In our continuing efforts towards the design of an ordered three-dimensional network of nonlinear-optical chromophore-substituted polymer chains with controlled optical properties (the so-called smart filter), molecular simulations of polypeptide-bound chromophores and siloxane-based liquid crystals are presented. The importance of chromophore substitution on the amount of polypeptide helix destabilization was demonstrated, and similar effects are shown to exist for (L-tyrosine) in this study. Molecular dynamics simulations also indicate that the charged Congo Red substituent destabilizes the polypeptide, showing larger helix bending and backbone dihedral angles variations resulting from interactions with the NLO moiety. Understanding these molecular ordering phenomena is critical to our ability to design new materials with tailored optical properties.

Theoretical models describing the dynamic behavior of the expansion and contraction of polyelectrolyte gels present numerically challenging problems. This paper describes how a method of weighted residuals approach has been used to solve the two-dimensional governing system of equations by finite element analysis. The modulation of the imbibition/expulsion of solvent by a gel disk is studied as an example.

In this paper, a method to make a new kind of piezoelectric composite material that can cancel the thermal bending deformation is proposed. The new composite material is composed of two layers: one layer of main material on the working surface and another layer of piezoelectric material on the opposite side which is used as an actuator to cancel thermal bending deformation. The finite element method is used to analyze the stress distribution and deformation in the new material. An example of application of this method to functionally gradient material is given out.

Conjugated polymers are currently of extensive interest because they can be doped to become electronically conductive. Actually, they can be repeatedly driven between the conductive and insulating states by electrochemical redox in an electrolyte solution or by chemical redox in a solution or in a gaseous atmosphere. Small volume changes, up to 10%, occur during the transitions. We use the bending bipolymer strips, with a conjugated polymer layer and an inert polymer substrate layer, to sense the volume changes in the responsive conjugated polymer layer.

Based on recent experimental observations on the behavior of ionic polymeric gels in the presence of pH and electric fields performed in our laboratories, a dual macroscopic theory is proposed for the nonhomogeneous large deformations of such gels. The proposed theory presents two distinct mechanisms for the nonhomogeneous reversible large deformations and in particular bending of strips of ionic polymeric gels in the presence of both a pH field and an electric field. It is concluded that direct voltage control of such nonhomogeneous large deformations in ionic polymeric gels is possible. These electrically controlled deformations may find unique applications in robotics, artificial muscles, large motion actuator designs, drug delivery systems and smart materials, adaptive structures and systems.

Smart materials are expected to adapt to their environment and provide a useful response to changes in the environment. Both the sensor and actuator functions with the appropriate feedback mechanism must be integrated and comprise the `brains' of the material. Piezoelectric ceramics have proved to be effective as both sensors and actuators for a wide variety of applications. Thus, realistic simulation models are needed that can predict the performance of smart materials that incorporate piezoceramics. The environment may include the structure on which the transducers are mounted, fluid medium and material damping. In all cases, the smart material should sense the change and make a useful response. A hybrid numerical method involving finite element modeling in the plate structure and transducer region and a plane wave representation in the fluid region is used. The simulation of the performance of smart materials are performed.

Two coupled systems of partial differential equations governing three-dimensional laminar viscous flow undergoing solidification or melting under the influence of arbitrarily oriented externally applied magnetic fields have been formulated. The model accounts for arbitrary temperature dependence of physical properties including latent heat release, effects of Joule heating, magnetic field forces, and mushy region existence. On the basis of this model a numerical algorithm has been developed and implemented using central differencing on a curvilinear boundary-conforming grid and Runge-Kutta explicit time-stepping. The numerical results clearly demonstrate possibilities for active and practically instantaneous control of melt/solid interface shape, the solidification/melting front propagation speed, and the amount and location of solid accrued.

To obtain a better understanding of the effects of electric fields on the fatigue lifetime of PZT materials, specimens of poled and unpoled PZT-8 were either pre-indented to generate a pre- crack or indented in the presence of an applied static electric field. Significant differences in the crack growth behavior perpendicular and parallel to the poling direction were observed in static and time-varying electric fields leading to a reduction in the fracture toughness normal to the poling axis. Fatigue crack growth was significant at field amplitudes as low as 5% of the poling fields. These results are shown to be related to the effects of electrical fields on the stresses at the crack tip.

