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Research Articles

Effects of the Longitudinal Surface Roughness on Fiber Pull-Out Behavior in Carbon Fiber-Reinforced Epoxy Resin Composites

[+] Author and Article Information
Shaohua Chen

e-mail: chenshaohua72@hotmail.com
The State Key Laboratory of
Nonlinear Mechanics,
Institute of Mechanics,
Chinese Academy of Sciences,
Beijing, 100190, China

1Corresponding author.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNALOF APPLIED MECHANICS. Manuscript received March 30, 2012; final manuscript received August 18, 2012; accepted manuscript posted August 23, 2012; published online January 22, 2013. Assoc. Editor: Daining Fang.

J. Appl. Mech 80(2), 021015 (Jan 22, 2013) (13 pages) Paper No: JAM-12-1126; doi: 10.1115/1.4007440 History: Received March 30, 2012; Revised August 18, 2012; Accepted August 23, 2012

Surface modifications are known as efficient technologies for advanced carbon fibers to achieve significant improvement of interface adhesion in composites, one of which is to increase the surface roughness in the fiber's longitudinal direction in practice. As a result, many microridges and grooves are produced on carbon fiber's surfaces. How does the surface roughness influence the carbon fiber's pull-out behavior? Are there any restrictions on the relation between the aspect ratio and surface roughness of fibers in order to obtain an optimal interface? Considering the real morphology on carbon fiber's surface, i.e., longitudinal roughness, an improved shear-lag theoretical model is developed in this paper in order to investigate the interface characteristics and fiber pull-out for carbon fiber-reinforced thermosetting epoxy resin (brittle) composites. Closed-form solutions to the carbon fiber stress are obtained as well as the analytical load-displacement relation during pullout, and the apparent interfacial shear strength (IFSS). It is found that the interfacial adhesion and the apparent IFSS are effectively strengthened and improved due to the surface roughness of carbon fibers. Under a given tensile load, an increasing roughness will result in a decreasing fiber stress in the debonded zone and a decreasing debonded length. Furthermore, it is interesting to find that, for a determined surface roughness, an optimal aspect ratio, about 30∼45, of carbon fibers exists, at which the apparent IFSS could achieve the maximum. Comparison to the existing experiments shows that the theoretical model is feasible and reasonable to predict the experimental results, and the theoretical results should have an instructive significance for practical designs of carbon/epoxy composites.

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Figures

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Fig. 1

Schematics of a carbon fiber with surface roughness. (a) 3D configuration of the fiber segment with longitudinal surface roughness; (b) cross section of the carbon fiber with circumferentially wavy contour curve; (c) periodically wavy interface in the r-θ plane.

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Fig. 2

Schematics of the loading form of carbon fiber-reinforced epoxy resin matrix composites. (a) Cylindrical model for a single fiber pulling out from the matrix; (b) an infinitesimal carbon fiber element with longitudinal surface roughness.

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Fig. 3

The normalized tensile load during the debonding stage versus the debonded fraction for different interface roughness

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Fig. 4

The whole pull-out process of a carbon fiber-reinforced epoxy resin matrix composite. (a) The relation between the normalized tensile load and the normalized sliding displacement for different interface roughness; (b) amplification of the curves of the tensile load versus sliding displacement in the region of 0≤δ¯≤0.005; (c) amplification of the experimental results [49] of load-displacement curve in the region of 0≤δ¯≤0.1.

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Fig. 5

The effects of the interface roughness on the mechanical behaviors of composites. (a) The debonded fraction β as a function of the roughness ratio Δ/λ under a fixed tensile load; (b) the tensile load σ¯0 varying with the roughness ratio Δ/λ for a given debonded fraction.

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Fig. 6

The distributions of carbon fiber axial stress along the fiber length. (a) In the debonded region under a given tensile load; (b) along the whole fiber length with a fixed debonded fraction.

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Fig. 7

The effect of the etching time on the apparent IFSS for cases with different aspect ratios, where the experimental results [28] are shown for comparison

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Fig. 8

The relation of the apparent IFSS versus the carbon fiber's aspect ratio for different interface roughness

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