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The effect of CuO nanowires on the improvement of the mechanical properties of woven carbon fiber (WCF)-based polyester resin composite was studied. The composite was manufactured by the vacuum-assisted resin transfer molding (VARTM) process. CuO nanowires were grown on woven carbon fiber sheets in subsequent steps of seeding followed by growth. Scanning electron microscopy (SEM) showed the growth of CuO nanowires on the surface of the carbon fibers; this growth increased with the number of seeding cycles and the length of the growth time. The concentration of the growth solution did not have a significant effect. The maximum amount of growth occurred for 8 seeding cycles with a 60 mM growth solution and a growth time of 8 h. An analysis of the percent weight change, along with X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy, supported the above findings. The crystalline peak height of the CuO nanowires increased with the nanowire growth. The new absorption peaks arising in the FTIR spectra also indicated growth of CuO nanowires on the WCF. The mechanical properties in terms of tensile strength, modulus, and impact resistance improved significantly after the growth of nanowires on the carbon fibers: the modulus and strength improved by up to 33.1% and 42.8%, while the impact energy absorption increased by 136.8% relative to bare WCF.

We synthesized Ag nanoparticle-decorated multilayered graphene nanosheets (Ag-graphene) from graphite nanoplatelets and silver nitrate through 90–100 s of microwave exposure, without the use of any mineral acids or harsh reducing agents. Fe nanoparticle-decorated carbon nanotubes (Fe-CNTs) were grown on polypyrrole (PPy) deposited on woven Kevlar fibre (WKF), using ferrocene as a catalyst, under microwave irradiation. Fe-CNTs grown on WKF and Ag-graphene dispersed in polyester resin (PES) were combined to fabricate Ag-graphene/Fe-CNT/PPy-coated WKF/PES composites by vacuum-assisted resin transfer moulding. The combined effect of Fe-CNTs and Ag-graphene in the resulting composites resulted in a remarkable enhancement of tensile properties (a 192.56% increase in strength and 100.64% increase in modulus) as well as impact resistance (a 116.33% increase). The electrical conductivity significantly increased for Ag-graphene/Fe-CNT/PPy-coated WKF/PES composites. The effectiveness of electromagnetic interference shielding, which relies strongly on the Ag-graphene content in the composites, was 25 times higher in Ag-graphene/Fe-CNT/PPy-coated WKF/PES than in neat WKF/PES composites. The current work offers a novel route for fabricating highly promising, cost effective WKF/PES composites through microwave-assisted synthesis of Fe-CNTs and Ag-graphene.

We present theoretical and experimental studies on the effects of platelet-like filler orientation on the mechanical properties of melt-spun exfoliated graphite nanoplatelet(xGnP)-nylon 6(PA6) composite fibers. In numerical studies, the Mori–Tanaka micromechanics model was employed to formulate analytical models to predict the mechanical properties of xGnP-PA6 composite fibers with varying xGnP orientations in a three-dimensional spatial domain. Simulation results showed that the predicted properties of xGnP-PA6 composite fibers were highly affected by xGnP orientation and were correlated with the measured properties of composite fibers treated with varying draw ratios. The tensile moduli of composite fibers at varying xGnP contents showed significant improvements, which is attributed to the drawing-induced alignment of PA6 molecular chains as well as the alignment of xGnPs. Both as-received and acid-treated xGnPs were incorporated in PA6, and mechanical test results suggested that acid-treated xGnPs provide stronger interfacial bonding with PA6.

The surface modification of materials by large pulsed electron beam (LPEB) processing is an emerging eco-friendly technique that can be applied to relatively large surface areas. In this study, a polyester-based woven carbon fiber (WCF)/ZnO nanorod hybrid composite was developed using a vacuum-assisted resin transfer molding process. LPEB processing was used to modify the surface of the carbon fiber (CF) composite prior to the growth of the ZnO nanorods. The effects of this electron beam treatment on WCFs were investigated by scanning electron microscopy as a function of ZnO nanorod growth. LPEB treatment resulted in a remarkable increase in the growth of ZnO nanorods. This increase, which resulted in an increase in the electrical resistance of the samples, was further investigated by X-ray diffraction analyses. LPEB-treated samples exhibited higher impact resistance due to strong interactions among the ZnO, CF, and polyester resin.

Thermal heating in the interlaminar region of ZnO/woven carbon fiber composite laminates was investigated. In ZnO/woven carbon fiber composite laminates, the interlaminar region, composed of ZnO nanostructured arrays embedded on woven carbon fiber sheets, interacts with the thermoset vinyl ester resin. ZnO nanostructured arrays were formed into nanorods (NRs) using a hydrothermal process. To investigate the electrical resistive heating behavior of the interlaminar region, we analyzed the temperature profile as a function of time in three zones: a heating zone, a maximum temperature zone, and a cooling zone. The morphology of the ZnO NRs was investigated using scanning electron microscopy, and X-ray diffraction analysis was used to characterize the crystallinity and ZnO concentration. Differential scanning calorimetry was employed to analyze the specific heat capacity of ZnO/woven carbon fiber composite laminates. Electrical resistive heating was achieved in the interlaminar region through multiple junctions formed between the intrinsic woven carbon fiber tows and among the ZnO NRs. The contribution of the ZnO NRs to the thermal heat gain was interconnected with the woven carbon fiber and resin in the interlaminar regions. The interlaminar resistance between the upper and lower laminas of ZnO/woven carbon fiber composites increased with incremental increases in the ZnO concentration up to 110 mM. This effect was due to the interlaminar interface and the high surface density of ZnO NRs, which inhibit electron transport into the woven carbon fibers. Resistance decreased following electrical resistive heating due to an increase in the density of free electrons at high temperatures.