The influence of interphase and matrix stiffness on the sensitivity of 1 - 3 piezocomposites is investigated. An analytical model is first developed to predict the static out-of-plane displacements of a single piezoelectric rod composite. The model accounts for the transversely isotropic nature of the ceramic rod and the presence of an interphase region with different properties from the surrounding matrix. Laser interferometry was then utilized to measure displacement profiles for samples consisting of a single PZT-5H rod embedded in Spurr epoxy. Three different interphase conditions were considered. Both the experimental measurements and theoretical predictions demonstrated that changes in the interphase modulus had a significant effect on the maximum displacement on the rod. Rod displacement and sensitivity decreased with increasing interphase stiffness.

This paper describes an investigation of the microstructural characteristics for three surface- mounted optical fiber sensors bonded to structural composites for high temperature applications. The primary objective was to identify defect generation mechanisms that occur during thermal cycling and to make processing and testing recommendations that would optimize their measurement performance. A second objective was to identify areas of microstructural research that would have the most significant impact on the development of high temperature smart materials. The three high temperature smart material systems investigated were: (1) a silica optical fiber sensor bonded to a titanium-matrix composite (TMC) using a nickel-base plasma spray, (2) a silica optical fiber sensor bonded to a TMC using a ceramic cement, and (3) a sapphire optical fiber sensor bonded to a carbon-carbon composite (CCC) using a ceramic cement. The microstructure of each system was characterized in terms of morphology and fracture mechanisms using conventional microscopic, metallographic, and analytical techniques.

The effects of embedded fiber optics (FO) on the mechanical properties of a graphite/epoxy composite host material were studied. Optical fibers 125 micrometers and 240 micrometers in diameter were embedded in AS4/3501-6 graphite/epoxy, and the static performance of the material was evaluated. FO were placed in the midplane of the specimens both parallel and perpendicular to the loading direction. The mechanical tests included O degree(s) compression, 90 degree(s) tension, (0, +/- 45, 90)_S tension, and first ply failure of (O₂, 90₂)_S specimens. Microstructural analysis of the fracture surfaces showed little influence of the FO on crack initiation or propagation. Test results showed no distinct influence of the FO on failure strength or modulus, but did open questions on the coupled effects of processing history, FO embedment, and failure strength.

This project demonstrated the implementation of embedded optical fibers as sensors for detecting the onset of shell buckling instabilities and compressive failure in composite cylinders. In the present work, five 6-inch diameter cylinders (four filament-wound and one prepreg tape) with integrated optical fiber strain sensors were fabricated and tested in compression. The cylinders were instrumented with an axial strain gage for local strain measurements and a helically wound 633 nm optical fiber for integrated strain measurement. The integrated strains along the optical fiber path were obtained by using a modified Mach- Zehnder interferometer with feedback electronics controlling PZTs in the reference arm. This distributed sensing technique provides a more reliable and sensitive means of detecting critical strains and the onset of pre-buckling deformations than the conventional local strain gage.

Versatile control of the microwave signature of a complex object under the command of a central/local processor(s) requires a bias/communications network to be embedded in a smart surface treatment and distributed over distances small compared to the shortest wavelength of interest. One requirement of the system is that the bias and microwave signal paths be isolated for all configurations of the smart surface. It is also required that the surface impedance of the treatment satisfy an impedance boundary condition to allow the processor to use an efficient electromagnetic computational code. A design approach that accommodates these requirements incorporates the bias conductors as an integral constituent of a new smart microwave material called an `effective surface;' the two dimensional equivalent of an effective media.

Carbon fiber plastic composite is prepared using vapor-grown carbon fibers (VGCF) as filler with thermo-plastic resin. Basic electrical properties and the stability of electrical conductivity of VGCF's composite in comparison with those using conventional carbon filler such as PAN- based carbon fibers (PAN) and electroconductive carbon black (CB) are studied. The VGCFs have lower resistivity than those of PAN and CB filler based composites at room temperature. The composite where the VGCF added with CB as mixing filler to matrix resin shows lower resistivity than those using VGCF or CB filler individually. This mixed filler composite has a high EMI shielding effect in the near-electric field. The value of EMI shielding effects is 70 dB at 2 mm sample thickness. On the stability of electrical conductivity, VGCFs and mixed filler composites have better performances than PAN-based ones under tensile stresses, bending stresses, temperature change and exposure test in air at a constant temperature (room temperature and 60 degree(s)C). The VGCF based composites are applicable as a useful electroconductive composite.

