In this paper we analyze the 3D modes of a linear homogeneous magnetoelectroelastic (MEE) material. We find that the behavior of the electromagnetic modes are strongly influenced by the mechanical coupling present in the MEE material system. A number of papers refer to the cross-coupling of laminated piezoelectric and piezomagnetic materials as magnetoelectric materials. We discuss here that the composite materials are MEE systems and that the constitutive relations need to reflect the mechanical coupling also. Further, we find that the mechanical coupling has a significant impact on the electromagnetic propagation modes of the composite material. Through examples of homogenized MEE materials we show possibilities for remarkable electromagnetic material characteristics which are not conventionally obtainable in single phase materials.

Electromechanical coupling in ferroelectric materials is extended to include the electric quadrupole. Internal lattice displacements are coupled to strain to calculate both the polarization and the quadrupole and to provide general methods to describe both acoustic and optical material behavior. Electromechanical coupling of a monodomain is first analyzed and followed by finite element phase field simulations of a 180° domain wall. A comparison between explicit electrostrictive coupling and nonlinear geometric effects is given which illustrate that phenomenological electrostriction gives exactly the same electromechanical coupling as obtained from introducing an effective field within the electrostatic Lorentz force.

High energy density capacitors are critically important in advanced electronic devices and electric power systems due to their reduced weight, size and cost to meet desired applications. Nanocomposites hold strong potential for increased performance, however, the energy density of most nanocomposites is still low compared to commercial capacitors and neat polymers. Here, high energy density nanocomposite capacitors are fabricated using surface-functionalized high aspect ratio barium titanate (BaTiO₃) nanowires (NWs) in a poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) matrix. These nanocomposites have 63.5% higher dielectric permittivity compared to previous nanocomposites with BaTiO₃ nanoparticles and also have high breakdown strength. At a 17.5% volume fraction, the nanocomposites show more than 145.3% increase in energy density above that of the pure P(VDF-TrFE- CFE) polymer (10.48 J/cm³ compared to 7.21 J/cm³). This value is significant and exceeds those reported for the conventional polymer-ceramic composites; it is also more than two times larger than high performance commercial materials. The findings of this research could lead to broad interest due to the potential for fabricating next generation energy storage devices.

Polymer nanocomposites containing high dielectric permittivity ceramic particles embedded into a dielectric polymer represent promising candidates to overcome the limitations of monolithic materials in both energy storage and energy conversion. Indeed, monolithic materials are hitting a plateau in terms of high energy storage capabilities due to the trade-off between the dielectric constant, the dielectric loss and the dielectric breakdown. Since ceramics have high dielectric constant but low dielectric breakdown, while polymers have high dielectric breakdown and low loss but low dielectric constant, the strategy of simply filling a polymer with ceramic particles will only yield incremental and limited success. In this study, we investigate the effect of adding commercial metal oxide nanoparticles, TiO₂, to a ferroelectric polymer on the dielectric constant, breakdown, ferroelectric behavior and energy density of the system; specifically, we focus on impact of the particles size, aspect ratio, and interaction with the polymer dipole. We find that at a very low TiO₂ content, namely 4.6vol%, the energy density increased by more than 400% as compared to the pristine polymer, with an enhancement in both the dielectric constant and the dielectric breakdown while the dielectric loss remained in the same range as that of the pure polymer. We also investigate the mechanism for this large improvement and demonstrate that the high aspect ratio particles have a planar distribution in the nanocomposite film, resulting in a low local field, and therefore a high dielectric breakdown.

A novel method is developed to prepare PVDF based graphene oxide (GO) nanocomposites using a co-solvent approach involving water and DMF. Nanocomposite films are prepared by solution casting the GO-PVDF solution. TEM images of these nanocomposites show better dispersion of GO in the PVDF prepared using the co-solvents as compared to the films made only using DMF. Following solvent evaporation, GO/PVDF nanocomposites are hot pressed at 150 °C, well below the melting temperature of PVDF, to maintain the dispersion of GO fillers while partially reducing the GO to functionalized graphene sheets. Dielectric constant and electrical conductivity of the nanocomposites show remarkable increase compared to values for PVDF for a low 0.005 weight fraction. The effect of the presence of GO and the hot press on the morphology of PVDF are discussed.

This study involves the investigation of spherically shaped filler diameter and interphase effects on the Young's modulus of micro and nano size silicon dioxide (SiO₂) particle reinforced epoxy composite materials. Specifically, 10μm and 80nm size SiO₂ particles and Epon 862 epoxy are chosen as fillers and a matrix material, respectively. While 10μm and 80nm SiO₂ particles are dispersed in the epoxy through a direct shear mixing method, nano-composites are fabricated with hardener at desirable ratios. Both micro- and nano-composites are prepared at 2 different particle loading fractions for tensile testing. It is observed that the nano-composites show significant increase in Young's modulus over micro-composites, showing a linear increase as particle volume fraction increases. This could indicate that for nano-composites, the interphase region between the particle and matrix can considerably affect their mechanical properties. Here, we develop a finite element analysis (FEA) model to investigate the interphase effect on the Young's modulus of both micro- and nano-composites. This model demonstrates how to estimate the effective volume fraction of a particle as filler using a combined experimental/numerical approach. The effective volume fraction is shown to be important in predicting the mechanical response of nano-scale particles reinforced composite materials.

Glassy, polydomain azobenzene liquid crystal polymer networks (azo-LCN) have been synthesized, characterized, and modeled to understand composition dependence on large amplitude, bidirectional bending and twisting deformation upon irradiation with linearly polarized blue-green (440-514 nm) light. These materials exhibit interesting properties for adaptive structure applications in which the shape of the photoresponsive solid state structure can be rapidly reconfigured with light. The basis for the photomechanical output observed in these materials is absorption of actinic light by azobenzene, which upon photoisomerization dictates an internal stress within the local polymer network. The photoinduced disruption of the order/orientation of the local polymer network accompanying photoisomerization is manifested in a macroscopic deformation. Accordingly, this work examines the polarization-controlled bidirectional bending of highly concentrated azo-LCN materials and compares the macroscopic bending to a nonlinear photoshell model. The resulting photomechanical output is highly dependent on the concentration of crosslinked azobenzene mesogens employed in the formulation. The model comparisons illustrate differences in internal photostrain and deformation rates as a function of composition.

