Interfacial toughness and its effect on compression strength in polycarbonate/carbon fiber composites

Processing Polycarbonate/carbon fiber composites for long times at high temperatures significantly improved adhesion between the matrix and the fibers. The interfacial properties were studied by measuring transverse fracture toughness, observing fracture specimens by scanning electron microscopy, and by monitoring composite cross-sections using atomic force microscopy. The processing treatment provided an ideal method for varying the properties of the interface without changing any other properties. We used this method to study the effect of interfacial properties on the axial compression properties of unidirectional composites. Both the compression strength and compression modulus increased significantly as the fiber/matrix adhesion improved. We concluded that improving interfacial adhesion increased compression properties by inhibiting fiber microbuckling.     

Mechanical behavior of two-dimensional carbon/carbon composites with interfacial carbon layers

Effect of interfacial carbon layers on the mechanical properties and fracture behavior of two-dimensional carbon fiber fabrics reinforced carbon matrix composites were investigated. Phenolic resin reinforced with two-dimensional plain woven carbon fiber fabrics was used as starting materials for carbon/carbon composites and was prepared using vacuum bag hot pressing technique. In order to study the effect of interfacial bonding, a carbon layer was applied to the carbon fabrics in advance. The carbon layers were prepared using petroleum pitch with different concentrations as precursors. The experimental results indicate that the carbon/carbon composites with interfacial carbon layers possess higher fracture energy than that without carbon layers after carbonization at 1000°C. For a pitch concentration of 0.15 g/ml, the carbon/carbon composites have both higher flexural strength and fracture energy than composites without carbon layers. Both flexural strength and fracture energy increased for composites with and without carbon layers after graphitization. The amount of increase in fracture energy was more significant for composites with interfacial carbon layers. Results indicate that a suitable pitch concentration should be used in order to tailor the mechanical behavior of carbon/carbon composites with interfacial carbon layers.     

Hierarchical material modeling of carbon/carbon composites

Unidirectional, long fiber carbon/carbon composites fabricated by chemical vapor infiltration (CVI) consisting of carbon fibers in a pyrolytic carbon matrix are anisotropic materials. It is practically impossible to identify experimentally the elastic properties (modules) of this anisotropic material. The aim of this investigation is to predict the elastic properties of this composite theoretically. The study of this material with the help of microscopy gives information about the very complicated anisotropic structure of this composite at each length scale. That is the reason that a hierarchical model for this material is developed, which consists of four length levels. A methodology for identification of the elastic properties for such composites is proposed. The problem is solved with the help of a homogenization procedure for each level.     

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.     

Modification of a carbon/carbon composite with a thermosetting resin precursor as a matrix by the addition of carbon black

Carbon/carbon composites were made through the pyrolysis of stabilized PAN felt and phenolic resin with the addition of 5 or 10 wt % carbon black to the matrix and then heat treatment at 600–2500°C. The effects of adding carbon black to the matrix precursor on the physical properties, microstructure, and mechanical properties of the resultant composites were investigated. Adding carbon black not only reduced the weight loss but also limited the shrinkage of the resultant composites. Adding carbon black also accelerated the formation of carbon basal planes in the matrix. At 2500°C, the crystalline stacking height in the composite with 10 wt % added carbon black was 200% greater than that with no additive. The flexural strength of the composite also increased from 15 to 42 MPa (almost 300%). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 333–337, 2006     

The role of maleic anhydride functionalized graphene oxide in improving the interfacial properties of carbon fibre/bismaleimide composites

This work aims to assess the effect of maleic anhydride functionalized graphene oxide (MAH‐f‐GO) on the interfacial properties of carbon fibre/bismaleimide (BMI) composites by experimental and finite element (FE) methods. Transverse fibre bundle (TFB) specimens with different contents of MAH‐f‐GO nanoparticles were manufactured to investigate the interfacial strength of the carbon fibre/BMI composites. The fracture surface of the TFB specimens was examined by scanning electron microscopy to observe the morphologies of the fibre ? matrix interface. The coefficient of thermal expansion, cure shrinkage and elastic modulus were measured and included in the FE simulation. An FE analysis model was established to simulate the thermal residual stress distribution around the carbon fibre and to estimate the interfacial bonding strength of the TFB specimens. The combination of experimental and FE analysis results indicated that the addition of MAH‐f‐GO nanoparticles noticeably reduced the concentration of residual stress at the fibre ? matrix interface and enhanced the interfacial properties of the carbon fibre/BMI composites.© 2017 Society of Chemical Industry     

Tribological application of carbon nanotubes in a metal-based composite coating and composites

Ni-P-carbon nanotube (CNT) composite coating and carbon nanotube/copper matrix composites were prepared by electroless plating and powder metallurgy techniques, respectively. The effects of CNTs on the tribological properties of these composites were evaluated. The results demonstrated that the Ni-P-CNT electroless composite coating exhibited higher wear resistance and lower friction coefficient than Ni-P-SiC and Ni-P-graphite composite coatings. After annealing at 673 K for 2 h, the wear resistance of the Ni-P-CNT composite coating was improved. Carbon nanotube/copper matrix composites revealed a lower wear rate and friction coefficient compared with pure copper, and their wear rates and friction coefficients showed a decreasing trend with increasing volume fraction of CNTs within the range from 0 to 12 vol.% due to the effects of the reinforcement and reduced friction of CNTs. The favorable effects of CNTs on the tribological properties are attributed to improved mechanical properties and unique topological structure of the hollow nanotubes.     