This paper describes a new smart material system using intercalated graphite as the material and using exfoliation as the phase transition that gives rise to the electromechanical switching action. In this action, a stress of up to 3 MPa (400 psi) or a strain of up to 4500% results reversibly from an applied electric field of only 7 V/cm. This high-stress high-strain low- electric-field type of electromechanical switching is in sharp contrast to the electromechanical switching provided by piezoelectric materials. The exfoliation is a phase transition involving the vaporization of the intercalate between the graphite layers to form bubbles. For bromine as the intercalate, the bubbles remain mostly closed and exfoliation is reversible. The resulting stress or strain is along the c-axis of the graphite, so highly oriented pyrolytic graphite and graphite flakes are both possible for achieving electromechanical switching.

One of the technical goals in underwater acoustics is to design coatings to reduce the acoustic echo from submerged structures to avoid detection versus active sonar systems. At sufficiently high frequencies, this can be done using passive materials. At low frequencies, however, the task is more difficult, and active systems are under consideration. The purpose of this paper is to summarize the different principles of acoustic active control that can be considered and to point out advantages and difficulties, with a few examples. They include: (1) piezoelectric (pseudo-passive) coatings; (2) control of the impedance of a piezoelectric transducer; (3) distributed array of local sensor/actuator systems; (4) combined sensor and actuator arrays.

A smart sensor, that can distinguish between different directional components in a superimposed acoustic pressure field, was developed as a part of the active acoustic coating system for absorbing sound energy incident on an underwater object. The smart sensor system includes a dual sensor pair encapsulated inside the coating and a multichannel digital delay-line network so that both the incident and the reflected wave signals can be extracted simultaneously. Furthermore, the delay-line network was interfaced with a personal computer to adaptively adjust the system parameters so that the performances of the smart sensor as well as the overall active system were optimized. The sensors were made of a piezoelectric polymer material known as polyvinylidene fluoride (PVDF). This flexible material offers significant advantages for underwater acoustic applications such as high and uniform sensitivity, impedance matching with water, etc. Theoretical model and experimental implementation and testing results are presented in this paper.

There is considerable interest in the development of microwave ceramic phase shifters because of limitations of currently available ferrite and PIN diode phase shifters regarding cost and reliability and complexity. Ceramic phase shifters may provide a cost breakthrough for the phased array antenna designer while maintaining low insertion losses and low drive power and high power handling capacity. This paper describes ceramic phase shifters which utilize a ferroelectric material [(Ba-Sr)TiO₃ series] for obtaining phase shifts from changes in dc biasing fields. Also, the dielectric properties are measured as a function of dc biasing fields, frequency and temperature for a few compositions of barium-strontium titanate material. For the frequency range of 400 MHz to 5 GHz, differential phase shift is obtained by a dc voltage-controlled lumped barium-strontium titanate capacitor in a coaxial line or stripline medium. For 5 to 18 GHz frequency range, a barium-strontium titanate material which partially or completely fills the rectangular waveguide is required for the construction of a ceramic phase shifter.

Using smart materials and skins, one could design a smart structure with suitable feedback system architecture. This paper is designed to address some technical advances and applications of smart materials, smart skins and coatings covering a broad spectrum of electromagnetic fields. The Smart Skin Antenna Technology Program's objectives are to (1) use smart skin technologies to develop an antenna system architecture which is structurally integratable, wideband, and embedded/conformal; (2) design, develop, and fabricate a thin, wideband, conformal/arrayable radiator that is structurally integratable and which uses advanced Penn State dielectric and absorber materials to achieve wideband ground planes, and together with low RCS, wideband radomes; (3) implement a smart skin antenna system architecture. Traditional practice has been to design radome and antenna as separate entities and then resolve any interface problems during an integration phase. A structurally integratable conformal antenna, however, demands that the functional components be highly integrated both conceptually and in practice. Our concept is to use the lower skin of the radome as a substrate on which the radiator can be made using standard photolithography, thick film, or LTCC techniques.

