Tensile Strength Of Carbon Fibers Research Articles

Interface modification of carbon fibers with TiC/Ti2AlC coating and its effect on the tensile strength

A uniform TiC/Ti2AlC gradient coating was obtained on carbon fibers via an in-situ reaction in molten salts. The results indicated that in-situ growth of TiC/Ti2AlC coating caused strong interfacial bonding and surface defects. In this case, evident stress concentration was induced and cracks penetrated the fiber easily during tensile loading. Thus the tensile strength of carbon fibers was dramatically decreased to 78 ± 13 MPa. In order to improve the performance of the as-prepared TiC/Ti2AlC-coated carbon fibers, a pyrolytic carbon layer was pre-fabricated on carbon fibers. By introducing pyrolytic carbon layer, the interfacial bonding strength and surface defects were reduced accordingly. These improvements lead to a decrease of stress concentration and cracks propagation, and facilitate the interfacial debonding during tensile loading. As a result, the tensile strength of the fiber was significantly increased to 550 ± 72 MPa. This fact indicates that pre-fabricating a pyrolytic carbon layer on carbon fibers is an effective method to improve the reliability of the TiC/Ti2AlC-coated carbon fibers. The present work also provides a feasible way to fabricate TiC/Ti2AlC interphase for high-performance Cf/SiC composites.

The direct architecture of carbon fiber‐carbon nanofiber hierarchical reinforcements for superior interfacial properties of CF/epoxy composites

A simple and efficient chemical method was developed to graft directly carbon nanofibers (CNFs) onto carbon fiber (CF) surface to construct a CF‐CNF hierarchical reinforcing structure. The grafted CF reinforcements via covalent ester linkage at low temperature without any usage of dendrimer or catalyst was investigated by FTIR, X‐ray photoelectron spectroscopy, Raman, scanning electron microscopy, atomic force microscopy, dynamic contact angle analysis, and single fiber tensile testing. The results indicated that the CNFs with high density could effectively increase the polarity, wettability, and roughness of the CF surface. Simultaneous enhancements of the interfacial shear strength, flexural strength, and dynamic mechanical properties as well as the tensile strength of CFs were achieved, for an increase of 75.8%, 21.9%, 21.7%, and 0.5%, respectively. We believe the facile and effective method may provide a novel and promising interface design strategy for next‐generation advanced composite structures.

Correlation between inhomogeneity in polyacrylonitrile spinning dopes and carbon fiber tensile strength

The nano‐scale and micro‐scale inhomogeneity of polyacrylonitrile (PAN) spinning dopes obtained from dynamic light scattering (DLS) experiment is correlated with the tensile strength of the resulting carbon fiber. The nanoscale inhomogeneity was estimated by calculating the diffusion coefficients from the slow relaxation mode of polymer solutions in DLS. The nanoscale inhomogeneity in the spinning dopes was found to be in the range of 1–45 nm. We also demonstrate mean of the count rate (MCR) obtained from DLS of PAN solution as a tool to detect the microscale inhomogeneity in the spinning dope for the first time. The MCR of spinning dopes varied from ~10.0 to 77.5 kcps (kilo‐counts per second). The tensile strength of carbon fibers from the precursor fiber spun from the spinning dopes in this study varied from 3 to 5.2 GPa. Correlation studies show that the microscale inhomogeneity in the spinning dope was a major contributor to the decrease in the tensile strength of carbon fibers in the range of 3–4.5 GPa. Contaminants causing microscale inhomogeneity in PAN powder were removed by using micelles, reverse micelles and frothing. The surfactant treated PAN polymer was characterized using a fourier transform infrared spectroscope, differential scanning calorimeter, and thermal gravimetic analyzer to demonstrate complete removal of surfactants. POLYM. ENG. SCI., 59:478–482, 2019. © 2018 Society of Plastics Engineers

