Study of composite interface strength and crack growth monitoring using carbon nanotubes

Abstract

Interface strength of woven fabric composite layers was studied using Mode II fracture strength testing. Both carbon fiber and glass fiber composites were used with the vinyl ester resin. First, the single-step cured (i.e., co-cured) composite interface strength was compared to that of the two-step cured interface as used in the scarf joint technique. The test results showed that the two-step cured interface was as strong as the co-cured interface, and the former had even higher fracture toughness than the latter. The second study applied carbon nanotubes to the composite interface using the two-step curing technique. Mode II fracture testing was performed for the interface containing carbon nanotubes. The results indicated great improvement of the interface fracture toughness due to carbon nanotubes. Finally, a study was conducted to detect interface crack growth using the carbon nanotubes introduced at the interface. Because carbon nanotubes have high electric conductivity, the electric resistance was measured though the interface. As the interface crack grew under a loading, there was a gradual increase of electric resistance. As a result, the change of electric resistance in terms of crack length change was determined. The study showed that using carbon nanotubes at a critical composite interface would not only strengthen its fracture toughness but also detect crack growth.