In the present work, the ultrasonic strain sensing performance of the large area PVDF thin film subjected to the thermal fatigue is studied. The PVDF thin film is prepared using hot press and the piezoelectric phase ( β-phase) has been achieved by thermo-mechanical treatment and poling under DC field. The sensors used in aircrafts for structural health monitoring applications are likely to be subjected to a wide range of temperature fluctuations which may create thermal fatigue in both aircraft structures and in the sensors. Thus, the sensitivity of the PVDF sensors for thermal fatigue needs to be studied for its effective implementation in the structural health monitoring applications. In present work, the fabricated films have been subjected to certain number of thermal cycles which serve as thermal fatigue and are further tested for ultrasonic strain sensitivity at various different frequencies. The PVDF sensor is bonded on the beam specimen at one end and the ultrasonic guided waves are launched with a piezoelectric wafer bonded on another end of the beam. Sensitivity of PVDF sensor in terms of voltage is obtained for increasing number of thermal cycles. Sensitivity variation is studied at various different extent of thermal fatigue. The variation of the sensor sensitivity with frequency due to thermal fatigue at different temperatures is also investigated. The present investigation shows an appropriate temperature range for the application of the PVDF sensors in structural health monitoring.

In this work, two methodologies were used in fabricating conductive electrospun polymer fibers with nano features. We first investigated the addition of multiwall carbon nanotubes (MWCNT) as conductive fillers at concentrations ranging from 1 to 10% into a polystyrene (PS) matrix. Electrospinning conditions were tailored to produce fibers with minimal beads. Next, we investigated the effects of coating electrospun fibers with nano structured conductive polymer. Oxidant (FeCl₃) fibers were electrospun in PS and then exposed to a pyrrole (Py) monomer in a vacuum chamber. As a result, polypyrrole (PPy) was coated on the fibers creating conductive pathways. In both methods, the electrospun conductive fibers were characterized in terms of their morphologies, thermal stability and electrical conductivity. Strong correlations were found among PPy coating nanostructures, oxidant concentration and polymerization time. Electrospun fibrous membranes with conductive polymer coating exhibit much higher electrical conductivities compare to fibers with conductive fillers. Highest conductivity achieved was 9.5E-4 S/cm with 40% FeCl₃/PS fibers polymerized with Py for 140 min.

The light transmission through a Lead Lanthanum Zirconate Titanate (PLZT) ceramic film, having a relaxor ferroelectric composition of (9.5/65/35) was modulated at both the first and second harmonic frequencies to that of an applied field. Large changes were observed in the optical path difference within the material due to a combination of the electrostrictive and quadratic electro-optic effects. A theoretical model was developed to obtain harmonic expressions for the Fabry-Pérot transmitted irradiance, and it was successfully fitted to the experimental results.

Ferroelectric materials are attractive for use in a wide range of applications due to their unique transduction capabilities. However, taking full advantage of these capabilities requires a control design which accounts for the materials' inherent hysteretic behavior. A common approach is to partially cancel the hysteretic effects in the system by employing an approximate inversion algorithm in the control input, resulting in an almost linear system. Using a recently developed modification to the homogenized energy model for ferroelectric materials, we combine this method with a sliding mode control design to track a reference trajectory even in the presence of modeling and inversion errors. Numerical simulations illustrate the effectiveness of the design.

Electret and polymer piezoelectric films have been previously integrated into Micro Electro Mechanical System (MEMS) acoustic sensors and energy harvesters. Common techniques employed in MEMS polymer integration include corona discharge [1] and backlighted thyratron [2], followed by macro-scale assembly of the polymer into the micro device. In contrast, this paper reports a method for post-fabrication in-situ polarization of polymer films embedded within the MEMS device itself. The method utilizes microplasma discharges with self-aligned charging grids integrated within the device to charge fluoropolymer films in a fashion similar to the common corona discharge technique. This in-situ approach enables the integration of uncharged polymer films into MEMS and subsequent post-fabrication and post-packaging polarization, simultaneously enabling the formation of buried or encapsulated electrets as well as eliminating the need to restrict fabrication and packaging processes that might otherwise discharge pre-charged materials. Using the in situ approach, a microscale charging grid structure is fabricated and suspended a short distance above the polymer film. After fabrication of the charging grid, standard microfabrication steps are performed to build MEMS sensors. After completing the entire fabrication and packaging flow, the polarization process is performed. When energized by a high voltage, the sharp metal edges of the charging grid lead to high dielectric fields that ionize the air in the gap and force electric charge onto the polymer surface. This paper presents modeling and results for this in situ polarization process.

The traditional sintering method was used to sinter the pure and Fe2O3 doped 0.55Pb(Ni_0.33Nb_0.67)O₃-0.45Pb(Zr_0.3Ti_0.7)O₃ (abbreviate as PNN-PZT and PFNN-PZT, respectively) ceramics. The addition of Fe₂O₃ significantly improved the microstructure and electrical properties. Compared with pure PNN-PZT ceramics, higher dielectric and piezoelectric properties of d₃₁~-390 pC/N, ε _r ~6298 were obtained for the PFNN-PZT sample sintered at 1175°C for 2 h. Hence, the PFNN-PZT ceramics sample was selected to fabricate piezoelectric ceramic fibers with Pt core (PFC). Both the green fibers and bulk ceramics were sintered at 1150-1225°C for 2 h in a closed crucible, respectively. The effect of sintering temperature on the microstructure and electrical properties of the PFNN-PZT fibers was investigated. The optimal piezoelectric properties are obtained for the sample sintered at 1175°C for 2 h. The relative dielectric constant and piezoelectric constant show peak values of ε _r~3683, d₃₁~-197.4 pC/N, respectively. The PFC is a new type piezoelectric device, which can be used for sensors or actuators. The results of sensing experiment show that the piezoelectric ceramic fiber with Pt core has high sensitivity for the Lamb waves.

