Microstructure and interlaminar shear property of carbon fiber-SiC nanowire/pyrolytic carbon composites with SiC nanowires growing at different positions

In order to improve the interlaminar shearing strength of carbon fiber/pyrolytic carbon (Cf/PyC) composites, SiC nanowires (SiCNWs) growing at different positions were introduced into carbon fiber/pyrolytic carbon composites to generate carbon fiber-SiC nanowire/pyrolytic carbon (Cf-SiCNWs/PyC) composites. Cf-SiCNWs/PyC composites were prepared by sol-gel and isothermal chemical vapor infiltration (ICVI) method. The morphology, microstructure and compositions of composites were investigated by SEM, TEM, XRD and XPS. The interlaminar shearing strength was tested and the effect of SiCNWs growth positions on the interlaminar shearing strength was investigated. The results showed that SiCNWs were consisted of perfect single crystalline structure of β-SiC with diameter of 160–200 nm. The SiCNWs could grow at four kinds of positions to combine with carbon fibers to form multi-scaled reinforcements (micro-scaled carbon fibers and nanoscaled SiCNWs). The interlaminar shear strength of Cf-SiCNWs/PyC composites were increased by 78% compared with Cf/PyC composites without SiCNWs. The improvement of interlaminar shear strength was attributed to bridging and pull-out of multi-scaled reinforcements composed of carbon fibers and SiCNWs as well as the enhancement of fiber/matrix interface bonding generated by SiCNWs growing at different positions.     

Effect of Plasma Treatment of Polyethylene Fibers on Interface and ementitious Composite Properties

It is well known that interfaces in composites play an important role in determining composite properties. In this paper, preliminary results of the improvement in tensile properties of a fiber-reinforced cementitious composite due to plasma treatment of the discontinuous polyethylene fibers are reported. Specific focus is placed on the pseudo strain-hardening composite properties induced by fiber reinforcements and associated load transfer from crackbridging fibers to matrix. Single fiber pullout tests support that the composite property improvement is indeed derived from interfacial property enhancement of the plasma treatment process.     

Effect of the fabrication process on the microstructural evolution of carbon fibers and flexural property on C/SiC composites by the NITE method

Nano-infiltration and transient eutectic phase (NITE) SiC matrix composites are designed for application in aerospace propulsion systems, particularly in fasteners and thrusters. A variety of carbon fibers with different properties have been selected as reinforcements for SiC matrix composites. Carbon fibers are known to be stable at high temperatures; however, the effects of high applied pressure at high temperatures on the fiber microstructure evolution and mechanical properties are not well-known. As a scoping study for fabricating NITE C/SiC composites, the behaviors of various carbon fibers in SiC composites. Pitch-based fibers, namely, GRANOX XN-05 and YS-90A, and a polyacrylonitrile-based fiber, namely, TORAYCA T-300B, were selected for matrix reinforcement. The 3-point bending test results indicated pseudo-ductile behaviors in the cases of YS-90A and T-300B fiber reinforcements. Fracture resistance evaluation based on the single-notch bending test indicated that the YS-90A fiber reinforced composite afforded the highest fracture resistance among the three C/SiC composites. The microstructure evolution on YS-90A and T-300B fibers was limited to near the fiber surface. Therefore, YS-90A and T-300B carbon fibers are potential candidates for reinforcement in NITE C/SiC composites.     

Mechanical properties of glass fiber/organic fiber mixed–mat reinforced thermoplastic composites

The purpose of this study is to investigate the influence of different types of fibers on the mechanical properties of hybrid composite materials. Long and short glass fibers (GF) and different types of organic fibers, viz. aramid fiber, DuPont Kevlar‐49 (KF), liquid crystalline polymer (LCP), and vinylon (VF) in hybrid composites, were used to reinforced the high density polyethylene (HDPE) matrix. The long fiber hybrid composites were prepared in a “fiber separating and flying machine,” while the short fiber hybrid composites were prepared in an “elastic extruder.” The total amount of fibers used in both long and short fiber hybrid composites was fixed at 20 vol%. The influence of fiber content, length, and mixing ratio on mechanical properties, such as tensile, bending, Izod and high rate impact strength, as well as viscoelastic propertics in the solid state, was studied. Fracture surfaces of the materials were also examined using a scanning electron microscopy.     