The advantages of integrating an electromagnetic antenna into the skin of an aircraft and the constraints imposed on the materials are described here in two precise examples: an ultra broadband antenna for a counter-measure pod and an active antenna for X band radar. The first part of this paper shows the improved electromagnetic performances and the simplified production methods allowed by the integration of an omnidirectional spiral ultra broadband antenna into the radome, constituting the head of the counter-measure pod. The performances of the preliminary version, made up of a flat spiral antenna localized behind its hemispheric radome, are described as a reference. The various solutions used for the integration of the radiating spiral and its balun directly inside the hemispheric radome are then described, and the constraints applicable to the materials are given for each solution. The second part of this paper investigates the problems faced when integrating an X band active radar antenna. Finally, we examine the new possibilities available in the furtivity field.

The dependence versus magnetic field of the different mechanisms which contribute to the permeability spectrum (mu) (f) of a ferrimagnetic material are studied. The observed permeability variations depend on the frequency and on the intensity and the direction of the applied field; they can be used in order to realize different tunable microwave components.

This paper reports the progress attained in reducing electromagnetic interference (EMI) using UV-cured conformal coatings. A glass-epoxy PC board with two signal traces on one side and a ground plane on the other was used to measure the reduction in crosstalk. Measurements were made for several ordinary conformal coatings and several new EMI reducing coatings. The effectiveness of the EMI reducing coatings was also tested on commercial walkie-talkies.

A method to study electromechanical behavior in piezoelectric laminated structures is presented. An accurate electromechanical description is mathematically involved, requiring quite often the adoption of ad hoc and unrealistic assumptions. An alternate approach to existing techniques is proposed in this paper. Emphasis is placed in a two-dimensional formulation to describe the behavior of electroelastic layered media. The methodology consists of rewriting the field equations of piezoelectricity in terms of a combination of certain electrical and mechanical variables collected into a state vector. Integral transformations are used to produce an ordinary differential equation for the state vector, whose solution is given in terms of a transfer matrix. The virtue of this approach is that the transfer matrix allows us to furnish information on local as well as global electromechanical behavior with equal ease. The resulting consequences of the methodology are the prediction of changes of geometry that will occur in a structure in response to a controlled command, and a more efficient means of structural actuation.

The design and analysis of finite length multiple layered induced strain actuators to further extend the application of piezoelectric actuators in active structural control is investigated. A model of an arbitrary surface bonded multiple layered actuator is utilized to predict the applied force and moment of the i^th piezoelectric layer on a beam. The equations of motion for the transverse vibration of a simply supported beam are derived using Timoshenko beam theory and cast in state space form. The forced response of the one dimensional actuator/substructure system to the piezoelectric induced loads is obtained using an assumed mode technique. The results of experiments performed on a simply supported beam, using various multiple layer piezoelectric actuator configurations for excitation, are compared to analytical predictions for model verification.

Piezoelectric actuators and sensors made of tubular structure can provide a great agility of the effective response in the radial direction. For a radially poled piezoelectric tube, the effective piezoelectric constant in that direction can be tuned to be positive, zero, and negative by varying the ratio of the outer radius (R₀) to the inner radius (r₀) of the tube. For a suitable ratio of R₀/r₀, this effective constant can also be changed in sign or set to zero by adjusting the dc bias field level for tubes made of electrostrictive materials. Therefore, one can make a piezoelectric transducer with all the effective piezoelectric tensile constants having the same sign. The end capped thin wall tubes also exhibit exceptionally high hydrostatic response and the small size of the tubular structure makes it very suitable for integration into 1 - 3 composite which possesses low acoustic impedance and high hydrostatic response.

