Showing papers in "Advanced Composite Materials in 2007"
TL;DR: The tensile strength of unidirectional carbon fiber reinforced plastics under a high strain rate was experimentally investigated in this article, where the tensile modulus and strength in the longitudinal direction are independent of the strain rate.
Abstract: The tensile strength of unidirectional carbon fiber reinforced plastics under a high strain rate was experimentally investigated. A high-strain-rate test was performed using the tension-type split Hopkinson bar technique. In order to obtain the tensile stress–strain relations, a special fixture was used for the impact tensile specimen. The experimental results demonstrated that the tensile modulus and strength in the longitudinal direction are independent of the strain rate. In contrast, the tensile properties in the transverse direction and the shear properties increase with the strain rate. Moreover, it was observed that the strain-rate dependence of the shear strength is much stronger than that of the transverse strength. The tensile strength of off-axis specimens was measured using an oblique tab, and the experimental results were compared with the tensile strength predicted based on the Tsai–Hill failure criterion. It was concluded that the tensile strength can be characterized quite well using the a...
109 citations
TL;DR: In this article, the thermal conductivity of PLA-bamboo fiber 'green' composites was evaluated by determination of thermal conductivities, which was measured using a hot-wire method.
Abstract: 'Green' composites were fabricated from poly lactic acid (PLA) and bamboo fibers by using a conventional hot pressing method. The insulating properties of the PLA-bamboo fiber 'green' composites were evaluated by determination of the thermal conductivity, which was measured using a hot-wire method. The thermal conductivity values were compared with theoretical estimations. It was demonstrated that thermal conductivity of PLA-bamboo fiber 'green' composites is smaller than that of conventional composites, such as glass fiber reinforced plastics (GFRPs) and carbon fiber reinforced plastics (CFRPs). The thermal conductivity of PLA-bamboo fiber 'green' composites was significantly influenced by their density, and was in fair agreement with theoretical predictions based on Russell's model. The PLA-bamboo fiber composites have low thermal conductivity comparable with that of woods.
101 citations
TL;DR: In this article, an IPN-like soy protein-based resin was further reinforced using nano-clay and micro-fibrillated cellulose fibers and the results suggest that these green composites have excellent mechanical properties and can be considered for use.
Abstract: Fully biodegradable high strength composites or 'advanced green composites' were fabricated using yearly renewable soy protein based resins and high strength liquid crystalline cellulose fibers. For comparison, E-glass and aramid (Kevlar®) fiber reinforced composites were also prepared using the same modified soy protein resins. The modification of soy protein included forming an interpenetrating network-like (IPN-like) resin with mechanical properties comparable to commonly used epoxy resins. The IPN-like soy protein based resin was further reinforced using nano-clay and microfibrillated cellulose. Fiber/resin interfacial shear strength was characterized using microbond method. Tensile and flexural properties of the composites were characterized as per ASTM standards. A comparison of the tensile and flexural properties of the high strength composites made using the three fibers is presented. The results suggest that these green composites have excellent mechanical properties and can be considered for use...
95 citations
TL;DR: In this paper, a damage accumulation mechanism in cross-ply CFRP laminates was described for out-of-plane loading drop-weight impact and static indentation tests.
Abstract: This paper describes a damage accumulation mechanism in cross-ply CFRP laminates [02/902]2S subjected to out-of-plane loading Drop-weight impact and static indentation tests were carried out, and
93 citations
TL;DR: In this article, the tensile and flexural properties of a composite consisting of acrylonitrile-butadiene-styrene (ABS) resin mixed with carbon fiber reinforced plastics (CFRP/ABS).
