Chopped Carbon Fiber Research Articles

Effects of heat treatment temperatures on microstructures and mechanical properties of the chopped carbon fibres SiC composites

ABSTRACTA simple wet papermaking technique was used to fabricate chopped carbon fibre paper (Csf-paper) with random fibre orientation and self-supporting network structures in this work. The Csf-papers were laminated layer by layer and further infiltrated with PyC interface and SiC matrix via chemical vapour infiltration (CVI) to obtain Csf/SiC composites. The effects of heat treatment temperatures on microstructures, phase composition, and mechanical properties were investigated. Results showed that the Csf-paper has played a good self-supporting role and its fibres form a completely random fibre orientation in 2D plane. The fibres almost remained undamaged and unbroken during the CVI. Proper heat treatment could improve the mechanical properties. At 1200°C, the maximum values of flexural strength and Young's modulus reached about 306 MPa and 196.5 GPa, respectively. Meanwhile, compared with tape casting, reaction sintering and spark plasma sintering, composites fabricated by wet papermaking and CVI can improve the mechanical properties.

Prediction of the Fiber Orientation State and the Resulting Structural and Thermal Properties of Fiber Reinforced Additive Manufactured Composites Fabricated Using the Big Area Additive Manufacturing Process

Recent advances in Fused Filament Fabrication (FFF) include large material deposition rates and the addition of chopped carbon fibers to the filament feedstock. During processing, the flow field within the polymer melt orients the fiber suspension, which is important to quantify as the underlying fiber orientation influences the mechanical and thermal properties. This paper investigates the correlation between processing conditions and the resulting locally varying thermal-structural properties that dictate both the final part performance and part dimensionality. The flow domain includes both the confined and unconfined flow indicative of the extruder nozzle within the FFF deposition process. The resulting orientation is obtained through two different isotropic rotary diffusion models, the model by Folgar and Tucker and that of Wang et al., and a comparison is made to demonstrate the sensitivity of the deposited bead’s spatially varying orientation as well as the final processed part’s thermal-structural performance. The results indicate the sensitivity of the final part behavior is quite sensitive to the choice of the slowness parameter in the Wang et al. model. Results also show the need, albeit less than that of the choice of fiber interaction model, to include the extrudate swell and deposition within the flow domain.

A Comparative Study of Two ASTM Shear Test Standards for Chopped Carbon Fiber SMC

A Comparative Study of Two ASTM Shear Test Standards for Chopped Carbon Fiber SMC

Optimization and Characterization of Preceramic Inks for Direct Ink Writing of Ceramic Matrix Composite Structures.

In a previous work, an ink based on a preceramic polymer, SiC fillers, and chopped carbon fibers was proposed for the production of Ceramic Matrix Composite (CMC) structures by Direct Ink Writing (DIW) and subsequent pyrolysis. Thanks to the shear stresses generated at the nozzle tip during extrusion, carbon fibers can be aligned along the printing direction. Fumed silica was added to the ink in order to enhance its rheological properties; however, the printed structures still showed some deformation in the Z direction. In this work, a second ink was successfully developed to limit deformation and at the same time avoid the addition of fumed silica, which limited the potential temperature of application of the composites. Instead, the positive role of the preceramic polymer on the ink rheology was exploited by increasing its concentration in the ink. Rheological characterization carried out on both inks confirmed that they possessed Bingham shear thinning behavior and fast viscosity recovery. Single filaments with different diameters (~310 µm and ~460 µm) were produced with the latter ink by DIW and subsequent pyrolysis. Tested under a four-point flexural test, the filaments showed a mean flexural strength above 30 MPa, graceful failure, and fiber pull-out. The results of this work suggest that CMC components can effectively be fabricated via DIW of a preceramic ink with embedded short fibers; the preceramic polymer is able to provide the desired rheology for the process and to develop a dense matrix capable of incorporating both fibers and ceramic particles, whereas the fibers addition contributes to an increase of the fracture toughness of the material and to the development of a graceful failure mode.

