This PDF file contains the front matter associated with SPIE Proceedings Volume 8689, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

Nanocomposites containing high dielectric permittivity ceramics embedded in high breakdown strength polymers are currently of considerable interest as a solution for the development of high energy density capacitors. However, the improvement of dielectric permittivity comes at expense of the breakdown strength leading to limit the final energy density. Here, an ultra-high energy density nanocomposite was fabricated based on high aspect ratio barium strontium titanate nanowires. The pyroelectric phase Ba_0.2Sr_0.8TiO₃ was chosen for the nanowires combined with quenched PVDF to fabricate high energy density nanocomposite. The energy density with 7.5% Ba_0.2Sr_0.8TiO₃ nanowires reached 14.86 J/cc at 450 MV/m, which represented a 42.9% increase in comparison to the PVDF with an energy density of 10.4 J/cc at the same electric field. The capacitors have 1138% greater than higher energy density than commercial biaxial oriented polypropylene capacitors (1.2 J/cc at 640). These results demonstrate that the high aspect ratio nanowires can be used to produce nanocomposite capacitors with greater performance than the neat polymers thus providing a novel process for the development of future pulsed-power capacitors.

Multi-Fiber Composites^™ (MFC’s) produced by Smart Materials Corp behave essentially like thin planar stacks where each piezoelectric layer is composed of a multitude of fibers. We investigate the suitability of using previously published inversion techniques [9] for the impedance resonances of monolithic co-fired piezoelectric stacks to the MFC^™ to determine the complex material constants from the impedance data. The impedance equations examined in this paper are those based on the derivation by Martin [5,6,10]. The utility of resonance techniques to invert the impedance data to determine the small signal complex material constants are presented for a series of MFC’s. The technique was applied to actuators with different geometries and the real coefficients were determined to be similar within changes of the boundary conditions due to change of geometry. The scatter in the imaginary coefficient was found to be larger. The technique was also applied to the same actuator type but manufactured in different batches with some design changes in the non active portion of the actuator and differences in the dielectric and the electromechanical coupling between the two batches were easily measureable. It is interesting to note that strain predicted by small signal impedance analysis is much lower than high field stains. Since the model is based on material properties rather than circuit constants, it could be used for the direct evaluation of specific aging or degradation mechanisms in the actuator as well as batch sorting and adjustment of manufacturing processes.

Correlations between quantum mechanics and continuum mechanics are investigated by exploring relations based on the electron density and electrostatic forces within an atomic lattice in ferroelectric materials. Theoretically, it is shown that anisotropic stress is dependent upon electrostatic forces that originate from the quadrupole density. This relation is directly determined if the nuclear charge and electron density are known. The result is an extension of the Hellmann-Feynman theory used to quantify stresses based on electrostatics. Further, flexoelectricity is found to be proportional to the next two higher order poles. These relations are obtained by correlating a nucleus-nucleus potential and nucleus-electron potential with the deformation gradient and second order gradient. An example is given for barium titanate by solving the electron density using density function theory (DFT) calculations. Changes in energy and stress under different lattice geometric constraints are modeled and compared to nonlinear continuum mechanics to understand differences in formulating a model directly from DFT calculations versus a nonlinear continuum model that uses polarization versus the quadrupole density as the order parameter.

Ferroelectric material losses in devices ranging from sonar transducers to energy harvesters result in the conversion of energy to heat. Under small amplitude sinusoidal drive, either electrical or mechanical, the losses are expressed in terms of a loss tangent. This study addressed the effects of temperature and bias stress on large field dielectric loss in the presence of thermal and mechanical loading in lanthanum-doped lead zirconate titanate, Pb_0.92La_0.08(Zr_0.65Ti_0.35)_0.98O₃ (PLZT 8/65/35). This loss is associated with domain wall motion. Large field dielectric loss was experimentally measured using a technique that matches the area within a unipolar electric displacement – electric field hysteresis loop to an equivalent area ellipse-shaped hysteresis loop. The results indicate that the dependence of dielectric loss on bias stress changes with the onset of a thermally induced transition to slim loop behavior. Stress causes the dielectric loss to increase at low temperature and decrease at high temperature. This is consistent with changes in remnant polarization and saturation of the unipolar electric field – electric displacement hysteresis loops.

The behavior of 95/5 PZT subjected to bipolar electrical loading and hydrostatic pressure is studied experimentally. When 95/5 PZT is subjected to high enough hydrostatic pressure it undergoes a ferroelectric to antiferroelectric (FEAFE) phase transformation. Specimens were subjected to two pressure cycles from 0 to 550 MPa at a rate of 50 MPa/min under short circuit conditions. It was found that under the first pressure cycle the specimens undergo a FEAFE phase transformation at 330 MPa indicated by an abrupt compression of 2500 microstrain. Under the second pressure cycle, the transformation no longer occurs at a single pressure level, but is smoothed throughout loading. In another set of experiments, bipolar electric fields were applied up to 3 MV/m at discrete pressure levels. At low pressures, electric displacement-electric field plots exhibited open loop behavior characteristic of soft ferroelectrics. As the pressure was increased past the FE-AFE phase transformation threshold, the open loops closed to nearly linear dielectric. When the driving pressure was decreased the open loop behavior returned at a notably lower pressure level. The transformation pressure is therefore path dependent and is evidence of a pressure hysteresis.

The effects of compositional modifications on the antiferroelectric (AFE) to ferroelectric (FE) transition of lead lanthanum zirconate stannate titanate, (Pb_1-3x/2La_x)(Zr_1-v-zSn_vTi_z)O₃ ceramics were used to optimize this material for energy storage. The experimental results show that an increase of Sn⁴⁺ respect to Ti⁴⁺ increases the coercive field of AFE-FE transition and keeps the hysteresis at the minimal level. This increases both the energy density of material and energy efficiency relative to a linear dielectric. Another advantage of Sn⁴⁺ addition was a polarization increase at the switching field. The substitution of Zn⁴⁺ for Sn⁴⁺ at fixed Ti⁴⁺ concentration of 0.1 was, however, undesirable for energy storage applications since this decreased the forward switching field and increased the hysteresis. This lowered both the energy density of the material and energy efficiency. Finally, addition of La³⁺ was performed and slim hysteresis loops were obtained resulting in energy efficiency of 80.1%. However, the slanted hysteresis behavior with La³⁺ results in a lower value of the maximum stored energy.