Poly(ethylene terephthalate) (PET)/CaCO3 and PET/modified-CaCO3 (m-CaCO3) nanocomposites were prepared by melt blending. The morphology indicated that m-CaCO3 produced by reacting sodium oxalate and calcium chloride, was well dispersed in PET matrix and showed good interfacial interaction with PET compared to CaCO3. No significant differences in the thermal properties such as, glass transition, melting and degradation temperatures, of the nanocomposites were observed. The thermal shrinkage of PET at 120 °C was 10.8 %, while those of PET/CaCO3 and PET/m-CaCO3 nanocomposites were 2.9–5.2 % and 1.2–2.8 %, respectively depending on filler content. The tensile strength of PET/CaCO3 nanocomposite decreased with CaCO3 loading, whereas that of PET/m-CaCO3 nanocomposites at 0.5 wt% loading showed a 17 % improvement as compared to neat PET. The storage modulus at 120 °C increased from 1660 MPa for PET to 2350 MPa for PET/CaCO3 nanocomposite at 3 wt% loading, and 3230 MPa for PET/m-CaCO3 nanocomposite at 1 wt% loading.

Poly(dopamine)-treated graphene oxide/poly(vinyl alcohol) ("dG-O/PVA") composite films were made and characterized. G-O was modified with poly(dopamine) in aqueous solution and then chemically reduced to yield poly(dopamine)-treated reduced G-O. A combination of hydrogen bonding, strong adhesion of poly(dopamine) at the interface of PVA and G-O sheets, and reinforcement by G-O resulted in increases in tensile modulus, ultimate tensile strength, and strain-to-failure by 39, 100, and 89%, respectively, at 0.5 wt % dG-O loading of the PVA. The dG-O serves as a moisture barrier for water-soluble PVA, and the dG-O/PVA composite films were shown to be effective humidity sensors over the relative humidity range 40-100%.

Two novel Cu(2+) sensors, 1 and 2, bearing naphthalimide and a DPA moiety were synthesized to study copper accumulation in organelles by selective Cu(2+) sensing. The ER-selective Cu(2+) sensor 1 that we developed serves as a valuable tool for understanding the subcellular compartmentalization and roles of copper ions in physiology and pathophysiology.

Measuring shear displacement and pressure simultaneously is essential for various applications, such as tactile sensors for robotic finger tips, shoe soles for gait monitoring, etc. We present a simple means of transducing shear displacement and pressure change to flexible composite sensor. The presented sensor consists of an array of cylindrical pillars standing on a flat substrate, which is composed of carbon nanotubes (CNTs) and polydimethylsiloxane. The sensing mechanism is based on changing CNT network in pillar and flat structure under shear and pressure. When a shear displacement change occurs in the pillar array, which transfers shear and pressure to flat structure in the sample, the CNT network in the sample is changed due to bending of the pillars. Under pressure, the load is transferred from the pillar array to flat structure inducing changes in relative resistance. Load transfer through this hierarchical structure enabled measurement of shear displacement and pressure up to 5 mm and 1200 kPa, respectively. Therefore, it shows great potential applications in monitoring or even recognizing various human physiological activities.

We investigated the tailored electromagnetic interference shielding effectiveness (EMI SE) of polyester-matrix composites consisting of glass fiber textiles coated with multiwalled carbon nanotubes (MWCNTs) and exfoliated graphite nanoplatelets (xGnPs). The effects of various combinations of material parameters, including MWCNT length, xGnP size, MWCNT:xGnP weight ratio, host-substrate surface configuration of carbon nanomaterials (CNMs), and their amount coated per unit area, on the EMI SE were studied. The shielding mechanisms, namely, absorption, reflection, and multiple reflections, are discussed based on the underlying governing physics. EMI SE measurements showed that coating glass fibers with hybrid MWCNTs/xGnPs at 8/2 ratio yields EMI SEs higher than those of composites containing the same content of a single-type of CNM, ranging from 56.8 dB at 30 MHz to 35.3 dB at 1.5 GHz. Morphological studies showed that, upon placement on glass fiber surfaces, 1D fiber-like MWCNTs serve as interconnects that bridge the randomly oriented 2D platelet-like xGnPs to form an efficient plane shield of electromagnetic waves.

In step with the development of Industry 4.0, research on automatic operation technology and components related to automobiles is continuously being conducted. In particular, the torque angle sensor (TAS) module of the steering wheel system is considered to be a core technology owing to its precise angle, torque sensing, and high-speed signal processing. In the case of conventional TAS modules, in addition to the complicated gear structure, there is an error in angle detection due to the backlash between the main and sub-gear. In this paper, we propose a multi-track encoder-based vehicle steering system, which is incorporated with a TAS module structure that minimizes the number of components and the angle detection error of the module compared with existing TAS modules. We also fabricated and tested an angle detection signal processing board and evaluated it on a test stand. As a result, we could confirm its excellent performance of an average deviation of 0.4&deg, and applicability to actual vehicles by evaluating its electromagnetic interference (EMI) environmental reliability. The ultimate goal of the TAS module is to detect the target steering angle with minimal computation by the steering or main electronic control unit (ECU) to meet the needs of the rapidly growing vehicle technology. The verified angle detection module can be applied to an actual steering system in accordance with the mentioned technical requirements.

