T300 Carbon Research Articles

Multichannel hollow carbon fibers: Processing, structure, and properties

Multifilament continuous hollow carbon fiber tows with a honeycomb cross-section have been produced using a gel-spun bicomponent islands-in-a-sea precursor with polyacrylonitrile (PAN) as the sea component and polymethylmethacrylate (PMMA) as the sacrificial island component. The density of the hollow carbon fibers is 1.15 g/cm3, more than 30% lower compared to commercial carbon fibers. The tensile strength of these fibers is in the range of 2.3–3.0 GPa and tensile modulus between 202 and 234 GPa. The tensile strength is over 80% higher than the 1.6 GPa strength value reported earlier for hollow carbon fibers. The specific tensile strength is 30% higher than T300 carbon fibers. The specific tensile modulus is 60% higher than T300 carbon fibers and 20% higher than aerospace grade IM7 carbon fibers. The manufacturing was successfully scaled up from a single filament to 740 filament tow without affecting the carbon fiber structural parameters. The tensile strength is limited by the size of the largest defects present, estimated to be in the range of 40–65 nm for the hollow carbon fibers.

Study on the damage behavior of carbon fiber composite after low‐velocity impact under hygrothermal aging

AbstractIn this article, T800 carbon fiber/epoxy resin composite was subjected to hygrothermal aging. By analyzing the mass change, surface morphology before and after aging, infrared spectra, and dynamic mechanical properties, the effect of hygrothermal aging on the composite properties was studied. The hygrothermal aging of the composite after low‐velocity impact, the effects of environmental factors on the damaged area, and the post‐impact compression properties of composites were studied. The results showed that the saturation moisture absorption rate of the composite after aging (71°C constant temperature) was 0.88%. Upon increasing the impact energy, an indentation appeared before the inflection point at 35 J. When the impact energy was less than 15 J, aging did not affect invisible damage. Above this, the damaged area and number of internal cracks and defects in the composite were increased. After aging, the compressive strength of composite laminates with impact damage decreased obviously. During the aging stage, the residual compressive strength of the sample was the lowest in the moisture saturated state, and hygrothermal aging had little effect on the compression failure mode after impact.

The Design and Calculation of the Exoskeleton Backplate Based on the Composite Sandwich Structure

Aiming at the problem of heavy mechanical structure of the exoskeleton backplate, a lightweight backplate of T700 carbon fiber reinforced hollow glass microspheres/epoxy composite based on sandwich structure is proposed in this paper. By analyzing the influence of the thickness of face layer and core layer on the mechanical properties of composite sandwich structure, a composite backplate structure with face layer thickness of 4mm and core layer thickness of 8mm is designed. The simulation calculation and test of the sandwich backplate were carried out. The results show that the error between the simulation results and the experimental values is small, and the reliability of the results is high, which provides more lightweight design of the exoskeleton backplate.

Quasi-static compression and hygrothermal stability of BMI/CE co-cured composite lattice cylindrical shell

Composite lattice cylindrical shell is a typical lightweight structure, which has been widely used in aerospace structures in recent years. In this paper, combined with the high temperature resistance of bismaleimide (BMI) resin and the dimensional stability of cyanate ester (CE) resin, it is proposed to cure T800 carbon fiber/CE composite composed grid and T800 carbon fiber/BMI composite composed skin at one time. The stability of shell height, out-of-roundness and axial pressure resistance of T800/BMI shell, T800/CE shell and T800/BMI-CE shell under hygrothermal conditions are compared and analyzed by experiment and simulation, and the mechanism and feasibility of this design method are verified and discussed.

