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.

Wear Displayed by the Scratch of Epoxy Composites Filled by Metallic Particles under the Influence of Magnetic Field

The tribological performance of the sliding bearings which are probably made of polymers, which is subjected to magnetic field, is of great intense. The wear of epoxy composites filled by metallic particles such as iron, copper and aluminum scratched by steel indenter is investigated. The wear scar width of the scratch was measured by an optical microscope. It was found that wear displayed by the scratch of epoxy filled by the metallic filling materials such as iron, copper and aluminum increased with increasing applied load. As the content of the metallic filling materials increased, wear slightly increased due to the reduction in cohesive stress inside the matrix as well as the epoxy transfer into the indenter surface might be responsible for that behavior. For epoxy filled by iron, when the magnetic field was applied to the contact area wear significantly decreased. Increasing the intensity of the magnetic field showed slight wear increase. Wear displayed by the scratch of epoxy filled by copper showed higher values than that observed for copper filled epoxy. Presence of the magnetic field might generate electric current at the contact area leading to an increase in the intensity of the electric static charge. Moreover, wear of epoxy filled by aluminum showed lower values than that observed for epoxy composites filled by copper and higher than that displayed by iron filled epoxy composites. Under the effect of magnetic field, wear significantly increased. This behavior could explained on the basis that the presence of magnetic field accompanied by the movement of the indenter in the epoxy composites generated electric current passing through the steel indenter which caused softening of the epoxy composites. In that condition removal of epoxy from the wear track was easier and epoxy transfer into the steel indenter was accelerated.

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.

Value-Added Utilization of Agro-Waste Derived Oil Palm Ash in Epoxy Composites

Oil palm ash(OPA)is an agro-industry waste and it has disposable problems.In the present study,an effort was made for value addition to OPA by incorporating it as a micro-filler in different concentration(0,10,20,30,40,and 50%)and sizes(100,200,and 300 mesh size particles)in the epoxy matrix.Prepared micro OPA was having a crystallinity index of 65.4%,high inorganic elements,and smooth surface morphology.Fabricated composites had higher void content as compared to neat epoxy matrix.Mechanical properties of fabricated composites had a maximum value at 30%loading of 300 mesh-size filler due to its low void content and size as compared to filler of 100 and 200 mesh size.Further increase in the concentration of OPA filler after 30 wt%of loading leads to the agglomeration of OPA microparticles and thereby resulted in the reduction of mechanical characteristics such as tensile strength,tensile modulus,flexural strength and flexural modulus of the composites.However,elongation at break decreased with increase in filler content at all percentage.Thermal stability and char residue percentage of composite increased with the concentration of filler at all percentage.Surface morphology of composite showed that OPA incorporation lead towards its roughness and cracks were originated from the site of OPA embedded in the epoxy matrix.The 300 mesh-size particles were having the best effect on composite as compared to 100 and 200 mesh-size filler.

Effect of surface oxidation on the interfacial and mechanical properties in graphite/epoxy composites composite bipolar plates

Epoxy resin-reinforced graphite composites have found extensive application as bipolar plates in fuel cells for stationary power supplies,valued for their lightweight nature and exceptional durability.To enhance the interfacial properties between graphite and epoxy resin(EP),surface oxidation of graphite was carried out using diverse functional groups.Experimental assessments illustrated that the composites with graphite oxide resulted in heightened mechanical strength and toughness compared to pristine graphite,which could be attributed to the excellent interface connection.Moreover,these composites displayed remarkable conductivity while simultaneously retaining their mechanical attributes.Furthermore,molecular dynamics simulations outcomes unveiled that the inclusion of oxygen-containing functional groups on the graphite surface augmented the interfacial energy with EP,and the interface morphology between graphite and resin exhibited heightened stability throughout the stretching process.This simple and effective technique presents opportunities for improving composites interfaces,enabling high load transfer efficiency,and opens up a potential path for developing strong and tough composite bipolar plates for fuel cells.

