Research activities in smart materials at the Army Research Office, over the past decade is briefly reviewed. Status of the current program is discussed. The current symposia is previewed and a look to the future needs and opportunities for smart materials research is presented.

The response time of TiNi has been the subject of several experimental and theoretical investigations over the past decade. One of the principal concerns with this material is the relatively low cycle speeds or operational bandwidth caused by the considerable length of time required to cool the material. In this paper a finite difference model of heat transfer including the latent heat dissipated during the phase transformation is used to predict the bandwidth of thin film TiNi. The film is modeled as a plate subjected to either forced or free convection along the exposed surfaces and clamped to a large thermal mass representative of silicon wafer at the ends of the specimens. Results indicate that both latent heat as well as the relative ratios of the transformation temperatures to ambient temperature strongly influence the bandwidth of the material. Good correlation between the analytical model and test data obtained on a 38 micron wire indicate the model contains the correct assumptions to predict bandwidths. The bandwidth of TiNi thin film are predicted to be on the order of 100 Hz necessary assuming that the transformation temperatures for the film are the same as the bulk material.

A new design for shape memory alloy rotatory joint actuators using shape memory effect and pseudoelastic effect is presented. In this design, one SMA wire works with its shape memory effect, while the other SMA wire works with its pseudoelastic effect. The pseudoelastic type of SMA wire provides the shape memory type of SMA wire with bias force, and therefore, the bias spring in a bias force type of SMA actuator can be eliminated. A quasi-static analysis of this type of actuators is performed which incorporates a varying load torque. General stress-strain relation and stress- temperature relation of the shape memory effect wire and a formula for an equivalent spring rate of the pseudoelastic wire are derived. Liang and Rogers' model for shape memory materials is used for the analysis. An experimental method to obtain the equivalent spring rate is also described. Design formulas for a simplified design are derived based on the quasi-static analysis of the actuator.

As a modification of Cu-Zn-Al shape memory alloy (SMA), the characteristics of Cu-21Zn-6Al-1Mn-0.5Zr (wt%) SMA are examined and compared with that of Cu-21Zn-6Al (wt%) SMA in the present work. After added Zr into the Cu-Zn-Al alloy, the average grain size of Cu-Zn-Mn-Zr alloy is reduced from 300 micrometers (that of Cu-Zn-Al alloy) to 75 micrometers . Two Zr-rich new phases were found in Zr added alloy by means of transmission electron microscopy. The tensile testing results and scanning electron microscopy observations show that the strength of grain boundary and the ductility of the Mn, Zr added alloy were enhanced. This has made the alloy exhibit better mechanical property than ordinary Cu-Zn-Al SMA. Moreover, upon ageing, the reordering phenomenon was not serious when the aging temperature was below 200 degree(s)C in Cu-Zn-Al-Mn-Zr alloy while significant decrease of order degree and shape memory capacity were found for Cu-Zn-Al alloy.

The purpose of the present work is to develop the materials with new functions by combining two kinds of particles electrified reciprocally. This paper reports a preparation method and the positive temperature coefficient of resistivity (PTCR) properties of complex particles consisting of semiconductive BaTiO₃ granules and metallic indium powder particles. The conclusion obtained by the present experiment are as follows. (1) Vibrating cylindrical electrode can forced-electrify metal, semiconductor and insulator particles positively or negatively. (2) When the particles electrified reciprocally are mixed in the same region at the same time, complex particles can be created by the electrostatically attractive force working between the two kinds of particles. (3) Indium-semiconductive BaTiO₃ complex particles made by this processing offer the new PTCR material which can be used in arbitrary shapes by filling and packing or drawing and painting.

We show how composites with extremal or unusual thermal expansion coefficients can be designed using a numerical topology optimization method. The composites are composed of two different material phases and void. The optimization method is illustrated by designing materials having maximum thermal expansion, zero thermal expansion, and negative thermal expansion. Assuming linear elasticity, it is shown that materials with effective negative thermal expansion coefficients can be obtained by mixing two phases with positive thermal expansion coefficients and void. We also show that there is no mechanistic relationship between negative thermal expansion and negative Poisson's ratio.