Natural phlogopite micas have anomalously high, yet reversible thermal expansion, over 100% at 600 degree(s)C, attributed to non-structural water entrapped between the silicate layers. Above 100 degree(s)C, the mica-water vapor composite expands like a gas in an elastic membrane, stable to repeated thermal cycling to over 600 degree(s)C. Muscovite mica-noble gas composites are prepared by implantation and are stable with time and temperature to 600 degree(s)C. The behavior of the implanted gas is studied by Rutherford backscattering and transmission electron microscopy. Helium diffuses out slowly over a period of six months. A capacitometer is required to measure the thermal expansion of implanted specimens less than 1 micrometers thick.

A pure PZT piezoceramic is unable to generate or sense twisting motion for applications including beams, plates, or shell panels because of its transverse isotropy (mm 6 symmetry), which permits only a bending motion. The design of a piezoceramic/polymer composite element which is orthotropic in the plane is the key to producing twisting motion, since this composite is stiff enough to provide actuation. The composite element can also sense twisting. With the requirement of orthotropy in mind, composites have been made by cutting rods from a PZT plate and placing them in an epoxy matrix. A plate theory analysis provides information on the optimum orientation angle of the PZT/epoxy composite to provide twisting actuation and sensing.

Exact relations are obtained between the effective thermoelectroelastic moduli of two-phase composite materials and their corresponding isothermal electroelastic moduli. The relations are a generalization of the well-known results of Levin and Rosen and Hashin to the inherently anisotropic coupling between the electric and elastic fields in thermoelectroelastic composites. The exact relations can be used to obtain the effective thermal expansion and pyroelectric coefficients of the composite when the effective electroelastic (elastic, piezoelectric, and dielectric) moduli are known, either by theory or experiment. Attention is focused on two- phase thermoelectroelastic laminates which admit an exact solution for the electroelastic, and thus the thermoelectroelastic, moduli. The results also provide a means to asses the internal consistency of any approximate micromechanics model that is proposed to estimate the thermoelectroelastic moduli of two-phase composite materials.

Acoustic fibers are potential candidates for developing sensors used in nondestructive evaluation (NDE) and process monitoring of composite materials. Acoustic fibers, like optical fibers, are easily embedded into polymeric composite materials. Because of the mechanical nature of the acoustic wave, acoustic fibers have direct sensing abilities on the variation of mechanical properties of their surrounding materials. Two experimental fiber acoustic sensors are developed. One is applied to detect the changes of properties of cured RHO-C rubber with temperature. Another is used to monitor the curing process of epoxy. Test results show the feasibility of applying the fiber acoustic sensors to NDE and process monitoring for polymeric materials.

Piezoelectric composites are being developed for use as active materials in isolation mounts. The ability to sense and respond to both longitudinal and shear waves is required. Composites have been fabricated with piezoelectric rods at different angles with respect to the surface. The response of the piezoelectric rods to a sharp impulse on the 1 - 3 composite plate increases abruptly at angles less than 60 degrees from the surface of the plate. Angled rods aligned radially are more sensitive then similarly angled rods aligned normal to the signal source. Mechanical impact and embedded acoustic generators at the center of the composite produced the signals for the sensitivity experiments. Oriented piezoelectric ceramic elements allow design of materials for specific mode control and also provide an excellent tool for in-situ nondestructive testing of materials.

This work presents experimental and theoretical results on the dynamic behavior of piezoelectric cantilever bimorph in the presence of surrounding air. The bimorph is composed of a pair of piezoelectric sheets bonded by a uniform elastic layer of adhesive in the center. The transverse motion of the bimorph is generated by a sequential application of two opposing electric fields on the piezoelectric sheets. Theoretically, the tip deflection and the natural frequency of the bimorph are obtained making use of an energy balance technique. The fluid in modeled as inviscid and incompressible whose motion induces locally additional mass in the transverse direction. An expression for the kinetic energy of the system is derived based on this additional mass from which the natural frequency of the combined system is obtained. Tests were performed on the piezoelectric bimorphs with similar geometries and varying adhesive thickness in a vacuum chamber. The air pressure in the chamber was varied from 10 kPa to one atmosphere. Good agreements between the theoretical predictions and the observed values were obtained. This study could have applications in the use of piezoelectric materials for fluid property measurements.

