Infiltration monitoring using carbon nanotube buckypaper for the characterization of out‐of‐plane unsaturated permeability

Abstract This paper developed an out‐of‐plane permeability measuring method by utilizing conductive carbon nanotube (CNT) buckypaper and its piezoresistivity. A series of CNT sensors was arranged orderly in different interlaminar regions to achieve infiltration monitoring for both glass and carbon fabrics. The response of electrical resistance to flow front was investigated, and the out‐of‐plane unsaturated permeabilities at different fiber volume fractions were further calculated according to the monitoring results of those CNT sensors. The results show that the electrical resistance variation and time curves can be divided into three stages, including the initial baseline stage, rapid growth stage, and smooth growth stage. For most CNT sensors, Δ R / R 0 becomes higher than 15% and 20% at the end of rapid growth stage and smooth growth stage, respectively. These CNT sensors show the sudden increase of electrical resistance successively along the infiltration direction. The squared infiltration distance and time show linear relationship, and the out‐of‐plane unsaturated permeability is further calculated based on Darcy's law. The out‐of‐plane unsaturated permeability of EW100 glass fabric is measured to be 4.76 × 10 −13 m 2 at a fiber volume faction of 63.0%. The unsaturated permeability increases with decreasing fiber volume fraction, and the carbon fabric with smaller fiber diameter shows smaller unsaturated permeability at the approximate fiber volume fraction.