Integration of long-gage fiber-optic sensor into a fiber-reinforced composite sensing tape

Thermoplastic and thermoset fiber-reinforced composite materials are well established in aerospace engineering, but also more and more used in the oil and gas industry as well as in civil engineering. In these applications they are mainly used to reinforce, repair or straighten existing structures, but recently full-composite structures have also been built. Independently from the domain of the use, there is a need for these composite structures to be monitored. Since the composite materials are usually applied in form of thin tapes or sheets, sensors have to be embedded within the structure, depending on structural layer that has to be monitored. Embedding the sensors may have as a consequence a significant decrease of the mechanical properties of the composite material due to the dimensions of the sensor. The solution presented in this paper is integration of a fiber optic sensor directly into the main composite component, i.e. into the composite tape. In this paper we present the development of a thermoplastic fiber-reinforced composite tape with integrated long-gage fiber-optic sensors. The fiber-optic sensors are selected due to small transversal dimension and good compatibility with the plastic materials. The tape with integrated optical fiber can be used for tape winding of a structural element, embedded between different layers, but also as a separate sensor - a sensing tape. The optical and mechanical properties of the tapes with sensor are tested. The sensing tape is then installed onto the rail along with standard long-gage fiber optic sensor, additional tests are performed and performance of both sensor compared. The integration of optical fiber into the composite tape, the results of the tests as well as the performances of the tape with integrated optical fiber are presented in this paper.