This paper presents a preliminary study of the effects residual plastic strains have on Lamb wave velocities and time of flight measurements. The potential application of this research is non-destructive evaluation and structural health monitoring, particularly reconstructing plastic strain fields. The finite deformation of a semi-infinite plate due to residual plastic strain is used to accommodate the changes in plate thickness and elongation. The results show that the S₀ mode exhibits significant variations in group velocity in the highly dispersive regions, as much as a 2% increase in velocity with a 1% plastic strain. However, for time of flight measurements, the plate elongation had an order of magnitude effect rather than showing velocity changes. By exploiting time delay measurements, it may be possible to use wave speed measurements to determine plastic zones through Lamb-like waves.

This paper presents the combined micromechanics analysis and finite element modeling of the electromechanical properties of piezoelectric structural fiber (PSF) composites. The active piezoelectric materials are widely used due to their high stiffness, voltage-dependent actuation capability, and broadband electro-mechanical interactions. However, the fragile nature of piezoceramics limits their sensing and actuating applications. In this study, the active PSF composites were made by deploying the longitudinally poled PSFs into a polymer matrix. The PSF itself consists a silicon carbide (SiC) or carbon core fiber as reinforcement to the fragile piezoceramic shell. To predict the electromechanical properties of PSF composites, the micromechanics analysis was firstly conducted with the dilute approximation model and the Mori-Tanaka approach. The extended Rule of Mixtures was also applied to accurately predict the transverse properties by considering the effects of microstructure including inclusion sizes and geometries. The piezoelectric finite element (FE) modeling was developed with the ABAQUS software to predict the detailed mechanical and electrical field distribution within a representative volume element (RVE) of PSF composites. The simulated energy or deformation under imposed specific boundary conditions was used to calculate each individual property with constitutive laws. The comparison between micromechanical analysis and finite element modeling indicates the combination of the dilute approximation model, the Mori-Tanaka approach and the extended Rule of Mixtures can favorably predict the electromechanical properties of three-phase PSF composites.

To keep a shape of a smart structure controlled by piezoelectric actuators attached to it, electric voltage must be also continued to be applied. To reduce amount of electricity usage, a new control method is proposed. In this method strains of the piezoelectric actuators generated by pulses of voltages are kept with zero/less applied voltage by utilizing the hysteresis in strain versus electric field relationship effectively. In this paper to examine feasibility of this control method residual strains of piezoelectric ceramic plates are measured for combinations of amplitude and period of the applied pulse of voltages. Moreover, a cantilever beam on which a piezoelectric ceramic plate is bonded is made as a simple example of applications to the smart structures, and its deformation behavior after a pulse of voltage is observed. The result shows that the present control method is useful from viewpoint of applied energy, although the strain generated by the piezoelectric actuator is less than the conventional control method where the electric voltage is continued to be applied.

The nonlinear photomechanics and thermodynamics of azobenzene liquid crystal polymer networks is studied to quantify interactions between wavelength dependent molecular conformation changes that occur within a polymer network. The transfer of energy from light to liquid crystals to a polymer network strongly depends on the wavelength and polarization of light where trans or rod shaped azobenzene chromophores convert to a cis or kinked conformation and simultaneously may relax back to the trans state but in a different orientation. This behavior requires an understanding of the dynamic interactions between light and azobenzene molecules and thermodynamics of light-matter interactions. We investigate this behavior by quantifying transmission and absorption of electro-magnetic energy with stored energy within the solid material. This is conducted by introducing a set of optical order parameters coupled to photochemistry that evolve as a function of electro-magnetic radiation.

Biobased/green polymers and nanotechnology warrant a multidisciplinary approach to promote the development of the next generation of materials, products, and processes that are environmentally sustainable. The scientific challenge is to find the suitable applications, and thereby to create the demand for large scale production of biobased/green polymers that would foster sustainable development of these eco-friendly materials in contrast to their petroleum/fossil fuel derived counterparts. In this context, this research aims to investigate the synergistic effect of green materials and nanotechnology to develop a new family of multifunctional biobased polymer composites with promoted thermal conductivity. For instance, such composite can be used as a heat management material in the electronics industry. A series of parametric studies were conducted to elucidate the science behind materials behavior and their structure-toproperty relationships. Using biobased polymers (e.g., polylactic acid (PLA)) as the matrix, heat transfer networks were developed and structured by embedding hexagonal boron nitride (hBN) and graphene nanoplatelets (GNP) in the PLA matrix. The use of hybrid filler system, with optimized material formulation, was found to promote the composite’s effective thermal conductivity by 10-folded over neat PLA. This was achieved by promoting the development of an interconnected thermally conductive network through structuring hybrid fillers. The thermally conductive composite is expected to afford unique opportunities to injection mold three-dimensional, net-shape, lightweight, and eco-friendly microelectronic enclosures with superior heat dissipation performance.