Fiber-reinforced Three-dimensional Graphene Aerogels for Electrically Conductive Epoxy Composites with Enhanced Mechanical Properties

To enhance the mechanical properties of three-dimensional graphene aerogels with aramid fibers, graphene/organic fiber aerogels are prepared by chemical reduction of graphene oxide in the presence of organic fibers of poly（p-phenylene terephthalamide） （PPTA） and followed by freeze-drying. Thermal annealing of the composite aerogels at 1300℃ is adopted not only to restore the conductivity of the reduced graphene oxide component but also to convert the insulating PPTA organic fibers to conductive carbon fibers by the carbonization. The resultant graphene/carbon fiber aerogels （GCFAs） exhibit high electrical conductivities and enhanced compressive properties, which are highly efficient in improving both mechanical and electrical performances of epoxy composites. Compared to those of neat epoxy, the compressive modulus, compressive strength and energy absorption of the electrically conductive GCFA/epoxy composite are significantly increased by 60%, 59% and 131%, respectively.

Experimental investigation and prediction of tribological behavior of unidirectional short castor oil fiber reinforced epoxy composites

The present study aims at introducing a newly developed natural fiber called castor oil fiber,termed ricinus communis,as a possible reinforcement in tribo-composites.Unidirectional short castor oil fiber reinforced epoxy resin composites of different fiber lengths with 40%volume fraction were fabricated using hand layup technique.Dry sliding wear tests were performed on a pin-on-disc tribometer based on full factorial design of experiments(DoE)at four fiber lengths(5,10,15,and 20 mm),three normal loads(15,30,and 45 N),and three sliding distances(1,000,2,000,and 3,000 m).The effect of individual parameters on the amount of wear,interfacial temperature,and coefficient of friction was studied using analysis of variance(ANOVA).The composite with 5 mm fiber length provided the best tribological properties than 10,15,and 20 mm fiber length composites.The worn surfaces were analyzed under scanning electron microscope.Also,the tribological behavior of the composites was predicted using regression,artificial neural network(ANN)-single hidden layer,and ANN-multi hidden layer models.The confirmatory test results show the reliability of predicted models.ANN with multi hidden layers are found to predict the tribological performance accurately and then followed by ANN with single hidden layer and regression model.

Tribological properties of short carbon fibers reinforced epoxy composites

Short carbon fiber(SCF)reinforced epoxy composites with different SCF contents were developed to investigate their tribological properties.The friction coefficient and wear of the epoxy composites slid in a circular path against a steel pin inclined at 45°to a vertical axis and a steel ball significantly decreased with increased SCF content due to the solid lubricating effect of SCFs along with the improved mechanical strength of the composites.The scanning electron microscope(SEM)observation showed that the epoxy composites had less sensitive to surface fatigue caused by the repeated sliding of the counterparts than the epoxy.The tribological results clearly showed that the incorporation of SCFs was an effective way to improve the tribological properties of the epoxy composites.

Enhanced tribological properties of aligned graphene-epoxy composites

The random distribution of graphene in epoxy matrix hinders the further applications of grapheneepoxy composites in the field of tribology.Hence,in order to fully utilize the anisotropic properties of graphene,highly aligned graphene-epoxy composites(AGEC)with horizontally oriented structure have been fabricated via an improved vacuum filtration freeze-drying method.The frictional tests results indicated that the wear rate of AGEC slowly increased from 5.19x10^(-6)mm^(3)/(N-m)to 2.87x10^(-5)mm^(3)/(N-m)with the increasing of the normal load from 2 to 10 N,whereas the friction coefficient(COF)remained a constant of 0.109.Compared to the neat epoxy and random graphene-epoxy composites(RGEC),the COF of AGEC was reduced by 87.5%and 71.2%,and the reduction of wear rate was 86.6%and 85.4%at most,respectively.Scanning electron microscope(SEM)observations illustrated that a compact graphene self-lubricant film was formed on the worn surface of AGEC,which enables AGEC to possess excellent tribological performance.Finally,in light of the excellent tribological properties of AGEC,this study highlights a pathway to expand the tribological applications of graphene-epoxy composites.

