Short-carbon-fiber/polypropylene composites (CF/PP composites) have high processability and recyclability but low strength. To improve the strength, various nanofillers were hybridized to form fiber-reinforced composites. Adding nanofillers improves not only the strength but also the elastic modulus, with the exception of clay nanofillers. To understand the strengthening mechanism resulting from the addition of nanofillers, the residual fiber length and interfacial shear strength were measured. For CF/PP composites, the addition of alumina, silica, and CNT improves the interfacial shear strength, and thereby, the mechanical properties. On the basis of this result, proper choice of nanofiller type and content for improving the mechanical properties of PP/CF composites is discussed. (C) 2013 Elsevier Ltd. All rights reserved.

Strict geometrical stability is required for the precise structures like telescopes. Unpredictable out-of-plane deformation is a serious problem when we use CFRP (Carbon Fiber Reinforced Plastic) laminate to the precise structure. This out-of plane deformation of symmetrical CFRP laminate mainly arise from combination effects of ply angle misalignment and temperature change. We discussed here is effective stacking sequence of CFRP laminate that mitigate the deformation caused by the ply angle misalignment. The analysis based on laminate theory was performed to calculate the thermal deformation. In this analysis, the random numbers were added to each layers as ply angle misalignments. The analytical results were obtained statistically by Monte Carlo method. Mohr's curvature circle was also incorporated to evaluate the deformation as P-V (peak to Valley) values. We performed the analysis with various stacking sequence. It was calculated that the symmetric cross-ply laminates deformed 10 times larger than the other quasi-symmetric laminates. In the case of the total ply number is less than 12, the stacking sequence in the laminate has a significant effects on the thermal deformation. However, if the total number ply number is more than 24, effect of stacking sequence on the thermal deformation becomes negligible. We also discussed the geometrical stability of CFRP mirror by considering unavoidable ply angle misalignment. It was presumed that the CFRP mirror can be used for wide range of wave length when the back structure was attached to CFRP laminates. © 2011 The Japan Society of Mechanical Engineers.

Despite the problem of graphene aggregation in cured epoxy resin, no studies have clarified the tendency of graphene aggregation in a wide variety of material systems and process. We hypothesized that the use of epoxy resins at high temperatures leads to an extreme decrease in resin surface tension and viscosity of epoxy, which would cause re-aggregation of graphene once dispersed. So, we examined process/material with/without high temperature treatment and epoxy resins of different viscosities, and properties of nanocomposites were evaluated by flexural/tensile test. Experiments revealed that the process not including high temperature treatment suppressed graphene re-aggregation and maintained the high mechanical properties of nanocomposites. In particular, the increased tensile modulus by 18.44% and flexural strength by 2.81% (@ 1 wt% graphene loading), which were quite high for non-functionalized graphene, were recorded when epoxy was treated and cured at 20 ˚C at all times to keep the surface tension of epoxy desirable.

The lightweight, high strength and excellent properties of composites allow an ideal choice for aerospace devices and structures. In recent years, the study of using two-dimensional materials as fillers for composites has attracted significant attention. Boron nitride nanosheets (BNNS), 2D materials similar to graphene, have been regarded as promising fillers due to their exceptional mechanical properties, thermal conductivity, chemical stability, and insulation properties, which are distinct from those of graphene. In this study, we present an efficient production technique to synthesize high-aspect ratio BNNS using a combination of oxygen doping pre-treatment and micro fluidization technology. The resulting BNNS exhibit an impressive aspect ratio of up to 850. Furthermore, we demonstrate that the incorporation of BNNS, along with surface-functionalized hydroxides, into an epoxy resin composite leads to a 39.4% enhancement in the Young’s modulus under a low loading condition of 0.5 wt%. This result is a significant improvement and highlights the potential for mass-producing BNNS, thus achieving another milestone toward the practical application of BNNS. Graphical abstract: [Figure not available: see fulltext.]

Effective non-destructive testing to evaluate chemical tank made of fiber reinforced plastic is necessary, and ultrasonic testing is one of the promising methods. This research aims to investigate the influence of ultrasonic waves frequency on the thickness measurement result of FRP specimens. Testing using transducers with frequencies of 1 MHz and 2.25 MHz was performed on several specimens prepared using different resins and fibers. Frequency of 2.25 MHz provided results with a better resolution and higher accuracy, however, the attenuation of sound wave during its propagation in FRP medium resulted in returning sound waves with low amplitude, which caused difficulty in the wave reading and contributed to the measurement error. On the other hand, measurement using a lower frequency (1 MHz) resulted in a reflected sound wave with higher amplitude, which is easier to analyze, despite its lower accuracy. The measurement of FRP specimens using both 1 MHz and 2.25 MHz transducers resulted in a comparable accuracy, and improvement in the accuracy of the measurement is still required. Moreover, calculation of two-layer specimens thickness showed comparable results to those of one-layers specimens, and it shows the possibility of using the method for two-layer specimens.

The chemical structures on the original abstract graphic of our article (https://pubs.acs.org/doi/10.1021/ acssuschemeng.1c01737) unintentionally collapsed due to its low resolution, which may cause confusion. Herein, the abstract graphic with chemical structures correctly displayed is provided.

Amine-crosslinked epoxy resins represent a large fraction of polymers used in structural and coating applications, meaning the characterization and modeling of environmental durability and mechanical reliability is of utmost importance. In particular, chemical storage tanks, sewage systems, and oil/gas infrastructure involve prolonged exposure to organic and inorganic acids. However, the majority of meso-scale models for polymer network degradation are more appropriate for hy-drogels than stiff thermosets; meanwhile, other models developed for acid degradation of ester-containing networks are not applicable to amine-cured epoxies due to the assumption that crosslink density decreases. In this paper, we report the acid uptake and subsequent degradation behavior of bisphenol-F epoxy cured with an aliphatic amine, as well as propose a simple but physically meaningful model for an ideal 2D network that effectively relates acid uptake and polymer structure to the decrease in elastic properties over time. Parameters include crosslink density and acid penetration rate, and the only best-fit parameter is the reaction rate constant. This analysis can be extended to more complex network structures and environmental conditions to model neat resins and composites.

