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Chen Y.,Beihang University | Wang Z.,Beihang University | Wang S.,Beihang University | Zhou Z.,Advanced Composites Center | And 2 more authors.
Journal of Applied Mechanics, Transactions ASME | Year: 2015

Carbon nanotube (CNT) reinforced composites have been drawing intense attentions of researchers due to their good mechanical and physical properties as well as potential applications. The diameter, as an important geometric parameter of CNTs, significantly affects the performance of CNTs in the reinforced composites, not only in a direct way but also in an indirect way by influencing the effective modulus and strength of reinforcing CNTs. This paper investigates the comprehensive effect of CNT diameter on the fracture toughness of CNT reinforced composites by accounting for both direct and indirect influences of CNT diameter based on the three-level failure analysis. The criteria for failure modes are established analytically, and the types of failure mode transition with the corresponding optimal CNT diameter are obtained. It is found that reducing CNT diameter can cause a sudden drop in fracture toughness of composites due to the transition of dominant failure mode. Therefore, the CNTs with smaller diameter do not definitely confer a better fracture toughness on their reinforced composites, and the optimal CNT diameter may exist in the transition between failure modes, especially from interfacial debonding to CNT break. In addition, according to the results, the failure mode of CNT break is suggested to be avoided in the composite design because of the low fracture toughness enhancement of CNTs in this mode. This study can provide guiding reference for CNT reinforced composite design. Copyright © 2015 by ASME. Source

Kusaka T.,Ritsumeikan University | Kono T.,Ritsumeikan University | Nomura Y.,Ritsumeikan University | Wakabayashi H.,Advanced Composites Center
Zairyo/Journal of the Society of Materials Science, Japan | Year: 2014

A novel experimental method was proposed for characterizing the compressive properties of composite materials under impact loading. Split Hopkinson pressure bar system was employed to carry out the dynamic compression tests. The dynamic stress-strain relations could be precisely estimated by the proposed method, where the ramped input, generated by the plastic deformation of a zinc buffer, was effective to reduce the oscillation of the stress field in the specimen. The longitudinal strain of gage area could be estimated from the nominal deformation of gage area, and consequently the failure process could be grasped in detail from the stress-strain relation. Finite element analysis was also carried out to confirm the validity of the proposed method. Numerical results demonstrated that the nonuniformity of the stress field could be negligible by using the ramped input. The dynamic compressive strength of a twilled-woven carbon-fiber/epoxy composite was slightly higher than the static compressive strength. © 2014 The Society of Materials Science, Japan. Source

Rajesh Kumar S.,Advanced Composites Center | Dhanasekaran J.,Advanced Composites Center | Krishna Mohan S.,Indian Defence Research And Development Laboratory
RSC Advances | Year: 2015

A new class of E glass fabric reinforced polybenzoxazine titanate composites (EBTA) were made with bisphenol F benzoxazine (BZ) and in situ generating reactive multi branched n-butoxy triethanol amine titanate (TEA) chelate in various ratios. The incorporation of TEA into a polybenzoxazine matrix could cause uniform dispersion within the polymer matrix and ring opening of oxazine at lower temperature, which result in an increase of the cross link density, stiffness and hindered network structures responsible for enhancing the thermal and water resistance. The hypothetical chemical reaction between BZ and TEA was understood by studying the reaction between model compounds such as phenol, tetra isobutyl titanate and triethanol amine. FTIR and DSC studies were utilized to optimize the curing studies and the final cure temperature was established for EBTA composites. The DMA analysis carried out on EBTA composites showed improved stiffness, crosslink density and service temperatures (Tg) with uniform phase distribution when compared to the E glass fabric reinforced polybenzoxazine composite. The thermal stability and char yield with TGA analysis, interfacial adhesion with SEM and hydrolytic stability for the EBTA composites using up to 23% of TEA were found to be improved when compared to the polybenzoxazine composite. The flame retardancy of EBTA composites were found to be retained for the V1 class of polybenzoxazine composite. The EBTA composites showed low maximum cure temperature, improved service temperature, cross link density, stiffness, water absorption resistance, thermal stability and char yield when compared to the E glass fabric polybenzoxazine composite. © 2015 The Royal Society of Chemistry. Source

Zhao Y.,Beijing University of Chemical Technology | Ma Z.,Beijing University of Chemical Technology | Song H.,Beijing University of Chemical Technology | Chen M.,Beijing University of Chemical Technology | Zhou Z.,Advanced Composites Center
Cailiao Yanjiu Xuebao/Chinese Journal of Materials Research | Year: 2016

A kind of carbon fiber/graphene oxide multi-scale reinforcement was prepared by "grafting to" method, with raw materials of the graphene oxide fabricated by a modified Hummers method and the carbon fiber treated with silane coupling agent Kh550. The prepared product was characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), Ramanspectroscopy (Raman), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The mechanical properties and the conductivity of the reinforced carbon fiber were measured by electronic tensile strength tester for fiber and resistivity instrument. The results showthatafter grafting, the graphene oxide can be grafted onto grooves and defects of the carbon fiber surface; the number of unsaturated carbon atom increases and the size of microcrystalline decreases on the surface of the carbon fiber; and the tensile strength and the fracture elongation of single carbon fiber may be increased up to 9.8% and 13.1%, respectively and however the conductivity of carbon fiber is reduced by 11.6%. © All right reserved. Source

Luo Y.-F.,Advanced Composites Center | Li Y.,Beihang University | Zhao Y.,Beihang University | Xie F.-Y.,Advanced Composites Center
Cailiao Gongcheng/Journal of Materials Engineering | Year: 2014

The surface properties of two domestic T800-grade sized and desized carbon fibers were characterized by scanning electron microscope (SEM), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). The micro-interface shear strength (IFSS) of single fiber composites was also analysed by single fiber fragmentation test (SFFT). The influences of surface properties on micro-interphase strength of single carbon fiber composites and hygrothermal properties were investigated. The results show that the amount of surface active functional groups decreases and surface roughness increases, but the interfacial adhesion between fiber and matrix enhances after desizing. In addition, the hygrothermal environments dramatically decrease the micro-interphase strength, especially degrade the chemical bond force on the interphase, but interphase properties can partially recover after humidity desorption. Source

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