Computational models are derived for predicting the behavior of artificial cellular networks for engineering applications. The systems simulated involve the use of a biomolecular unit cell, a multiphase material that incorporates a lipid bilayer between two hydrophilic compartments. These unit cells may be considered building blocks that enable the fabrication of complex electrochemical networks. These networks can incorporate a variety of stimuli-responsive biomolecules to enable a diverse range of multifunctional behavior. Through the collective properties of these biomolecules, the system demonstrates abilities that recreate natural cellular phenomena such as mechanotransduction, optoelectronic response, and response to chemical gradients. A crucial step to increase the utility of these biomolecular networks is to develop mathematical models of their stimuli-responsive behavior. While models have been constructed deriving from the classical Hodgkin-Huxley model focusing on describing the system as a combination of traditional electrical components (capacitors and resistors), these electrical elements do not sufficiently describe the phenomena seen in experiment as they are not linked to the molecular scale processes. From this realization an advanced model is proposed that links the traditional unit cell parameters such as conductance and capacitance to the molecular structure of the system. Rather than approaching the membrane as an isolated parallel plate capacitor, the model seeks to link the electrical properties to the underlying chemical characteristics. This model is then applied towards experimental cases in order that a more complete picture of the underlying phenomena responsible for the desired sensing mechanisms may be constructed. In this way the stimuli-responsive characteristics may be understood and optimized.

Gels are a new material having three-dimensional network structures of macromolecules. They possess excellent properties as swellability, high permeability and biocompatibility, and have been applied in various fields of daily life, food, medicine, architecture, and chemistry. In this study, we tried to prepare new multi-functional and high-strength gels by using Meso-Decoration (Meso-Deco), one new method of structure design at intermediate mesoscale. High-performance rigid-rod aromatic polymorphic crystals, and the functional groups of thermoreversible Diels-Alder reaction were introduced into soft gels as crosslinkable pendent chains. The functionalization and strengthening of gels can be realized by meso-decorating the gels’ structure using high-performance polymorphic crystals and thermoreversible pendent chains. New gels with good mechanical properties, novel optical properties and thermal properties are expected to be developed.

Gels are soft and wet materials that differ from hard and dry materials like metals, plastics and ceramics. These have some unique characteristic such as low frictional properties, high water content and materials permeability. A decade earlier, DN gels having a mechanical strength of 30MPa of the maximum breaking stress in compression was developed and it is a prospective material as the biomaterial of the human body. Indeed it frictional coefficient and mechanical strength are comparable to our cartilages. In this study, we focus on the dynamic frictional interface of hydrogels and aim to develop a new apparatus with a polarization microscope for observation. The dynamical interface is observed by the friction of gel and glass with hudroxypropylcellulose (HPC) polymer solution sandwiching. At the beginning, we rubbed hydrogel and glass with HPC solution sandwiching on stage of polarization microscope. Second step, we designed a new system which combined microscope with friction measuring machine. The comparison between direct observation with this instrument and measurement of friction coefficient will become a foothold to elucidate distinctive frictional phenomena that can be seen in soft and wet materials.

In this paper, experimental results are reported to study the influence of high-temperature aging on the thermo-mechanical behavior of a commercially-available, thermo-responsive shape memory polymer (SMP), Veri ex-E^™ (glass transition temperature, T_g = 90−105 °C). To achieve a shape memory effect in high T_g SMPs such as this, high temperature cycles are required that can result in macromolecular scission and/or crosslinking, which we term thermo-mechanical aging (or chemo-rheological degradation). This process results in mechanical property changes and possible permanent set of the material that can limit the useful life of SMPs in practice. We compare experimental results of shape memory recovery with and without aging. Similar to the approach originated by Tobolsky in the 1950's, a combination of uniaxial constant stress and intermittent stretch experiments are also used in high temperature creep-recovery experiments to deduce the kinetics of scission of the original macromolecular network and the generation of newly formed networks having different reference configurations. The macroscopic effects of thermo-mechanical aging, in terms of the evolution of residual strains and change in elastic response, are quantified.

The thermal shape memory effect in polymeric materials refers to the ability of a sample to retain a deformed shape when cooled below T_g, and then recover its initial shape when subsequently heated. Although these properties are thought to be related to temperature-dependent changes in network structure and polymer chain mobility, a consistent picture of the molecular mechanisms which determine shape memory behavior does not exist. This, along with large differences in the shape memory cycling response for different materials, has made model development and specific property optimization difficult. In this work we use coarse-grained molecular dynamics (MD) simulations of the thermal shape memory effect to inform micro-macro relationships and systematically identify the salient features leading to desirable shape behavior. We consider a simulation test set including chains with increasing levels of the microscopic restrictions on chain motion (the freely-jointed, freely-rotating, and rotational isomeric state chain models), each simulated with both the NPT and NVT ensembles. It is found that the NPT ensemble with attractive interactions between monomers enabled is the most appropriate for simulating the temperature-dependent mechanical behavior of a polymer using coarse-grained MD. Of the different models, the freely-jointed chain system shows the most desirable shape memory characteristics; this behavior is attributed to the ability of the particles in this system to pack closely together in an energetically favorable configuration. A comparison with experimental data demonstrates that the coarse-grained simulations display all of the relevant trends in mechanical behavior during constant strain shape memory cycling. We conclude that atomistic detail is not needed to represent a shape memory polymer, and that multi-scale modeling techniques may build on the mechanisms embodied in the simple coarse-grained model.

Smart materials and structures is an international frontier field in current development of engineering and science. Representative of soft smart materials include Electroactive polymers (EAPs) and Shape Memory Polymers (SMPs), etc..As a new kind of smart deformation material, SMPs have a wide range of applications in the field of smart material and structures due to their controllable shape memory effects. Deformation mechanism of SMP material is the basis of its applications. This paper proposed an useful thermoviscoelastic constitutive model by considering thermal expansion, structure relaxation and viscoelastic properties of Epoxy-SMP material. To verify the applicability of the model, various experiments such as isothermal uniaxial tensile tests were carried out and then be simulated. The results showed that the constitutive model could nicely predict mechanical behavior of Epoxy-SMP, the proposed constitutive model is useful for the design of SMPs structures.

