Flexural fatigue behaviour of carbon nanofiber/epoxy nanocomposites

In this research, the effect of adding carbon nanofibers (CNFs) on fatigue life of epoxy resin under flexural bending fatigue loading conditions was investigated. The fatigue tests of specimens were performed under displacement‐controlled bending loading at different displacement amplitudes at room temperature. Due to the addition of CNFs, a remarkable improvement in fatigue life of epoxy resin was observed. For instance, 24‐fold improvement in fatigue life for 0.25 wt% CNF/epoxy nanocomposites at a strength ratio of 0.43 observed in comparison with the neat epoxy resin.     

Microstructures and toughening mechanisms of organoclay/polyethersulphone/epoxy hybrid nanocomposites

Hybrid nanocomposites (HNCs) with high fracture toughness were successfully prepared by incorporating polyethersulphone (PES) and organoclay into epoxy resin. Their microstructures were studied. They were composed of homogeneous PES/epoxy matrices and micron-scale organoclay agglomerates. These agglomerates consisted of smaller tactoid-like regions which were comprised of ordered exfoliated nanolayers. The toughening mechanisms of the two tougheners were also studied and then related to their microstructures. For one thing, the PES which was dissolved in the epoxy resin homogeneously improved the ductility of the epoxy resin and made it easier to deform. For another, the organoclay agglomerates induced crack front bowing, crack bridging, crack deflection, crack bifurcation and plastic deformation of the matrices on the micron-scale, respectively. These toughening processes were achieved by the ordered exfoliated nanolayers with various orientations, which debonded from the matrices, bridged the cracks and induced the plastic deformation of the matrices on the nanoscale.     

The effect of strain-rate on the tensile and compressive behavior of graphene reinforced epoxy/nanocomposites

The effect of strain rate on the mechanical behavior of epoxy reinforced with graphene nanoplatelets (GNPs) is investigated. Nanocomposites containing various amounts of GNP are prepared and tested at four different strain rates (0.01, 0.1, 1 and 10/s) under compressive and tensile loading regimes. The results show that incorporation of GNP highly affects the behavior of epoxy. The fracture surfaces of tensile specimens are also investigated using scanning electron microscopy (SEM) to discern the surface features and dispersion state of GNP. Finally, the predictive capability of some of the available models for evaluating the strength of nanocomposites are assessed and compared against the experimental results. Moreover, a modification factor to the widely used Halpin–Tsai model is proposed to improve the accuracy of the model when evaluating the Young’s modulus of nanocomposites at various strain rates.     

The effect of Ag loading on supercapacitor performance of graphene based nanocomposites

In the present study, we prepared reduced graphene oxide (rGO) decorated with Ag nanoparticles by a one pot, simultaneous reduction method. The effect of AgNO₃ amount on the chemical, morphological and electrochemical properties of binary rGO-Ag nanocomposite for supercapacitor application was investigated. The chemical and morphological characterization of prepared rGO-Ag nanocomposites was realized with field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). For supercapacitor application, electrochemical performance of the nanocomposites was investigated with cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques. As a result of their excellent conductivity and spacer role which prevent aggregation of rGO nanosheets and maintain the electroactive surface area, Ag nanoparticles significantly enhance the electrochemical performance of the nanocomposite. The rGO-Ag nanoparticle nanocomposite exhibited a maximum specific capacitance of 34.2?mF?cm^?2 at 0.6?A?cm^?2 current density. The nanocomposite electrode also has excellent rate capability and cycle life. The capacitance retention of rGO-Ag electrode is 98% after 1000 charge-discharge cycle. The results showed that rGO-Ag nanocomposite is a building block for ternary or other multicomponent nanocomposites.     

Effects of graphene nanoplatelets and graphene nanosheets on fracture toughness of epoxy nanocomposites

The effects of graphene nanoplatelets (GPLs) and graphene nanosheets (GNSs) on fracture toughness and tensile properties of epoxy resin have been studied. A new technique for synthesis of GPLs based on changing magnetic field is developed. The transmission‐electron microscopy and the Raman spectroscopy were employed to characterize the size and chemical structure of the synthesized graphene platelets. The critical stress intensity factor and tensile properties of epoxy matrix filled with GPL and GNS particles were measured. Influence of filler content, filler size and dispersion state was examined. It was found that the GPLs have greater impact on both fracture toughness and tensile strength of nanocomposites compared with the GNSs. For instance, fracture toughness increased by 39% using 0.5 wt% GPLs and 16% for 0.5 wt% GNSs.     