Piezoresistive behavior of CF- and CNT-based reinforced concrete beams subjected to static flexural loading: Shear failure investigation

Self-sensing property of concrete is mostly assessed using small specimens without reinforcement, which may be misleading for real-time structures. To better simulate the actual field conditions, this study examined self-sensing of damage in large-scale reinforced concrete beams tested under four-point bending. During flexural testing, special attention was paid to the self-sensing capability of shear failure, since this type of failure occurs suddenly and catastrophically. Inadequate shear reinforcements were used to increase shear failure possibility of 100 × 150 × 1000 mm3 (width × height × length) reinforced large-scale beams and beams were produced with a high shear span (a = 350 mm) to effective depth (d = 125 mm) ratio of 2.8. To increase the electrical conductivity of large-scale beams, chopped carbon fibers (CF) and multi-walled carbon nano tubes (CNT) were used. Instantaneous self-sensing recordings were made using brass electrodes embedded in different shear spans of beams. In addition to conducting self-sensing evaluations, researchers also investigated the effects of CF and CNT particles on the mechanical properties/structural behavior of large-scale beam specimens with the proposed reinforcement configuration. Results showed that compared to CNT, CF usage significantly improved the load carrying capacity and ductility, resulting in bending mode of failure even with indaquate shear reinforcement. Shear damage was successfully self-sensed in all tested beams, although all CF-based specimens started self-sensing from the beginning of loading with significantly higher changes in electrical resistivity results, unlike CNT-based specimens. Conductive network of CF-based specimens seemed to be disturbed more easily at high load levels. CF usage seems like a better option compared to CNT given its lower cost and easier mixability.

Correlation between failure and local material property in chopped carbon fiber chip‐reinforced sheet molding compound composites under tensile load

To develop further understanding towards the role of a heterogeneous microstructure on tensile crack initiation and failure behavior in chopped carbon fiber chip‐reinforced composites, uni‐axial tensile tests are performed on coupons cut from compression molded plaque with varying directions. Experimental results indicate that failure initiation is relevant to the strain localization, and a new criterion with the nominal modulus to predict the failure location is proposed based on the strain analysis. Furthermore, optical microscopic images show that the nominal modulus is determined by the chip orientation distribution. At the area with low nominal modulus, it is found that chips are mostly aligning along directions transverse to loading direction and/or less concentrated, while at the area with high nominal modulus, more chips are aligning to tensile direction. On the basis of failure mechanism analysis, it is concluded that transversely oriented chips or resin‐rich regions are easier for damage initiation, while longitudinally oriented chips postpone the fracture. Good agreement is found among failure mechanism, strain localization and chip orientation distribution. POLYM. COMPOS., 40:E962–E974, 2019. © 2018 Society of Plastics Engineers

Influences of dispersion types and area densities of chopped fiber‐based interfacial reinforcements on mechanical properties of sandwich structures

Chopped carbon fibers with different dispersion types (colony type and uniform type) and area densities were inserted at sandwich beams, consisting of a PVC foam core covered with two glass fiber/epoxy composite face sheets. The effects of this reinforcement on the interfacial bonding between PVC foam core and glass fiber face sheets were evaluated. Their mechanical properties were measured by three‐point‐bending and Charpy impact tests. Their structures after mechanical failure were observed by scanning electron microscopy. Compared with the beam without interfacial reinforcement, the bending strength, energy absorption, and impact strength after interfacial reinforcement using 20 g/m2 uniform chopped fibers increased by up to 109%, 184%, and 47%, respectively, surpassing those of other chopped fiber mats. The weight percentage of carbon fibers/sandwich structure was less than 1%, so the chopped carbon fiber interleave had both cost effectiveness and outstanding structural performance. The improvement of interlayer toughness can mainly be attributed to the fiber bridging structure and the interlayer strength. POLYM. COMPOS., 40:E449–E455, 2019. © 2018 Society of Plastics Engineers

