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Research Papers

Fracture Toughness of Composite Joints With Carbon Nanotube Reinforcement

[+] Author and Article Information
S. D. Faulkner

Department of Mechanical & Aerospace Engineering, Naval Postgraduate School, Monterey, CA 93943

Y. W. Kwon1

Department of Mechanical & Aerospace Engineering, Naval Postgraduate School, Monterey, CA 93943

1

Corresponding author.

J. Pressure Vessel Technol 133(2), 021002 (Feb 09, 2011) (5 pages) doi:10.1115/1.4002676 History: Received August 06, 2008; Revised December 18, 2008; Published February 09, 2011; Online February 09, 2011

Fracture toughness tests were conducted for carbon composite scarf joints with and without carbon nanotube (CNT) reinforcement in order to study the effect of CNT on enhancing the fracture toughness of the scarf joint interface. Both mode I (i.e., opening mode) and mode II (i.e., shear mode) fracture tests were undertaken with and without CNT applied locally at the joint interface. During the study, the image correlation technique was used to examine the fracture mechanisms altered by the introduction of CNT. The experimental study showed that CNT increased the fracture toughness of the composite interface significantly, especially for the mode II fracture, with altering the fracture mechanism. On the other hand, there was no significant change on mode I fracture caused by CNT reinforcement. The enhancement of mode II fracture toughness was considered to result from the mechanical interlocking between polymers and CNT at the scarf joint interface.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Construction of composite scarf joint

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Figure 3

Double cantilever beam test for mode I (i.e., crack opening) fracture

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Figure 4

Three point bending test for mode II (i.e., shearing mode)

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Figure 5

Mode I normalized GI values

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Figure 6

Image of normal strain perpendicular to crack orientation just prior to mode I (opening mode) crack propagation

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Figure 7

Mode II normalized GII values

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Figure 8

Representative load versus extension plot for mode II (shear mode) testing of nonreinforced sample (the point of crack propagation is marked with an X)

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Figure 9

Representative load versus extension plot for mode II testing of CNT reinforced sample (the point of crack propagation is marked with an X)

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Figure 10

Initial crack propagation of resin only sample (crack propagated from the initial crack tip)

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Figure 11

Initial crack propagation of CNT reinforced sample (the internal crack was nucleated away from the initial crack tip; then the internal crack grew to meet the initial crack tip as the load increased)

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Figure 12

Plot of shear strain from digital image correlation system for mode II (i.e., shearing mode)

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Figure 13

Mode II crack surface of nonreinforced sample (note the crack propagated through the resin; in some areas the resin failed and in others the resin pulled away from the fibers)

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Figure 14

Mode II crack surface of CNT reinforced sample (note the crack propagated through the fibers and through a neighboring fiber layer in one region)

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Figure 15

Schematic of mechanical interlocking between polymers and CNT

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