Torsion fatigue behavior of unidirectional carbon/epoxy and glass/epoxy composites

This paper presents results of the feasibility of carbon/epoxy composites (CFRP) as a future helicopter flexbeam material. Torsional behaviors of unidirectional CFRP and glass/epoxy composites (GFRP) with the same resin matrix were investigated. The initial torsional rigidity of CFRP was almost identical to that of GFRP. The torsional rigidities calculated using finite element analyses (FEA) agreed with the experimental results: the torsional rigidities are governed mainly by the material’s shear stiffness. Torsion fatigue tests were also conducted by controlling the angle of twist of the sinusoidal wave under a constant tensile axial load. No catastrophic failure occurred with either GFRP or CFRP, although decreased amplitudes of torque and torsional rigidities were observed according to the number of cycles. Results of X-ray CT inspections and numerical calculation by FEA revealed that degradation of a torsional rigidity is caused mainly by splitting crack propagation along the fiber direction. The torsion fatigue life of CFRP was superior to that of GFRP. Consequently, results confirmed that CFRP exhibits excellent properties as a torsional element of a helicopter flexbeam in terms of torsional rigidity and tension–torsion fatigue behaviors.     

A novel combined molecular dynamics–micromechanics method for modeling of stiffness of graphene/epoxy nanocomposites with randomly distributed graphene

In this paper, by combining molecular dynamics and micromechanics methods, a new approach for prediction of the stiffness of the nanocomposites with randomly distributed nanoparticles in the macro level is presented. The molecular dynamics method is used to model the stiffness of the graphene/epoxy nanocomposites containing one layer of an aligned nano graphene embedded in epoxy resin. By considering the large sizes of the length and width of the nano graphene in comparison with its thickness and the shortcomings of the available hardware and software for simulation purposes, a new approach for modeling is also developed. This new approach, by using the moduli of different graphene sheets with different sizes embedded in a representative volume element, can predict the moduli of a real size graphene embedded in the matrix along the longitudinal, transverse and normal directions in the nano-scale. In order to consider the effect of the random distribution of graphene sheets in epoxy resin, a micromechanical approach is used. The results obtained by the molecular dynamics method are used by the micromechanics approach and the stiffness of graphene/epoxy nanocomposites with randomly distributed graphene in the macro-scale is predicted. An experimental program is conducted to evaluate the capability of the model. The result of the modeling is in a very good agreement with the experimental data.     

压力梯度CVI工艺制备2D炭/炭复合材料的弯曲断裂行为

采用三点弯曲方法测试了压力梯度化学气相浸渗法(CVI)工艺制备的2D炭／炭复合材料的性能，借助于扫描电镜研究了断口和界面形貌，分析了密度和纤维基体界面对材料力学性能的影响。结果表明，随试样密度增加，2D炭／炭复合材料的断裂模式从剪切断裂、层问分离向拉伸断裂转变。材料密度对弯曲强度和模量影响很大，但对弯曲挠度基本没有影响。揭示了影响2D炭／炭复合材料弯曲挠度的关键因素是纤维与热解炭基体界面的结合情况。     

玻璃纤维增强树脂基复合材料夹芯板-钢板连接接头的弯曲性能

以PVC泡沫或Balsa轻木为芯材的玻璃纤维增强树脂基复合材料（GRP）夹芯板目前广泛应用于船舶与海洋工程结构中。论文设计不同参数的GRP夹芯板-钢板混合接头模型,进行四点弯曲加载下的静力及疲劳试验研究,同时运用ABAQUS软件结合MSC.fatigue软件对接头的静态及疲劳弯曲失效进行数值模拟,分析了接头的弯曲强度、刚度和失效模式,并研究了接头填充区材料及长度、钢板嵌入填充区长度等参数对接头弯曲性能的影响。结果表明：弯曲载荷作用下接头破坏发生在连接结合部,失效模式则因填充区的不同设计而不同;对提高接头的弯曲性能较为明显的设计参数包括将钢板延伸到接头填充区或者选择Balsa轻木替代PVC泡沫芯材;对于受到疲劳弯曲载荷的接头模型,在较大疲劳载荷水平下,所有试件在未达到10⁶次循环时均发生了疲劳破坏;而在相对较小的疲劳载荷水平下,经过10⁶次循环后所有试件全部完好,并且接头的剩余强度与疲劳试验前的静强度相近,表明小载荷水平下接头的疲劳次数对其承载能力无影响。     

Flexural behavior of reinforced concrete (RC) beams retrofitted with hybrid fiber reinforced polymers (FRPs) under sustaining loads

This paper reports experimental studies of reinforced concrete (RC) beams retrofitted with new hybrid fiber reinforced polymer (FRP) system consisting carbon FRP (CFRP) and glass FRP (GFRP). The objective of this study is to examine effect of hybrid FRPs on structural behavior of retrofitted RC beams and to investigate if different sequences of CFRP and GFRP sheets of the hybrid FRPs have influences on improvement of strengthening RC beams. Toward that goal, 14 RC beams are fabricated and retrofitted with hybrid FRPs having different combinations of CFRP and GFRP sheets. The beams are loaded with different magnitudes prior to retrofitting in order to investigate the effect of initial loading on the flexural behavior of the retrofitted beam. The main test variables are sequences of attaching hybrid FRP layers and magnitudes of preloads. Under loaded condition, beams are retrofitted with two or three layers of hybrid FRPs, then the load increases until the beams reach failure. Test results conclude that strengthening effects of hybrid FRPs on ductility and stiffness of RC beams depend on orders of FRP layers.     

