Tensile Strength Of Carbon Fibers Research Articles

A Study on the Tensile Strength of the Layer Splice Laminates

The tensile strength of carbon fiber reinforced resin matrix layer splice laminate was studied. Three specimens (M1.M2.M3) were cut from laminates with different joint location and the number of layer splice. Load schemes were performed and typical load-displacement curves of three specimens were recorded. The result shows that the joint location has seriously effect on the tensile strength and modulus of specimens. The tensile strength of M2 is obviously lower than that of M1 and M3. Furthermore finite element ABAQUS6.5 was also used to simulate the course of experimental test. The result shows that shear stress concentration occurs on the joint of model. The shear stress on the model M1 and M2 has the similar trend and concentrates in the middle of the joint area. And on the model of M3 the shear stress has a completely different trend from the M1 and M2 model. On the M2 the shear stress concentration is slightly higher than the other two. It indicates that the tensile strength of M2 is the lowest among the three models. So, the inter-laminar shear stress is the major factor leading tensile failure. The experimental tests are consistent with the finite element analysis.

High-temperature vapor deposition polymerization polyimide coating for elimination of surface nano-flaws in high-strength carbon fiber

The effect of polyimide coatings on the filament tensile strength of high-strength polyacrylonitrile-based carbon fiber was studied by using dip and high-temperature vapor deposition polymerization (VDP) coating processes. Unlike a VDP on a cold substrate, high-temperature VDP has the potential to directly synthesize and isotropically deposit a polyimide, from diamine and dihydride monomers without any by-products, on a substrate heated up to 200 °C. The average filament tensile strength of the flaw-sensitive carbon fiber improved with all the polyimide coatings used. Nevertheless, for the same monomers, the high-temperature VDP coating process was advantageous for high-efficiency surface flaw healing compared to the dip-coating process, resulting in a 25% increase in the average tensile strength of the carbon fiber. These results were evident not only for the carbon fibers without artificial nano-notches but also for those with artificial notches less than 30 nm in depth. Thus, we clearly showed the potential for the VDP polyimide coating to heal surface nano-flaws of the carbon fiber. The different infiltrations of the coating into nano-notches and its effect on the filament tensile properties were characterized, as well as discussing the impact of the VDP coating with an interlayer between the coating and the fiber.

Improving carbon fiber adhesion to polyimide with atmospheric pressure plasma treatment

Plasma treatment is frequently used to modify carbon fiber surfaces to improve adhesion of the fiber to matrices although it may also influence carbon fiber tensile strength. In order to determine the effect of atmospheric pressure plasma treatment on carbon fiber tensile strength and interfacial bonding strength to polyimide, polyacrylonitrile (PAN) based carbon fibers are treated with atmospheric pressure oxygen/helium plasmas for different durations. Tensile strength change of the fiber is studied at different gage lengths before and after the plasma treatment. Interfacial bonding between the carbon fiber and a thermoplastic polyimide matrix is evaluated using a single fiber composite test system. Weibull analysis of the single fiber tensile test data shows no obvious changes in the tensile strength at short gage lengths after plasma treatment while the fiber strength tends to decrease at larger gage lengths. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) show that the plasma treatments roughen the fiber surfaces. X-ray photoelectron spectroscopy (XPS) analysis of fiber surface shows a significant increase of oxygen concentration after plasma treatment and the oxygen containing functional groups reach their maximum levels after 32s treatment time and further increasing treatment time does not achieve a higher level of oxidation. Plasma treatments decrease dynamic water contact angles and increase the surface energy of the carbon fibers as measured by the modified Wilhelmy method. The interfacial shear strength is improved 21% after the atmospheric pressure plasma treatment for 32s. It is concluded that the increase of oxygen containing functional groups and changing of the surface topology may contribute collectively to the improvement of fiber/resin interfacial adhesion.