In this paper, we developed a theoretical model which is able to predict the tensile strength and elasticmodulus of hybrid composites reinforced by two types of randomly distributed discontinuous reinforcements. For this,we considered two known models; One is a prediction model based on the assumption that the composite isreinforced by two types of well aligned continuous reinforcements. The other is a statistical model for the compositewhich is reinforced by only one type of randomly distributed discontinuous reinforcements. In order to evaluate thevalidity of accuracy of our prediction model, we measured the strength and elastic modulus of polypropylene hybridcomposite reinforced by talc and short glass fiber. We found that the present model drastically enhances the accuracyof strength prediction compared to an existing model, and predicts the elastic modulus within the same order withexperimentally measured values.초록 : 본 연구에서는 입자형태인 두 가지 이상의 강화제가 기지 내에 무작위로 분포하여 하이브리드 복합재료를 이룰 때, 강화제의 함유량에 따른 복합재료의 인장강도 및 탄성계수를 예측할 수 있는 이론 모델을 제안하였다. 이를 위하여 연속적인 두 강화제가 기지 내에 평행하게 분포한 복합재료 모델에 입자형태의 한 가지 강화제가 무작위하게 분포한 복합재료 모델을 수정 적용하였다. 본 연구에서 제안한 모델의 정확성과 타당성을 논의하기 위해, 산업체에서 널리 쓰이고 있는 폴리프로필렌을 기지로 하고, 탈크와 유리단섬유를 서로 다른 강화제로 한복합재료를 제작하여 인장강도 및 탄성계수를 측정하였다. 인장강도 값을 예측하는 경우, 이전의 이론 모델이 실험 측정값과 7배 이상의 오차를 보이는 반면 본 연구의 모델은 비슷한 값을 예측하였다. 탄성계수의 경우에도 본연구의 모델은 비교적 정확하게 실험 측정 값을 예측할 수 있었다.

Polypropylene films reinforced with multi-walled carbon nanotubes and exfoliated graphite nanoplateletswere fabricated by extrusion, and the effects of filler type and take-up speed on the mechanical properties andmicrostructure of composite films were investigated. Differential scanning calorimetry revealed that the addition ofcarbon nanomaterials resulted in increased degree of crystallinity. However, increasing the take-up speed reduced thedegree of crystallinity, which indicates that tension-induced orientations of polymer chains and carbon nanomaterialsand the loss of degree of crystallinity due to rapid cooling at high take-up speeds act as competing mechanisms.These observations were in good agreement with tensile properties, which are governed by the degree of crystallinity,where the C-grade exfoliated graphite nanoplatelet with a surface area of 750 m 2 /g showed the greatest reinforcingeffect among all types of carbon nanomaterials used. Scanning electron microscopy was employed to observe thecarbon nanomaterial dispersion and orientation, respectively.초록

We investigated the electromagnetic interference shielding effectiveness (EMI SE) of composites consisting of an unsaturated polyester matrix containing woven glass or carbon fibers that had been coated with multiwalled carbon nanotubes (MWCNTs). Composite panels consisting of fiber fabrics with various combinations of fabric type and stacking sequence were fabricated. Their EMI SE was measured in the frequency range of 30 MHz–1.5 GHz. The underlying physics governing the EMI shielding mechanisms of the materials, namely, absorption, reflection, and multiple reflections, was investigated and used in analytical models to predict the EMI SE. Simulation and experimental results showed that the contributions of reflection and absorption to EMI shielding is enhanced by sufficient impedance mismatching, while multiple reflections have a negative effect. For a given amount of MWCNTs in the glass-fiber–reinforced composite, coating the outermost, instead of intermediate, glass fiber plies with MWCNTs was found to maximize the conductivity and SE.

This study explores the resistive heating characteristics of discontinuous carbon fiber (CF)-epoxy composites. Test samples including 1, 3, and 5 wt.% CF were fabricated using sonication and cast molding processes. For heating performance characterization, DC currents were applied to the composite samples, and surface temperatures were evaluated visually and quantitatively using an infrared camera. To estimate the thermal performance of composites and verify the experimental results, finite element analyses were performed. The resistive heating mechanism was investigated in connection with CF loading and applied voltages. Resistive heating efficiency increased proportionately with CF concentration and applied voltage. To obtain homogeneous temperature distribution of the samples, high degree of CF dispersion is required.

In this paper, nanofluids containing xGnPs and xGnPs oxide were prepared due to superb thermal properties and low cost. Pool boiling experiments were performed for different particle concentrations. The critical heat flux (CHF) of nanofluids when boiled over a NiCr wire increased with increasing concentrations of xGnP and xGnP oxide particles in the base fluid. We determined that the xGnP oxide nanofluids with 0.005 vol% dispersed particle concentration had the most enhanced CHF. Although the largest CHF enhancement was observed for the nanofluid with 0.005 vol% xGnP oxide, no reduction was observed in the contact angle.