Drilling is a principal machining process that is generally operated to make holes in composite parts to join and assemble into a complicated structures. Recently, the use of natural fiber composites (NFCs) has increased in engineering and industrial applications. Choosing an appropriate non-destructive technique to evaluate the drilling-induced delamination in NFCs is a vital and essential task. This paper investigates three different non-destructive techniques for evaluating and determining the size and shape of drilling-induced delamination in NFCs. According to the results from this research, it can be inferred that the image processing technique using a flatbed scanner can be utilized as an accessible, economical, and efficient method for assessment of drilling-induced delamination in NFCs.

Due to the increase in the amount of produced epoxy resin waste, it is desirable to recycle this material to reduce the burden on the environment. Despite many studies focusing on recovering fibers from composites, few studies have focused on recycling the resin itself. In this study, we developed a new approach for recycling the decomposed amine-cured epoxy resin as an amine curing agent. Following the decomposition of the epoxy resin in nitric acid, a nitrated and decomposed resin product was extracted from the nitric acid solution. The resulting extract was then hydrogenated to convert the nitro group into amino group, and the hydrogenated extract was incorporated into the epoxy resin by replacing a portion of the original curing agent. The obtained recycled resin exhibited a higher tensile strength and comparable tensile modulus compared to the virgin resin due to the presence of aromatic amino groups. Moreover, when 20 mass% of the curing agent was replaced with the hydrogenated extract, the recycled resin with the optimized formulation exhibited tensile strength comparable to that of the virgin one. This approach demonstrates a novel recycling method for creating a closed loop of amine-cured epoxy resins.

The effect of oxygen and additional oxygen providers on furfuryl alcohol polymerization was investigated through chemical analyses and mechanical evaluation. NMR, UV–vis, Fourier transform infrared, and gas chromatography–mass spectrometry (GC–MS) results suggested that atmospheric oxygen and the further addition of an oxygen source functioned as an activator for the entire network polymerization. Interestingly, the construction of a conjugated structure on the furan linear chain, which is key to three-dimensional cross-linking, also appears to be accelerated in the presence of oxygen. Furthermore, the introduction of oxygen providers into the curing system successfully enhanced the mechanical properties of the cured furan resin.

Epoxy resin is an essential material for the society, although it poses challenges for recycling because of its cross-linked three-dimensional (3D) structure. Nitric acid decomposition is an effective recycling method for such a 3D network resin; this process can be performed at low temperature (80 °C) and normal pressure compared to other recycling methods. However, no systematic investigation on the relationship between the decomposition and chemical structure of raw epoxy resin is available. In this study, various types of epoxy resins which consist of bisphenol F-type epoxy resin and typical amine curing agent are prepared and decomposed using nitric acid. This is the first study to have systematically investigated the epoxy resin decomposition using nitric acid. Our results reveal that the chemical structure around the C–N bond and the ring structure of the curing agent strongly affect the epoxy resin decomposition, which is the first such report in the existing literature on such processes. The findings of this study are applicable for improving the nitric acid decomposition method employed for chemical recycling and to identify epoxy resins suitable for such recycling.

Functionalization of graphite is crucial for efficient and effective exfoliation to graphene. When negative charges are fixed to the edges of natural graphite, the resulting anionic graphite shows negative charging in a polar solvent. This enhanced negative charging is assumed to contribute the exfoliation of graphite during liquid-phase exfoliation (LPE). In this study, we prepared large anionic graphite flakes (~10 μm) by salt-assisted ball milling, as well as natural graphite flakes of the same size for comparison. During the LPE process, centrifugation speed and solvent type have dominant effects on graphene concentration and quality (e.g., size and thickness), so we investigated these factors for anionic graphite flakes in detail. The anionic graphite showed higher exfoliation efficiency in every type of solvent (isopropanol, methyl ethyl ketone, acetone, and water-based cosolvent) compared with the natural graphite. Monolayer graphene, with an average size of 80-200 nm, was obtained with relatively high yield (>10%) at only 3 min of sonication. The small size of graphene was due to edge fragmentation during the LPE process. The recyclability of the sediment and the characterization of the exfoliated powders for anionic graphene were also investigated.

In this study, few-layer graphenes (FLGs) were produced by new liquid phase exfoliation (LPE), exfoliation of graphite with weak acid salts. A high concentration dispersion of FLGs in low-boiling point solvents is successfully carried out, achieved by binding molecules with a dispersing function. And then graphene/epoxy nanocomposites were fabricated and tensile properties were evaluated in order to understand the effect of FLGs introduced into the resin. Graphene/epoxy nanocomposite showed improved mechanical properties. Tensile strength and fracture strain were increased by 11.5% and 55.6% compared with as-received one's. Especially, the improvement of fracture strain was outstanding, which indicated that adding FLGs had a positive impact on suppressing effect on crack propagation and improving fracture toughness of matrix resin. These beneficial results were derived from crack trapping by uniformly dispersed FLGs.

In this study, it was investigated that the validity of small punch (SP) test for the lifetime prediction of polyvinyl chloride (PVC) resin used as an electric insulation material for the electric cable. The degradation behavior of PVC resin under the accelerated high-temperature condition was analyzed using Fourier transform-infrared spectroscopy (FT-IR), tensile testing, and SP testing. The activation energies and estimated lifetime obtained from the Arrhenius method were compared. The peak ratio of the carbonyl group obtained by FT-IR, the elastic modulus obtained by tensile testing, and the apparent elastic modulus obtained by SP testing were used as indicators for lifetime estimation, and the logarithm of these values showed a linear correlation with exposure time. The activation energy obtained from the apparent elastic modulus using SP testing was the smallest and the predicted lifetime was the shortest among all mechanical properties in this research. It indicates that SP testing is sensitive to the degradation. This is because the stress at the surface becomes maximum for SP testing, and the degradation occurs at the surface of the materials by priority degradation. SP testing is an excellent minimally destructive lifetime prediction method for detecting of early-stage degradation.