Mixed resin and carbon fibres surface treatment for preparation of carbon fibres composites with good interfacial bonding strength

The objective of this work is to improve the interlaminar shear strength of composites by mixing epoxy resin and modifying carbon fibres. The effect of mixed resin matrix’s structure on carbon fibres composites was studied. Anodic oxidation treatment was used to modify the surface of carbon fibres. The tensile strength of multifilament and interlaminar shear strength of composites were investigated respectively. The morphologies of untreated and treated carbon fibres were characterized by scanning electron microscope and X-ray photoelectron spectroscopy. Surface analysis indicates that the amount of carbon fibres chemisorbed oxygen-containing groups, active carbon atom, the surface roughness, and wetting ability increases after treatment. The tensile strength of carbon fibres decreased little after treatment by anodic oxidation. The results show that the treated carbon fibres composites could possess excellent interfacial properties with mixed resins, and interlaminar shear strength of the composites is up to 85.41 MPa. The mechanism of mixed resins and treated carbon fibres to improve the interfacial property of composites is obtained.

Surface and Composite Interface of Carbon Fibre Modified by Pre-Irradiation

The γ-ray pre-irradiation induced method was employed to study the effect of chloroepoxypropane modification on the surface of carbon fibre (CF) and the interfacial properties of CF/epoxy. Systematic experimental work was conducted to determine the fibre surface topography, fibre surface energy, fibre tensile strength and interfacial adhesion of CF/epoxy before and after γ-ray pre-irradiation grafting. The roughness and surface energy were all found to increase significantly. The tensile strength of carbon fibres was improved marginally by γ-ray pre-irradiation. The surface modification of carbon fibres led to an improvement (at most 18.2%) of the interlaminar shear strength of CF/epoxy composites. The mechanisms of pre-irradiation of CF are proposed.

Tensile Strength of Carbon Fibers Reclaimed from CF/Epoxy Composite Using Subcritical Water and Supercritical Methanol

Carbon-fiber reinforced epoxy was decomposed using subcritical water and supercritical methanol to reclaim carbon fibers. The tensile strength of the reclaimed carbon fibers was measured. Then SEM observation, XPS, and Raman spectral analysis were conducted to elucidate the change of tensile strength caused by decomposition. The tensile strength decreased by 6% in the case of decomposition with supercritical methanol, and by 12~17% with subcritical water. The surfaces of reclaimed carbon fibers were resin-free. Decomposition did not affect the fiber surface and fracture surface morphology. Subsequent XPS analysis revealed that functional groups of the carbon fiber surface had been removed. Raman spectral analysis showed decreased graphitization of the carbon fiber surface. These results imply that the fracture toughness of the carbon fiber surface decreased because of breakage of carbon-carbon bonds in the carbon fibers as a result of decomposition.

Tensile Properties of CFRP and Hybrid FRP Composites at Elevated Temperatures

The performance of fiber reinforced polymer (FRP) composites at high temperatures is a serious concern that needs investigation before the incorporation of these composites into important engineering structures. This article presents an experimental study on the tensile properties of carbon fiber reinforced polymer (CFRP) sheets, hybrid carbon/glass fiber reinforced polymer (C/GFRP) sheets and hybrid carbon/basalt fiber reinforced polymer (C/BFRP) sheets at different temperatures. The specimens of FRP sheets were tested at temperatures ranging from 16 to 200°C, while corresponding dry fiber sheets (without resin impregnation) were tested at 16°C as a reference. The test results show that the tensile strength of carbon fibers in different FRP sheets decreases significantly with increasing temperature, and remains almost stable at an ultimate value (3000 MPa) after the polymer exceeds its glass transition temperature (T g), which is higher than the tensile strength of the non-impregnated fiber sheets at room temperature. At elevated temperatures, the hybridization of fibers can reduce the scatter of the tensile strengths of CFRP composites. Additionally, the tensile strength of CFRP sheets with different dimensions is significantly different, but size dependence is independent of temperature. Furthermore, elevated temperature also influences the failure modes of FRP composites.

