Showing papers on "Smart material published in 2007"

Magnetic Field-Responsive Smart Polymer Composites

Abstract: The combination of polymers with nano- or microsized solid materials displays novel and often enhancedproperties compared to the traditional materials. They can open up possibilities for new technologicalapplications. Materials whose physical properties can be varied by application of magnetic fields belongto a specific class of smart materials. The broad family of magnetic field-controllable soft materialsincludes ferrofluids, magneto-rheological fluids, magnetic gels, and magnetic elastomers. The magneticgels and elastomers (magnetoelasts) represent a new type of composite and consist of small magneticparticles, usually in the nanometer to micron range, dispersed in a highly elastic polymeric matrix.The magnetic particles can be incorporated into the elastic body either randomly or in ordered structure.If a uniform magnetic field is applied to the reactive mixture during the cross-linking process, particlechains form and become locked into the elastomer. The resulting composites exhibit anisotropic properties.

Playing with carbon and silicon at the nanoscale.

Abstract: Because of its superior properties silicon carbide is one of the most promising materials for power electronics, hard- and biomaterials. In the solid phase, the electronic and optical properties are controlled by the stacking of double layers of Si and C atoms. In thin films, a change in the stacking order often requires stress, which can be achieved naturally in systems with nanometre length scale. For this reason, nanotubes, nanowires and clusters can be used as building blocks for the synthesis of novel materials. Furthermore, playing at the nanometre length scale enables the nature of the SiC bonding to be modified, which is of prime importance for atomic engineering of nanostructures. In this review, emphasis is placed on the theoretical principles associated with SiC cage-like clusters and experimental work resulting from them.

Engineering Analysis of Smart Material Systems

Abstract: Preface. 1. Introduction to Smart Material Systems. 2. Modeling Mechanical and Electrical Systems. 3. Mathematical Representations of Smart Material Systems. 4. Piezoelectric Materials. 5. Piezoelectric Material Systems. 6. Shape Memory Alloys. 7. Electroactive Polymer Materials. 8. Motion Control Applications. 9. Passive and Semiactive Damping. 10. Active Vibration Control. 11. Power Analysis for Smart Material Systems. References. Index.

Intelligent control of surface hydrophobicity.

Abstract: Switchable surfaces are highly useful materials with surface properties that change in response to external stimuli. These surfaces can be employed in both research and industrial applications, where the ability to actively control surface properties can be used to develop smart materials and intelligent surfaces. Herein, we review a range of surfaces in which hydrophobicity can be controlled. We present the principal ideas of surface switching, discuss recent developments, explore experimental issues and examine factors that influence surface switching, including the nature of the stimuli, the underlying material, the morphology of the surface and the surrounding environment. We have categorised switchable surfaces according to the stimuli that trigger changes in surface hydrophobicity. These are electrically, electrochemically, thermally, mechanically, photo- and environmentally inducible surfaces. In addition, we review the use of chemical reactions to modify the properties of switchable surfaces and produce changes in the molecular structure and nanoscale features of the surface.

Viscoelastic properties of silicone-based magnetorheological elastomers

Abstract: Magnetorheological (MR) elastomers are composite materials consisting of magnetic particles in elastomer matrices, whose mechanical properties can be influenced by applying a magnetic field. Main parameters which determine the behavior of these smart materials are the concentration of the magnetic particles and the mechanical stiffness of the elastomer matrix. The viscoelastic properties of silicone-based MR elastomers are outlined in terms of their storage and loss moduli. The mechanical behavior of the material is also influenced by a magnetic field during the curing of the elastomer matrix, which leads to materials with anisotropic microstructures. The storage modulus of soft elastomer matrix composites can be increased in the presence of a magnetic field by significantly more than one order of magnitude or several hundreds of kPa. The relative increase exceeds that of all previously reported data. A shape memory effect, i. e. the deformation of an MR elastomer in a magnetic field and its return to original shape on cessasion of the magnetic field, is described.