This paper presents an experimental study on the enhancement of electromagnetic shielding (EMI) properties of glass fiber, carbon fiber, and glass-carbon fiber composites by adding layers of multi-walled carbon nanotubes (MWCNTs). In the case of glass-fiber composites, spraying 0.1~0.2 g of MWCNT over a fiber area of 200 mm X 200 mm (1.8~3.6 μm in thickness) resulted in significant improvement in EMI shielding effectiveness (SE). Also, when applying multiple MWCNT layers, it was more effective to place the layers concentrated near the center of the composite rather than spreading them out. On the contrary, inherently conductive carbon fiber and glass-carbon fiber composites did not show appreciable improvement with the addition of MWCNT layers. In order to maximize the effectiveness of carbon nanomaterials as EMI shielding fillers, it is imperative to understand the effect of these materials on various EMI shielding mechanisms and their interactions. 초 록 본 연구에서는 유리섬유, 탄소섬유 및 유리섬유-탄소섬유 복합재에 MWCNT층을 삽입하는 경우 복합재의 전자파차폐 물성에 대한 연구를 수행하였다. 유리섬유 복합재의 경우, 200 mm X 200 mm 면적에 0.1~0.2 g의 MWCNT를 도포했을 때 (1.8~3.6 μm 두께) 전자파차폐효과가 현격히 증가함을 발견하였다. 아울러, 두 개 이상의 MWCNT층을 삽입하는 경우, 이들을 분산배치 하는 것 보다는 복합재 중앙에 집중배치 하는 것이 더 효과적이었다. 반면, 탄소섬유 및 유리섬유-탄소섬유 복합재의 경우, MWCNT층이 전자파차폐효과에 영향을 미치지 않음을 알 수 있었다. MWCNT를 비롯한 탄소나노소재를 전자파차폐용 소재로 효과적으로 활용하기 위해서는, 탄소나노소재의 첨가에 의한 다양한 전자파차폐 메커니즘 간 상관관계를 이해하는 것이 중요하다.

We discuss the influence of few-walled carbon nanotubes (FWCNTs) treated with nitric acid and/or sulfuric acid on field emission characteristics. FWCNTs/tetraethyl orthosilicate (TEOS) thin film field emitters were fabricated by a spray method using FWCNTs/TEOS sol one-component solution onto indium tin oxide (ITO) glass. After thermal curing, they were found tightly adhered to the ITO glass, and after an activation process by a taping method, numerous FWCNTs were aligned preferentially in the vertical direction. Pristine FWCNT/TEOS-based field emitters revealed higher current density, lower turn-on field, and a higher field enhancement factor than the oxidized FWCNTs-based field emitters. However, the unstable dispersion of pristine FWCNT in TEOS/N,N-dimethylformamide solution was not applicable to the field emitter fabrication using a spray method. Although the field emitter of nitric acid-treated FWCNT showed slightly lower field emission characteristics, this could be improved by the introduction of metal nanoparticles or resistive layer coating. Thus, we can conclude that our spray method using nitric acid-treated FWCNT could be useful for fabricating a field emitter and offers several advantages compared to previously reported techniques such as chemical vapor deposition and screen printing.

In this work, we successfully fabricated graphene oxide (GO) and GO-based PMMA composite fiber and nylon films. Dynamic mechanical and tensile properties of PMMA-GO composite fiber showed that GO is efficient reinforcement for polymer matrices. However, Nylon 6,6-GO composite films showed low reinforcement efficiency in terms of dynamic mechanical and tensile properties due to the colloid instability of GO in formic acid at a low pH level.

The demand for manufacturing microscale components for applications in electronic, biological, and microtool industries has resulted in a reduction in the overall size of machine tools. This trend has motivated the development of new measurement techniques to accurately determine the position of the tool. In this study, two noncontact methods to control the initial position of micro- and meso-scale tools and trace the tool position are described: a laser-based measurement system and a halogen lamp-based measurement system. To evaluate the feasibility of these measurement systems, the prototype per each measurement has been constructed. The laser-based measurement system had a positioning error of ±4.5 μm and the halogen lamp-based measurement system had a positioning error of ±2 μm. Several experiments and simulations were performed to identify the effects of a range of factors likely to be encountered in real-world situations.

Conventional machine tools are being miniaturized because of the technical and economic advantages that this approach produces. Apart from these issues, the response time for marketing mesoscale machine tools is growing shorter. Thus, further development in this area will require a systematic design scheme to reduce subjectivity at the early design stage. This paper covers the structural optimization of a miniaturized milling machine using an integrated design strategy based on individual modeling and simulations of key parameters, such as volumetric error and machine working space, as well as static, thermal, and dynamic stiffness. This integrated approach was developed using analytical methods and then validated experimentally. Individual computations based on the mathematical model were carried out to produce a penalty function for the miniaturized milling machine that was then used to determine the optimal structure. This paper also discusses the sensitivity of weighting factors to determine which weighting factor is the most effective in an optimal solution. This study contributes to the development of more reliable mesoscale machine tools.

Carbon/carbon composites consisting of single-walled carbon nanotube (SWCNT) buckypaper (BP) and mesophase pitch resin have been produced through impregnation of BP with pitch using toluene as a solvent. Drying, stabilization and carbonization processes were performed sequentially, and repeated to increase the pitch content. Voids in the carbon/carbon composite samples decreased with increasing impregnation process cycles. Electrical conductivity and density of the composites increased with carbonization by two to three times that of pristine BP. These results indicate that discontinuity and intertube contact barriers of SWCNTs in the BP are partially overcome by the carbonization process of pitch. The temperature dependence of the Raman shift shows that mechanical strain is increased since carbonized pitch matrix surrounds the nanotubes.