Abstract: This paper presents the mechanical properties of a composite consisting of acrylonitrile-butadiene-styrene (ABS) resin mixed with carbon fiber reinforced plastics (CFRP) pieces (CFRP/ABS). CFRP pieces made by crushing CFRP wastes were utilized in this material. Nine kinds of CFRP/ABS compounds with different weight fraction and size of CFRP pieces were prepared. Firstly, tensile and flexural tests were performed for the specimens with various CFRP content. Next, fracture surfaces of the specimens were microscopically observed to investigate fracture behavior and fiber/resin interface. Finally, the tensile modulus and strength were discussed based on the macromechanical model. It is found that the elastic modulus increases linearly with increasing CFRP content while the strength changes nonlinearly. Microscopic observation revealed that most carbon fibers are separated individually and dispersed homogeneously in ABS resin. Epoxy resin particles originally from CFRP are dispersed in ABS resin and seem to be...
72 citations
TL;DR: In this paper, the electrical resistance change under strain of CNF/flexible-epoxy composites was investigated experimentally and analytically, and it was shown that the sensitivity of electrical resistance to strain decreases as the weight fraction of carbon nanofibers increases.
Abstract: Carbon nanofibers (CNFs) have good electrical conductivity. Addition of a few percent of carbon nanofibers to polymers yields electrical conductivity but hardly affects the mechanical properties of the polymers. These conductive polymers may be useful for sensing applications, such as strain sensors and chem-resist sensors. Many researchers have reported on the electrical conductivity, but the electrical resistance change under strain, i.e. piezoresistivity, of the carbon nanofiber filled resin has not been fully investigated. In this study, the electrical resistance change under strain of CNF/flexible-epoxy composites was investigated experimentally and analytically. Experimental results show that the electrical resistance change under strain is non-linear and much larger than that in metal, and the sensitivity of the electrical resistance change to strain decreases as the weight fraction of CNF increases. The mechanism of the electrical resistance change under strain of CNF/polymer composites was discus...
57 citations
TL;DR: In this article, natural fibers (jute, kenaf and henequen) reinforced thermoplastic (poly(lactic acid) and polypropylene) and thermosetting (unsaturated polyester) matrix composites were well fabricated by a compression molding technique using all chopped natural fibers of about 10 mm long, respectively.
Abstract: In the present study, natural fibers (jute, kenaf and henequen) reinforced thermoplastic (poly(lactic acid) and polypropylene) and thermosetting (unsaturated polyester) matrix composites were well fabricated by a compression molding technique using all chopped natural fibers of about 10 mm long, respectively. Prior to green composite fabrication, natural fiber bundles were surface-treated with tap water by static soaking and dynamic ultrasonication methods, respectively. The interfacial shear strength, flexural properties, and dynamic mechanical properties of each green composite system were investigated by means of single fiber microbonding test, 3-point flexural test, and dynamic mechanical analysis, respectively. The result indicated that the properties of the polymeric resins were significantly improved by incorporating the natural fibers into the resin matrix and also the properties of untreated green composites were further improved by the water treatment done to the natural fibers used. Also, the p...
56 citations
TL;DR: In this paper, the tensile strength of unidirectional carbon fiber-reinforced plastic (CFRP) composites was predicted by numerical simulation plus size scaling.
Abstract: The tensile strength of unidirectional carbon fiber-reinforced plastic (CFRP) composites was predicted by numerical simulation plus size scaling. The fiber strength distribution used in the numerical simulation was determined from the fragmentation process in a single fiber composite. Since the experimental data obviously did not fit the normal Weibull distribution, we fitted them with the Weibull of Weibull model, considering the statistical distribution of scale parameters of fiber strength in the normal Weibull model. Moreover, the constitutive law of the matrix was derived from the stress–strain curves of the angle ply laminates, utilizing the micromechanics approach proposed by Tohgo et al. [9]. Based on these parameters, we simulated the tensile fracture of unidirectional CFRP composites with the spring element model (SEM). The predicted tensile strength by numerical simulation plus size scaling agreed well with the experimental data. The results also confirmed that the Weibull of Weibull model is i...
45 citations
TL;DR: In this paper, the authors investigated high-cycle fatigue characteristics of quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates [−45/0/45/90]s up to 108 cycles.