Low-velocity impact behavior and residual tensile strength of CFRP laminates

This paper experimentally studies the low-velocity impact behaviors and residual tensile strength of carbon fiber reinforced plastics (CFRP) laminates. Firstly, the effects of four factors, i.e. impact angle, impactor diameter, the proportion of ply orientation and stacking sequence, on the impact responses of laminates are studied. The damage characteristics are evaluated by dent depth, delamination damage projection area (DDPA) and energy dissipation. Secondly, the tensile responses of the laminates after impact are investigated based on residual tensile strength (RTS). Finally, the correlations between the four damage evaluation criteria, i.e. dent depth, DDPA, energy dissipation and RTS, are sorted out. Experimental results demonstrate that the four factors have significant effects on the impact behaviors of laminates in different ways. The DDPA is negatively correlated with the dent depth of laminates, and the dent depth can be treated as an important reference for the RTS. Besides, a fracture phenomenon, i.e. a clear band of fiber fracture around the impact area after impact, has been observed and discussed.

Spinnability of Polyacrylonitrile Gel Dope in the Mixed Solvent of Dimethyl Sulfoxide/Dimethylacetamide and Characterization of the Nascent Fibers

In this work, acrylonitrile copolymers were prepared via precipitation polymerization. The copolymer solutions prepared at various ratio of dimethyl sulfoxide and dimethylacetamide were tested to prepare the nascent fibers by one-step wet-spun method. The effect of temperature, solvent ratio, molecular weight and the solid content on the rheological properties of polyacrylonitrile gel solution in different mixed solvent were studied. It was shown that the viscosity decreased with the increase of the temperature and fluctuated with the different solvent ratio reaching the minimal value at the ratio of dimethyl sulfoxide to dimethylacetamide equal to 1.25. The crystallinity of copolymers and the structure of the nascent fiber surface also depended from the solvent ratio in polymerization. The optimum conditions for spinnability of copolymers were determined. The high-quality polyacrylonitrile precursor was achieved with the controllable range of 0.5–0.8 dtex and the toughness of polyacrylonitrile precursor was greater than 6.0 cN/dtex after the wet spinning process, while the tensile strength of carbon fiber is up to 6.25 GPa after their pre-oxidation and carbonization process.

Synthesis and growth mechanism of carbon nanotubes growing on carbon fiber surfaces with improved tensile strength

An effective approach has been developed for the catalytic decomposition of acetylene (C2H2) by chemical vapor deposition (CVD), to achieve homogeneous growth of carbon nanotubes (CNTs) on the surfaces of carbon fibers. The morphology of CNTs grown on carbon fiber surfaces was observed by a scanning electron microscope and high-resolution transmission electron microscope, which revealed the uniform coverage of CNTs on the carbon fiber surfaces. The single fiber tensile test demonstrated that the tensile strength of carbon fibers could be increased by more than 12% with the catalytic growth of CNTs on their surface. The reparation of the damage caused during the formation of catalyst nanoparticles, and the cross-link of neighboring graphite crystallites induced by CNTs all occurred during the CVD process, which were considered to be the main reasons for improvement. The growth mechanism model of CNTs formation was established based on the thermodynamics principle and the interface microstructure of CNT-grown carbon fiber, illuminating the detailed mechanism for the growth of CNTs and the change of the shape of catalyst particles.

Generalized Weibull model-based statistical tensile strength of carbon fibres

A generalized Weibull model is presented for reliability characterization of single carbon fibres. This generalized distribution gives the probability of tensile failure of fibres as a function of length, surface area and volume of fibres, separately in different models using a statistically significant experimental data set. This model accounts for the unusual variation in the strength of the fibres as the physical parameters capture the severity of the most severe flaws in the ensemble of fibres. The experimental campaign involved analysing the diametric variation in each carbon fibre using photomicrographs. The micro-texture and morphology were further analysed using scanning electron microscopy images. An extensive characterization of the strength dependence on the fibre gage length was performed through “single-fibre uniaxial tensile tests” on several hundred carbon fibres of different grades. The goal of the study is to ensure the reliability of strength characterization of a single fibre, accounting for geometric irregularities and property variation. The present Weibull models are compared to assess their descriptive accuracy, that is, the “goodness-of-fit” in describing the observed statistical data as well their generalizability in predicting future values. The Kolmogorov–Smirnov (KS) test was used to ascertain the goodness of fit for the predicted Weibull plots. It was found that the descriptive adequacy of the models improved with the increase in the number of parameters used in the definition of the Weibull model. The conventional model failed the KS test for the most number of cases and hence was deemed unfit in terms of generalizability. Furthermore, the generalized Weibull model was found to have better descriptive accuracy and predictive power compared to the conventional model.

