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Electromechanical behavior of carbon-fiber-reinforced plastics (CFRPs) was investigated by monitoring the electrical resistance changes with respect to mechanical loading to utilize its self-sensing capability for real-time non-destructive evaluation (NDE). Electrical resistance changed as mechanical deformations occurred in CFRPs. CFRP consists of polymer matrix and carbon fiber consisting of several thousands of carbon fiber monofilaments. The intrinsic piezoresistive behavior of a carbon fiber monofilament was characterized by an increase in electrical resistance when subjected to tensile elongation. A carbon fiber tow, essentially a bundle of monofilaments, also displayed a similar electromechanical behavior. In addition, the electrical resistance was affected by the interaction between adjacent tows and plies, known as “inter-tow” and “inter-ply” interactions, respectively. These interactions can be modeled as electrically equivalent circuits with variable electrical resistors. The developed model aids in the design of self-sensing CFRPs, which holds real-time NDE ability. Variable electrical resistors were parameterized by both empirical results and numerical analysis, decoupling each factor containing the stacking sequence as well as orientation of carbon fiber plies. The proof-of-concept of self-sensing CFRP was demonstrated using a 3D-printed miniaturized bridge. CFRP strips were attached under the bridge, and electrical resistances were monitored real-time with respect to the deflection. The acquired resistance changes were converted using the in-house developed algorithm, and deflections were calculated. It was shown that the proposed method can detect both the locations and magnitudes of deflections in the bridge real-time even when moving loads are applied.
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