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The surface of carbon fiber is treated with sizing agent containing hydroxylated carbon nanotubes, fullerenols, and graphene oxide, respectively. The effects of carbon nanomaterials and their structures on the surface properties of carbon fiber, the interfacial properties and the mechanical properties of carbon fiber/epoxy composites are investigated. All three types of carbon nanomaterial can improve the interfacial bonding strength and modulus, thereby enhancing the interlaminar shear strength (ILSS) of composites. Moreover, the ILSS increases with the increase of interfacial bonding strength, due to the roughness and the number of active groups. Compared with the composite without carbon nanomaterials, the interfacial bonding strength of the three nanoparticle‐modified composites increased by 14%, 5% and 4%, the modulus increased by 10%, 26%, and 9%, and the ILSS increased by 14%, 8%, and 7%, respectively. The interfacial bonding strength has a more significant impact on the ILSS than the interfacial modulus. Highlights: CNTs, graphene oxide and fullerenols regulate the surface characteristics of carbon fibers.The influence of carbon nanomaterials on the interfacial properties of composites.The relationship between the fiber surface, the interface and the composites. [ABSTRACT FROM AUTHOR]

Delamination is one form of damage in composite laminates. The effects of delamination damage locations (thickness direction of laminates) on the residual compressive strength and failure mechanism of carbon fiber/polyphenylene sulfide (CF/PPS) composites are studied by damage morphology, full‐field strain and finite element simulation. The closer the delamination is to the center of the composite, the lower the residual compressive strength. The failure mode of composites is dominated by 0° fiber fracture, which is divided into bulging, delamination propagation, and fracture. The delamination locations significantly affect the first two stages. Highlights: Constructing delamination damage in composites by interlayer preset defects.Simulation and damage analysis to reveal the mechanism of compression failure.The relationship between delamination depth and damage stage is revealed. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polyamide composites have outstanding properties, but their applications are significantly affected by the service environment. This work evaluates the effects of temperature (25, 80, 140, and 200°C) and hygrothermal conditions on the mechanical properties of CF/PA6 composite containing delamination damage, and studies its damage behaviors and failure mechanisms. After hygrothermal aging, recrystallization of PA6 improves the heat resistance of CF/PA6 composites, but water absorption reduces the interfacial strength of composites, resulting in the decrease of modulus and compressive strength (24% and 42%, respectively). With the increase in temperature, the compressive strength of CF/PA6 composites gradually decreases (from 132 MPa at 25°C to 24 MPa at 200°C), and the failure mode transitions from fiber fractures, interlayer shear fractures, delamination to kinking. In addition, the compressive failure process of CF/PA6 composites is divided into three stages: buckling, delamination bulging and kinking failure. Highlights: Hygrothermal aging reduces the fiber/resin interface performance.Fiber fracture, interlayer shear and delamination convert to kinking failure.The failure process is divided into buckling, delamination and kinking. [ABSTRACT FROM AUTHOR]

Low‐velocity impact damage is one of the main defects of composite laminates, which seriously affects the bearing capacity and service life of composite laminates. Multiple impact experiments of carbon fiber/epoxy composite laminates were carried out under different impact energies. The finite‐element model was established according to the experimental conditions. The impact damage mechanism of laminated plates was studied by means of simulated damage cloud image, water immersion ultrasonic C‐scan, and computed tomography. The results showed that the matrix damage occurred mainly during the whole impact process, and the tensile damage of the matrix was dominant. As the number of impacts increased, the impact resistance of composite laminates decreased and the damaged area increased, with the second impact having the greatest influence on the degree of damage to the laminates; multiple impacts with low energy were easy to cause delamination at the top of the laminated plate. With the increase in impact energy, the damage at the bottom of the laminated plate was more serious, and the propagation mode of delamination damage in laminates changed from top‐bottom to bottom‐up. Highlights: Establishing a multiple impact finite‐element model for composites.Accurately predicting the impact mechanical response of composites.Revealing multiple impact damage evolution of composites by simulation. [ABSTRACT FROM AUTHOR]