Abstract: High-cycle fatigue characteristics of quasi-isotropic carbon fiber reinforced plastic (CFRP) laminates [−45/0/45/90]s up to 108 cycles were investigated To assess the fatigue behavior in the high-cycle region, fatigue tests were conducted at a frequency of 100 Hz, since it is difficult to investigate the fatigue characteristics in high-cycle at 5 Hz Then, the damage behavior of the specimen was observed with a microscope, soft X-ray photography and a 3D ultrasonic inspection system In this study, to evaluate quantitative characteristics of both transverse crack propagation and delamination growth in the high-cycle region, the energy release rate associated with damage growth in the width direction was calculated Transverse crack propagation and delamination growth in the width direction were evaluated based on a modified Paris law approach The results revealed that transverse crack propagation delayed under the test conditions of less than σ max/σ b = 03 of the applied stress level
43 citations
TL;DR: In this paper, green composites using kenaf fiber yarn bundles and PLA (poly(lactic acid)) are fabricated and their tensile properties are evaluated in the experiment.
Abstract: Disposing of conventional fiber-reinforced polymers (FRPs) poses an environmentally challenging problem. Disposal of FRPs by combustion discharges carbon dioxide in the air because the resin of FRPs is made of fossil fuel. When they are disposed of in the ground, FRPs remain semi-permanently without decomposing. In response to these problems, green composites are now being developed and are extensively studied as a material that produces a lower environmental burden. In this paper, green composites using kenaf fiber yarn bundles and PLA (poly(lactic acid)) are fabricated and their tensile properties are evaluated in the experiment. The tensile Young's modulus of all of the laminations is larger than that of PLA alone and the tensile strength of some laminations is larger than that of PLA alone. In particular, the value of UD composite of 0° shows double the tensile strength of PLA alone. Furthermore, the molding conditions for fabricating with a hot press are investigated and the heat resistant tensile pr...
41 citations
TL;DR: In this paper, a quadric electric field is induced inside a piezoelectric lamina under a given applied voltage and mechanical bending, and the governing equations for the PZT plate derived from the principle of virtual work in terms of the electric enthalpy have the same forms as those for a conventional composite laminated plate.
Abstract: Based on the Kirchhoff hypothesis of normal-remain-normal, the present work analyses piezoelectric laminated plates, wherein poled piezoelectric laminae are transversely isotropic and function as actuators. A quadric electric field is induced inside a piezoelectric lamina under a given applied voltage and mechanical bending. The governing equations for the piezoelectric laminated plate derived from the principle of virtual work in terms of the electric enthalpy have the same forms as those for a conventional composite laminated plate. We use rectangular sandwich plates of Al/PZT/Al and PZT/Al/PZT with four simply supported edges to demonstrate the prediction of the maximum bending stress in the PZT layer. The analytic solutions are verified by three-dimensional finite element analysis.
TL;DR: In this paper, an environment-friendly composites reinforced with bagasse fiber (BF), a kind of natural fiber as the remains from squeezed sugarcane, were fabricated by injection molding and press molding.
Abstract: Environment-friendly composites reinforced with bagasse fiber (BF), a kind of natural fiber as the remains from squeezed sugarcane, were fabricated by injection molding and press molding. As appropriate matrices for injection molding and press molding, polypropylene (PP) and polycaprolactone-cornstarch (PCL-C) were selected, as a typical recyclable resin and biodegradable resin, respectively. The mechanical properties of BF/PP composites were investigated in view of fiber mass fraction and injection molding conditions. And the mechanical properties and the biodegradation of BF/PCL composites were also evaluated. In the case of injection molding, the flexural modulus increased with an increase in fiber mass fraction, and the mechanical properties decreased with an increase in cylinder temperature due to the thermal degradation of BF. The optimum conditions increasing the flexural properties and the impact strength were 90°C mold temperature, 30 s injection interval, and in the range of 165 to 185°C cylinde...