Variable-focus liquid microlenses and microlens arrays actuated by thermoresponsive hydrogels

Abstract: Traditional optical systems utilize mechanical parts (e.g., gears, motors, and drivers) to allow adjustable focusing and magnification. Emerging variable-focus microlenses have exhibited the potential to miniaturize and advance optical systems without the need for mechanical parts, impacting significantly on a multitude of fields, such as cameras, biomedical instruments, and lab-on-a-chip systems. A variety of variable-focus liquid microlenses have been demonstrated based on different mechanisms, including reorientation of liquid crystals, electrowetting of a liquid droplet, and mechanical actuation of polymeric materials. These microlens technologies rely on external controls and power supplies; for example, additional electric fields are necessary to drive both electrowetting liquid microlenses and liquid-crystal microlenses, and external actuation devices are required to control the pressure in flexible polymer microlenses. The requirement for additional discrete components increases the complexity and makes integration, especially in lab-on-a-chip applications, challenging. We are interested in taking advantage of smart materials to realize variable-focus liquid microlenses without requiring external controls and power supplies. Responsive hydrogels are smart materials that undergo significant and reversible volume change in response to environmental stimuli by absorbing and releasing water through the network interstitials of the hydrogels. The ability to convert chemical energy directly into mechanical work means that the hydrogels can function as sensors, actuators, and power sources in specific conditions (e.g., the human body) where most external controls and power supplies are limited or difficult to obtain. By taking advantage of responsive hydrogels, we previously reported an innovative approach for realizing smart-liquid microlenses responsive to environmental changes. The liquid microlens extends the concept of pinned liquid/liquid interfaces to apertures to form a liquid microlens. A hydrogel ring located within a microfluidic channel responds to an environmental change by expanding and contracting, which regulates the shape of a water/oil interface (i.e., a liquid microlens), thus, tuning the focal length of the microlens. In this paper, we demonstrate thermoresponsive variable-focus cylindrical microlenses and spherical microlens arrays formed using liquid/liquid interfaces. Thermoresponsive reversible N-isopropylacrylamide (NIPAAm) hydrogels were employed; unconstrained NIPAAm hydrogels swell by as much as a factor of ten when the temperature decreases from above to below the hydrogel’s lower critical solution temperature (LCST). First, arbitrary shapes of microlenses (e.g., cylindrical and spherical) can be realized by patterning apertures that have corresponding shapes (e.g., rectangular and circular, respectively). This benefits the implementation of various microlenses with different shapes, among which variable-focus cylindrical lenses are of strong interest for a multitude of optical applications such as stretching an image, focusing light into a slit, and correcting low-order aberration. Second, we extended single variable-focus spherical microlenses to microlens arrays, allowing the devices not only to have wide-angle observation and parallel optical signal acquisition, but also to implement combinatorial interrogation of complicated environments in microfluidics by individually regulating the focal lengths of the microlens elements. In a typical variable-focus cylindrical microlens (Fig. 1a), a rectangular window was photopatterned in a 250 lm thick polymer slip to form an aperture. The sidewall of the aperture was treated to be hydrophilic (water contact angle of 29°) through an oxygen plasma treatment; the top-side surface of the aperture was rendered hydrophobic (water contact angle of 118°) by coating it with an octadecyltrichlorosilane solution. Thus, a hydrophobic/hydrophilic contact line coincided at the boundary between the sidewall and top-side surface of the aperture. A thermoresponsive NIPAAm hydrogel (LCST = 32 °C) ring was photopatterned in a 750 lm deep microfluidic channel. When the hydrogel ring was filled with deionized water through the aperture, a water meniscus emerged from the rectangular aperture, and the peripheral boundary of the meniscus was pinned stably at the hydrophobic/hydrophilic contact line. Mineral oil was stored within a C O M M U N IC A IO N

Smart polymeric coatings—recent advances

Abstract: There is an ever-growing number of developments that aim to bring novel functionalities to polymer-coating systems with nanotechnology being one of them. This article will cover recent advances in the field of smart polymeric structures that are used in protective coatings in terms of stimulus and response, sensing mechanisms, and current or potential applications. Such structures are commonly based on polymers modified through organic or inorganic additives. Emphasis is placed on smart sensors used for detecting the onset of corrosion on polymer coated ferrous and nonferrous substrates. Examples of self-healing and repair through the action of microcapsules are also presented. © 2007 Wiley Periodicals, Inc. Adv Polym Techn 26:1–13, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20083