In the past, optical fiber switches have typically been constructed from plastics or ceramics. However, the inability of these materials to operate effectively at high temperatures has greatly restricted the utilization of these devices. Recently, fiber optic switches have been manufactured from two thermally stable materials: carbon- carbon and BS50, a high temperature ceramic. The integration of these dimensionally stable materials into the fabrication of the optical switch will allow the switch to be utilized in an increased number of applications including optics, aerospace, mechanical, medical, and electronics. Preliminary testing included examining these new optical switches for structural damage due to the manufacturing process and testing the switches to demonstrate that the fibers could be realigned after processing. The tests concluded that no structural damage was induced, and the critical fiber realignment was achieved.

During the last several years novel piezoelectric bending actuators have been developed: RAINBOW, CERAMBOW, CRESCENT, d₃₃ bimorph and THUNDER. A comparative experimental investigation of electromechanical characteristics of these devices along with conventional d₃₁ bimorph and unimorph actuators was conducted in this work. All transducers were fabricated from soft piezoelectric ceramics. The experimental results show the d₃₃ bimorph and unimorph elements have superior quasistatic characteristics as compared to other type of bending-mode actuators. All these piezoelectric devices demonstrate a significant dependence of electromechanical performance on the magnitude of the driving electric field. It was found that the decrease in the mechanical quality factor and resonant frequency of bending vibrations in d₃₁ unimorph, RAINBOW, CRESCENT (CERAMBOW) and THUNDER with increasing electric field is much smaller than that in bimorph and d₃₃ unimorph actuators. The dependence of the behavior of these devices on the operating conditions governs the selection of a particular device for a specific application.

Recent developments in the technology of ferroelectric, piezoelectric, electrostrictive and antiferroelectric ceramic actuators have clearly demonstrated that the materials required for future applications such as positioners, levelers, pumps, vibration-free structures and variable-focus elements will need to be more sophisticated (multifunctional and smart), more economical and possess a higher degree of performance than presently available. One recently developed method for producing considerably higher- than-normal displacement in these materials is known as the RAINBOW (Reduced and INternally Biased Oxide Wafer) technology. This acronym denotes the basic active structure of the Rainbow device which is produced by a special high temperature chemical reduction process. In its most basic sense, a Rainbow can be considered to be a pre-stressed, monolithic, axial-mode bender; however, because of its unique dome or saddle-shaped configuration, it is able to produce much higher displacements (up to several mm depending on size) and sustain moderate loads (up to 10 kg depending on thickness) than normal benders such as unimorphs and bimorphs. The technology of producing and characterizing such Rainbows as well as methods for increasing their utility by means of stacked actuators for increased linear displacement and matrix arrays for enhanced coverage in wide-area applications such as smart skins, autoleveling structures and deformable coatings are described.

We have fabricated multilayer electromechanical composites with controlled piezoelectric coefficient distributions using tape casting. Tapes of doped lead zirconate titanate were cut and stacked in accordance with their characteristic electromechanical coupling values and modulus of elasticity. This technique is an extremely versatile method to fabricate displacement actuators to fabricate monolithic ceramic parts with controlled material property gradients. To obtain a quantifiable method to optimize this type of transducer, we have devised a processing model. Given the functional distribution of the electromechanical coupling coefficient, d₃₁, and the functional distribution of elastic modulus through the thickness of the transducer, the analysis predicts the displacement as a function of loading. The tape casting method coupled with the model provides an actuator that maximizes displacement and generated force for the given material properties.

The design of ferroelectric/piezoelectric smart structures is limited by the accuracy to which the material properties of the sensor/actuator materials are determined. In particular, it is important to understand the effects of losses, dispersion, and the non-linearities that become significant when large fields are applied. This paper presents the small signal properties, including losses of Motorola PZT 3203 HD, a typical piezoelectric material, and it reports on the field dependence of the material constants for large electric fields. A set of PZT 3203 HD unloaded resonators manufactured by Motorola was cut to specifications outlined in the IEEE Standard on Piezoelectricity Std 176-1987, to ensure the appropriate boundary conditions of each resonance mode. Quasi-static measurements were performed on some of the samples at various field levels above and below the coercive field of the material. The impedance/admittance spectra of the resonators were measured for different values of the DC bias field. In both cases the average slope as a function of field, which is a measure of the piezoelectric or the dielectric constant, was found to increase linearly with the maximum field applied. The values of the material constants determined from the DC biased spectra were found to be smaller by a factor of 4 - 6. This is attributed to differences in the nature of the measurements. The quasistatic measurements are done at high field and low frequency and involve irreversible domain switching. The DC bias measurement is at high frequency and the AC measurement field is much smaller and the domain motion is reversible.