Acoustic Emission Testing of Early Generation of Defects in CFRP Samples under Static and Thermal Loading

Static tests of the samples of Torayca T700, T800 carbon fiber reinforced plastics consisting of nine monolayers with $$\left[ { \pm 45{\text{/}}90{\text{/}}{{0}_{3}}{\text{/}}90{\text{/}} \pm 45} \right]$$ stacking and geometric dimensions $$600 \times 100 \times 0.9$$ mm and $$500 \times 100 \times 1.4$$ mm were carried out. In the process of static and thermal loading, defects were monitored by the acoustic emission (AE) method. Two samples were statically loaded and simultaneously exposed to temperature $$T = 100$$ °C. Six samples were statically loaded at temperature $$T = 20$$ °C. The sources of AE signals corresponding to sample material destruction were localized in real time. For these signals, thin polished sections were prepared from location zones in the sample, and the fractography of the CFRP material was carried out. The analysis of the recorded AE information has been carried out. The main informative parameters of the AE signals localized in the working area of the samples are considered. Using cluster analysis by digital waveform, three types of clusters are identified for the AE signals. For the first type of clusters, the frequency of AE signals exceeded 175 kHz, and a relatively high level of the MARSE energy parameter was noted. In clusters of the second type, AE signals recorded under static loading and sample heating had lower MARSE values and a median frequency not exceeding 170 kHz. When testing samples with no heating, the median frequency did not exceed 140 kHz. The third type of clusters was formed by AE signals with the frequency not exceeding 400 kHz. Such clusters were typical only for samples tested at temperature $$T = 20$$ °C.

Preparation and properties of propargyl ether-terminated poly(imide siloxane)s and their composites

The novel propargyl ether-terminated oligo(imide siloxane)s (PTISs) based on 2,2’-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), aminopropyl-terminated polydimethylsiloxane (APPS), 4,4’-diaminodiphenylmethane (MDA) and p-aminophenyl propargyl ether (APPE) were synthesized. The chemical structures of PTISs were characterized by proton nuclear magnetic resonance (1H NMR) and Fourier transform infrared spectroscopy (FTIR). The PTISs exhibited excellent solubility in organic solvent and had broad processing window. The T300 carbon fabric was used to reinforce the PTIS matrices and prepare the composites (T300CF/PTISs). The thermal stability of the cured PTISs was analyzed by thermogravimetric analysis (TGA). The dynamic thermal mechanical properties of the composites were measured by dynamic thermomechanical analysis (DMA). The results show that the temperature at 5% weight loss (Td5) and residual yield at 800°C (Yr800°C) of the cured PTISs in N2 increase with incorporation of the aromatic diamine, whereas the Yr800°C of the cured PTISs in air decreases with introduction of the aromatic diamine. The elasticity of the composite increases with incorporation of the aromatic diamine, and the peak temperature of loss factor for the composites are higher than 300°C. The flexural strength, tensile strength and interlaminar layer shear strength (ILSS) of the T300CF/PTIS composite display the values of 439 MPa, 427 MPa and 32 MPa at room temperature, respectively. The retention of the flexural strength and ILSS for the T300CF/PTIS composite are above 80% at 250°C.

Nonlinear vibration analysis of fiber reinforced composite cylindrical shells with partial constrained layer damping treatment

This research proposes a novel analytical model capable of accurately predicting the strain-dependent characteristics of fiber reinforced composite shells (FRCSs) with partial constrained layer damping (CLD) treatment by considering the nonlinearities of fiber reinforced composite and viscoelastic materials simultaneously. The nonlinear material properties are represented based on Jones-Nelson nonlinear theory, energy-based strain energy method, and complex modulus method. Then, the governing equations of motion for FRCSs are developed via Ritz method, and the identification procedure of nonlinear fitting parameters is also presented. By taking a T300 carbon fiber/epoxy resin cylindrical shell with partial CLD patches as an example, a series of experiments are carried out to validate the proposed modeling approach. Finally, the effects of material properties on nonlinear vibration behaviors of FRCSs covered with partial CLD patches are evaluated. Comparisons show that the proposed nonlinear model is more accuracy than that without considering strain dependence, where the maximum errors between the proposed model and measured data for natural frequencies, damping ratios and resonant response are 6.9%, 11.3%, and 11.2%, respectively.

Study on mode-I fracture toughness of composite laminates with curved plies applied by automated fiber placement

Interlaminar fracture toughness is an important parameter to characterize the delamination performance of carbon fiber-reinforced epoxy laminates. In this study, the mode-I fracture toughness of interlaminar interfaces with different local ply angles were studied by experiments and numerical simulations. A set of double cantilever beam specimens of T800 carbon fiber/EH104 epoxy were prepared according to the ASTM-D5528–01 standard, where four specimens had straight ply interfaces (0°//0°, 15°//−15°, 30°//−30°, and 45°//−45°) and two specimens had curved ply interfaces (curvature radius: 300 and 500 mm). The mode-I fracture toughness was characterized using a data reduction scheme based on the modified beam theory. The results revealed that the mode-I fracture toughness values for the specimens with a curved ply interface were significantly higher than those for specimens with a straight ply interface.