Piezoceramic actuators are of increasing interest within the field of adaptive optics through their ability for macro and nano positioning. However, a major drawback for their use is the inherent, non linear hysteresis that is present, which will reduce the accuracy in positioning. Typical (raw) hysteresis for multilayered piezoceramic actuators is 20% of full extension. Methods have been researched to overcome the hysteresis but they often involve complex additions to the actuators and its positioning system. This paper discusses two methods to overcome the hysteresis in a simpler approach. The first method is using capacitance measurements which correlate with the extension of the actuators and reduces hysteresis to 5%. The second method involves measuring the frequency at a specific impedance phase, which can reduce hysteresis to between 0 - 2%. Both methods provide reduction in hysteresis during extension sensing.

The paper presents electrical and mechanical properties of structural supercapacitors and discusses limitations associated with the approach taken for the electrical properties evaluation. The structural supercapacitors characterized in this work had the electrodes made of carbon fiber weave, separator made of several cellulose based products, and the solid electrolyte made as PEGDGE based polymer blend. The reported electrical properties include capacitance and leakage resistance; the former was measured using cyclic voltammetry. Mechanical properties have been evaluated thorough tensile and three point bending tests performed on structural supercapacitor coupons. The results indicate that the separator material plays an important role on the electrical as well as mechanical properties of the structural capacitor, and that Celgard 3501 used as separator leads to most benefits for both mechanical and electrical properties. Specific capacitance and leakage resistance as high as 1.4kF/m³ and 380kΩ, respectively, were achieved. Two types of solid polymer electrolytes were used in fabrication, with one leading to higher and more consistent leakage resistance values at the expense of a slight decrease in specific capacitance when compared to the other SPE formulation. The ultimate tensile strength and modulus of elasticity of the developed power storage composite were evaluated at 466MPa and 18.9MPa, respectively. These values are 58% and 69% of the tensile strength and modulus of elasticity values measured for a single layer composite material made with the same type of carbon fiber and with a West System 105 epoxy instead of solid polymer electrolyte.

Toughness of a polymer is a key material property for energy absorbing capability for various engineering applications. Significant effort has been made to improve toughness of a polymer and hence increase the energy absorbing capability; typically rigid-particles in thermoplastics or rubbery modifiers in a brittle polymer matrix. The focus of this study is to investigate toughening mechanisms of a thermoplastic polymer composite. Micron-size thermoplastic particle reinforced polycarbonate (PC) composite materials was fabricated via a solution mixing method. The mechanical properties of the polymer composites were characterized in tensile testing while the acoustic emission was monitored to assess the material failure modes during the tensile test. Substantial improvement in tensile toughness was observed for the polymer composites and the toughening mechanisms responsible for the improvement were identified and quantified for each contribution to the observation.

This research deals with the investigation of the self-healing behavior after ballistic damage of ethylene-methacrylic acid ionomers and theirs blends with epoxidized natural rubber (ENR). The self-healing capability was studied by ballistic puncture tests under different experimental conditions as sample thickness, bullet speed, diameter and shape. Bullet speed ranging from few hundreds meters per second to few km/s were employed. The healing efficiency was evaluated by applying a pressure gradient trough the plates and by checking for possible flow at the damage zone. A morphology analysis of the impact area was made observing all samples by scanning electron microscope.

Recent studies show that continuously reinforced multi-walled carbon nanotubes (MWCNT) composite can have extraordinary mechanical properties. It was observed that the continuous MWCNT polymer composites exhibit both significant reinforcement and large damping capability in compressive loadings, which typically remain compromised. The damping property might result from buckling behavior of the MWCNT in composites. Here, this paper is to study the buckling response of carbon nanotubes (CNT) within a polymer matrix by using analytical models including Euler, Timoshenko and shell buckling models. Also, the modeling results are analyzed and compared to better understand the bucking behavior of the CNT in the composite and also investigate the effect of their aspect ratio (L/D) on buckling behavior. This study provides us with insight to better understand the structure-property relation for such continuous CNT polymer composites.

A nanofluid with effective energy dissipation capability is developed with functionalized carbon nanotubes (CNTs) and nonwetting high surface tension liquid. Both CF₄ plasma treating and fluorosilane grafting methods were performed to modify the properties of tube inner walls. By adjusting the plasma treating pressure, time and the chain length of the grafted fluorosilane, the functionalized CNTs based nanofluids could achieve different energy dissipation capabilities. From the XPS, TGA and TEM test results, it is found that the tube inner surface treating rate mainly determines this energy dissipation capability. Among the functionalized CNTs, the CF₄ plasma treated SWCNTs achieve the highest dissipation capability, which is mainly due to the small pore diameter and high inner surface treating rate.

Auxetic (negative Poisson's ratio) configurations have recently been used to build prototypes of deployable structures using classical shape memory alloys (Nickel-Titanium-Copper). Chiral configurations, featuring three or more inter-connected spiral-wound hubs, exploit efficient tensile-rotational mechanisms. These structures offer high deployability ratios in structural elements with load-bearing characteristics. Shape memory polymers have the potential to replace these shape memory alloys and other stored-energy actuators, and have the attractive properties of low mass, high actuation strain, easy fabrication and tuneable thermal properties. In this work we discuss how shape memory polymers (SMP) integrated into a chiral core could offer enhanced deployable characteristics and increase the efficiency of the auxetic deformations in these unusual cellular structures. We consider the spiral-wound fundamental component needed for SMP n-chiral prototypes and present test results showing actuation motion of expanding SMP deployable structures. Applications likely to benefit from these structures include lightweight elements for structural engineering applications, deployable structures for space applications and implantable medical devices.

In this paper, we demonstrate an assisted self-assembly fabrication method for unidirectional patterns using pre-programmed shape memory polymer (SMP) as the substrate in an organic/inorganic bi-layer structure. By heating the hybrid structure above the SMP's shape recovery temperature, the substrate expands because of positive CTE in one direction, while in the perpendicular direction it shrinks due to shape memory effect overpowering thermal expansion. Consequently, the metal thin film coated on the substrate is subjected to an orthogonal compression-tension stress field and forms unidirectional wavy patterns. The experimentally obtained wrinkles are well-aligned with uniform wavelength ranging from about 850 nm to 1.5 μm corresponding to various programming strains and film thicknesses. A parametric study was carried out to study the influence of programming strain and film thickness on wrinkle wavelength. It was found that both the decrease of programming strain and the increase of film thickness can result in a longer wavelength. The present study is expected to offer a convenient and simple path of fabricating unidirectional wavy patterns.

