Self‐healing and interfacially toughened carbon fibre‐epoxy composites based on electrospun core–shell nanofibres

Dual components of a self‐healing epoxy system comprising a low viscosity epoxy resin, along with its amine based curing agent, were separately encapsulated in a polyacrylonitrile shell via coaxial electrospinning. These nanofiber layers were then incorporated between sheets of carbon fiber fabric during the wet layup process followed by vacuum‐assisted resin transfer molding to fabricate self‐healing carbon fiber composites. Mechanical analysis of the nanofiber toughened composites demonstrated an 11% improvement in tensile strength, 19% increase in short beam shear strength, 14% greater flexural strength, and a 4% gain in impact energy absorption compared to the control composite without nanofibers. Three point bending tests affirmed the spontaneous, room temperature healing characteristics of the nanofiber containing composites, with a 96% recovery in flexural strength observed 24 h after the initial bending fracture, and a 102% recovery recorded 24 h after the successive bending fracture. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44956.     

Effect of carbon nanotubes growth topology on the mechanical behavior of hybrid carbon nanotube/carbon fiber polymer composites

In this study, carbon nanotubes (CNTs) were incorporated into carbon fiber‐reinforced polymer composites (CFRPs) by growing them on the surface of PAN‐based carbon fibers utilizing a relatively low temperature technique. The effect of various surface treatments of the carbon fibers on the in‐plane and out‐of‐plane mechanical performance of the hybrid CFRPs (e.g., exposure to or shielding against elevated temperatures, patterned vs. unpatterned growth of the CNTs over the carbon fibers) were investigated. The in‐plane quasi‐static mechanical properties and out‐of‐plane dynamic properties of the hybrid CFRPs were examined utilizing tension and dynamic impact tests, respectively. To study the progressive damage mechanism of the hybrid CFRPs, spherical punch tests as well as X‐ray radiography of the impact damaged hybrid CFRPs were carried out. The results revealed that the strength and impact energy dissipation of the CFRPs improved by 11% and 127%, respectively, utilizing patterned growth of CNTs on the surface of the carbon fibers. POLYM. COMPOS., 37:2639–2648, 2016. © 2015 Society of Plastics Engineers     

High residual mechanical properties at elevated temperatures of bamboo/glass reinforced‐polybenzoxazine hybrid composite

We successfully added bamboo and glass fibers into bisphenol A‐aniline based benzoxazine (BA‐a) resin by hot‐pressing method. In order to improve the interfacial adhesion between bamboo fibers and the matrix, bamboo fibers were pretreated in 6 wt% NaOH solutions for 12 h. The results showed alkali‐treatment had a positive effect on mechanical properties of the composites at both room and elevated temperatures (60°C, 110°C, 160°C, and 210°C). Due to the incorporation of glass fibers, the bamboo/glass reinforced‐polybenzoxazine hybrid composites exhibited highest strength and modulus among all samples and had high residual mechanical properties at elevated temperatures (residual mechanical properties refers to the ratio of strength and modulus of the composites at elevated temperatures to that measured at room temperature). The fractured surface morphologies of the composites were observed by scanning electron microscope. The results showed with the increase of temperature, the debonding and fiber pull‐out became apparent, and the matrix softening could be clearly observed at 210°C. In addition, thermal and thermomechanical properties of neat benzoxazine and the composites were also investigated through thermogravimetric analysis and dynamic mechanical analyzer, respectively. POLYM. ENG. SCI., 59:1818–1829, 2019. © 2019 Society of Plastics Engineers     

Quasi‐static and dynamic experiment investigations on the crashworthiness response of composite tubes