Small angle X-ray scattering study of microvoid evolution and pertinence of microvoid and mechanical properties in γ-irradiated CFs.

To explore the mechanism of microvoid evolution and the pertinence of microvoid and mechanical behavior of carbon fibers (CFs) in γ-irradiation, T700 CFs were exposed to γ-rays under epoxy chloropropane (ECP) and argon (Ar) at room temperature. The results from small angle X-ray scattering (SAXS) showed that the average microvoid radius of the CFs decreased gradually from 4.8406 nm for pristine fibers to 3.6868 nm (ECP) and 3.4223 nm (Ar), indicating that γ-irradiation could obviously decrease the microvoid in CFs owing to annealing and rearrangement effects. More significantly, active media would enlarge the surface microvoid of fibers, thus the microvoid of CFs irradiated in ECP was overall larger than that in Ar. The tensile strength of CFs was increased from 5.74 GPa for the pristine fibers to 6.78 GPa (Ar) and 6.18 GPa (ECP) for the irradiated CFs along with a decrease in the microvoid. Therefore, this would provide a key to investigate the evolution of the CF microvoid during γ-irradiation, which was conducive to improving the mechanical properties of γ-irradiated CFs.

A CVD Method for Preparing CNTs-Grafted Carbon Fiber Fabrics under Quasi-Vacuum at Low Temperature

Carbon nanotubes (CNTs) were grown on the surface of carbon fiber fabrics by a novel chemical vapor deposition (CVD) with Co and Ni catalyst precursors loaded on their surfaces by impregnation respectively. The method is carried out at 600°C keeping the pressure at quasi-vacuum. It was found that when Co is used as catalyst and CVD time is 5 min, the yield of CNTs is moderate, the degree of graphitization is high and the tensile strength has the maximum value. The effect of parameters on the morphology and properties of CNTs-grafted carbon fiber fabrics has been revealed, which can serve as a fundamental engineering basis for exploring the optimized process. A damage and healing model of carbon crystals has been formulated to reveal the main reason that causes the variation in tensile strength of carbon fibers after the growth of CNTs, in which the reinforcing effect of CNTs is emphasized. Such results have provided the good foundation for the large-scale preparation of high-performance multi-scale reinforcements.

Silver nanoparticles/graphene oxide decorated carbon fiber synergistic reinforcement in epoxy-based composites

A novel two-layer reinforced carbon fiber (CF), i.e., Ag nanoparticles (Ag NPs)/graphene oxide (GO) reinforced CF (named as CF/Ag/GO) was prepared by an electrochemical deposition and electrophoretic deposition (EPD) consequently. The modified fiber showed an increased interfacial shear strength (IFSS) and tensile strength. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectra (FTIR), X-ray photoelectron spectroscopy (XPS), Raman spectrometer, atomic force microscopic (AFM) and dynamic contact angle analysis (DCA) were carried out to investigate CF reinforced composites. And test results demonstrated that the presence of Ag NPs and GO sheets increased the surface roughness and surface energy of CFs significantly. IFSS of CF/epoxy and the tensile strength of CFs were increased by 86.1% and 36.8%, respectively. Ag NPs filled in the cracks in CF effectively to enhance the tensile strength, while GO sheets improved the wettability of resin on CFs and formed mechanical interlocking between CFs and epoxy resin. These Ag NPs and GO sheets worked together in a ferocious synergy on the interface of CF and epoxy to cause the enhanced mechanical properties.

