Search

For the past six years, we have been benefiting from the discovery by Tsai and Melo (2014) that the trace of the plane stress stiffness matrix ( tr ( Q ) ) of an orthotropic composite is a fundamental and powerful scaling property of laminated composite materials. Algebraically, tr ( Q ) turns out to be a measure of the summation of the moduli of the material. It is, therefore, a material property. Additionally, since tr ( Q ) is an invariant of the stiffness tensor Q , independently of the coordinate system, the number of layers, layup sequence and loading condition (in-plane or flexural) in a laminate, if the material system remains the same, tr ( Q ) = tr ( A ∗ ) = tr ( D ∗ ) is still the same. Therefore, tr ( Q ) is the total stiffness that one can work with making it one of the most powerful and fundamental concepts discovered in the theory of composites recently. By reducing the number of variables, this concept shall simplify the design, analysis and optimization of composite laminates, thus enabling lighter, stronger and better parts. The reduced number of variables shall result in reducing the number and type of tests required for characterization of composite laminates, thus reducing bureaucratic certification burden. These effects shall enable a new era in the progress of composites in the future. For the above-mentioned reasons, it is proposed here to call this fundamental property, tr ( Q ) , as Tsai’s Modulus.

A magnetodielectric substrate is firstly proposed for implantable antennas in medical implant communication service (MICS) band. Ba 3 Co 2 Fe 24 O 41 (Co 2 Z), Z-type hexaferrite flakes synthesized by molten-salt method were incorporated with a polymer matrix, having a real permeability of 2.88 and a magnetic loss of 0.029 at 402 MHz. A spiral antenna with the magnetodielectric substrate has a bandwidth 70% and 50% broader than that with a commercial dielectric substrate, Rogers 3210, in a 2/3-phantom model and a multi-layered body model, respectively. The band broadening retains the bandwidth to be overlapped after implant positions change, leading to an enhancement in insensitivity to the implant position.

Hierarchical +1 composites consisting of carbon fibers with carbon nanotubes (CNTs) grown onto them and an epoxy matrix were processed, and the mode I fracture toughness of these composites was evaluated. The mode I fracture toughness of the initial batches of the hierarchical composites was lower than that of the baseline samples without CNTs. Hence, efforts to enhance the adhesion between carbon fibers and CNTs were made, resulting in enhanced adhesion. The enhanced adhesion was confirmed by Scotch tape tests and mode I fracture toughness tests followed by fractographic studies. The mode I fracture toughness of the hierarchical composites with enhanced adhesion was 51% and 89% higher than those of the baseline samples and hierarchical composites with poor adhesion, respectively. Moreover, fractographic studies of the fracture surfaces of the hierarchical composites with enhanced adhesion showed that CNTs were still attached to carbon fibers even after the mechanical tests.

A method is introduced to study the effects of flexural deformation on the electrical performance of thin-film lithium-ion batteries. Flexural deformation of thin films is of interest to engineers for applications that can be effective in conformal spaces in conjunction with multi-functional composite laminates in structural members under mechanical deflections such as thin airfoils used in unmanned aerial vehicles (UAVs). A test fixture was designed and built using rapid prototyping techniques. A baseline reference charge/discharge cycle was initially obtained with the device in its un-flexed state, in order to later contrast the performance of the thin-film battery when subjected to deflections. Progressively larger deflections were introduced to the device starting with its un-deformed state. The cord flexure was applied in increments of 1.3% flex ratio, up to a maximum of 7.9%. At each successive increment, a complete charge/discharge cycle was performed. Up to a flex ratio of 1.3%, no effects of mechanical flexure on battery performance were observed, and the device performed reliably and predictably. Failure occurred at deflections above 1.3% flex ratio.