Dynamic displacement measurements have been made on type 1 - 3 piezocomposite materials using scanning heterodyne interferometry to map the magnitude and phase of surface displacements. Specimens were electrically driven using sinusoidal voltages at frequencies below 25.0 kHz. All the materials studied consisted of square cross section PZT-5H rods arranged in a periodic square array and embedded in an epoxy resin matrix. The volume percentage of rods varied between 9 and 20 percent and matrices of varying hardness were used. In addition, a sample with a modified matrix to rod interface was measured. For the hard interface material, the rods and matrix tended to move together, while for the soft interface materials, rods displaced much more than the matrix. At low audio frequencies the samples exhibited both plate wave and thickness modes. The plate wave amplitudes were comparable to or larger than rod amplitudes for specific combinations of frequency and boundary conditions.

Solid state nuclear magnetic resonance (NMR) has been shown to be a unique spectroscopic tool for determining molecular composition, crystallinity, packing, orientation and motion in as-obtained and end-use materials. We have developed several methods for evaluating the molecular-level properties and behavior of polymeric materials, especially piezoelectric nylons. Analysis of nylon 7 homopolymer under various sample treatment histories related to poling and generation of piezoelectric properties allows qualitative evaluation of the two main types of crystal forms present, the (alpha) -form which appears to be the one responsible for piezoelectric behavior in this polymer, and the (gamma) -form which can co-exist with the (alpha) -form in some samples. Based on the possibility that molecular composition could be used to control crystallinity and microscopic packing, and thereby affect macroscopic properties such as piezoelectricity, we have synthesized and characterized two families of nylon co-polymers consisting of even-odd A-B monomer combinations. We have determined degrees and types of crystallinity for these materials using a combination of thermal, FTIR and NMR, measurements. The molecular-level behavior of these materials is related to observed properties. Evaluation of piezoelectric properties is underway, and initial results are summarized.

An effort in designing and manufacturing a tunable frequency-selective multilayer coating material is reported. When a material (metallic or dielectric) is coated with such a composite layer, the reflection from this coated surface will follow a particular frequency spectrum which is application oriented. In addition, to achieve the required temporal frequency response, voltages of different magnitudes can be applied to different layers of the composite coating material at a different time. Because the dielectric constants of a number of layers can be altered temporally under this tuning process, the coated surface will respond to the observer in a specific manner at a given time. A multilayer coating whose constituent layers are made of different Porous Barium Strontium Titanate materials (BST) can provide great freedom and an unprecedented advantage in the design work. We can tailor and tune the properties of BST materials used in each layer provided these materials can be actually made in our research center. In addition, to satisfy the required spectral response, the detailed dispersion characteristics of the coating properties can be achieved by introducing sandwiched dielectric composite layers.

We provide exact equivalent network representations for the electromechanical behavior of crystal stacks that are piezoelectrically driven in simple thickness modes of vibration. These configurations are archetypes for many sensors and actuators under development for smart structure applications. The stacked configuration may consists of any number of layers, with each layer comprised of an homogeneous, but arbitrarily anisotropic crystal medium, whose constitutive equations are linear. No further limitations are imposed upon the elastic, piezoelectric, and dielectric coefficients of each stratum other than those required by energy considerations.

Mineralized biological tissues can be regarded as composites where a fine reinforcement is laid down in a very controlled fashion within a tough polymeric matrix. Such materials include bone, antler, tooth enamel, mollusc shell, and crustacean shell. We have been exploring ways of forming similar structures by synthetic routes involving precipitation of reinforcing particles directly into a polymeric matrix. Part of this biomimetic approach requires polymer matrices which can exert a high degree of control over the mineralization process. Polymer gels have been formed from cross-linked methacrylates with various types of functionality within the gel. By incorporating calcium binding groups we have been producing gels which lead to preferential mineralization of the gel when it is incubated in a supersaturated solution of calcium oxalate or calcium carbonate. Similarly we have been incorporating silane groups within the gel in order to promote the deposition of silica in a gel body when it is immersed in a metastable solution of partly hydrolysed silicon alkoxides.

