Showing papers on "Smart material published in 2009"

Shape-Memory Polymers—A Class of Novel Smart Materials

Abstract: Shape-memory polymers (SMPs) offer a number of potential technical advantages that surpass other shape-memory materials such as shape-memory metallic alloys and shape-memory ceramics. The advantages include high recoverable strain (up to 400%), low density, ease of processing and the ability to tailor the recovery temperature, programmable and controllable recovery behavior, and more importantly, low cost. This article presents the state-of-the-art regarding SMPs. First, the architecture, type, and main properties of the traditional and recently developed SMPs are introduced. Second, structural and multifunctional SMP composites are summarized and discussed. These composites greatly enhance the performance of the SMPs and widen their potential applications. Finally, current applications of SMP materials in aerospace engineering, textiles, automobiles, and medicine are presented.

Electrostatic spin crossover effect in polar magnetic molecules

Abstract: The magnetic configuration of a nanostructure can be altered by an external magnetic field, by spin-transfer torque or by its magnetoelastic response. Here, we explore an alternative route, namely the possibility of switching the sign of the exchange coupling between two magnetic centres by means of an electric potential. This general effect, which we name electrostatic spin crossover, occurs in insulating molecules with super-exchange magnetic interaction and inversion symmetry breaking. As an example we present the case of a family of di-cobaltocene-based molecules. The critical fields for switching, calculated from first principles, are of the order of 1 V nm−1 and can be achieved in two-terminal devices. More crucially, such critical fields can be engineered with an appropriate choice of substituents to add to the basic di-cobaltocene unit. This suggests that an easy chemical strategy for achieving the synthesis of suitable molecules is possible. Controlling the magnetic properties by using an electric field is a promising route towards spintronics or magnetic data storage applications. Using dicobaltocene as a test case, it is now demonstrated theoretically that an electrostatic potential can be used to control the spin states in molecules.

Progress in the Development of Adaptive Nitride-Based Coatings for High Temperature Tribological Applications

Abstract: Adaptive tribological coatings were recently developed as a new class of smart materials that were designed to adjust their surface chemical composition and structure as a function of changes in the working environment to minimize friction coefficient and wear between contact surfaces. This paper provides an overview of the current research developments in this field, including: (1) Chameleon nanocomposite coatings which are produced by depositing a multi-phase structure whereby some of the phases provide mechanical strength and others are lubricious; (2) Micro- and nano-textured coatings which consist of hard nitride films with highly ordered micropores and nanopores that are subsequently filled with solid lubricants using various techniques such as lithography, reactive ion etching, laser texturing, pulsed air arc treatment, and ceramic beads as placeholders for sputter deposition; and, (3) Carbon and nitride nanotubes that are filled electrochemically with solid lubricants. The frictional and wear properties of the above three classes of newly developed adaptive structures, tested in various controlled environmental conditions (temperature, humidity), will be discussed in detail.

Magnetic nano- and microparticles in biotechnology

Abstract: Both synthetic and biologically produced magnetic nano- and microparticles exhibit several types of responses to external magnetic field which have been already employed in various areas of biosciences, biotechnology, medicine, environmental technology, etc. This short review shows selected important biotechnological applications of magnetic particles, and the biological processes leading to biogenic magnetic particles formation.

Adaptive neuro-fuzzy inference system-based controllers for smart material actuator modelling:

Abstract: An intelligent approach for smart material actuator modelling of the actuation lines in a morphing wing system is presented, based on adaptive neuro-fuzzy inference systems. Four independent neuro-fuzzy controllers are created from the experimental data using a hybrid method — a combination of back propagation and least-mean-square methods — to train the fuzzy inference systems. The controllers' objective is to correlate each set of forces and electrical currents applied on the smart material actuator to the actuator's elongation. The actuator experi-mental testing is performed for five force cases, using a variable electrical current. An integrated controller is created from four neuro-fuzzy controllers, developed with Matlab/Simulink software for electrical current increases, constant electrical current, electrical current decreases, and for null electrical current in the cooling phase of the actuator, and is then validated by comparison with the experimentally obtained data.