Nanomaterials, such as carbon nanotubes, graphene, and various types of nanosheets, form aggregates in dry powder due to attractive van der Walls forces. To bring out their unique properties, dispersion of the nanomaterial in solid or liquid is essential. However, the dispersion media for these materials are limited; the surface tension of liquid should be as close as possible to that of the nanomaterial. This limitation restricts the effective usage of nanomaterials. Here, we find that nanomaterials are easily dispersed or exfoliated in water and low-boiling point solvents after simple pretreatment. Pulverization of nanomaterials induces many dangling bonds at the newly created edge, and these active species react with weak acid salts. In polar solvent, the bonded salts are dissociated and enhance the negative charging of nanomaterials. The enhanced electric charging prevents the aggregation or restacking of nanosheets even in typically incompatible solvent such as water and alcohol. The functionalized powder can be easily exfoliated, giving more than 20% yield of nanosheets after only 5 min of sonication.

Natural fiber composites (NFCs) have strong potential to replace glass fiber-reinforced plastics. An instrumental operation in machining composite structures is hole making which facilitates assembly of parts. Understanding the effects of drilling process parameters on feature properties of NFCs has great benefits. In this regard, to make a good quality and accurate hole in composite structures, appropriate selection of drill bit and cutting parameters is important. This paper investigates delamination behavior and hole quality of flax/epoxy composite laminates in response to feed, spindle speed, and three different types of drill bit. As indicated by analysis of variance results, drill bit type and feed have greater influences on the thrust force. It appeared that delamination factor and surface roughness were significantly influenced by drill bit, but not by feed and spindle speed. The choice of drill bit has great impact on the delamination factor (67.27%) and surface roughness (74.44%), respectively.

The use of natural fiber composites is growing at a fast rate in terms of industrial applications due to their eco-friendly, recyclable, renewable nature, and low density/costs. Recently, jute fiber is being used as a reinforcement material in the development of natural fiber reinforced plastics for engineering applications. Drilling is an essential machining operation that is frequently performed for making of holes in composite structures to facilitate assembly of several components into a complex part. The literature reviews indicate that only a few of research articles investigated drilling of natural fiber reinforced composites. Hence, in the present research, drilling of woven jute fiber reinforced polymer composites has been examined. This study aimed at evaluation of cutting parameters and drill bit types effect on thrust force, delamination size, and surface roughness in the jute fiber reinforced polymer composites drilling using an experimental design based on full factorial technique. The percentage contribution of the cutting parameters and drill bit types were determined through the analysis of variance. The optimal setting of these parameters was found through observation. The experimental results indicated that the most significant effect was the drill bit type influencing both delamination factor and surface roughness.

Composite materials based on bio-derived furan resin and natural fiber as reinforcing elements were studied. The purpose of this research is to improve the mechanical properties of this composite material by focusing on the natural fiber treatment methods. Unidirectional flax fabric was pretreated by alkaline treatment, silane coupling treatment, and the combination between alkaline and silane treatment before impregnating with furan resin. Three-point bending test, SEM observation, and ATR-IR analysis were carried out to evaluate the effects of treatment methods on the composite samples. Results reveal that the flexural strength of the composite was increased to 215MPa, 232MPa, 247MPa for alkaline, silane, and alkaline-silane treated composites respectively while the flexural strength of the untreated composite sample is 200MPa. SEM images show the effects of alkaline treatment on a single flax fiber at different treatment durations. The coupling of silane on the surface of flax fiber was confirmed by ATR-IR.

© 2018 Elsevier Ltd In this paper, we investigate the case of bisphenol-type epoxy crosslinked with poly(ether)amine, immersed in sulfuric acid at elevated temperature. The results show that very high equilibrium mass-change (up to 40%) is observed, and that amine protonation is largely responsible for this behavior. When the acid solution concentration is 5mass% or higher, alcohol dehydration and aromatic ether cleavage reactions occur by excess acid (after amine protonation). A mechanistic degradation model is proposed, which requires no empirical parameters and accounts for polymer network structure differences. The model is supported by calculating the theoretical crosslink density using gravimetric data of penetrated acid at equilibrium.

Fiber reinforced polymer (FRP) composites are commonly used in the chemical industry for storage tanks and pipelines, since most metallic alloys suffer from corrosion and result in costly maintenance and safety hazards. E-glass fiber is commonly used because of its low cost, but it is extremely susceptible to rapid degradation in low-pH environments. C-glass is an acid-resistant substitute, and while not as durable as carbon, it is much cheaper. Nevertheless, durable fibers are not the only key aspect of designing corrosion-resistant composites, as various degradation mechanisms must be considered. In this study, plain-weave laminates of C-glass and amine-cured epoxy are exposed to water and sulfuric acid solutions, and the relationship between diffusion kinetics and strength-loss is discussed. Results show that both solutions attack the fiber surface to some degree, but more importantly sulfuric acid increases the saturation uptake of water in the material, causing high swelling stresses that significantly reduce mechanical properties.

Since thermoset resins that contain ester groups (including vinylester, polyester, and anhydride-cured epoxy) are susceptible to hydrolytic degradation, amine curing agents with epoxy are a widely used alternative because they are much more stable against water or alkaline solutions and also allow for curing at lower temperature compared to anhydride. However, amine groups react with inorganic acids to form a salt which can have detrimental effects on the epoxy resin depending on the composition and curing conditions. Experimental data pertaining to diffusion kinetics of sulfuric acid in aminecured epoxy resin is lacking in the literature, but the available studies have shown that it forms a step-like concentration profile, rather than a Fickian-Type gradient, and its mass-change tends to be proportional to the square-root of time, similar to Fickian diffusion. Although usually no cracking or mass-loss is observed, strength and stiffness decrease over time with almost no warning, making it a very dangerous durability problem. The current study examines the unique high-swelling phenomenon of bisphenol-F epoxy (DGEBF) cured by polyamine in hot/wet and low-pH environments. Most studies of epoxy or vinylester matrix resins report swelling between 0.5-3%, within small-strain approximation for coupled diffusion-deformation models. However, considerable swelling of DGEBF/polyamine is observed, reaching a total volume increase over 30% for the most aggressive condition. This creates considerable internal stresses that in turn severely affect the mechanical properties of the resin in the shortterm time scale (i.e., pre-saturation). The step-like concentration profile of sulfuric acid creates a moving swelling front where rubbery and glassy phases are separated by a small transition region
compressive stress is distributed through the swollen layer while the glassy core experiences tensile stress as it constrains some swelling, and the transition layer has some associated shear stress. This affects long-Term strength and overall material performance.