At high temperatures, SMPs share attributes like rubber and exhibit long-range reversibility. In contrast, at low temperatures they become very rigid and are susceptible to plastic, only small strains are allowable. But there relatively little literature has considered the unique small stain (rubber phase) and large stain (glass phase) coupling in SMPs when developing the constitutive modeling. In this work, we present a 3D constitutive model for shape memory polymers in both low temperature small strain regime and high temperature large strain regime. The theory is based on the work of Liu et al. [15]. Four steps of SMP’s thermomechanical loadings cycle are considered in the constitutive model completely. The linear elastic and hyperelastic effects of SMP in different temperatures are also fully accounted for in the proposed model by adopt the neo-Hookean model and the Generalized Hooke’s laws.

The present work studies the synergistic effect of graphene and carbon nanofiber (CNF) in nanopaper on the electrical properties and electro-active recovery behavior of shape memory polymer (SMP) nanocomposite. The combination of graphene and CNF is used to improve the electrical and thermal conductivities of the SMP. Graphene is first employed to significantly improve the electrical conductivity along horizontal orientation, as well as CNFs were expected to bridge the gap among individual graphene and improve the through-thickness electrical performance of nanopaper. Furthermore, the conductive nanopaper is coated on the surface and improves the electrical properties of the SMP nanocomposite, resulting in the shape recovery can be achieved by electricity. Finally, the temperature distribution has been characterized to experimentally testify the effect of nanopaper on the SMP nanocomposite in the electro-responsive recovery process.

Magnetic shape memory alloys (MSMAs) are materials that can display up to 10% recoverable strain in response to the application of a magnetic field or compressive mechanical stress. The recoverable strain depends on the magnitude of the stress and magnetic field that is applied to the material. Due to their large strains as well as fast response, MSMAs are suitable for actuation, power harvesting, and sensing applications. Broadening the range of applications for MSMAs requires an understanding of their magneto-mechanical behavior beyond 2D loading cases that have been studied to date. The response of MSMAs is primarily driven by the reorientation of martensite variants. During the reorientation process a change in material’s magnetization occurs. Using a pick-up coil (placed around, or on the side, of the specimen) one may convert this change in magnetization into an electric potential/voltage, making the material act as a power harvester. The magnitude of the output voltage depends on the number of turns of the pick-up coil, the amplitude of the reorientation strain, the magnitude and direction of the biased magnetic field, and the frequency at which the reorientation occurs. This paper presents experimental results for the material behavior under 3D loading conditions, including power harvesting data generated under such loading conditions. The 3D experimental data includes the material’s response to two compressive mechanical stresses, applied in perpendicular directions, simultaneously with the application of a magnetic field applied in the remaining orthogonal direction. The power harvesting data includes magnetic fields in multiple directions and different orientations of the pick-up coil. Results indicate that the presence of a bias magnetic field along the specimen length (i.e. the direction of application of the compressive stress) in addition to that applied normal to the specimen length, leads to an increase in the electric potential output.

An experimental characterization is presented of the thermo-mechanical response of honeycombs and corrugations made of a NiTi shape memory alloy (SMA). Of particular interest are the shape memory cycle, the superelastic response, the shape memory thermal lag and the superelastic rate sensitivity. A series of in-plane compression experiments are presented on fabricated honeycombs and their responses are compared to typical monolithic SMAs, such as NiTi wire. Given local material strain limits, NiTi honeycombs exhibit an order of magnitude increase in recoverable deformation, both in the shape memory effect and superelastic effect. This comes at the cost of a reduced load carrying capacity by two orders of magnitude and a reduced (homogenized) compressive stiffness by four orders of magnitude. Due to their sparse structure and enhanced heat transfer characteristics, SMA honeycombs exhibit less superelastic rate sensitivity by two orders of magnitude while having similar thermal lag to SMA wire. The implications of these scaling results are discussed, including possible new regimes of application of SMAs for reusable energy absorption devices and high stroke actuators.

The mechanical and fatigue characteristics of superelastic NiTi thin plates in the large strain area were obtained by tensile and pulsating 4-point bending tests to establish the design guidelines for the ferromagnetic shape memory alloy (FSMA) composite actuator and its fatigue life. The stress-strain curves of NiTi thin plates were found to be strain rate dependent. The finite element analysis (FEA) result using the stress-strain curve measured by tensile test is in good agreement with the experimental results of the 4-point bending tests. The relationship between the maximum bending strain and the number of cycles to failure in pulsating 4-point bending fatigue tests was obtained as well as an analysis of the fatigue fracture surfaces of NiTi thin plates.

The issue of material performance over its designed life is of prime concern with designers lately due to increasing use of shape memory alloy (SMA) components in different engineering applications. In this work, a concept of "Driving force amplitude v/s no of cycles" is proposed to analyze functional degradation of SMA components under torsion. The model is formulated using experimentally measurable quantities such as torque and angle of twist with the inclusion of both mechanical and thermal loading in the same framework. Such an approach can potentially substitute the traditional fatigue theories like S-N, epsilon-N theories which primarily use mechanical loading effects with temperature being an external control parameter. Such traditional S-N, epsilon-N fatigue theories work well for capturing superelastic effects at a given temperature but not for shape memory effects or temperature dependent superelastic effects which involves mechanical and thermal coupling. Experiments on SMA extension springs are performed using a custom designed thermomechanical test rig capable of mimicking shape memory effect on thermally activated SMA springs held under constant deformation. For every thermomechanical cycle, load and temperature sensor readings are continually recorded as a function of time using LabVIEW software. The sensor data over the specimen lifetime is used to construct a "Driving force amplitude v/s no of cycles" relationship that can be used as a guideline for analyzing functional degradation of SMA components.