Polypropylene/aluminum–multi-walled carbon nanotube (PP/Al–CNT) composites were prepared by a twin-screw extruder. The morphology indicates that the CNTs are well embedded or implanted within Al-flakes rather than attached on the surface. During preparation of composites, the CNTs came apart from Al–CNT so that free CNTs as well as Al–CNT were observed in PP/Al–CNT composite. The crystallization temperatures of PP/CNT and PP/Al–CNT composites were increased from 111 °C for PP to 127 °C for the composites. The decomposition temperature increased by 55 °C for PP/CNT composite and 75 °C for PP/Al–CNT composite. The PP/Al–CNT composite showed higher thermal conductivity than PP/CNT and PP/Al-flake composites with increasing filler content. PP/Al–CNT composites showed the viscosity values between PP/CNT and PP/Al-flake composites. PP/Al–CNT composite showed higher tensile modulus and lower tensile strength with increasing filler content compared to PP/CNT and PP/Al-flake composites.

Carbon nanotube reinforced aluminum powders (Al-CNT) were fabricated by ball milling. The morphology observed by a scanning electron microscope showed impregnation of CNTs on the surface of aluminum flakes (Al-flakes). Polycarbonate (PC)/Al-CNT nanocomposites were prepared by a twin-screw extruder. The electrical resistivity of PC/Al-flake composites did not change with Al-flake content, while that of PC/CNT nanocomposites decreased with increasing CNT content, and the percolation threshold was obtained at 2 wt% CNT loading. The electrical resistivity of PC/Al-CNT nanocomposites showed a behavior similar to PC/CNT nanocomposites. The thermal conductivity of the composites increased with increasing filler contents. The PC/Al-CNT composites showed a viscosity trend that is similar to PC/CNT composites; however, it showed higher viscosities (G*, G") than PC/Al-flake composites in the low frequency range (up to ∼10 Hz) and lower viscosities in the higher frequency range (>10 Hz). The tensile modulus of PC/ Al-CNT composite increased while the strength decreased with increasing filler content. The modulus of PC/Al-CNT composite was higher than PC/CNT and PC/ Al-flake composites.

Multiwalled carbon nanotube (MWCNT)-filled polycarbonate composites were prepared by a corotating intermeshing twin-screw extruder. The surface resistivities of compression- and injection-molded specimens were quite different, the difference ranging from 103 to 107 Ω/sq at varying MWCNT concentrations. The surface resistivity of the injection-molded specimen at 2 wt % loading varied up to 105 Ω/sq in the specimen thickness direction and up 104 Ω/sq in the polymer flow direction with respect to the gate. The difference in surface resistivity with the positions of injection-molded specimen was confirmed with the morphology, which showed the difference in MWCNT number density (numbers/surface area). There was no significant effect on surface resistivity with injection pressure, holding pressure, and molding temperature. The specimens prepared at the injection speed of 13 mm/s showed surface resistivities 103–104 Ω/sq depending on the positions, which was comparable with the compression-molded specimens, which had a surface resistivity of 103 Ω/sq. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

This article details the behavior of polycarbonate films utilized in the resin infusion between double flexible tooling (RIDFT) process as means to achieve in-mold decoration (IMD) of composites. This work evaluated forming capability with respect to surface quality of the composite assembly. Improved drawability was achieved with increasing temperature. However, this yielded in print-through of the fibers through the film. Five process parameters (temperature, mold type, time, fiber reinforcements, and vacuum pull), were optimized through sequential experimentation using analysis of variance (ANOVA) in terms of print-through, as the response variable. Statistical validation indicated minimal print-through at a forming temperature of 147 °C. However, at this temperature formability of the film was limited to subtle contours. At 160 °C, the forming capability of the composite assembly was maximized, yet surface finishes exhibited high print-through. This article describes achievements, difficulties, and future work in the utilization of polycarbonate films for the RIDFT process.

Carbon fiber-reinforced epoxy composites modified with carbon nanotubes (CNTs) were fabricated and characterized. High-energy sonication was used to disperse CNTs in the resin, followed by infiltration of fiber preform with the resin/CNT mixture. The effects of sonication time on the mechanical properties of “multiscale” composites, which contain reinforcements at varying scales, were studied. A low CNT loading of 0.3 wt% in resin had little influence on tensile properties, while it improved the flexural modulus, strength, and percent strain to break by 11.6%, 18.0%, and 11.4%, respectively, as compared to the control carbon fiber/epoxy composite. While sonication is an effective method to disperse CNTs in a resin, duration, intensity, and temperature need to be controlled to prevent damages imposed on CNTs and premature resin curing. A combination of Halpin–Tsai equations and woven fiber micromechanics was used in hierarchy to predict the mechanical properties of multiscale composites, and the discrepancies between the predicted and experimental values are explained.

Recent discoveries of various forms of carbon nanostructure have stimulated research on their applications and hold promise for applications in medicine and other related engineering areas. Although carbon nanotubes (CNTs) are already being produced on a massive scale, few studies have been performed which test the potential harmful effects of this new technology. The authors used a three-dimensional in vitro model of the human airway using a coculture of normal human bronchial epithelial cells and normal human fibroblasts for the health risk assessment of CNTs on the human respiratory systems. The authors used aqueous single-walled carbon nanotube (SWCNT) solution. The average length and diameter of nanotube ropes were about 500 nm and less than 10 nm, respectively. The authors measured the production of nitric oxide (NO) as an inflammatory marker and mitochondrial activity using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay as a cytotoxic response of the cell layers following exposure of different concentration of aqueous SWCNT solution. The results indicated that NO production was dramatically increased and cell viability was decreased following exposure of different concentrations of SWCNTs. Transepithelial electrical resistance (TER) across the coculture layers was measured to observe the changes in airway physiological function following exposure of different concentrations of SWCNTs. TER value was dramatically decreased following exposure of 20% SWCNT (8 μg/ml). In this study, the authors presented viable alternatives to in vivo tests to evaluate the toxicity of engineered SWCNTs. Cytotoxic/inflammatory responses and barrier function of the human lung layers following exposure of SWCNTs were observed using in vitro coculture system of airway.