Two-dimensional mapping of the laser-induced breakdown spectroscopy (LIBS) signal of chemical species information in liquefied petroleum gas (LPG) and electrolytic oxy-hydrogen (EOH) flames was performed with in situ flame diagnostics. Base LIBS signals averaged from measurements at wavelengths of 320 nm to 350 nm describe the density information of a flame. The CN LIBS signal provides the concentration of fuel, while the H/O signal represents the fuel/air equivalence ratio. Here, we demonstrate the meaningful use of two-dimensional LIBS mappings to provide key combustion information, such as density, fuel concentration, and fuel/air equivalence ratio.

A quick recovery: A semitransparent composite conductor comprising a layer of silver nanowire percolation network inlaid in the surface layer of a Diels-Alder-based healable polymer film is fabricated. The composite is flexible and highly conductive, and is capable of both structural and electrical healing via heating. Cut samples that completely lose their conductivity can recover 97% of it within 5 minutes of heating at 110 °C. The cutting and healing can be repeated at the same location for multiple cycles.

The aim of this study was to investigate the effects of adding maleic anhydride grafted polypropylene (MA-PP) and graphite nanoplatelets (GNPs) into polypropylene. The tensile strength and flexural properties of the GNP/PP composite were enhanced with an increase in the MA-PP content and the GNP content. The maximum increase of mechanical properties was shown at 10 wt.% of MA-PP having a constant GNP content of 8 wt.% and at 20 wt.% of GNP having a constant MA-PP content of 5 wt.%, whereas a decrease in tensile strength and flexural properties was observed at 20 wt.% of MA-PP. The impact strength was decreased by increasing the MA-PP content and the GNP content. The electrical resistivity of the GNP/PP composite exhibited an anisotropic characteristic due to the direction of the injection molding flow. Electrical resistivity of less than 106 Ω cm regardless of the direction of the resin flow could be obtained by adding more than 20 wt.% of GNP when the MA-PP content was 5 wt.%. The differential scanning calorimetry results suggest that an increase of the GNP content makes it act as a nucleating agent and thus causes an increase in the crystallinity of the PP.

We report the synthesis of graphene/fullerene-capped gold nanoparticle nanocomposite film which was used to construct supercapacitor electrodes. The fullerene-based self-assembled monolayers on gold nanoparticles (AuNPs) were attained via the fullerene(C60)-gold interaction. The fullerene-capped AuNPs effectively separated the graphene sheets preventing aggregation. A synergistic effect was observed—the specific capacitance of graphene/fullerene-capped AuNP electrode is197 F/g, which is higher than that of graphene electrode (31 F/g), graphene/AuNP electrode (126 F/g), and graphene/fullerene electrode (118 F/g). The results render a novel route of synthesis and modification of graphene-based materials for the construction of electrochemical energy storage devices.

This study presents a multiscale numerical framework designed to predict the nonlinear constitutive behavior of metal-composite interfaces in titanium-graphite fiber metal laminates. Molecular-level property predictions derived in a separate analysis are used to parameterize a finite element model of the interface by means of a traction-separation constitutive law. Additional continuum-level energy dissipation and progressive failure phenomena are implemented into commercial finite element software through a user-defined material subroutine. Results obtained from this multiscale interface model are compared against experimental measurements of titanium-graphite fiber metal laminates in a short-beam shear loading configuration. The model predictive accuracy and its application to other bonded metal-composite systems are subsequently discussed.

This paper aims to develop an autonomic thermal management system of graphite fiber/polymer composite structures using their electrical property. A number of copper tapes are integrated on top and bottom surfaces of a composite plate, and through the thickness resistances between these tapes are measured on a hotplate for temperature monitoring. The resistance at warmer area successfully reflected the temperature distribution taken by an IR imaging camera. The same copper tapes are subsequently used for generating resistive heat by supplying a large amount of current. The effective heat generation is investigated by a finite element analysis, showing that the temperature of a laminate can be controlled by adjusting the conductivity in the fiber and thickness directions.