Hysteresis causes a delayed response to a given input in a magnetostrictive actuator (MA). It becomes critical when the MA has to be controlled in precise and real-time mode. An efficient way to compensate hysteresis must be considered. The Jiles-Atherton and Preisach models have been applied mostly in the literature, but these models need complex mathematics that makes them difficult to be applied in precise and real-time mode. Thus, this paper presents a semi-empirical model to compensate hysteresis in the MA. The idea comes from the similarity of the shapes between the hysteresis-compensated input voltage to the MA, and the output voltage of R-C circuit. The respective hysteresis-compensated input voltage and R-C circuit are expressed as polynomial and exponential equations, resulting in two closed-form equations about capacitance. One set of capacitance values for each frequency is selected by simulating the derived equations. Experiments are performed to choose one capacitance value among a set of capacitance values from simulation, based on trial-and-error. The concept of the hysteresis loss is introduced and defined as the ratio of areas between the hysteretic and reference curves. It is observed that the percent change of hysteresis loss increases as the frequency increases up to 400 Hz, but decreases with further increase of the frequency up to 800 Hz. It can be concluded that the proposed approach is effective to compensate hysteresis in the MA, and that hysteresis loss definition introduced by us can be used as a helpful measure of hysteresis compensation.

This paper focuses on the development of a three-dimensional (3D) hysteretic Galfenol model which is implemented using the finite element method (FEM) in COMSOL Multiphysics. The model describes Galfenol responses and those of passive components including flux return path, coils and surrounding air. A key contribution of this work is that it lifts the limitations of symmetric geometry utilized in the previous literature and demonstrates the implementation of the approach for more complex systems than before. Unlike anhysteretic FEM models, the proposed model can simulate minor loops which are essential for both Galfenol sensor and actuator design. A group of stress-flux density loops for different bias currents is used to verify the accuracy of the model in the quasi-static regime.

This paper investigates properties about electrical resistivity and piezoresistivity of multi-wall carbon nanotubes (MWCNTs)-filled epoxy-based composite and its further use for strain sensing. The MWCNTs dispersed epoxy resin, using MWCNTs in the amount of 1.5~3.0 vol.%, was first prepared by combined high-speed stirring and sonication methods. Then, the MWCNTs dispersed epoxy resin was cast into an aluminum mold to form specimens measuring 10×10×36 mm. After curing, DC electrical resistance measurements were performed along the longitudinal axis using the four-probe method, in which copper nets served as electrical contacts. The percolation threshold zone of resistivity was got as MWCNTs in the amount of 2.00–2.50 vol.%. Further compressive testing of these specimens was conducted with four-probe method for resistance measurements at the same time. Testing results show that the electrical resistivity of the composites changes with the strain’s development, namely piezoresistivity. While for practical strain sensing use, signals of electric resistance and current in the acquisition circuits were both studied. Results show that the signal of current, compared with that of resistance, had better linear relationship with the compressive strain, better stability and longer effective section to reflect the whole deformation process of the specimens under pressure. Further works about the effects of low magnetic field on the electrical resistivity and piezoresistivity of Ni-CNTs filled epoxy-based composites were presented briefly at the end of the paper.

Modeling superelastic behavior of shape memory alloys (SMA) has received considerable attention due to SMAs ability to recover large strains with associated loading{unloading hysteresis enabling them to find many applications. In this work, a simple mechanics of materials modeling approach for simulating superelastic responses of SMA components under tension and bending loading conditions is developed. Following Doraiswamy, Rao and Srinivasa's¹ approach, the key idea here would be in separating the thermoelastic and the dissipative part of the hysteretic response with a Gibbs potential based formulation which includes both thermal and mechanical loading in the same framework. The dissipative part is then handled by a discrete Preisach model. The model is formulated directly using tensile stress{strain or bending moment{curvature rather than solving for non-homogeneous stress and strains across the specimen cross-sections and then integrating the same especially for bending loading conditions. The model is capable of simulating complex superelastic responses with multiple internal loops and provides an improved treatment for temperature dependence associated with superelastic responses. The model results are verified with experimental results on SMA components like wires and beams at different temperatures.

Magnetic Shape Memory Alloys (MSMAs) are a type of smart material that exhibit a large amount of recoverable strain when subjected to an applied compressive stress in the presence of a magnetic field or an applied magnetic field in the presence of a compressive stress. These macroscopic recoverable strains are the result of the reorientation of tetragonal martensite variants. Potential applications for MSMAs include power harvesters, sensors, and actuators. For these applications, the stress is assumed to be applied only in the axial direction, and the magnetic field is assumed to be applied only in the transverse direction. To realize the full potential of MSMA and optimize designs, a mathematical model that can predict the material response under all potential loading conditions is needed. Keifer and Lagoudas [1, 2] developed a phenomenological model that characterizes the response of the MSMA to axial compressive stress and transversely applied magnetic field based on thermodynamic principles. In this paper, a similar thermodynamic framework is used. However, a simpler hardening function is proposed based on the observation that the reorientation phenomenon is the same in both forward and reverse loading, as well as under both magnetic and mechanical loading. The magnetic domains are redefined to more accurately reflect the magnetic field measured experimentally [3]. This revised model is shown to adequately predict the magneto-mechanical response of the MSMA in 2D loading, i.e. axial compressive stress and transversely applied magnetic field.

This paper reports a study of the thermal response of an infinitely extended shape memory alloy thin film. Motivated by experiments reported in the literature about SMA thin films on a silicon substrate, the thin film is taken to have three layers from the bottom to the top – an amorphous layer, a non-transforming austenitic layer and a transforming SMA layer. The boundary conditions are taken to be adiabatic and convective at the bottom of the film and the top respectively. The material properties of the transforming layer (thermal conductivity, electrical resistivity and specific heat) are taken to evolve hysteretically with temperature, commencing from an initial room temperature state of martensite. All the results are presented in non-dimensional form. The steady state results are compared with an analytical solution. The computations of the transient response are carried out with ANSYS. The thermal response of the 3-layer model is compared with that of a 1-layer model (where the entire film is a SMA transforming layer) and it is seen that the the temperature of the top surface for the 3-layer model is higher than that of the 1-layer model. It is also seen that the evolution of the specific heat has the least effect whereas the evolution of the electrical resistivity has the most effect on the thermal response of the 3-layer model. The thermal response of the infinitely extended films provides a benchmark against which the response of finite sized films can be assessed.

