A comparison of the interfacial, thermal, and ablative properties between spun and filament yarn type carbon fabric/phenolic composites

In the present paper, the interfacial, thermal, and ablative properties of phenolic composites reinforced with spun yarn type carbon fabrics (spun C/P composite) and filament yarn type carbon fabrics (filament C/P composite) heat-treated at 1100 °C have been extensively compared. The interlaminar shear strength, crack growth rate, and fracture surface were studied to evaluate the interfacial characteristics of the composites using short-beam shear test, double cantilever beam test, and scanning electron microscopy, respectively. The thermal conductivity and the coefficient of thermal expansion were also measured in the longitudinal and transverse directions, respectively. To explore the ablative characteristics of the composites in terms of insulation index, erosion rate, and microscopic pattern of ablation, an arc plasma torch was used. The interfacial properties of the spun C/P composite are significantly greater than those of the filament C/P composite, with qualitative support of fracture surface observations. It has been investigated that the presence of protruded fibers in the phenolic matrix of the spun C/P composite may play an important role in enhancing the properties due to a fiber bridging effect. The longitudinal thermal conductivity of the spun C/P composite is about 7% lower than that of the filament C/P counterpart. It has been found from the ablation test using arc plasma torch flame that the erosion rate is 14% higher than that of the filament C/P counterpart. Consequently, all the experimental results suggest that use of spun yarn type carbon fabrics heat-treated at low carbonization temperature as reinforcement in a phenolic composite may significantly contribute to improving the interfacial, thermal, and ablative properties of C/P composites.     

Electrical and thermal conductivities of polyethylene composites filled with biaxial oriented short-cut carbon fibers

Polyethylene composites filled with various types of carbon fiber were prepared for electrical and thermal conductivity measurements. By estimation of the anisotropic parameter (Hermans' parameter), the fibers were confirmed to be significantly biaxially oriented in the composites. The critical volume fractions in the electrical conductivity of these composites for the two oriented directions (X and Y) were equal to each other and smaller than that for a direction (Z) vertical to the above. The electrical anisotropy, i.e., ratio of electrical conductivity of the composite for the Z direction to the X and Y directions varied drastically with increase in filler content. The longer the length of carbon fiber was, the higher became the electrical conductivity of the biaxially oriented carbon fiber composites for all directions. But, the thermal conductivity of the composite was almost unchanged for the Z direction, even if fiber length was sufficiently long. Our equation, previously proposed, proved adaptable to these thermal conductivities. The factors of C_p and C_f in the equation are kept unchanged, in spite of increasing fiber length. © 1994 John Wiley & Sons, Inc.     

Mechanical, thermal and ablative properties of interply continuous/spun hybrid carbon composites

The mechanical and thermal properties of interply hybrid carbon fiber (continuous and spun fabric)/phenolic composite materials have been studied. Hybrid carbon/phenolic composites (hybrid CP) with continuous carbon fabric of high tensile, flexural strength and spun carbon fabric of better interlaminar shear strength and lower thermal conductivity are investigated in terms of mechanical properties as well as thermal properties.Through hybridization, tensile strength and modulus of spun type carbon fabric reinforced phenolic composites (spun CP) increased by approximately 28% and 20%, respectively. Hybrid CP also exhibits better interlaminar shear strength than continuous carbon fabric/phenolic composites (continuous CP).The in-plane thermal conductivity of hybrid CP is 4-8% lower than that of continuous CP. As continuous filament type carbon fiber volume fraction increases, the transversal thermal conductivity of hybrid CP decreases.The erosion rate and insulation index were examined using torch test. Spun CP has a higher insulation index than continuous CP and hybrid CP over the entire temperature range. Hybrid CP with higher content of spun fabric exhibits higher insulation index as well as lower erosion rate.     

