Influence of graphite filler on two-body abrasive wear behaviour of carbon fabric reinforced epoxy composites

The influence of graphite filler additions on two-body abrasive wear behaviour of compression moulded carbon–epoxy (C–E) composites have been evaluated using reciprocating wear unit and pin-on-disc wear unit under single pass and multi-pass conditions respectively. The carbon fabric used in the present study is a plain one; each warp fiber pass alternately under and over each weft fiber. The fabric is symmetrical, with good stability and reasonable porosity. Abrasive wear studies were carried out under different loads/abrading distance using different grades of SiC abrasive paper (150 and 320 grit size). Graphite filler in C–E reduced the specific wear rate. Further, the wear volume loss drops significantly with increase in graphite content. Comparative wear performance of all the composites showed higher specific wear rate in two-body wear (single-pass conditions) compared to multi-pass conditions. Further, the tribo-performance of C–E indicated that the graphite filler inclusion resulted in enhancement of wear behaviour significantly. Wear mechanisms were suggested and strongly supported by worn surface morphology using scanning electron microscopy.     

Effect vapor grown carbon nanofiber on thermal and mechanical properties of epoxy

In the present investigation, dynamic mechanical analysis (DMA), thermo gravimetric analysis (TGA), tensile tests, fatigue tests and the single edge notch tensile (SENT) tests were performed on unfilled, 1, 2 and 3 wt.% vapor grown carbon nanofiber (CNF) filled SC-15 epoxy to identify the loading effect on thermal and mechanical properties of the composites. DMA studies revealed that filling the 3% carbon nanofiber into epoxy can produce 65% enhancement in storage modulus at room temperature and 6 °C increase in T _g. However, TGA results show that thermal stability of composite is insensitive to the CNF content. Tensile tests were carried out at the strain rate range from 0.02 min⁻¹ to 2 min⁻¹. Results show that CNF/epoxy are strain rate sensitive materials, the modulus and tensile strength increased with increasing of strain rate. Experimental results also indicate that modulus of the nanophased epoxy increases continuously with increasing CNF content. But the 2% CNF infusion system exhibit maximum enhancement in tensile strength, fatigue performance and fracture toughness as compared with other system.     

热塑性塑料对环氧树脂热膨胀系数的影响研究

环氧树脂基体的热膨胀系数(CTE)对碳纤维增强环氧树脂层状材料的性能影响巨大,如何降低环氧树脂基体的CTE是提高碳纤维增强环氧树脂复合材料低温使用性能的关键。本研究采用聚对苯二甲酸丁二醇酯(PBT)、聚碳酸酯(PC)和聚醚酰亚胺(PEI)3种热塑性塑料改性环氧树脂,研究了这3种热塑性塑料对环氧树脂基体CTE的影响。结果表明:这3种热塑性塑料分子链中的羰基在环氧树脂固化过程中可与环氧分子侧链上的羟基形成氢键作用,从而加强了热塑性塑料与环氧树脂的界面作用;采用这3种热塑性塑料改性环氧树脂均可提高环氧树脂基体的玻璃化转变温度;相对于纯环氧树脂,PBT、PEI和PC改性的环氧树脂在玻璃化转变温度下的CTE分别降低了14.99%、17.44%和23.96%,但在玻璃化转变温度上的CTE均高于纯环氧树脂。     

Electrical properties of carbon nanofiber reinforced multiscale polymer composites

Carbon nanofiber (CNF) reinforced epoxy matrix nanocomposites and CNF reinforced glass hollow particle filled syntactic foams are studied for electrical properties. The effect of CNF weight fraction, hollow particle volume fraction, and hollow particle wall thickness on impedance and dielectric constant are characterized. The results show that the impedance decreases and the dielectric constant increases with increasing CNF content in the composites. Nanocomposites containing 10 wt.% CNFs showed significantly higher dielectric constant because of the presence of a continuous network of CNFs in the composite. CNF reinforced syntactic foams showed higher dielectric constant than the neat resin. The CNF content had a more prominent effect on the dielectric constant than the glass hollow particle volume fraction and wall thickness. The Maxwell–Garnett and the Jayasundere–Smith models are modified to include the effect of hollow particle wall thickness and obtain predictions of dielectric constants of syntactic foams. The semi-empirical predictions obtained from Maxwell–Garnett models are closer to the experimental values. Lightweight syntactic foams, tailored for electrical properties, can be useful in electronic packaging applications.     