Since thermosetting resins have excellent resistance to chemicals, fiber reinforced plastics composed of such resins and reinforcement fibers are widely used as construction materials for equipment in chemical plants. Such equipment is usually used for several decades under severe corrosive conditions so that failure due to degradation may result. One of the degradation behaviors in thermosetting resins under chemical solutions is "corrosion-layer-forming" degradation. In this type of degradation, surface resins in contact with a solution corrode, and some of them remain as a corrosion layer on the pristine part. It is difficult to precisely measure the thickness of the pristine part of such degradation type materials by conventional pulse-echo ultrasonic testing, because the sound velocity depends on the degree of corrosion of the polymeric material. In addition, the ultrasonic reflection interface between the pristine part and the corrosion layer is obscure. Thus, we propose a pitch-catch method using a pair of normal and angle probes to measure four parameters: the thicknesses of the pristine part and the corrosion layer, and their respective sound velocities. The validity of the proposed method was confirmed by measuring a two-layer sample and a sample including corroded parts. The results demonstrate that the pitch-catch method can successfully measure the four parameters and evaluate the residual thickness of the pristine part in the corrosion-layer-forming sample. (C) 2017 Elsevier B.V. All rights reserved.

Fiber reinforced plastics (FRPs) are often used for chemical equipment because of their high chemical resistance, especially their resistance to acidic conditions. However, serious accidents have been reported when using such tanks with hydrochloric acid (HCl). We gathered FRP tanks used for 35% HCl storage from various chemical companies, and analyzed their changes in appearance, HCl penetration and residual flexural strength. We found that residual strength of FRP decreased to < 50 MPa after 24 years of usage. The strength degradation at the tank roofs was more severe than at other positions in the tanks; in these parts the residual strength was 10-25 MPa after 20 years of usage. The strength degradation of FRP is caused by diffusion of HCl into the FRP. If the diffusion of HCl reaches the reinforced layer of the FRP tank, the FRP strength sharply decreases. Based on our comprehensive analysis of FRP tanks, the lifetime of current FRP tanks for 35% HCl storage is estimated at < 20 years.

Liquid-phase exfoliation (LPE) of graphite is a promising method to produce few-layer graphene (FLG) in large quantities. Selection of the solvent or surfactant is the most important factor in determining the productivity of LPE and the stability of the liquid FLG dispersion. To find efficient solvent systems for improving the production of FLG, various approaches based on previous research, including addition of a surfactant and use of binary solvents, are investigated using a pressure homogenizer. Over the range of solvents and surfactants used in our study, we find that the greatest improvement in the production of FLG results from the addition of an alkaline aqueous solution (pH 11) into organic solvents. Moreover, we find that this approach works for the probe-sonication method of FLG production as well as for various types of natural graphite. Solvent molecular size and electrostatic repulsion of graphene in liquid play important roles in improving the production of FLG because they mitigate the restacking of FLG during exfoliation. (C) 2017 Elsevier Ltd. All rights reserved.

<p>Recently, Indium tin oxide (ITO) has been widely used as transparent conductive films (TCFs) in various electronic devices. However, ITO has many drawbacks such as high cost and brittleness. Nowadays, graphene is the ideal alternative for ITO because of its excellent transparency, electrical conductivity and mechanical flexibility by the effect of sp² hybridized orbital. However, the electrical properties of graphene TCFs are inferior to those of ITO so additional processing to improve electrical properties is required. Achieving the purpose, there is a number of studies on composite graphene and conductive materials such as Ag. And now, new simple, low-cost methods are required. In this study, we used the liquid plasma method to combine graphene and Ag. This is a low-cost, simple method for the hybridization. Then we made graphene / Ag hybridized TCFs using thin layer graphene-supported Ag and evaluated some characteristics. Finally, we acquired transmittance and sheet resistance of the graphene / Ag hybridized TCFs.</p>

An efficient graphene production technique is essential to realize the commercial use of graphene. Liquid-phase exfoliation (LPE) of graphene is a low-cost method of graphene production. LPE is based on shear mixing or sonication in proper liquid. The applied force to graphite has not been optimized. Thus, the production rate and quality of graphene via LPE can be improved by controlling fluid dynamics in liquid. We demonstrate that the high-speed laminar flow generated by a pressure homogenizer effectively exfoliates large quantities of high-quality graphene. In a lab-scale trial, a production rate of 3.6 g/h of graphene in aqueous solution was achieved. In addition, the average lateral size of graphene obtained by the proposed method was larger than that by traditional sonication method. An industrial-scale machine could exceed a production rate of 1 kg/h, marking a significant step in the commercialization of graphene. We show that the graphene obtained using this method improves the mechanical properties of polymers more than graphene obtained via sonication. (C) 2016 Elsevier Ltd. All rights reserved.

Applications of fiber reinforced plastics have been expanding due to improvement of not only fuel efficiency but also the motion performance of some recent vehicles. Especially, the demand for injection-molded fiber reinforced thermoplastics is expected to increase because of their superior moldability, productivity and recyclability. In this study, the influence the fiber diameter has on the impact tensile properties of long glass-fiber reinforced polyamide (GF/PA) is investigated using the split Hopkinson pressure bar method. Prior to the tensile tests, an investigation of the fiber-orientation distribution was conducted in order to cut out specimens with the same fiber orientation angle from the injection molded plate. Two types of specimens, referred to as specimens with high- and low orientation angle, were manufactured using glass fibers with average diameters of 13, 17, 23 μm. In the tensile test, the GF/PA with smallest fiber diameter showed the highest tensile strength and the most significant strain rate dependency on the strength. These effects were more significant for the specimens with high orientation angle. From SEM observations on the fracture surface and an average fiber length measurement, it was observed that the interfacial fracture and the fiber breakage were dominant failure modes under the considered tensile loading conditions. It was suggested that decreasing the stress acting on the fiber/matrix interface by reducing the fiber diameter affected the improvement of the GF/PA strength. Using the modified linear rule of mixtures, the tensile strength was predicted. The predictions showed good agreement with experimental results. Therefore, it is believed that the decrease of critical fiber length is the reason that the impact tensile properties are higher for the samples with smaller fiber diameter.