Shape memory cyanate polymers (SMCPs) are a new kind of smart materials, which have huge development potential and a promising future. A series of shape memory cyanate polymers were prepared by cyanate ester and varying content of a linear modifier. The thermal properties of the SMCPs were investigated by Differential Scanning Calorimetry (DSC), Thermal Gravimetric Analysis (TGA) and Dynamic Mechanical Analysis (DMA). The SMCPs we prepared have high glass transition temperature and show good heat resistance. The glass transition temperature T_g can be adjusted from 156.9°C to 259.6°C with the modifier. The initial temperature of thermal decomposition comes up to 300°C, which is enough high for the application in aerospace fields. The shape memory polymer we prepared shows a good shape memory effect, as the shape recovery time is less than 65s and the shape recovery rate reaches 95%.

Functional polymer composite is expected to be applied to the potential material for space deployable structures. Especially, thermally-activated shape-memory polymer (SMP) composites are increasingly investigated due to their excellent shape fixity and shape recovery; the thermomechanical properties of these materials greatly change around their glass transition temperature T_g. To enhance the ability of space deployable structures, the microstructural design at the fiber-matrix level in the material is required to pursuit the better performance of SMP composite. The present study focused on a micromechanics consideration of shape-memory polymer (SMP) composite with slits in the fiber mat, and attempted to discuss the effect of microstructural heterogeneities (slit positions) on the shape-fixity and shape-recovery performance. Analysis of the shape-recovery performance of SMP composites was conducted using the micromechanical model based on a viscoelastic thermomechanical constitutive model. According to the numerical results, only when the slits gather at the same location, the best shape-fixity property and shape-recovery performance is achieved, while sacrificing its bending stiffness. This is because the slits act as a hinge in the material under a bending loading.

On application of heat, shape memory polymers (SMPs) are able to revert to a primary shape from a secondary shape induced by mechanical deformation. It may be desirable to induce shape recovery at controlled rates under quasi-isothermal conditions, e.g. in certain biomedical applications in which actuation occurs at body temperature, requiring knowledge of the time dependent response of SMPs. In the present work, the time dependence of isothermal shape recovery has been investigated for two shape memory polyurethanes (SMPUs) with different molecular architectures. These are discussed in terms of a simple linear thermo-viscoelastic model for the time and temperature dependence of the shape memory response at small deformations, based on data obtained from a single constant frequency dynamic mechanical analysis (DMA) temperature sweep. This approach is based on the establishment of an approximate relationship between the storage modulus E'(T), the loss factor tan δ(T) and the shift factor, a_T(T), more usually derived from time-temperature superposition of isothermal data obtained at different temperatures. The DMA data are thus shown to be sufficient to describe the relaxation and retardation time spectra. As well as providing a useful phenomenological description of the shape memory effect, the model derived from the DMA data permits quantitative comparison of materials, and may hence be used as guidelines for materials design for specific applications. This is demonstrated for the two SMPUs considered in the present work, whose viscoelastic spectra vary significantly in width, affording considerable insight into the distribution of segmental mobility within the polymer network.

Shape memory composites (SMCs) made of shape memory alloy (SMA) wires embedded in a shape memory polymer (SMP) matrix show great promise in adaptive structures due to their ability to combine strong actuation force of SMAs with the large deformation of SMPs. However, in order to advance these SMCs past the proof-of-concept stage, methods for optimizing the material selection and volume fraction balance between the alloy and the polymer must be developed. Before such multi-objective optimization can take place, sensitivity studies must be conducted to determine which parameters are most impactful in determining the ultimate behavior of the SMC. The present study focuses on thermal and mechanical characterization of a group of SMCs composed of Nickel-Titanium SMA and a styrene based SMP in order to elucidate the critical material properties for a functioning SMC. Here, the SMA wires have been trained with a one-way shape memory effect (SME) and integrated on the surface of the SMP. A morphing system has been obtained by introducing SMA wires on the SMP system in the volume fraction range of 0.5% to 1.2%. The results show that the proper modulus balance between the SMP and SMA as well as the balance of activation forces are important features to consider when developing a SMC. Also important is a proper pairing of glass transition temperature for the SMP with the Austenite and Martensite transition temperatures for the SMA. In addition, the current study has shown that during the heating process of the SMC, the thermal expansion of the SMP appears to overcome the actuation forces of the SMA wires, showing that the thermal expansion is also a critical variable for the composite performance. Based on these results, both the SMA and the SMP constituent parameters of temperatures, elastic modulus, actuation force, and thermal expansion are considered with regards to future tailoring the SMC performance.

A new nanopaper that exhibits exciting electrical and electromagnetic performances is fabricated by incorporating magnetically aligned carbon nanotube (CNT) with carbon nanofibers (CNFs). Electromagnetic CNTs were blended with and aligned into the nanopaper using a magnetic field, to significantly improve the electrical and electromagnetic performances of nanopaper and its enabled shape-memory polymer (SMP) composite. The morphology and structure of the aligned CNT arrays in nanopaper were characterized with scanning electronic microscopy (SEM). A continuous and compact network of CNFs and aligned CNTs indicated that the nanopaper could have highly conductive properties. Furthermore, the electromagnetic interference (EMI) shielding efficiency of the SMP composites with different weight content of aligned CNT arrays was characterized. Finally, the aligned CNT arrays in nanopapers were employed to achieve the electrical actuation and accelerate the recovery speed of SMP composites.

In this presented paper, spandex fibers with high elasticity and high recovery ratio were added into shape memory epoxy resin, and the mechanical properties were improved obviously compared with pure shape memory resin. Compared with pure material, elastic modulus of the sample with 20vol% spandex was increased by 28.2%, tensile stress by 49.7%, and fracture strain by 16.4%. Then graphitized multi-walled carbon nanotubes (GMWNTs) were mixed into the spandex reinforced SMPCs to make it conductive. It was found that surface-modified (by acid treatment) GMWNTs incorporated very well with resin, and dispersion was achieved by high-energy sonication. In order to study the electrical conductivity, the Four-point Probe Method was conducted on the surface-modified GMWTs reinforced composites. ( an order of 6.86 x10⁴ Ω •cm was obtained in samples with 4.5wt% modified-GMWNTs). In comparison with the pure spandex reinforced SMPCs, the elastic modulus of the surface-modified GMWTs (4.5wt%) reinforced composites was increased by 300%, the tensile stress by 26%. However, the elongation at break of the SMPCs was decreased when GWMNTs were mixed in it.