This paper reports the development of conductive, carbon nanotube (CNT)-filled, polymer composite films that can be used as strain sensors with tailored sensitivity. The films were fabricated via either melt processing or solution casting of poly(methyl methacrylate) (PMMA) matrices containing low concentrations of multi-walled carbon nanotubes (MWNTs). The electrical resistivities of the films were measured in situ using laboratory-designed fixtures and data acquisition system. The measured resistivities were correlated with the applied strains to evaluate the sensitivity of the nanocomposite film sensor. The study suggests that conductive network formation, thus strain sensitivity of the conductive films, can be tailored by controlling nanotube loading, degree of nanotube dispersion, and film fabrication process. The developed sensors exhibited a broad range of sensitivity, the upper limit showing nearly an order of magnitude increase compared to conventional, resistance-type strain gages. A semi-empirical model that shows the relationship between CNT volume fraction and sensitivity is proposed.

Poly(ethylene terephthalate) (PET)/multi-walled carbon nanotube (MWCNT) composites were prepared by in situ polymerization. To improve the dispersion of MWCNTs in PET matrix, the surface modified MWCNTs having acid groups (acid-MWCNT) and diamine groups (diamine-MWCNT) were used. The functional groups on the surface of modified MWCNTs were confirmed by infrared (IR) spectrometry. SEM analysis showed better dispersion of diamine-MWCNTs as compared to pristine-MWCNTs and acid-MWCNTs in the PET. The reaction between PET and diamine-MWCNTs was evidenced by the shifting of the G band to a higher frequency in Raman spectroscopy and an increase of the complex viscosity in rheological properties. The composites containing functionalized MWCNTs showed a large increase in the tensile strength and modulus. The PET/diamine-MWCNT composites showed maximum tensile strength and modulus increases by 350% and 290% at 0.5 and 2.0 wt%, respectively, as compared to pure PET.

Poly(ethylene terephthalate) (PET)/multiwalled carbon nanotube (MWCNT) composites were prepared by in situ polymerization. To improve the dispersion of MWCNTs in the PET matrix, functionalized MWCNTs having acid groups (acid-MWCNTs) and acetic groups (acetic-MWCNTs) on their surfaces were used. The functional groups were confirmed by infrared spectrometry. Scanning electron microscopy showed that acetic-MWCNTs had a better dispersion in the PET matrix than pristine MWCNTs and acid-MWCNTs. A reaction between PET and acetic-MWCNTs was confirmed by a shift of the Raman G band to a higher frequency and an increase of the complex viscosity in the rheological properties. The composites containing functionalized MWCNTs showed a large increase in their tensile strengths and moduli. The values of the strengths and moduli of the PET/acetic-MWCNT composites were higher than those of the PET/acid-MWCNT composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Poly(ethylene terephthalate) (PET)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were prepared by in situ polymerization. Light scattering measurement suggested that there is significant change in molecular weight arising from gel formation by chemical crosslinking during polymerization. The thermal decomposition temperatures of the composites measured at 5 wt % weight loss were 5–10°C higher than that of PET. There is no significant change in other thermal properties. Scanning electron microscopy observations suggest that there is obvious phase separation in PET/POSS composites, composites containing 1 wt % of disilanolisobutyl and trisilanolisobytyl-POSS show fine dispersions of POSS (30–40 nm in diameter), which arise from strong interfacial interactions between POSS and PET during polymerization. The viscosity of the composites increased with the addition of POSS. The observation of a plateau region of composites containing 1 wt % of POSS in the plot of log G′ vs. log G″ indicates strong interfacial interactions between POSS and PET. Sixty-three percent and 41% increase in tensile strength and 300 and 380% increase in modulus were achieved in the composites containing 1 wt % of disilanol- and trisilanol-POSS, respectively. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Fatigue in metal forming dies is an important issue in the manufacturing industry. Fatigue failure leads to repair or replacement of the die, which interrupts and slows down the manufacturing process. Fatigue of bulk metal forming (such as, forging and extrusion) dies has been the focus of most die failure studies because the nature of the process tends to subject the die to high stresses, thus increasing the likelihood of die failure. However, as polymer composite tooling materials are making inroads into rapid tooling technologies, die failure in sheet metal forming, in which the dies are subjected to significantly lower stresses, is drawing attention. This paper presents a fatigue failure analysis of V-bending dies machined from a polyurethane-based tooling board. The mechanical properties of the tooling materials are characterized to identify the underlying failure mechanisms. Various fatigue failure criteria, namely, maximum tensile principal stress, effective stress, Smith–Watson–Topper, and critical plane approaches are investigated as die life prediction methods, among which the latter two approaches were most accurate. Finite element analyses and experiments are performed to verify the results.