Alloy films of Cu-Zn, Au-Cd, In-Tl, and In-Cd were produced using electrolytic techniques and their shape memory properties were evaluated. Cyanide solutions were used for the Cu-Zn and Au-Cd deposits, but sulfate solutions were preferred for the indium alloys. The use of pulsed current was beneficial in giving dense and uniform deposits. The Cu-Zn and Au-Cd alloys did exhibit a degree of brittle behavior in the as-deposited condition. Simple bending tests were conducted and shape memory effects were confirmed on the Cu-Zn and indium alloys. The phases present were determined at different temperatures using X-ray diffraction. The results show that electrolysis appears to be a feasible means of producing certain shape memory thin films with potentially interesting properties. However, more extensive studies are needed to optimize the performance of the electrodeposited alloy films.

Metal matrix composites (MMCs) have been studied intensively with expectation of applying MMCs to various structural and machine components. A recent summary of the thermomechanical behavior of MMCs has been given elsewhere.1'2 One of the important findings in the recent studies is that strengthening of MMCs is identified by two mechanisms: back stress strengthening and dislocation punching.3'4 In most MMC systems, the coefficient of thermal expansion (CTh) of reinforcement is smaller than that of metal matrix, resulting in tensile residual stress in the matrix at room temperature. This tensile residual stress in the matrix reduces the tensile flow stress (particularly yield stress) of a MMC.5 If the residual stress in the matrix in a MMC is controlled to be compressive, the tensile flow stress of the MMC is expected to be increased. A shape memory alloy (SMA) fiber, after its shape is memorized and presirained at martensitic phase, can shrink to its original length upon heating to austenitic finish temperature. If such shrinkable SMA fibers are embedded in a metal matrix to form a MMC, compressive residual stress in the matrix is induced at austenitic stage, resulting in enhanced tensile flow stress of the MMC, see the process of inducing such compressive residual stress in the matrix in Fig. 16. Motivated by the above idea depicted in Fig. 1 ,we are led to process TiNi SMA fiber/i 100 Al matrix (TiNi/Al) composite by pressure casting route, the details of which has been given elsewhere6. As-processed TiNi/Al composite was machined to tensile specimen of flat bar type and given tensile prestrain c at martensitic stage, then heated to 363K just above the austenitic finish temperature (337K), followed by tensile testing at 363K. The results of the stress-strain curves of TiNi/Al composite with and without prestrain, and unreinforced Al are shown in Fig. 2. It is obvious from Fig. 2 that the flow stress of the TiNi/Al composite with prestrain is higher than that of the composite without it, which in turn is higher than the unreinforced metal due to back stress strengthening mechanism. The strengthening due to prestrain is the main subject of this paper. The analytical model similar to the present one has been developed for the analysis of a short fiber SMA fiber MMC.7 Analytical modeling will be stated in section II and numerical results and comparison with the experimental results will be discussed in Section III, followed by the conclusion in Section IV.

Smart materials composed of ferroelastic and ferroelectric materials are described for damping of mechanical waves. These heterostructures using active and adaptive materials will likely be represented by heterostructures of several types of thin and thick films. In this investigation, deposition and processing of thin film ferroelastic TiNi and thin film ferroelectric BaTiO₃ and Pb(Zr,Ti)O₃ are discussed. Growth conditions as well as the thermodynamic conditions for successful synthesis are described. it was found that amorphous thin films of TiNi and BaTiO₃ can be crystallized simultaneously by air annealing at 600 degree(s)C. Onto bulk TiNi samples, PZT was synthesized successfully, with good mechanical bonding.

Critical components of many smart systems employ multilayer piezoelectric actuators based on lead zirconate titanate (PZT) ceramics. Applications include active vibration systems, noise suppression, acoustic camouflage, actuated structures, reconfigurable surfaces, and structural health monitoring. Two strategies involving novel materials processing techniques are discussed for improving the performance and reliability of PZT ceramic components. The first is the use of an advanced powder synthesis, which was recently developed for a range of DoD specification materials. The second strategy involves two improved ceramic manufacturing routes designed to replace the current tape casting and co-firing method. One is the use of roll- compaction for tape forming. The other is the application of the infiltrated electrode approach. Both of these methods provide improved electrical and mechanical performances and superior reliability.

