Non-destructive testing of FRP by d.c. and a.c. electrical methods

In situ stress and strain detection, together with health monitoring, would give improved durability and safety of composite structures. Different tec hniques for in situ observation and non-destructive testing have been used in the past. This paper gives an overview on investigations and possible ap plications of electrical methods such as d.c. and a.c. measurements on fibr e reinforced polymers. In the case of d.c. measurements in CFRP the reinfor cing carbon fibres themselves are used as sensors, functioning as electrica l resistors. In GRP a conductive matrix filler such as carbon black can tak e on the role of a resistance sensor. In the case of a.c. measurements, i.e . capacitance and dissipation, the carbon fibres and their connecting point s function as resistors, while the spaces between the fibres function as ca pacitors. It has been shown that it is possible to monitor strain and failu re as well as to classify different failure mechanisms in static and dynami c load conditions using electrical methods. (C) 2001 Elsevier Science Ltd. All rights reserved.