Effect of a Ni–P coating on the tensile strength of carbon fibers evaluated by a Weibull statistical method

Ni-P coated carbon fibers were prepared by a chemical plating method. The microstructures of uncoated and coated carbon fibers were investigated by SEM and XRD, and the surface atom compositions were studied by EDS. The tensile strength of the carbon fibers was analyzed by a Weibull statistical method. Results show that the number of defects on the carbon fiber surfaces decreases after Ni-P coating. When the thickness of the Ni-P coating reaches 0.149μm, the tensile strength of carbon fibers exhibits a maximum value of 3.10GPa, a 8.77% increase compared to the uncoated carbon fibers, which might be ascribed to the elimination of a number of surface defects by the Ni-P coating.

Carbonization of pre-oxidized polyacrylonitrile fibers

The microstructural evolution, elemental composition and gas releasing character of preoxided poly-acrylonitrile (PAN) fibers during continuous carbonization were investigated by Raman spectroscopy, XRD, XPS and TG-MS. Results indicate that the sp2 C—C bond length, crystal size and graphitization degree increase. The increase of orientation degree and the decrease of micropore volume are the fundamental reasons for the improvement of density and tensile strength of carbon fibers. Surface and global carbon contents of pre-oxidized PAN fibers, and both low temperature and high temperature carbonized fibers indicate that the loss of non-carbon atoms during carbonization propagates from the exterior to the interior of the fibers. TG-MS indicates that gases are released mainly at low temperature in carbonization. The cross-linking of trapezoid giant molecular chains to release nitrogen takes place at a high temperature during carbonization.

Surface Oxidation of Carbon Fiber and its Influence on the Properties of Carbon Fiber Reinforced BN-Si<sub>3</sub>N<sub>4</sub> Composites

Toray T300 PAN-based carbon fibers were surface oxidized in air at 300, 400 and 500 °C. The composition of surface was determined by X-ray photoelectron spectrometry (XPS), and the monofilaments of original carbon fiber and surface oxidized carbon fibers were tensile tested at room temperature. Three-dimensional carbon fiber reinforced BN-Si3N4 matrix composites were prepared by precursor infiltration and pyrolysis using a hybrid precursor mixed by borazine and perhydropolysilazane. With the increase of the oxidation temperature, the content of size on the surface of fiber reduces, and the tensile strength of carbon fiber declines. Carbon fiber oxidized at 400 °C has a 93% residual strength and the fiber oxidized at 500 °C is seriously decayed. The composite reinforced by original carbon fibers exhibits excellent mechanical properties, including high flexural strength (182.3 MPa) and good toughness; while the composite reinforced by 400 °C oxidized carbon fibers is weak (only 102.4 MPa) and brittle. The distinct difference of mechanical properties between the two composite is attributed to the change of the interfaces between carbon fibers and nitride matrices.

Influence of interfacial chemical reaction for tensile strength of carbon fiber reinforced aluminum-magnesium alloy composites fabricated by ultrasonic infiltration method

Carbon fiber reinforced aluminum alloy composites (CF/Al composites) are expected in aerospace and electric power cable industries due to superior specific strength and specific modulus. But, it is known that CF/Al composites form aluminum carbide (Al4C3) at the interface between carbon fiber and aluminum alloy when CF/Al composites are fabricated. However, effects of type of carbon fiber (PAN, pitch) on growth mechanism of Al4C3 and tensile strength of CF/Al composites have not been clarified. In this study, at first, CF/Al composites are fabricated with ultrasonic infiltration method. Secondary, effects of type of carbon fiber and fabricating time on quantity and size of Al4C3 were investigated. Thirdly, effects of quantity and size of Al4C3 on tensile strength of CF/Al composites were examined. The length of Al4C3 increased with increase in fabricating time for PAN-based composites. It was suggested that the numbers of nucleating sites of Al4C3 increased with an increase in fabricating time for pitch-based composites. As the result, as to the PAN-based composites, it should be controlled less than 100 nm of the length of Al4C3 to inhibit degradation of tensile strength. As to the pitch-based composites, fabricating time should be shorter.