Crashworthiness performance of carbon and glass composite tubes have been comprehensive investigated under quasi‐static and dynamic axial crush testing. In this study, collapse modes and specific energy absorption (SEA) of different ply orientation of carbon fabric composites and unidirectional glass tubes were analyzed. For the weaker tensile strength and bending strength of glass composites, crack propagated approximately perpendicular to the fiber direction when the ply angle was small. Large amount of fibers breakage made the specific energy absorption over 80 kJ/kg under dynamic load. Thickness effect had inverse influence on SEA under different impact rate. The specific energy absorption declined as tube thickness increased under dynamic crush tests, however, increased under quasi‐static tests. Hybridization of glass/carbon tubes and carbon/carbon composites were analyzed by increased the axial fiber content. It was found that hybridization tubes of G803/3234 fabric and G827/3234 axial tapes with higher G827/3234 content present excellent energy‐absorption capability under dynamic and quasi‐static tests for all specimens tested. POLYM. COMPOS., 34:1099–1109, 2013. © 2013 Society of Plastics Engineers     

Toughened carbon fiber fabric‐reinforced pCBT composites

Toughened carbon fiber‐fabric reinforced polymerized cyclic butylene terephthalate (pCBT) composites were obtained by chemical modification of cyclic butylene terephthalate (CBT) with small amounts of epoxy resin and isocyanates as chain extenders. Homogeneous CBT/epoxy and CBT/isocyanate blends were prepared by melt blending the components in a lab‐scale batch mixer at low temperatures and high shear rate. Melt blending was stopped before the ring‐opening polymerization of CBT could start. The modified CBT was the starting material for carbon fiber fabric‐reinforced pCBT composites (fiber content at about 65 wt%) which were prepared by ring‐opening polymerization during compression molding using a simple powder prepreg method. Interlaminar shear strength, flexural strength, and failure strain of the chemically modified composites increased up to 60% with respect to unmodified pCBT composites. Nevertheless, the flexural moduli slightly decreased due to the toughening effect of the chain extender on the pCBT matrix. Drop weight impact tests revealed that the energy absorption of the modified composites was relatively higher as compared to unmodified pCBT composites. POLYM. COMPOS., 37:1453–1460, 2016. © 2014 Society of Plastics Engineers     

Application of the thermal energy storage concept to novel epoxy–short carbon fiber composites

For the first time, multifunctional epoxy–short carbon fiber reinforced composites suitable for thermal energy storage technology were developed. Paraffin microcapsules (MC) and short carbon fibers (CFs) were added at different relative amounts to an epoxy matrix, and the microstructural and thermomechanical properties of the resulting materials were investigated. Scanning electron microscopy images of the composites showed a uniform distribution of the capsules within the matrix, with a rather good interfacial adhesion, while the increase in the polymer viscosity at elevated CF and MC amounts caused an increase in the void content. Differential scanning calorimetry tests revealed that melting enthalpy values (up to 60 J/g) can be obtained at high MC concentrations. The mixing and thermal curing of the composites did not lead to breakage of the capsules and to the consequent leakage of the paraffin out of the epoxy matrix. The thermal stability of the prepared composites is not negatively affected by the MC addition, and the temperatures at which the thermal degradation process begins were far above the curing or service temperature of the composites. Flexural and impact tests highlighted that the presence of MC reduces the mechanical properties of the samples, while CF positively contributes to retaining the original stiffness and mechanical resistance. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47434.     

Temperature effect on graphene‐filled interface between glass–carbon hybrid fibers and epoxy resin characterized by fiber‐bundle pull‐out test

The overall mechanical performance of glass–carbon hybrid fibers reinforced epoxy composites depends heavily upon fiber–matrix interfacial properties and the service temperatures. Fiber‐bundle pull‐out tests of glass (GF) and/or carbon fiber (CF) reinforced epoxy composites were carried out at room and elevated temperatures. Graphene nanoplatelets were added in the interfacial region to investigate their influence on the interfacial shear strength (IFSS). Results show that IFSS of specimens with fiber‐bundle number ratio of GF:CF = 1:2 is the largest among the hybrid composites, and a positive hybridization effect is found at elevated temperatures. IFSS of all the specimens decreases with the increasing of test temperatures, while the toughness shows a contrary tendency. As verified by scanning electron microscopy observations, graphene nanoplatelets on fiber surface could enhance the IFSS of pure glass/carbon and hybrid fibers reinforced epoxy composites at higher temperatures significantly. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46263.     