Abstract: A new tri‐layer Yb2SiO5/Yb2Si2O7/Si coating was fabricated on SiC, C/SiC, and SiC/SiC substrates, respectively, using atmospheric plasma spray (APS) technique. All coated samples were subjected to thermal shock test at 1350°C. The evolution of phase composition and microstructure and thermo‐mechanical properties of those samples before and after thermal shock test were characterized. Results showed that adhesion between all the 3 layers and substrates appeared good. After thermal shock tests, through microcracks which penetrated the Yb2SiO5 top layer were mostly halted at the Yb2SiO5‐Yb2Si2O7 interface and no thermal growth oxide (TGO) was formed after 40‐50 quenching cycles, implying the excellent crack propagation resistance of the environmental barrier coating (EBC) system. Transmission electron microscopy analysis confirmed that twinnings and dislocations were the main mechanisms of plastic deformation of the Yb2Si2O7 coating, which might have positive effects on crack propagation resistance. The thermal shock behaviors were clarified based on thermal stresses combined with thermal expansion behaviors and elastic modulus analysis. This study provides a strategy for designing EBC systems with excellent crack propagation resistance. [ABSTRACT FROM AUTHOR]

Rare-earth monosilicates (RE2SiO5, RE: rare-earth elements), such as Yb2SiO5, have been developed for potential application as environmental barrier coating (EBC) materials. Yb2SiO5 coating would experience microstructure evolution under high-temperature environment and accordingly its thermomechanical properties would be altered. In this study, Yb2SiO5 coating was fabricated by atmospheric plasma spray technique. The phase stability and microstructure change before and after thermal aging at 1300°C, 1400°C, and 1500°C were investigated. The changes in mechanical and thermal properties were characterized. The results showed that the as-sprayed coating was mainly composed of Yb2SiO5 with a small amount of Yb2O3 and amorphous phase. Defects in the coating, including interfaces, pores, and microcracks, were greatly reduced with grain growth after thermal treatment. Thermal aging significantly modified the thermal and mechanical properties of the coating. The average CTE was increased by 13.1%, and the hardness and elastic modulus was increased by 42.4% and 49.4%, respectively, after thermal aging at 1500°C for 50 hour. The thermal conductivity of thermal-aged coating was much higher than that of the as-sprayed coating, which was still less than 2 W/(m·K). The influence of coating microstructure on the properties was analyzed and related to the failure mechanism of EBCs. [ABSTRACT FROM AUTHOR]

The investigations were carried out into the cure kinetics and thermal stability of multifunctional epoxy/anhydride/imidazole/release agent system (matrix) and carbon fiber reinforced matrix composite. Two experimental techniques were applied: dynamic differential scanning calorimetry (DSC) at different heating rates, and non-isothermal thermogravimetric analysis (TGA). The results were indicated that the two-parameter model was found to describe the cure kinetics for the matrix and the composite. The kinetic parameters such as pre-exponential factor, apparent activation energy, and reaction orders were calculated. And, the carbon fiber had a significant effect on the apparent activation energy and the thermal stability. POLYM. COMPOS., 35:596-601, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]