Preparation and 3D printing of high-thermal-conductivity continuous mesophase-pitch-based carbon fiber/epoxy composites

To meet the requirements of spacecraft for the thermal conductivity of resins and solve the problem of low thermal conduction efficiency when 3D printing complex parts,we propose a new type of continuous mesophase-pitch-based carbon fiber/thermoplastic polyurethane/epoxy(CMPCF/TPU/epoxy)composite filament and its preparation process in this study.The composite filament is based on the high thermal conductivity of CMPCF,the high elasticity of TPU,and the high-temperature resistance of epoxy.The tensile strength and thermal conductivity of the CMPCF/TPU/epoxy composite filament were tested.The CMPCF/TPU/epoxy composites are formed by 3D printing technology,and the composite filament is laid according to the direction of heat conduction so that the printed part can meet the needs of directional heat conduction.The experimental results show that the thermal conductivity of the printed sample is 40.549 W/(m·K),which is 160 times that of pure epoxy resin(0.254 W/(m·K)).It is also approximately 13 times better than that of polyacrylonitrile carbon fiber/epoxy(PAN-CF/epoxy)composites.This study breaks through the technical bottleneck of poor printability of CMPCF.It provides a new method for achieving directional thermal conductivity printing,which is important for the development of complex high-performance thermal conductivity products.

Research on properties of hollow glass microspheres/epoxy resin composites applied in deep rock in-situ temperature-preserved coring

Deep petroleum resources are in a high-temperature environment.However,the traditional deep rock coring method has no temperature preserved measures and ignores the effect of temperature on rock porosity and permeability,which will lead to the distortion of the petroleum resources reserves assessment.Therefore,the hollow glass microspheres/epoxy resin(HGM/EP)composites were innovatively proposed as temperature preserved materials for in-situ temperature-preserved coring(ITP-Coring),and the physical,mechanical,and temperature preserved properties were evaluated.The results indicated that:As the HGM content increased,the density and mechanical properties of the composites gradually decreased,while the water absorption was deficient without hydrostatic pressure.For composites with 50 vol%HGM,when the hydrostatic pressure reached 60 MPa,the water absorption was above 30.19%,and the physical and mechanical properties of composites were weakened.When the hydrostatic pressure was lower than 40 MPa,the mechanical properties and thermal conductivity of composites were almost unchanged.Therefore,the composites with 50 vol%HGM can be used for ITPCoring operations in deep environments with the highest hydrostatic pressure of 40 MPa.Finally,to further understand the temperature preserved performance of composites in practical applications,the temperature preserved properties were measured.An unsteady-state heat transfer model was established based on the test results,then the theoretical change of the core temperature during the coring process was obtained.The above tests results can provide a research basis for deep rock in-situ temperature preserved corer and support accurate assessment of deep petroleum reserves.

Epoxy Resin/Nano Ni@C Composites Exhibiting NTC Effect with Tunable Resistivity

Epoxy resin/Ni@C nanoparticle composites with aligned microstructure were prepared by using a procedure of magnetic field assisted curing. The results show that the resistivity of composites exhibits negative temperature coefficient （NTC） effect above room temperature, and can be adjusted by varying the content filler and the magnitude of magnetic field applied. Hill＇s quantum tunneling model was modified to understand the electrical conduction mechanism in the composites. It shows that the NTC effect ascribes to the dominant thermal activated tunneling transport of electron across adjacent nanoparticles, as well as the low thermal expansivity of epoxy resin matrix.

3D Lamellar-Structured Graphene Aerogels for Thermal Interface Composites with High Through-Plane Thermal Conductivity and Fracture Toughness

Although thermally conductive graphene sheets are efficient in enhancing in-plane thermal conductivities of polymers,the resulting nanocomposites usually exhibit low through-plane thermal conductivities,limiting their application as thermal interface materials.Herein,lamellarstructured polyamic acid salt/graphene oxide(PAAS/GO)hybrid aerogels are constructed by bidirectional freezing of PAAS/GO suspension followed by lyophilization.Subsequently,PAAS monomers are polymerized to polyimide(PI),while GO is converted to thermally reduced graphene oxide(RGO)during thermal annealing at 300℃.Final graphitization at 2800℃ converts PI to graphitized carbon with the inductive effect of RGO,and simultaneously,RGO is thermally reduced and healed to high-quality graphene.Consequently,lamellar-structured graphene aerogels with superior through-plane thermal conduction capacity are fabricated for the first time,and its superior through-plane thermal conduction capacity results from its vertically aligned and closely stacked high-quality graphene lamellae.After vacuum-assisted impregnation with epoxy,the resultant epoxy composite with 2.30 vol% of graphene exhibits an outstanding through-plane thermal conductivity of as high as 20.0 W m^−1 K^−1,100 times of that of epoxy,with a record-high specific thermal conductivity enhancement of 4310%.Furthermore,the lamellar-structured graphene aerogel endows epoxy with a high fracture toughness,~1.71 times of that of epoxy.