<p>Transparent conductive films (TCFs) are widely used in various electronic devices. In addition, due to the excellent transparency (T=97.7%) and electrical conductivity by the effect of sp2 hybridized orbital, using graphene for the materials of TCFs is ideal. Typical method for manufacturing graphene TCFs is chemical vapor deposition (CVD) method. However, CVD method takes a high cost. On the other hand, liquid phase exfoliation (LPE) is the method for obtaining thin-layer graphene by peeling graphite in the organic solvent. In the LPE, method of making graphite oxide and peeling graphite is often used, but this method has problem that falling down conductivity due to structural defect in graphene. In this study, we used pressure homogenizer to obtain thin-layer graphene without using chemical treatment. Then, we made TCFs by using thin-layer graphene and evaluated some characteristics. Finally, we investigated transmittance and sheet resistance of the TCFs.</p>

Graphene can be obtained via sonication-assisted liquid-phase exfoliation, but the production rate of few-layer graphene (FLG) is still low. A high-power probe sonicator was used in this study to improve the production rate of FLG, and its performance was optimized by controlling processing parameters such as the initial graphite concentration, surfactant concentration and liquid volume. By optimizing processing parameters, production rate of FLG dispersions in N-methyl-2-pyrrolidone (NMP) were greater than 1 g/h, which is the best value achieved in the sonication-assisted exfoliation process. In the case of liquid exfoliation in water/surfactant solution, production rate of FLG was achieved approximately 0.28 g/h. Our work here demonstrates that graphene concentration in a probe-sonication process does not depend on the shape of vessel, and it is predictable by power law models. (C) 2015 Elsevier Ltd. All rights reserved.

We investigated the efficient use of cellulose to resolve the problem of the depletion of fossil resources. In this study, as the biomass material, the green composite based on natural rubber (NR) and the flake-shaped cellulose particles (FSCP) was produced. in order to further improvement of functional characteristics, epoxidized natural rubber (ENR) was also used instead of NR. The FSCP were produced by mechanical milling in a planetary ball mill with a grinding aid as a cellulose aggregation inhibitor. Moreover, talc and mica particles were used to compare with FSCP. NR and ENR was mixed with vulcanizing agents and then each filler was added to NR compound in an internal mixer. The vulcanizing agents are as follows: stearic acid, zinc oxide, sulfur, and vulcanization accelerator. The functionalities of the composites were evaluated by a vibration-damping experiment and a gas permeability experiment. As a result, we found that FSCP filler has effects similar to (or more than) inorganic filler in vibration-damping and O-2 barrier properties. And then, vibration-damping and O-2 barrier properties of the composite including FSCP was increased with use of ENR. in particular, we found that ENR-50 composite containing 50 phi FSCP has three times as high vibration-damping property as ENR-50 without FSCP.

Extensional flow has been taken notice as the more efficient solution for improving the dispersion of nanocomposites than shear flow. One of the production processes of nanocomposites is melt extrusion with co-rotating twin-screw extruder (TSE) which is superior in terms of productivity and mixing performance. Then, we focused on "Blister Disk" which had many small holes for generating the extensional flow. However, the influences on the mixing performance by changing the geometry of Blister Disk have not been investigated as far as we know. Therefore, the objective of this study is the optimization of Blister Disk geometry (e.g. hole numbers, hole diameter and disk length) for improving the dispersion of nanocomposites. Primary, the extensional flow state was investigated at the Blister Disk with FEM analysis. Secondly, to validate the simulation results experimentally, the polypropylene reinforced multi-walled carbon nanotube (PP/CNT nanocomposite) was used as the model of nanocomposite, and the dispersion state of CNT was investigated by morphological observation. As the result of these experiments, the better dispersion state of CNT was obtained as total permeation area and shorter hole length of Blister Disk was smaller because extensional and shear stress were increased.

In this article, the dimensional stability of epoxy- and cyanate-based laminates is discussed, focusing on the thermal deformation, moisture-induced deformation, and deformation induced by relaxation of thermal residual stress. Each of the deformations was calculated independently based on the laminate theory. The material properties of the unidirectional laminates were obtained by conducting thermal mechanical analysis, moisture absorption tests, and tensile creep tests. These material properties were adopted to the laminate theory to predict the deformation of quasi-isotropic laminate, and it was calculated that each type of deformation induced micron-level dimensional instability. The moisture-induced deformation was an order of magnitude larger than that caused by the other factors. The validity of the calculations was confirmed by comparing the calculated results with the experimental ones. It is important to control moisture absorption even if cyanate resin, which has high moisture resistance, is used.

Fiber breakage occurs during the injection molding of fiber-reinforced thermoplastics, resulting in the deterioration of the mechanical properties of the molded parts. In this paper, we propose an effective screw geometry for improving both fiber dispersion and residual fiber length. The proposition is based on the results of our study in which we evaluated five types of screws by investigating the molded specimens. We found that the screw geometry in the compression zone dominantly affected the residual fiber length, and that the choice of an appropriate geometry for the melting and mixing processes was the most important factor for improving both fiber dispersion and residual fiber length. Our experimental observations were compared with the results of flow analysis and consistency was observed. We also discuss the effects of the screw size on the quality of the molded parts.

Nanofillers such as carbon nanotubes and clay are attractive materials, because addition of small amount of nanofillers can improve mechanical, thermal and electrical properties of plastics without changing processability. However, nanofillers themselves do not show excellent fire retardancy such as self-extinguish properties. Nanofillers should be combined with other fire retardants. Some combination showed positive synergy effect in fire retardancy, but some case showed negative synergy. It is important to know fire retardant mechanism of nanofiller to develop more efficient fire-retardant nanocomposites. In this chapter, we’ll show the fire retardant mechanism of nanofillers. Then, effective combination of nanofiller and conventional fire retardant is introduced reviewing lots of papers.

von Karman's effective width theory is constructed on the assumption that thin plate of elastic-perfectly plastic solid is subjected to static buckling. We examined whether von Karman's effective width theory is applicable to design of crush absorption structure. As a result, cross section of the member becomes effective against axial crush with increasing crush speed. It is found that the design based on the conventional theory is provided enough evidence of safety, thus, optimized design criteria can be proposed.