Polymerization compounding of HDPE/Kevlar composites. I. Morphology and mechanical properties

The aim of this work is to perform the polymerization compounding to improve the properties of Kevlar/PE composites. The approach consists in involving the surface of a reinforcement in a polymerization process of a polymer to be used either as a matrix in the final composite or as a special surface treatment to enhance solid/polymer interface properties in the composite. The polymerization compounding process is illustrated here with the polyaramid fibers as reinforcements and polyethylene as a matrix. The number of active sites on the fiber surface, initially insufficient to anchor the catalyst, were increased by a hydrolysis reaction prior to the polymerization. The anchored catalyst was subsequently used to conduct the Ziegler–Natta polymerization reaction of ethylene. The modified fibers were incorporated into the polyethylene resin to produce composites at fiber concentrations as high as 15 wt%. The morphology of the fibers and the composites was tested using electron microscopy. Finally, the mechanical properties of the composites (in impact and tensile tests) were measured to characterize the properties of model composites. Polym. Compos. 27:129–137, 2006. © 2006 Society of Plastics Engineers.     

Comparative study of interphase evolution in polysiloxane resin-derived matrix containing carbon micro and nanofibers during thermal treatment

The work presents the results of research on composite materials made of silicon-containing polymer-derived ceramic matrix composites (PDC-Cs) and nanocomposites (PDC-NCs). Carbon micro and nanofibers (CFs and CNFs) were used as reinforcements. The interactions between carbon micro and nanofibers and polysiloxane matrix, as well as interphase evolution mechanism in composite samples during their heating to 1000 °C were studied. CF/resin and CNF/resin composites were prepared via liquid precursor infiltration process of unidirectionally aligned fibers. After heating to 700 °C–800 °C, decomposition of the resin in the presence of CNFs led to the formation of fiber/organic-inorganic composites with pseudo-plastic properties and improved oxidation resistance compared to as-prepared fiber/resin composites. The most favourable mechanical properties and oxidation resistance were obtained for composites and nanocomposites containing the maximum amount of carbon nanoparticles precipitated in the SiOC matrix during the heat treatment at 800 °C. The precipitated carbon phase improves fiber/matrix adhesion of composites.     

Influence of fiber wettability on the interfacial adhesion of continuous fiber‐reinforced PPESK composite

Interfacial adhesion between fiber and matrix has a strong influence on composite mechanical performance: better interfacial adhesion can enhance composite transverse properties, flexural properties, and interlaminar shear strength, and so on. To exploit the reinforcement potential of the fibers in advanced composite, it is necessary to reach a deeper understanding on the relation between fiber wettability and interfacial adhesion. In our experiment, we study the influence of fiber wettability on interfacial properties of fiber/PPESK composites by choosing three kinds of fibers with different wettabilities. The relation between fiber wettability and surface free energy was discussed, and the influence of fiber wettability on the interfacial property of fiber/PPESK composites was analyzed. Results indicate that higher surface free energy can enhance the wettability between fiber and matrix, and the humid resistance and interfacial adhesion can be improved at the same time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2544–2551, 2006     

Effects of fiber length on the tensile strength of epoxy/glass fiber and polyester/glass fiber composites

In discontinuous fiber-reinforced composites, the shear strength at the fiber–matrix interface plays an important role in determining the reinforcing effect. In this paper, a method was devised to accurately determine this shear strength, taking the strength distribution of glass fiber into consideration. Calculated strength values based on the shear strenght obtained by the method were in better agreement with the experimental observations than those calculated by employing the shear strength obtained on the assumption that the fiber strength was uniform. The tensile strength of composites increases with increasing aspect ratio of the reinforcing fibers. This trend is almost the same regardless of the kind of matrix, the nature of interfacial treatment, and the environmental temperature. When composites are reinforced with random-planar orientation of short glass fibers of 1.5 times the mean critical fiber length, the tensile strength of composite reaches about 90% of the theoretical strength of composites reinforced with continuous glass fiber. Reinforcing with glass fibers 5 times the critical length, the tensile strength reaches about 97% of theoretical. However, from a practical point of view, it is adequate to reinforce with short fibers of 1.5–2.0 times the mean critical fiber lenght.     

