Indentation damage detection in glass/epoxy composite laminates with electrically tailored conductive nanofiller

Laminated fiber-reinforced polymer composites are known for excellent in-plane strength and stiffness per unit density, but variable susceptibility to out-of-plane impact and indentation loading on account of their relatively low interlaminar strength. Methods of monitoring damage caused by out-of-plane loads are therefore sought. This investigation aims to demonstrate the two-dimensional electrical resistance mapping method using co-cured carbon fiber electrodes, a glass fiber-reinforced composite system, and electrically tailored carbon black filler networks for sensing indentation damage. It is shown that damage sensing accuracy is improved by increasing the electrical conductivity of the carbon black network in the through-thickness direction. The anisotropic tailoring of conductivity is accomplished by using alternating-current dielectrophoresis, which entails the application of an electric field to polarize and chain the carbon black particles preferentially through the thickness during liquid processing of the composite. Co-cured carbon fiber tows arranged in a perpendicular array on the top and bottom surfaces of the laminate provide a qualitative assessment of the size and severity of the indentation damage via a two-dimensional resistance change map.