Evaluation of interfacial properties and microfailure mechanisms in single fiber‐reinforced epoxy composites at low temperature

In this preliminary study, micromechanical techniques were used to compare the interfacial properties of both carbon and glass fiber composites with two structurally different epoxy matrices (YD‐114 and YDF‐175) at ambient and relatively low temperatures (25°C and −10°C). Tensile modulus of elasticity for both epoxies was higher at lower temperature. Although both fibers exhibited more bimodality at lower temperature than at ambient temperature, glass fiber composites exhibited a statistically greater improvement in tensile strength. This may be attributed to differences in inherent flaws and rigidity. A decrement in stress was observed for YDF‐175 epoxy composites under cyclic loadings at both temperatures, which was attributed to lower interfacial shear strength (IFSS). In contrast to the IFSS of conventional YD‐114 epoxy composites, the IFSS of both the carbon and glass fibers/YDF‐175 epoxy composites studied was higher at the lower temperature. The microfailure pattern observed in microdroplet pullout tests was consistent with the other IFSS results. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Repeated impact behavior of glass/epoxy laminates

The response of glass–epoxy composites to repeated impact for various impact energies ranging from 5 to 15 J was investigated. Specimens with two different stacking sequences were studied; [0/90/0/90]_S and [0/90/+45/−45]_S. In addition to the room temperature, impact tests were also performed at −40°C environmental test temperature for impact energy of 15 J. Contact force‐deflection and energy‐time curves at each test and the number of impacts to failure (N_f) were obtained for each experiment. Compression after impact (CAI) tests were also conducted to determine the residual load carrying capacity of the damaged specimens. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Influence of irradiation conditions on the electrical behavior of polyethylene–carbon black conductive composites

The temperature‐dependent resistivity behavior of carbon black–loaded polyethylene (PE) composites irradiated both at room temperature and 170°C above the PE melting point was studied. The irradiation doses were varied. At a given loading level, irradiation at room temperature corresponded to an energy treatment on a low‐resistive, solid, three‐phase composite system, while at a high temperature it corresponded to a treatment on high‐resistive, viscous, two‐phase system. The irradiation condition had a complicated influence on the electrical response to temperature. The resulting composite structure was analyzed by using differential scanning calorimetry, gel fraction, and wide‐angle X‐ray diffraction. The results were then discussed by comparing them with those of the unirradiated sample. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 494–499, 2000     

A comparative study on the tensile properties and failure mechanism of 3D MWK composites at room and liquid nitrogen temperature

The tensile experiments on the three‐dimensional (3D) multi‐axial warp knitted (MWK) composites with four types of fiber architecture were performed at room and liquid nitrogen temperatures (as low as −196°C). Macroscopic fracture morphology and SEM micrographs both are examined to understand the deformation and failure mechanism. The results showed that the tensile properties can be affected greatly by the fiber architecture and these decrease significantly with the increase of the fiber orientation angle at room and liquid nitrogen temperatures. Meanwhile, the tensile properties at liquid nitrogen temperature have improved significantly than that of those at room temperature. Moreover, the damage and failure patterns of composites vary with the test temperature. At liquid nitrogen temperature, more microcracks appear and the brittle failure feature becomes more obvious; however, the interfacial adhesion capacity is enhanced significantly. In addition, the fiber architecture has remarkable effect on the failure mechanism at room and liquid nitrogen temperatures. POLYM. COMPOS., 35:1294–1305, 2014. © 2013 Society of Plastics Engineers     

Nanoscratch testing to assess the fiber adhesion of short‐carbon‐fiber composites