Thermodynamical Modeling of the Electromechanical Behavior of Ionic Polymer Metal Composites

Abstract: Ionomeric polymer transducers are a class of smart materials which exhibit electromechanical coupling when subjected to low voltage ( 5%) but correspondingly low force output. The mechanisms producing electromechanical coupling have so far not been completely understood. It is clear from experimental and theoretical investigations that diffusion and migration of ionic species within the polymer are the main cause for electromechanical coupling. For this reason we have developed a thermodynamically based mechanical model — using chemo-electrical inputs — which is able to predict the mechanical output i.e., deformation, bending, etc. for a given applied voltage to the IPMC strip. The chemo-electrical transport model is capable of computing the charge density profile in space and time as well as the current flux for applied electric fields. Based upon thermodynamic laws, the mechanical model has been developed to...

Transversely isotropic non-linear electro-active elastomers

Abstract: Electro-active or electro-sensitive elastomers are ‘smart materials’, which are composed of a rubber-like basis material filled with electro-active particles, and as a result, their properties are able to change significantly by the application of electric fields. In this paper, we provide the theoretical basis of the non-linear properties for a special class of these materials, namely, the transversely isotropic electro-active elastomers, whose characteristic is that during the curing process, due to the presence of an external applied field, the electro-active particles are aligned in a preferred direction. The theory is applied to some boundary value problems. As well as this, a linear approximation is obtained from the general non-linear formulation, which is compared with the results of the classical theory for piezoelectric materials.

Wing Shape Control through an SMA-Based Device:

Abstract: Based on numerical and experimental analyses, this article proposes an application of the smart structure concept aimed at realizing a bump on an airfoil profile, finalized to reduce transonic drag, through the use of shape memory alloys (SMAs) The ability of morphing the wing profile is functional to maximize the aerodynamic efficiency in different mission conditions The use of the so-called smart materials allows a favorable actuation performance per weight ratio, also leading to simple and integrated devices Currently, to model their mechanical behavior is still an open issue and this work presents some original ideas about this Numerical results and experimental tests herein presented, demonstrate the efficacy of the developed concept device, calling for further studies on real structures; their correlation also validate the implemented simulation procedure

Micromechanical modeling of the multiphysical behavior of smart materials using the variational asymptotic method

Abstract: A multiphysics micromechanics model is developed to predict the effective properties as well as the local fields of periodic smart materials responsive to fully coupled electric, magnetic, thermal and mechanical fields. This work is based on the framework of the variational asymptotic method for unit cell homogenization (VAMUCH), a recently developed micromechanics modeling scheme. To treat the general microstructure of smart materials, we implemented this model using the finite element technique. Several examples of smart materials are used to demonstrate the application of the proposed model for prediction of multiphysical behavior.

Periodic rotation of magnetization in a non-centrosymmetric soft magnet induced by an electric field

Abstract: The electric control of magnetism in magnetic devices has remained problematic, particularly as energy losses due to current flow can be large. The demonstration of electric control of magnetization in a non-centrosymmetric insulating magnetic material therefore represents a new strategy for future applications.

A glass transition model for shape memory polymer and its composite

Abstract: As novel smart materials, shape memory polymer (SMP) and its composite (SMPC) have the ability to regain its original shape after undergoing significant deformation upon heating or other external stimuli such as light, chemic condition and so on. Their special behaviors much depends on the glass transitions due to the increasing of material temperature. Dynamic Mechanical Analysis (DMA) tests are performed on the styrene-based SMP and its carbon fiber fabric reinforced SMPC to investigate their glass transition behaviors. Three glass transition critical temperatures of SMP or SMPC are defined and a method to determine their values from DMA tests is supposed. A glass transition model is developed to describe the glass transition behaviors of SMP or SMPC based on the results of DMA tests. Numerical calculations illustrate the method determining the glass transition critical temperature is reasonable and the model can well predict the glass transition behaviors of SMP or SMPC.