In an effort to fabricate prototypes with improved mechanical properties in the selective laser sintering process, functionalized graphite nanoplatelets were added to polyamide-12 powder to produce a nanocomposite powder. The polyamide-12 powder was chosen as the matrix polymer because it has features conducive to laser sintering, such as a low melting temperature and high mechanical properties. As fillers, the graphite nanoplatelets were oxidized through a nitric acid treatment to improve the interfacial bonding. For the syntheses of the nanocomposite solution, intercalation in an autoclave was conducted to obtain good dispersion and manufacturability. The micro/nanostructures of the synthesized nanocomposites were examined through scanning electron microscopy. The distribution of particles was also analyzed to look at the feasibility for the selective laser sintering process. The synthesized nanocomposite powder was layered and sintered by a laser. The mechanical properties for specimens made of neat polyamide-12, polyamide-12/TiO2, and polyamide-12/functionalized graphite nanoplatelet were tested and compared. The results indicate that the functionalization of nanofiller reinforces interfacial bonding force. For this reason, a small amount of nanofiller, which does not influence the thermal and rheological behavior, can improve the material properties.

This article considers the practical use of electrical resistance change method (ERCM) for damage detection in graphite/polymer composites. ERCM utilizes the high electrical conductivity of graphite fibers in the composites and can detect damage by change in electrical resistance. Since the effectiveness of ERCM has been shown extensively in the literature, it is now necessary to consider how to apply ERCM into existing structures. For practical use of ERCM, a new concept of an addressable conducting network (ACN) has been proposed, which consists of two sets of conducting lines normal to each other. One set of lines resides on the top surface of the laminate and the other resides on the bottom surface. Damage can be detected by monitoring resistance change between two lines across the laminate thickness. In this article, composite panels with several sets of conducting lines are locally loaded by a static indentation test and examined to monitor the distribution of electrical resistance changes. Monitoring the changes in resistance successfully indicated the damage occurrence, but it is sometimes difficult to pinpoint the damage location due to the resistance changes caused by compressive deformation. To improve the sensitivity of ACN to damage, the relationship between damage location and electrical conductivity was investigated using a design of experiments. The changes in resistance with various damage locations and electrical conductivities were acquired from finite element analysis, and the results suggested several ways to optimize damage detection. Depending on the damage tolerance of target structure, spacing of conducting lines and the electrical conductivities can be preferably selected toward practical application of ACN.

Novel nanocomposite films of polycarbonate (PC) with fullerene derivatives, such as pristine fullerene C60 and polyhydroxylated-fullerenes, C60(OH)12 and C60(OH)36, were prepared. The optical, thermal, and mechanical properties of the composites were measured. Nanocomposite films of poly (vinyl alcohol) (PVA) with C60(OH)36 were prepared as a reference to show how improved dispersion of the nanofiller affects the overall transparency of the composites. Ultraviolet-visible spectroscopy showed that the addition of hydroxylated fullerenes did not affect visible light transmittance of the films significantly in the range of 400–800 nm. Differential scanning calorimetry (DSC) and thermo–gravimetric analysis (TGA) measurements showed the increased thermal stability of PC/C60(OH)12 film as compared to pristine PC film. This phenomenon was explained by the rigid polymer interphase regions formed around C60(OH)12 due to the plausible hydrogen bonding and hydrophobic interaction. On the other hand, the lower thermal stability of PC–C60(OH)36 was assumed to be caused by large agglomeration of the C60(OH)36 particles and the partial hydrolysis of the polycarbonate matrix. Tensile testing of the composites showed reduction in elongation at break and yield tensile strength. These results may be caused by the particle agglomerations which act as the initiation points for cracks.

This article investigates the dependency of electrical resistance on temperature for graphite/polymer composites. The electrical resistance change of a unidirectional laminate is measured with elevated temperature in the fiber, transverse and through-thickness directions. Because of the properties of graphite fibers, the electrical resistance decreases as temperature increases in any direction. The activation energy is calculated from an Arrhenius plot to evaluate the difference among the different directions. The activation energy is the lowest in the fiber direction due to the high electrical conductivity of graphite fibers. Since electric current flows thorough the contacts between neighboring graphite fibers, similar activation energies are required in the transverse and through-thickness directions, indicating transversely isotropic properties. These characteristics will be used to establish the relationship between electrical resistance outputs and structural conditions, and will be eventually applied to an in-service structural management system using addressable conducting network, which is a grid arrangement of conducting lines on a composite panel.

