Characterization of piezoresistance behavior in a CFRP unidirectional laminate

This paper aims at characterizing the piezoresistance behavior in a carbon fiber reinforced plastics (CFRP) unidirectional laminate under mechanical loading. A two-dimensional model is proposed using a DC circuit equivalent to an electric resistance network in the laminate to predict the resistance change due to tensile loading. The surface resistivity and the initial gage factor are expressed as a function of the off-axis angle in the model. The piezoresistance behavior in the fiber and transverse directions is predicted based on the resistance model associated with the probabilistic failure of conduction paths parallel and perpendicular to the fiber direction. The measured resistance in these directions increases linearly within the small tensile strain, while it increases nonlinearly at large strains. The measured resistance in the off-axis directions exhibits remarkable nonlinearity except the first linear region. The predicted initial gage factor becomes the maximum at an off-axis angle of 12° and is in reasonably good agreement with the experimental results.