Reference: J.M. Torrents, T.O. Mason, A. Peled, S.P. Shah, E.J. Garboczi, Journal of Materials Science, 36 (16), 4003-4012, August (2001).
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Next: Introduction
J. M. Torrents*, T. O. Mason
Department of Materials Science and Engineering, Northwestern University,
Evanston, IL 60208, USA
A. Peled, S. P. Shah
Department of Civil Engineering, Northwestern University, Evanston, IL 60208,
USA
E. J. Garboczi
National Institute of Standards and Technology, Building Materials Division,
Gaithersburg, MD 20899, USA
The presence of small amounts of short conductive fibers in a composite of
finite matrix conductivity results in the subdivision of the one matrix
impedance arc into two separate low and high frequency arcs in the complex
impedance plane. These features are attributable to a
"frequency-switchable" interfacial impedance on the fiber surfaces,
rendering them insulating at DC and low AC frequencies, but conducting at
intermediate frequencies. A combination of physical simulations (single wires
in tap water) and pixel-based computer modeling was employed to investigate
the roles of fiber pull-out, debonding, and orientation on the impedance
response of fiber-reinforced composites. The ratio of the low frequency arc
size to the overall DC resistance (
-parameter) is sensitive to pull-out and/or debonding, especially when a fiber
just barely makes contact with the matrix. The -parameter is also quite sensitive to fiber orientation with
respect to the direction of the applied field. Ramifications for the
characterization of cement, ceramic, and polymer matrix composites are
discussed.
Key words: composites, fibers, electrical conductivity, impedance, simulations