Filled with iron particles, polymers can be made responsive to magnetic fields. Specifically, the elastomers that change stiffness in response to a magnetic field are usually called magneto-rheological elastomers (MREs). Anisotropic MREs, in which the particles are aligned during curing and form chain-like structures, exhibit a more significant magneto-rheological (MR) effect, i.e. the field-induced stiffening. In this paper, we first develop a constitutive model for the nonlinear behavior of deformable solids under magnetic field. Based on the filler-substrate microstructure of MREs, we further implement the theory into a finite element method. The magneto-mechanical response of a representative unit cell of MRE is studied using the finite element method. The MR effect in both the shear modulus and the tensile modulus of an MRE is studied. In addition, we consider the viscoelasticity of the polymer matrix and study its effect on the properties of an MRE. Using the viscoelastic model for MRE, we also investigate the frequency dependence of the MR effect.

The microstructure of magnetic shape memory alloys (MSMAs) is comprised of tetragonal martensite variants, each with their preferred internal magnetization orientation. In the presence of an external magnetic field, the martensite variants tend to reorient so that the preferred internal magnetization aligns with the external magnetic field. Thus MSMAs exhibit the shape memory effect when there is a magnetic field in the vicinity of a material point. Furthermore, the tetragonal nature of the martensite variants allows for a compressive stress to cause variant reorientation. This paper focuses on the experimental evaluation of MSMAs in power harvesting as well as on the response of the material under complex loading conditions. The experimental data reported here provides a basis for the evaluation of MSMAs suitability for applications other than the traditional actuation under a constant magnetic field. For power harvesting applications, consider an MSMA element subject to a large enough magnetic field so that all the variants begin in a field preferred state. Keeping the magnetic field constant and adding a variable compressive stress in a direction normal to that of the magnetic field, some or all of the martensitic variants may rotate into a stress preferred state. As the variants reorient, the internal magnetization vectors rotate, and the specimen's magnetization changes. The change in magnetization induces a current in a pick-up coil, resulting in an output voltage at its terminals according to Faraday's law of inductance. For other applications, the loads that an MSMA element is subject to may be different. Investigation into other potential loadings of an MSMA will give a better overall understanding of the magneto-mechanical behavior of MSMAs and perhaps highlight potential applications of these materials. Thus complex loads on MSMAs should be investigated experimentally and eventually modeled mathematically. For example, this work will study variable field and variable stress loading, which might occur if an actuator is being designed to displace a variable load over a controlled distance.

It has been observed that carbon nanotubes (CNT) have a measurable inherent piezoresistive eect, that is to say that changes in carbon nanotube strain can induce changes in its resistivity, which may lead to observable macroscale piezoresistive response of nanocomposites. In this paper, the focus is on modeling the eect of inherent piezoresistivity of carbon nanotubes on the nanocomposites piezoresistive behavior by using computational micromechanics techniques based on nite element analysis. The computational results show the magnitude of the piezoresistive coecients needed for the piezoresistive response of the macroscale nanocomposites to be comparable with experimental data in literature if inherent piezoresistive eect of CNTs is the only driving force for the piezoresistive response of the macroscale nanocomposites.

The various excellent properties of carbon nanotubes (CNTs) are in the focus of researchers since years. Moreover architectures, built of CNTs, show active behavior in terms of deflections. Therefore they have to be set up like a capacitor within an electric field and covered by a matrix of free movable ions. The mechanism behind this phenomenon is still discussed obsessively rather to be an quantum-mechanical elongation of the C-bonds or to be caused by electrostatic repulsion of charged agglomerated CNTs. Formally investigated paper-like architectures, known as Bucky-papers, consist of randomly oriented CNTs. This paper presents several experimental approaches and results documenting doubts about the ability to clarify the active mechanism by investigating the electro-mechanical properties of those paper-like architectures. In contrast a novel test set-up for analyzing specimen, providing highly vertically aligned CNTs, is presented. This high resolution test set-up is designed to analyze CNT-specimen in thickness-direction optically. The vertically aligned CNT-architectures, also called CNT-arrays, consist of multi-walled CNTs (MWCNTs). The MWCNT-arrays are highly hydrophobic and can only be moistened by polar liquids like ionic liquids (ILs). The latest results of the electro-mechanical system as well as further challenges dealing with ILs and different kinds of CNT-arrays are presented. The presented measurement method allows an even more precise investigation of the electro-mechanical behavior of a single MWCNT and the strain-mechanism simultaneously. Furthermore this configuration points out an efficient mode of future CNT-based actuators.

The development of structural health monitoring techniques leads to the integration of sensing capability within engineering structures. This study investigates the application of multi walled carbon nanotubes in polymer matrix composites for autonomous damage detection through changes in electrical resistance. The autonomous sensing capabilities of fiber reinforced nanocomposites are studied under multiple loading conditions including tension loads. Single-lap joints with different joint lengths are tested. Acoustic emission sensing is used to validate the matrix crack propagation. A digital image correlation system is used to measure the shear strain field of the joint area. The joints with 1.5 inch length have better autonomous sensing capabilities than those with 0.5 inch length. The autonomous sensing capabilities of nanocomposites are found to be sensitive to crack propagation and can revolutionize the research on composite structural health management in the near future.