Melt fluidity and thermal property of thermosetting siloxane-containing polyimide resins and their organic/inorganic hybrid characteristics

A series of thermosetting siloxane-containing polyimide resins were synthesized by incorporating of bis(p-aminophenoxy)dimethylsilane or bis(p-aminophenoxy)tetramethyldisiloxane with various concentrations into formulated oligoimides. These thermosetting polyimide resins exhibited good combination of processability and thermal resistance. It was found that siloxane-containing oligoimides provided significant advantages over unmodified oligoimides, relative to melt fluidity and processing window, due to the flexibility of D[(CH3)2SiO2/2] siloxy units. The siloxane-containing polyimide resins cured at 380 °C revealed relatively higher glass transition temperatures (Tg) than that of unmodified polyimides, despite the incorporation of flexible siloxane segment in oligoimides. Dynamic mechanical analysis and microstructure investigation suggested that some D[(CH3)2SiO2/2] siloxy units in the surface layer of polyimide transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units in the curing procedure besides crosslinking of phenylethynyl groups, due to oxidation crosslinking of siloxane. That led to inorganic silica-like structures formed in situ, and inter-connected by organic polyimide segments. This organic/inorganic hybrid characteristics endowed polyimide resins with enhanced thermal property. After post-curing at 450 °C, D[(CH3)2SiO2/2] siloxy units completely transformed into T[CH3SiO3/2] and Q[SiO4/2] siloxy units, and the polyimide reins gave the Tg even exceeding 550 °C. Meanwhile, the corresponding T700 carbon fiber reinforced composite presented excellent mechanical property and durability at the temperature as high as 500 °C.

Effect of the Aluminum Matrix on Tensile Properties of Carbon Fiber/Al Composites Prepared by Liquid Extrusion Infiltration

Two-dimensional T300 carbon fiber-reinforced aluminum alloy matrix (2D CF/Al) composites were prepared by the liquid extrusion infiltration (LEI) process with the matrices of 6061Al and ZL102 alloys. Scanning electron microscopy (SEM) detected a satisfactory infiltration effect for both composites. The fiber distribution was uniform, and casting microdefects were not revealed. Transmission electron microscopy (TEM) analysis disclosed the matrix-carbon fibers interface reaction, the brittle Al4C3 phase. Al4C3 sizes were found to be about 150 and 400 nm in 2D CF/6061Al and 2D CF/ZL102 composites, respectively, the interface reaction of a ZL102 matrix was more pronounced. As compared to pure cast alloys, the ultimate tensile strength increased by 134.5. SEM analysis of the tensile specimen fracture demonstrated that the fracture of a 2D CF/6061Al composite was reasonable and for a 2D CF/ZL102 composite it was via the brittle mode, these were caused by the interface bonding.

Simple carbon fiber graphitization device for in-situ measurement of small angle X-ray scattering (SAXS)

A small and simple device for the in-situ small angle X-ray scattering (SAXS) measurement of carbon fibers graphitization by direct electrical heating was developed. The graphitization process of polyacrylonitrile-based T700 carbon fibers from 1450 °C to 2100 °C with this device was followed in-situ by synchrotron radiation SAXS. The results show that there are needle-shaped voids oriented preferentially along the fibers axis with a surface fractal structure during graphitization of carbon fibers. The change in the fractal dimension as a function of temperature includes a dip with a minimum value at approximately 1700 °C. This short contribution briefly describes the device and analyzes the obtained experimental results.