Effect of fiber treatment on the mechanical properties of LDPE-henequen cellulosic fiber composites

The degree of mechanical reinforcement that could be obtained by the introduction of henequen cellulosic fibers in a low-density polyethylene, LDPE, matrix was assessed experimentally. Composite materials of LDPE-henequen cellulosic fibers were prepared by mechanical mixing. The concentration of randomly oriented fibers in the composite ranged between 0 and 30% by volume. The tensile strength of these composite materials increased up to 50% compared to that of LDPE. There is also a noticeable increase in Young's modulus for the composite materials that compares favorably with that of LDPE. As expected, the addition of the fibers decreases the ultimate strain values for the composite materials. The thermal behavior of the LDPE-henequen cellulosic fibers materials, studied by differential scanning calorimetry, DSC, showed that the presence of the fibers does not affect the thermal behavior of the LDPE matrix; thus, the interaction between fiber and matrix is probably not very intimate. Preimpregnation of the cellulosic fibers in a LDPE-xylene solution and the use of a silane coupling agent results in a small increment in the mechanical properties of the composites, which is attributed to an improvement in the interface between the fibers and the matrix. The shear properties of the composites also increased with increasing fiber content and fiber surface treatment. It was also noted that the fiber surface treatment improves fiber dispersion in the matrix. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 197–207, 1997     

Nanoscale toughening of carbon fiber‐reinforced epoxy composites through different surface treatments

Interests in improving poor interfacial adhesion in carbon fiber‐reinforced polymer (CFRP) composites has always been a hotspot. In this work, four physicochemical surface treatments for enhancing fiber/matrix adhesion are conducted on carbon fibers (CFs) including acid oxidation, sizing coating, silane coupling, and graphene oxide (GO) deposition. The surface characteristics of CFs are investigated by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, interfacial shear strength, and interlaminar shear strength. The results showed that GO deposition can remarkably promote fiber/matrix bonding due to improved surface reactivity and irregularity. In comparison, epoxy sizing and acid oxidation afford enhancement of IFSS owing to effective molecular chemical contact and interlocking forces between the fiber and the matrix. Besides, limited covalent bonds between silane coupling and epoxy matrix cannot make up for the negative effects of excessive smoothness of modified CFs, endowing them inferior mechanical properties. Based on these results, three micro‐strengthening mechanisms are proposed to broadly categorize the interphase micro‐configuration of CFRP composite, namely, “Etching” “Coating”, and “Grafting” modifications, demonstrating that proper treatments should be chosen for combining optimum interfacial properties in CFRP composites. POLYM. ENG. SCI., 59:625–632, 2019. © 2018 Society of Plastics Engineers     

Tensile properties of short sisal fiber-reinforced polyethylene composites

Sisal fibers (Agave-Veracruz) have been used as reinforcements in low-density polyethylene (LDPE). The influence of the processing method and the effect of fiber content, fiber length, and orientation on tensile properties of the composites have been evaluated. The fiber damage that normally occurs during blending of fiber and polyethylene by the meltmixing method is avoided by adopting a solution-mixing procedure. The tensile properties of the composites thus prepared show a gradual increase with fiber content. The properties also increased with fiber length, to a maximum at a fiber length of about 6 mm. Unidirectional alignment of the short fibers achieved by an extrusion process enhanced the tensile strength and modulus of the composites along the axis of fiber alignment by more than twofold compared to randomly oriented fiber composites. © 1993 John Wiley & Sons, Inc.     

