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Using the Eshelby equivalent inclusion theory and the Mori–Tanaka method, a new micromechanical model is proposed to predict the tensile modulus of carbon fibers by considering crystallites, amorphous components, and microvoids of the fiber structure. Factors that affect the tensile modulus included the aspect ratio of crystallites, the aspect rati...
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The hot-drawing process of polyacrylonitrile (PAN) fibers is an important step during the production of PAN-based carbon fibers. In this study, supercritical carbon dioxide (Sc-CO2) was used as one kind of media for thermal stretching of PAN fibers to study the effect of different pressures of Sc-CO2 on crystallinity, degree of orientation and mech...
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... 3 Three-dimensional printing of polymer-based composite materials modified by CF CF is a new type of fiber material with a carbon content of more than 95%, high strength and high modulus [93]. It is composed of graphite microcrystals and other inorganic fibers stacked along the fiber axis, and processed by carbonization and graphitization processes to obtain microcrystalline graphite aggregates [36][37][38]. CF has excellent mechanical properties, it is a good conductor of electricity and heat, meanwhile has excellent corrosion resistance [39,40]. And it has been widely used in sports goods, automobile manufacturing, national defense, medical equipment, aerospace, and other fields [41,42]. ...
Three-dimensional (3D) printing technology is an additive manufacturing technology designed to rapidly process and manufacture complex geometrical components based on computer model design. Based on a 3D data model, materials are accumulated layer by layer through computer control, and the 3D model is finally turned into a stereoscopic object. Compared with traditional manufacturing methods, 3D printing technology has the advantages of saving man-hours, easy operation, no need for molds, and strong controllability of component geometry. With the development of this technology, according to the core materials and equipment and other elements of the printing molding technology, several types of 3D printing technologies such as fused deposition modeling, selective laser sintering, stereolithography, and solvent cast-3D printing have gradually formed. This review focuses on the principles and characteristics of several of the most representative 3D printing molding processes. And based on carbon nanomaterial (carbon fibers, graphene, and carbon nanotubes) reinforced polymer composite materials, the research progress of different 3D printing molding processes in recent years is reviewed. At the same time, the commercial application of 3D printing molding process in this field is analyzed and prospected.
... Since the amorphous carbon as a matrix plays an important role in transferring load during tensile, its effect on the mechanical properties of carbon fibers cannot be ignored. Recently, the fact that a nanocomposite mechanical model only took into account the properties of both the graphite crystallites and the amorphous carbon has successfully explained the dependence of the tensile strength, tensile modulus and compressive strength of PAN-based carbon fibers on their microstructure [1,[27][28][29][30]. It is suggested that the microstructure of the amorphous carbon is a key factor in further improving the performances of carbon fibers. ...
The effects of the microstructure evolution of amorphous carbon on the tensile behavior of polyacrylonitrile (PAN)-based carbon fibers were investigated. The microstructure as a function of heat treatment temperature was characterized by means of XRD, HRTEM and Raman spectra. It is found that the amorphous carbon content decreases with increasing heat treatment temperature and that the densities of the carbon fibers increase is due to the removal of the impurity elements and the shrinking of the graphite planes. The amorphous carbon parallel to the graphite planes transforms into graphite planes and stacks on the graphite crystallites, leading to the increase in the graphite crystallite thickness. And the graphite crystallite length is increased through the amorphous-to-crystallite transition which occurs at the edges of graphite planes and the coalescence between two adjacent graphite crystallites. It is found that the tensile behavior of PAN-based carbon fibers mainly depends on the microstructure evolution of amorphous carbon. The reactions between sp² carbon clusters and graphite planes improve the cross-linking among graphite crystallites, which has a positive effect on the tensile strength of the carbon fibers. However, a large number of structural defects and residual stresses, introduced by the rearrangement of graphite planes, are the main reasons for the degradation of the tensile strength. The tensile strains of the carbon fibers decrease and the tensile modulus increase with the decrease in the amorphous carbon content, which are mainly due to the amorphous-to-crystallite transition in the skin region.
... Moreover, the carbon fibers exhibit maximal increases of 14.73% in TS and 10.08% in TM when the stabilized fibers are post-treated at 300°C. From 300 to 345°C, although the orientation of the carbon fibers decreases, the increase in the crystal size (Table 3) leads to the TM remaining nearly the same [43]. As the crystal size continues to increase, the internal flaws of the carbon fibers increase, as well as the orientation of crystallite decreases (Fig. 9), resulting in the reduction in TS [44]. ...