Shape memory alloy (SMA) wires are capable of providing contractile strain mimicking the functionality of muscle fibers. They are promising for the development of biomimetic robots due to their high power density and desired form factor. However, they suffer from significantly high power consumption. The focus of this paper was to address this drawback associated with SMAs. Two different parameters were investigated in this study: i) lowering of the martensite to austentite phase transition temperatures and ii) the reduction of the thermal hysteresis. For an equiatomic Ni-Ti alloy, replacing nickel with 10 at% copper reduces the thermal hysteresis by 50% or more. For Ni- Ti alloys with nickel content greater than 50 at%, transition temperature decreases linearly at a rate of 100 °C/Ni at%. Given these two power reducing factors, an alloy with composition of Ni_40+xTi_50-xCu₁₀ was synthesized with x = 0, ±1, ±2, ±3, ±4, ±5. Metal powders were melted in an argon atmosphere using an RF induction furnace to produce ingots. All the synthesized samples were characterized by differential scanning calorimetric (DSC) analysis to reveal martensite to austenite and austenite to martensite transition temperatures during heating and cooling cycles respectively. Scanning electron microscopy (SEM) was conducted to identify the density and microstructure of the fractured samples. The alloy composition and synthesis method presented in this preliminary work shows the possibility of achieving low power consuming, high performance SMAs.

This paper addresses the development of active metal-matrix composites manufactured by Ultrasonic Additive Manufacturing (UAM), an emerging manufacturing process that allows the embedding of materials into seemingly solid metal components. In the UAM process, successive layers of metal tapes are ultrasonically bonded together at low temperatures to form a metal-matrix. Being a low-temperature process, UAM offers unprecedented opportunities to create metal components with embedded thermally-sensitive materials, such as shape memory alloys. In this study UAM is used to create composites with aluminum matrices and embedded NiTi ribbons. These composites exhibit tunability of both the coefficient of thermal expansion and natural frequencies. These effects are due to the phase-dependent modulus and transformation stresses developed by the prestrained NiTi phase. Since the embedded NiTi ribbons are constrained by the matrix, thermally-induced transformation from detwinned martensite to austenite will be accompanied by the generation of transformation stresses. The effect of transformation stress and changing phase of NiTi on thermally-induced strain is observed and modeled by combining strain matching algorithms with thermodynamic-based constitutive models. The composite model accurately describes effects due to changing NiTi modulus and strain recovery due to initial stress-induced martensitic volume fractions including a 200 με contraction with increasing temperature. The observed dynamic behaviors include up to a 16.6% increase in natural frequency at 100°C as compared to room temperature tests. No substantial increase in damping ratio was observed relative to solid aluminum.

Fibers can play a major role in post cracking behavior of concrete members, because of their ability to bridge cracks and distribute the stress across the crack. Addition of steel fibers in mortar and concrete can improve toughness of the structural member and impart significant energy dissipation through slow pull out. However, steel fibers undergo plastic deformation at low strain levels, and cannot regain their shape upon unloading. This is a major disadvantage in strong cyclic loading conditions, such as those caused by earthquakes, where self-centering ability of the fibers is a desired characteristic in addition to ductility of the reinforced cement concrete. Fibers made from an alternative material such as shape memory alloy (SMA) could offer a scope for re-centering, thus improving performance especially after a severe loading has occurred. In this study, the load-deformation characteristics of SMA fiber reinforced cement mortar beams under cyclic loading conditions were investigated to assess the re-centering performance. This study involved experiments on prismatic members, and related analysis for the assessment and prediction of re-centering. The performances of NiTi fiber reinforced mortars are compared with mortars with same volume fraction of steel fibers. Since re-entrant corners and beam columns joints are prone to failure during a strong ground motion, a study was conducted to determine the behavior of these reinforced with NiTi fiber. Comparison is made with the results of steel fiber reinforced cases. NiTi fibers showed significantly improved re-centering and energy dissipation characteristics compared to the steel fibers.

This paper considers new extensions to a three-dimensional constitutive model originally developed by Lagoudas and co-workers. The proposed model accurately and robustly captures the highly anisotropic transformation strain generation and recovery observed in actuator components that have been subjected to common material processing and training methods. A constant back stress tensor is introduced into the model, which is implemented in an exact form for simple tension/torsion loading as well as into a commercial finite element code to perform a 3-D analysis of a Shape Memory Alloy (SMA) torque tube actuator subjected to different loading schemes. Numerical correlations between predicted and available experimental results demonstrate the accuracy of the model.

In this paper, we employ a homogenized energy model (HEM) for shape memory alloy (SMA) bending actuators. Additionally, we utilize a Bayesian method for quantifying parameter uncertainty. The system consists of a SMA wire attached to a flexible beam. As the actuator is heated, the beam bends, providing endoscopic motion. The model parameters are fit to experimental data using an ordinary least-squares approach. The uncertainty in the fit model parameters is then quantified using Markov Chain Monte Carlo (MCMC) methods. The MCMC algorithm provides bounds on the parameters, which will ultimately be used in robust control algorithms. One purpose of the paper is to test the feasibility of the Random Walk Metropolis algorithm, the MCMC method used here.

A macroscopic phenomenological framework is used for developing a closed-form solution for analyzing the pure bending of shape memory alloy (SMA) beams. In order to study the effect of tension-compression asymmetry on the bending response, two different transformation functions are considered; a J₂-based solution with symmetric tension-compression response, and a J₂ - I₁-based solution capable of modeling the tension-compression asymmetry. The constitutive equations are reduced to an appropriate form for studying the pseudoelastic bending response of SMAs, and closed-form expressions are obtained for the stress and martensitic volume fraction distributions in the cross section. These expressions are used for calculating the bending moment-curvature analytically. Both circular and rectangular cross sections are considered and several case studies are presented for analyzing the accuracy of the presented method and also the effect of considering the tension-compression asymmetry on the bending response of SMAs.

Stress arrest of loading or unloading during pseudoelastic phase transformations in shape memory alloys has shown to exhibit creep-like phenomenon even at strain rates that can be considered quasi-static and devoid of any thermal effects. This phenomenon termed as pseudo-creep is manifested as positive (negative) accumulation in strain during loading (unloading) when arrested at constant stress. Pseudo-creep is also found to occur during reorientation loading, where thermomechanical coupling is absent. In this paper, we report results of extensive studies conducted on poly-crystal Ni-Ti wires for stress arrest of loading and unloading at normalized strain rates ranging from 4.25E-7 (virtually isothermal conditions) to 4.25E-5 in conjunction with a video multi-extensometry technique developed in our laboratory to measure spatially non-uniform deformations in the sample and have recorded evolution in phase transformations or reorientation in three consecutive segments of the wire (constituting the total gauge length for video multi-extensometry) during stress arrest.

