Smart Material Systems Research Articles

Cyclic Viscoplastic-Viscodamage Analysis of Shape Memory Polymers Fibers With Application to Self-Healing Smart Materials

The cold-drawn, programmed shape memory polymer (SMP) fibers show excellent stress recovery property, which promotes their application as mechanical actuators in smart material systems. A full understanding of the thermomechanical-damage responses of these fibers is crucial to minimize the trial-and-error manufacturing processes of these material systems. In this work, a multiscale viscoplastic-viscodamage theory is developed to predict the cyclic mechanical responses of SMP fibers. The proposed viscoplastic theory is based on the governing relations for each of the individual microconstituents and establishes the microscale state of the stress and strain in each of the subphases. These microscale fields are then averaged through the micromechanics framework to demonstrate the macroscale constitutive mechanical behavior. The cyclic loss in the functionality of the SMP fibers is interpreted as the damage process herein, and this cyclic loss of stress recovery property is calibrated to identify the state of the damage. The continuum damage mechanics (CDM) together with a thermodynamic consistent viscodamage theory is incorporated to simulate the damage process. The developed coupled viscoplastic-viscodamage theory provides an excellent correlation between the experimental and simulation results. The cyclic loading-damage analysis in this work relies on the underlying physical facts and accounts for the microstructural changes in each of the micro constituents. The established framework provides a well-structured method to capture the cyclic responses of the SMP fibers, which is of utmost importance for designing the SMP fiber-based smart material systems.

Design of multi-state and smart-bias components using Shape Memory Alloy and Shape Memory Polymer composites

A Multifunctional Smart Material System (MSMS) consists of two or more different smart material phases in the form of a hybrid system, in which every phase performs a different but necessary function. In this work, thermally responsive Shape Memory Alloys (SMAs) and Shape Memory Polymers (SMPs) are combined to form a MSMS. The transformation temperatures martensitic start (Ms), martensitic finish (Mf), austenitic start (As) and austenitic finish (Af) of SMA and the glass transition (Tg) for the SMP play a critical role in designing such a MSMS. Multi-state smart bias systems with varying stiffnesses can be obtained by varying the Tg of SMP between the transformation temperatures Mf and Af of SMA. Guidelines to form such MSMS have been established by estimating the volume fractions of the individual constituents. Various ideas for “smart-bias” tools/devices have been proposed, such that they can operate under three different temperature regimes, with one material constituent being passive and the other active at a given temperature.

POLYVINYLIDENE FLUORIDE AND ZINC OXIDE SMART COMPOSITE MATERIAL

This work aimed at fabrication and electromechanical characterization of a smart material system composed of electroactive polymer and ceramic materials. The idea of composite material system is on account of complementary characteristics of the polymer and ceramic for flexibility and piezoelectric activity. Our preliminary work included Polyvinylidene Fluoride (PVDF) as the flexible piezoelectric polymer, and Zinc Oxide (ZnO) as the piezoelectric ceramic brittle, but capable to respond strains without poling. Two alternative processes were investigated. The first process makes use of ZnO fibrous formation achieved by sintering PVA/zinc acetate precursor fibers via electrospinning. Highly brittle fibrous ZnO mat was dipped into a PVDF polymer solution and then pressed to form pellets. The second process employed commercial ZnO nanopowder material. The powder was mixed into a PVDF/acetone polymer solution, and the resultant paste was pressed to form pellets. The free standing composite pellets with electrodes on the top and bottom surfaces were then subjected to sinusoidal electric excitation and response was recorded using a fotonic sensor. An earlier work on electrospun PVDF fiber mats was also summarized here and the electromechanical characterization is reported.

The performance of integrated active fiber composites in carbon fiber laminates

Piezoelectric elements integrated into fiber-reinforced polymer-matrix laminates canprovide various functions in the resulting adaptive or smart composite. Active fibercomposites (AFC) composed of lead zirconate titanate (PZT) fibers can be used as acomponent in a smart material system, and can be easily integrated into woven composites.However, the impact of integration on the device and its functionality has not been fullyinvestigated. The current work focuses on the integration and performance of AFCintegrated into carbon-fiber-reinforced plastic (CFRP) laminates, focusing on the strainsensor performance of the AFC–CFRP laminate under tensile loading conditions.AFC were integrated into cross-ply CFRP laminates using simple insertionand interlacing of the CFRP plies, with the AFC always placed in the90° ply cutout area. Test specimens were strained to different strain levels and then cycled witha 0.01% strain amplitude, and the resulting signal from the AFC was monitored.Acoustic emission monitoring was performed during tensile testing to provide insightto the failure characteristics of the PZT fibers. The results were compared tothose from past studies on AFC integration; the strain signal of AFC integratedinto CFRP was much lower than that for AFC integrated into woven glass fiberlaminates. However, the profiles of the degradations of the AFC signal resulting fromthe strain were nearly identical, showing that the PZT fibers fragmented in asimilar manner for a given global strain. The sensor performance recovered uponunloading, which is attributed to the closure of cracks between PZT fiber fragments.