TL;DR: In this article, a crack arrester is proposed for the suppression of the delamination at the interfacial layer between a surface skin and a foam core, which has a semi-cylindrical shape and is arranged in the foam core and attached to the surface skin.
Abstract: Since delamination often propagates at the interfacial layer between a surface skin and a foam core, a crack arrester is proposed for the suppression of the delamination. The arrester has a semi-cylindrical shape and is arranged in the foam core and is attached to the surface skin. Here, energy release rates and complex stress intensity factors are calculated using finite element analysis. Effects of the arrester size and its elastic moduli on the crack suppressing capability are investigated. Considerable reductions of the energy release rates at the crack tip are achieved as the crack tip approached the leading edge of the crack arrester. Thus, this new concept of a crack arrester may become a promising device to suppress crack initiation and propagation of the foam core sandwich panels.
TL;DR: In this article, the effect of E-beam intensity on the interfacial, mechanical and thermal properties of randomly oriented henequen/polypropylene composites with the fiber contents of 40 vol% was investigated focusing on interfacial shear strength, flexural and tensile properties, dynamic mechanical properties, thermal stability, and fracture behavior.
Abstract: In the present study, chopped henequen natural fibers without and with surface modification by electron beam (E-beam) treatment were incorporated into a polypropylene matrix. Prior to composite fabrication, a bundle of raw henequen fibers were treated at various E-beam intensities from 10 kGy to 500 kGy. The effect of E-beam intensity on the interfacial, mechanical and thermal properties of randomly oriented henequen/polypropylene composites with the fiber contents of 40 vol% was investigated focusing on the interfacial shear strength, flexural and tensile properties, dynamic mechanical properties, thermal stability, and fracture behavior. Each characteristic of the material strongly depended on the E-beam intensity irradiated, showing an increasing or decreasing effect. The present study demonstrates that henequen fiber surfaces can be modified successfully with an appropriate dosage of electron beam and use of a low E-beam intensity of 10 kGy results in the improvement of the interfacial properties, fle...
TL;DR: In this article, the effect of molding condition on the tensile properties of plain woven hemp fiber reinforced green composite was examined and compared with those of the plain woven jute fiber composite fabricated by the same process.
Abstract: In this study, the effect of molding condition on the tensile properties for plain woven hemp fiber reinforced green composite was examined The tensile properties of the composite were compared with those of the plain woven jute fiber composite fabricated by the same process Emulsion type biodegradable resin or polypropylene sheet was used as matrix The composites were processed by the compression molding where the molding temperature and its heating time were changed from 160 to 190°C and from 15 to 25 min, respectively The following results were obtained from the experiment The tensile property of hemp fiber reinforced polypropylene is improved in comparison with polypropylene bulk The strength of composite is about 26 times that of the resin bulk specimen Hemp fiber is more effective than jute fiber as reinforcement for green composite from the viewpoint of strength The molding temperature and time are suitable below 180°C and 20 min for hemp fiber reinforced green composite Hemp fiber green
TL;DR: In this article, a variety of processing parameters such as fiber area fraction, molding temperature and forming pressure were systematically controlled and their influence on the tensile properties was investigated, and it was revealed that both tensile strength and elastic modulus of the composites increase steadily depending on the increase in fiber area fractions, suggesting a general conformity to the rule of mixtures (ROM), particularly up to 55% fiber areas fraction.
Abstract: Green composites composed of long maize fibers and poly e-caprolactone (PCL) biodegradable polyester matrix were manufactured by the thermo-mechanical processing termed as 'Sequential Molding and Forming Process' that was developed previously by the authors' research group. A variety of processing parameters such as fiber area fraction, molding temperature and forming pressure were systematically controlled and their influence on the tensile properties was investigated. It was revealed that both tensile strength and elastic modulus of the composites increase steadily depending on the increase in fiber area fraction, suggesting a general conformity to the rule of mixtures (ROM), particularly up to 55% fiber area fraction. The improvement in tensile properties was found to be closely related to the good interfacial adhesion between the fiber and polymer matrix, and was observed to be more pronounced under the optimum processing condition of 130°C molding temperature and 10 MPa forming pressure. However, pro...