Shape memory alloys (SMAs) remain one of the most commercially viable active materials, thanks to a high specific work and the wide availability of high quality material. Still, significant challenges remain in predicting the degradation of SMA actuators during thermal cycling. One challenges in both the motivation and verification of degradation models is the measurement of retained martensite fraction during cycling. Direct measurement via diffraction is difficult to perform in situ, impossible for thin wires, (< 0.5mm) and prohibitively difficult for lengthy studies. As an alternative, the temperature coefficient of electrical resistivity (TCR) is used as an indicator of martensite phase fraction during thermal cycling of SMA wires. We investigate this technique with an example cycling experiment, using the TCR to successfully measure a 20% increase in retained martensite fraction over 80000 thermal cycles. As SMA wire temperature is difficult to measure directly during resistive heating, we also introduce a method to infer temperature to within 5 °C by integrating the lumped heat equation.

An adaptive precision ball screw drive concept is presented in which a self-sufficient actuator is able to adjust the axial preload during the operation. The adjustment is effected by thermal shape memory alloy pucks, which either expand or contract according to the surrounding temperature field of the process. For this purpose, no external energy is needed and so the system is self-supported (energy harvesting). In this case, the extrinsic two-way shape memory effect occurs and the reversible full cycle of shape change is accomplished by a bias force of a flexure. Basing on temperature and force measurements on a double nut ball screw, a thermo-mechanical model is developed. Using the investigated principles adaptive mechanisms, a shape memory-based actuator is designed. Initial tests reveal an unwanted reduction of the preload of up to 800 N with rising temperature. Due to the shape memory actuation device, experiments results show an increase in axial load in approximated 70 % of the reduction.

NiTi is promising for the use as bone scaffold, because the pseudoelasticity or the one- and two-way shape memory effect in the physiological window can mechanically stimulate the adherent cells. Such stimuli can enhance osseointegration and might reduce stress shielding associated with load bearing implants. The present study is based on the additive manufacturing technique of selective laser melting (SLM) to fabricate three-dimensional NiTi scaffolds. We demonstrate that the morphology of the scaffolds can be quantified using synchrotron radiation-based micro computed tomography (SRμCT) and sophisticated registration software. Comparing the CAD file with the SLM scaffolds, quality factors are derived. With respect to the CAD file, the overlap corresponds to (92.5 ± 0.6) %. (7.4 ± 0.42) % of material was missing and (48.9 ± 2.3) % of excess material found. This means that the actual scaffold is less porous than expected, a fact that has to be considered for the scaffold design. In order to quantify the shape memory effect during the shape recovery process, we acquired radiographs rotating an initially deformed scaffold in angular steps of 0.2 degree during controlled heating. The continuously acquired radiographs were combined to tomography data, showing that the quality factors evolved with temperature as the scaffold height, measured by conventional thermo-mechanical analysis. Furthermore, the data comprise the presence of compressive and tensile local strains in the three-dimensional scaffolds to be compared with the physiological situation.

This paper is a study on the numerical modeling and the accordance between model and experiment of the behavior of Shape Memory Alloys (SMA) used as functional devices for application in Instrumentations for Astronomy. Some NiTi alloy samples was characterized using different experimental techniques, with the purpose of obtaining the material parameters, necessary to evaluate the correspondence between the simulation and the experimental behavior of the materials. The sensibility of the computational model to the variation of this parameters for the materials was investigated as well. Opto-mechanical mounting with pseudoelastic kinematic behavior and damping of launch loads onto optical elements are feasible applications that are investigated in this paper. The practical realization of a scaled down prototype is described. The device was thought for ground-based applications and made up of four small flexures that support an optical component and was designed and modeled in order to be able to evaluate the mechanical effects of different materials. The results of numerical modeling was compared to the data obtained from the prototype. We obtained a first evaluation of the development, selection and processing of NiTi-based supports for optomechanical applications and verified the performances of a complete system as a respect to an analogous system made up using traditional materials like steels.

The paper presents results associated with the electro-mechanical characterization of a composite material with power storage capability, identified throughout the paper as a structural supercapacitor. The structural supercapacitor uses electrodes made of carbon fiber weave, a separator made of Celgard 3501, and a solid PEG-based polymer blend electrolyte. To be a viable structural supercapacitor, the material has to have good mechanical and power storage/electrical properties. The literature in this area is inconsistent on which electrical properties are evaluated, and how those properties are assessed. In general, measurements of capacitance or specific capacitance (i.e. capacitance per unit area or per unit volume) are made, without considering other properties such as leakage resistance and equivalent series resistance of the supercapacitor. This paper highlights the significance of these additional electrical properties, discusses the fluctuation of capacitance over time, and proposes methods to improve the stability of the material’s electric properties over time.

Lithium ion batteries (LIB) have been receiving extensive attention due to the high specific energy density for wide applications such as electronic vehicles, commercial mobile electronics, and military applications. In LIB, graphite is the most commonly used anode material; however, lithium ion intercalation in graphite is limited, hindering the battery charge rate and capacity. To overcome this obstacle, nanostructured anode assembly has been extensively studied to increase the lithium ion diffusion rate. Among these approaches, high specific surface area metal oxide nanowires connecting nanostructured carbon materials accumulation have shown propitious results for enhanced lithium intercalation. Recently, nanowire/graphene hybrids were developed for the enhancement of LIB performance; however, almost all previous efforts employed nanowires on graphene in a random fashion, which limited lithium ion diffusion rate. Therefore, we demonstrate a new approach by hydrothermally growing uniform nanowires on graphene aerogel to further improve the performance. This nanowire/graphene aerogel hybrid not only uses the high surface area of the graphene aerogel but also increases the specific surface area for electrodeelectrolyte interaction. Therefore, this new nanowire/graphene aerogel hybrid anode material could enhance the specific capacity and charge-discharge rate. Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) are used for materials characterization. Battery Analyzer and Potentio-galvanostat are used for measuring the electrical performance of the battery. The testing results show that nanowire graphene hybrid anode gives significantly improved performance compared to graphene anode.