Enhancing the thermal conductivities of SiO2/Epoxy composites by orientation

To improve the thermal conductivity of epoxy resin, tensile way was used to orient the molecular chain of epoxy resin with SiO₂ particles filled. In this article, SiO₂/Epoxy composites which had approximately one‐dimensional lattice structure were prepared. The heat generated by LED chip rapidly passed along the direction of the one‐dimensional orientation in SiO₂/Epoxy composites. The results showed that the thermal conductivity of oriented composites increased with the increase of silica concentration and draw ratio (If S is the cross‐sectional areas of composites at the mold outlet, S₀ is the cross‐sectional areas of composites after molding set, and draw ratio is S/S₀). With the addition of 50 wt% SiO₂ to the epoxy resin, the thermal conductivity of oriented SiO₂/Epoxy composites with the draw ratio of 4 was 0.873 W/m K, which was 2.55 times that of unoriented SiO₂/Epoxy composites. And a thermal conductivity, 5.97 times that of the epoxy resin, was obtained with 80 wt% SiO₂ and the draw ratio of 4. Nevertheless, the relative permittivities of epoxy composites which had 50 wt% SiO₂ with the draw ratio of 4 are stable with increasing frequency. POLYM. COMPOS., 37:818–823, 2016. © 2014 Society of Plastics Engineers     

Measuring thermal conductivities of anisotropic synthetic graphite–liquid crystal polymer composites

In this study, synthetic graphite particles were added to a liquid crystal polymer and the resulting composites were tested for both the through‐plane thermal conductivity k_thru and the in‐plane thermal conductivity k_in using the transient plane source method. The end use application for these composites is in fuel cell bipolar plate fabrication. The goal of this work was to expand upon a previously developed simple empirical model for the in‐plane thermal conductivity, which is easily measured with the transient plane source method. The results show that the square root of the product of the through‐plane and in‐plane thermal conductivities is an exponential function of the volume percent of filler, ϕ. As the through‐plane thermal conductivity of these composites is accurately predicted with a modified Nielsen model, this empirical relationship can be used to estimate in‐plane thermal conductivities for a range of applications. POLYM. COMPOS., 27:388–394, 2006. © 2006 Society of Plastics Engineers     

Super-elastic carbon-bonded carbon fibre composites impregnated with carbon aerogel for high-temperature thermal insulation

A novel super-elastic carbon fibre composite was prepared by impregnating carbon aerogel into carbon-bonded carbon fibre (CBCF) through vacuum impregnation. The compressive strength of CBCF-CA was increased to 1.24?MPa in the z-direction, which was 6-fold more than that of neat CBCF. The CBCF-CA spontaneously recovered its size and shape without significant deformation when the pressure was released. The thermal conductivity of CBCF-CA was 0.246?W?(m·K)^?1 at 1400°C in the z-direction, which is lower than that of CBCF (0.341?W?(m·K)^?1). The average electromagnetic interference shielding e?ectiveness of CBCF-CA composites in the range of 12.4–18?GHz was higher than 40?dB, suggesting an absorption-dominant shielding feature. The CBCF-CA composite will be a new multifunctional material due to its low density, low thermal conductivity, high specific strength, excellent processability, super-elastic property and high electromagnetic shielding, which can be used for thermal insulation and protection of aerospace.     

Mechanical and thermal properties of polypropylene/modified basalt fabric composites

Basalt fabric (BF) was first treated with silane coupling agent KH550, modified basalt fabric (MBF) was obtained. Then MBF were molded with polypropylene (PP) matrix, and polypropylene/modified basalt fabrics (PP/MBF) composites were obtained. The influence of concentration and treating time of KH550 on MBF were characterized by hydrophilicity and lipophilicity. The tensile strength and morphology of basalt fabric were tested by single filament strength tester and scanning electron microscopy. The mechanical properties of composites were measured with electronic universal testing machine and impact testing machine, and the thermal properties were tested by thermogravimetric analysis and dynamic mechanical analysis. The results showed that the lipophilicity of MBF is improved significantly by KH550 while the tensile is nearly damaged. The mechanical properties of composites are larger than that of pure PP, among which the impact property was improved the most, showing 194.12% enhancement. The thermal stability and dynamic viscoelasticity were better than pure PP; furthermore, the concentration of KH550 virtually had no effect on the thermal stability. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42504.     