TL;DR: In this article, carbon nanofiber (CNF)/unsaturated polyester resin (UPR) was prepared by a solvent evaporation method, and the temperature dependency of electrical conductivity was investigated.
Abstract: Carbon nanofiber (CNF)/unsaturated polyester resin (UPR) was prepared by a solvent evaporation method, and the temperature dependency of electrical conductivity was investigated. The CNF/UPR composites had quite a low percolation threshold due to CNF having a larger aspect ratio and being well dispersed in the UPR matrix. The positive temperature coefficient (PTC) was found in the CNF/UPR composites and it showed stronger effect around the percolation threshold. The electrical resistance of the CNF/UPR composites decreased and had lower temperature dependency with increasing numbers of thermal cycles.
TL;DR: In this article, the interlaminar tension tests were carried out under an out-of-plane directional loading using a single carbon fiber stitch thread in the CFRP laminates and the results indicated that the relationship between the volume fractions of the CF stitch thread (V ft) and mode I critical energy release rate (G Ic) showed a mostly linear function with a higher gradient than that of the Kevlar® stitched CFRP Laminates.
Abstract: Experimental investigations of interlaminar mechanical properties for carbon fiber rein-forced plastic (CFRP) laminates were carried out using aramid fiber (Kevlar®-29 1000d) and carbon fiber (TR40-1K 612d, Mitsubishi Rayon) stitching. Various carbon fiber (CF) stitch densities were used to prepare a number of CF stitched CFRP laminates for double cantilever beam (DCB) tests. An insert tongue-type loading fixture, developed by the Japan Aerospace Exploration Agency (formerly the National Aerospace Laboratory of Japan), was also employed in the DCB test. Interlaminar tension tests were carried out under an out-of-plane directional loading using a single CF stitch thread in the CFRP laminates. The DCB test results clarified that the relationship between the volume fractions of the CF stitch thread (V ft) and mode I critical energy release rate (G Ic) showed a mostly linear function with a higher gradient than that of the Kevlar® stitched CFRP laminates. The CF stitched CFRP tension test results indicated th...
TL;DR: Wang et al. as mentioned in this paper proposed a method of producing artistic composite from artistic fabric by using silk fiber reinforced biodegradable plastic, which is designated as "silk composite", for reinforcement.
Abstract: Recently, natural fiber reinforced composite is attracting attention and considered as an environmentally friendly material. Usually cellulosic fibers are used to reinforce the composites, but some protein fibers such as silk and wool serve the same purpose. In this paper, we proposed a method of producing artistic composite from artistic fabric by using silk fiber reinforced biodegradable plastic, which is designated as 'silk composite', for reinforcement. In order to expand applications of the silk composite, we performed the compression molding of decorative laminates with woody material, which was selected as a core material, and examined the properties of molded decorative laminates with various content of the silk composite. Since plywood and medium-density fiberboard (MDF) are widely used for decorative laminates, we selected them as core materials. As a result, flexible decorative laminates with high flexural strength were obtained by compounding the silk composite with wood materials.
TL;DR: In this article, an all-sustainable composite, composed of papyrus stem-milled particles as reinforcement and poly-L-lactic acid (PLLA) resin as matrix, was investigated.
Abstract: Mechanical reinforcement of an all-sustainable composite, composed of papyrus stem-milled particles as reinforcement and poly-L-lactic acid (PLLA) resin as matrix, was investigated. The papyrus particles (average diameter of 70 μm) could be well dispersed in PLLA resin up to 50 wt% without any surface modification. Young's modulus of the composite was 4.2 GPa at 50 wt% of the papyrus content. This is a two-fold increment in modulus as compared to that of the PLLA matrix. The tensile strength of the composite was almost constant around 48 MPa irrespective of the papyrus content. Temperature dependence of the storage modulus demonstrated that the incorporation of papyrus restricts the large drop in the modulus above the glass transition of PLLA.
