Intelligent Material Systems Research Articles

Tunable carbon nanotube ionic polymer actuators that are operable in dry conditions

Actuators are widely used in intelligent material systems. However, electromagnetic, piezoelectric or shape memory alloy actuators are too heavy, complicated and too slow for such applications. In contrast, electroactive polymers (EAPs) are relatively lightweight, rather simple and fast enough to suit the requirements of an actuator. In this study, we have developed CNT ionic polymer actuators that are operable in a wide range of humidities. Optimum performance can be tunable by the addition of different CNT concentrations. A low percentage of CNT will form well distributed sponge-like structures which enable effective entrapment of moisture within the polymer matrix and thus favor the work of the actuator in dry environments, while a higher CNT percentage will lower the water absorption rate, and increase the elastic pressure of the matrix to reduce swelling and deformation. Therefore, the actuators also work well in very high humidity. It is likely that this actuator will have a wide range of bio-inspired applications.

Design and application of the ice force sensor based on fiber Bragg grating

Ice load is one of the most dangerous factors which threaten the health of offshore structures in cold area. The ice-loading model experiment is an effective method to identify the ice load and to evaluate its influence towards structures. Fiber Bragg grating (FBG) with advantages of reliability, durability and high accuracy, has become one of the most popular sensing element for structural health monitoring and intelligent materials system. In this paper, a novel FBG ice force sensor is presented and applied in the tests of ice loading on bridge pier model. Its sensing property is theoretically analyzed and calibration experiments are conducted. The research results demonstrate that the FBG-based ice force sensor has advantages of small size, high precision and low influence on the structure, showing great prospect for measurement of ice force in model test.

Research on μ-Stability of Unbounded Time-Varying Delays Neural Networks with Impulsion in Intelligent Materials System

This paper is concerned with the problem of μ-stability of unbounded time-varying delays neural systems with impulsion. Some μ-stability criteria are derived by using Lyapunov- Krasovski functional method. Those criteria are expressed in the form of linear matrix inequalities (LMIs).

Synthesizing Effect Model Based on Quasi-Linear Function in Intelligent Materials System

Interval number is a common tool to describe uncertain information. Its ranking method plays a role in solving uncertain decision-making problems. In Ref. [1], by analyzing the feature and shortcomings of the current ranking methods, we proposed a ranking method based on quantity property, and systematically discussed the structure criteria, based on it, in this paper, we firstly introduce the definition of quasi-linear function and establishan order model of interval numbers based on it; secondly, with a specific example, we further analysis the property the order structure built in Ref. [1]. The result shows that this method can merge decision making consciousness into the decision making process effectively. In complex optimization system, decision making and other fields have a wide range of applications.

Preface: Educating Engineers About Intelligent Material Systems and Structures

Preface: Educating Engineers About Intelligent Material Systems and Structures

Comments on: ‘Curvature Mode Shape-based Damage Assessment of Carbon/Epoxy Composite Beams’

The primary motivation for the article sprouts from the article by Lestari et al. [Lestari, W., Qiao, P. and Hanagud, S, 2007. ‘‘Curvature Mode Shape-based Damage Assesment of Carbon/Epoxy Composite Beams,’’ Journal of Intelligent Material System and Structures, 18:189—208], published in a previous issue of this journal. The article although very useful and informative, as it conducts a wide array of experiments on different types of damages for a beam, has some discrepancies in the solution to the perturbed ordinary differential equation. The inconsistency manifests itself as a higher order effect. A possible solution to the equations is presented. Also, in this article the process is extended and the change in mass is taken into account along with change of stiffness. Only stiffness change is modeled in the original article.

Modeling of Intelligent Material Systems by the MLPG

Modeling of Intelligent Material Systems by the MLPG

Training by research - program of, and experiences in, the Smart Structures Research Training Network project

Smart Structures is a Marie Curie Research Training network (RTN) named “A Computer Aided Engineering Approach to Smart Structures Design”. The overall objective of the RTN is to develop an educational and research framework for developing macroscale noise control applications based on intelligent material systems. The scientific and technological objective of the network is to advance the state-of-the-art in smart materials research to the level of system integration and industrial applicability, with a specific focus on solutions for noise and vibration reduction and for vibration-based damage detection. The paper gives a short overview of the project partners' activity and summarizes the experiences of the researchers and their tutors after the first 18 months of the network.