Effect of carbon fabric type on the mechanical performance of 2D carbon/carbon composites

A stabilized PAN fabric was carbonized and graphitized from 800°C to 2500°C. Two-dimensional (2D) carbon/carbon composites were made using the stabilized PAN fabric, carbonized fabrics, and a resol-type phenol-formaldehyde resin. These composites were heat-treated from 600°C to 2500°C. The influence of different heat-treated fabrics and heat treatment on the fracture and flexural strength of these composites was also studied. The composite reinforced with higher heat-treated fabrics showed a lower weight loss than that with lower heat-treated fabrics. When the composites were graphitized at 2500°C, the loss was 49.7 wt% for the composite made with stabilized PAN fabric and 26 wt% for that with carbonized fabric at 2500°C. Those composites also have a higher density than composites produced by other methods. Composites made with stabilized PAN fabric exhibited a strong bonding in the fiber/matrix during pyrolysis. This composite showed catastrophic fracture and a smooth fracture surface with no fiber pullout. Composites made with higher carbonized fabrics exhibited a weak interface bonding. These composites showed a pseudo-plastic fracture pattern with fiber pullout during pyrolysis. Composites made with carbonized fabrics at 2000°C and 2500°C showed the highest flexural strength at the prolysis temperature of 1000°C. Composites made with carbonized fabric at 1300°C showed the highest flexural strength above 1500°C to 2500°C. The composite made with stabilized PAN fabric exhibited the lowest flexural strength during pyrolysis.     

Dispersion and thermal conductivity of carbon nanotube composites

A mechanical method was used to shorten carbon nanotubes (CNTs) for improving dispersion without reducing their thermal conductivity. Single walled carbon nanotubes (SWCNTs) were mechanically cut to produce short and open-ended fullerene pipes. These shortened SWCNTs were then used in polymer composites. Both atomic force microscopy and scanning electron microscopy characterizations suggested that nanotube shortening significantly improved CNT dispersion. Thermal conductivity of composites containing short CNTs were found to be much better than those containing pristine CNTs.     

Nielsen thermal conductivity model for single filler carbon/polypropylene composites

In this study, three different carbon fillers (Thermocarb TC‐300 synthetic graphite, Ketjenblack EC‐600 JD carbon black, and Hyperion Catalysis International's FIBRIL? carbon nanotubes) were added to a polypropylene matrix to produce single filler composites with filler concentrations of up to 80 wt % synthetic graphite (61.6 vol %), 15 wt % carbon black (8.1 vol %), and 15 wt % carbon nanotubes (7.4 vol %). The through‐plane thermal conductivity for each formulation was measured. For the synthetic graphite, carbon black, and carbon nanotubes composites, the Nielsen model was applied to the experimental through‐plane thermal conductivity data. The Nielsen Model presented in this work showed very good agreement with experimental data. The model parameters were similar to those used in the literature for these fillers in other polymers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The contribution of thermal stresses to the failure of Kevlar fabric composites

The mismatch in thermoelastic properties between fiber and matrix in Kevlar 49 fabric-epoxy composites is shown to result in significant thermal stresses with cool down from processing temperatures. Cooling generates local transverse tensile stresses that can potentially initiate microcracking at ambient conditions. A temperature reduction also places the curved fiber in the fabric composite in axial compression. This compression adds to the bending strain in the fiber, resulting in significant local reduction of its inherently low compressive load-bearing capability. The combination of thermal stresses and external compressive loads that are below ultimate values can cause local compressive failure of the fiber. The kink bands formed as a result of compressive failure of Kevlar fiber are expected to cause debonding between fiber and matrix and, therefore, are also potential sites for crack initiation. Thus, thermal stresses can contribute to the initiation of at least two damage mechanisms that may severely limit the compressive and flexural fatigue strength of Kevlar fabric composites at and below ambient temperature.     

再生聚酯直纺涤纶工业丝成套设备技术探讨

采用回收聚酯(PET)瓶片,通过液相增黏直接纺丝生产涤纶工业丝,探讨了再生聚酯直纺涤纶工业丝的成套设备和工艺技术。结果表明:对干燥设备和螺杆挤压机进行改造,利用双级熔体预过滤器和液相增黏系统,聚酯瓶片再生增黏后特性黏数可达(0.85±0.01)dL/g;该成套设备的关键是采用单轴式液相增黏反应器;调整纺丝和拉伸工艺,直接纺丝生产的涤纶工业丝线密度为1 189 dtex,断裂强度为7.98 cN/dtex,断裂伸长率为14.66%,达到了常规固相增黏法生产的涤纶工业丝的性能指标。     

Thermophysical properties of carbon/carbon composites and physical mechanism of thermal expansion and thermal conductivity