Embedding of Superelastic SMA Wires into Composite Structures: Evaluation of Impact Properties

Abstract: Shape memory alloy (SMA) represents the most versatile way to realize smart materials with sensing, controlling, and actuating functions. Due to their unique mechanical and thermodynamic properties and to the possibility to obtain SMA wires with very small diameters, they are used as smart components embedded into the conventional resins or composites, obtaining active abilities, tunable properties, self-healing properties, and damping capacity. Moreover, superelastic SMAs are used to increase the impact resistance properties of composite materials. In this study, the influence of the integration of thin superelastic wires to suppress propagating damage of composite structures has been investigated. Superelastic SMAs have very high strain to failure and recoverable elastic strain, due to a stress-induced martensitic phase transition creating a plateau region in the stress-strain curve. NiTi superelastic wires (Af = −15 °C fully annealed) of 0.10 mm in diameter have been produced and characterized by SAES Getters. The straight annealed wire shows the typical flag stress-strain behavior. The measured loading plateau is about 450 MPa at ambient temperature with a recoverable elastic strain of more than 6%. For these reasons superelastic SMA fibers can absorb much more strain energy than other fibers before their failure, partly with a constant stress level. In this paper, the improvement of composite laminates impact properties by embedding SMA wires is evaluated and indications for design and manufacturing of SMA composites with high-impact properties are also given.

Numerical investigation of smart base isolation system employing MR elastomer

Abstract: This paper evaluates the dynamic performance of a newly proposed smart base isolation system employing Magneto-Rheological Elastomers (MREs). MREs belong to a class of smart materials whose elastic modulus or stiffness can be adjusted by varying the magnitude of the magnetic field. The base isolation systems are considered as one of the most effective devices for vibration reduction of civil engineering structures in the event of earthquakes. The proposed base isolation system strives to enhance the performance of the conventional base-isolation system by using controllable MREs. To validate the effectiveness of the MRE-based isolation system, an extensive simulation study has been performed using a five degree-of-freedom structure under several historical earthquake excitations. The results show that the proposed system outperformed the conventional system in reducing the responses of the structure in all the seismic excitations considered in the study.

Organically Soluble Bifunctional Polyaniline–Magnetite Composites for Sensing and Supercapacitor Applications

Abstract: Conducting polymers CPs now own a special status in the field of electroactive materials, especially after the pioneering and noble prize winning work by Shirakawa et al. 1 A great deal of progress has been made on these synthetic metals in terms of their synthesis, processability, and device applications. 2-4 Particular attention on polyaniline PAni has been given due to its environmental stability, thin-film–forming property with tunable conductivity and commercial viability. Polyanilines have been studied extensively due to their applications to practical devices for energy storage, electrochemical sensors, electrochromic devices, electromagnetic interference shielding, and corrosion protection. 3-10 Application of the CPs in energy storage devices is also well known, 11 and recent studies 12 in this area gave impetus to fundamental and applied research on CPbased materials. Recent literature 13 identified the polyaniline composite materials as potential electrochemical sensors for various biomolecules. Applications of conducting polymers are broadened by compositing with other inorganic materials. For example, polyaniline-metal nanoparticle composites exhibit enhanced sensing and catalytic properties, compared to pure polyaniline. 14-19 Apart from the properties mentioned above, conducting polymers are useful as magneto/ electrorheological ER materials/fluids. 20-23 ER fluids is a class of materials whose rheological characteristics are controllable through the application of an electric field. ER fluids are usually made of particle suspensions with a large dielectric constant mismatch between the particles and the fluid. Because of the controllable rheological properties, ER fluids can potentially be used as a smart material for active devices, which transform electric energy to mechanical energy. Polyaniline can change its property from a conducting to an insulating state using simple protonic acid treatment. This allows for a change in dielectric constant and conductivity of particles while keeping all other particle properties the same. In the present communication, we report the synthesis of organically soluble bifunctional polyaniline-magnetite composites, which can sense dopamine and also act as supercapacitor electrode material. The results are presented and discussed.