Mode I fracture toughness of hybrid co-cured Al-CFRP and NiTi-CFRP interfaces: An experimental and computational study

In the spirit of advancing joining concepts as well as adoption of hybrid composites, the interface of a metallic foil and carbon fabric reinforced polymer matrix composite was explored experimentally and computationally. An out-of-autoclave manufacturing method, double-infusion VARTM, was successfully employed to create a hybrid composite laminate that was composed of a layer of metal foil (Al or NiTi) placed at the center of sixteen layer plain weave T300 carbon fabric with epoxy Epikote-Epikure 04908 matrix. The fracture behavior was obtained via the Double Cantilever Beam (DCB) tests at room and elevated temperatures and were monitored on-line using Rayleigh backscattering fiber optics technique. Distributed strain profiles were measured on both at the top and bottom surfaces of the specimen to validate/assist computational models. This new technique to measure distributed strains in-situ during testing has introduced a new dimension to the visualization of strain energy release upon crack propagation.The virtual crack closure method was employed to simulate crack propagation at the hybrid interface. The experimental results revealed the dominant mode of failure as cohesive. Load-displacement and strain profiles measured from the experiments were in good agreement with the numerical results. The foremost research highlight is the novel integration of computational simulation with fiber optics Distributed Strain System (DSS) in DCB experiments to elucidate crack growth at a hybrid interface.

Uncertainty in Fibre Strength Characterisation Due to Uncertainty in Measurement and Sampling Randomness

Carbon fibres have exceptional mechanical properties and are used for critical structural applications such as composite pressure vessels and aerospace components. For such high performance applications, reliability-based designs and lifetime assessments require very accurate strength models. Accuracy of the predictions made by composite strength models depend on realistic material properties of constituents, which are used as input. In practice however, fibre strength properties reported by different sources show significant variations. The work described here aims at understanding the influence of measurement uncertainty and sampling randomness on the uncertainty in calculated tensile strength distribution parameters. Tensile strength data for T700 carbon fibres obtained from single fibre testing process has been analysed for uncertainties. A parametric bootstrap method has been used for the evaluation. It has been shown that although both the causes studied of uncertainty are critical, the sampling randomness has a larger influence on the uncertainty of fibre strength, as compared to the uncertainty due to measurement. Choosing an insufficient sample size for analysis can thus result in uncertain or even inaccurate fibre strength properties, which would limit the reliability of composite strength models. The knowledge of the causes and effects of these uncertainties can help in taking appropriate measures for improving the accuracy of results. This would thereby enhance the capability of composite strength models to estimate the behaviour of different composite structures more accurately.

Prediction of Manufacturing Quality of Holes Based on a BP Neural Network

In order to improve the manufacturing quality of holes (Φ3–Φ8 mm) and to optimize the hole drilling process in T300 carbon fiber-reinforced plastic (CFRP) and 7050-T7 Al alloy stacks, a prediction model of multiple objective parameter optimization was proposed based on a back propagation (BP) neural network algorithm. Four parameters of feed rate, spindle speed, drilling diameter, and cushion plate were taken as the input layer parameters to study the manufacturing quality of holes in four stack types: CFRP/Al, Al/CFRP, Al/CFRP/Al, and CFRP/Al/CFRP. Delamination and tearing defects often appear in the drilling process; thus, a certain degree of defects in CFRP was selected as the output parameter, in an effort to build a prediction model of drilling quality. After the neural network model of the optimized hole-making process of an 8–14–1 three-layer topology was corrected by 170 steps, the error was reduced to 0.00016882, the regression fitting was 0.99978, and the fitting error of training samples was 10−2~10−5. The prediction model of the number of defective holes provided basically similar results to the experimental data. This indicates that the prediction model based on a BP neural network has good prediction ability. Based on the prediction of parameters, verification tests were performed, and the number of defective holes in CFRP was reduced while the manufacturing quality of the holes was improved significantly; the qualified rate of manufactured holes reached 97%.

Mode II fracture toughness related to ply angle for composite delamination analysis

Inter-laminar fracture toughness is an important parameter to characterize the delamination propagation performance of composite laminates. Compared with the mode I fracture, the results of mode II fracture behavior are limited. In this study, the effect of varying ply angle on the mode II delamination behavior of carbon/polymer was studied. T800 carbon fiber/EH104 epoxy resin laminates with different ply interfaces were prepared and tested according to ASTM D7905 standard. Four kinds of straight ply interfaces (0°//−0°, 15°//−15°, 30°//−30°, and 45°//−45°) and two kinds of curved ply interfaces with the curvature radius of 300 mm and 500 mm were considered. The fracture toughness G IIC of different ply interfaces was obtained by compliance method. The experimental results revealed that the mode II toughness of the variable angle ply interface is significantly larger than that of the straight ply interface. The mode II delamination behavior was characterized by finite element model with a bilinear traction separation law and was validated by the experimental data.