Experimental and Theoretical Behavior of Self-healing Bolted Joints

This article focuses on improving the experimental behavior of a self-healing bolted joint using shape memory alloys (SMAs). Self-healing bolted joints are used to reduce the likelihood of failure of structures due to loosening of bolted joints. The clamping force (CF) in a bolted joint assembly plays an important role in maintaining the integrity of the structure. Controlling the preload in a bolted joint assembly by external heating activates the heat-to-recover (HTR) SMA washer. The SMA washer is initially in the martensitic state. When the bolt is loosened to a certain amount of preload, a heater enveloping the ring is activated allowing an axial constrained recovery of the SMA and a control of the preload in the bolt. Several experiments are conducted to ascertain the effect of heating rate, cooling rate, relaxation of assembly, and initial preload, on the preload-temperature relationship. Experimental results indicate that the use of SMA rings is promising for retightening and controlling preload in bolted joint assemblies. Two analytical models are established; one is based on the Liang-Rogers model (Liang, C. and Rogers, C.A. 1990. “One-dimensional Thermo-mechanical Constitutive Relations for Shape Memory Materials,” Journal of Intelligent Materials Systems and Structures, 1:207-234) and the other draws on the analogy between the cyclic stress-strain curves.

Dynamics of structures with wideband autoparametric vibration absorbers: theory

This article analyses the dynamics of a resonantly excited single–degree–of–freedom linear system coupled to an array of nonlinear autoparametric vibration absorbers (pendulums). Each pendulum is also coupled to the neighbouring pendulums by linear elastic springs. The case of a 1:1:…:2 internal resonance between pendulums and the primary oscillator is studied for stationary (harmonic) and non–stationary (slow frequency sweep) excitations. The method of averaging is used to obtain amplitude equations that determine the first–order approximation to the nonlinear response of the system. The amplitude equations are analysed for their equilibrium as well as non–stationary solutions as a function of the parameters associated with the absorber pendulums. For stationary excitation, most steady–state solutions correspond to modes in which only one pendulum and the primary system execute coupled motions. Conditions for the existence of manifolds of equilibria are revealed when the averaged equations are expressed in modal coordinates. In the non–stationary case with linear frequency sweep through the primary resonance region, delays through pitchforks, smooth but rapid transitions through jumps, and transitions from one stable coupled–mode branch to another are studied using numerical simulations of the amplitude equations. The array of autoparametric pendulums is shown to effectively attenuate the large–amplitude resonant response of structures over a wide band of excitation frequencies.

Conductive electroactive polymers: intelligent materials systems, 2nd ed. [Book Review

Conductive electroactive polymers: intelligent materials systems, 2nd ed. [Book Review

Mechanical Behavior of Engineering Materials, Volume 2: Dynamic Loading and Intelligent Material Systems

11R11. Mechanical Behavior of Engineering Materials, Volume 2: Dynamic Loading and Intelligent Material Systems. - YM Haddad (Mech Eng, Univ of Ottawa, Canada). Kluwer Acad Publ, Dordrecht, Netherlands. 2000. 484 pp. ISBN 0-7923-6355-8. $225.00.Reviewed by YA Rossikhin (Dept of Theor Mech, Voronezh State Univ of Architec and Civil Eng, ul Kirova 3-75, Voronezh, 394018, Russia).The book under review is the second volume of the two-volume monograph Mechanical Behavior of Engineering Materials. This volume is devoted to the evaluation of the engineering materials properties under dynamic loading. However, due to the wide scope of topics covered and its popular presentation, this book is not a monograph, it can be classified as a tutorial on dynamic behavior of engineering materials. In each chapter, a review of well-known results in particular aspects of dynamic loading is given, which paves the way for a person inexperienced in the field for perceiving the current state of the art in the development of mechanics of materials. Having read this book, a reader will be ready to embark on in-depth study of the subject. The second volume begins with Chapter 9. The previous eight chapters, devoted to static and quasi-static loading of linear and nonlinear elastic, viscoelastic, and elastic-plastic continuum media, are contained in Volume 1 (an interested reader is referred to the review of Volume 1 by J-C Roegiers published in AMR, July 2002, p B61). Chapter 9 introduces the subject of the response of metallic materials to dynamic loading both under high and low rates. Behavior of the materials within the plastic range, with due account for plastic instability and localization effects, is reviewed in Chapter 10. Chapter 11 presents brief information concerning elastic bulk and plane wave propagation in unbounded and semi-infinite elastic media, as well as surface waves. It is worth noting that aspects of dynamic behavior of rods and plates are discussed rather weakly and superficially. Dynamic plastic behavior of engineering materials, as well as plastic shock wave propagation, are presented in Chapter 12. Linear viscoelastic properties of materials under dynamic loading are discussed in Chapter 13, and linear and nonlinear viscoelastic wave propagation is considered in Chapter 14. The dynamic behavior of fiber-reinforced composite materials is presented in Chapter 16. Chapter 17 gives an introduction into the concept of intelligence in engineering materials, as well as a review of different models, control algorithms, and analyses developed by various researchers. Pattern recognition and classification methodology for the characterization of material response states is discussed in the last chapter, 18. Each chapter ends with a list of main references, as well as the references for further reading, but this reviewer should note that only a few of them, excluding those of the author, were published during the last 10 years. Chapters 10, 11, 14, and 15 contain problems for student self-checking. Volume 2 concludes with a subject index and cumulative subject index. This reviewer can recommend Mechanical Behavior of Engineering Materials, Volume 2 only for undergraduate students of civil engineering and mechanical engineering departments as an introductory course in dynamic behavior of engineering materials.