Post-thermal treatment prior to carbonization was used to modify polyacrylonitrile stabilized fibers, and in this study, the effects of this modification on the structures of the stabilized fibers and the resulting carbon fibers were investigated. The stabilized fibers were modified by thermal treatment under a nitrogen atmosphere at different temperatures, followed by continuous carbonization to obtain carbon fibers. The reaction mechanism and structural changes in the stabilized fibers during the post-treatment process were investigated by ¹³C solid-state nuclear magnetic resonance and X-ray diffraction analysis. The degree of stabilization of the post-treated stabilized fibers is higher than that of the as-received stabilized fibers and increases with increasing post-treatment temperature. The crystal width of the resulting carbon fibers increases continuously, whereas the crystal thickness remains nearly the same with increasing post-treatment temperature. When the post-thermal treatment for modification is conducted at 300 °C, the stabilized fibers possess the highest degree of orientation. This property is inherited by the resulting carbon fibers, which exhibit the highest degree of orientation and optimal mechanical properties.
... These works include tensile tests combined with optical microscopy [10], laser diffraction [11,12], Xray diffraction [12e14], micro-Raman spectroscopy [15] on single carbon fibres or bundles, and nanoindentation studies [15e19] on C-fibre reinforced composites. In order to predict the C-fibre elastic properties, several models have been developed and improved during the last couple of decades [10,12,14,20,21]. Lately, the most accurate studies use micromechanical models taking into account both crystalline, amorphous and void content of C-fibres [14,21] and molecular dynamics simulations [20]. ...
... In order to predict the C-fibre elastic properties, several models have been developed and improved during the last couple of decades [10,12,14,20,21]. Lately, the most accurate studies use micromechanical models taking into account both crystalline, amorphous and void content of C-fibres [14,21] and molecular dynamics simulations [20]. ...
... Even the simulation approach is also not sufficient. Finally, recent micromechanical models [14,21] were developed to predict the Young 0 s modulus of fibres and were not tested on the complete set of elastic constants. ...
Elastic constants of single carbon fibres were estimated by a novel nanoindentation based method and subsequently predicted by modified two- and three-phase Eshelby-Mori-Tanaka (EMT) micromechanical models which takes into account both crystalline, amorphous phases and microvoids of the fibre structure. This case study was carried out on a T-300 PAN-based carbon fibre reinforced SiC composite material at room temperature. Transversal and longitudinal cross-sections of individual fibres were indented by a sharp Berkovich tip up to the maximum depth of 150 nm. Assuming transverse isotropy of the fibres, their five elastic constants were deduced from the measured indentation moduli using numerical (Vlassak-Nix) and analytical models (Delafrague-Ulm), and finite element method simulations. The elastic constants were estimated to c11=30.9, c12=9.7, c13=12.2, c33=237.3 and c44=10.9 GPa. The complete set of measured elastic constants were analyzed and then predicted by the proposed modified EMT models. The application of anisotropic nanoindentation coupled with the amorphous-crystalline structure model is unique to carbon fibre which revealed that an anisotropic ‘amorphous’ matrix should be assumed to achieve an appropriate fit with experimental results. This matrix was considered as a mixture of microvoids and aligned graphite planes, and their volume ratio was determined.
Nanocomposite microstructures dominating the anisotropic elastic properties in carbon fibers were studied, to construct a micromechanics model that can explain the anisotropic elastic properties of carbon fibers. Aluminum-based composites containing five types of carbon fibers were prepared, and their anisotropic elastic properties were measured using resonant ultrasound spectroscopy combined with electromagnetic acoustic resonance. Then, all the independent elastic stiffness components of the carbon fibers were extracted from those of the composites using a composite model based on Eshelby's inclusion theory, Mori–Tanaka mean-field theory, and effective-medium approximation. Moreover, we newly developed a nanocomposite microstructure model that can fully reproduce all the anisotropic constants of carbon fibers exhibiting a wide variety of Young's moduli. In the developed model, the microstructures of carbon fibers were approximated as nanocomposites comprised of an amorphous carbon matrix and graphite-crystal inclusions that are aggregations of graphite nanocrystallites. Based on this nanocomposite microstructure model, the shape of the graphite-crystal inclusions and the elastic properties of the amorphous carbon matrix were analyzed, considering the volume fraction and orientation of the graphite nanocrystallites, as determined using X-ray diffraction. The analysis revealed that the shapes of the graphite-crystal inclusions are flat ellipsoids elongated along the fiber axis, and the aspect ratio of the graphite-crystal inclusions dominantly affects the anisotropy in the Young's modulus. This indicates that the graphite nanocrystallites are connected along the in-plane directions of the graphitic layers, and not the shape of nanocrystallites but their two-dimensional connectivity dominates the anisotropic elastic modulus in carbon fibers.
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 two-phase micromechanical model composed of crystallites and amorphous components can be employed to address the relationship between the microstructure and the tensile modulus of carbon fibers. It turns out that the tensile modulus increases with the increase of three factors: the aspect ratio of crystallites, volume fraction of crystallites and degree orientation of crystallites. Subsequently, seven types of carbon fibers are compared, and their differences of the tensile moduli affected by the three factors are calculated. The results show that the differences of the tensile moduli affected by the factors of microstructures between different types of carbon fibers can be discussed using the two-phase micromechanical model.