From Molecular Machines to Microscale Motility of Objects: Application as “Smart Materials”, Sensors, and Nanodevices

Abstract: Machinelike operations are common functions in biological systems, and substantial recent research efforts are directed to mimic such processes at the molecular or nanoscale dimensions. The present Feature Article presents three complementary approachscate the present es to design machinelike operations: by the signal-triggered mechanical shuttling of molecular components; by the signal-triggering of chemical processes on surfaces, resulting in mechanical motion of micro/nanoscale objects; and by the fuel-triggered motility of biomolecule-metal nanowire hybrid systems. The shuttling of molecular components on molecular wires assembled on surfaces in semirotaxane configurations using electrical or optical triggering signals is described. The control of the hydrophilic/hydrophobic surface properties through molecular shuttling or by molecular bending/stretching processes is presented. Stress generated on microelements, such as cantilevers, results in the mechanical deflection of the cantilever. The deposition of a redox-active polyaniline film on a cantilever allows the reversible electrochemically induced deflection and retraction of the cantilever by the electrochemical oxidation or reduction of the polymer film, respectively. A micro-robot consisting of the polypyrrole (PPy) polymer deposited on a multi-addressable configuration of electrodes is described. Au magnetic core/shell nanoparticles are incorporated into a polyaniline film, and the conductivity of the composite polymer is controlled by an external magnet. Finally, the synthesis of a hybrid nanostructure consisting of two actin filaments tethered to the two ends of a Au nanowire is described. The adenosine triphosphate (ATP)-fueled motility of the hybrid nanostructure on a myosin monolayer associated with a solid support is demonstrated.

Model-Based Robust Control Design for Magnetostrictive Transducers Operating in Hysteretic and Nonlinear Regimes

Abstract: This paper addresses the development of robust control designs for high-performance smart material transducers operating in nonlinear and hysteretic regimes. While developed in the context of a magnetostrictive transducer used for high-speed, high-accuracy milling, the resulting model-based control techniques can be directly extended to systems utilizing piezoceramic or shape memory alloy compounds due to the unified nature of models used to quantify hysteresis and nonlinearities inherent to all of these materials. When developing models and corresponding inverse filters or compensators, significant emphasis is placed on the utilization of the material's physics to provide the accuracy and efficiency required for real-time implementation of resulting model-based control designs. In the material models, this is achieved by combining energy analysis with stochastic homogenization techniques, whereas the efficiency of forward algorithms is combined with monotonicity properties of the material behavior to provide highly efficient inverse algorithms. These inverse filters are then incorporated in H2 and Hinfin theory to provide robust control algorithms capable of providing high-accuracy tracking even though the actuators are operating in nonlinear and hysteretic regimes. Through numerical examples, it is illustrated that the robust designs incorporating inverse compensators can achieve the required tracking tolerance of 1-2 mum for the motivating milling application, whereas robust designs which treat the uncompensated hysteresis and nonlinearities as unmodeled disturbances cannot achieve design specifications

Vibration suppression of laminated composite beams using actuators of giant magnetostrictive materials

Abstract: This paper presents a simulation of vibration suppression of a laminated composite beam embedded with actuators of a giant magnetostrictive material subjected to control magnetic fields. It has been found that the strains generated in the material are not only significantly larger than ones created by many other smart materials but also exhibit some inherent nonlinearities. To utilize the full potential of these materials in active vibration control, these nonlinearities should be characterized in the control system as accurately as possible. In this simulation of nonlinear dynamic controls, the control law with negative velocity feedback and the analytical nonlinear constitutive model of the magnetostrictive layer are employed. The numerical results show that this proposed approach is efficient not only in a linear zone but also in nonlinear zones (dead zone and saturation zone) of magnetostrictive curves in vibration suppression. Compared with those from the control system based on the linear constitutive relations of the material, it is found that the simulation results based on the linear model are efficient only when the magnetostrictive relations are located in the linear zone. Once the system has some departure from the linear zone, however, the results from the linear model become unacceptable. Finally, the effect of material properties, lamination schemes and location of the magnetostrictive layers on vibration suppression of the practical system is evaluated.