In a composite material, the degree of adhesion between the fiber and the matrix plays an important role in the overall performance of the material. Because the load between the fiber and the matrix is realized throughout the interphase region material, a lot of effort has gone into characterizing the strength of the interphase. In this study, nanoscratch tests on the composite samples were used to provide a relative measure of adhesion in different composite materials. Carbon‐filled nylon 6,6 and polycarbonate resins were evaluated with this method. The carbon fillers we used were polyacrylonitrile‐based carbon fibers sized and surface‐treated for the respective matrix and pitch‐based carbon fibers without any sizing or surface treatment. Tensile and X‐ray photoelectron spectroscopy data for the composites we considered are also presented to compare to the nanoscratch results. It is shown that nanoscratch testing on the composites, with the proposed data analysis, can be an effective tool for determining the relative degree of adhesion between different composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 328–335, 2007     

Effect of fiber volume fraction,fiber length and fiber tow size on the energy absorption of chopped carbon fiber–polymer composites

Composite materials have the potential to reduce the overall cost and weight of automotive structures with the added benefit of being able to dissipate large amounts of impact energy by progressive crushing. To identify and quantify the energy‐absorbing mechanisms in candidate automotive composite materials, modified test methodologies were developed for conducting progressive crush tests on flat‐plate composite specimens. The test method development and experimental setup focused on isolating the damage modes associated with the frond formation that occurs in dynamic testing of composite tubes. The Automotive Composites Consortium (ACC) is interested in investigating the use of chopped carbon fiber–reinforced composites as crash‐energy absorbers primarily because the low costs involved in their manufacture make them cost‐effective for automotive applications. While many in the past have investigated the energy‐absorption characteristics in various continuous fiber–reinforced composite materials, no literature is available on the energy‐absorption and crushing characteristics of chopped carbon fiber–reinforced composite materials. Hence quasi‐static progressive crush tests were performed on composite plates manufactured from chopped carbon fiber (CCF) with an epoxy resin system using compression‐molding techniques, and the effect of material parameters (fiber volume fraction, fiber length, and fiber tow size) on energy absorption was evaluated by varying them during testing. Of the parameters evaluated, fiber length appeared to be the most critical material parameter determining the specific energy absorption of a composite material, with shorter fibers having a higher specific energy absorption than longer fibers, possibly because of the increased concentration of stress raisers in the shorter fiber specimens, resulting in a larger number of fracture‐initiation sites. The combination of material parameters that yielded the highest energy‐absorbing material was identified. The test observations and trends established from this work would help support the development of low‐cost energy absorbers for the automotive industry. POLYM. COMPOS. 26:293–305 2005. Published 2005 Society of Plastics Engineers.     

Mechanical properties of hybrid structural composites reinforced with nanosilica

Epoxy‐based hybrid structural composites reinforced with 14 nm spherical silica particles were investigated for mechanical properties as a function of nanosilica loading fractions. Composites were fabricated using continuous glass or carbon fiber of unidirectional architecture and nanosilica dispersed epoxy, through resin film infusion process. Uniform dispersion of nanoparticles in resin matrix was ensured by an optimized ultrasound‐assisted process. Although resin viscosity marginally reduces in the presence of nanosilica enabling a better control in composite manufacturing process, glass transition temperature of epoxy remained unaffected at low weight fractions. Compressive strength of hybrid glass or carbon fiber/epoxy composites showed more than 30–35% increase with nanosilica at a concentration as low as 0.2 wt%. Tensile and compressive properties of hybrid composites in transverse direction to the reinforcement remained unaffected. POLYM. COMPOS. 37:1216–1222, 2016. © 2014 Society of Plastics Engineers     

Simultaneous effects of silanized coal fly ash and nano/micro glass fiber on fracture toughness and mechanical properties of carbon fiber‐reinforced vinyl ester resin composites