Study of Voids Effect on Tensile Strength of Carbon Fiber Reinforced Composites for Structural Applications

Study of Voids Effect on Tensile Strength of Carbon Fiber Reinforced Composites for Structural Applications

Anisotropic compressive behaviour of turbostratic graphite in carbon fibre

Whilst measuring fibre properties in tension is relatively simple, measurement of compressive properties, particularly in the radial direction, has remained elusive for carbon fibres due to the small diameter. Here, the compressive mechanical properties of individual carbon fibres are quantified using micropillar compression testing. Combining the measured compressive properties with a full characterisation of the microstructure has provided a deep understanding of the mechanical behaviours of turbostratic graphite structure in carbon fibres. Under compression, the turbostratic graphite sheets are prone to bend and buckle, leading to a marked reduction in elastic modulus compared to tension. Two-fold mechanical anisotropy has been found for the turbostratic graphite structure in carbon fibres, which can be exacerbated by a higher degree of crystallinity. Although the tensile strength of carbon fibres is known to be dictated by fibre defects, the intrinsic compressive strength is found to be determined by crystal size, showing the applicability of the classical Hall-Petch hardening model to carbon-based materials. Furthermore, the failure mode for carbon fibres under compression is concluded to be by separation of turbostratic graphite, irrespective of the loading direction.

Amino-terminated nitrogen-rich layer to improve the interlaminar shear strength between carbon fiber and a thermoplastic matrix

An amino-terminated nitrogen-rich layer of poly(cyclotriphosphazene-co-melamine) (PPM) coating was used to functionalize carbon fiber (CF) to strengthen the interfacial adhesion of CF reinforced copoly(phthalazinone ether sulfone)s (PPBES) through a facile in-situ polymerization. FTIR, Raman and XPS confirm the chemical bonds between CF and PPM. SEM and dynamic contact angle tests demonstrate that PPM coating can enhance surface wettability, roughnes of CF, which can improve interlaminar shear strength and flexural strength of CF/PPBES by 23.2% and 29.3% with no discernable decrease on tensile strength of CFs. According to DMA test, storage modulus and service temperature increase by 15GPa and 6°C. SEM observations certify that the failure mechanism transforms from interface failure for CF/PPBES to matrix failure and fiber broken for CF-PPM/PPBES. Moreover, the successful preparation of PPM coatings on CF surface provides new insights for the fabrication of advanced thermoplastic composites from readily available components via a facile route.

Fractal study on fracture surface of PAN-based carbon fiber

ABSTRACTPAN-based carbon fiber is a type of brittle material whose fracture surface has a structure peculiar to brittle materials. The tensile strength of a carbon fiber is determined by the strength of weak links in the fiber to a large extent. Since fracture surface is a type of weak link, the fracture surfaces of PAN-based carbon fibers were investigated in this article. SEM (Scanning Electron Microscopy) micrographs of selected carbon fibers with different tensile strengths were analyzed on computer and the fractal dimensions of fracture surfaces were obtained on the basis of fractal theories. The relationship between the tensile strength of PAN-based carbon fiber and the fractal dimension of its fracture surface was demonstrated.

Enhancing the interfacial strength of carbon fiber reinforced epoxy composites by green grafting of poly(oxypropylene) diamines

We report on a green method of using poly(oxypropylene) diamines (D400) as coupling and curing agent to functionalize carbon fiber in water. We propose to enhance the interfacial properties of carbon fiber composites, together with the tensile strength of carbon fibers. The microstructure and mechanical properties of carbon fibers before and after modification are investigated. The results show that D400 do not change the surface morphology, but significantly increase the polarity, wettability and roughness of the carbon fiber surface. The interfacial shear strength (IFSS) of modified carbon fiber/epoxy composite and the tensile strength of carbon fibers increase by 79.1% and 8.2%, respectively. It is believed that D400 can effectively improve the interfacial adhesion of the composites by improving resin wettability, increasing chemical bonding and mechanical interlocking. This green and simple method can have applications in continuous production of high-performance carbon fiber composites.