A comparative study of two kinds of T800 carbon fibers produced by different spinning methods for the production of filament-wound pressure vessels

A comparative study of two kinds of T800 carbon fibers produced by different spinning methods for the production of filament-wound pressure vessels

Effect of sizing agent on carbon fiber density measurements using a floatation method

The density of T300 carbon fiber, as well as the amount of sizing and micro-structure were measured, before and after removing the sizing. The results showed that there was apparent stratification when measuring the density of the carbon fiber by the sink/float method, without removing the sizing. The upper sample layer was seriously flocculated with an excessive sizing amount of 2.17%, while the bottom-layer also flocculated. Two methods including acetone extraction and pyrolysis, were conducted to removing the sizing. It was shown that the measured amounts of sizing for the two methods were 1.20% and 1.53%, respectively. For the sample after immersion in acetone, there was still stratification in the sink/float test, with the upper sample layer flocculated because of the remaining sizing; while samples at the bottom dispersed relatively well. However, for the thermally treated samples the sizing was adequately removed, which resulted in the uniform density and dispersion during the test. This indicates that the non-uniform distribution of sizing agent on the surface of the CFs is the main reason for stratification during the density measurement. Therefore, the sizing must be fully removed in order to obtain an accurate density for the carbon fibers. Moreover, it can be seen that pyrolysis is an effective way to remove the CF sizing agent.

Acoustic emission-based real-time monitoring of fatigue damage evolution of T800 carbon fiber/bismaleimide composites

For the damage mode recognition in the fatigue coupon test of T800 carbon fiber/bismaleimide, the acoustic emission is employed. However, the latter application is hindered by noises produced by various environmental factors, which may suppress damage-induced ones. In this study, external noises are effectively reduced by the absorbing adhesive. For damage mode recognition, an integrated strategy is proposed, which features a combination of a characteristic signal extraction and damage mechanism analysis via piezoelectric and fiber Bragg grating sensors. The final verification shows that the different damage modes of the composite specimen can be clearly distinguished based on this method.

Effects of aging process and testing temperature on the open-hole compressive properties of a carbon fiber composite

The properties of T800 carbon fiber–epoxy composite specimens with a hole were studied in terms of mass change, scanning electron microscopy, glass transition temperature ( T g), heat-resistant temperature, Fourier-transform infrared (FTIR) spectroscopy, open-hole compressive strength at different temperatures, and stereomicroscopic observations after being subjected to hygrothermal aging and thermal-oxidative aging processes. FTIR spectra indicated that after hygrothermal aging at 70°C and 85% relative humidity (RH), chemical aging did not occur, whereas after thermal-oxidative aging at 190°C, the specimens exhibited chemical aging. The unaged specimens had a T g of 229°C and an extreme heat-resistant temperature T gmod of 184°C; after hygrothermal aging, the specimens had a T g and T gmod of 207°C and 143°C, respectively; and after thermal-oxidative aging, the specimens had a T g and T gmod of 252°C and 215°C, respectively. The effects of temperature on open-hole compressive strength were evaluated at room temperature of 23°C, 50°C, 100°C, 150°C, and 200°C. The compressive strengths of the specimens decreased after aging and with the increasing test temperature. At the highest test temperature, the unaged specimens, hygrothermal-aged, and thermal-oxidative-aged specimens retained over 73.7%, 65.5%, and 67.9%, respectively, of their compressive strength. Thus, the T800 carbon fiber–epoxy composite evaluated in this study exhibited good resistance to the effects of aging and high temperature. These results should be beneficial to the understanding of the long-term performance of composites.

Strengthening in MgLi matrix composites reinforced with unidirectional T300 and Granoc carbon fibres

Strengthening in MgLi matrix composites reinforced with unidirectional T300 and Granoc carbon fibres