Wireless Sensor Networks Security Issues as Smart Materials Systems

With the wide application of wireless sensor networks, their securities become research hotspot. Firstly, introduced the limiting factors of wireless sensor networks, summarized the security attack types and gave prevention strategies accordingly. Secondly, proposed the security technologies of wireless sensor networks, these technologies include key management and distribution, authentication and verification, and data fusion encryption technologies. Finally, discussed further security research interests.

Univariate input models for stochastic simulation

Techniques are presented for modelling and then randomly sampling many of the continuous univariate probabilistic input processes that drive discrete-event simulation experiments. Emphasis is given to the generalized beta distribution family, the Johnson translation system of distributions, and the Bézier distribution family because of the flexibility of these families to model a wide range of distributional shapes that arise in practical applications. Methods are described for rapidly fitting these distributions to data or to subjective information (expert opinion) and for randomly sampling from the fitted distributions. Also discussed are applications ranging from pharmaceutical manufacturing and medical decision analysis to smart-materials research and health-care systems analysis.

Effect of Applied Load on Dry Sliding Wear Property of Aged TiNiCu Alloy

Titanium Nickel Shape Memory Alloy (SMA) has demonstrated its great potential for a large variety of applications. This alloy is being actively applied to the development of new energy conversion systems, to the design for new robots and smart material systems and to the development of medical implants and instruments. In addition to its shape memory effect, it is necessary to understand the wear behavior of Titanium Nickel SMA Alloys. Hence in this article the wear behaviour of a TiNiCu+ alloy aged at different temperature have been studied against EN 31 steel (62HRc). The results indicate that the ageing temperature greatly affect the dry sliding wear behavior of TiNiCu alloy.

Experiment and Analysis of Smart Concrete Beam Strengthened Using Shape Memory Alloy Wires

Shape memory alloy (SMA) has many potential applications as an actuator in smart material systems due to its abilities of shape memory, pseudo-elasticity, high damping and wear resistant. In this paper, a smart concrete beam has been developed by taking advantage of the shape memory effect of SMA and the characteristic of applying large forces on the resisting member in the transformation of SMA on heating. Deformation behavior and influence of factors on the deformation behavior of SAM smart concrete beam were investigated experimentally. Actuation mechanics of SMA was analyzed. Experimental results show that SMA wires significantly increase structural survivability and allow structural to recover from residual deformation by damaged earthquake and typhoon, and the crack almost closes completely after electrically heating the SMA wires. The number or areas of SMA wires has no influence on the tendency of deformation during loading and the tendency of reversion by heating. An increasing of the initial pre-strain of SMA wire can significantly improve the capacity of self-restoration of SMA concrete beams, but the steel main bars play a very negative role in reducing residual deformation.

A Comparison between SISO and MIMO Modal Analysis Techniques on a Membrane Mirror Satellite

The future of space satellite technology lies in the development of ultra-large, ultra-lightweight space structures, orders of magnitude greater in size than the current satellites. Such large crafts will increase communication and imaging capabilities from orbits. Many such proposed ultra-flexible satellites are inflated structures. To get these ultra-large structures in space, they will have to be stored within the Space Shuttle cargo bay and then inflated on-orbit. However, the highly flexible and pressurized nature of these ultra-large spacecraft poses several daunting vibration and control problems. Disturbances (i.e., on-orbit maneuvering, guidance and attitude control, and the harsh environment of space) wreck havoc with the on-orbit stability, pointing accuracy, and surface resolution capability of the inflated satellite. Fortunately, recent advances in integrated smart material systems promise to provide solutions to these problems. Recent research into the use of Macro-Fiber Composite (MFC®) devices integrated into the dynamic measurement and vibration control of inflated structures has had promising results (Wilkie et al., 2000). These piezoelectric-based devices possess a superior electro-mechanical coupling coefficient making them superb actuators and decent sensors in dynamic analysis applications. Initially, research was performed on an inflated torus using single-input, single-output (SISO) testing techniques. Since then, steps have been taken to outline a new, multiple-input, multiple-output (MIMO) testing technique for these ultra-large structures. This study applies these results to an inflated torus with bonded membrane mirror to extract modal parameters, such as the damped natural frequencies, associated damping, and mode shapes within the frequency bandwidth of interest for these structures (5–200 Hz). Further, the nonlinear dynamic behavior of the inflated torus and membrane mirror is accentuated through a comparison of SISO and MIMO modal analysis techniques, and a discussion of the nonlinear results follows. The purpose of this work is to apply the results from prior works to an inflated torus with bonded membrane mirror to accomplish the following three goals: (1) to establish a baseline dynamic characterization of the test structure using SISO modal analysis techniques;(2) to perform a MIMO modal analysis of the test structure to identify natural frequencies, mode shapes, and damping ratios, and compare these MIMO results to the SISO analysis; and(3) to use the discrepancies between the two testing technique results as a platform for discussing the nonlinear nature of the test structure. In the future, the results of this work may form the premise for an autonomous, self-contained system that can both identify the vibratory characteristics of an ultra-large, inflated space craft and apply an appropriate control algorithm to suppress any unwanted vibration – all while on-orbit.

