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Analysis of the impedance spectra of short conductive fiber-reinforced composites
Authors:J. M. Torrents  T. O. Mason  A. Peled  S. P. Shah  E. J. Garboczi
Affiliation:(1) Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208, USA;(2) Department of Civil Engineering, Northwestern University, Evanston, IL 60208, USA;(3) Building Materials Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA
Abstract: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 ldquofrequency-switchablerdquo 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 (gamma-parameter) is sensitive to pull-out and/or debonding, especially when a fiber just barely makes contact with the matrix. The gamma-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.
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