Tensile Strength Of Carbon Fibers Research Articles

Schematic construction of carbon fiber tow microstructure models and their effect on tensile strength of carbon fiber tow/epoxy composites: Quantification of carbon fiber distribution, misalignment, and interlacing

Carbon fiber reinforced polymers (CFRPs) are increasingly being used in cutting-edge technologies, thus rendering accurate material characterization essential. However, the unexpected microstructures of carbon fiber (CF) tows, such as random fiber distribution, misalignment, and interlacing, degrade the mechanical properties of CFRPs and render them unpredictable. Hence, the microstructures of CF tows and their effect on the performance of CFRPs must be investigated.Herein, we propose a framework for quantifying the microstructural parameters of three types of T700 grade CF tows and investigate their effects on the tensile strengths of CF tows and CF tow-reinforced composites. CF cross sections are analyzed via microscopy to measure the fiber distribution and misalignment with respect to the location. A two-roll mill experiment is designed to evaluate fiber interlacing by compressing the CF tow in the thickness direction. The tensile strengths of CFs, CF tows, and CF tow-reinforced composites are measured, whereas their interfacial shear strengths are obtained via a micro-droplet test.Two CF tow microstructure models are proposed: the uniform distribution model with a low degree of fiber misalignment resulted in a higher tensile strength ratio of CF tow compared to the core-shell model, as well as a higher tensile strength of CF tow/epoxy composites. Results indicate that the microstructure of the CF tow significantly affects the properties of the composite materials. Therefore, utilizing the framework proposed herein as a tow design parameter is expected to fulfill the varying requirements of important properties in composite material design based on the application field.

Boosting mechanical properties of carbon fibers by gas-liquid dual-effect approach

The tensile strength and tensile modulus of existing carbon fibers (CFs) are 3 %–5 % of the theoretical values, which greatly limits the performance of CFs when used alone or as a reinforcing material. To increase the chemical reaction activity and roughness of the surface of CFs based on the enhancement of their mechanical properties, a comprehensive treatment of CFs was carried out by the gas-liquid dual-effect method. CFs were oxidized at high temperatures after immersion treatment using cobalt nitrate solution, and the effects of cobalt nitrate solution concentration, oxidation time, and calcination temperature on the surface morphology, functional groups, structural defects, and mechanical properties of CFs were investigated by the controlled-variable method. The results showed that when the concentration of cobalt nitrate solution was 0.2 molL-1, the calcination temperature was 200 °C, and the oxidation time was 4 h, the modification effect was the best. At this time, the tensile strength of CF is 6104.50 MPa, which is 40.35 % higher than that of the pure CF, and the tensile modulus is 378.56 GPa, which is 13.27 % higher than that of the pure CF, with a significant enhancement effect. It can offer feasible ideas for further research and development of CF composites, and provide an effective way to promote the industrialization of modified CFs for application.

Grafting Carbon Fibers with Graphene via a One-Pot Aryl Diazonium Reaction to Refine the Interface Performance of T1100-Grade CF/BMI Composites.

In this study, a one-pot aryl diazonium reaction was used as a simple and mild method to graft graphene onto the smooth and inert surface of T1100-grade carbon fiber (CF) through covalent bonding without any damage on CF, to refine the interface performance of CF/bismaleimide (BMI) composites. XPS, SEM, AFM, and dynamic contact angle testing (DCAT) were used to characterize chemical activity, morphologies, and wettability on untreated and grafted CF surfaces. Meanwhile, the impact of the graft method on the tensile strength of CF was also examined using the monofilament tensile test. IFSS between CF grafted with graphene and BMI resin achieved 104.2 MPa after modification, increasing from 85.5 MPa by 21.8%, while the tensile strength did not decrease compared to the pristine CF. The mechanism of this interface enhancement might be better chemical bonding and mechanical interlock between CF grafted with graphene and BMI resin, which is generated from the high surface chemical activity and rough structure of graphene. This study may propose a simple and mild method to functionalize the CF surface and enhance the interface performance of composites without compromising the tensile properties of T1100-grade CF.