Sol gel processing of ceramic materials has attracted much interest in the past decade because of its inherent advantages in homogeneity of the resulting powder, fine grain size, high purity, and ability to mix disparate materials well. Sol gel processing is particularly apt to tunable electroceramics such as barium strontium titanate (BST) because of the fine grain size and purity desirable in such materials. It may be desirable to develop a semiautomatic system to produce the tunable ceramic powder, thin film and ceramic devices. Thin film tunable ceramics can be deposited on to a substrate with or without conductive traces by using a microwave plasma deposition system. In this paper, we have shown such a system incorporating microwave power for calcination, binder burn out and final sintering to a near net shape manufacturing of ceramic devices. This paper also describes the sol gel processing method for BST and compares properties of materials prepared by the sol gel method and the more conventional carbonate and oxide powder method.

A theoretical model is presented for the derivation of a mathematical relationship between the volumetric strain of an ionic polymeric gel and its pH. The model presented also applies to polyelectrolytes in aqueous solutions. The derivation uses an expression for the total electrostatic free energy per single polyelectrolyte molecule which involves a quasi-Debye curvature, the local absolute temperature, the geometric features of polyelectrolyte molecule, the dielectric constant of the gel as well as the local ionic concentrations for the fixed and the mobile charges. The gradient of the free energy with respect to the number of fixed ions is then related to the pH, i.e., the local concentration of hydrogen ions H⁺, the absolute temperature T and the degree of ionization (alpha) which is defined as the ratio of the number of moles of H⁺ to the number of moles of the ionizable groups fixed to the ionic gel network. Subsequently, the gradient of the free energy is related to the volumetric strain of the ionic gel network.

Smart structures with active ceramic segments typically consist of piezoceramic layers bonded to elastic members. Analytical modeling of piezoceramics has been addressed by many authors. Developments to date allow one to model planar structures and homogeneous piezoceramic continua. Most smart structures with piezoceramic control layers have multi- layered plate and shell geometries distributed in three-dimensional space. In this study, a composite shell finite element is developed for modeling such structures. The element developed is a general quadrilateral shell with eight nodes and curved edges. This paper describes the development of the element including a method for modeling the excitations to the bonded piezoceramic. Analytical and experimental results are presented for a commercial bimorph validating the performance of the element.

An investigation was made into the feasibility of developing a smart polymer matrix composite which has the ability to self-repair internal microcracks due to thermo-mechanical loading. The investigation focuses on the controlled cracking of hollow repair fibers dispersed in a composite and the subsequent timed release of chemicals which results in the sealing of matrix microcracks and the rebonding of damaged interfaces. In this preliminary work, the mechanisms of chemical release from a single repair fiber embedded in a polymer matrix were investigated using experimental analyses. It was found that controlled cracking of the repair fiber and subsequent release of the repair chemicals could be achieved by applying a polymer coating to the surface of the repair fibers. Release of chemicals into cracks was observed using optical microscopy and photoelasticity. Fiber pull-out and impact tests were performed to examine the ability to rebond fibers and fill cracks, respectively.

Electrically conducting concrete, as provided by the addition of short carbon fibers (0.2 - 0.4 vol.%) to concrete, can function as a smart structure material that allows non-destructive electrical probing for the monitoring of flaws. The electrical signal is related to an increase in the concrete's volume resistivity during crack generation or propagation and a decrease in the resistivity during crack closure. The linearity between the volume resistivity change and the compressive stress was good for the mortar containing carbon fibers together with methylcellulose as a dispersant; when the compressive stress was increased in the first cycle up to the fracture stress, the volume resistivity increased by 1040%. In contrast, mortars without carbon fibers showed no variation of the resistivity upon compression up to fracture.

Like every dynamic output device, piezoceramic (PZT) actuators have their own output characteristics. The output characteristics of PZT actuators are functions of frequency and may be treated as frequency independent only in a certain frequency range. The dynamic excitation provided by a PZT actuator depends on its dynamic characteristics and structural mechanical impedance. The conventional method of using the statically determined induced moment or the force of PZT actuators as forcing functions is not correct. This paper uses a simple example, a PZT actuator-driven one-degree-of-freedom spring-damper-mass system, to illustrate the methodology used to determine the dynamic characteristics of PZT actuators and the structural response based on the concept of structural impedance.