The addition of wood flour improves the mechanical properties of thermoplastics, but also increases the burning rate of neat plastics profoundly. To modify the flammability of wood-plastic composites (WPCs), various additive-type fire retardants such as ammonium polyphosphate (APP), melamine polyphosphate (MPP), and aluminum hydroxide were added to improve the fire performance of WPCs. Both UL94 flame tests and cone calorimetry were used to evaluate the fire performance of WPCs, and the results proved that the addition of 10 wt% APP lead to enhanced self-extinguishing properties. On the other hand, polypropylene with 30 wt% of APP did not achieve self-extinguish properties. The effective parameters in the cone calorimetry test to give self-extinguishing properties were discussed by comparing the results of the burning tests. It was presumed that the most important parameters for self-extinguishing of WPCs was an average heat release rate at initial stage of burning. The effect of fire retardants on the mechanical properties of WPCs was also investigated. The tensile strength and modulus of the composites decreased with the addition of fire retardants. (C) 2013 Elsevier Ltd. All rights reserved.

The purpose of this study is to develop automotive frictional parts, especially continuously variable transmission (CVT) blocks by using a composite material made of thermoplastics resin and fiber. CVT blocks are used at about 100°C under high pressure and friction condition. So, we have used nylon 9T, PA9T. PA9T has high a melting point that is higher than maximum temperature of the state of slip. To apply composite materials to CVT blocks, the material properties such as high strength, modulus of elasticity and fatigue strength are important. Therefore, a purpose of this study is improvements of mechanical properties by adding fillers to PA9T with various compounding and molding condition. PA9T and CF were mixed by using twin screw extruder. After compounding, dumbbell specimens were made by using injection molding machine. Bending, fatigue and abrasion tests were conducted. Moreover, we evaluated the transmission capacity of CVT belt made of PA9T composites and conducted slip test. According to results of tests, PA9T with CF38.8 vol% achieved desired values of CVT. The CVT belt has 40 Nm of torque under 2.0 kN of axle load. © 2014 WIT Press.

Addition of wood flour improve the mechanical properties of thermoplastics, on the other hand it increases the burning speed of the materials. To modify the flammability of wood-plastic composites(WPC), various fire retardants, such as ammonium polysphosphate (APP), melamine polyphosphate (MPP) and aluminum hydroxide were added to WPCs. Burning tests based on UL94 and cone calorimetry were conducted to evaluate a fire performance of WPCs with fire retardants. The addition of fire retardants could lead to self-extinguishing materials when 10 wt% of APP was used. However, in the case of pure polypropylene, addition of 10 wt% of APP did not improve the flammability. Wood flour accelerates the burning behavior of PP, but it can reduce the use of APP to achieve self-extinguishing materials. Synergy effects between wood flour and APP was confirmed. Wood flour facilitates the forming of foamed char layer by APP during the combustion. This protective char surface can reduce the heat and oxygen diffusion toward the WPCs. The effect of fire retardants of mechanical properties of WPCs was also investigated. Tensile strength and modulus of composites decreased with addition of fire retardants. (C) 2014 Elsevier Ltd.

Injection molding of fiber-reinforced thermoplastics (FRTP) leads to fiber breakage and in turn deterioration of mechanical properties of the molded parts. In this paper, we propose an effective screw geometry for improving both fiber dispersion and residual fiber length. By evaluating four types of screws by investigation of the molded specimens, we found that the screw geometry in the compression zone had a dominant effect on the residual fiber length, and that choosing the proper geometry for the melting and mixing process was the most important factor for improving both fiber dispersion and residual fiber length. The screw improves both properties at the same time owing to the appropriateness of its geometry for both the melting and mixing zone. Our experimental observations were compared with the results of flow analysis and consistency was observed.

The mechanism of strain rate dependence on the Bauschinger effect in dualphase type high strength steel sheets is investigated and the influence of mesostructure differences on spring-back is estimated in this study. Compression-tensile tests at a strain rate from 0.007/s to 100/s is conducted. To differentiate between the multiphase structure-induced effect and the matrix properties, the same tests are also conducted for ferrite single phase steel. As a result, the Bauschinger effect on dual phase steel is not associated with the matrix properties independently. Moreover, it is revealed that a multiphase structure-induced effect acts a dominant function for deformation characteristics through experiments and micro observations. © 2014 WIT Press.

We investigated the efficient use of cellulose to resolve the problem of the depletion of fossil resources. In this study, as the biomass material, the green composite based on natural rubber (NR) and the flake-shaped cellulose particles (FSCP) was produced. The FSCP were produced by mechanical milling in a planetary ball mill with a grinding aid as a cellulose aggregation inhibitor. Moreover, talc and mica particles were used to compare with FSCP. NR was mixed with vulcanizing agents in an internal mixer. And then each filler was added to NR compound in an internal mixer. The vulcanizing agents are as follows: stearic acid, zinc oxide, sulfur, and vulcanization accelerator. The functionalities of the composites were evaluated by a vibration-damping experiment and a gas permeability experiment. As a result, we found that FSCP filler has effects similar to (or more than) inorganic filler in vibration-damping and O-2 barrier properties.

A bottle with a vacuum insulation structure is generally called a thermos bottle. It has a dual structure with inner and outer cylinders and a vacuum layer between them. The bottle with the structure maintains the heat and cold. It has been found useful for many years as a container that carries drinking water. Recently, the lightweight design of a vacuum bottle has been required to meet consumer demand. However, the bottle's wall collapses during the process of drawing a vacuum if the stiffness of the cylinder is not enough. To construct the design guide that can prevent the collapse of a double-structured bottle induced by the pressure difference, a numerical simulation was performed. The critical thickness tc, which is the thickness of the bottle when the bottle starts to deform under 1 atm, was defined. tc depends on the length and diameter of the bottle. The index to determine tc from the length and diameter of the bottle was suggested. To evaluate the validity of the analysis, vacuum bottles were prepared and experiments were conducted. The index we suggested showed good agreement with the experimental results. The shift of index within the increase of Young's modulus can be formulated. © 2013 WIT Press.