We report on key challenges of the development of steel cords reinforced thermoplastic elastomer composites with smart functionalities: adhesion tailoring for a durable mechanical load transfer through steel cords or other transmission elements by the use of surface treatments and primers, and integrated distributed temperature and strain sensing by the use of embedded fiber optic sensors. Traditional surface treatments including silane coupling agent were outperformed in processing time, adhesion and durability by a fast-curing coupling method using a UV-curable primer; and the integrated distributed temperature and strain sensing capability was demonstrated. The practical applications of the resulting multifunctional transmission element are then discussed in light of these results.

Sandwich composite structures have highly desirable properties including superior stiffness and strength-to-weight ratios. Such properties arise from combining thin, stiff materials called face sheets with a soft, thick core. Unfortunately these properties give rise to poor acoustic performance, as sandwich structures efficiently radiate noise at low vibrational frequencies. Therefore much consideration has been given to improve acoustic performance with small sacrifices in key mechanical performances, such as bending stiffness and weight. This study focuses on sandwich composite structures with both high noise mitigation and passive structural dampening. Specifically, it is sought to understand how the vibrational responses of carbon-fiber face sheet sandwich composite beams are affected by the core's thickness, as well as its properties. Here, it is shown that the relationship between bending stiffness and coincidence frequency (a metric of acoustic performance) is non-linear. By reducing the core thickness from 10.7mm to 8.4mm, approximately 120% improvement is seen in acoustic performance. Also, the core materials' specific shear modulus is inversely proportional to acoustic performance. Finally, superior damping performance can lead to substantial noise mitigation in low vibrational frequencies. Thus coupling these concepts will provide vastly improved acoustic performance with minimal sacrifices in mechanical performance or weight.

Mechanoluminescence (ML) materials have recently attracted considerable attention due to their potential applications as an imaging sensor for detecting damages and measuring stress distributions in complex structures, which is difficult for conventional methods. SrAl₂O₄:Eu²⁺ (SAOE) is a ML material with the best performance but it hydrolyzes rapidly under humid environment, which limits the scope of its applications especially in outdoor environments, e.g. structural health monitoring for buildings, bridges and tunnels. Thus ML materials with water resistance such as silicates and aluminosilicates have been developed, but the brightness of which is still much lower than SAOE. In this study, we report a novel method to improve the impact-induced ML in ML materials using the swift heavy ion (SHI) irradiation. The impact-induced ML intensity of CaSrAl₂Si₂O8:Eu²⁺ was dramatically enhanced by about one order of magnitude using SHI irradiation. Furthermore, higher electronic stopping power and higher irradiation fluence were found to be more effective for improving the impact-induced ML. It is considered that the trap density suitable for the impactinduced ML was increased by the SHI irradiation, resulting in the impact-induced ML enhancement. The underlying mechanism was discussed, which is of great importance for developing new ML materials for structure health monitoring.

A new multi-stable lattice structure which is assembled by rectangular bi-stable composite laminates is designed. The snap-through of rectangular cross-ply composite laminates and a lattice structure is numerically and experimentally studied. The experiments to measure the snapping force levels of rectangular laminates and lattice structures are conducted. A method based on commercial software ABAQUS to simulate the snap-through behaviors of lattice structures is presented. Snap through of lattice structures are successfully described with the use of this method. The same phenomenon between the FEA and experiments are observed. The predicted curvatures show a good agreement with experimental results while there are some errors between predicted and measured critical loads.

In this paper, Polyaniline-based fibrous membranes were fabricated with multi-walled carbon nanotubes and polyethylene oxide (PEO) by the electrospinning method. And then PANi/PEO/MWCNT fibrous membranes reinforced epoxy based nanocomposite was then fabricated. The morphology and electrical properties of PANi /MWCNT /PEO fibrous membrane was characterized by scanning electron microscope (SEM). The morphologies of the membranes indicate that the electrospining method can fabricate well nano structures fibrous membrane. The EM properties of the composite reinforced with the electrospining fibrous membrane were measured by vector network analyzer. The results show that the permittivity real, image parts and permeability real part of the composite increase by filling with PANI/PEO and PANI/CNT/PEO membrane. The EM shielding and absorb performance is base on the dielectric dissipation. And different membranes made of different materials show different EM parameter, and different EM shielding performance, which can be used to the EM shielding and stealth material design and fabrication.

Molecular mechanics simulations have been used to study the deformation and mechanical properties of crystalline cellulose II. Good agreement was achieved with the experimental lattice parameters, bond lengths and angles, and hydrogen bond network. Auxetic (negative Poisson' ratio) behaviour was predicted in the y-z plane in crystalline cellulose II, in agreement with experiment.

On the basis of size effect models of aluminum oxide particle optical constant, this paper introduces temperature amendment of complex refractive index below melting point using the relationship between complex refractive index and temperature; while the amendment is introduced above melting point using the relationship between oscillator density and quality density. To found the dependence of complex refractive index of aluminum oxide particle on varying with diameter, then calculate it at the wavelength of 0.6328μm and the temperature ranged from 300K to 3000K. Through comparing with experimental value of complex refractive index for bulk aluminum oxide, the response of optical constant to temperature is obtained. It is concluded that the evolution of complex refractive index of aluminum oxide particles with temperature is basic in agreement with the bulk aluminum oxide, and showing obvious size effect of complex refraction index of particles within 1.3<χ <7.4. Finally, the index of complex refraction of aluminum oxide particles with the diameter of 0.97μm is calculated from 300K to 3000K, which further validates the size effect.

Cellulose has been investigated as a promising green material. Piezoelectricity is the embedded property of this material. Sandwiched layer of electro-spun cellulose may produce enhanced mechanical and electrical properties because of the nano-scaled electro-spun cellulose layer. Mechanical tests are executed to observe the strength of cellulose composite. Scanning electron microcope is investigated to observe the formation of layers and cross section of composite. Electrical properties such as capacitance are measured as a function of temperature to assess the dielectric constant of this material.

