Effect of Accelerated Aging Temperature under Artificial Seawater on the Properties of Carbon Fiber/Epoxy Composites and the Erosion Mechanism

In order to explore the effect of artificial accelerated aging temperature on the performance of carbon fiber/epoxy resin composites,we used artificial seawater as the aging medium,designed the aging environment of seawater at different temperatures under normal pressure,and studied the aging behavior of carbon fiber/epoxy composites.The infrared spectroscopy results show that,with the increase of aging temperature,the degree of hydrolysis of the composite is greater.At the same time,after 250 days of aging of artificial seawater at regular temperature,40 and 60 ℃,the moisture absorption rates of composite materials were 0.45%,0.63%,and 1.05%,and the retention rates of interlaminar shear strength were 91%,78%,and 62%,respectively.It is shown that the temperature of the aging environment has a significant impact on the hygroscopic behavior and mechanical properties of the composite,that is,the higher the temperature,the faster the moisture absorption of the composite,and the faster the decay of the mechanical properties of the composite.

Durability Testing of Composite Aerospace Materials Based on a New Polymer Carbon Fiber-Reinforced Epoxy Resin

In this study,the durability of a new polymer carbonfiber-reinforced epoxy resin used to produce composite material in the aerospacefield is investigated through analysis of the corrosion phenomena occurring at the microscopic scale,and the related infrared spectra and thermal properties.It is found that light and heat can con-tribute to the aging process.In particular,the longitudinal tensile strength displays a non-monotonic trend,i.e.,itfirst increases and then decreases over time.By contrast,the longitudinal compressive and inter-laminar shear strengths do not show significant changes.It is also shown that the inter-laminar shear strength of carbonfiber/epoxy resin composites with inter-laminar hybrid structure is better than that of pure carbonfiber materials.The related resistance to corrosion can be improved by more than 41%.

Enhanced corrosion resistance of epoxy resin coating via addition of CeO_(2) and benzotriazole

The use of fillers to enhance the corrosion protection of epoxy resins has been widely applied.In this work,cerium dioxide(CeO_(2))and benzotriazole(BTA)were introduced into an epoxy resin to enhance the corrosion resistance of Q235 carbon steel.Scanning electron microscopy results indicated that the CeO_(2) grains were rod-like and ellipsoidal in shape,and the distribution pattern of BTA was analyzed by energy dispersive spectroscope.The dynamic potential polarization curve proved the excellent corrosion resistance of the composite epoxy resin with CeO_(2) and BTA co-addition,and electrochemical impedance spectroscopy test analysis indicated the significantly enhanced long-term corrosion protection performance of the composite coating.And the optimal protective performance was provided by the coating containing 0.3%(mass)CeO_(2) and 20%(mass)BTA,which was attributed to the barrier performance of CeO_(2) particles and the chemical barrier effect of BTA.The formation of corrosion products was analyzed using X-ray diffraction.In addition,the corrosion resistance mechanism of the coating was also discussed in detail.

Carbon-Epoxy圆管件的静态吸能特征

Carbon/Epoxy 复合材料可以用作理想的吸能材料。为了考察材料体系对结构吸能性能的影响,对一系列Carbon/Epoxy圆管件进行了静态吸能性能试验。试验结果表明,在基体种类相同的条件下,结构的压溃失效模式有很大的区别。材料的吸能性能不仅同材料性能关系密切,而且也受材料纤维方式影响。

Carbon Turnover in a Crop Rotation Under Free Air CO_2 Enrichment (FACE)

Mostly based on assumptions derived from controlled-environment studies, predicted future atmospheric CO2 concentrations [CO2] are expected to have considerable impacts on carbon （C） turnover in agro-ecosystems. In order to allow the in situ examination of C-transformations in the plant-soil system of arable crop rotations under future [002], a free air carbon dioxide enrichment （FACE） experiment （550 μmol mol^-1 CO2） was started at Braunschweig, Germany in 1999. The crop rotation under investigation comprised winter barley, a cover crop （ryegrass）, sugar beets and winter wheat. Assessments of CO2 effects included the determination of above- and belowground biomass production, measurements of canopy CO2- and H2O- fluxes, soil microbial biomass and in situ soil respiration. The results obtained during the 1st crop rotation cycle （3 years） showed that for the selected crops elevated [CO2] entailed significant positive effects （P 〈 0.05） on aboveground （6%-14% stimulation） and belowground biomass production （up to 90% stimulation）, while canopy evapotranspiration was reduced. This resulted in increased soil water content. Also, depending on crop type and season, high CO2 stimulated in situ soil respiration （up to 30%）, while soil microbial biomass did not show significant respouses to elevated [CO2] during the first rotation cycle.