Exploring biomass based carbon black as filler in epoxy composites: Flexural and thermal properties

Carbon blacks (CB), derived from bamboo stem (BS-CB), coconut shells (CNS-CB) and oil palm empty fiber bunch (EFB-CB), were obtained by pyrolysis of fibers at 700 °C, characterized and used as filler in epoxy composites. The results obtained showed that the prepared carbon black possessed well-developed porosities and are predominantly made up of micropores. The BS-CB, CNS-CB and EFB-CB filled composites were prepared and characterized using scanning electron microscope (SEM) and thermogravimetric analyzer (TGA). The SEM showed that the fractured surface of the composite indicates its high resistance to fracture. The CBs–epoxy composites exhibited better flexural properties than the neat epoxy, which was attributed to better adhesion between the CBs and the epoxy resin. TGA showed that there was improvement in thermal stability of the carbon black filled composites compared to the neat epoxy resin.     

The coefficient of thermal expansion of biomimetic composites

The excellent mechanical properties of biocomposites has attracted a lot of research attention, and people have started attempting to fabricate biomimetic staggered composites. In this paper, the relationship between the equivalent coefficient of thermal expansion (CTE) and the microstructure of a biomimetic staggered composite is investigated. A shear-lag based thermalelastic analytical model is developed and is found to agree well with the finite element simulations. It is found that besides the volume fraction and the material constants of the constituent phases, the aspect ratio of the hard platelet plays an important role in the CTE of biocomposites. Hence, there are additional design parameters in staggered composites that can be used to adjust the CTE, which makes this type of composite promising in thermalelastic loading.     

The coefficient of thermal expansion of biomimetic composites

The excellent mechanical properties of biocomposites has attracted a lot of research attention, and people have started attempting to fabricate biomimetic staggered composites. In this paper, the relationship between the equivalent coefficient of thermal expansion (CTE) and the microstructure of a biomimetic staggered composite is investigated. A shear-lag based thermalelastic analytical model is developed and is found to agree well with the finite element simulations. It is found that besides the volume fraction and the material constants of the constituent phases, the aspect ratio of the hard platelet plays an important role in the CTE of biocomposites. Hence, there are additional design parameters in staggered composites that can be used to adjust the CTE, which makes this type of composite promising in thermalelastic loading.     

C_f/Mg复合材料的热膨胀系数及其理论计算

采用负压浸渗-液固挤压法制备了定向短切碳纤维(aligned Csf)及穿刺-2D碳纤维织物(2.5DCf)增强镁合金复合材料,观察了两种复合材料的微观组织结构,测定了其在30～350℃范围的热膨胀系数(α),并在Schapery模型的基础上提出了计算定向Csf/Mg复合材料及2.5DCf/Mg复合材料α值的修正模型。结果表明,在30～200℃范围内,两种Cf/Mg复合材料的α值均表现出随温度的升高而升高的趋势,但在超过250℃以后,α值出现降低或稳定的现象,其原因为随着温度的升高,铝元素固溶度的增大、基体发生部分塑性变形等因素导致的;提出的修正模型理论计算值与其相应的实验测试α值之间的误差均在5%之内,表明该修正模型能够有效预测实验中的α值。     

Interface toughness of carbon nanotube reinforced epoxy composites

Traditional single-fiber pull-out type experiments were conducted on individual multiwalled carbon nanotubes (MWNT) embedded in an epoxy matrix using a novel technique. Remarkably, the results are qualitatively consistent with the predictions of continuum fracture mechanics models. Unstable interface crack propagation occurred at short MWNT embedments, which essentially exhibited a linear load-displacement response prior to peak load. Deep embedments, however, enabled stable crack extension and produced a nonlinear load-displacement response prior to peak load. The maximum pull-out forces corresponding to a wide range of embedments were used to compute the nominal interfacial shear strength and the interfacial fracture energy of the pristine MWNT-epoxy interface.     

The thermal expansion of carbon/carbon composites

The thermal expansion from 20 to 180°C of three samples of woven cloth based carbon/carbon composites and one sample of unidirectional carbon/epoxy (cfrp) composite (with high modulus fibre) has been measured. In the direction perpendicular to the fibres the cfrp has much the highest expansion, but parallel to the fibres its expansion is considerably less than that parallel to one set of fibres in the C/C samples. One C/C sample contained rayon-based fibre and the other two pan-based fibre. The differences in their behaviour can be explained by assuming that the rayon-based material is not so well aligned crystallographically as the pan material.     

Effect of epoxy coatings on carbon fibers during manufacture of carbon fiber reinforced resin matrix composites

The changes in oxygen and nitrogen during manufacture of the carbon fiber reinforced resin matrix composites were measured using the X-ray photoelectron spectroscopy method. The effects of the change in oxygen and nitrogen on the strength of the carbon fibers were investigated and the results revealed that the change of the tensile strength with increasing heat curing temperature was attributed to the change in the surface flaws of the carbon fibers because the carbon fibers are sensitive to the surface flaws. The effect of the surface energy that was calculated using Kaelble’s method on the strength of the carbon fibers was investigated. Furthermore, the surface roughness of the carbon fibers was measured using atom force microscopy. The change trend of roughness was reverse to that of the strength, which was because of the brittle fracture of the carbon fibers.     