Mechanical property characterization of carbon nanofiber/epoxy nanocomposites reinforced by GMA-grafted UHMWPE fibers

Carbon nanofibers (CNFs) dispersed epoxy resin was reinforced with unidirectional glycidyl methacrylate (GMA) grafted ultra-high molecular weight polyethylene (UHMWPE) fibers. Tensile tests were performed on unfilled, and CNF filled epoxy to identify the effect of adding CNFs on the mechanical properties of epoxy. The highest improvement in strength was obtained with 1 wt% of CNF. Tensile and flexural properties improvements in three-component nanocomposites were confirmed by obtained results. The combined use of CNFs and GMA-grafted UHMWPE fibers leads to a significant synergy in the mechanical properties of nanocomposites. The mechanisms of such synergism were analyzed by fracture studies using scanning electron microscopy.     

Highly conductive graphene oxide/polyaniline hybrid polymer nanocomposites with simultaneously improved mechanical properties

Graphene oxide (GO) was added to a polymer composites system consisting of surfactant-wrapped/doped polyaniline (PANI) and divinylbenzene (DVB). The nanocomposites were fabricated by a simple blending, ultrasonic dispersion and curing process. The new composites show higher conductivity (0.02–9.8 S/cm) than the other reported polymer system filled with PANI (10⁻⁹–10⁻¹ S/cm). With only 0.45 wt% loading of GO, at least 29% enhancement in electric conductivity and 29.8% increase in bending modulus of the composites were gained. Besides, thermal stability of the composites was also improved. UV–Vis spectroscopy, X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) revealed that addition of GO improves the dispersion of PANI in the polymer composite, which is the key to realize high conductivity.     

氧化锌/环氧纳米复合材料的制备及其光学性能研究

采用均相沉淀法制备了氧化锌(ZnO)前驱体,通过煅烧前驱体制备了不同粒径的ZnO纳米颗粒,并在此基础上制备了ZnO/环氧纳米复合材料.借助TG、XRD和TEM等手段对纳米ZnO进行了表征,采用UV-VIS研究了ZnO含量、颗粒粒径等因素对复合材料光学性能的影响.研究结果表明:在紫外光区,提高ZnO的含量和选择ZnO最佳粒径,可以改善对紫外光的屏蔽效果;随着ZnO粒径的减小,ZnO对紫外光的屏蔽存在明显的蓝移现象,因此选择合适的粒径尤为重要.在可见光区,ZnO含量和颗粒粒径的影响相似,当ZnO含量低于0.07wt%、粒径小于27nm时复合材料的透过率几乎没有变化,增加含量或增大粒径透过率则随之下降.当ZnO的粒径为27nm时,添加0.07wt%的ZnO所制备的ZnO/环氧纳米复合材料具有优异的光学性能:在保持可见光区高透明性的同时又能够对紫外光区有良好的屏蔽效果,能够满足LED封装等光学器件的需要.     

Mean stress/strain effect on fatigue behavior of an epoxy resin

Mean stress/strain effect on the fatigue life of an Epon 826/Epi-Cure Curing Agent 9551 epoxy system has been investigated by carrying out series uniaxial fatigue tests with four different mean strain ratios under strain-range-controlled mode. Quantitative analysis of the mechanical properties, such as mean stress relaxation, evolution of stress range and strain energy density, have been performed based on the stress–strain data recorded by a non-contact real-time strain measurement and control system. Mean stress/strain functions have been introduced into the equivalent damage parameters to include the mean stress/strain effect on the fatigue life of the epoxy polymer material. The procedure to characterize the mean stress/strain functions has been demonstrated and material constants were calibrated in the case of either stress, strain or energy approach, respectively. Good agreement can be seen between the predictions and the test data.     

Mechanical fatigue behavior in treated/stabilized soils subjected to a uniaxial flexural test

The use of in situ fine-grained soils treated with lime and/or hydraulic binders as subgrade in common civil engineering infrastructures is a sustainable upgrading process for natural materials with low mechanical performances. In the case of land transport projects, the lack of knowledge on mechanical fatigue behavior in these materials leads either to empirical oversized design of the layers made with these materials or to their rejection. However, the development of a relevant test now enables us to accurately measure the mechanical fatigue performances of treated soils. First, sample preparation appears to explain most fatigue performances, not sample mineralogy. Second, based on original results on three treated soils and previous results from the literature, it seems that a behavior law governs these performances. Finally, a simple classification tool shows that these materials can be considered within the entirety of transport infrastructures from subgrade layers to subbase layers.     