Electric field induced antiferroelectric (AFE) to ferroelectric (FE) phase transformations are accompanied by large strain and significant hysteresis. The properties of these materials can be tailored to fit specific applications such as high strain actuators and charge capacitors. As an attempt to reduced hysteresis, Barium and Strontium A-site substitution of the phase transformation behavior of (Pb_0.98-(delta )La_0.02A_(delta )) (Zr_xSn_yTi_z)O₃ (A equals Ba, Sr) ceramics have been investigated. The ceramic samples in this study produced 0.2% to 0.3% strain level. Barium proved to be a strong FE stabilizer with decreasing both switching field and hysteresis, while Strontium proved to be a strong AFE stabilizer. Some practical data, including temperature stability and current requirements, are also to be discussed.

In this paper we describe the results of an ongoing experimental program to measure the strain distribution around a simulated void in a piezoceramic material subjected to large electric fields. The simulated void is a two- dimensional circular cylinder fabricated into the sample. Strain information is acquired with a Moire interferometric system which permits both quantitative evaluation of surface strains and qualitative information regarding domain reorientation. Results indicate that large stresses/strains arise around the perimeter of the hole prior to domain reorientation. Domain switching initiates at the locations where the largest stress/strain occurs around the perimeter of the simulated void and do so to reduce the localized concentrations. During this evolutionary process the material contains a multi-domain structure with regions polarized in 180 degree(s) apart. Domain switching appears to be predominately 180 degree(s) without any 90 degree(s) domain reorientation occurring at the mesoscopic level. Results suggest that large stress/strain concentrations around voids could be a source for electric fatigue degradation.

Fatigue behavior for a piezoceramic material was studied. Fatigue tests using compact tension specimens of PZT-4 under various combinations of electric and mechanical load were conducted to develop a crack growth law. Experimental results indicated that crack growth could be significantly influenced by electric fields. The fatigue crack growth cannot be accounted for by stress intensity factor alone. The result of this study indicates that the mechanical strain energy release rate is a single parameter that can account for the combined mechanical and electrical load that governs crack growth. A Paris law type of fatigue crack model was derived based on the fatigue tests.

Piezoelectric polyvinylidenefluoride films have been embedded between layers of composite laminates and cured at temperatures up to 200 degree(s)C. The films retain much of their piezoelectric response upon cooling even though the cure temperature exceeds the melting point of the film. The response of these embedded sensors to impact loading is discussed. We have also used embedded sensors to monitor curing of reinforced low temperature curing epoxy films sandwiched between polycarbonate sheets and subjected to an intermittent external load perpendicular to the surface. The sensor response drops as cure continues since the stiffer resin transfers less load to the film.

The potential applications of pure piezoelectric ceramics as embedded sensors are limited by the stiffness and brittleness of these materials. To achieve a more compliant sensor, composites have been developed which incorporate calcium-modified lead titanate particles in an polymer matrix. Such compliant sensors, in thin film form, may be useful within thick composite structures such as tank hulls and helicopter blades. The mechanical response of 0 - 3 composite films of Ca-modified lead titanate in polyvinylidene fluoride-trifluoroethylene and Epon828 epoxy matrices is investigated in this work. The electrical response of these composites is currently being studied by Wenger et al. The viscoelastic properties of these thin film composites with various volume fractions have been measured over a wide range of frequencies and temperatures. The observed mechanical response of these heterogeneous materials is compared with the predictions of several simple models for such composites. Preliminary piezoelectric results are also presented.