Thermo-mechanical behavior of epoxy composite reinforced by carbon and Kevlar fiber

Newer manufacturing techniques were invented and introduced during the last few decades; some of them were increasingly popular due to their enhanced advantages and ease of manufacturing over the conventional processes. Polymer composite material such as glass, carbon and Kevlar fiber reinforced composite are popular in high performance and light weight applications such as aerospace and automobile fields. This research has been done by reinforcing the matrix (epoxy) resin with two kinds of the reinforcement fibers. One weight fractions were used (20%) wt., Epoxy reinforced with chopped carbon fiber and second reinforcement was epoxy reinforced with hybrid reinforcements Kevlar fiber and improved one was the three laminates Kevlar fiber and chopped carbon fibers reinforced epoxy resin. After preparation of composite materials some of the mechanical properties have been studied. Four different fiber loading, i.e., 0 wt. %, 20wt. % CCF, 20wt. % SKF, AND 20wt. %CCF + 20wt. % SKF were taken for evaluating the above said properties. The thermal and mechanical properties, i.e., hardness load, impact strength, flexural strength (bending load), and thermal conductivity are determined to represent the behaviour of composite structures with that of fibers loading. The results show that with the increase in fiber loading the mechanical properties of carbon fiber reinforced epoxy composites increases as compared to short carbon fiber reinforced epoxy composites except in case of hardness, short carbon fiber reinforced composites shows better results. Similarly, flexural strength test, Impact test, and Brinell hardness test the results show the flexural strength, impact strength of the hybrid composites values were increased with existence of Kevlar fibers, while the hardness was decrease. But the reinforcement with carbon fibers increases the hardness and decreases other tests.

Graphene Oxide Admixed Aerated Concrete Composite with Carbon Fibres

Concrete is the widely used construction material and research focus is towards customizing the mixture proportion to suit the application for various construction facilities. Advancement in construction industry has resulted in fast track construction facilities with the use of precast structural elements. Lightweight concrete is gaining importance due to the popularity of prefabricated construction. This paper highlights the optimized mixture proportion of aerated concrete composite with certain chemical and mineral admixtures so that it can be suitably used for precast structural elements. Aluminium powder was used as the aerating agent. Lime powder of about 30% by weight of cement was used to facilitate the aeration process. Lime reacts with aluminium powder liberating hydrogen gas which is responsible for the air voids in concrete. Fly ash class F was used as replacement for sand by 20%. The sand used for this concrete was pulverized and the fraction passing 1.18 mm sieve was used for the concrete. Since the mixture proportion is a multivariable process, statistically designed experiments using central composite design of response surface methodology was used to design the trial mixes. The significance of the interacting factors and the validity of experimentation were analyzed using ANOVA analysis. The strength properties and durability tests were performed to access the characteristics of the material. The density of the concrete was 1285 kg/m3 .The compressive strength obtained was 27.5 MPa, the tensile strength was 2.89 MPa and flexural strength was 3.4 MPa. Chopped carbon fibres and graphene oxide were admixed to the concrete and it was observed that there was 13% increase in the compressive strength when 0.05% of graphene oxide was added. Also carbon fibres increased the flexural strength of the concrete bridging the cracks that were formed when load was applied. Response surface graphs were drawn for all the characteristics that were studied. The significant interaction effects were assessed for all the observed characteristics. There is a general view that aerated concrete being a porous material will not be durable in terms of performance. Hence durability tests like carbonation test, concrete impermeability test and rapid chloride penetration tests were performed to access the durability of the material. It was observed that there were isolated pores and hence the durability of the concrete was the same as conventional concrete. Hence optimized mixture ratio was obtained for low density, high strength and low water permeability. This material can be potentially used for the fabrication of precast structural components so that the process of handling these members will be easy due to the reduced weight of the concrete. Also it has been reported that aerated concrete has good acoustical and thermal insulation properties.