Surface Characteristics of Rare Earth Treated Carbon Fibers and Interfacial Properties of Composites

Effect of rare earth treatment on surface physicochemical properties of carbon fibers and interfacial properties of carbon fiber/epoxy composites was investigated, and the interfacial adhesion mechanism of treated carbon fiber/epoxy composite was analyzed. It was found that rare earth treatment led to an increase of fiber surface roughness, improvement of oxygeaa-containing groups, and introduction of rare earth element on the carbon fiber surface. As a result, coordination linkages between fibers and rare earth, and between rare earth and resin matrix were formed separately, thereby the interlaminar shear strength （ILSS） of composites increased, which indicated the improvement of the interfacial adhesion between fibers and matrix resin resulting from the increase of carboxyl and carbonyl.

Determination of Water Diffusion Coefficients and Dynamics in Adhesive/Carbon Fiber Reinforced Epoxy Resin Composite Joints

To determinate the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints, energy dispersive X-ray spectroscopy analysis（EDX） is used to establish the content change of oxy- gen in the adhesive in adhesive/carbon fther reinforced epoxy resin composite joints. As water is made up of oxygen and hydrogen, the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints can be obtained from the change in the content of oxygen in the adhesive during humidity aging, via EDX analy-sis. The authors have calculated the water diffusion coefficients and dynamics in the adhesive/carbon fiber reinforced epoxy resin composite joints with the aid of beth energy dispersive X-ray spectroscopy and elemental analysis. The de- termined results with EDX analysis are almost the same as those determined with elemental analysis and the results al- so show that the durability of the adhesive/carbon fther reinforced epoxy resin composite joints subjected to silane cou- pling agent treatment is better than those subjected to sand paper burnishing treatment and chemical oxidation treat- ment.

Effects of Cure Pressure Induced Voids on the Mechanical Strength of Carbon/Epoxy Laminates

This work aims at designing a set of curing pressure routes to produce laminates with various void contents. The effects of various consolidation pressures resulting in different void contents on mechanical strength of carbon/epoxy laminates have been examined. Characterization of the voids, in terms of void volume fraction, void distribution, size, and shape, was performed by standard test, ultrasonic inspection and metallographic analysis. The interlaminar shear strength was measured by the short-beam method. An empirical model was used to predict the strength vs porosity. The predicted strengths conform well with the experimental data and voids were found to be uniformly distributed throughout the laminate.

Microwave Absorption Properties of Carbon Nanotubes-Epoxy Composites in a Frequency Range of 2 - 20 GHz

In this work, multi-walled carbon nanotubes (MWCNTs)-epoxy composites with MWCNTs (outer diameter less 8 nm) loadings from 1 to 10 wt% were fabricated. The microstructures, dielectric constant, and microwave absorption properties of the MWCNTs-epoxy composite samples were investigated. The measurement results showed that the microwave absorption ratio of the MWCNTs-epoxy composite strongly depend on the MWCNT loading in the composites. The microwave absorption ratio up to 20%-26% around 18-20 GHz was reached for the samples with 8-10 wt% MWCNT loadings. The high absorption performance is mainly attributed to the microwave absorption of MWCNTs and the dielectric loss of MWCNTs-epoxy composites.

Fracture behavior of hybrid epoxy nanocomposites based on multi-walled carbon nanotube and core-shell rubber

The dispersion of nanoparticles plays a key role in enhancing the mechanical performance of polymer nanocomposites.In this work,one hybrid epoxy nanocomposite reinforced by a well dispersed,zinc oxide functionalized,multi-wall carbon nanotube (Zn O-MWCNT) and core-shell rubber (CSR) was prepared,which possesses both high modulus and fracture toughness while maintaining relatively high glass transition temperature (Tg).The improved fracture toughness from 0.82 MPa mfor neat epoxy to 1.46 MPa mfor the ternary epoxy nanocomposites is resulted from a series of synergistic toughening mechanisms,including cavitation of CSR-induced matrix shear banding,along with the fracture of MWCNTs and crack deflection.The implication of the present study for the preparation of high-performance polymer nanocomposites is discussed.

Kinetic Study of Resin-Curing on Carbon Fiber/Epoxy Resin Composites by Microwave Irradiation

Microwave processing has great potential for improving composite manufacturing such as reduction of curing time, energy requirements and operational costs. In this paper, the effects of microwave irradiation for resin-curing of carbon fiber/epoxy resin composite that was composed of discontinuous carbon fibers of 130 μm or 3 mm were investigated. The mechanical properties of carbon fiber/epoxy resin composite cured by microwave irradiation for 20 min at 120°C were similar to ones of the sample prepared by conventional oven for 180 min at 120°C. Microwavecured carbon fiber/epoxy resin composite had higher glass transition temperature than the one prepared by conventional oven. The relation between curing time and flexural modulus indicated that the curing velocity of microwave-irradiated carbon fiber/epoxy resin composite was 9 times faster than the one prepared by conventional oven. Furthermore, activation energies for resincuring reaction on microwave and conventional-cured carbon fiber/epoxy resin composite were estimated. The resin-curing reaction in carbon fiber/epoxy resin composite was promoted by microwave irradiation.