Carbon nanotubes (CNTs) were grown uniformity on the surface of carbon fibers to create hierarchical fibers by use of floating catalyst chemical vapor deposition. The tensile properties of CNTs grafted fibers were measured. The strength of grafted fibers decreased approximately 12% compared to raw carbon fibers in this process. A fiber pull-out test revealed that the interfacial shear strength (IFSS) in polypropylene composites improved by 35% by grafting CNTs onto carbon fibers. It indicates the use of hierarchical fibers in thermoplastic composites is effective due to the improvement of IFSS by mechanical interlocking between CNTs and the matrix. The CNT/fiber joint strength is the most critical property, and the experimental observations also revealed that the joint fracture was the major failure mode. © 2013 WIT Press.

In this paper, time-dependent dimensional change in quasi-isotropic laminates induced by relaxation of thermal residual stress and physical aging was predicted by the classical lamination theory. CFRP with pitch-based carbon fiber and cyanate ester resin was chosen for the study. Viscoelastic properties were investigated by performing tensile creep test for unidirectional laminates in the transverse direction. In addition, shrinkage strain induced by physical aging was studied by measuring the strain change of unidirectional laminates as well. Shrinkage strain in off-axis layers was calculated by using the coordinate-transform method. Shrinkage strain in 60° and 45° laminates were measured and the results were compared with the calculation. From the comparison, it was found that shrinkage strain of off-axis layers can be calculated by using the coordinate-transform method. Experimental results were applied to the classical theory in order to predict the time-dependent dimensional change of quasi-isotropic laminates. The strain change in quasi-isotropic laminates was obtained experimentally, and the result was compared with the prediction. It was verified that the time-dependent deformation of quasi-isotropic laminates can be predicted with a με-order by using proposed prediction method. © 2013 The Japan Society of Mechanical Engineers.

In recent years, polymer nanocomposite that is composed of polymer and nano scale filler is getting much attention. The clay, which is a layer compound, is mainly used as filler. One of the most common mixing methods is melt-compounding. A twin-screw extruder is usually used to compound the melted polymer and clay. However, it is difficult to discuss the effective compounding method for exfoliation and dispersion of clay in the polymer because shear stress and flow direction around screws are extremely complex. Therefore, physical factors of clay exfoliation have been not known. From the above reason, the purposes of this research are to clarify the factors for making clay exfoliated to a single layer and to acquire the guideline for optimizing mixing conditions using high speed flow in narrow tube that can give simple high shear stress to the resin. TEM observation and rheological analysis were conducted to quantify the exfoliation state of clay. It was verified that the specific energy was the most important parameter for the exfoliation of clay platelet. © 2013 The Japan Society of Mechanical Engineers.

It is well known that the strength of glass fibers increases with increasing strain rate. Consequently, impact strength of glass fiber is competitive with that of carbon fiber. This strengthening phenomenon is well recognized for bulk glass. Strain-rate dependence of the strength for bulk glass was described by considering slow crack growth in glass. The analytical model that considered the slow crack growth of glass is proposed to predict the strength of glass fibers. The proposed model considered the stress corrosion limit and a constant crack velocity region. Calculations showed almost same results with the previous model, however, some differences were confirmed. To discuss the validity of the analysis, tensile tests of E-glass fiber bundles were conducted at various strain rates. It was observed that the fracture behaviors differ with the strain rates. Experimental results showed that the strength of E-glass fibers increased with increasing strain rate. Furthermore, we confirmed that the analytical results were in good agreement with the experimental results. The strain-rate dependence of the strength of glass fibers was successfully predicted by considering the slow crack growth in glass.

A simple method for obtaining viscoelastic parameters from the results of static tensile tests is presented herein. Viscoelastic parameters were obtained by fitting experimental results and calculated results based on the power law model and linear viscoelasticity. The static tensile tests were carried out at various pre-aging times and the effect of physical aging was determined. The data confirmed that the physical aging process has a significant effect on the viscoelastic behavior. A creep test was conducted in order to discuss the validity of the prediction using the results of the static tensile test. It was confirmed that the predictions based on the viscoelastic parameters obtained from static tensile tests cannot adequately model actual viscoelastic behavior. The effective time theory was incorporated into the prediction in order to account for the progress of physical aging. It was verified that incorporating effective time theory into the prediction allows for the precise prediction of the long-term viscoelastic behavior.

The continuous ECAP process which can provide three-dimensional strain was developed in this study. A die with tri-axis crossed channels having channel angle φ of 90° and curvature ψ of 0° was created. As a result, continuous ECAP process via route Bc for AC4CH aluminium semi-solid alloy could be performed at 573K at pressing speed of 0.5mm/sec using the developed die. The continuous method cut the processing time in half compared to the non-continuously conventional method. The grains became fine from 100μm to approximately 2μm. Workpiece processed 8 passes exhibited four times higher toughness than as-cast alloy. © 2012 WIT Press.

The tensile properties of E-glass, which is the most popular reinforcement fiber in composite materials, were determined from the experimental results of fiber bundle testing under a high strain rate. The tests were performed by using two types of experimental methods. One is the tension-type split Hopkinson bar system and the other is the universal highspeed tensile-testing machine. In the results, it was demonstrated that the tensile strength and fracture strain of E-glass fiber increased with the strain rate. The absorbed strain energy, therefore, significantly increased. It was also shown that the strain rate dependency of E-glass fiber tensile strength was strongly affected by fiber diameter. The smaller diameter of E-glass fiber has the stronger strain rate dependency. Finally, the impact tensile strengths of high-strength glass and carbon fibers were investigated. It was confirmed that the tensile strength of the high-strength glass fiber also increased with the strain rate, but the tensile properties of carbon fiber were almost independent of the strain rate.

This study presents an analytical model to predict compressive strength of unidirectional FRP. Proposed model considers the effect of strain-rate dependency on mechanical properties of constituent materials. The model is based on the elastic foundation model and the microbuckling model of fiber which has initial misalignment in matrix. Compressive deformation of unidirectional FRP is considered by dividing into fiber microbuckling region and plastic kinking region. Additionally, to take into consideration the change in compressive deformation mode accompanying fiber volume fraction or fiber microbuckling, A mode function is introduced. The predictions from the proposed model are compared with experimental results of unidirectional E-glass/Epoxy and T700SC/Epoxy evaluated by using the conventional split Hopkinson pressure bar method. Incorporating strain-rate dependency on compressive modulus of reinforcement calculated from composite mixture law, the predictions are found to be in good agreement with experimental results of strain-rate dependency on compressive strength. Accuracy of the prediction is improved by changing the mode function. © 2012 The Japan Society of Mechanical Engineers.