Polymers are ubiquitous in nature, owing to their use as both structural and active components in dynamic, living systems. From a synthetic point of view man has utilized the excellent structural properties of polymers (light weight/high strength) for some decades now. However, the integration of active functional polymers into engineered systems and structures is a more recent endeavour with numerous challenges still to be overcome. Conducting electroactive polymers such as polypyrroles, polythiophenes and polyanilines are a fascinating group of functional polymers. They are electronic conductors and in addition they response to chemical or electrical stimuli in a number of ways. They are truly electrofunctional polymers. This unique combination of properties has led to the use of conducting polymers for electronic components, chemical sensors and biosensors, membranes for solution or gas separations, electromechanical actuators, electro-optical devices, biomaterials capable of controlled release of drugs or stimulation of biological processes, and for corrosion protection.

The objective of these characterization tests was to find the optimum conditions that maximize the length variation of the chemically activated polyacrylonitrile (PAN) muscles. There are two steps of annealing and chemical treatment in the development of the PAN muscles. The effects of the annealing temperature, the duration of annealing, and the duration of the boiling in the NaOH solution on the variation of the length of PAN muscle were studied. The effect of the pH of the saturating solution on the expansion-contraction behavior of the PAN muscle was further studied. The expansion-contraction behavior of the PAN muscle when saturated with HNO₃, H₂SO₄, and HCl was also studied.

Magnetorheological (MR) fluids are stable suspensions of magnetic particles in a carrying fluid exhibiting controllable rheological behavior in the presence of a magnetic field. Magnetorheological effect represents a reversible increase, due to an external magnetic field, of effective viscosity. MR fluids and devices have the potential to revolutionize the design of hydraulic systems, actuators, valves, active shock and vibration dampers, and other components used in mechanical systems. MR fluids that are currently available suffer from high initial viscosity values and low stability. Hence, there is a compelling need to optimize the MR fluid manufacturing process to produce optimum MR fluid characteristics. The present study proposes to manufacture an optimum composition of a MR fluid in terms of its quality and properties. A high-speed bead mill blending machine is used to manufacture the fluid. Characterization studies are conducted to evaluate the produced fluid.

Magnetic and magnetorheological properties of a number of compositions are examined. The compositions are based on barium and strontium ferrites, magnetite, and (gamma) -Fe₂O₃, both commercial and synthesized using specially developed methods, suspended in transformer oil and synthetic binders based on phenol-formaldehyde, epoxyacrylic and pentaphthalic resins. The influence of numerous factors, such as the type and magnetic properties of the filler, types of the binder, magnetic properties of the composition on the orientational effect of the filler in a magnetic field was evaluated. The latter was judged by a magnitude of magnetorheological effect.

Self assembled molecular systems are a focus of attention for material scientists as they provide an inherent molecular level organization responsible for enhanced material properties. We have developed polymeric molecular systems with interesting optical properties by biochemical engineering, which can be self assembled to thin films. Horseradish peroxidase catalyzed polymerizations of phenolic monomers: 9-hydroxyquinoline-5-sulfonic acid, acid red and decyl ester (d&l isomers) of tyrosine, have been achieved in the presence of hydrogen peroxide. The polymer of 8- hydroxyquinoline-5-sulfonic acid acts as a polymeric ligand that can be used for metal ion sensing. The polymer of acid red, with azo functional groups in the polymer backbone, shows interesting optical properties. Amphiphilic derivatives of tyrosine self assemble into tubules from micelles in aqueous solutions. These tubules have been enzymatically polymerized to polymeric tubules. The tubules are of 5 micrometers average diameter and > 200 micrometers length. The formation and properties of these tubules are discussed.

Molecular recognition sites on cell membranes serve as the main communication channels between the inside of a cell and its surroundings. Upon receptor binding, cellular messages such as ion channel opening or activation of enzymes are triggered. In this report, we demonstrate that artificial cell membranes made from conjugated lipid polymers (polydiacetylene) can, on a simple level, mimic membrane processes of molecular recognition and signal transduction. The ganglioside, GMI was incorporated into polydiacetylene liposomes. Molecular recognition of cholera toxin at the interface of the liposome resulted in a change of the membrane color due to conformational changes in the conjugated (ene-yne) polymer backbone. The `colored liposomes' might be used as simple colorimetric sensors for drug screening or as new tools to study membrane-membrane or membrane-receptor interactions.