Synergistic effect of spinning drawing and preoxidation stretching on the orientation structure of mesophase pitch carbon fibers

Mesophase pitch carbon fiber has shown remarkable prospects in specialty carbon material. The mechanical properties of mesophase pitch carbon fiber (CF) cannot be precisely controlled because of the difficulty of forming process regulation. The early forming of carbon fiber (precursor fiber (PF) and pre-oxidation fiber (OF)) is difficult to regulate, such as carbon microcrystal and carbon layer texture, while cause the irreversible growth of carbonization process. Herein, a synergy strategy of spinning drawing and preoxidation stretching is developed to optimize orientation structure, eliminate morphology defects and improve mechanical properties. A synergistic effect of superior spinning drawing and suitable preoxidation stretching is beneficial to adjust the more order rearrangement of carbon microcrystals. The tensile strength of carbon fibers with spinning drawing and preoxidation stretching is increased by 1.7 times, and their defects are reduced by 40%. The results show that the excellent mechanical property of carbon fiber is contributed by the extrusion stress caused by high oxidation crosslinked surface layer under tension, and the micro-flow and rearrangement of carbon microcrystals induced by extrusion stress. A mechanical strengthening mechanism of carbon fiber is proposed, which provides guidance for high-performance mesophase pitch carbon fiber.

Monitoring the inverted exponentiated half logistic quantiles under the adaptive progressive type II hybrid censoring scheme

Numerous studies have solved the problem of monitoring statistical processes with complete samples. However, censored or incomplete samples are commonly encountered due to constraints such as time and cost. Adaptive progressive Type II hybrid censoring is a novel method with the advantages of saving time and improving efficiency. On the basis of this scheme, the problem of monitoring a downward shift in the quantiles of the inverted exponentiated half logistic distribution is considered. The conventional Shewhart control chart is insensitive to detect quantile shifts from faulty data processes that exhibit deviations from normality or symmetry. To overcome this limitation, Bootstrap control charts combining with the exponentially weighted moving average method based on the Bayesian estimation and maximum likelihood estimation are proposed, respectively. They are compared with the conventional Shewhart control chart via average run length through Monte-Carlo simulations. Finally, a real dataset related to the tensile strength of carbon fibers is employed to demonstrate the ascendancy of the Bootstrap control charts.

Multiscale enhancement of carbon/carbon composite performance by self-assembly of sulfonated graphene with silane-treated carbon fibers

The application prospects of carbon/carbon composites are greatly limited by interfacial cracks and pores caused by binder pitch displacement and cracking during high-temperature carbonization. In this study, silane coupling agent was coated on the surface of oxygen plasma-treated carbon fibers (CFs) and subsequently electrostatically self-assembled with sulfonated graphene (SG) to improve the interfacial bonding between filler and CTP. The results indicate that the tensile strength of carbon fiber treated with silane coupling agent increased by 19 % compared to untreated CF. This increase in strength may be related to the layer of silane coupling agent that repaired the grooves and imperfections on the CF surface. The addition of SG not only improves the distribution characteristics of the fibers, allowing the silane-treated CF to play a greater role in the matrix, but also creates a three-dimensional hydrogen-bonded cross-linking between the SG and the coal tar pitch (CTP) on the surface of the fibers. This inhibits CTP displacement and pyrolysis, achieving a tight bonding of the fiber to the matrix. The composites' structural integrity and mechanical properties were significantly improved due to the synergistic effect of silane-treated CF and SG. The compressive strength was 216.98 MPa, with a flexural strength of 54.78 MPa, 250 % higher than the untreated carbon fiber-reinforced composites. Additionally, the porosity decreased by 31.5 %, and the antioxidant properties increased. The study presents a potential solution to improve the performance of carbon/carbon composites by using the silane-treated CF-SG multiscale reinforced phase.

