a need for new, alternative materials. Such new materials are already being referred to by a recently coined term: "Intelligent Materials".There is little hope for finding such intelligent materials in nature. It may, however, be possible to develop them through a kind of "genetic control in materials science".This paper discusses "intelligent materials" from the viewpoint of an individual whose experience is in the field of electronics.

A Novel Liquid Core Fiber Temperature Sensor for Smart Structure Applications

Abstract: In this paper we describe the principles of operation and performance of a novel, liquid core fiber (LCF) temperature sensor for possible applications in smart struc ture environments. The sensor consists of an optical, time domain, monitoring station and a liquid core fiber probe that contains fluids with very large thermo-optic coefficients. This design makes the sensor fiber very sensitive to temperature fluctuations that have been measured by monitoring induced optical pulse delay. Operating temperature ranges are ex pected to span from —55 to +400°C, with ultimate temperature measurement resolution in the order of 0.05°C/m. Limitations such as sensor packaging and fiber loss/dispersion are also addressed.

Threshold Control for Nonlinear and Time-Varying Structures Using Equivalent Linearization

Abstract: A minimum force, threshold control strategy is developed for the vibration control of mechanical structures modeled as a nonlinear, time-varying, single-degree-of- freedom oscillator. The threshold control strategy results in a control that is applied over short control time intervals. During each control time interval, the control law is con strained to be a linear combination of the structure's position and velocity. The necessary conditions that define the optimal control are shown to consist of a two-point boundary value problem and a pair of coupled, definite integral equality constraints. A numerical solution technique is then developed to determine the optimal control.

The Design of Natural Materials and Structures

Abstract: nature can use and which we have yet to learn to manipulate to their full advantage. In this review a number of these rules and requirements are enumerated, illustrated and discussed. Taken together, they can maximise success in our attempts at biomimicry. A prime factor, which is continually overlooked, is that in order to make best use of the variety of designs in nature, one needs to know just how vast that variety is. The best way to get this information is to talk to a good biologist or nat-

Structural Monitoring, Sensor Technology and Performance Assessment

Abstract: Brief descriptions of several recent programs of monitoring in-service re sponse of bridges, buildings and offshore structures and the associated research in sensor technology are presented. For bridge structures, new technologies have been developed for monitoring atmospheric corrosion, fatigue crack growth, progressive failure and local structural defects. The work on buildings is related to earthquake ground motion measure ment and dynamic response monitoring. The information obtained allows direct evaluation of seismic performance of the structures, including damage assessment. For offshore plat forms, the monitoring programs involve both environmental and structural data gathering and their correlation with design predictions.