Five different carbon/carbon composites (C/C) have been prepared and their thermophysical properties studied. These were three needled carbon felts impregnated with pyrocarbons (PyC) of different microstructures, chopped fibers/resin carbon + PyC, and carbon cloth/PyC. The results show that the X-Y direction thermal expansion coefficient (CTE) is negative in the range 0-100 °C with values ranging from −0.29 to −0.85 × 10⁻⁶/K. In the range 0-900 °C, their CTE is also very low, and the CTE vs. T curves have almost the same slope. In the same temperature range composites prepared using chopped fibers show the smallest CTE values and those using the felts show the highest. The microstructure of the PyC has no obvious effect on the CTE for composites with the same preform architecture. Their expansion is mainly caused by atomic vibration, pore shrinkage and volatilization of water. However, the PyC structure has a large effect on thermal conductivity (TC) with rough laminar PyC giving the highest value and isotropic PyC giving the lowest. All five composites have a high TC, and values in the X-Y direction (25.6-174 W/m K) are much larger than in the Z direction (3.5-50 W/m K). Heat transmission in these composites is by phonon interaction and is related to the preform and PyC structures.     

Erosive wear of carbon fabric reinforced polyetherimide composites: Role of amount of fabric and processing technique

Plain weave carbon fabric (CF) reinforced Polyetherimide (PEI) composites, hereafter referred to as CF‐PEI composites, containing 40, 55, 65, 75, and 85 vol% of CF were developed using impregnation technique and compression moulding. An additional CF‐PEI composite containing 52 vol% of CF was also fabricated using film technique and compression moulding. These composites were developed in order to explore the effect of fabric content and processing technique on strength properties and erosive wear performance of PEI. These six composites along with unfilled PEI were evaluated for their physical and mechanical properties. The erosive wear performance of these materials was evaluated using angular silica particles as erodent at an impingement angle of 30°. It was observed that fabric content strongly influenced the strength properties as well as erosion resistance. Strength performance, however, did not linearly increase with increase in fabric content. Lowest (40%) and highest (85%) amount of fabric proved least effective in this regard. Similar observations were observed in the case of wear resistance (W_R). CF in the range of 55–75 vol% proved optimum for strength properties and wear performance barring PEI, which showed highest W_R. Between the two processing techniques, impregnation technique (I) proved far superior to the film technique (F) in both strength and wear performance. A fairly good correlation was observed between erosion resistance and a product of interlaminar shear strength, resilience, and elongation. SEM studies on worn surfaces supported the wear behavior. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Pitch-based ribbon-shaped carbon-fiber-reinforced one-dimensional carbon/carbon composites with ultrahigh thermal conductivity

Ribbon-shaped carbon fibers have been prepared from mesophase pitch by melt-spinning, oxidative stabilization and further heat treatment. The internal graphitic layers of ribbon-shaped carbon fibers graphitized at 2800 °C show a highly preferred orientation along the longitudinal direction. Parallel stretched and unidirectional arranged ribbon-shaped carbon fibers treated at about 450 °C were sprayed with a mesophase pitch powder grout, and then hot-pressed at 500 °C and subsequently carbonized and graphitized at various temperatures to produce one-dimensional carbon/carbon (C/C) composite blocks. The shape and microstructural orientation of ribbon fibers have been maintained in the process of hot-pressing and subsequent heat treatments and the main planes of the ribbon fibers are orderly accumulated along the hot-pressing direction. Microstructural analyses indicate that the C/C composite blocks have a typical structural anisotropy derived from the unidirectional arrangement of the highly oriented wide ribbon-shaped fibers in the composite block. The thermal conductivities of the C/C composites along the longitudinal direction of ribbon fibers increase with heat-treatment temperatures. The longitudinal thermal conductivity and thermal diffusivity at room temperature of the C/C composite blocks graphitized at 3100 °C are 896 W/m K and 642 mm²/s, respectively.     