A novel core-shell C/SiC bolt prepared by chemical vapor infiltration and its fiber strengthening mechanisms

Integrated manufacturing techniques have been extensively utilized to assemble thermal structural components made of continuous fiber reinforced silicon carbide composites (C/SiC) to fabricate large and complex components. The mechanical joint, always in terms of C/SiC bolts, become the weakest link in the components. Laminated C/SiC bolts have been invented to meet the requirements of the high temperature applications. Due to the low shear strengths of C/SiC, the threads are prone to be damaged. In order to fully employ the high tensile strength of carbon fibers, core-shell C/SiC bolt is proposed with the shell prepared by woven fiber architecture. Uniform circumferential microstructure of the threaded teeth has been obtained and the corresponding strength has been improved through fiber bridging mechanism. The results shows that the thread pull-off strength is 17.96% greater than that of the laminated thread tooth, and the stud tensile strength is slightly improved up to 2.96%. The stud shear strength is enhanced by 45.29% and 46.88% with unidirectional C/SiC rod and ZrO2 ceramic rod, respectively. The improvements are mainly caused by the fiber tension-shear coupling effects. Especially the introduction of unidirectional C/SiC rod improves the shear strength of the bolts by fully utilizing the fiber strengthening mechanisms under in-plane shear loading.

Influence of carbon fiber failure mode caused by TiO2 coating on the high temperature tensile strength of carbon fiber reinforced 7075 Al alloy composites

To enhance the mechanical properties of carbon fiber (CF) reinforced 7075 Al alloy material at high temperature conditions, TiO2 coating was prepared on the surface of CF by chemical vapor deposition. The composites were prepared by hot pressing sintering and hot extrusion methods. The evolution of the compositional components of the composite interface was investigated. The density, hardness, and tensile strength of the samples were measured, and the strength/density ratio of the samples was calculated at 150 °C. The results indicate that the tensile strength of coated CF reinforced composite (535 MPa) was increased by 21.3% and 5.7% compared to the tensile strength of 7075 Al alloy (441 MPa) and uncoated CF reinforced composite (506 MPa), respectively. Furthermore, the strength/density ratio of the composite also increased with the addition of TiO2 coating. The enhancement of coating on CF on tensile strength is attributed to the transformation of CF failure mode.

Interfacial and interlayer enhancement of highly hydrophilic dual-affinity waterborne polyurethane sizing agent acting on carbon fiber/epoxy resin composites

Dual-affinity waterborne polyurethane (WPU) sizing agents with different solid concentrations were designed to achieve two-stage interfacial properties of carbon fiber (CF) and epoxy resin (EP) reinforced composites. The effects of hydrophilic monomer content on the emulsion dispersion of WPU sizing agents and the thermal properties of the coating films were investigated, and the best performing component was selected as the sizing agent of CF to prepare WPU treated-CF. The analysis focuses on the changes of surface morphology and roughness, ionic group types, tensile strength of CF before and after WPU sizing, and the interfacial properties, interfacial strengthening mechanism of CF/EP composites. Compared with conventional commercial CF, the WPU treated-CF shows a 4 % increase in surface free energy and a noticeable improvement in surface roughness and morphology. The wettability, compatibility and adhesion of WPU treated-CF/EP composites were improved according to the strong polar “similarity intermiscibility” between the strong polar functional groups in WPU and EP. Most importantly, the interfacial shear properties (IFSS) of WPU treated-CF/EP composites were improved by 17.2 % and the interlaminar shear properties (ILSS) were improved by 23.8 %. The dual-affinity WPU sizing agent optimizes the practical effect of CF/EP composites for applications such as instrument components and surface coatings used in new energy vehicles, high-speed rail trains, aerospace and provides a boost to the development of new environmentally friendly high-performance chemical coatings.