Evidence for the benefit of adding a carbon interphase in an all-carbon composite

T-800 polyacrylonitrile-based carbon fibres were coated with pyrolytic carbon and carbon/carbon/carbon (C/C/C) composites were prepared from them using coal tar pitch as the matrix precursor. Composites were characterised regarding pyrolysis behaviour, mechanical properties, microtexture, nanotexture, and fracture behaviour. All of the composite components, including interfacial areas, were characterised by high resolution transmission electron microscopy. It was checked that the presence of the carbon interphase did not affect the development of the matrix texture, nor deeply modified the fibre surface energetics. However, adding a pyrolytic carbon interphase resulted in improved mechanical properties for the C/C/C composites with respect to the similarly prepared but interphase-free composites (C/C), such as the increase in the flexural strength by a factor of five, and that of the flexural modulus a factor of two. It is shown that such a benefit brought by adding a carbon interphase is possible merely through the appropriate texture of the latter. Typically, the interphase has to exhibit features from both the matrix (anisotropic) and the fibres (isotropic) so that to reduce the discontinuity effect at the fibre/matrix contact, and should also exhibit features (elongated porosity) that promote multiple micro-cracking from the primary cracks, so that to somewhat absorb part of the fracture energy.     

Fiber bundle push-out test and image-based finite element simulation for 3D carbon/carbon composites

The interfacial properties such as debond strength, fracture energy release rate in Mode-II and coefficient of friction play important roles in determining the mechanical properties and strength of carbon/carbon (C/C) composites. Push-out tests were conducted on 3D C/C composites and the experimental results were fitted to the shear lag model to determine these interfacial properties. X-ray tomography was used to explore the internal material structure of the composite. The fiber bundle and matrix interfaces were observed as being partially damaged in the tomographic images and the crack network was explored in detail. The tomographic images were also used to reconstruct a finite element (FE) mesh for simulating push-out tests. The interface of the fiber bundle and matrix in the FE mesh was represented by cohesive surfaces with frictional contact. The cohesive surface properties were obtained by matching FE results with the experimental results. The simulations had a good agreement with experiments and values of 0.75 for coefficient of friction, 2–5 N/mm² for debond stress, 1–4 N/mm² for clamping stress and 3–6 N/m for fracture energy release rate were obtained as interfacial parameters for the composite.     

Study on the mechanical properties and microstructure of high-performance carbon fiber/epoxy composites

A high-toughness epoxy has been prepared using carboxyl-terminated butadiene acrylonitrile (CTBN) as a toughening agent to modify the AG-80 epoxy resin. High-performance carbon fiber/epoxy (CF/EP) composites are fabricated using the CTBN-toughened epoxy resin as the matrix and two types of CF, namely, T800SC and T800HB, as reinforcement. The mechanical properties of the matrix, surface properties of the CFs, tensile properties, and fracture morphologies of the composites are systematically investigated to elucidate the key factors influencing interfacial bonding in high-performance CF/EP composites. The results reveal that the most significant improvement in toughness is achieved when the CTBN content is 6.90 wt.% in the epoxy resin. Owing to the high content of polar functional groups and excellent surface wettability of T800SC, the T800SC/EP composite exhibits superior mechanical properties compared with the T800HB/EP composite.     

Rapid, low temperature microwave synthesis of novel carbon nanotube-silicon carbide composite

Single wall carbon nanotubes (SWNTs) incorporated into ceramic matrices are known to impart enhanced mechanical, thermal and electrical properties to the composites formed. Current procedures for their synthesis face challenges, such as, the non-uniform dispersion of the SWNTs and their damage during high temperature processing in a reactive environment. These have led to poor interfacial matrix to SWNT adhesion and the ineffective utilization of the unique properties of the nanotubes. Here we report a rapid, low temperature microwave-induced reaction to create a novel nanoscale silicon carbide (SiC)-SWNT composite. The reaction, which was completed in 10 min, involves the decomposition of chloro-trimethylsilane and the simultaneous nucleation of nanoscale SiC spheres on the SWNT bundles. The bulk composite is a branched tree-like structure comprised of three-dimensionally arrayed SiC-SWNTs. The uniqueness of this approach lies in the formation of a ceramic directly on the SWNTs, rather than physical mixing, or the growth of nanotubes in a ceramic matrix.     