Multiscale finite element modeling of sheet molding compound (SMC) composite structure based on stochastic mesostructure reconstruction

Predicting the mechanical behavior of the chopped carbon fiber Sheet Molding Compound (SMC) due to spatial variations in local material properties is critical for the structural performance analysis but is computationally challenging. Such spatial variations are induced by the material flow in the compression molding process. In this work, a new multiscale SMC modeling framework and the associated computational techniques are developed to provide accurate and efficient predictions of SMC mechanical performance. The proposed multiscale modeling framework contains three modules. First, a stochastic algorithm for 3D chip-packing reconstruction is developed to efficiently generate the SMC mesoscale Representative Volume Element (RVE) model for Finite Element Analysis (FEA). A new fiber orientation tensor recovery function is embedded in the reconstruction algorithm to match reconstructions with the target characteristics of fiber orientation distribution. Second, a metamodeling module is established to improve the computational efficiency by creating the surrogates of mesoscale analyses. Third, the macroscale behaviors are predicted by an efficient multiscale model, in which the spatially varying material properties are obtained based on the local fiber orientation tensors. Our approach is validated through experiments at both meso- and macro-scales, such as tensile tests assisted by Digital Image Correlation (DIC) and mesostructure imaging.

Electrically Conductive Mortar Characterization for Self-Heating Airfield Concrete Pavement Mix Design

The overall objective of this paper is to investigate the types and proportions of nano-carbon based conductive materials (carbon powders and fiber), the mixing procedures, and the characteristics of conductive mortar, including the heating performance, with a focus on optimizing self-heating ECON mix design with desirable electrical and mechanical properties for airfield pavement deicing applications. A state-of-the-art review on relevant literature was conducted to identify the various conductive materials that have been investigated in the past, their optimal concentration levels to achieve desirable system-level engineering properties, and the various challenges in optimizing the ECON mix design and achieving a cost-effective ECON system. In the experimental investigation, mortar specimens modified with conductive materials at different concentration levels were compared with untreated (control) specimens in terms of electrical and mechanical properties. Conductivity and strength performance assessment of the experimental results revealed that 6-mm chopped carbon fiber (CCF) utilized in this study is capable of providing improved electrical conductivity in comparison to carbon based conductive powders without loss of strength and workability. Among carbon based conductive powders, the coarsest graphite powder provides acceptable electrical conductivity improvement and lesser loss of strength and workability. Heating characteristic of conductive mortar indicates that conductive materials which can enhance ECON conductivity could provide heating performance improvement for airfield pavement deicing application.

Comparative study on self-compacting concrete reinforced with different chopped fibers

The development of self-compacting concrete (SCC) is a revolutionary landmark in the history of the construction industry. Incorporation of fibres further enhances the properties, especially those related to the post-crack behaviour of SCC. The fibres used in the study are 12 mm long chopped glass fibre, carbon fibre and basalt fibre. The volume fractions of fibre taken are 0·0, 0·1, 0·15, 0·2, 0·25 and 0·3%. The research comprised two stages: the first stage consisted of the development of an SCC mix design of M30 grade; in the second stage, different fibres, such as glass, basalt and carbon fibres, were added to the SCC mixes and their fresh and hardened properties were determined and compared. Carbon fibre-reinforced SCC (FRSCC) exhibited the best performance followed by basalt FRSCC and glass FRSCC in the hardened state, whereas it exhibited the poorest performance in the fresh state due to its high water absorption. Glass FRSCC exhibited the best performance in the fresh state. This study concludes that, in terms of overall performance, optimum dosage and cost, basalt fibre is the best option for improving the overall quality of SCC.

The Study of Thermal, Mechanical and Shape Memory Properties of Chopped Carbon Fiber-Reinforced TPI Shape Memory Polymer Composites.