The multifunctional hybrid composite structure studied here consists of a ceramic outer layer capable of withstanding high temperatures, a functionally graded ceramic layer combining shape memory alloy (SMA) properties of NiTi together with Ti2AlC (called Graded Ceramic/Metal Composite, or GCMeC), and a high temperature sensor patch, followed by a polymer matrix composite laced with vascular cooling channels all held together with various epoxies. Due to the recoverable nature of SMA and adhesive properties of Ti2AlC, the damping behavior of the GCMeC is largely viscoelastic. This paper presents a finite element formulation for this multifunctional hybrid structure with embedded viscoelastic material. In order to implement the viscoelastic model into the finite element formulation, a second order three parameter Golla-Hughes-McTavish (GHM) method is used to describe the viscoelastic behavior. Considering the parameter identification, a strategy to estimate the fractional order of the time derivative and the relaxation time is outlined. The curve-fitting aspects of both GHM and ADF show good agreement with experimental data obtained from dynamic mechanics analysis. The performance of the finite element of the layered multifunctional beam is verified through experimental model analysis.

In this paper we present a method to design composites which are acoustically impedance matched with a homogeneous medium at a desired frequency. We use dynamic homogenization of layered elastic composites to calculate their effective acoustic impedance. It is shown that the microstructure of a layered composite can be designed so that its acoustic impedance matches the impedance of the homogeneous medium at the desired frequency. As a result, the reflection at the interface of such a composite with the homogeneous medium is minimized. Transfer matrix calculation and finite element modeling of wave propagation through a layered periodic composite sandwiched between two homogenous media are done. It is observed that at the design frequency where the composite has matched impedance with homogenous media the reflection at the interfaces is almost zero.

Acoustic impedance is a material property that depends on mass density and acoustic wave speed. An impedance mismatch between two media leads to the partial reflection of an acoustic wave sent from one medium to another. Active sonar is one example of a useful application of this phenomenon, where reflected and scattered acoustic waves enable the detection of objects. If the impedance of an object is matched to that of the surrounding medium, however, the object may be hidden from observation (at least directly) by sonar. In this study, polyurea composites are developed to facilitate such impedance matching. Polyurea is used due to its excellent blast-mitigating properties, easy casting, corrosion protection, abrasion resistance, and various uses in current military technology. Since pure polyurea has impedance higher than that of water (the current medium of interest), low mass density phenolic microballoon particles are added to create composite materials with reduced effective impedances. The volume fraction of particles is varied to study the effect of filler quantity on the acoustic impedance of the resulting composite. The composites are experimentally characterized via ultrasonic measurements. Computational models based on the method of dilute-randomly-distributed inclusions are developed and compared with the experimental results. These experiments and models will facilitate the design of new elastomeric composites with desirable acoustic impedances.

Due to its excellent thermo-mechanical properties, polyurea is attracting more and more attention in blast-mitigating applications. In order to enhance its capability of blast-induced stress-wave management, we seek to develop polyurea-based composites in this work. Fly ash which consists of hollow particles with porous shell and low apparent density was chosen as filler and a series of fly ash/polyurea composites with various fly ash volume fractions were fabricated. The dynamic mechanical behavior of the composites was determined by a personal computer (PC) based ultrasonic system in the 0.5-2MHz frequency range between -60°C to 30°C temperatures. Velocity and attenuation of both longitudinal and shear ultrasonic waves were measured. The complex longitudinal and shear moduli were then computed from these measurements. Combining these results provided an estimate of the complex bulk and Young’s moduli of the fly ash/polyurea composites at high frequencies. These results will be presented and compared with those of pure polyurea elastomer.

Carbon-fiber reinforced polymer (CFRP) composites offer benefits of reduced weight and increased specific strength; however, these materials can have relatively weak interlaminar toughness. The first modes of composite material failure often remain undetected, since failure is not always visually apparent on the surface of composite materials. In this study, several nano-sized materials and integration approaches are investigated as nanoreinforcement for composite materials. Performance is characterized by the ability of each nanoreinforced composite type to improve Mode I interlaminar toughness. The nanomaterials include 1) commercially available surface-modified silica nanoparticles and 2) continuous polyacrylonitrile (PAN) nanofibers. Test articles are manufactured using hand-layup vacuum bagging and feature either reinforced unidirectional carbon fiber or woven carbon fiber material and one of two investigated epoxy-based resin systems. The nanosilica particles were integrated into the fiber composite structure by mixing with the resin system prior to layup. The PAN nanofibers were produced by an electrospinning process; these fibers were integrated by either collecting the fibers of various areal densities as respective “nanomats” on an interim substrate for subsequent transfer during layup, or directly electrospun onto dry carbon fiber ply surfaces. Test articles were characterized according to ASTM D5528 for finding Mode I strain energy release rates. Results were compared to baseline coupons to determine fracture toughness performance. Results showed that the nanosilica-reinforced coupons increased an average of 35% and 25% in strain energy release rates for the coupons featuring unidirectional fibers and woven fibers, respectively, as compared to the corresponding baseline, whereas the nanomat-reinforced and directly deposited nanofiber-reinforced composites decreased. Low strain energy release rates for the PAN nanofiber-reinforced coupons is attributed to voids in the test coupons as a result of unconventional composite coupon manufacturing.

The aim of this study is to investigate characteristics of fatigue damage of CFRP modified with MFC by TDA under tensile cyclic loading. In this paper, fatigue life of CFRP modified with MFC was investigated under cyclic loading. Characteristics of fatigue damage of CFRP modified with MFC were evaluated by thermo-elastic damage analysis. Maximum improvement in fatigue life was also obtained under cyclic loading when epoxy matrix was enhanced with 0.3wt% of MFC as well as under static loading. Result of TDA showed same tendency as the result of fatigue test, and the result of TDA well expressed the fatigue damage behavior of plain woven CFRP plate. Eventually, TDA was effective for clear understanding the degree of fatigue damage progression of CFRP modified with MFC.