Interfacial improvement of carbon fiber/epoxy composites using a simple process for depositing commercially functionalized carbon nanotubes on the fibers

An aqueous suspension deposition method was used to coat the sized carbon fibers T700SC and T300B with commercially carboxylic acid-functionalized and hydroxyl-functionalized carbon nanotubes (CNTs). The CNTs on the fiber surfaces were expected to improve the interfacial strength between the fibers and the epoxy. The factors affecting the deposition, especially the fiber sizing, were studied. According to single fiber-composite fragmentation tests, the deposition process results in improved fiber/matrix interfacial adhesion. Using carboxylic acid-functionalized CNTs, the interfacial shear strength was increased 43% for the T700SC composite and 12% for the T300B composite. The relationship between surface functional groups of the CNTs and the interfacial improvement was discussed. The interfacial reinforcing mechanism was explored by analyzing the surface morphology of the carbon fibers, the wettability between the carbon fibers and the epoxy resin, the chemical bonding between the fiber sizing and the CNTs, and fractographic observation of cross-sections of the composites. Results indicate that interfacial friction, chemical bonding and resin toughening are responsible for the interfacial improvement of nanostructured carbon fiber/epoxy composites. The mechanical properties of the CNT-deposited composite laminate were further measured to confirm the effectiveness of this strategy.     

Comparative study of interphase evolution in polysiloxane resin-derived matrix containing carbon micro and nanofibers during thermal treatment

The work presents the results of research on composite materials made of silicon-containing polymer-derived ceramic matrix composites (PDC-Cs) and nanocomposites (PDC-NCs). Carbon micro and nanofibers (CFs and CNFs) were used as reinforcements. The interactions between carbon micro and nanofibers and polysiloxane matrix, as well as interphase evolution mechanism in composite samples during their heating to 1000 °C were studied. CF/resin and CNF/resin composites were prepared via liquid precursor infiltration process of unidirectionally aligned fibers. After heating to 700 °C–800 °C, decomposition of the resin in the presence of CNFs led to the formation of fiber/organic-inorganic composites with pseudo-plastic properties and improved oxidation resistance compared to as-prepared fiber/resin composites. The most favourable mechanical properties and oxidation resistance were obtained for composites and nanocomposites containing the maximum amount of carbon nanoparticles precipitated in the SiOC matrix during the heat treatment at 800 °C. The precipitated carbon phase improves fiber/matrix adhesion of composites.     

Melt processing and mechanical property characterization of multi-walled carbon nanotube/high density polyethylene (MWNT/HDPE) composite films

High density polyethylene (HDPE) was used as the matrix material for a carbon nanotube (CNT) polymer composites. This combination of composite constituents has not been previously reported in the literature. Multi-wall carbon nanotube (MWNT)/HDPE composite films were fabricated using the melt processing method. The composite films with 0, 1, 3 and 5% nanotube content by weight were analyzed under SEM and TEM to observe nanotube dispersion. The mechanical properties of the films were measured by small punch test. Results show increases in the stiffness, peak load and work to failure for the composite films with increasing MWNT content.     

Co-Firing of Spatially Varying Dielectric Ca–Mg–Silicate and Bi–Ba–Nd–Titanate Composite

A spatially variant dielectric Ca–Mg–silicate (CMS)/Bi–Ba–Nd–titania (BBNT) composite, in which periodic BBNT inclusions were embedded in the CMS matrix, was fabricated using the thermoplastic extrusion. The co-firing behavior of the composite was evaluated in terms of its shrinkage compatibility, thermoplastic compatibility, and chemical compatibility. The noticeable shrinkage mismatch between CMS and BBNT materials was observed. Such shrinkage mismatch strongly affected the interfacial bonding types of the composites. The good interfacial bonding was observed for the composite having BBNT inclusions in the CMS matrix; however, the interfacial cracking and matrix cracking for the opposite design (i.e., CMS inclusions in the BBNT matrix). In addition, the (Ca, Zn)-rich glassy phase in the CMS region migrated into the BBNT region, forming an interfacial reaction layer. The dielectric properties of the CMS, BBNT, and CMS–BBNT mixture were measured to evaluate the spatially variant dielectric CMS/BBNT composite as a novel dielectric substrate.     