Self-assembled functional molecules in mesoporous materials are synthesized directly either by co-assembly of dye-bound surfactant of ferrocenyl TMA with silicate or Pc (phthalocyanine) molecules doped in the C₁₆TMA micelles with oxides framework such as V₂O₅, MoO₃, WO₃ and SiO₂. The process provides well-organized molecular doped mesoporous structure by direct and simple procedure.

A common method of reducing vibration levels in structures is to coat the surfaces of the structure with a layer of viscoelastic materials which dissipates the elastic strain energy induced by the dynamic loading. The passive damping material is placed in areas of high strain energy to extract as much energy as possible from the structure, but the exact location of the material can tend to be arbitrary. A more systematic approach is demonstrated which uses an evolutionary method which allows viscoelastic surface coatings to be gradually built up until the required damping is achieved. In this way the material can be placed in a more efficient manner, and it is proposed that this leads to a better damping performance.

Quantifying changes in the tension of an anterior cruciate ligament (ACL) graft in vivo during rehabilitative exercises is vital for developing the optimal rehabilitation for patients who have had reconstructive surgery. The purpose of this project was to design, built, and test a telemetry system that can measure the in vivo ACL graft tension postoperatively. A commercially available fixation device was modified to sense the graft tension, house electronic components, transmit an output signal, and pass the power generating signal. A transcutaneous inductive link was used to power the implanted telemetry electronics. The current difference technique was used to measure changes in two strain gages that monitored shear strain developed on the femoral fixation device by the ACL graft. This current regulated a frequency modulated output signal and transmitted it, by using the ionic properties of body tissue as the medium, to external EMG surface electrodes. A signal conditioning board detected and converted the output to an analog voltage for collection by a computer data acquisition system. A performance evaluation demonstrated that the telemetry system either met or exceeded al of the criteria necessary for the application.

This paper outlines the progress in the development of a biomimetic, prefabricated synthetic building material that is to have the superior properties of bone. The goal was to make polymer/ceramic composite which mimics bone in both process of fabrication and resultant properties and bond between phases, because bones and shells have been found to have greater toughness and strength than conventional ceramics alone due to the presence of organic bonding materials. The intimate connection between material phases is due to careful growth sequences, i.e. the fibers are made first and the matrix grown around them as opposed to conventional ceramics in which any fibers are added to the matrix. We followed the rules under which bone material naturally forms albeit at a macroscale, as spelled out by researchers in biological materials.

Cyclodextrin thin films were fabricated using either self- assembled monolayers (SAM) or sol-gel techniques. The resulting host receptor thin films on the substrates of surface acoustic wave (SAW) resonators were studied as a method of tracking organic toxins in vapor phase. The mass loading of surface-attached host monolayers on SAW resonators gave frequency shifts corresponding to typical monolayer surface coverage for SAM methods and `multilayer' coverage for sol-gel techniques. Subsequent exposure of the coated SAW resonators to organic vapors at various concentrations, typically 500 parts per millions down to 100 parts per billions (ppb) by mole, gave responses indicating middle-ppb-sensitivity (approximately 50 ppb) for those sensor-host-receptors and organic-toxin pairs with optimum mutual matching of polarity, size, and structural properties.

This paper describes the effect of electromechanical phase on electrical resistivity of a composite consisting of magnetostrictive phase, conductive phase and insulating phase. It is found that the resistance of three-phase composite increases with increase of applied magnetic field beyond a certain va1e ot magnetic field. This resistivity vs. magnetic field characteric seems to be a novel magnetoresistance effect, which is different from the conventional magnetoresistors. The mechanism of resistance variation of three-phase composite with applied magnetic field is analysed, and the influence of material parameter of the polymer matrix like elastic modulus on the resistance vs. magnetic field characterics is discussed.