Catalyst optimization and reduction condition of continuous growth of carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs)/carbon fiber (CF) reinforcements were synthesized under different catalyst compositions and reduction conditions. The effects of the catalyst, reduction temperature and reduction time on the surface morphology, graphitization, and single filament tensile strength of the prepared CNTs/CF samples were investigated. When nickel was used as the catalyst and copper as the catalyst promoter, with the increase of copper concentration, the catalytic activity increased. Thus, the carbon source was consumed more completely, improving the abundance of CNTs with good graphitization. And the effect of repairing CF defects was more obvious, hence the single filament tensile strength accordingly increased. Besides, the increase of catalyst reduction temperature and reduction time intensified the etching of CF by catalyst, and decreased the single filament tensile strength of CF. With the deposition of CNTs, the tensile strength of CF was enhanced in varying degrees. When the concentration of cooper was 0.01 mol/L with the reduction time of 10 min and reduction temperature of 450 °C, CNTs/CF had the highest tensile strength, which can reach up to 4.51 GPa. We determined that bimetallic catalysts could adjust the catalytic activity of nickel. The change of reduction time and temperature would affect the quality of CNTs, which was helpful to obtain high quality CNTs on CF surface and improve the mechanical properties of CNTs/CF and its composites.

Enhancing the Interfacial Shear Strength and Tensile Strength of Carbon Fibers through Chemical Grafting of Chitosan and Carbon Nanotubes.

Multi-scale "rigid-soft" material coating has been an effective strategy for enhancing the interfacial shear strength (IFSS) of carbon fibers (CFs), which is one of the key themes in composite research. In this study, a soft material, chitosan (CS), and a rigid material, carbon nanotubes (CNTs), were sequentially grafted onto the CFs surface by a two-step amination reaction. The construction of the "rigid-soft" structure significantly increased the roughness and activity of the CFs surface, which improved the mechanical interlocking and chemical bonding between the CFs and resin. The interfacial shear strength (IFSS) of the CS- and CNT-modified CFs composites increased by 186.9% to 123.65 MPa compared to the desized fibers. In addition, the tensile strength of the modified CFs was also enhanced by 26.79% after coating with CS and CNTs. This strategy of establishing a "rigid-soft" gradient modulus interfacial layer with simple and non-destructive operation provides a valuable reference for obtaining high-performance CFs composites.

Changes in microstructure and mechanical properties of the carbon fiber and their effects on C/SiC composites

The changes in microstructure and mechanical properties of the carbon fiber and their effects on C/SiC composites were studied. The H, N and O atoms escaped and the carbon content in the carbon fiber increased when the heat treatment temperature exceeds 1200 °C. Meanwhile, the growth of graphite crystallite leaded to stress concentration and reduced the tensile strength of carbon fiber to 2.98 GPa by 1200 °C heat treatment. The active atoms on the surface of the carbon fiber were reduced, thus weakening the bonding force between the carbon fiber and the pyrolytic carbon interface layer and improving the pullout mechanism of the carbon fiber. This result was also observed by synchrotron radiation X-ray computed tomography. The flexural strength of the C/SiC composite increased from 300 MPa without treatment to 364 MPa after 1600 °C heat treatment.

Design of carbon fiber with nano accuracy for enrichment interface

The interface is the pivot of the mechanical properties of Carbon fiber reinforced plastic composites (CFRP). Presently, interface researches are numerous but few involve carbonized interface. Herein, the effect of temperature on the physicochemical properties of the carbonized interface is investigated using PDA as a precursor. The results show that the high temperature causes the amorphous carbon structure in the carbon coating to transform into nanocrystalline graphite structure, and the polarity of the fiber surface is reduced. The increase in surface roughness due to temperature fails to compensate for the negative effect of reduced polarity on the interfacial bonding properties. Both the tensile strength of carbon fiber and ILSS of CFRP decreased with the increase in temperature. This study will have interesting implications for the construction of the model in the carbonized interface.

The Use of Carbon Fibers Recovered by Pyrolysis from End-of-Life Wind Turbine Blades in Epoxy-Based Composite Panels.