A feasibility study on smart base isolation systems using magneto-rheological elastomers

Abstract: This study proposes a new smart base isolation system that employs Magneto-Rheological Elastomers (MREs), a class of smart materials whose elastic modulus or stiffness can be varied depending on the magnitude of an applied magnetic field. It also evaluates the dynamic performance of the MRE-based isolation system in reducing vibrations in structures subject to various seismic excitations. As controllable stiffness elements, MREs can increase the dynamic control bandwidth of the isolation system, improving its vibration reduction capability. To study the effectiveness of the MRE-based isolation system, this paper compares its dynamic performance in reducing vibration responses of a base-isolated single-story structure (i.e., 2DOF) with that of a conventional base-isolation system. Moreover, two control algorithms (linear quadratic regulator (LQR)-based control and state-switched control) are considered for regulating the stiffness of MREs. The simulation results show that the MRE-based isolation system outperformed the conventional system in suppressing the maximum base drift, acceleration, and displacement of the structure.

Thermal Buckling Analysis of SMA Fiber-Reinforced Composite Plates Using Layerwise Model

Abstract: Thermal buckling analysis of laminated smart composite plates subjected to uniform temperature distribution has been presented. Shape memory alloy (SMA) fibers whose material properties depend on temperature have been used as a smart material. A three-dimensional layerwise plate model has been employed in developing the system equations using variational approach. Finite-element method has been adopted for discretization of the laminate. Lagrangian interpolation functions have been used to approximate the displacement components along the thickness as well as in the in-plane direction. The actual variation of prebuckling stresses has been accounted for in the derivation of the geometric stiffness matrix of the laminates. An incremental load technique has been used in the analysis to take into account the nonlinearity in the material properties of the SMA arising due to their temperature dependence. The effects of thickness ratio, orthotropic ratio, fiber orientation, aspect ratio, stacking sequence and va...

System and method for self-authenticating token

Abstract: A secure token, possibly in the form of a smartcard, has a smart window with smart materials such as an electrophoretic or an electrochromic layer or assembly. When authenticated, such as by using biometrics or a password, the smart window layer is electronically pulsed, thereby transforming the once opaque layer to transparent and revealing information printed under, on or over the layer, or vice versa, transforming once transparent laminate to opaque and obfuscating printed information. In another embodiment, when the smart window layer is electronically pulsed to transform the once opaque laminate to transparent, a timer is started. At the end of a certain amount of time, the smart window layer is pulsed a second time, thereby transforming the layer back from transparent to opaque.

Smart materials in dentistry - future prospects

Abstract: INTRODUCTIONTraditionally, materials designed for long term use in the body or more specifically in the mouth are thought to survive longer if they are ‘passive’ and have no interaction with their environment. Materials such as amalgams, composites and cements are often judged on their ability to survive without interacting with the oral environment. Perhaps the first inclination that an ‘active’ rather than ‘passive’ material could be attractive was the realisation of the benefit of fluoride release from materials.THE NATURE OF SMART MATERIALSBy definition and general agreement, smart materials are materials that have properties which may be altered in a controlled fashion by stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields. A key feature of smart behaviour includes an ability to return to the original state after 1the stimulus has been removed

Whispering gallery mode-based micro-optical sensors for structural health monitoring of composite materials

Abstract: Development of smart materials with inherent damage sensing capabilities is of great interest to aerospace and other structural applications. Most of the existing smart materials are based on using embedded sensors for structural health monitoring. However, embedded sensors can lead to undesirable effects such as stress concentration and can cause premature failure. Therefore, using microstructural components for additional function of sensing of the structural health is the only option. Such possibilities exist only in selected few materials. The present study investigates the feasibility of developing fiber- and particle-reinforced composites into smart materials. The sensing approach considered is based on the morphology-dependent shifts of optical modes, referred to as the whispering gallery modes (WGMs), of spherical dielectric micro-particles. The WGMs are excited by coupling light from a tunable diode laser using single mode fibers. The WGMs of the micro-particles can be observed as sharp dips in the transmission spectrum through the fiber and are highly sensitive to the morphology of the particle. A minute change in the size, shape, or refractive index causes a shift of the optical modes, which can be interpreted quantitatively in terms of the parameter that caused the change. A theoretical framework is developed for such sensor systems that provides quantitative relations between the stress applied on the micro-particles and corresponding shift in WGMs. These relations are validated against the available experimental results.