Epoxy resin nanocomposites reinforced with three different ionic liquid functionalized carbon nanotubes (f-CNTs) were fabricated by an in situpolymerization method. The influence of the anions on the curing process was studied through differential scanning calorimetry (DSC) and normalized Fourier transform infrared (FTIR) spectroscopy. The composition of the nanocomposites was analyzed by X-ray photoelectron spectroscopy. Two different mechanisms are proposed to explain the curing process of the neat epoxy and its composites. The electric conductivity and mechanical properties of the nanocomposites are also reported. The tensile strength was increased dramatically due to the insertion of f-CNTs. Scanning electron microsopy fracture surface analysis indicates a strong interfacial bonding between the carbon nanotubes and the polymer matrix.

Vacuum filtration process to fabricate a transparent conducting carbon nanotube (CNT) film is reported. A CNT mat, which is a fibrous sheet of long multi-walled carbon nanotubes (MWNT), was prepared and dispersed in oleum by solution-sonication. The suspension was then vacuum filtered to obtain a thin MWNT layer with improved dispersion. Sheet resistance of the obtained MWNT layer was increased despite the improved dispersion. SEM micrographs and energy dispersive spectroscopy results indicated that the increase of the sheet resistance could be attributed to degradation and oxidation of the MWNT bundles. Though the chemical approach in this study did not improve the electrical property of the CNT mat, a mechanical approach proposed in our recent work was deemed suitable to enhance optical and electrical properties of the CNT mat.

We describe in this paper a transparent conducting film (TCF). It is a fibrous layer of multiwalled carbon nanotubes (MWNTs), labeled a dilute CNT mat, that was prepared and unidirectionally stretched to improve both the optical and electrical properties. After stretching by 80% strain, transmittance at 550 nm wavelength was improved by 37% and sheet resistance was reduced to 71% of the original value. The improvement of the transmittance can be explained by increased area of the CNT mat after stretch, and the reduced sheet resistance can be explained by increased density of the CNT alignment in lateral direction due to contraction. Based on the microscopic observation before and after stretch, models to describe the phenomena are proposed. By further expanding on this method, it may be possible to obtain a transparent conducting carbon nanotube film which is crack-resistant for solar cell applications.

This study presents the first stage of a multi-scale numerical framework designed to predict the non-linear constitutive behavior of metal-composite interfaces in titanium-graphite fiber metal laminates. Scanning electron microscopy and x-ray diffraction techniques are used to characterize the baseline physical and chemical state of the interface. The physics of adhesion between the metal and polymer matrix composite components are then evaluated on the atomistic scale using molecular dynamics simulations. Interfacial mechanical properties are subsequently derived from these simulations using classical mechanics and thermodynamics. These molecular-level property predictions are used in a companion study to parameterize a continuum-level finite element model of the interface by means of a traction-separation constitutive law. Extension of the proposed approach to other dissimilar metal- or metal oxide-polymer interfaces is also discussed.

Self-healing composites using a thermally mendable polymer, bis-maleimide tetrafuran (2MEP4F), based on Diels–Alder reaction and electrical resistive heating were fabricated using a vacuum assisted injection molding method. Delaminations were induced using short span three point bending on composite coupons. The induced damage and permanent deformation of the composite coupons were observed using X-ray micro-tomography. The same procedure was repeated to confirm multiple healings after electrical resistive heating and healing efficiency of the samples was determined. The permanent deformations and induced delaminations were repaired after the heating process, which is due to both healing and shape memory effects. The multiple healing ability and shape memory effect of the fabricated composite combined with electrical resistive heating realizes a noble self-healing composite.