Smart Composite Sandwich Structures for Future Aerospace Application -Damage Detection and Suppression-: a Review

Abstract: Sandwich structures with advanced composite facesheets are attracting much attention as a solution to maximize the potential of composite materials. However, the composite sandwich structures are prone to damage, such as impact damage and debonding. Although these damages are difficult to detect using conventional nondestructive inspection method, they cause significant reduction in the mechanical properties. Hence, several researchers have attempted to detect and suppress the damages using smart sensors and actuators. In this paper recent developments on smart technologies to improve reliability of the composite sandwich structures are reviewed. First, the state-of-the-art sandwich technology in aerospace application is presented. Next, typical damages in composite sandwich structures are described, which is essential to effectively apply the smart technologies to sandwich structures. Then, smart technologies which have been applied to sandwich structures are briefly shown with focusing specific properties of sandwich structures. It includes damage detection using dynamic response, wave propagation and optical fiber sensors. Finally, a smart honeycomb sandwich concept is also presented.

Modeling and simulation of chemo-electro-mechanical behavior of pH-electric-sensitive hydrogel

Abstract: A chemo-electro-mechanical multi-field model, termed the multi-effect-coupling pH-electric-stimuli (MECpHe) model, has been developed to simulate the response behavior of smart hydrogels subject to pH and electric voltage coupled stimuli when the hydrogels are immersed in a pH buffer solution subject to an externally applied electric field. The MECpHe model developed considers multiphysics effects and formulates the fixed charge density with the coupled buffer solution pH and electric voltage effects, expressed by a set of nonlinear partial differential governing equations. The model can be used to predict the hydrogel displacement and the distributive profiles of the concentrations of diffusive ionic species and the electric potential and the fixed charge density in both the hydrogels and surrounding solution. After validation of the model by comparison of current numerical results with experiment data extracted from the literature, one-dimensional steady-state simulations were carried out for equilibrium of the smart hydrogels subject to pH and electric coupled stimuli. The effects of several important physical conditions, including the externally applied electric voltage, on the distributions of the concentrations of diffusive ionic species, the electric potential, the fixed charge density, and the displacement of the hydrogel strip were studied in detail. The effects of the ionic strength on the bending deformation of the hydrogels under the solution pH and electric voltage coupled stimuli are also discussed.

A deformation sensitive pad-structure embedded with hetero-core optic fiber sensors

Abstract: A new approach has been described to discuss how smart materials could be devised using the novel hetero-core sensors intended for monitoring large deformation in terms both of the curvature and the direction of bending in the form of pad-structures made of rubber. The result showed that the proposed pad-structures were sufficiently sensitive to the given curvature and directions for deformation with a sufficient linearity of sensor characteristics. The hetero-core embedded pad sensors were successfully perceptive for the first time with typical sensitivities of 0.066 and 0.153 dB/mm as a smart material to know not only the deformation direction but also the degree and convex/concave direction of curvatures.

Vertically Reinforced 1-3 Piezoelectric Composites for Active Damping of Functionally Graded Plates

Abstract: ONOLITHIC piezoelectric materials (PZTs) have beenwidely used as distributed sensors and actuators fordeveloping smart structures with self-monitoring and self-controlling capabilities [1–10]. However, their major drawback islow control authority as the magnitude of their electromechanicalcoefficientsisverysmall.Thesituationcanbeimprovedbyusinganactive constrained layer damping (ACLD) treatment [11,12] whichconsists of a layer of a viscoelastic material constrained between ahost structure and an active constraining PZT layer. When theconstraining layer is activated with a voltage applied to the PZTlayer, the shearing deformations of the viscoelastic layer areenhanced to improve the damping characteristics of the overallstructures. Since its inception, the ACLD treatment has beenextensively used for efficient and reliable control of flexiblestructures [13–17].Piezoelectric composites, also called piezocomposites, haveemerged as a new class of smart materials and have found wideapplicationsasdistributedactuatorsandsensors.Apiezocomposite,composedofPZTreinforcementsembeddedinaconventionalepoxymatrix, provides a wide range of effective material properties notofferedbyexistingPZTs,isanisotropic,andhasgoodconformabilityand strength. We note that laminae of vertically reinforced 1-3piezocomposites are commercially available [18] and are beingeffectively used as underwater high-frequency transducers and inmedicalimagingapplications[19,20].A1-3piezocompositelaminahas PZT fibers vertically reinforced in the epoxy matrix across thethicknessofthelamina,thefibersarepoledalongtheirlength,andthetop and the bottom surfaces of the lamina are electroded. Theeffective PZT coefficient (e