In this study, the simultaneous effects of both silanized coal fly ash (S‐CFA) and nano/micro glass fiber (nGF) on fracture toughness and mechanical properties of vinyl ester (VE) resin filled with carbon fiber‐based composite materials were investigated. The CFA was treated with (3‐trimethoxysilyl) propyl methacrylate to introduce the methacryloxy groups into the surface of CFA, and was confirmed by using FTIR technique. The nGF and S‐CFA with different weight ratios were well mixed with VE resin by using of high‐speed mechanical stirrer, and ultrasonic technique before using as matrices for fabrication of carbon fiber‐based composite materials via sheet molding compound (SMC) method and hot curing processing. Many characteristics of both cured VE resin composites and carbon fiber‐based composite were examined such as mechanical properties, fracture toughness, and morphology. The results showed that by adding of both 0.1 wt% nGF and 1 wt% S‐CFA into VE resin the tensile strength, tensile modulus, flexural strength, K_IC, impact strength as well as the Mode I interlaminar fracture toughness (G_IC) of VE composites and carbon fiber based composites get optimum values and increased about 61.39%; 39.83%; 36.21%; 103.1%; 81.79%; 48.61%, respectively when compared with pristine materials. POLYM. ENG. SCI., 59:584–591, 2019. © 2018 Society of Plastics Engineers     

Wear and mechanical properties of reactive thermotropic liquid crystalline polymer/unsaturated polyester/glass fiber hybrid composites

To improve the performance of unsaturated polyester (UP) under cold‐heat alternate temperature, self‐synthesized reactive thermotropic liquid crystalline polymer (TLCP)‐methacryloyl copolymer (LCMC), UP, and glass fiber (GF) hybrid composites was prepared by molding technology. The apparent activation energy and crystal behavior analysis of LCMC/UP blends were investigated by Differential scanning calorimetry and X‐ray diffraction (XRD), respectively, the results showed that the addition of LCMC can reduce apparent activation energy and accelerate the curing reaction of UP, the XRD analysis indicated that the crystal phase of LCMC still exist in the blends after blending with UP. The effect of LCMC content on the properties of LCMC/UP/GF hybrid composites such as impact strength, bending strength, and ring‐on‐block wear were also investigated through static mechanical tests and wear tests. The mechanical properties of hybrid composites increased significantly because of the addition of LCMC. The wear tests showed that LCMC can improve the wear resistance of the UP/GF/LCMC hybrid composites even though the content of LCMC was at a relatively low level (5–7.5 wt %). This makes it possible to develop novel kind of UP‐based materials with good wear resistance for various applications. The Worn surface was observed by scanning electron microscopy (SEM) and the mechanism for the improvement is discussed in this paper. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3899–3906, 2007     

Viscoelastic behavior of epoxy/carbon fiber/Zno nano‐rods hybrid composites

The insufficient viscoelastic resistance of fiber reinforced plastics can be retrofitted by the addition of more rigid nano fillers to the polymer matrix. In this study, carbon fibers plies were grafted with zinc oxide (ZnO) nano‐rods and the hybridized reinforcement was utilized in laminated composites. Flexural creep tests were carried out using dynamic mechanical analysis (DMA) and the time/temperature superposition principle was employed for accelerated testing. To verify the applicability of TTPS, prolonged stress relaxation tests were also carried out in flexural mode. Data from the DMA flexural creep tests revealed that the whiskerization of carbon fibers with ZnO nano rods reduced the creep compliance by 23% at elevated temperatures and prolonged durations. Also, the relaxation data confirmed the applicability of TTPS to these hybrid composites. The stress relaxation modulus improved by 65% in comparison to composites based on neat carbon fibers. POLYM. COMPOS., 36:1967–1972, 2015. © 2014 Society of Plastics Engineer     

Improving delamination resistance of carbon fiber reinforced polymeric composite by interface engineering using carbonaceous nanofillers through electrophoretic deposition: An assessment at different in-service temperatures

