Self-sensing of damage in carbon fiber polymer-matrix composite by measurement of the electrical resistance or potential away from the damaged region

Self-sensing of damage by measurement of the DC electrical resistance or potential away from the damaged region was demonstrated in quasi-isotropic continuous carbon fiber epoxy-matrix composite laminates under impact at energy up to 5 J. The through-thickness potential was substantial up to 240– 480 mm (at 0.25–99 mA correspondingly) in the longitudinal direction from the position of through-thickness current application, due to current spreading in the longitudinal direction. A model for the current spreading is provided. The fractional change in resistance resulting from damage decreased with increasing distance from the point of impact (diameter of indentation up to 3.5 mm and depth of indentation up to 0.16 mm), such that it was non-zero even at a distance of 150 mm from the point of impact. Both the through-thickness resistance and the oblique resistance were effective indicators. The ability for the resistance measured away from the damaged region to indicate damage in the damaged region is due to the much lower electrical resistivity in the longitudinal than through-thickness or oblique directions in the composite. C 2005 Springer Science + Business Media, Inc.