We demonstrated a novel method for the formation of alloy nano-islands on carbon nanotube (CNT). The two metal layers (Pt, Au) were sputtered on CNTs and the intense pulsed light (IPL) was irradiated on the metal layers. The absorbed light provides enough energy for the diffusion mixing between Pt and Au, forming Pt–Au alloy phase. While the alloy is being formed by the IPL irradiation, the metal layers are broken into nano-islands on CNT due to the surface energy minimization between the metal layers and CNT. The surface characterizations of the Pt–Au/CNT were performed with X-ray diffraction, scanning electron microscope, and energy-dispersive X-ray spectroscopy. Different compositions of alloy nanoparticles were obtained by adjusting the deposition thicknesses of Pt and Au on CNT. Pt 50 Au 50 /CNT electrode showed the highest glucose oxidation current peak among Pt, Pt 70 Au 30 , Pt 50 Au 50 , Pt 30 Au 70 , and Au/CNT electrodes while the electroactive surface areas of them are kept to be similar (average surface area = 7.00 cm 2 , coefficient of variation = 0.06). The amperometric response of Pt 50 Au 50 /CNT electrode to the glucose concentrations showed a wide linear range up to 24.44 mM with a high detection sensitivity of 10.71 μA mM −1 cm −2 . Reproducibility and long-term stability of the Pt–Au/CNT electrode were also proven in the experiments.

Intense pulsed light (IPL) technique has been proposed to make large grains Cu(In 0.7 Ga 0.3 )Se 2 (CIGS) film using CIGS particles. The proposed process is non-vacuum based and performed at room temperature without selenization treatment. Melting and recrystallization of CIGS particles to larger grains without structural deformation and phase transformation are proved with adequate characterization evidences. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersion analysis (EDS) were used to characterize the prepared films. Melting of the CIGS particles and recrystallization to larger grains by light energy in 20 ms short reaction time could be the reason for no structural deformation and secondary phase generation during the process. The CIGS film prepared from its constituent nanoparticles by IPL treatment has great potential for use as absorber layer for solar cell application and is expected to have large impact on cell fabrication process in terms of cost reduction and simplified processing.

Most commercial copper nanoparticles are covered with an oxide shell and cannot be sintered into conducting lines/films by conventional thermal sintering. To address this issue, past efforts have utilized complex reduction schemes and sophisticated chambers to prevent oxidation, thereby rendering the process cost ineffective. To alleviate these problems, we demonstrate a reactive sintering process using intense pulsed light (IPL) in the present study. The IPL process successfully removed the oxide shells of copper nanoparticles, leaving a conductive, pure copper film in a short period of time (2 ms) under ambient conditions. The in situ copper oxide reduction mechanism was studied using several different experiments and analyses. We observed instant copper oxide reduction and sintering through poly(N-vinylpyrrolidone) functionalization of copper nanoparticles, followed by IPL irradiation. This phenomenon may be explained by oxide reduction either via an intermediate acid created by ultraviolet (UV) light irradiation or by hydroxyl (-OH) end groups, which act like long-chain alcohol reductants.

Multifunction integration of solar cells in load-bearing structures can enhance overall system performance by reducing parasitic components and material redundancy. The article describes a manufacturing strategy, named the co-curing scheme, to integrate thin-film silicon solar cells on carbon-fiber-reinforced epoxy composites and eliminate parasitic packaging layers. In this scheme, an assembly of a solar cell and a prepreg is cured to form a multifunctional composite in one processing step. The photovoltaic performance of the manufactured structures is then characterized under controlled cyclic mechanical loading. The study finds that the solar cell performance does not degrade under 0.3%-strain cyclic tension loading up to 100 cycles. Significant degradation, however, is observed when the magnitude of cyclic loading is increased to 1% strain. The present study provides an initial set of data to guide and motivate further studies of multifunctional energy harvesting structures.