1,1,3,5-tetraphenoxy-3,5-bis(4-aminoanilino)cyclotriphosphazene, 1,1,3,5-tetraphenoxy-3,5-bis[4-(4-aminophenysulfone)anilino)]cyclotriphosphazene, and 1,1,3,5-tetraphenoxy-3,5-bis( N, N′-ethanediamine)cyclotriphosphazene were synthesized in two steps from the p-Phenylenediamine, 4,4′-diaminodiphenylsulfone, and ethylenediamine via nucleophilic substitution and catalytic reduction with hexachlorocyclotriphosphazene. Three novel aromatic polyamides such as poly(cyclotriphosphazene-p-phenylene amide), poly(cyclotriphosphazene-p-sulfuryl amide), and poly(cyclotriphosphazene-ethyl amide) were synthesized from these diamines by direct polycondensation reaction with terephthaloyl chloride and pyridine in N-methyl pyrrolidone, respectively. The chemical structures of the diamine monomers and three novel poly(cyclotriphosphazene-aryl amide)s were characterized by Fourier Transform Infrared, (1H and 31P) Nuclear Magnetic Resonance, and Elemental Analysis. The thermal properties of the polyamides were determined by Differential Scanning Calorimetry and Thermogravimetric Analysis (TGA). The crystallization behaviors of the polyamides were studied by Wide-ray X-ray diffraction, and the morphology of the pyrolysis residues were observed by Scanning Electron Microscope. The three poly(cyclotriphosphazene-aryl amide)s with amorphous structure would exhibit an enhanced solubility in polar aprotic solvents and a superior thermal stability with initial decomposition temperature being at about 198-259°C. TGA curves of the poly(cyclotriphosphazene-aryl amide)s exhibit mainly three thermal decomposition steps, and the poly(cyclotriphosphazene-p-phenylene amide) presents the highest solid residue rate 62.6% heated to 600°C. In the morphology analysis of the poly(cyclotriphosphazene-aryl amide) solid residues, organophosphorus gelatum forms in the surface layer were observed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 [ABSTRACT FROM AUTHOR]

The development of a conductive fiber with flame resistance is an urgent concern particularly in national defense and other specialized fields. Aramid fibers ( para- or meta-) exihibit high strength and excellent fire resistance. Electroless silver plating on para-aramid fibers and growth morphology of silver deposits was investigated in the present work. The surface of para-aramid fibers was roughened using sodium hydride/dimethyl sulfoxide to guarantee successful electroless plating. Two complexing agents (ethylene diamine/ammonia) and two reducing agents (glucose/seignette salt) were used for the electroless silver plating bath design. Structure and properties of the resulting silver-deposited para-aramid fibers were evaluated based on scanning electron microscopy, silver weight gain percentage calculation, electrical resistance measurement, crystal structure analysis, and mechanical properties test. The results showed that a higher silver weight gain was advantageous to the improvement of conductivity for the silver-deposited para-aramid fibers. The obtained silver deposit was homogenous and compact. Electroless silver-plating deposits were considered to be three-dimensional nucleation and growth model (Volmer-Weber). Black, silver gray, and white deposits appeared sequentially with progressive plating. The breaking strength of silver-deposited para-aramid fibers remained at value up to 44 N. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 [ABSTRACT FROM AUTHOR]

Highlights The effect of membrane thickness of electrospinning polyethersulfone (PES) nanofiber membranes on interlayer toughness and impact resistance of carbon fiber reinforced epoxy resin (CF/EP) composites are researched. Intercalation composites with different nanofiber membrane thicknesses, ranging from 10 to 50 μm, are tested at mode I and mode II interlaminar fracture toughness. The impact resistance of nanofiber membranes with different thicknesses is evaluated by the compression after impact (CAI) strength test. Moreover, nanofiber toughening contributions are investigated using the crack path and surface analysis. Results indicate that PES nanofibers increase the toughness of interlayer resin and change the interlaminar crack propagation path of CF/EP composites. The optimum nanofiber membrane thickness for mode I (GI = + 58%) and CAI (CAI strength = + 33%) is 50 μm, while for mode II is 30 μm (GII = + 16.4%). The storage modulus of CF/EP composites increases with the increase of nanofiber membrane thickness. The study also confirms the insertion of a nanofiber membrane slightly improves the tensile strength and interlaminar shear strength (ILSS) of the CF/EP composites. PES nanofiber membranes of different thicknesses were inserted into the CF/EP. CAI and GI improved by 33% and 58%, respectively of CF/EP composites. The relationship between interlayer fracture toughness and CAI was discussed. [ABSTRACT FROM AUTHOR]