Trans-l,4-polyisoprene (TPI) shape memory polymer composites with different chopped carbon fiber mass fractions were prepared to study the effects of different chopped carbon fiber mass fractions and temperatures on the TPI shape memory polymer composites in this paper. While guaranteeing the shape memory effect of TPI shape memory polymers, the carbon fiber fillers also significantly enhanced the mechanical properties of the polymers. The thermodynamic properties and shape memory properties of TPI shape memory polymers were studied by a differential scanning calorimeter (DSC) test, dynamic mechanical analysis (DMA) test, thermal conductivity test, static tensile test, mechanical cycle test, thermodynamic cycling test and shape memory test. Furthermore, the tensile fracture interface of TPI shape memory polymer composites was analyzed by scanning electron microscopy. The experimental results show that when the chopped carbon mass fraction fiber is 8%, TPI shape memory polymers have good shape memory properties and the best mechanical properties.

Tribological Properties of a C/C–SiC–Cu Composite Brake Disc

A life-size composite brake disc was produced from Si, carbon–carbon composite, copper, and phenol resin. The disc had an outer radius O380, inner radius O180, and thickness of 36 mm. Chopped carbon fibers were used to reinforce frictional and structural layers. To obtain a preform of each layer, resin and carbon-fibers were mixed and hot-pressed. The preforms were pyrolyzed, and bonded by hot pressing. Finally Si and Cu infiltration in vacuum atmosphere was carried out to obtain a C/C–SiC–Cu x Si y composite brake disc. The density of the disc was 2.17 g/cm3. The bending strength was 61 MPa. The heat transfer coefficients in vertical and horizontal directions were 30.7, and 85.2 W/m-°C at 25°C, respectively. Friction coefficients of the C/C–SiC–Cu x Si y brake disc were more stable than those of C/C–SiC brake discs. X-ray diffraction analysis showed that Cu formed a compound, Cu3Si.

Polypropylene Composites Manufactured from Recycled Carbon Fibers from Aeronautic Materials Waste

Carbon fiber composites are used in several industries such as, aerospace, automotive, civil engineering, sports goods and technical applications due to its low-weight, strength and stiffness. However, the technology of recycling of these thermosetting polymer composites remains an engineering challenge because of their cross-linked structures that impede their reprocessing by simple heating. The aim of this work was to study the influence of the amount and dimensions of carbon fibers arising from composite waste into a new composite of polypropylene matrix. In order to carry out the study, the carbon fiber composite waste has been mechanically processed for the production of chopped fibers with two different lengths (4.5 mm and 3.0 mm). Thermoplastic composites made of chopped carbon fiber/ polypropylene at proportions 1%, 5% and 7% in fiber weight content were obtained by extrusion and injection process. Then, a series of laboratory test (mechanical, thermal and morphological) were performed in order to characterize the composite material obtained. The results showed that the fibers were capable of causing a reinforcing, even though the new composite presents a complex phase system with low adhesion between the recycled carbon fibers and the polypropylene matrix.

Formability and flow front observation of carbon/polyamide 6 randomly oriented strand composites during compression molding

Chopped carbon fiber tape-reinforced thermoplastics are randomly oriented strand materials that are easy to process and have good mechanical properties. Studying the formability and flow evolution during compression molding is essential; in particular, clarifying the relationship between the forming parameters and mold-filling characteristics of highly concentrated fiber suspensions. Here, we investigated the key parameters of strand size and effective pressure and demonstrated filling a complex mold cavity under practical processing conditions. In addition, a simplified method for observing the progression of the flow front using a video camera was proposed, where the dependence of the applied load on the mold-filling time could be observed. Filling complex-shaped mold cavity using chopped carbon fiber tape-reinforced thermoplastics is achievable using shorter strands and higher pressures. Also, the degradation of mechanical performance should be carefully considered when the material undergoes large deformation to form complex-shaped products.