TL;DR: In this paper, the Stokes approximation was used to calculate the flow field in the fiber mat and most of the injected resins entered into the gap during the injection phase, which results in preferential flow path.
Abstract: The filling process of resin injection/compression molding (I/CM) can be divided into injection and compression phases. During the resin injection the mold is kept only partially closed and thus a gap is present between the reinforcements and the upper mold. The gap results in preferential flow path. After the gap is filled with the resin, the compression action initiates and forces the resin to penetrate into the fiber preform. In the present study, the resin flow in the gap is simplified by using the Stokes approximation, while Darcy's law is used to calculate the flow field in the fiber mats. Results show that most of the injected resins enter into the gap during the injection phase. The resin injection time is extremely short so the duration of the filling process is determined by the final closing action of the mold cavity. Compared with resin transfer molding (RTM), I/CM process can reduce the mold filling time or injection pressure significantly.
TL;DR: In this article, a carbon fiber sewing thread has been used as a low cost laminate failure sensing element to monitor the delamination of metallic inserts from the basic composite laminate structure.
Abstract: In the automobile industry, structural health monitoring of fiber reinforced polymer composite parts is a widespread need for maintenance before breakdown of the functional elements or a complete vehicle. High performance sensors are generally used in many of the structural health monitoring operations. Within this study, a carbon fiber sewing thread has been used as a low cost laminate failure sensing element. The experimentation plan was set up according to the electrical conductance and flexibility of carbon fiber threads, advantages of preforming operations, and sewing mechanisms. The influence of the single thread damages by changing the electrical resistance and monitoring the impact location by using carbon thread sensors has been performed. Innovative utilization of relatively cost-effective carbon threads for monitoring the delamination of metallic inserts from the basic composite laminate structure is a highlighting feature of this study.
TL;DR: In this article, the authors evaluated fracture toughness, tensile and three-point bending properties of woven sisal textile fiber reinforced composites, and found that water uptake of the epoxy composites was found to increase with cycle times.
Abstract: Woven sisal textile fiber reinforced composites were used to evaluate fracture toughness, tensile and three-point bending. The water absorption testing of all specimens was repeated five times in this study. All specimens were immersed in pure water during 9 days at room temperature, and dried in 1 day at 50°C. Two kinds of polymer matrices such as epoxy and vinyl-ester were used. Fractured surfaces were taken to study the failure mechanism and fiber/matrix interfacial adhesion. It is shown that it can be enhanced to improve their mechanical performance to reveal the relationship between fracture toughness and water absorption fatigue according to different polymer matrices. Water uptake of the epoxy composites was found to increase with cycle times. Mechanical properties are dramatically affected by the water absorption cycles. Water-absorbed samples showed poor mechanical properties, such as lower values of maximum strength and extreme elongation. The K IC values demonstrated a decrease in inclination w...
TL;DR: In this paper, the energy release rate associated with crack growth in adhesive double cantilever beam (DCB) specimens, including the effect of residual stresses, was formulated using beam theory.
Abstract: The energy release rate associated with crack growth in adhesive double cantilever beam (DCB) specimens, including the effect of residual stresses, was formulated using beam theory. Because of the rotation of the asymmetric arms in the adhesive DCB specimens due to temperature change, it is necessary to correct the evaluated fracture toughness of the DCB specimens, specifically in the case of a large temperature change. This study shows that the difference between the true toughness and an apparent toughness due to the consequence of ignoring residual stresses can be calculated for a given specimen geometry and thermo-mechanical properties (e.g. coefficient of thermal expansion). The calculated difference in the energy release rates based on the present correction method is compared with that from FEM in order to verify the present correction method. The residual stress effects on the evaluation of the adhesive fracture toughness are discussed.