Damage detection in composite interfaces through carbon nanotube reinforcement

Abstract

Use of carbon nanotubes along composite interfaces was studied to both improve fracture strength and monitor interfacial damage progression. Both carbon fiber and E-glass fiber composites were manufactured with vinyl ester resin using vacuumassisted resin transfer molding. First, the effects of single-step curing (i.e., co-curing) versus two-step curing (i.e., curing a new section to a previously cured section) was studied using Mode II fracture testing. The results showed the two-step cured interface was as strong as the co-cured interface, thus validating the use of two-step curing during modular construction or repair of composite sections. Application of carbon nanotubes to the composite interfaces was then accomplished through two-step curing, using acetone as a dispersant. Mode II testing indicated significant improvement of the interface fracture toughness for both carbon fiber and glass fiber samples with carbon nanotubes. Because carbon nanotubes have very high electrical conductivity, the electrical resistance was measured across the interface during Mode II loading. As the interface crack grew, there was an increase in electrical resistance (approximately linear for carbon fiber specimens until final failure). The study demonstrated the feasibility of electrical resistance measurement with dispersed carbon nanotubes to monitor damage along critical interfaces, while simultaneously improving fracture properties.