Water uptake of epoxy composites reinforced with carbon nanofillers

The water absorption behaviour of neat epoxy resin and reinforced with different contents of carbon nanotubes (CNTs) and nanofibres (CNFs) is reported. The water absorption was monitored gravimetrically and its effect on the thermal and mechanical properties was studied. The maximum water content absorbed significantly decreases with the addition of nanofillers, especially in epoxy/CNT composites. This decrease is higher than the behaviour predicted from ideal mixing law. The evolution of glass transition temperature during ageing confirms that water uptake causes several phenomena, such as plasticization and postcuring matrix processes. The effect of water absorption on mechanical properties changes during hygrothermal ageing. At the beginning, the mechanical strength decreases but then it is recovered. This is justified by the presence of different mechanisms of water absorption and interaction with the epoxy matrix.     

同质纳米纤维增强制备透明低膨胀系数聚酰亚胺

应用于柔性显示的聚酰亚胺(Polyimide,PI)膜要求高透明性和低热膨胀系数C_TE,而目前高透明聚酰亚胺的C_TE普遍高于40×10?6/℃。本研究采用同质增强法,将高强度的纳米PI纤维与无色透明热塑性含氟聚酰亚胺(PI-F)复合,得到的纳米PI纤维增强PI-F基复合薄膜不仅保持PI-F的高透明,同时具有更低的C_TE和优异的拉伸性能。研究结果表明:纳米尺寸的纤维可减少光透过时发生的散射,使复合薄膜维持了较高的透明性。当纳米PI纤维质量分数为10%时,在可见光区其透光率达到80.5%,与纯PI-F薄膜相比,复合薄膜的C_TE值降低了40.3%,为28.3×10?6/℃。其拉伸强度提高了132.9%,达到107.6 MPa,拉伸模量增大了89.5%,达到1152.2 MPa。      

The thermal expansion of carbon fibre reinforced plastics

Measurements of the principal linear thermal expansion coefficients of a tridirectional (–45°, 0°, +45°) carbon fibre reinforced plastics laminate are reported in the approximate temperature range 90 K to 500 K. A quantitative evaluation of the in-plane results in thermoelastic terms has yielded an agreement with these results consistent with the approximations and uncertainties involved. The qualitative agreement with expectations based upon the behaviour of unidirectional and bidirectional laminates is also demonstrated. The account concludes with an examination of some effects which are peculiar to multidirectional laminates.     

Electrical properties and stability of epoxy reinforced carbon black composites

The conductivity of an insulating epoxy matrix increases continuously with carbon black (CB) content and is well explained by percolation theory. The effects of CB content and sintering on the electrical conductivity (σ) of epoxy composite as a function of temperature during heating and cooling cycles were discussed. The current–voltage–temperature (I–V–T) and working power–temperature (P–T) characteristics of these composites as a function of CB content were investigated. The thermal stability was tested by means of temperature–time (T–t) curve at certain applied power on and off for one cycle.     

三维网络碳纳米管增强环氧树脂复合材料的细观力学

根据网络碳纳米管/环氧树脂(Reticulate Carbon Nanotubes/Epoxy, R-CNTs/EP)复合材料的结构特点, 假设R-CNT均匀分布, 建立了R-CNT/EP复合材料的三维有限元模型。利用有限元法分析了R-CNT/EP复合材料单胞的细观变形, 用二尺度展开法计算了R-CNT/EP复合材料在不同应变下的有效刚度系数。分析结果表明: R-CNT/EP复合材料为各向异性材料, 沿蒸汽流动方向的强度远大于其他方向的强度, 且R-CNT的形状对R-CNT/EP复合材料的力学性能有显著影响, 各刚度系数以及杨氏模量在Y型接头处各角相等时最大; R-CNT的体积分数对R-CNT/EP复合材料的力学性能有显著影响, 各有效性能均随着R-CNT体积分数的增大而增大, 但是增大程度不同。     

Synthesis and mechanical properties of interconnected carbon nanofiber network reinforced polydimethylsiloxane composites

Carbon nanofiber (CNF) reinforced elastomer composites with light weight, sustainability of large deformation, chemical stability, corrosion and fatigue resistance, and vibration and noise reduction capability can have positive impact on a wide range of applications. However, this type of composite is still a under studied research area due to the difficulties in material handling and processing. To improve processing control and reproducibility for large scale engineering applications, cost effective carbon nanofibers (CNFs) in form of interconnected porous network structure were used as nanofillers. Processing, microstructure and mechanical properties of carbon nanofibers reinforced polydimethylsiloxane (PDMS) have been studied. Mechanical measurements on the composites show that the CNF-PDMS interfacial bonding can be until failure, interfacial debonding happens in the CNF-PDMS composites and the resulted permanent deformation stabilizes with increasing load-unload cycles with significant energy dissipation.