Characterization and Variational Modeling of Ionic Polymer Transducers

Abstract: Ionomeric polymers are a promising class of intelligent material which exhibit electromechanical coupling similar to that of piezoelectric bimorphs. ionomeric polymers are much more compliant than piezoelectric ceramics or polymers and have been shown to produce actuation strain on the order of 2% at operating voltages between 1 V and 3 V (Akle et al., 2004, Proceedings IMECE). Their high compliance is advantageous in low force sensing configurations because ionic polymers have a very little impact on the dynamics of the measured system. Here we present a variational approach to the dynamic modeling of structures which incorporate ionic polymer materials. To demonstrate the method a cantilever beam model is developed using this variational approach. The modeling approach requires a priori knowledge of three empirically determined material properties: elastic modulus, dielectric permittivity, and effective strain coefficient. Previous work by Newbury and Leo has demonstrated that these three parameters are strongly frequency dependent in the range between less than 1 Hz to frequencies greater than 1 kHz. Combining the frequency-dependent material parameters with the variational method produces a second-order matrix representation of the structure. The frequency dependence of the material parameters is incorporated using a complex-property approach similar to the techniques for modeling viscoelastic materials. A transducer is manufactured and the method of material characterization is applied to determine the mtaerial properties. Additional experiments are performed on this transducer and both the material and structural model are validated. Finally, the model is shown to predict sensing response very well in comparison to experimental results, which supports the use of an energy-based variational approach for modeling ionomeric polymer transducers.

Magnetorheological Valve for Hybrid Electrohydrostatic Actuation

Abstract: There is an increasing demand for compact actuators capable of producing large deflections, large forces, and broad frequency bandwidths. Due to their solid state nature, smart materials can enable novel actuator solutions that compete favorably with established technologies based on electric, hydraulic, or pneumatic motors. However, in all existing active materials, large force and broadband responses are obtained at small displacements and methods for transmitting very short transducer element motion to large deformations need to be developed. We present a new hybrid actuator which operates on the principle of rectification of magnetostrictive vibrations by means of magnetorheological (MR) flow control. Experiments and theoretical calculations are aimed at substantiating the feasibility of the hybrid actuator and establishing design criteria for the development of an effective MR valve. The experiments presented here demonstrate the ability of the valve to completely block the flow due to the combined action of a pressure differential and MR fluid activation. For characterization purposes, two variations of the main valve concept are considered, one with moving coils and the other with fixed coils. Actuation measurements conducted on the complete actuator show deflections of 6.5 in. in response to fluid inputs produced with a hydraulic piston in combination with an applied quasistatic voltage of amplitude 5 V. A system-level model is presented which is developed by treating the system as an RLC equivalent electrical circuit with operation across electrical, mechanical, and fluid domains. Attributes and shortcomings of the model are discussed through comparison of model results with experimental data.

Inelastic properties of magnetorheological composites: I. Fabrication, experimental tests, cyclic shear properties

Abstract: In this two-part research project the inelastic properties of a selected group of magnetorheological composites under cyclic shear have been identified. Composites whose matrices were elastic porous structures with pores filled with a magnetorheological fluid were investigated. The composite materials' functional properties are similar to those of magnetorheological fluids. But, as opposed to the fluid alone, the composite's geometry and dimensions can be freely shaped. Owing to this, the costs can be reduced and the applicability can be extended. In the literature on the subject such composites are also referred to as magnetorheological fluid impregnated solids. In the first part of this work an overview of smart magnetic materials is presented. Then the originally fabricated composite, consisting of a matrix and a filling fluid, is described. The test stand, including a system of control, acquisition and processing of measuring (mechanical and magnetic) signals, is presented. The experimentally determined hysteresis loops for cyclic shear are used in the second part of this research project to identify constitutive models.