Toward forced assembly of in situ low‐density polyethylene composites reinforced with low‐Tg phosphate glass fibers: Effects of matrix crystallization and shear deformation

This study is aimed at investigating the feasibility of using facile forced assembly methods (temperature and shear strain‐induced orientation of the dispersed phase) to create novel “in situ” low‐density polyethylene (LDPE) composites containing fibrillar inorganic phosphate glass (P‐glass) reinforcing phase during the composite fabrication. Clearly, the experimental results show that unique thermo‐rheological conditions exist under which the “in situ” LDPE composites containing fibrillar P‐glass with potential enhanced benefits can be prepared. DSC results showed that the P‐glass has a moderate nucleating effect on the LDPE crystallization that restricts in situ deformation of the P‐glass during the composite fabrication. Rheo‐optical data showed that a 5% P‐glass/95% LDPE hybrid composition, subjected to a shear rate of 20 s^?1 in the parallel plate configuration and 130°C gave “in situ” LDPE composite samples with the largest amount of P‐glass fibers in the limited range of experimental conditions used. This study may spur interests in a better understanding of the potential for the “in situ” reinforcement of engineering plastics with inorganic P‐glasses, at the molecular level, to produce novel “in situ” polymer composites with very high aspect ratios of the reinforcing inorganic phase. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Adhesive joints between carbon fiber and aluminum foam reinforced by surface‐treated aramid fibers

Short aramid fibers have been successfully used to reinforce the interface adhesive property between carbon fiber/epoxy composites and aluminum foam, and to form aramid‐fiber “composite adhesive joints.” In this study, to further improve the reinforcing effect of the aramid‐fiber‐reinforced adhesive joints, aramid fibers were ultrasonic treated to conduct different surface conditions. Critical energy release rate of the carbon fiber/aluminum foam sandwich beams with as‐received and treated interfacial aramid fibers were measured to study the influence of the surface treatment on aramid fibers. It was found that reinforcements in critical energy release rate were achieved for all samples with treated aramid fiber as measured under double cantilever beam condition. The interfacial characteristics of the short aramid fibers with different surface condition were investigated and discussed based on scanning electron microscopy observations. It is suggested that advanced bonding between aramid fibers and epoxy resin was conducted after surface treatment, and more energy was therefore absorbed through fiber bridging during crack opening and extension process. POLYM. COMPOS., 36:192–197, 2015. © 2014 Society of Plastics Engineers     

Comparison of mechanical performance and fracture behavior of gelatin composites reinforced with carbon fibers of different fiber architectures

Gelatin‐based composites reinforced, respectively, with continuous carbon fibers, short carbon fibers, plain woven carbon fibers, and carbon fiber felt were investigated. Tensile and shear strengths, and their changes with fiber volume fraction (V_f) of these four composites were compared. It was demonstrated that at all fiber levels, the composite containing continuous carbon fibers showed the largest strength, while the composite reinforced with carbon fiber felt exhibited the lowest strength of the four composites. The above results were analyzed by comparing the fracture surfaces of the four composites. SEM confirmed the great differences in fracture surfaces for composites of different fiber architectures. The presence of a large number of pores in the C_F/Gel composite was responsible for its lowest strength, and cracks within fiber tows caused the lower strength of the C_W/Gel composite when compared to its C_L/Gel counterpart. It was suggested that fiber architecture exerted a great effect on composite performance and the effect was dependent on the nature of the matrix material.     

The properties of dry-spun carbon nanotube fibers and their interfacial shear strength in an epoxy composite

Continuous fibers composed of carbon nanotubes have been adopted as reinforcements for polymeric composites. This paper presents several fundamental studies relevant to the mechanical behavior of CNT fibers, including fiber tensile behavior; in situ SEM observation of fiber deformation mechanisms; and fiber modulus, ultimate strength and fracture strain measurements. A modified Weibull strength distribution model that takes into account the flaw density variation with fiber diameter has been adopted for the statistical strength analysis. The interfacial shear strength between the carbon nanotube fiber and the epoxy matrix has been measured using fragmentation tests of single-fiber composites.     