Stress and buckling analysis of a thick-walled micro sandwich panel with a flexible foam core and carbon nanotube reinforced composite (CNTRC) face sheets

In this paper,the stresses and buckling behaviors of a thick-walled mi-cro sandwich panel with a flexible foam core and carbon nanotube reinforced composite(CNTRC)face sheets are considered based on the high-order shear deformation theory(HSDT)and the modified couple stress theory(MCST).The governing equations of equi-librium are obtained based on the total potential energy principle.The effects of various parameters such as the aspect ratio,elastic foundation,temperature changes,and volume fraction of the canbon nanotubes(CNTs)on the critical buckling loads,normal stress,shear stress,and deflection of the thick-walled micro cylindrical sandwich panel consider-ing different distributions of CNTs are examined.The results are compared and validated with other studies,and showing an excellent compatibility.CNTs have become very use-ful and common candidates in sandwich structures,and they have been extensively used in many applications including nanotechnology,aerospace,and micro-structures.This paper also extends further applications of reinforced sandwich panels by providing the modified equations and formulae.

The Reinforcing Effect of Graphene on the Mechanical Properties of Carbon-Epoxy Composites

Graphene nanoplatelets (GNPs) are novel nanofillers holding attractive characteristics, including vigorous compatibility with majority polymers, outstanding mechanical, thermal, and electrical properties. In this study, the outstanding GNPs filler was reinforced to the epoxy matrix and carbon fabric/epoxy hybrid composite slabs to enrich their mechanical properties. Graphene nanoplatelets of 0.5, 1, 1.5 and 2 weight percentages were integrated into the epoxy and the physico-mechanical (microstructure, density, tensile, flexural and impact strength) properties were investigated. Furthermore, the mechanical properties of unfilled and 1 wt% GNPs filled carbon fabric/epoxy hybrid composite slabs were investigated. Subsequently, noteworthy improvement in the mechanical properties was conquered for the carbon fabric/epoxy hybrid composites.

Toughness and Fracture Mechanism of Carbon Fiber Reinforced Epoxy Composites

The fracture toughness of carbon fiber reinforced epoxy composite(CFRP)was investigated through mode I and mode II shaped fracture system in this paper.A novel polyimide with trifluoromethyl groups and grafted nanosilica were used to modify epoxy resin.Effect of modified resin and unmodified resin on fracture toughness of CFRP was compared and discussed.Lay-up angles and thicknesses effects on fracture toughness of composites were also investigated.The fracture toughness of CFRP was obtained through double cantilever beam(DCB)and end notched flexure(ENF)tests.The results showed that the composites prepared by modified resin exhibited high fracture toughness compared with unmodified composites.The fracture toughness value of mode I increased from 1.83 kJ/m2 to 4.55 kJ/m2.The fracture toughness value of mode II increased from 2.30 kJ/m2 to 6.47 kJ/m2.

Enhancing the Mechanical Strength for a Microwave Absorption Composite Based on Graphene Nanoplatelet/Epoxy with Carbon Fibers

Microwave absorption (MWA) materials such as graphene nanoplatelet (GNP)/epoxy are mostly used as coatings on existing structures without considering mechanical properties. In this work, we aim to enhance the mechanical strength of the composite for multifunctional potentials. We used carbon fiber (four layers) to reinforce GNP/epoxy composite (2 mm thick) and investigated their multifunctional properties with GNP loading from 3 to 7 wt%. We measured the tensile strength, hardness, and MW absorption (26.5 - 40 GHz) of composite samples. Our results showed an increase in tensile strength to 109.1 ± 7.9 MPa with 7 wt% GNP in the composite from 15.3 MPa for pure epoxy. The hardness of the composites was also substantially enhanced with GNP loading up to 7 wt%. A MW absorption ratio of 72% was attained for the sample with 7 wt% GNP loading near 40 GHz. The homogenous dispersion of GNPs in the matrix reduces the stress concentration and minimizes the influence of the defects. The high MW absorption and large transmission loss together with enhanced mechanical strength provides a novel multifunctional material for potential applications.