This paper discusses the accuracy of ply angle alignment and how it relates to out-of-plane deformation in carbon fiber reinforced plastics (CFRP) laminates. We investigated the deformation of symmetrical cross-ply laminates under hot and humid conditions. In spite of the symmetrically stacked laminates, unpredictable out-of-plane deformation occurred over time due to ply angle misalignment. The deformation was unstable and disproportionate to the absorbed moisture. A Monte Carlo simulation based on laminate theory was performed to quantify the deformation induced by the ply angle misalignment. Symmetrical cross-ply laminates were found to twist as they absorbed water when they underwent ply angle misalignments. By comparing the analytical results with experimental results, we concluded that a standard deviation of approximately 0.4 exists as ply angle misalignment in the laminates used in this study and that this slight ply angle misalignment can be a significant factor in out-of-plane deformation of cross-ply laminates. (C) 2010 Elsevier Ltd. All rights reserved.

This paper reports a development of space telescope mirror made by light and thermally stable CFRP. We first compare thermal stabilities of a mirror made by CFRP with a conventional that made by glass material. The superior point regarding the thermal stability of the CFRP mirror to the glass mirror is described. One of the most critical issues for CFRP mirror is the mirror-surface roughness deterioration induced by "fiber-print through". We made a prototype mirror consisting of only CFRP with a gel-coating on the mirror surface, addressing the issue. The gel-coated mirror-surface roughness was 20 nmRMS just after fabrication. Durability of the surface roughness under various hostile conditions is examined in the present study.

We measured residual stress relaxation in epoxy-based CFRP laminates and cyanate-based CFRP laminates. We estimated the residual stress in symmetric cross-ply laminates by measuring the curvature of unsymmetric cross-ply laminates and investigated the relaxation of the residual stress by measuring the curvature of unbalanced laminates in a nitrogen environment. Our experimental results demonstrated that the residual stress in both kinds of laminate can decay by approximately 15% after 500 hours at 40°C. The stress relaxation can be modeled by the power law model. Viscoelastic parameters were obtained by a quasi-static tensile test to predict stress relaxation. The validity of the prediction is discussed.

In this study, we focused on the geometrical change of cross-ply laminates that are widely used for the composite structures. The behavior of time-dependent out-of-plane deformation under high temperature and humidity was examined. The CFRP plates were exposed at 80°C, 90% RH and their change in geometry was measured at arbitrary elapsed time. The initial shape of the specimens was twisted saddle shape, and the shape gradually became flat with time. Up to 500 μm of out-of-plane deformation arose during moisture absorption for CFRP symmetric plate with the size of 280×280×2.4 mm. The displacement in the thickness direction was the most along ±45° directions in which reinforcing fiber was not aligned. Finite element analysis (FEA) was performed to simulate the out-of-plane deformation of cross-ply laminates. The diffusivities D and coefficient of moisture expansion β, which were obtained other experiments in authors' previous work (Arao et al.: Adv. Compos. Mater., 17 (2008), 359-372), were used. The ply angle misalignment was considered as factors of generating out-of-plane deformation. For the analytical results, it was confirmed that the model the surface layer of which was rotated 1° deformed approximately 700 μm, and the plate geometry became twisted saddle shape by moisture absorption.

As CFRPs (Carbon Fiber Reinforced Plastics) are being sought for the greater use in aerospace and aircraft structures, it is necessary to understand the mechanical behavior for long-term usage. Furthermore, its low thermal expansion and high specific stiffness has brought attention to the application of CFRPs for the next-generation materials of the ultra-precise structure, such as antenna and mirror. In spite of the advantages of CFRPs, it is well known fact that the long-term dimensional stability of CFRP laminates are affected by several factors, such as moisture absorption, residual stress relaxation, and physical aging. Among these factors, residual stresses are due to the mismatch of thermal expansion rate and cannot be eliminated. This research paper introduces an experimental method of using unsymmetrical cross-ply laminates to determine the behavior of residual stress relaxation. Experimental results are compared to the analytical results derived by classical lamination theory (CLT).

Moisture absorption behavior of CFRP and its effect on dimensional stability was examined. Moisture diffusivity in CFRP was determined by measuring specimen weight during the moisture absorption test. Three types of CFRP specimens, unidirectionally reinforced, quasi-isotropically laminated and cloth-laminated composites were prepared. Each CFRP was processed into two geometries; a thin plate for determination of diffusion constants and a rod with square cross-section for the discussion of two-dimensional diffusion behavior. Coefficient of moisture expansion (CME) was also obtained from specimen deformation involving moisture absorption. During moisture absorption, the specimen surfaces strongly deformed especially near the edges because of three-dimensional moisture concentration distribution. This deformation was reasonably predicted by the finite element analysis using diffusion constants and CME, which have been experimentally determined. For unidirectional CFRP, an effect of fiber location distribution on CME is discussed by a micromechanical FEA.

Moisture absorption behavior of CFRP and its effect on dimensional stability was examined. Moisture diffusivity in CFRP was determined by measuring specimen weight during the moisture absorption test. Three types CFRP specimens, unidirectional, quasi-isotropic and cloth-laminated composites were prepared. Each CFRP was processed into two geometries; a thin plate for determination of diffusion constants and a rod with square cross-section for the discussion of two-dimensional diffusion behavior. Coefficient of moisture expansion (CME) was also measured from specimen deformation involving moisture absorption. During moisture absorption, the specimen surfaces deformed especially strongly near the edges because of three-dimensional moisture concentration distribution. This deformation mechanism was reasonably predicted by the finite element analysis using diffusion constants and CME, which have been experimentally determined.

Viscoelastic property of CFRP is one of most critical parameters which dominate its dimensional stability. In order to investigate the time-temperature dependency of micro-scale deformation, four point bending creep tests were conducted. It is reported that extremely slow cure causes microscopic-scale deformation. So the influence of aged shrinkage upon secular change of dimension was investigated and creep behaviors with two different curing conditions were compared.