This work is devoted to evaluating the effectiveness of the recovery of carbon fibers from end-of-life wind turbine blades in the pyrolysis process, and the use of those fibers in the production of flat composite panels. The recovery of carbon fibers from wind turbine blades uses a pyrolysis process at 500–600 °C in a non-oxidizing atmosphere, in such a way that makes it possible to preserve the shape and dimensions of the fibers. Using recycled carbon fibers, flat CFRP sheets with epoxy resin matrix were produced by pressing. Seven different series of samples were tested, which differed in fiber length, fiber orientation, and pressure holding time. The results obtained on the recycled fibers were compared to the original carbon fibers, cut to corresponding lengths. Additionally, one of the series was reinforced with a biaxial fabric. The most favorable pressing parameters are empirically found to be pre-pressing 2 MPa (10 min), and further pressing at a pressure of 7 MPa until the resin completely cross-linked (about 120 min). A number of tests were carried out to demonstrate the usefulness of pyrolytic fibers, including tensile strength of carbon fibers, bending strength, SEM observations, FT-IR, and Raman spectroscopy. The tests carried out on the carbon fibers show that the pyrolysis process used leaves about 2% of the matrix on the surface of the fiber, and the tensile strength of the fibers drops by about 20% compared to the new carbon fibers. The research results show that the use of the recycled carbon fibers in the production of flat composite plates is reliable, and their mechanical properties do not differ significantly from plates made of corresponding original carbon fibers. Composite panels with the pyrolytic fibers (274 MPa) show up to a 35% higher flexural strength than similarly produced panels with the original new carbon fibers (203 MPa), which means that the panels can be used in the production of elements for footbridges, bridges, pipelines, or structural elements of buildings and roofing.

Environmental Assessment of Carbon Concrete Based on Life-Cycle Wide Climate, Material, Energy and Water Footprints.

The construction industry contributes a major share to global warming and resource consumption. Steel-reinforced concrete (SC) is the world’s most important building material, with over 100 million cubic meters used per year in Germany. In order to achieve a resource-efficient and climate-friendly construction sector, innovative technologies and the substitution of materials are required. Carbon concrete (CC) is a composite material made of concrete and a reinforcement of carbon fibers. Due to the non-rusting and high-strength carbon reinforcement, a much longer life-time can be expected than with today’s designs. In addition, the tensile strength of carbon fibers is about six times higher than that of steel, so CC can be designed with a relatively lower concrete content, thus saving cement and aggregates. This research analyzes and compares SC with CC over its entire life-cycle with regard to its climate, material, energy, and water footprints. The assessment is done on material and building level. The results show that the production phase contributes majorly to the environmental impacts. The reinforcements made from rebar steel or carbon fibers make a significant contribution, in particular to the climate, energy, and water footprint. The material footprint is mainly determined by cement and aggregates production. The comparison on the building level, using a pedestrian bridge as an example, shows that the footprints of the CC bridge are lower compared to the SC bridge. The highest saving of 64% is in the material footprint. The water footprint is reduced by 46% and the energy and climate footprint by 26 to 27%. The production of carbon fibers makes a significant contribution of 37% to the climate footprint.

An Attempt to Evaluate the Short Gage Tensile Strength of Carbon Fibers in Tests under an Optical Microscope

An Attempt to Evaluate the Short Gage Tensile Strength of Carbon Fibers in Tests under an Optical Microscope

Enhanced tensile strength of acrylonitrile butadiene styrene composite specimens fabricated by overheat fused filament fabrication printing

In this study, we apply a simple but effective method to enhance tensile strength of carbon fiber (CF)/acrylonitrile butadiene styrene (ABS) and glass fiber (GF)/ABS specimens via fused filament fabrication (FFF). By employing a significant high printing temperature while turning off the cooling fan, the extruded ABS composite melt could be overheated, resulting in better diffusion process between composite rasters with reduced cooling rate and prolonged diffusion time . Consequently, the printed ABS composite specimens could achieve a porosity as low as 3.65%, corresponding to a decrease of up to 60% compared to those printed by a normal printing process. More importantly, the weld lengths formed between the adjacent rasters of the printed composite specimens increased by up to 122%, indicating a considerable enhancement in the raster interfacial bonding . Furthermore, the overheat printed composite specimens exhibited an increase of up to 20% in maximum bearing load, tensile strength, and Young's modulus compared to their normal printed counterparts. This work demonstrates that the overheat FFF printing has great potential to fabricate ABS composite specimens with enhanced structure and mechanical performance for end-use structural applications. • Facile but effective method proposed to fabricate dense and high-performance FFF printed ABS composite parts. • Comprehensive study of process-structure-property correlation. • Overheat printing reduces porosity of printed ABS composite parts by up to 60%. • Overheat printing increases maximum bearing load, tensile strength, and Young's modulus of printed ABS composite parts by up to 20%, respectively.

