Can carbon nanotubes be used to sense damage in composites?

In situ stress and strain detection, together with health monitoring, would give improved durability and safety of composite structures. Different techniques for in situ observation and nondestructive testing have been used in the past. This paper gives an overview on investigations and possible applications of electrical methods such as d.c. measurements on fibre reinforced polymers. In the case of d.c. measurements in carbon-fibre reinforced polymer (CFRP), the reinforcing carbon fibres themselves are used as sensors. In glass-fibre reinforced polymer (GFRP) a conductive matrix filler such as carbon black (CB) and carbon nanotubes (CNT) can adopt the role of a resistance sensor. It has been shown that it is possible to monitor strain and failure as well as to classify different failure mechanisms in static and dynamic load conditions using electrical methods. In order to utilize the ablility of carbon nanoparticles, appropriate manufacturing methods have to be found. Resin transfer moulding (RTM) could successfully be applied in order to manufacture nanoparticle-reinforced GFRPs, containing CB and CNTs as conductive filler. A filtering effect of the nanoparticles by the glass fibre bundles was not observed. The glass-fibre reinforced polymer (GFRP) with nanotube/epoxy-matrix exhibits significantly improved matrix dominated properties like interlaminar shear strength. The GFRP containing 0.3 wt.% amino-functionalised double-wall carbon nanotubes (DWCNT-NH2) exhibit an anisotropic electrical conductivity, whereas the conductivity in plane is one order of magnitude higher than out of plane.