聚丙烯腈/石墨烯纳米复合物的制备、表征及其热性能

采用以水和N,N-二甲基甲酰胺的混合溶剂作反应介质的沉淀聚合法制备了聚丙烯腈/石墨烯纳米复合物。利用傅里叶红外光谱(FT-IR)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和广角X射线衍射(XRD)研究了聚丙烯腈/石墨烯复合物的组成、结构、形貌及两组份的相互作用。利用差式扫描量热分析(DSC)研究了聚丙烯腈及纳米复合物的热性能。结果表明,强极性的聚丙烯腈与石墨烯之间存在较强的非共价相互作用;由于石墨烯的加入,聚丙烯腈的玻璃化转变温度提高了30℃;石墨烯添加量为3%(质量分数)时,聚丙烯腈在氮气和空气中的环化反应放热峰值分别提高了3和11℃;石墨烯使聚丙烯腈在热稳定化过程中的环化反应和氧化反应放热峰宽化、缓和。     

Enhanced fatigue behavior of a glass fiber reinforced hybrid particles modified epoxy nanocomposite under WISPERX spectrum load sequence

Two types of glass fiber reinforced plastic (GFRP) composites were fabricated viz., GFRP with neat epoxy matrix (GFRP-neat) and GFRP with hybrid modified epoxy matrix (GFRP-hybrid) containing 9 wt.% of rubber microparticles and 10 wt.% of silica nanoparticles. Fatigue tests were conducted on both the composites under WISPERX load sequence. The fatigue life of the GFRP-hybrid composite was about 4–5 times higher than that of GFRP-neat composite. The underlying mechanisms for improved fatigue performance are discussed. A reasonably good correlation was observed between the experimental fatigue life and the fatigue life predicted under spectrum loads.     

Preparation and characterisation of graphene/ZnS nanocomposites via a surfactant-free method

In this article, we present a surfactant-free method for the preparation of graphene/ZnS nanocomposites. The as-synthesised products were characterised by the X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy and ultraviolet-visible spectroscopy. It is shown that in the nanocomposites, individual ZnS nanoparticles are well-spread out on the graphene sheets. The good distribution of ZnS nanoparticles on graphene sheets would be promising for practical applications in future nanotechnology.     

Silica coating onto graphene for improving thermal conductivity and electrical insulation of graphene/polydimethylsiloxane nanocomposites

Graphene possess extremely high thermal conductivity, and they have been regarded as prominent candidates to be used in thermal management of electronic devices. However, addition of graphene inevitably causes dramatic decrease in electrical insulation, which is generally unacceptable for thermal interface materials(TIMs) in real electronic industry. Developing graphene-based nanocomposites with high thermal conductivity and satisfactory electrical insulation is still a challenging issue. In this study,we developed a novel hybrid nanocomposite by incorporating silica-coated graphene nanoplatelets(Silica@GNPs) with polydimethylsiloxane(PDMS) matrix. The obtained Silica@GNP/PDMS composites showed satisfactory electrical insulation(electrical resistivity of over 10~(13)Ωcm) and high thermal conductivity of 0.497 W m-1K-1, increasing by 155% compared with that of neat PDMS, even higher than that of GNP/PDMS composites. Such high thermal conductivity and satisfactory electrical insulation is mainly attributed to the insulating silica-coating, good compatibility between components, strong interfacial bonding, uniform dispersion, and high-efficiency heat transport pathways. There is great potential for the Silica@GNP/PDMS composites to be used as high-performance TIMs in electronic industry.     

In situ synthesis of graphene/cobalt nanocomposites and their magnetic properties

Graphene, which possesses unique nanostructure and excellent properties, is considered as a low cost alternative to carbon nanotubes in nanocomposites. In this study, we present a simple in situ approach for the deposition of cobalt (Co) nanoparticles onto surfaces of graphene sheets by hydrazine hydrate reduction. The as-synthesized composites were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM) and thermogravimetry and differential scanning calorimetry. It was shown that the as-formed Co nanoparticles were densely and homogeneously deposited on the surfaces of the graphene sheets and as a result, the restacking of the as-reduced graphene sheets was effectively inhibited. Magnetic studies reveal that the graphene/Co nanocomposite displays ferromagnetic behavior with saturation magnetizations of 53.4 emu g⁻¹, remanent magnetization of 6.0 emu g⁻¹ and coercivity of 226 Oe at room temperature, which make it promising for practical applications in future nanotechnology.