Yoffe–type moving crack in a functionally graded piezoelectric material

In this paper, the problem of a functionally graded piezoelectric material (FGPM) with a constantvelocity Yoffetype moving crack is considered. The strip is assumed to be under an antiplane mechani...

KL-4 Active Composite Panels and Active Composite Struts as Building Blocks of Adaptive Structures

Active Composite Panels (ACPs) and Active Composite Struts (ACSs) are explained as basic building blocks of adaptive structures with precision positioning and vibration suppression capabilities. The use of these ACPs and ACSs in adaptive structures as building blocks with vibration suppression and precision positioning capabilities are explained. Many examples on the use of the ACP and ACS building blocks in intelligent material systems and structures are given in this paper.

Active material micro-actuator arrays fabricated with SU-8 resin

Active materials such as piezoelectric ceramics and shape memory metal alloys commonly actuate active control and intelligent material systems. Commercially available piezoelectric materials exhibit small actuation stroke and shape memory metal alloys have limited bandwidth. The proposed micro-actuator array design and fabrication process increases the actuation stroke of piezoceramic material by a factor of 1.5 for a 2 × 2 array; two active material segments connected in parallel and two in series, and doubles the response time of a 1 × 4 shape memory alloy driven array; four active materials segments connected in series. A high aspect ratio fabrication method incorporating SU-8 resin and conventional lithography is the process that forms the array linkages. The SU-8 resin array structures are 300 μm tall.

Vibration Suppression of Structures Using Passive Shape Memory Alloy Energy Dissipation Devices

The paper presents a preliminary study on feasibility using shape memory alloy (SMA) passive devices for vibration suppression of building structures. A one-story prototype-building model is used. The structure is subjected to a base excitation and is strengthened by SMA diagonal bracing wires. Constitutive behavior of SMA wires used in the study was experimentally characterized to properly model the SMA super- or pseudoelastic material properties and results were compared with the numerical simulation based on theoretical SMA constitutive models by Lexcellent and Bourbon ((1996). Thermodynamical model of cyclic behavior of Ti-Ni and Cu-Zn-Al shape memory alloys under isothermal undulated tensile tests. Mechanics of Materials, 24: 59-73) and Brinson ((1993). One-dimensional constitutive behavior of shape memory alloys: Thermomechanical derivation with non-constant material functions and redefined martensite internal variable. Journal of Intelligent Material Systems and Structures, 4: 229). The Single-degree-of-freedom structural system was also experimentally calibrated to determine the structural parameters. Both the experimentally calibrated structural model and SMA constitutive model were then employed in numerical simulation to predict dynamic response of the building structure with SMA bracing wires subjected to a base input and results showed a good agreement with experimental data. The results were also compared with both cases of conventional steel bracing wires and no bracing at all. The results showed that SMA passive devices maybe effectively used to suppress vibration by introducing additional stiffness to shift the system natural frequency away from the resonance and/or providing additional energy dissipation by its superelastic hysteresis. The SMA damping is adaptive and is especially attractive for the case when the loading is random in nature. When an unexpected excitation causes excessive vibration, more energy will be dissipated through larger SMA superelastic hysteretic loops and therefore, the vibration will eventually be mitigated. Numerical simulation also showed that the SMA device dissipated more energy than the viscous damping in the case studied.