Shape memory alloys (SMA) like Nickel-Titanium possess a very high mechanical energy density in relation to conventional drives. Fiber reinforced plastics (FRP) will be increasingly applied to create lightweight structures. Combining both innovative materials will evolve synergy effects. Due to functional integration of SMA sheets into a base of FRP it is possible to realize adaptive composites for resource-efficient constructions as for instance flaps or spoilers on cars. For this purpose the interaction between SMA as an actuator and FRP as a return spring need to be designed in a suitable way. The computation of such structures is complex because of its non-linear (SMA) and anisotropic (FRP) mechanical behavior. Therefore, a structural simulation model based on the finite element method was developed by means of the software ANSYS. Based on that simulation model it is possible to determine proper geometrical parameters for a composite made of SMA and FRP to perform a certain mechanism. The material properties of SMA or FRP could also be varied to investigate their influence. For exemplary components it could be shown that the stress-strain behavior is computable.

Shape-memory materials (SMMs) are fascinating materials, with the potential for application as “smart materials” and also as actively moving materials, which can change their shape in a predefined way between/among shapes in presence of an appropriate stimulus. The intention of this article is to present a systematic and up-to-date account of chemoresponsive amorphous shape-memory polymers (SMPs) from basic principles in phase transition to experiments. Based on the previous work, phase transition of the chemo-responsive SMPs. of which the transition temperature is originated from the glass transition, is presented. Studies have been explored for chemo-responsive SMPs in various design principles in water/solvent induced shape-memory effect. Some examples, including are also presented.

This paper presents modeling and analysis methods for design of a smart metamaterial structure consisting of an isotropic beam and small spring-mass-damper subsystems for broadband absorption of transverse elastic waves. Two models of a unit cell are derived and used to demonstrate the existence of a stopband right to the high-frequency side of the local resonance frequency of spring-mass absorbers. A linear finite element method is used for detailed modeling and analysis of simply supported finite beams with different designs of absorbers. We show that the actual working mechanism is that, if the propagating elastic wave’s frequency is within the absorbers’ stopband, the wave resonates the integrated spring-mass absorbers to vibrate in their optical mode to create shear forces and bending moments to stop the wave propagation. We demonstrate that this unique phenomenon can be used to design broadband absorbers that work for elastic waves of short and long wavelengths. With appropriate design optimization calculations, finite discrete spring-mass absorbers can be used, and hence expensive micro- or nano-manufacturing techniques are not needed for such metamaterial beams for broadband vibration absorption/isolation. At last we do experiment to verify the simulation result.

Damping behavior of polymeric composites with nano structured phases is significantly different from usual polymer composites. Viscoelastic homopolymers exhibit high material damping over a relatively narrow range of temperature and frequencies. In many practical situations a polymeric structure is required to possess better strength and stiffness properties together with a reasonable damping behavior. Viscoelastic polymers show higher loss factor beyond the glassy region which comes with a significant drop in the specific modulus. Addition of nano alumina particles to epoxy leads to improved strength and stiffness properties with an increase in glass transition temperature while retaining its damping capabilities. Experimental investigations are carried out on composite beam specimen fabricated with different volume fractions of alumina nano particles in epoxy to determine loss factor, tan δ. Impact damping method is used for time response analysis. A single point Laser is used to record the transverse displacement of a point on the composite beam specimen. Experimental results are compared with theoretical estimation of loss factor using Voigt estimation. The effect of interphase is included in theoretical estimation of loss factor. Passive vibration suppression may be introduced in the polymeric structures along with improved structural properties by tailored dynamic characteristics using nano alumina particle filled epoxy composites.

The introduction of nanoscaled reinforcement in otherwise conventional fiber reinforced composite materials has opened an exciting new area in composites research. The unique properties of these materials combined with the design versatility of fibrous composites may offer both enhanced mechanical properties and multiple functionalities which has been a focus area of the aerospace technology on the last decades. Due to unique properties of carbon nanofillers such as huge aspect ratio, extremely large specific surface area as well as high electrical and thermal conductivity, Carbon Nanotubes have benn investigated as multifunvtional materials for electrical, thermal and mechanical applications. In this study, MWCNTs were incorporated in a typical epoxy system using a sonicator. The volume of the nanoreinforcement was 0.5 % by weight. Two different levels of sonication amplitude were used, 50% and 100% respectively. After the sonication, the hardener was introduced in the epoxy, and the system was cured according to the recommended cycle. For comparison purposes, specimens from neat epoxy system were prepared. The thermomechanical properties of the materials manufactured were investigated using a Dynamic Mechanical Analyser. The exposed specimens were subjected to thermal shock. Thermal cycles from +30 °C to -30 °C were carried out and each cycle lasted 24 hours. The thermomechanical properties were studied after 30 cycles . Furthermore, the epoxy systems prepared during the first stage of the study were used for the manufacturing of 16 plies quasi isotropic laminates CFRPs. The modified CFRPs were subjected to thermal shock. For comparison reasons unmodified CFRPs were manufactured and subjected to the same conditions. In addition, the interlaminar shear strength of the specimens was studied using 3-point bending tests before and after the thermal shock. The effect of the nanoreinforcement on the environmental degradation is critically assessed.

In this project, shape memory polystyrene foam was fabricated from shape memory polystyrene and ethyl acetate/n-hexane as physical foaming agent based on suspension polymerization method. The foam of uniform pore structure with porosity ranging from 36%～45% have been made successfully. Both shape memory properties and physical properties were characterized. Shape memory polystyrene foam exhibited good shape memory properties-- completely recovery the initial undeformed shape after multiple cycles. The higher thermal stability was achieved compared with pure shape memory polystyrene. The glassy state property of the foam was increased from 75°C to 85°C as the content of filler increased from 0 to 30%.