A novel method using intense pulsed light (IPL) for the metal nano-island formation on carbon nanotube (CNT) was introduced. The IPL-induced photothermal dewetting process improved platinum (Pt) catalyst utilization by transforming nano-islands from Pt film on CNT and increasing the surface area for the subsequent sputtering. The irradiation of high intensity of light on the Pt film causes surface-energy-driven diffusion of Pt atoms and forms the array of nano-islands on CNT. The thickness of Pt film can change the size of nano-islands. Cyclic voltammetry showed a dramatically improved glucose oxidation at the IPL morphology modified Pt-CNT electrode compared to the Pt sputtered CNT electrode without IPL irradiation. The power densities of glucose/air biofuel cell based on the morphology modified Pt-CNT electrode and the as-sputtered Pt-CNT electrode were 0.768 microW/cm(2) and 0.178 microW/cm(2), respectively. The biofuel cell based on morphology modified Pt-CNT electrode showed highly stable output in long-term performance. The power density dropped 14.1% in 30 days. Efforts are underway to improve the interface transfer to achieve higher potential and current output.

Inkjet printing of electrode using copper nanoparticle ink is presented. Electrode was printed on a flexible glass epoxy composite substrate using drop on demand piezoelectric dispenser and was sintered at 200 °C of low temperature in N2 gas condition. The printed electrodes were made with various widths and thickness. In order to control the thickness of the printed electrode, number of printing was varied. Resistivity of printed electrode was calculated from the cross-sectional area measured by a profilometer and resistance measured by a digital multimeter. Surface morphology of electrode was analyzed using scanning electron microscope (SEM) and atomic force microscope (AFM). From the study, it was found that 10 times printed electrode has the most stable grain structure and low resistivity of 36.7 nΩ m.

We report the performance and characterization of a material based on poly[(3-mercaptopropyl)methylsiloxane] (PMMS) in various soft lithography applications. PMMS stamps were made by cross-linking ...

Copper nano-ink with a drop-on-demand (DOD) piezoelectric inkjet printing method was introduced. The printed electrodes were thermally sintered to ensure high-quality electrical and mechanical performances. To check the reliability of the printed electrodes on a polymer layer, resistance changes were measured under static loading. The electrodes with various widths and thicknesses were used to find the optimal dimensions. A multifunctional composite laminate which can harvest and store a solar energy was fabricated using printed electrodes. An amorphous silicon solar cell and a thin film solid state lithium-ion battery were adhesively joined and electrically connected to a thin flexible printed circuit board (PCB). Then, the passive components such as resistor and diode were electrically connected to the printed circuit board by silver pasting. The integrated PCB was co-cured with a carbon/epoxy composite laminate by the vacuum bag molding process in an autoclave. The structural and functional performance of the final energy harvesting/storage composite laminate was tested under mechanical loading.

The cure kinetics of a thermally mendable polymer based on Diels-Alder (DA) and retro-Diels-Alder (rDA) reactions, mendomer 401, was investigated using dynamic differential scanning calorimetry (DSC). The resulting behavior was modeled using a conventional cure kinetic model for thermosetting polymers. A composite panel with two layers of carbon fabric and mendomer 401 was fabricated following the cure cycle suggested by the cure kinetics model. Micro-indentation tests were performed to investigate mechanical properties and dynamic mechanical thermal analysis (DMTA) was conducted to study thermal behavior and to find the trigger temperature for healing. Self-healing behavior of the carbon fiber/mendomer composite was demonstrated using electrical resistive heating over the glass transition temperature.

Two different ceramic (cerium oxide and titanium oxide) nanoparticles were introduced into vinyl ester resin for nanocomposite fabrication. The curing process of the vinyl ester resin was investigated by a differential scanning calorimetery (DSC). The incorporation of nanoparticles in the resin affects the curing process due to the physicochemical interaction between the nanoparticles and the polymer matrix. The particle loading has a significant effect on the initial and peak curing temperatures, reaction heat and curing extent. The fully cured vinyl ester resin nanocomposites reinforced with cerium oxide nanoparticles were fabricated after a 24-hour room temperature curing and a one-hour postcuring at 85 degrees C. Particle functionalization favors the composite fabrication with a higher curing extent after room-temperature curing as compared to the as-received nanoparticle filled vinyl ester resin nanocomposites. The nanofiller materials were observed to significantly affect the curing process. In comparison to cerium oxide nanoparticles, titanium oxide nanoparticles prohibit the curing process with a much higher initiating curing temperatures. The fully cured nanocomposites reinforced with titanium oxide nanoparticles were fabricated by one-hour postcuring at 85 degrees C.