Mechanical Properties of Bio-Based Epoxy Composites Reinforced with Hybrid-Interlayer Ramie and Recycled Carbon Fibres

The growing environmental concerns have led to attention on bio-based composite materials, such as the natural fibres, recycled carbon fibres and bio-based resins. Herein, the bio-based epoxy composites were reinforced with ramie fibre (RF) and recycled carbon fibre (rCF) via inter-layer hybridisation. The dynamic mechanical analysis, tensile, flexural and impact properties characterisation were conducted to analyse the mechanical behaviour of the specimens. Also, the morphology of fractured surface after mechanical tests was studied under a scanning electron microscope. When the volume ratio between RF and rCF was varied from 100/0 to 0/100, the flexural and tensile strength of composites was significantly increased, while the impact strength was reduced. Thus the maximum values of flexural strength (182 MPa) and tensile strength (165 MPa) were observed for rCF reinforced composite, whilst impact strength of 24 kJ/m2 was found for RF reinforced composite. Furthermore, the values of storage and loss modulus were increased with the rCF incorporation due to a greater degree of restriction with the addition of rCF into the matrix. The hybridisation was able to combine the specific properties of RF and rCF and optimise the mechanical performance of composites. Therefore, the alternative low-cost green composites are prepared which can replace synthetic materials for semi-structural applications.

Detecting Impact Damage in Carbon Fabric/epoxy-matrix Composites by Ultrasonic F-scan and Electrical Resistance Measurement

The status and the variation of electrical resistance of impacted carbon fiber/epoxy-matrix composites were studied by ultrasonic F-scan and electrical resistance measurement The experimental results shows that impact damage energy threshold value of carbon fabric/epoxy-matrix composites can determine by using ultrasonic F-scan. When the impact energy exceeds the threshold value, damage is generated in composites. Electrical resistance of impacted composites is changed owing to the contact of each carbon fiber unit in composites, which cause a change of the series-parallel in conductors. The veracity of detecting impact damage in composites can be improved in this case.

High microwave absorption performances for single-walled carbon nanotube–epoxy composites with ultra-low loadings

Microwave-absorbing polymeric composites based on single-walled carbon nanotubes （SWNTs） are fabricated via a simple yet versatile method, and these SWNT-epoxy composites exhibit very impressive microwave absorption perfor- mances in a range of 2 GHz-18 GHz. For instance, a maximum absorbing value as high as 28 dB can be achieved for each of these SWNT-epoxy composites （1.3-mm thickness） with only 1 wt% loading of SWNTs, and about 4.8 GHz bandwidth, corresponding to a microwave absorption performance higher than 10 dB, is obtained. Furthermore, such low and appro- priate loadings of SWNTs also enhance the mechanical strength of the composite. It is suggested that these remarkable results are mainly attributable to the excellent intrinsic properties of SWNTs and their homogeneous dispersion state in the polymer matrix.

Preparation of Three-Dimensional Carbon Network Reinforced Epoxy Composites and Their Thermal Conductivity

As a thermosetting resin with excellent properties,epoxy resin is used in many areas such as electronics,transportation,aerospace,and other fields.However,its relatively low thermal conductivity limits its wide application in more demanding fields.Here,a three-dimensional carbon(3DC)network was prepared through NaCl template-assisted in situ chemical vapor deposition(CVD)and used to reinforce epoxy resin for enhancing its thermal conductivity.The 3DC was prepared with a molar ratio of sodium atom to carbon atom of 100:20,and argon atmosphere in CVD led to an optimal improvement in the thermal conductivity of epoxy resin.The thermal conductivity of epoxy resin increased by 18%when the filling content was 3 wt.%of 3DC network because of the high contact area,uniform dispersion,and enhanced formation of conductive paths with epoxy resin.As the amount of 3DC addition increases,the thermal conductivity of composites also increases.As an innovative exploration,the work presented in this paper is of great significance for the thermal conductivity application of epoxy resin in the future.

Role of Metallic Nanofillers on Mechanical and Tribological Behaviour of Carbon Fabric Reinforced Epoxy Composites

In this study, hybrid composites based on carbon fabric and epoxy (C/Ep) were fabricated by hand lay-up method followed by compression moulding. The C/Ep with optimum carbon fiber (60 wt%) was chosen as a reference material, and to it, the metallic nanoparticles like aluminum (Al) and zinc (Zn) of different wt% (0.5 and 1.0) were included as secondary fillers. To understand the synergism effect of these hybrid reinforcements, mechanical properties and tribological behavior of composites were studied. From the test results, it was proved that hybridization improved the mechanical and tribological properties. The C/Ep consisting of 0.5 wt% Zn and Al showed higher tensile properties in comparison with all other fabricated composites. Increase in flexural strength and flexural modulus also observed as the filler content increased in C/Ep composite. Higher impact strength is noted at 1 wt% Zn filled C/Ep composite. Wear test data revealed that 0.5 wt% Zn in C/Ep has got superior wear resistance. Wear mechanisms were discussed using scanning electron micrographs of selected worn surfaces of the composites.