Electroosmotically driven microfluidic actuators

Abstract: A prototype electroactive polymer actuator has been developed based on electroosmotic (EO) pumping to create hydraulic pressure. The actuator was fabricated from poly(dimethylsiloxane) (PDMS) with embedded micro-scale channels, reservoirs, and electrodes surmounted by a membrane. An applied voltage caused one reservoir to expand as fluid was pumped into it, and the other reservoir to contract, with the membrane above the expansion reservoir rising by 400 μm within a few seconds. Since the prototype was made from PDMS, which is an elastomer, the device was entirely flexible. The actuator performance was characterized, and it agreed well with predicted values. Furthermore, the calculations indicate that, once optimized, such actuators could have high stress as well as high strain and high speed. By combining unit cells such as these into a material and actuating them individually via independently controlled flexible electrodes, one could realize smart materials that could change shape. Other future applications may include micro-valves, micro-positioners, soft robots, and active camouflage layers.

Demonstration of an integrated electroactive polymer actuator on a microfluidic electrophoresis device

Abstract: The construction of microfluidic devices from siloxane-based polymers is widely reported in the current literature. While the use of these materials is primarily due to their rapid and facile fabrication, low cost and robustness, they also have the ability to function as smart materials. This feature, however, has not been commonly exploited in conjunction with their fluid-handling capabilities. Siloxanes are considered smart materials because their shapes can be modified in the presence of an electric field. The energy in the electric field can be transduced into mechanical energy and directly coupled with a microfabricated channel network in order to affect or initiate the movement of fluids. Here, we present a novel microfluidic device into which an electroactive polymer (EAP) actuation unit is integrated. The EAP actuation unit features a microfluidic channel placed above a patterned electrode. The patterned electrode is insulated from the channel by an EAP layer that is composed of PDMS. When a potential is applied across the EAP layer, it changes shape, which also changes the volume of the microfluidic channel above it. With this proof-of-concept device we demonstrated the ability to inject plugs of sample on a standard electrophoresis cross chip solely by changing the magnitude of the electric field between the channel and the electrode. Using an EAP actuation unit, the size of the injection plugs can be varied as a function of the electric field, the active area of the EAP actuation unit and the softness of the EAP.

Optoelectronics: Combining chemical worlds

Abstract: Using self-assembly and electrodeposition, complementary organic and inorganic building blocks are combined to form a lamellar hybrid that is an efficient photoconductor.

Ferroelectric Characterization of Single PZT Fibers

Abstract: In a previous work, the authors have presented a comprehensive procedure for the direct characterization of single piezoelectric ceramic fibers in terms of butterfly and polarization loops and blocking force. The ability to investigate single fibers is relevant for optimizing their manufacturing processes, for quality control purposes, and for modeling the response of components and structures. In this study the novel testing procedure is used to characterize commercially available fibers distributed by Advanced Cerametrics Inc., CeraNova Corp., and Smart Material Corp., respectively, and to compare their performance with fibers developed at Empa. Their porosity, grain size and phase composition were investigated to correlate the ferroelectric properties with the microstructure. Fibers supplied by Smart Material Corp. exhibited the best ferroelectric performance, in particular the highest saturation and remnant polarization, the lowest coercive field and the highest P—E loop squareness. The said properties result from a low porosity, a sufficiently large grain size and a phase composition near the morphotropic phase boundary. After removing a surface layer dominated by a rhombohedral phase, Empa fibers developed maximum average free-strains 15% larger than any commercially available fiber. Better control of the sintering atmosphere thus promises to be the key to very high performance fibers.