A novel dispersant “mono-2-(methacryloyloxy)ethyl succinate” was formulated for dispersing 30-nm SiC nanoparticles in vinyl ester resin. The eight carbon rule was used as the guideline to achieve a particle–particle separation of 20 to 60 nm for colloid stability. Fourier transform infrared spectroscopy was performed to characterize the SiC particle surfaces. Only a negligible amount of oxidized layer was observed; which illustrates that the SiC surface is basic. Thus, the Lewis base-Lewis acid reactions make the functional group –COOH an effective adsorbate to the SiC nanoparticle surface. The organofunctional group “methacrylates,” which exhibits the best wet strength with polyester copolymerizes with styrene monomers in the vinyl ester during cure. Hence, this novel dispersant also acts as an efficient coupling agent that reacts with both SiC and vinyl ester. The monolayer coverage dosage of 62 fractional wt% of the dispersant was used to attain the minimum filled resin viscosity. The multicomponent compositional imaging using atomic force microscopy confirmed the monodisperse SiC nanoparticles in vinyl ester. The 3 vol% SiC reinforced vinyl ester achieved a 75% increase in modulus, 42% increase in strength, and 75% increase in toughness as compared with the neat resin without nanofiller reinforcement.

An electrically curable resist has been developed that can make electric imprint lithography (EIL) a reality. The resist is composed of a diaryliodonium salt photo acid generator and a cycloaliphatic epoxy monomer. Its polymerization takes place when an electric potential is applied between a conductive imprint mold and a substrate which sandwich the resist. A proof-of-concept pattern transfer by EIL with a micron-scale resolution has been demonstrated.

This study demonstrates the construction of a multifunctional composite structure capable of energy storage in addition to load bearing. These structures were assembled and integrated within the confines of a multifunctional structural composite in order to save weight and space. Carbon fiber reinforced plastic (CFRP) composites were laminated with energy storage all-solid-state thin-film lithium cells. The processes of physically embedding all-solid-state thin-film lithium energy cells into carbon fiber reinforced plastics (CFRPs) and the approaches used are reviewed. The effects of uniaxial tensile loading on the embedded structure are investigated. The mechanical, electrical, and physical aspects of energy harvesting and storage devices incorporated into composite structures are discussed. Embedding all-solid-state thin-film lithium energy cells into CFRPs did not significantly alter the CFRP mechanical properties (yield strength and Young's modulus). The CFRP embedded energy cells performed at baseline charge/discharge levels up to a loading of about 50% of the ultimate CFRP uniaxial tensile rupture loading.

The effect of iron oxide nanoparticle addition on the physicochemical properties of the polypyrrole (PPy) was investigated. In the presence of iron oxide nanoparticles, PPy was observed in the form of discrete nanoparticles, not the usual network structure. PPy showed crystalline structure in the nanocomposites and pure PPy formed without iron oxide nanoparticles. PPy exhibited amorphous structure and nanoparticles were completely etched away in the nanocomposites formed with mechanical stirring over a 7-h reaction. The thermal stability of the PPy in the nanocomposites was enhanced under the thermo-gravimetric analysis (TGA). The electrical conductivity of the nanocomposites increased greatly upon the initial addition (20 wt%) of iron oxide nanoparticles. However, a higher nanoparticle loading (50 wt%) decreased the conductivity as a result of the dominance of the insulating iron oxide nanoparticles. Standard four-probe measurements indicated a three-dimensional variable-range-hopping conductivity mechanism. The magnetic properties of the fabricated nanocomposites were dependent on the particle loading. Ultrasonic stirring was observed to have a favorable effect on the protection of iron oxide nanoparticles from dissolution in acid. A tight polymer structure surrounds the magnetic nanoparticles, as compared to a complete loss of the magnetic iron oxide nanoparticles during conventional mechanical stirring for the micron-sized iron oxide particles filled PPy composite fabrication.