In this article, modification of carbon fiber surface by carbon based nanofillers (multi-walled carbon nanotubes [CNT], carbon nanofibers, and multi-layered graphene) has been achieved by electrophoretic deposition technique to improve its interfacial bonding with epoxy matrix, with a target to improve the mechanical performance of carbon fiber reinforced polymer composites. Flexural and short beam shear properties of the composites were studied at extreme temperature conditions; in-situ cryo, room and elevated temperature (−196, 30, and 120°C respectively). Laminate reinforced with CNT grafted carbon fibers exhibited highest delamination resistance with maximum improvement in flexural strength as well as in inter-laminar shear strength (ILSS) among all the carbon fiber reinforced epoxy (CE) composites at all in-situ temperatures. CNT modified CE composite showed increment of 9% in flexural strength and 17.43% in ILSS when compared to that of unmodified CE composite at room temperature (30°C). Thermomechanical properties were investigated using dynamic mechanical analysis. Fractography was also carried out to study different modes of failure of the composites.     

Low‐velocity impact response and compression after impact assessment of recycled carbon fiber‐reinforced polymer composites for future applications

The influence of recycling on the impact damage resistance of recycled carbon fiber‐reinforced polymer (CFRP) composites was investigated using low‐velocity impact and compression after impact (CAI) tests. The relationships among load, force, and time were analyzed to gain insight into the damage characteristics of three types of composite laminate: virgin CF‐reinforced polymer (V‐CFRP), recycled CF‐reinforced polymer (R‐CFRP), and treated recycled CF‐reinforced polymer (TR‐CFRP). Special emphasis was placed on evaluating the extent of damage and the residual mechanical properties as affected by three different fiber surface states. Substantial differences were noted in the shape, area, and damage mode of impact using ultrasonic c‐scanning, photography, and scanning electron microscopy (SEM). V‐CFRP indicated significant improvement in impact damage resistance in the form of less damage, higher residual strength, and greater shear failure angle. Damage resistance was improved up to 80% of V‐CFRP by surface cleaning while R‐CFRP is 50% of V‐CFRP. Shear failure angle of 16° was attained from R‐CFRP and it was increased to 24° when the recycled fibers were cleaned. The result of SEM showed that there was less delamination of TR‐CFRP compared with R‐CFRP. This work proves that the low‐velocity impact response of recycled composites can rival that of virgin composites, while providing a basis for future applications of recycled carbon in many fields. POLYM. COMPOS., 35:1494–1506, 2014. © 2013 Society of Plastics Engineers     

Design and fabrication of long‐carbon‐fiber‐reinforced polyamide‐6/nickel powder composites for electromagnetic interference shielding and high mechanical performance

The long‐carbon‐fiber‐reinforced polyamide‐6/nickel powder composites were designed as electromagnetic interference (EMI) shielding materials and then were prepared through the joint processing of melt blending and thermoplastic pultrusion. The obtained composites show high conductivity and permittivity as well as a high dielectric loss with co‐addition of carbon fiber and nickel powders, which makes the resulting composites a higher level of shielding effectiveness due to the combination of conductive and magnetic fillers. The composites are capable of shielding mainly through absorption rather than reflection. On the other hand, the composites achieved significant improvements in tensile, flexural, and impact strength due to the superiority of the long‐carbon‐fiber‐reinforced technique. The residual fiber length in the injection‐molded specimens is greatly superior to the critical one predicted by the Kelly–Tyson model. This takes full advantage of the strength of the reinforcing fiber itself, thus leading to a promising reinforcement effect. The enhancement of impact toughness is due to the energy dissipation by fiber fracture as a result of long fiber effect. The morphologic investigation indicated that the fiber fracture and fiber pullout concurred on the impact and tensile fracture surfaces, and the former preceded the latter. Highlighted with both good EMI shielding properties and excellent mechanical performance, the composites designed by this work exhibit potential applications for the automotive, electronic, aerospace, and military industries. POLYM. COMPOS., 37:2705–2718, 2016. © 2015 Society of Plastics Engineers