A parametric study has been accomplished to figure out the effects of elliptic cylinder thickness, angle of attack, and Reynolds number on the unsteady lift and drag forces exerted on the elliptic cylinder. A two-dimensional incompressible Navier-Stokes flow solver is developed based on the SIMPLER method in the body-intrinsic coordinates system to analyze the unsteady viscous flow over elliptic cylinder. Thickness-to-chord ratios of 0.2, 0.4, and 0.6 elliptic cylinders are simulated at different Reynolds numbers of 400 and 600, and angles of attack of 10°, 20°, and 30°. Through this study, it is observed that the elliptic cylinder thickness, angle of attack, and Reynolds number are very important parameters to decide the lift and drag forces. All these parameters also affect significantly the frequencies of the unsteady force oscillations.

A parametric study has been accomplished to figure out the effects of the elliptic cylinder thickness, angle of attack, and Reynolds number on the lift and drag forces exerted on the elliptic cylinder. A two-dimensional incompressible Navier-Stokes flow solver is developed using SIMPLER method to analyze the unsteady viscous flow over elliptic cylinder. Thickness-to-chord ratios of 0.2, 0.4, and 0.6 elliptic cylinders are simulated at different Reynolds numbers of 400 and 600, and angles of attack of 10°, 20°, and 30°. Through this study, it is observed that the elliptic cylinder thickness, angle of attack, and Reynolds number affect significantly not only the time-mean values and the amplitudes of the drag and lift forces but also the frequencies of the force oscillations.

The demand for rapid, low-cost die fabrication and modification technology is greater than ever in the sheet metal forming industry. One category of rapid tooling technology involves the use of advanced polymers and composite materials to fabricate metal forming dies. However, due to their lack of strength as compared to conventional metal dies, the use of polymer dies is often limited to prototype or short-run production. In addition, because the mechanisms by which they fail are not fully understood, the dies are designed on the basis of experience and intuition. This study investigates the failure of V-bending dies fabricated from an easy-to-machine, polyurethane-based, composite board stock. Based on the mechanical behavior of the die material, several failure criteria are proposed to predict die failure mode and the corresponding die life. Both computational and experimental methods are employed to assess the accuracy of the criteria and to identify the dominant process parameters in V-die bending.

To meet the growing demand for rapid, low-cost die fabrication technology in the sheet metal forming industry, easy-to-machine, polyurethane-based, composite board stock is widely used as a rapid tooling material. However, the failure mechanisms of the rapid prototyped tools are not clearly understood, thus making the prediction of tool life difficult. As a fundamental step for effective tool life estimation, the microstructure and the mechanical properties of the polymer composite tooling material were characterized. A finite element model of 90° V-die bending process was developed, and the effects of process parameters on stress distribution in punch and die were investigated through simulation. The simulation results were verified through experiments using instrumented, laboratory-scale punch and die sets.

Continuous sliding mode control is applied to turning processes for cutting force regulation. The motivation of the use of the slide mode control scheme is to solve the nonlinearity problem caused by the feedrate override command element in the commercial CNC machine tool. When the adaptive control algorithm is applied to the commercial CNC machine tool, it is one of the practical methods that the programmed feedrate is overridden after the control algorithm is carried out. However, most CNC lathe manufacturers offer limited number of data bits for feedrate override, thus resulting in nonlinear behavior of the machine tools. Such nonlinearity brings `quantized' or discrete effect so that the optimal feedrate is rounded off before being fed into the CNC system. To compensate for this problem, continuous sliding mode control is applied. Simulation and experimental results are presented in comparison with those obtained from applying adaptive control which is a widely used approach in cutting force regulation. Adaptive control loses its effectiveness in the presence of nonlinearity since it generally requires linear parametrization of the control law or the system dynamics. Experiments are conducted under various machining conditions, subject to changes in spindle speed, material of work-piece, and type of machining process. The suggested slide mode controller shows smoother cutting force fluctuation, which cannot be achieved by the conventional adaptive controller. The experimental set-up reflects the emphasis on the practicality of the sliding mode controller. In order to avoid the use of a dynamometer in the course of measuring the cutting force, the indirect cutting force measuring system is used by means of feed drive servo-motor current sensing.

Polymers have traditionally been considered to be good electrical insulators, and a variety of applications have relied on this insulating property. However, in 1958, Natta et al.1 succeeded in synthesizing polyacetylene (PA), a semiconducting conjugated polymer, which paved the way for the upsurge ...

Since the first discovery of carbon nanotubes (CNTs) in 1991, CNTs have generated enormous research activities in many areas of science and engineering due to their combined exceptional mechanical, thermal and electronic properties. These properties make nanotubes ideal, not only for a wide range of applications but also as a test-bed for fundamental scientific studies (Baughman et al., 2002). They can be described as a graphite sheet rolled up into a nanoscale tube. Two structural forms of CNTs exist: single-walled (SWCNTs) and multi-walled (MWCNTs) nanotubes. CNT lengths can be as short as a few hundred nanometers or as long as several micrometers. SWCNT have diameters between 1 and 10 nm and normally capped ends. In contrast, MWCNT diameters range from 5 to a few hundred nanometers because their structure consists of many concentric cylinders held together by van der Waals forces. CNTs are synthesized in a variety of ways, such as arc discharge, laser ablation, high pressure carbon monoxide (HiPCO), and chemical vapor deposition (CVD) (Dresselhaus, 1997). CNTs exhibit excellent mechanical, electrical, thermal and magnetic properties. The exact magnitudes of these properties depend on the diameter and chirality of the nanotubes and whether their structure is singleor multi-walled. Fig. 1 shows a segment of a single graphene plane that can be transformed into a carbon nanotube by rolling up into a cylinder. To describe this structure, a chiral vector is defined as OA = na1 + ma2, where a1 and a2 are unit vectors for the hexagonal lattice of the graphene sheet, n and m are integers, along with a chiral angle θ, which is the angle of the chiral vector with respect to the x direction. Using this (n, m) scheme, the three types of nanotubes are characterized. If n = m, the nanotubes are called ‘‘armchair”. If m = 0, the nanotubes are called ‘‘zigzag”. Otherwise, they are called ‘‘chiral”. The chirality of nanotubes has significant impact on their transport properties, particularly the electronic properties. For a given (n, m) nanotube, if (2n + m) is a multiple of 3, then the nanotube is metallic, otherwise the nanotube is a semiconductor. Each MWCNT contains a multi-layer of graphene, and each layer can have different chiralities, so the prediction of its physical properties is more complicated than that of SWCNT (Jin & Yuan, 2003).