Intelligent material and fluid systems

This article presents a review of recent-important developments in the field of intelligent material and fluid systems. Intelligent material and fluid systems, sometimes referred to as smart materials and fluids, can adjust their behavior to changes of external or internal parameters analogously to biological systems. In these systems, sensors, actuators and controllers are seamlessly integrated with structural materials at the macroscopic or mesoscopic level. In general, sensors and actuators are made of functional materials and fluids such as piezoelectric materials, magnetostrictive materials, shape memory alloys, polymer hydrogels, electro- and magneto-rheological fluids and so on. This article is specifically focused on the design of intelligent material and fluid systems used to control the deformation, vibration and fracture of composite materials and structures.

Energy dissipation through joints: theory and experiments

A new qualitative non-destructive evaluation (NDE) technique based on a modification of the high-frequency impedance measured with an integrated piezoceramic (PZT) actuator–sensor has been successfully demonstrated at the Center for Intelligent Material Systems and Structures. An important characteristic of this NDE technique is the localization of the PZT’s sensing area due to energy dissipation. For a better understanding of this phenomena, this paper will present an analytical method to determine the energy dissipated through joints at high frequency and its relation to the localized actuation-sensing region. The structure used for this analysis consists of two beams connected with a bolted joint and each having free boundary conditions. Due to the high-frequency range employed, theoretical assessments are made using a wave propagation approach. For the same reason, the Timoshenko beam theory is used to model the structure. Using the equations of motion, the dynamic stiffness matrix is assembled in the frequency domain. Then, the energy dissipated in the joint is modeled linearly using mass-spring-dash pot systems and nonlinearly with the application of nonconservative friction clearance systems. This work is the first effort in the high-frequency modeling of structural joints: other work was only concerned with the modeling of the few first modes of vibration. Case studies and experimental verification will then follow.

Random vibration studies of an SDOF system with shape memory restoring force

Intelligent and adaptive material systems and structures have become very important in engineering applications. The basic characteristic of these systems is the ability to adapt to the environmental conditions. A new class of materials with promising applications in structural and mechanical systems is shape memory alloy (SMA). The mechanical behavior of shape memory alloys in particular shows a strong dependence on temperature. This property provides opportunities for the utilization of SMAs in actuators or energy dissipation devices. However, the behavior of systems containing shape memory components under random excitation has not yet been addressed in the literature. Such a study is important to verify the feasibility of using SMAs in structural systems. In this work a nondeterministic study of the dynamic behavior of a single-degree-of-freedom (SDOF) mechanical system, having a Nitinol spring as a restoring force element is presented. The SMA spring is characterized using a one-dimensional phenomenological constitutive model based on the classical Devonshire theory. Response statistics for zero mean random vibration of the SDOF under a wide range of temperature is obtained. Furthermore, nonzero mean analysis of these systems is carried out.

Intelligent Material Systems Using Epoxy Particles to Repair Microcracks and Delamination Damage in GFRP

The objective of this study is to propose an intelligent material system that can perform a self-repairing operation against initial damage that might occur in GFRP laminates. Specifically, we highlight the development of a novel actuator to be used in such self-repairing operations. There has been much research on sensor systems to detect damage and some actuators to control the shape of the structure or to control the vibration. However, no literature can be found on the actuator aiming at the self-repair of damage. For this purpose, a small grain particle-type adhesive is embedded in a glass/epoxy composite (GFRP) laminate. The diameter of the particle is approximately 50 gim. Hence, in the developed intelligent material system, coldsetting epoxy resin is used as the matrix, uni-directionally arranged glass fiber is used as the reinforcement, and a thermosetting epoxy particle is used as a repairing actuator. The volume fraction of the particles in the matrix was approximately 40%. The embedded particles can repair the damage, when melted by heat. Basic characteristics of the particles were investigated first, and we confirmed that the embedded particles in the matrix can melt by heat and flow to repair the crack. We also confirmed that the embedded particles do not deteriorate the stiffness of the GFRP laminate. Then we investigated the efficiency of the repairing operation against initial damage such as microscopic matrix cracks and delamination, by conducting two typical tests, i.e., static three-point bending of [0/90] laminate and tensile fatigue of [O/90], laminate. Damage was observed by CCD camera. As a result, the decrease in the stiffness due to initial damage has been recovered and consequently increased the residual fatigue life.