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TECHNICAL PAPERS

Fracture Toughness of Highly Ordered Carbon Nanotube/Alumina Nanocomposites

[+] Author and Article Information
Z. Xia, W. A. Curtin, B. W. Sheldon

Division of Engineering, Brown University, Providence, Rhode Island, 02912

J. Eng. Mater. Technol 126(3), 238-244 (Jun 29, 2004) (7 pages) doi:10.1115/1.1751179 History: Received July 30, 2003; Revised March 01, 2004; Online June 29, 2004
Copyright © 2004 by ASME
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References

Figures

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SEM photographs of (a) porous alumina matrix only and (b) multi-wall CNT/Al2O3 nanocomposite (90-μm-thick sample)
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TEM Photographs of CNT in the 90 μm thick sample
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(a) Side indentation crack pattern on 90 μm thick sample at a load of 400 mN; and (b) the magnification of circled area in (a) showing bridging CNTs close to the indent
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(a) Side indentation crack pattern on 90 μm thick sample at a load of 650 mN; (b) the magnification of circled area in (a) showing bridging CNTs at a distance away from the indent; and (c) magnification of the completely cracked area, showing broken nanotubes, nanotube pullout, and subsurface nanotube bridging
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Geometry of the finite element model with cohesive zone region
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Matrix and total tractions versus crack half-opening, for 30% CNT in Al2O3 matrix, with a matrix residual stress σmr=300 MPa, matrix fracture toughness of 0.4 MPa-m1/2 , and interfacial sliding stress τ = 40 MPa
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Stress distribution as predicted by the cohesive zone model for the largest indent crack at an applied load of 580 mN
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Predicted crack front with and without residual stress at a load of 580 mN
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Predicted bridging fracture toughness versus matrix residual tensile stress (c=30.3 μm,P=650 mN,Km=0.4 MPa-m1/2); for reference, the contribution of the residual stress to the stress intensity of a penny crack is shown
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CNT bridging traction versus half-crack opening, for the three cases shown in Table 4. X denoting the maximum opening point and associated CNT tensile stress. The shadowed area corresponds to the bridging fracture energy (Eq. 3) to determine composite fracture toughness. The dotted line shows a possible unifying bridging law that accounts for the statistical nanotube strength 34.

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