This experimental study investigated the machinability of polymethylmethacrylate (PMMA)/multi-walled carbon nanotube (MWCNT) nanocomposites with 20 wt% MWCNTs in focused ion beam (FIB) micromachining. PMMA/MWCNT nanocomposites were fabricated using a solution casting method, in which PMMA and MWCNTs were dispersed in a solvent by ultrasonication. Microscale rectangular pockets were created on the PMMA/MWCNT nanocomposites to study the material removal mechanism in FIB. Effects of FIB input current and the ion beam overlap parameter (overlap %) on the material removal rate and geometric accuracy were studied. It was observed that the material removal rate increased with increasing input current and decreasing overlap %. Soft lithography was used to translate the ion-milled pockets on PMMA/MWCNT nanocomposites into microscale posts on polydimethylsiloxane (PDMS) for accurate measurement of the pocket geometries. A Scanning Electron Microscope (SEM) was used to investigate the characteristics of the micromachined features, nanocomposite surfaces, and replicated PDMS patterns. Our results demonstrated an effective method to produce microscale patterns on MWCNT-based nanocomposites.Copyright © 2011 by ASME

Optimal design of a piping system connected in the multi‐stage turbo blower has been performed using response surface method and three‐dimensional Navier‐Stokes analysis to reduce pressure loss in the piping system. To analyze three‐dimensional flow field in the piping system including a multi‐stage turbo blower, general analysis code, CFX, is employed in the present work. SST turbulence model is employed to estimate the eddy viscosity. Unstructured grids are used to represent a composite grid system including circular duct, blower impeller, casing and gate valve. Throughout the optimization of a piping system using two design variables defined the radius of an inlet and outlet ducts, the pressure loss in the piping system is successfully reduced by decreasing local losses in the piping system. Detailed flow analysis is performed using the reference and optimum shape of the connecting duct.

Multi-walled carbon nanotubes (MWCNTs) filled polypropylene (PP) composites were prepared by a corotating intermeshing twin screw extruder. To improve the dispersion of MWCNTs, the surface of MWCNT was modified with 1,10-diaminodecane, and maleic anhydride grafted polypropylene (MA-g-PP) was used as a compatibilizer. Micrographs of well dispersed functionalized MWCNTs (diamine-MWCNT) were observed due to the reaction between MA-g-PP and diamine-MWCNT in PP/MA-g-PP/diamine-MWCNTs composites. The different behaviors in crystallization and melting temperatures of PP/MA-g-PP/diamine-MWCNTs composite were observed compared to PP and PP/neat-MWCNT. Especially, the decomposition temperature of the composite was increased by 50°C compared to PP. PP/MA-g-PP/diamine-MWCNTs composite showed the highest complex viscosity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Since the discovery of carbon nanotubes (CNTs), there has been great interest in CNT-based composites. Well-developed micromachining processes are necessary to realize micron-size CNT-based composite products. Micro electro discharge machining (micro-EDM) has been applied into many challenge-to-cut materials such as ceramic composites. In this study, micro-EDM is used to machine CNT-reinforced polymer composites in the micro scale. CNT-based polymer composites were fabricated using solution casting, in which CNTs were dispersed in the polymer-solvent solution via high energy sonication, followed by precipitation and hot pressing. The investigation uses design of experiments (DOE) approach to screen of influential input factors for process measures. A 2 level fractional factorial design was used with four input factors; CNT loading on the workpiece, μ-EDM supply voltage, pulse on-time duration, and pulse on-time ratio. With 16 μ-EDM experiments, supply voltage was found to be most influential to the material-removal-rate (MRR). Scanning electron microscope (SEM) was used to investigate characteristics of the machined CNT-based nanocomposite surfaces.

Carbon nanotubes are considered one of the most promising reinforcements for developing high performance and multifunctional composites. Due to their nanoscale dimensions, carbon nanotubes are expected to improve through-thickness direction performance as well as other resin dominated properties of nanotube/fiber multiscale nanocomposites. In this research, 0.12 wt.% SWNT/75 wt.% glass fiber/EPON 862 multiscale nanocomposites were fabricated with different curing parameters to investigate the effect of SWNTs and curing parameters on mechanical and thermal properties. Considerable improvement of mechanical properties and glass transition temperature (Tg) of the multiscale nanocomposites have been obtained through the addition of SWNTs and the modified curing parameters. The improvements in the mechanical properties of the resultant multiscale nanocomposites were demonstrated by 26%, 6.7% and 20% for the storage modulus, flexural modulus, and flexural strength, respectively, with the addition of only 0.12 wt.% SWNT. The possible synergetic effect between nanotube and fiber reinforcement is also observed and discussed.