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.

GALVANIC CORROSION BETWEEN GRAPHITE EPOXY COMPOSITE MATERIALS AND LY12CZ ALUMINUM ALLOY

The electrochemical approach was used to show the nature of the galvanic corrosion when graphite epoxy composite materials(GECM)were coupled to LY12CZ aluminum alloy. An open circuit potential difference of one volt was obtained in 3.5% NaCl solution between GECM and LY12CZ. Corrosion current data (zero impedance technique) indicated that there was serious corrosion at GECM/LY12CZ couple.When GECM/LY12CZ couples were exposed to ASTM salt spray and alternate immersion condition, fiber glass cloth and H06-2 epoxy primer paint were effective methods for preventing galvanic corrosion.The slow strain rate test (SSRT) showed that GECM increased the LY12CZ stress corrosion crack growth rate.

Hygrothermal effect on high-velocity impact resistance of woven composites

The woven glass fiber reinforced composites(GFRP)subjected to high-speed impact is investigated to identify the hygrothermal aging effect on the impact resistance.Both the hygrothermal aged and unaged glass/epoxy laminates are subjected to different impact velocities,which is confirmed as a sensitive factor for the failure modes and mechanisms.The results show the hygrothermal aging effect decreases the ballistic limit by 14.9%,but the influence on ballistic performance is limited within the impact velocity closed to the ballistic limit.The failure modes and energy dissipation mechanisms are confirmed to be slightly influenced by the hygrothermal aging effect.The hygrothermal aging effect induced localization of structural deformation and degradation of mechanical properties are the main reasons for the composite undergoing the same failure modes at smaller impact velocities.Based on the energy absorption mechanisms,analytical expressions predict the ballistic limit and energy absorption to reasonable accuracy,the underestimated total energy absorption results in a relatively poor agreement between the measured and predicted energy absorption efficiency.

Electrical and optical properties of indium tin oxide/epoxy composite film

The electrical and optical properties of the indium tin oxide （ITO）/epoxy composite exhibit dramatic variations as functions of the ITO composition and ITO particle size. Sharp increases in the conductivity in the vicinity of a critical volume fraction have been found within the framework of percolation theory. A conductive and insulating transition model is extracted by the ITO particle network in the SEM image, and verified by the resistivity dependence on the temperature. The dependence of the optical transmittance on the particle size was studied. Further decreasing the ITO particle size could further improve the percolation threshold and light transparency of the composite film.

Comparative Study of Micro and Nano Size WO3/E44 Epoxy Composite as Gamma Radiation Shielding Using MCNP and Experiment

The radiation shielding characteristics of 50wt% WO3/E44 epoxy composite in various gamma energies from 80 keV to 1.33 MeV are investigated via the MCNP code. Thus two scales are considered for WOa filler particles： micro and nano with sizes of i #m and 5Onto, respectively. The simulation results show that W03 nano particles exhibit a larger increase in linear attenuation coefficient in comparison with micro size particles. Finally, validation of simulation results with the published experimental data shows a good agreement.

Fracture Behavior of Epoxy Asphalt Pavement on Steel Bridges based on Optical Fiber Sensing Technology and Numerical Simulation

The distributed optical fiber sensing technology was used to investigate the fracture behavior of the Epoxy Asphalt Mixture. The spatial distribution and variation of the strain development with crack propagation were acquired using the brillouin optical time-domain reflectometer through the loading experiments of the composite beam structure. In addition, a finite element model of the composite beam structure was developed to analyze the mechanical responses of the epoxy asphalt mixture using the extended finite element method. The experimental results show that the development of crack propagation becomes instable with the increase of the load, and larger loads will generate deeper cracks. Moreover, the numerical results show that the mechanical response of the crack tip changes with the crack propagation, and the worst areas that subjected to crack damage are located on both sides of the composite beam structure.