Research on dynamic microwave low-temperature carbonization of high performance carbon fiber

Polyacrylonitrile precursor was obtained by one-step method of polymerization and spinning. After conventional pre-oxidation at 180–280 °C in air, the polyacrylonitrile pre-oxidized fiber was carbonized at 600–1000 °C by microwave heating and conventional heating in nitrogen. An infrared thermometer is used to detect the surface temperature of the fiber in real time. The dielectric loss tangent (tanδ) increases first and then decreases with increasing temperature. The intensity of the A line of the MCF-1000 sample increases, the G line gradually separates from the D line, and the ID/IG value decreases. Compared with CCF-700, the tensile strength of MCF-700 is increased by 10.06%. The microwave carbonization method creates excellent carbon fiber tensile strength at a temperature of 200 °C lower than the conventional carbonization temperature. The initial modulus of MCF-700 is 51.33% higher than that of CCF-700. Microwave carbonization can obtain carbon fiber with a higher initial modulus at a lower carbonization temperature.

Effect of fiber hybridization types on the mechanical properties of carbon/glass fiber reinforced polymer composite rod

In order to balance the cost performance of carbon and glass fibers, the unidirectional carbon/glass hybrid fiber reinforced polymer composite rods were developed through the pultrusion technology in the present paper. Two kinds of fiber hybridization types were proposed including intra-yarn hybrid (uniform dispersed hybrid, UDH) and inter-layer hybrid (core-shell hybrid, CSH). Furthermore, the effects of fiber hybridization types on the mechanical properties (interface/short beam shear strength, three-point bending strength and tensile strength) were investigated experimentally. The full-field strain was obtained through the digital image correlation method to reveal the hybrid mechanism. It was found that the effects of fiber hybridization types on mechanical properties were remarkable. Through uniformly dispersing the carbon fiber into the glass fiber, the maximum increase percentages of available strength were up to 10.9% for short beam shear, 60.3% for three-point bending and 58.7% for tensile strength, respectively. The results of full-field strain analysis revealed that the mechanical failure of CSH rods was dominant by the interface debonding of shell/core, which significantly decreased the mechanical properties. In comparison, UDH rods had the intact interface bonding of carbon/glass fiber/resin, the mechanical failure was derived from the fracture of carbon fiber. The tensile strength of carbon fiber was fully utilized, which contributed to the higher mechanical properties. The larger scale carbon fiber tow may form the weaker interface layer of carbon/glass fiber/resin, which led to uneven interface stress distribution under the external loading and the decrease of interface shear strength.

Combination and development of carbon filament tows: Application of coextrusion with long fiber‐reinforced thermoplastics

AbstractIn this study, long fiber‐reinforced thermoplastics (LFT) and coextrusion are applied to wrap carbon fiber tows in a thermoplastic polyurethane (TPU) outer layer. In this way, the proposed wrapped yarns have a sheath–core structure. Scanning electron microscopy observation reveals that TPU and carbon fiber tows form a physical combination that allows TPU to further enhance the tensile strength of carbon fiber tows by 35.87%, which is 19.62 ± 1.88 MPa. The tensile strain of carbon fiber tows also improves. LFT and coextrusion are performed to produce successive carbon fiber tows that can be successfully fabricated into textiles, possessing good fabric flexibility. The technique of carbon fiber tows can be applied to mass production feasibility for the field of carbon fiber composites.