Experimental and Statistical Optimization of the Tensile Strength of Carbon Fibers from Pitches with Different Composition

A factorial analysis was used to maximize the tensile strength of the carbon fibers obtained from pitch by means of a rational selection of variables and precursor properties. The combined influence of the fiber diameter, the soaking time at the optimum stabilization temperature, and the effect of the polycondensation degree of the pitch on the tensile strength of the carbonized fibers was assessed using a factorial design. For the first time, the strong influence of the degree of polycondensation of the parent pitch was evidenced, even though less polycondensed pitches were spun at a higher yield and favored the homogeneous fixation of oxygen during stabilization. Fibers prepared from the most polycondensed pitches exhibited the best values of tensile strength. However, very highly polycondensed pitch compositions may hinder oxygen diffusion and the formation of cross-linked structures during stabilization, leading to a poorer mechanical performance that can be overcome by increasing the stabilization time.

Building Nanoporous Metal-Organic Frameworks "Armor" on Fibers for High-Performance Composite Materials.

The nanoporous metal-organic frameworks (MOFs) "armor" is in situ intergrown onto the surfaces of carbon fibers (CFs) by nitric acid oxidization to supply nucleation sites and serves as a novel interfacial linker between the fiber and polymer matrix and a smart cushion to release interior and exterior applied forces. Simultaneous enhancements of the interfacial and interlaminar shear strength as well as the tensile strength of CFs were achieved. With the aid of an ultrasonic "cleaning" process, the optimized surface energy and tensile strength of CFs with a MOF "armor" are 83.79 mN m-1 and 5.09 GPa, for an increase of 102% and 11.6%, respectively. Our work finds that the template-induced nucleation of 3D MOF onto 1D fibers is a general and promising approach toward advanced composite materials for diverse applications to meet scientific and technical demands.

Influence of pretension on mechanical properties of carbon fiber in the filament winding process

The present study has investigated the effect of the roving tension (pretension force) on the strength of continuous carbon fiber used in the Filament Winding (FW) process. Pretension force is generally applied to composite products manufactured by FW technology to lay out the carbon fiber onto the cylindrical tube in a correct way. However, a considerable amount of damage occurs in the fibers during fiber movement trough pulleys in the pretension unit. A winding system was designed to simulate the process to understand the effects of the parameters such as roving tension, pulley diameter, and contact angle between pulley and fiber. Several experimental tests have been performed by changing pulley diameters and tension forces to understand the effect of these parameters. According to these experiments, the angle between the pulley and the amount of force applied to the carbon fiber generate the damage on the carbon fiber. Tension tests were also conducted to evaluate the strength of the damaged and undamaged carbon fiber. Experimental results indicate that the tensile strength of carbon fiber is reduced by 10 to 43% because of a change to the roving tension (pretensioning) parameters.

予負荷による炭素繊維の引張強度への影響

予負荷による炭素繊維の引張強度への影響

Carboxyl functionalized carbon fibers with preserved tensile strength and electrochemical performance used as anodes of structural lithium-ion batteries

Carboxyl functionalized carbon fibers with preserved tensile strength and electrochemical properties were acquired through a simple chemical oxidation method, and the proposed underlying mechanism was verified. The surface of carboxyl functionalizing carbon fibers is necessary in acquiring functional groups on the surface of carbon fibers to further improve the thermal, electrical or mechanical properties of the fibers. Functionalization should preserve the tensile strength and electrochemical properties of carbon fibers, because the anodes of structural batteries need to have high strength and electrochemical properties. Functionalized with mixed H2SO4/HNO3 considerably reduced the tensile strength of carbon fibers. By contrast, the appearance of H3PO4 preserved the tensile strength of functionalized carbon fibers, reduced the dispersion level of tensile strength values, and effectively increased the concentration of functional acid groups on the surface of carbon fibers. The presence of phosphoric acid hindered the over-oxidation of turbostratic carbon, and consequently preserved the tensile strength of carbon fibers. The increased proportion of turbostratic carbon on the surface of carbon fibers concurrently enhanced the electrochemical properties of carbon fibers.