A Study on the Thermomechanical Properties of Shape Memory Alloys-based Actuators used in Artificial Muscles

Abstract: Shape memory alloys (SMAs) are a class of smart material having the unique ability to return to a predefined shape when heated. These materials are employed in a variety of emerging applications, and may potentially be used to avoid traditionally voluminous and heavy prosthetic actuators. The primary focus of this article is to convey the design and evaluation of a compact, lightweight, and high-strain SMA ribbon-based artificial muscle for use in such biomimetic applications. A key factor in the design of such an actuator is a thorough understanding of the thermomechanical response of the shape memory material. As such, a review of the relevant constitutive models is included. A selected hysteresis model is evaluated for potential application to ribbon type elements. The proposed actuator achieves strains of 31.6%; a marked improvement over previously documented SMA-based actuators.

Micromechanical analysis of effective piezoelastic properties of smart composite sandwich shells made of generally orthotropic materials

Abstract: A micromechanical model for smart composite shells with periodically arranged embedded piezoelectric actuators and rapidly varying thickness is developed. The pertinent mathematical framework is that of asymptotic homogenization. The model enables the determination of both local fields and effective elastic and actuation coefficients of smart composite sandwich shells made of generally orthotropic materials. Orthotropy of the constituent materials leads to a significantly more complex set of local problems and is considered in the present paper for the first time. The effective coefficients are determined by means of a set of four simpler problems called 'unit-cell' problems. The actuation coefficients, for example piezoelectric or magnetostrictive, characterize the intrinsic transducer nature of active smart materials that can be used to induce strains and stresses in a co-ordinated fashion. The theory is illustrated by means of examples pertaining to hexagonal honeycomb cored and hexagonal–triangular mixed cored smart sandwich shells made of orthotropic materials. The effective elastic and piezoelectric coefficients for these structures are calculated and analyzed. It is shown that the model can be used to tailor the effective properties of any smart shell to meet the requirements of a particular application by changing some geometric or material parameters.

Application of smart materials in vibration control systems

Abstract: Purpose: The goal of this paper is to present application and method of numerical modelling smart materials in vibration control systems. Two methods of vibration control was presented in this work. First one is based on shape memory alloy absorber. Second method use magnetorheological bearing which was placed in revolute join of manipulator mechanism. Design/methodology/approach: The numerical models of presented mechanical systems were created in APDL language, which is internal ANSYS language. Dynamic characteristics of shape memory alloy absorber were determined by using algorithm which automatically changes absorber’s length. The manipulator mechanism with magnetorheological bearing was modelled by using multibody dynamics method connected with finite element method in ANSYS environment. Findings: Through this study it was determined shape memory alloy absorber’s length which eliminated specified resonance due to natural frequencies of mechanical system. The dynamic characteristics of mechanical system with magnetorheological bearing were also obtained. Research limitations/implications: The main disadvantage of presented methods is the necessity to calculate parameters for each iteration step. In the case of shape memory alloy absorber this process significantly extends the calculation time. Practical implications: Presented methods allowed to determine dynamic characteristics of vibration control systems using smart materials and enabled implementation of the method to commercial finite element method environment. Originality/value: This work contains new aspects, which are: determination of shape memory alloy absorber’s length, practical implementation of magnetorheological fluids in vibration control systems.

Dynamic response analysis and vibration control of a cantilever beam with a squeeze-mode electrorheological damper

Abstract: Electrorheological (ER) fluids are a class of smart materials in which their rheological properties can be changed reversibly under the influence of an applied electric field. In recent years, many industrial applications of these smart fluids have been introduced by researchers, especially in the damping control of systems. In the present work, the applicability of squeeze-mode ER dampers in suppressing the vibration of a cantilever beam is investigated. The dynamic response of the beam for an impulse exciting force is obtained using a direct integration method based on a finite-element model for the structure. The nonlinear displacement and velocity-dependent characteristics of the squeeze-mode ER damper are considered in each of the iterations. Although the proposed ER damper has been found to have a significant influence on the dynamic response of the structure, adding a closed-loop control system could improve the damping behavior of the structure considerably. While the strength of the electric field depends on the gap between the electrodes, the control system uses displacement feedback for producing a controlling voltage to prevent the electric field exceeding its allowable bounds.