Research Papers

Carbon Nanotube Reinforced Composites: The Smaller Diameter, the Higher Fracture Toughness?

[+] Author and Article Information
Yuli Chen

Institute of Solid Mechanics,
Beihang University,
Beijing 100191, China
e-mail: yulichen@buaa.edu.cn

Zhiyong Wang, Shengtao Wang

Institute of Solid Mechanics,
Beihang University,
Beijing 100191, China

Zhenggang Zhou

AVIC Advanced Composites Center,
Beijing 100095, China

Jianyu Zhang

College of Aerospace Engineering,
Chongqing University,
Chongqing 400044, China

Bin Liu

Department of Engineering Mechanics,
Tsinghua University,
Beijing 100084, China

1Corresponding author.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received April 14, 2015; final manuscript received May 7, 2015; published online June 9, 2015. Editor: Yonggang Huang.

J. Appl. Mech 82(8), 081009 (Aug 01, 2015) (14 pages) Paper No: JAM-15-1196; doi: 10.1115/1.4030618 History: Received April 14, 2015; Revised May 07, 2015; Online June 09, 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
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Fig. 1

Schematic of three-level failure analysis models: (a) fracture zone bridged with CNTs at the crack tip, (b) macroscopic-level model with equivalent bridging nonlinear springs, (c) mesoscopic-level model to study the CNT failure and obtain the force–displacement relation of equivalent nonlinear spring, and (d) atomistic-level failure model for characterizing CNT/matrix interfacial bond breaking

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Fig. 2

Schematic of mesoscopic shear-lag model: (a) cross section of CNT in matrix and (b) side view of CNT pulled from matrix by a force F

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Fig. 3

Theoretical prediction and MD simulation results of (a) axial effective modulus Ef and (b) axial effective strength σfb of single-wall armchair CNTs with different diameters

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Fig. 4

Chart of failure modes for CNT reinforced composites: (a) weak interface τb < (σGb)2t(dfmin-t)/(2EGδbdfmin), (b) moderate interface (σGb)2t(dfmin-t)/(2EGδbdfmin) < τb < (σGb)2t/(EGδb), and (c) strong interface τb>(σGb)2t/(EGδb)

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Fig. 5

Relation between fracture toughness enhancement ΔK and equivalent CNT diameter df of CNT reinforced composites with weak CNT/matrix interface τb<(σGb)2t(dfmin-t)/(2EGδbdfmin): (a) the normalized matrix modulus E∧m> 4t(dfmin-t)/(dfmin)2 and (b) the normalized matrix modulus E∧m < 4t(dfmin-t)/(dfmin)2

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Fig. 6

Relation between fracture toughness enhancement ΔK and equivalent CNT diameter df of CNT reinforced composites with moderate CNT/matrix interface (σGb)2t(dfmin-t)/(2EGδbdfmin) < τb < (σGb)2t/(EGδb)

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Fig. 7

Relation between fracture toughness enhancement ΔK and equivalent CNT diameter df of CNT reinforced composites with strong CNT/matrix interface τb > (σGb)2t/(EGδb)

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Fig. 8

Types of failure mode transition with increasing CNT diameter and the optimal equivalent CNT diameter for each transition type (I: CNT break, II: interface debonding from the end away from pulling force, and III: interface debonding from the end of pulling force)




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