New technological development of passive and active vibration control: analysis andtest

We present a brief summary of new technical developments of passive and active vibrationcontrols which we have performed for the last several years partly as an internationalcollaborative R&D project on Smart Materials and Structural Systems sponsored by theJapanese Ministry of Economy, Trade and Industry. In connection with the passivedamping control, shape memory alloys (SMAs) were used as damping elements. Toexamine the effect of damping enhancement, beams with SMA films bonded ontothem or SMA wires embedded into them were made, and free damped oscillationswere measured. The damping coefficient increased by more than 100% comparedwith the beams without SMAs. Thermodynamic behaviors of an SMA wire andfilm were also investigated experimentally and numerically. In active vibrationcontrol, a new concept of smart material systems was proposed. That is a partiallymagnetized alloy, which is stiff and strong enough as a structural element and respondssufficiently quickly as an actuator due to an electromagnetic force. A simplifiedexperiment and numerical simulation were performed and the results showed thefeasibility of the proposed smart material system using the electromagnetic force.

Development of Texture-Controlled Bulky Actuator/Sensor Materials by Combining Rapid-Solidified Fiber/Ribbon Elements and Spark Plasma Sintering/Joining(SPSJ)

ABSTRACTThe authors have showed that rapid-solidified (RS) melt-spun fiber/ribbon/foil type samples have very often strongly textured fine columnar grains, and those can have very high performance of the metallic actuator/sensor properties. However, as for the applications of these sample materials in smart material systems, the developed rapid-solidified samples are thought to be inevitably too small force to move the machines and structures in the engineering field. In this paper, we propose one novel material processing technique that can produce the bulk type solid-state actuator/sensor materials by combing the rapid-solidified fiber/ribbon and short time spark plasma sintering/joining (SPS) method. The produced samples, both 1) the disk-type sample from stacked layers of RS-ribbons and 2)the sintered compact from ball-milled RS-fibers of shape memory Ti50Ni40Cu10 (NITINOL) alloy, showed clear thermoelastic phase transformation by DSC evaluation as well as shape recovery. The same approach was also tried for making bulky magnetostrictive FeGa(Galfenol) alloy systems from stacked FeGa ribbons. Laminated FeGa ribbons maintained large magnetostriction of about 100–200ppm under increasing stressed condition as much as in the case of the strongly textured ribbon sample.

Smart and designer structural material systems

AbstractAn efficient civil infrastructure system is essential to every country's productivity, security, and quality of life. Basic research and development in smart structures and designer materials have shown great potential for enhancing the functionality, serviceability, and increased lifespan of civil infrastructure systems. New construction and the intelligent renewal of ageing and deteriorating civil infrastructure systems include efficient and innovative use of high‐performance designer materials, sensors, actuators, and mechanical and structural systems. High‐performance designer materials, in particular, require new methods of computational materials science, some of which are described herein. In this paper, some examples of National Science Foundation (NSF) funded awards, some examples of National Institute of Standards and Technology (NIST) ‘designer material’ projects, and future research needs, as well as new research initiatives on nanotechnology, are presented.

Dynamic smart material and structural systems

Dynamic smart material and structural systems

Dynamic smart material and structural systems

Basic research in smart materials and structural systems and their development have demonstrated great potential for enhancing the functionality, serviceability and durability of civil and mechanical infrastructure systems and, as a result, offer the potential for significant contributions to the improvement of every nation's productivity, efficiency and quality of life. The intelligent renewal of aging and deteriorating civil and mechanical infrastructure systems includes efficient and innovative use of high performance sensors, actuators, materials, mechanical and structural systems. In this paper some examples of NSF-funded projects and research needs as well as some initiatives are presented.