Resonant frequency study of tensile and shear elasticity moduli of carbon fibre reinforced composites (CFRC)

The dynamic elastic properties are important characteristics of composite materials. They control the vibrational behaviour of composite structures and are also an ideal tool for monitoring of the development of CFRCs’ mechanical properties during their processing (heat treatment, densification). The present studies have been performed to explore relations between the dynamic tensile and shear moduli and some structural features (viz., fibre fraction, fibre type, porosity, weave pattern of woven reinforcement) of various unidirectional or bi-directional fibre reinforced carbon/carbon composites, made out of PAN- or pitch-based fibres as reinforcements and phenolic resin or coal tar pitch as matrix precursors. The dynamic tensile and in-plane shear moduli were determined from resonant frequencies of a beam with free ends. The longitudinal dynamic Young’s modulus of unidirectional CFRC composites – besides its dependence on the original fibre modulus and fibre volume contents – also reflects changes induced in matrix and fibres by heat treatment. The in-plane shear modulus does not depend on the fibre type but there exists its distinct tendency to increase with increasing fibre fraction. For bi-directionally reinforced composites, the longitudinal tensile modulus is more sensitive to the fabric weave pattern than to the fibre type. Tensile modulus of diagonally cut specimens and in-plane shear modulus of longitudinally cut ones are mutually correlated and, therefore, simultaneously controlled by densification steps and graphitisation heat treatment.     

Interfacial design of the nonpolar polyolefin ternary composite with high strength,high toughness,and high modulus

An interfacial model was proposed for the ternary thermoplastics (matrix)/elastomer/rigidparticle filler composite with high strength, high toughness, and high modulus. A dispersed phase of rigid particle as a core and elastomer as a shell that has a good interfacial adhesion with the matrix is the key point of the model. A composite with high strength, high toughness, and high modulus was obtained in the styrene (ST) and maleic anhydride (MAH) modified high-density polyethylene (HDPE)/ethylene-propylene-diene monomer (EPDM) rubber/carbon black (CB) with ditertiary butyl peroxide (DTBP) as the initiator through the reactive extrusion. The electrical resistivity measurement showed that CB of the unmodified composites distributed at the interface of the HDPE and EPDM, while that of the modified composites distributed mainly in the EPDM phase. The morphology of the ternary composite was consistent with the wetting coefficient analysis. That the mechanical properties of the α-ray–irradiated unmodified composites were not as good as those of the modified composites further indicated that the mechanical properties of the composite could not be improved significantly purely by introducing the interfacial adhesion and matrix crosslinking without forming the proposed dispersed phase structure. SEM observation supported the conclusion that the different phase structures are the major reason that leads to the different toughness. © 1996 John Wiley & Sons, Inc.     

Three-dimensional carbon fiber-reinforced silicon carbide matrix composites by vapor silicon infiltration

Three-dimensional carbon fiber-reinforced SiC matrix composites (C_f/SiC) were fabricated by vapor silicon infiltration (VSI) successfully. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and wavelength dispersive spectrometer (WDS) analysis revealed that the microstructure and composition of constituent phases are strongly dependent on temperature. At 1973 K, the obtained C_f/SiC composite mainly consists of SiC, carbon fiber and residual Si, and shows a densified microstructure. The flexural tests show non-catastrophic fracture behavior for composites fabricated by VSI process, and the ultimate flexural stress is comparable to those of composites fabricated by other processing techniques, demonstrating VSI is an effective way to fabricate the dense C_f/SiC composites with good mechanical properties.     

Dielectric effects on positive temperature coefficient composites of polyethylene and short carbon fibers

By adding the short carbon fibers to the polyethylene matrix, excellent positive temperature coefficient (PTC) effect was achieved. Alternating current (AC) electrical properties of this PTC composite were studied as a function of frequency. The analysis of AC electrical conductivity and dielectric permittivity was done by using a micro-morphology model, which included conductive carbon fiber-aggregates in series with an equivalent circuit of resistor-capacitor parallel that represent the blends at these contact regions. The observed electrical properties of PTC composites were due to the breakage of the conduction networks caused by thermal expansion. The dielectric behaviors of the interfacial polarization between polyethylene matrix and carbon fibers could be described by Maxwell-Wagner-Sillars relaxation when the composite was heated above 116 °C. The analysis of the electric modulus in the frequency range from 100 Hz to 10 MHz revealed that the interfacial relaxation followed the Cole-Davidson distribution of relaxation time.     

环氧树脂/短切碳纤维复合材料性能研究

制备出了短切碳纤维增强TDE-85环氧树脂复合材料,研究了碳纤维的含量对复合材料力学性能和耐热性能的影响。结果表明,碳纤维的加入有利于复合材料力学性能和耐热性能的提高,并在碳纤维含量为0.25%时,复合材料的拉伸强度、冲击韧性、弯曲强度和弯曲模量达到最大,分别提高了29.33%、25.31%、30.28%和68.93%。此外,对复合材料的弯曲断裂面进行了微观形貌分析,结果表明一定量的碳纤维可以较好地分散在树脂基体中,同时,碳纤维原丝和树脂基体的界面结合比较弱,主要依赖于两相之间的物理嵌合。