Wettability of carbon fibers modified by acrylic acid and interface properties of carbon fiber/epoxy

The oxidation–reduction and pre-irradiation induced methods were employed to study the effect of acrylic acid modification on the wetting and adsorption ability of carbon fiber (CF) in epoxy solution and the interfacial properties of CF/epoxy. Systematic experimental work was conducted to determine the surface topography, surface energy, surface chemical composition, absorbability and tensile strength of carbon fibers and interfacial adhesion of CF/epoxy before and after modification. The roughness, surface energy, amount of containing-oxygen functional groups and wetting ability were all found to increase significantly after modifications. The tensile strength of carbon fibers was improved marginally by γ-ray pre-irradiation while was decreased little by oxidation–reduction modification. Consequently, the surface modifications of carbon fibers via both oxidation–reduction and pre-irradiation led to an improvement (more than 15%) of the interlaminar shear strength of CF/epoxy composites. The mechanisms of interfacial improvement of modified CF/epoxy composites are proposed.

Strengthening of carbon fibers by a magnetic field imposed in the stabilization and carbonization process

A magnetic field was imposed on the stabilization and the carbonization processes in the fabrication stage of carbon fibers and the effect of the imposed magnetic field on the mechanical strength of fabricated carbon fibers was studied in the relation with the tension imposed in stabilization process. The tensile strength of carbon fibers obtained by heat-treating at 1773 K increased up to approximately 1 GPa by the imposition of a magnetic field, regardless of the values of the imposed tension. The mechanism of strengthening of carbon fibers due to the imposition of the magnetic field has been discussed in the viewpoint of the decrease of defects.

Effect of γ-ray irradiation grafting on the carbon fibers and interfacial adhesion of epoxy composites

A special technique using γ-ray irradiation-induced graft-polymerization was applied to carbon fibers. Epoxy resin and chloroepoxy propane reacted with carbon fibers by a co-irradiation grafting method and acrylic acid was graft-polymerized onto the fiber surface via a pre-irradiation grafting method. The roughness, amount of containing-oxygen functional groups and surface energy were all found to increase significantly after irradiation grafting. Gamma-ray irradiation grafting improved marginally the tensile strength of carbon fibers, which was evaluated by statistical analysis using the Weibull distribution. The interlaminar shear strength of treated carbon fiber/epoxy was enhanced by at least 17.5%, compared with that of untreated carbon fiber/epoxy. The mechanisms of irradiation grafting are proposed by radical reactions. The γ-ray co-irradiation grafting and pre-irradiation grafting are both an effective method for modifying the physicochemical properties of carbon fibers and improving the interfacial adhesion of composites.

Texture and Properties of Acrylonitrile–Ammonium Itaconate Copolymer Precursor Fibers and Carbon Fibers

Acrylonitrile–ammonium itaconate copolymer {P[AN-co-(NH4)2IA]} was fabricated by free-radical solution copolymerization of acrylonitrile (AN) and ammonium itaconate [(NH4)2IA]. The copolymer was confected into a spinning solution (dope) and spun into precursor fibers. Then the precursor fibers were converted to carbon fibers by stabilization and carbonization processes. Another copolymer of acrylonitrile–itaconic acid [P(AN-co-IA)] and its resultant fibers were studied in contrast. Due to preferable hydrophilicity and facilitating cyclization reaction in stabilization process, P[AN-co-(NH4)2IA] fibers could increase the draw-ratio in the spinning process and in the stabilization process to attenuate some property-limiting facts in precursor fibers and carbon fibers. It has been found P[AN-co-(NH4)2IA] precursor fibers gave a 30% improvement in tenacity over P(AN-co-IA) precursor fibers. Results for P[AN-co-(NH4)2IA] precursor fibers carbonized at 1400°C ultimately showed a 26.7% increase in carbon fiber tensile strength over P(AN-co-IA) based carbon fibers. Characterization analysis using scanning electron microscope (SEM), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM) manifested that these improvements are due to fewer surface defects, better interior morphology, higher degree of orientation and graphitization.