A novel sensing material has been developed for constructing a sensor of solvent vapours using chemical coupling effect of composite, which is different from conventional electron-moving chemiresistors for use as gas sensors. The composites consisting of polymer loaded with conductive filler near the percolation threshold exhibit sensitive characters comparable to that of conventional semiconductor gas sensor but can be realized with much simpler technology and operated at room temperature. This sensor can also obtain better selectivity by choosing different polymer matrix. Theoretic analysis and experimental results show sensitive properties of composite sensor greatly depend on composition of composite and grain size of conducting particles. In general resistance variation R/Rin the presence of vapor is more for higher volume fraction offiller and larger grain size of conducting particles.

Structure-sensitive materials, or the so-called "smart materials", which change their properties under the action of external fields (e.g. electric, light or temperature field) can find a wide use in various industrial applications as sensors, measuring elements of various types, radiation detectors, membranes, etc. In this connection, we have examined the conditions of formation of electrosensitive films based on copolymers of vinyledene fluoride (VDF) with tn- and tetrafluoroethylene. The films have been prepared from solutions in organic solvents (acetone, dimethyl sulfoxide (DMCO), dimethyl formamide (DMFA) and ethyl acetate). Based on the results of investigations of the temperature dependencies of the dielectric permittivity, surface charge density and tangent of dielectric losses, we have evaluated the effect of film formation conditions and a copolymer type on the molecular mobility, formation of electrets and charge relaxation in the temperature range 20-200 °C. It has been concluded that in the non-orientated films there exists a relationship between the charge relaxation and the molecular mobility of the C-F dipoles in amorphous and crystalline regions of the polymer matrix. At the same time, the charge relaxation in orientated materials occurs in the crystalline regions of the polymer matrix. The optimal conditions have been specified for the production of such materials from solutions in organic solvents.

In composites reinforced with Shape Memory Alloy (SMA) wires, SMA wires play a role of distributed actuators to achieve athptive functions while in seivice. This paper presents the theoretical study on the thermo-mechanical characteristics of composites reinforced with SMA wires, based on the one-dimensional constitutive relation of SMA. Experimental results derived from tension, free recovery and restrained recovery of composites reinforced with SMA wires are presented and compared th the simulated results.

The Ti(C,N) film has been synthesised by ion beam assisted deposition in our study, in which a TiC target was bombarded by argon ion beam. Sputtreing depositionof Ti, C and bombardment with argon ion beam were done simultaneously under the environment of nitrogen gas. The component depth profiles and structure of the film were analysed by means of AES and X-ray diffraction. Our results shows that the Ti(C,N) film was composed of TiC crystallites with random orientation and composed of TiN crystallites with preferential orientation and with small grain size. It was confirmed that there is a wide intermixed region of Ti, C, N and Fe atinterface between the film and the substrate. The Ti(C,N) film formed by ion beam assisted deposition exhibits superior hardness and improvement over the wear resistance and friction properties.

Reported in this work are load characterization of electroactive films made out of polymeric ion-exchange membrane materials treated with a noble metal such as platinum. Load characterization under oscillating voltage input on the resulting composite samples was then performed using a PC-platform data acquisition system, variable signal generator, amplifier and load cells. For fixed signal frequency, various shape signals at low voltage amplitudes were then applied and the corresponding induced forces measured by the load cells and recorded via the data acquisition setup. The applied input signals consisted of sinusoid, square, saw tooth, and triangular form in order to observe the difference in behavior and the resulting output forces of the actuators. A briefdescription ofa proposed theory for this type ofactuator was then discussed. The results showed that these actuators exhibit good force to weight characteristics in the presence oflow applied voltages.

In this research, feasibility of using ion-exchange- membrane-metal composite artificial muscles as linear platform type actuators was studied. In order to achieve linear motion from these typically bending type actuators, a series of muscles made from ion-exchange-membrane-metal composites were cut in strips and attached either end-to-end or to one fixed platform and another movable platform in a cylindrical configuration. By especially prepared electrodes embedded within the platforms one can convert the bending response of each strip into linear movement of the mobile platform. By applying a low voltage the movement of free end of the actuator could be calibrated and its response could be measured, accordingly. A theoretical model was developed and was compared to experimental results. Ion-exchange- membrane-model composites are highly active actuators that show very large deformation in the presence of low applied voltage and exhibit low impedance.