Improvement of carbon fiber/PEEK hybrid fabric composites using plasma treatment

A carbon fiber (CF)/polyetheretherketone (PEEK) composite was manufactured using hybrid fabrics composed of CF and PEEK fiber. The fiber/matrix interface was modified by low temperature oxygen plasma treatment. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform attenuated total reflection infrared spectroscopy (FTIR-ATR) were used to relate the roughness and the functionality of the CF surface with the interfacial adhesion strength of the CF/PEEK composite. Scanning electron micrographs showed that plasma treatment increased the roughness of the CF surface up to 3 min of plasma treatment time; and prolonged treatment resulted in overall smoothing. XPS results confirmed that increasing treatment time marginally increased surface functionality: treatment for more than 5 min decreased the surface functionality by removing the active site of the CF surface. In addition, flexural strength and interlaminarshear strength (ILSS) of the CF/PEEK composite were measured. Their maximum values were observed at 3 min of plasma treatment time as a result of surface roughening by plasma etching. The SEM results were correlated with mechanical properties of the CF/PEEK composite.     

The use of carbon nanofibers for thermal residual stress reduction in carbon fiber/epoxy laminated composites

Carbon nanofibers (CNFs) were incorporated into an epoxy matrix with three weight fractions of 0.1%, 0.5% and 1% which were then reinforced with unidirectional carbon fibers (CFs) to fabricate laminated composites with cross-ply configuration. Thermomechanical analysis and tensile tests of the specimens were carried out to characterize thermal and mechanical properties of CNF/epoxy composites and compare them with the behavior of the neat resin. Characterization showed that the coefficient of thermal expansion (CTE) of the epoxy matrix is significantly reduced by adding small amounts of CNF. CNFs also moderately increase the Young’s modulus of the epoxy. The slitting method was used for the measurement of residual stresses in cross-ply CF/epoxy and CNF-reinforced CF/epoxy laminates. It involves cutting a narrow slit progressively from one surface of the laminate, and measuring the released strains at the other surface. The results showed that the addition of 0.1%, 0.5% and 1 wt.% CNF leads to 4.4%, 18.8% and 25.1% reductions in residual stress, respectively. These findings confirm that CNFs possess excellent potential to be used as a thermal expansion compensator for the modification of the thermal behavior of the epoxy matrix and the reduction of the thermal residual stresses in the fiber/epoxy laminated composites.     

航空用复合材料纤维织物标准研究

复合材料在航空领域的广泛应用,使得标准体系的研究也不断深入.以直升机为例,介绍我国直升机复合材料用纤维织物标准,通过对国内外复合材料用织物标准现状的分析研究,确定我国直升机所用织物标准的主要技术要素及试验方法.最后对我国直升机用复合材料标准体系的建立提出了合理化建议.     

Electrophoretic deposition of carbon nanotubes onto carbon-fiber fabric for production of carbon/epoxy composites with improved mechanical properties

Carbon nanotubes (CNTs) have been deposited onto carbon-fiber fabric using electrophoretic deposition (EPD) prior to the infusion of epoxy resin for the production of carbon/epoxy composites. The carbon-fiber fabric employed for EPD was used in the as-received condition, in which the proprietary epoxy sizing-agent was present. CNTs were functionalized prior to EPD using ozone treatment for oxidation, followed by chemical reaction with polyethyleneimine. The CNT oxidation used a novel recirculating system which enabled ozonolysis to be conducted on large-volume solutions of CNTs in the presence of high-powered sonication, facilitating preparation of stable dispersions suitable for EPD. Significant increases in the shear strength and fracture toughness of the carbon/epoxy composites with the CNT treatment have been measured relative to composites without the CNT treatment. Analysis of fracture surfaces revealed interlaminar regions with high levels of CNTs and evidence of good adhesion between the carbon nanotubes and sized carbon-fiber, which is believed to have contributed to the measured improvement in mechanical properties.     

Aluminum nitride‐single walled carbon nanotube nanocomposite with superior electrical and thermal conductivities

Development of aluminum nitride (AlN)‐single walled carbon nanotube (SWCNT) ceramic‐matrix composite containing 1‐6 vol% SWCNT by hot pressing has been reported in this article. The composites containing 6 vol% SWCNT are dense (~99% relative density) and show high dc electrical conductivity (200 Sm^?1) and thermal conductivity (62 Wm^?1K^?1) at room temperature. SWCNTs contain mostly metallic variety tubes obtained by controlled processing of the pristine tubes before incorporation into the ceramic matrix. Raman spectroscopy and field emission scanning electron microscopy (FESEM) of the fracture surface of the samples show the excellent survivability of the SWCNTs even after high‐temperature hot pressing. The results indicate the possibility of preparation of AlN nanocomposite for use in plasma devices and electromagnetic shielding.