A Bootstrap Control Chart for Weibull Percentiles

The problem of detecting a shift of a percentile of a Weibull population in a process monitoring situation is considered. The parametric bootstrap method is used to establish lower and upper control limits for monitoring percentiles when process measurements have a Weibull distribution. Small percentiles are of importance when observing tensile strength and it is desirable to detect their downward shift. The performance of the proposed bootstrap percentile charts is considered based on computer simulations, and some comparisons are made with an existing Weibull percentile chart. The new bootstrap chart indicates a shift in the process percentile substantially quicker than the previously existing chart, while maintaining comparable average run lengths when the process is in control. An illustrative example concerning the tensile strength of carbon fibers is presented. Copyright © 2005 John Wiley & Sons, Ltd.

ゾル‐ゲル法による炭素繊維へのアルミナコーティング

Alumina precursor film was coated on carbon fibers by a sol-gel method using aluminum alkoxide solution. The optimum coating condition for the concentration of alumina alkoxide and silane coupling agent was determined to uniformly coat alumina precursor on carbon fibers. Alumina precursor converted to alumina ceramics by heating at 750 °C. SEM and EPMA showed that alumina ceramics was uniformly coated on carbon fibers. The thickness of alumina layer increased with increasing coating times. The crack and uneven surface was observed on alumina layer when the thickness was over 0.8 μm. Tensile strength of carbon fibers coated by alumina ceramics was higher than that of original carbon fibers.

Influence of heat treatment on physical–chemical properties of PAN-based carbon fiber

The influence of heat treatment at 1400 °C on physical–chemical properties of PAN-based high strength carbon fiber was investigated by means of TG, XRD, XPS as well as the tensile test. The results showed that heat treatment could improve the thermal stability and the degree of graphitization of carbon fiber and decrease the amount of functional groups on the surface. The tensile strength of carbon fiber was not found declined after heat treatment because the change of the microstructure caused by heat treatment was limited.

Influence of tension on the oxidative stabilization process of polyacrylonitrile fibers

AbstractPolyacrylonitrile fibers were heat‐treated in air, and a series of stretching experiments were conducted in different temperature zones. The effects of tension on the microstructure of the heat‐treated fibers and the tensile strength of the resultant carbon fibers were investigated. The results show the variations in morphological characteristics affected by stretching were different as stabilization proceeded. A possible mechanism of tension on cyclization and, thus, stabilization was elucidated. During stabilization, tension at low temperatures led to a great increase in the tensile strength of the carbon fibers, whereas tension at high temperatures resulted in only small improvement in the tensile strength of the carbon fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1029–1034, 2005

Size effect on the fiber strength of composite pressure vessels

In this study, experimental tests and an analytical approach are conducted to verify the size effect on the fiber strength of a composite pressure vessel. As an analytical method, the Weibull weakest link model and the sequential multi-step failure model are considered and mutually compared. In the case of carbon fiber tensile strength, there is no large difference between the analytical methods for the volumetric size effect. To verify the validity of the analytical approach, experimental tests were performed using fiber strand specimens, unidirectional laminate specimens and composite pressure vessels. Good agreement for fiber strength distribution was shown between the test data and predicted results. The volumetric size effect shows the clearly observed tendency towards fiber strength degradation with increasing stressed volume. Because the volumetric size effect depends on material and processing factors, the reduction of fiber strength due to the stressed volume shows different values according to the variation of material and processing conditions.