Thermoplastic polymers are often reinforced by adding short fibers to improve mechanical properties including Young's modulus and tensile strength of the polymers. In many engineering applications, energy absorbing characteristics in such particulate polymers is known to be a very important property to be considered in composite designs, and meanwhile debonding at the interface between fiber and matrix in the composites may affect the energy absorption properties. Here, the focus of this study is to employ a semi-empirical approach to determine the debonding stress and investigate the effect of the debonding stress on energy absorbing properties of short glass fiber reinforced polycarbonate composites. Glass short fiber reinforced polycarbonate composites are fabricated via a solution mixing technique. Tensile testing and acoustic emission measurement are simultaneously performed for the polycarbonate composites. The test results including toughness are compared for the composites over neat polycarbonate. Also the local debonding stress in the vicinity of each glass fiber in composites is estimated by combining modeling and experiments. A finite element model is developed to determine local debonding stress at the interface between the fiber and matrix. The local debonding stress appears to considerably affect the toughness of the composites.

In this paper we show that the bandstructure of a periodic elastic composite, in addition to being dependent upon the micro-constituents and their microarchitecture, may also be controlled by changing the temperature. The essential idea is to fabricate a periodic composite with constituent materials which have temperature dependent elastic properties. As temperature is changed, such a composite is expected to exhibit a bandstructure which changes with the temperature dependent properties of its micro-constituents. For our purpose, we use polyurea and steel to make a 1-D periodic composite. Ultrasonic measurements are done on the sample from 0.5 kHz to 1.5 MHz under changing temperature and the change in the second passband is studied. It is observed that the change in the bandstructure is significant when the temperature is changed from -50°C to 50°C. Experimental results are compared with the theoretical calculations and it is shown that good agreement exists for the observed bandstructure.

We used a new method to fabricate salami-type porous metal from glass microcapsules and liquid metal. Each pore of its salami-like structure behaves as a micro-bell. This metal, which is more than 20% lighter than bulk material, also shows a unique characteristic: high-frequency oscillation is greatly attenuated when propagated in its medium. This method offers great potential for size, shape, and conformation control, with changed attenuation characteristics of its salami-like pore structure achieved merely by changing the mixing technique. This study was conducted to measure compressive deformation behavior and attenuation characteristic of salami-type porous SnSbCu. To begin with, we fabricated two salami-type porous metals using 16um or 60um diameter microcapsule, which have different salami structures in its body. Next, compressive loading test was conducted for the metals. Then, the attenuation characteristic was investigated using laser ultrasonic measurement. Thereby, compressive deformation behavior was same between fabricated two salami-type porous metals. In contrast, the attenuation characteristic was different at low frequency range between them.

Most of the analysis techniques used on functionally graded piezoelectric plates consider the effects of through-thickness strains since they can be significant in thick plates. Many practical applications of such plates, however, are in the form of actuators which are not necessarily thick. A simple theory such as the classical lamination theory can, therefore, provide useful estimates of in-plane deflections and stresses in thin and moderately thick plates. This theory does not, however, directly accommodate material properties that change progressively and it is desirable to develop a method with this capability. This paper presents such an approach, formulated as an extension to classical lamination theory. Polynomial series are used to approximate the true through-thickness variation in material properties and electric field strength. The resulting mathematical problem can be explicitly formulated irrespective of the actual variation in these parameters. A comparison against results from an exact three dimensional analysis demonstrates the use and accuracy of the method.

Polyvinylidene difluoride (PVDF) is a piezoelectric polymer with a low-cost, high flexibility and biocompatibility that is suitable for various energy conversion applications between the electrical and mechanical forms of energy. One of the novel techniques to create PVDF fibers is electro-spinning. In the present work, the above technique has been applied to develop electro-spun thin-film based on PVDF with the use of high electric field and a high-frequency mechanical vibratory motion as an electro-spinning setup. The high-frequency vibratory motion is used to create effective fluid viscous forces to achieve a localized fluid spreading and thinning behavior of extremely thin polymer fiber solution.

When designing optical devices, the alignment of every element is integral to the proper functionality of the device. If any of these elements is secured by means of a friction joint, it is important to understand the limitations of the joint when vibrations (mainly during launch) occur; a phenomenon called "stick-slip" may happen and permanently displace joints relying on friction and cause optical misalignments. There is little to no data documenting the characteristics of the "stick-slip" phenomenon on friction joints under random vibratory motion. The test program was designed with the aim of gathering data that would broaden the understanding of the "stick-slip" phenomenon and among other things provide sufficient information to quantify the static coefficients of friction of several single-bolt friction joint material pairings. This paper describes the test program in detail including test sample description, test procedures, and vibration test results of multiple test samples. The material pairs used in the experiment were Aluminum-Aluminum, Aluminum- Dicronite coated Aluminum, and Aluminum-Plasmadize coated Aluminum. Levels of vibration for each set of twelve samples of each material pairing were gradually increased until all samples experienced substantial displacement. Data was collected on 1) acceleration in all three axes, 2) relative static displacement between vibration runs utilizing photogrammetry techniques, and 3) surface galling and contaminant generation. This data was used to estimate the values of static friction during random vibratory motion when "stick-slip" occurs and compare these to static friction coefficients measured before and after vibration testing.

Designers of electronic devices and telecommunications equipment have used three-dimensional chip architecture, comprised of a vertically integrated stack of chips, to increase the number of transistors on integrated circuits. These latest chips generate excessive amount of heat, and thus can reach unacceptably high temperatures. In this context, this research aims to develop thermally conductive liquid crystal polymer (LCP)/hexagonal boron nitride (hBN) composite films to replace the traditionally-used Kapton films that satisfy the electrical insulation requirements for the attachment of heat sinks to the chips without compromising the heat dissipation performance. Parametric study was conducted to elucidate the effects of hBN contents on the heat dissipation ability of the composite. The performance of the hybrid heat sinks were experimentally simulated by measuring the temperature distribution of the hybrid heat sinks attached to a 10 W square-faced (i.e., 10 cm by 10 cm) heater. Experimental simulation show that the maximum temperature of the heater mounted with a hybrid heat sink reduced with increased hBN content. It is believed the fibrillation of LCP matrix leads to highly ordered structure, promoting heat dissipation ability of the electrically insulating pad of the hybrid heat sink.