Amending the thermo-mechanical response and mechanical properties of epoxy composites with silanized chopped carbon fibers

This study demonstrates the ability of functionalized chopped carbon fibers (CCFs) chosen from industrial waste to improve the thermo-mechanical properties of CCFs/epoxy composites. The defect sites onto the CCFs were created by their oxidation and the oxidized CCFs were covalently linked with siloxane functional groups to conceal their defects. The surface functionalization of CCFs was characterized by a simple chemical route, FTIR and TGA analysis, respectively. The surface morphology of functionalized CCFs showed the generation of highly dense networked globules. Epoxy composites filled with 0.5wt% of siloxane attached CCFs (S-CCFs) showed a tremendous enhancement in storage modulus (∼376%) without sacrificing their thermal stability. Furthermore, the S-CCFs reinforced epoxy composites demonstrate a significant improvement in the tensile and fracture properties. Such enhancement in the mechanical properties can open up the scope for the utilization of CCFs as a potential cost-effective candidate for high-performance next generation structural composites.

Dispersion of carbon fibers and conductivity of carbon fiber-reinforced cement-based composites

Abstract Dispersion of carbon fibers in the cement matrix remains a hot topic in the preparation of carbon fiber-reinforced cement-based composites (CFRC) because it affects greatly both the mechanical and electrical properties of the composites. In this work, a new dispersant hydroxyethyl cellulose was used with the aids of pre-dispersion by ultrasonic wave to realize the uniform distribution of chopped carbon fibers in the cement matrix. The fracture surface of the prepared CFRC was observed by scanning electron microscopy, the elemental distribution was investigated by energy dispersive spectroscopy, and the components was analyzed by X-ray diffraction. Influences of carbon fiber lengths and contents, water/cement weight ratio, molding process, curing time, and silica fume content over the conductivity of the CFRC composites were studied. The mechanism of conductivity was discussed. Results shown that the electrical resistivity intended to decrease with the increasing of carbon fiber contents. The mass fraction 0.6% of carbon fibers was a turning point. The concentration of hydroxyethyl cellulose between 1.66% and 1.86% was mostly beneficial for the dispersion of carbon fibers. The resistivity was increased first and decreased then with the increase of water/cement ratio. When the CFRC sample was prepared by the vibrating pressing method, the resistivity of the sample was reduced far greatly than that of the sample by the vibrating method. The incorporation of silica fume into the CFRC composites exerted not only a good effect on the dispersion of carbon fibers, but also increased the density of the composites to further influence the conductivity of the CFRC.

Microstructure, hardness and fracture toughness of spark plasma sintered ZrB2–SiC–Cf composites

Abstract The combined effects of SiC particles and chopped carbon fibers (C f ) as well as sintering conditions on the microstructure and mechanical properties of spark plasma sintered ZrB 2 -based composites were investigated by Taguchi methodology. Analysis of variance was used to optimize the spark plasma sintering variables (temperature, time and pressure) and the composition (SiC/C f ratio) in order to enhance the hardness of ZrB 2 –SiC–C f composites. The sintering temperature was found as the most effective variable, with a significance of 83%, on the hardness. The hardest ZrB 2 -based ceramic was achievable by adding 20 vol% SiC and 10 vol% C f after spark plasma sintering at 1850 °C for 6 min under 30 MPa. Fracture toughness improvement were related to the simultaneous presence of SiC and C f phases as well as the in-situ formation of nano-sized interfacial ZrC particles. Crack deflection, crack branching and crack bridging were detected as the toughening mechanisms. A Vickers hardness of 14.8 GPa and an indentation fracture toughness of 6.8 MPa m 1/2 were measured for the sample fabricated at optimal processing conditions.

Non-linear Finite Element Analysis for Three-point Bending Behavior of Discontinuous and Randomly-Oriented Chopped Carbon Fiber Tape-Reinforced Thermoplastic

Non-linear Finite Element Analysis for Three-point Bending Behavior of Discontinuous and Randomly-Oriented Chopped Carbon Fiber Tape-Reinforced Thermoplastic