Piezoresistive behavior of epoxy matrix‐carbon fiber composites with different reinforcement arrangements

In this work, the self‐monitoring capability of epoxy matrix‐carbon fiber composites has been studied. Different concentrations and arrangements of reinforcements were used, including random chopped, unidirectional and bi‐directional continuous carbon fibers, weaved and nonweaved. Mechanical properties were determined by uniaxial tensile tests. The composite electric to mechanical behavior was established by determining its electrical resistivity variation as a function of the stress‐strain curve. It was observed that the composites electrical resistance increased during tensile tests, a trend that indicates piezoresistive behavior. The increase was linear for the chopped reinforced composites, while it exhibits different slopes in the continuous reinforced composites. The initial smaller slope corresponds mainly to separation of the 90° oriented fibers and/or transversal cracking of the matrix, whereas the latter higher slope is caused by fiber fracture. The results demonstrated how each reinforcement configuration exhibited a unique and typical electrical response depending on the specific reinforcement, which might be appropriate either for strain‐monitoring or damage‐monitoring. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Graphite-Epoxy Composites: Effects of An Applied Interphase

An applied interphase, between matrix resin and fibers in continuous fiber composites, resulted in a significant improvement in composite impact strength and fracture toughness concurrently with a moderate improvement or unchanged interlaminar shear strength. The temperature resistance of tailored interphases and composites was high. An optimum thickness was observed. The merits of such interphases and a novel means of application are discussed.     

The effect of the interface/interphase on fiber composite properties

The interfacial region between fibers and matrix in fiber composites governs the transfer of forces between the relatively weak and compliant matrix and the reinforcing fibers. An effective interphase can ensure that the mechanical properties of the composite reflect the high strength and modulus of the fibers. Although composites can be made with the expected strengths and moduli, it is not entirely clear why this is achieved: Tests with critical composites, i.e., those containing very short aligned fibers, do not show the expected stress-strain behavior. This paper examines the effect of an interphase having a shear modulus that is less than that of the matrix. It is found that to explain the Young's moduli of the short fiber composites, the interphase must have a very low modulus indeed; i.e., a few kPa at most. In addition, the strength results can be accounted for only if we assume that the short lengths of fiber used in the experiments had higher strengths than anticipated. Although agreement between experiments and theory is thus not very good, the small amount of experimental evidence available indicates a need for further systematic experiments on critical (i.e. short aligned fiber) composites before firm conclusions are drawn.     

Melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites. I. Untreated fibers

The melt rheological behavior of intimately mixed short sisal–glass hybrid fiber‐reinforced low‐density polyethylene composites was studied with an Instron capillary rheometer. The variation of melt viscosity with shear rate and shear stress at different temperatures was studied. The effect of relative composition of component fibers on the overall rheological behavior also was examined. A temperature range of 130 to 150°C and shear rate of 16.4 to 5470 s^?1 were chosen for the analysis. The melt viscosity of the hybrid composite increased with increase in the volume fraction of glass fibers and reached a maximum for the composite containing glass fiber alone. Also, experimental viscosity values of hybrid composites were in good agreement with the theoretical values calculated using the additive rule of hybrid mixtures, except at low volume fractions of glass fibers. Master curves were plotted by superpositioning shear stress and temperature results. The breakage of fibers during the extrusion process, estimated by optical microscopy, was higher for glass fiber than sisal fiber. The surface morphology of the extrudates was analyzed by optical and scanning electron microscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 432–442, 2003     

Evaluation of fiber surfaces treatment and sizing on the shear and transverse tensile strengths of carbon fiber-reinforced thermoset and thermoplastic matrix composites

The mechanical performance of advanced composite materials depends to a large extent on the adhesion between the fiber and matrix. This is especially true for maximizing the strength of unidirectional composites in off-axis directions. The materials of interest in this study were PAN-based carbon fibers (XA and A4) used in combination with a thermoset (EPON 828 epoxy) and a thermoplastic (liquid crystal poymer) matrix. The effect of surface treatment and sizing were evaluated by measuring the short-beam shear (SBS) and transverse flexural (TF) tensile strengths of unidirectional composites. Results indicated that fiber surface treatment improves the shear and trasverse tensile strengths for both thermosetting and thermoplastic matrix/carbon fiber-reinforced unidirectional composites. A small additional improvement in strengths was observed as the result of sizing treated fibers for the epoxy composites. Scanning electron microscope photomicrographs were used to determine the location of composite failure, relative to the fiber-matrix interface. Finally, the epoxy composites SBS and TF strengths appear to be limited to the maximum transeverse tensile strength of the epoxy matrix, while the thermoplastic composite SBS and TF strengths are limited by the LCP matrix shear and transverse tensile strengths, respectively.