This paper presents a finite element model used to predict the bearing strength of hybrid titanium composite fiber-metal laminates. The model is used to examine the effects of material parameters such as titanium content and edge-distance ratio on specific bearing strength. In addition, a three-dimensional progressive failure user material subroutine is implemented into the commercial finite element code ABAQUS to model stiffness degradation in the graphite-polyimide layers of the hybrid laminate. These results are used to optimize the fiber-metal laminate layup by determining to the ideal tradeoff between joint strength and structural weight.

This paper reports on the recent progress towards the development of power composite structures capable of energy harvesting and storage in addition to load bearing. The process of physically embedding all-solid-state thin-film lithium energy cells into a carbon fiber reinforced plastic (CFRP) and the performance of the resulting power composites are reported. The embedded thin-film lithium-ion energy cells did not significantly alter the mechanical properties of the composite (modulus and strength) under quasi-static uniaxial loading conditions. The embedded energy cells performed at baseline charge/discharge levels up to a loading of about 50% of the CFRP tensile strength.

Robust magnetic vinyl ester resin nanocomposites reinforced with iron oxide (Fe2O3) nanoparticles were fabricated. The particle functionalization with a bi-functional coupling agent methacryloxypropyl-trimethoxysilane (MPS) was observed to have a significant effect on the curing process and subsequent physical properties of the nanocomposites. Particle functionalization favors the composite fabrication with a lower curing temperature as compared to the as-received nanoparticles filled vinyl ester resin nanocomposites. Thermo-gravimetric analysis showed an increased thermo-stability in the functionalized nanoparticles filled vinyl ester resin nanocomposites as compared to the unmodified nanoparticle filled counterparts. The more uniform particle dispersion and the chemical bonding between nanoparticle and vinyl ester resin matrix were found to contribute to the increased thermal stability and enhanced tensile strength. The nanoparticles become magnetically harder after incorporation into the vinyl ester resin matrix.

Through-the-thickness stitching is one of the promising approaches to improve the impact damage tolerance of stiffened composite structures. In this research, the effect of selective stitching on impact damage tolerance and fatigue durability of stiffened composite panels was extensively investigated and compared with unstitched stiffened composite panels. Two-blade stiffened composite panels were fabricated by resin film infiltration technique. Impact damage was inflicted on the stiffened panels using a drop-weight with the impact energy of 30 J from the skin-side over the stiffener and the flange. The experimental results indicate that selective stitching is an effective way to improve the compressive failure strength and fatigue strength of stiffened panels with both clearly visible flange damage (CVFD) and clearly visible stiffener damage (CVSD). The bulking and post-buckling finite element analyses were performed to predict the static compressive strength of the selectively stitched stiffened panels. A good agreement was obtained between analytical and experimental results. The failure behaviors of the undamaged, CVFD and CVSD panels were also investigated.

Silicon carbide reinforced polyurethane nanocomposites were fabricated by a facile surface-initiated-polymerization (SIP) method. The particle loading was tuned to up to 35 wt% without any obvious shrinkage and breakage as compared with the conventional direct mixing method. An increased thermal stability of the composites was observed with the addition of the silicon carbide nanoparticles under thermo-gravimetric analysis (TGA). Tensile strength was observed to increase dramatically with the increase of the particle loading. Both the uniform particle dispersion and the strong chemical bonding between the nanoparticles and the polymer–matrix contributed to the enhanced thermal stability and improved mechanical properties.

Thermally remendable polymers have recently become available that are paving the way for the creation of self-healing composites. This article investigates the use of carbon fibers as a resistive heating network for future use in a self-healing composite. Various electrode methods are studied in an attempt to reduce the contact resistance that causes localized heating around the electrode. In addition to localized heating, electrical conduction through the fibers creates heat through composite resistance. It was observed that for short distances between electrodes, contact resistance dominates while over longer distances, composite resistance dominates. The balance between the two types of heating is measured and modeled using finite element modeling (FEM).