Properties of Lead Zirconate Titanate Ceramics Determined Using Microwave and Hot-Press Hybrid Sintering Process

Piezoelectric materials play an important role in smart material and structural systems, and high-performance piezoelectric actuators with larger force and displacement output are in demand. It was shown in our previous work that the hybrid sintering process using a 28 GHz microwave technique and hot pressing offers advantages over conventional technologies reference. It was also confirmed that the maximum achieved value of piezoelectric constant d31 of the specimens of the hybrid-sintering process is approximately 360×10-12 m/V, which is about 38% larger than 260×10-12 m/V, the d31 of the conventionally sintered specimens. In this study, the material properties, including electromechanical coupling factor, Young's modulus, frequency constant, Curie temperature and dielectric constant, of the specimens fabricated with the microwave sintering process were further investigated for different sintering temperatures. The Curie point Tc decreases, but the dielectric constant εr at Tc increases with the grain size of specimens for all sintering methods. The influence of grain size on Tc and εr can be attributed to the residual stress induced by the lattice mismatch between the cubic phase and the tetragonal-rhombohedral mixed phase.

Development of new shape memory actuator materials and their applications for smart material systems.

Development of new shape memory actuator materials and their applications for smart material systems.

Study of induced strain transfer in piezoceramic smart material systems

Smart materials such as piezoceramics are being used as actuators and sensors to achieve active control of elastic deformations of structures. Intelligent structures, with highly distributed actuators and sensors, can be designed with intrinsic vibration and shape control capabilities. Piezoceramics can be integrated with a structure either by being embedded within or bonded onto the structure. Particularly for the case of surface bonding, it is important to have an effective strain transfer from the smart material to the metallic substrate through the adhesive layer. In this paper, study of the strain transfer of piezoceramic actuators bonded to the surface of a structure with a finite-thickness adhesive bond is presented. A structure with actuators bonded to the top and bottom surfaces of a cantilever beam, which can deform in either bending or extension, is analysed. A detailed two-dimensional model of the structure is developed to study this strain transfer through an adhesive layer using the finite-difference method to solve the equations of elasticity, with appropriate boundary conditions. The resulting strains in the actuator and those induced in the substructure are compared with a finite-element model and two existing one-dimensional analytical models. The limitations of the simplified analytical models are brought out. The uniform-strain analytical model was found to be in agreement with the numerical models only for the case of extension actuation. The Bernoulli-Euler analytical bending model agreed with the numerical models only at points near the center of the structure. The finite-difference and finite-element models were in agreement in almost all cases. For the case of bending actuation, the finite-difference and finite-element methods differed in their predictions of induced strains.

Remarks on well-posedness theorems for damped second-order systems

We consider an operator theoretic formulation for distributed damped second-order (in time) forced linear elastic systems. A brief summary of previous well-posedness results is presented along with new results which allow relaxed spatial regularity (which is important in smart material systems applications) on the forcing or input function. Extensions to nonlinear systems are also indicated. The results are presented in a variational format for easy development of finite element approximation methods.

Electrical Discharge Machining Of Smart Materials Parts

Smart materials systems are a relatively new concept that has gained widespread attention in the defense, aerospace and academic communities. They provide smartness, a functionality that adds significant value to materials, technologies, or end-products. Smartness enables system performance enhancements that are not possible with traditional non-smart approaches. Smart materials systems offer substantial near-term business potential across a broad range of technologies, applications and markets. A full scale application of such advanced materials (especially in automotive and aircraft industry) is hindered by the high cost of manufacturing. Unacceptable short tool life and the resulted sub-surface damage are the major issues when some smart materials are machined by conventional machining processes. The paper investigates the feasibility of applying electrical discharge machining (EDM) process for ceramics, an important class of smart materials parts. The effect of the EDM parameters and their interaction on the surface roughness and efficiency of the process are analyzed. Transactions on the Built Environment vol 35, © 1998 WIT Press, www.witpress.com, ISSN 1743-3509

A smart material microamplification mechanism fabricated using LIGA

A unique microamplification mechanism formed through the merging of smart material and microelectromechanical system concepts is presented. This microamplification device increases the useful actuation stroke of piezoceramic material through the amplification of piezoceramic strain. The technology demonstrated has utility as a microactuation mechanism for driving micropiezomotors, hearing aid transducers and precision optical switches. The microamplifier, approximately , is composed of electroplated nickel and was constructed using LIGA. An overview of microactuator system requirements and the advantages of scaling the flexure based amplifier illustrates the utility of the new device. The microamplifier is a radically scaled version of a mesoscopic mechanism. An analytical discussion of the operation is presented along with a finite-element analysis of the static and dynamic properties of the microlever. The analytical study is used to develop the operation principles and expected performance of the microamplifier. Experimental static and dynamic testing results are presented that confirm the analytical study. The mechanism has a mean amplification ratio of 5.48, an elastic stroke range of 8 m and a fundamental frequency of 82 kHz.